Effects of Remifentanil on Esophageal Sphincters and
Swallowing Function
To Martin and Kajsa
Örebro Studies in Medicine 119
JOHANNA SAVILAMPI
Effects of Remifentanil on Esophageal Sphincters and
Swallowing Function
© Johanna Savilampi, 2015
Title: Effects of Remifentanil on Esophageal Sphincters and Swallowing Function
Publisher: Örebro University 2015
www.oru.se/publikationer-avhandlingar
Print: Örebro University, Repro 03/2015
ISSN 1652-4063
ISBN 978-91-7529-065-2
Abstract
Johanna Savilampi (2015): Effects of remifentanil on esophageal sphincters
and swallowing function, Örebro Studies in Medicine 119.
Pulmonary complications like pneumonia are common perioperatively,
and one potentially important cause is thought to be silent aspiration.
There are several levels of defence against pulmonary aspiration that can
be affected by drugs in anaesthesia. Competence of esophageal sphincters prevents regurgitation of gastric content, and complex reflex systems
(with or without coincident swallowing) guard direct entrance into the
airway. Furthermore, in our previous studies healthy volunteers spontaneously complained about swallowing difficulties when they received
remifentanil, and difficult swallowing may be a poorly recognized side
effect of remifentanil. The aim of this thesis was to study the effect of
remifentanil on different components of airway protection with and
without coincident swallowing, and to explore whether remifentanil increases the risk of pulmonary aspiration. The purpose was also to determine
to what extent remifentanil induces subjective swallowing difficulties.
The competence of the esophagogastric junction and esophageal peristalsis were studied using high resolution manometry. Pharyngeal swallowing was evaluated using a novel method called automated impedance
manometry analysis. Infusion of a tracer infusion into the nasopharynx
and subsequent lung scans was employed to detect remifentanil-induced
aspiration, and subjective swallowing difficulties were evaluated on a
four-point scale.
This thesis found that, at doses used in clinical settings, remifentanil
increases the incidence of aspiration in healthy volunteers. Remifentanil
influences several mechanisms that protect the airway towards greater
dysfunction, which may increase the risk of pulmonary aspiration. Remifentanil also appears to induce subjective swallowing difficulties when
dry swallows are performed, although no association between aspiration
and swallowing difficulties was observed. These findings may improve
clinical practise toward cautious use of the drug, especially regarding spontaneously breathing patients in the monitored anaesthesia care setting.
Keywords: Pulmonary aspiration, postoperative lung complications, silent
aspiration, defence against pulmonary aspiration, remifentanil, competence
of esophageal sphincters, esophageal peristalsis, pharyngeal swallowing,
high resolution manometry
Johanna Savilampi, School of Health and Medical Sciences,
Örebro University, SE-701 82 Örebro, Sweden,
e-mail: [email protected]
Contents
CONTENTS .............................................................................................. 1
ABBREVIATIONS ..................................................................................... 9
LIST OF ORIGINAL STUDIES................................................................ 10
INTRODUCTION ................................................................................... 11
Background .............................................................................................. 11
Dual action of the upper aerodigestive tract ............................................. 11
Levels of defence against aspiration ......................................................... 11
Esophagogastric junction ..................................................................... 11
Upper esophageal sphincter .................................................................. 12
Pharyngeal and laryngeal reflexes ........................................................ 13
Swallowing........................................................................................... 13
Pharyngeal swallowing ..................................................................... 14
Esophageal swallowing .................................................................... 14
The impact of aging ......................................................................... 15
Opioids .................................................................................................... 15
Remifentanil......................................................................................... 16
AIMS........................................................................................................ 17
VOLUNTEERS AND METHODS ........................................................... 18
Approvals ................................................................................................. 18
Volunteers ................................................................................................ 18
High resolution solid-state manometry .................................................... 18
Esophageal pressure topography .......................................................... 19
Analysis procedures ......................................................................... 19
High resolution impedance manometry .................................................... 21
Automated impedance manometry analysis ......................................... 21
Analysis procedure ........................................................................... 21
Radionuclide scans ................................................................................... 24
Assessment of subjective swallowing difficulties....................................... 25
Drug administration and monitoring ....................................................... 25
Study protocols ........................................................................................ 26
Statistics ................................................................................................... 28
RESULTS ................................................................................................. 29
Study I ...................................................................................................... 29
Study II..................................................................................................... 32
Study III.................................................................................................... 34
Study IV ................................................................................................... 36
DISCUSSION ........................................................................................... 39
Aspiration induced by remifentanil........................................................... 39
Effects of remifentanil on the esophagogastric junction ............................ 40
Effects of remifentanil on esophageal motility .......................................... 40
Effects of remifentanil on pharyngeal swallowing .................................... 41
Subjective swallowing difficulties ............................................................. 42
Limitations ............................................................................................... 43
Clinical implications ................................................................................. 44
Future perspectives ................................................................................... 45
CONCLUSIONS ...................................................................................... 47
SUMMARY IN SWEDISH ....................................................................... 48
ACKNOWLEDGEMENTS ...................................................................... 49
REFERENCES ......................................................................................... 51
Abbreviations
4s-IRP
AIM analysis
ARDS
CD
CDP
CFV
CP
DCI
DL
EGJ
EPT
HRIM
HRM
IBP
iZn/Z
LES
PeakP
PZn
SRI
TCI
TZn-PeakP
UES
UES-IBP
UES-Nad-P
UES-RI
VIP
Z
Zn
Integrated relaxation pressure
Automated impedance manometry analysis
Acute respiratory distress syndrome
Crural diaphragm
Contractile deceleration point
Contractile front velocity
Cricopharyngeus muscle
Distal contractile integral
Distal latency
Esophagogastric junction
Esophageal pressure topography
High resolution impedance manometry
High resolution manometry
Intrabolus pressure
Ratio of nadir impedance to post-swallow impedance
Lower esophageal sphincter
Peak pharyngeal pressure
Pressure at pharyngeal nadir impedance
Swallow risk index
Target controlled infusion
Time from nadir impedance to peak pressure
Upper esophageal sphincter
Intrabolus pressure during UES relaxation
Nadir pressure during UES relaxation
UES relaxation interval
Vasoactive intestinal peptide
Impedance
Nadir impedance
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Effects of remifentanil on esophageal sphincters
9
List of original studies
This thesis is based on the following papers, which will be referred to in
the text by their Roman numerals.
I.
Savilampi J, Ahlstrand R, Magnuson A, Wattwil M.
Effects of remifentanil on the esophagogastric junction
and swallowing
Acta Anaesthesiologica Scandinavica 2013; 57: 1002–1009
II.
Savilampi J, Ahlstrand A, Magnuson A, Geijer H, Wattwil M
Aspiration induced by remifentanil: a double-blind, randomized, crossover study in healthy volunteers.
Anesthesiology. 2014 Jul; 121(1):52-8
III.
Savilampi J, Magnuson A, Ahlstrand R
Effects of remifentanil on esophageal motility: A double blind,
randomized, cross-over study in healthy volunteers
Accepted for publication in ACTA Anesthesiologica Scandinavica.
IV.
Savilampi J, Magnuson A, Ahlstrand R
Effects of Remifentanil and Morphine on Pharyngeal Swallowing: A Double Blind Randomized Cross-over Study in Healthy
Volunteers
Submitted for publication
Reprints were made with kind permission from the publishers.
Study I reprinted with kind permission from John Wiley and Sons.
Study II reprinted with kind permission from Wolters Kluwer Health.
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Introduction
Background
Pulmonary aspiration in anaesthesia patients was first described by Mendelson in 1946 (1), and is defined as the inhalation of oropharyngeal or
gastric contents into the lower respiratory tract (2). Fulminant aspiration
is an infrequent perioperative event; an incidence of 3 to 5 events per
10 000 general anaesthetics has been suggested (3-6). In contrast, postoperative lung complications such as pneumonia are common, with incidence
from 5% to 20% depending on different risk factors (e.g. advanced age),
and result in both longer hospital stays and increased morbidity and mortality (7, 8). One potentially important cause is thought to be silent, unwitnessed pulmonary aspiration that occurs perioperatively (9), for instance during the immediate postoperative period or other circumstances
when the patient is breathing spontaneously and the requirement for analgesia is high. Furthermore, aspiration pneumonia is the leading cause of
pneumonia in the intensive care unit (9).
Dual action of the upper aerodigestive tract
The common conduit for gases during breathing and for swallowed or
vomited material is the pharynx. This anatomical challenge requires intact
physiological defence mechanisms against aspiration during anterograde
and retrograde flow of fluids and solids through the pharynx.
Levels of defence against aspiration
There are several levels of physiological defense against pulmonary aspiration that can fail in the event of aspiration. Competence of the esophageal
sphincters and intact esophageal peristalsis prevent retrograde regurgitation of already swallowed material, while the direct entrance to the airway
is protected by several pharyngeal and laryngeal mechanisms, with or
without coincident swallowing.
Esophagogastric junction
The main barrier against the reflux of gastric content into the esophagus is
the esophagogastric junction (EGJ). The unique anatomical configuration
of the EGJ and two sphincters contribute to EGJ competence: the intrinsic
lower esophageal sphincter (LES), and the crural diaphragm (CD), which
JOHANNA SAVILAMPI
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11
externally embraces the LES. The CD has both respiratory and gastrointestinal functions; it contracts during inspiration and makes the greatest
contribution to inspiratory EGJ pressure, while tone in the LES is the main
cause of expiratory EGJ pressure. The clinical assessment of EGJ competence has mainly focused on EGJ pressure during expiration, when it is
lowest, and this moment has been considered the most likely time for reflux (10). However, agreement has not been widely established how to
measure EGJ pressure (11, 12), and only inspiratory EGJ augmentation is
independently significantly associated with objectively confirmed gastroesophageal reflux (12). Inspiratory EGJ augmentation, the difference between inspiratory and expiratory EGJ pressures, is thought to compensate
for the increased abdominothoracic pressure gradient during inspiration,
and is an indicator of the functional integrity of the CD (12).
The LES is thicker than rest of the smooth muscles of the distal esophagus, with properties that distinguish it from the esophageal body. The LES
exhibits constant myogenic tone (13), which is augmented and reduced by
cholinergic excitatory respective nitrergic inhibitory myenteric neurons
(14, 15). The LES is centrally innervated by cholinergic vagal efferents
from the preganglionic fibers of the dorsal motor nucleus of the vagus;
these efferents relay through postganglionic neurons in the myenteric
plexus. Although the vagus exerts the main regulatory action on the LES,
the postganglionic myenteric neurons receive input from esophageal and
gastric intrinsic sensory neurons and from preganglionic sympathetic fibres. In addition to acetylcholine, nitric oxide, and vasoactive intestinal
peptide (VIP), various other excitatory and inhibitory transmitters are
present in the LES; however, their physiologic importance is unclear (16,
17).
The CD is comprised of skeletal muscle. It is innervated by branches of
the phrenic nerve, as well as by inhibitory motor fibers from esophageal
nitrergic myenteric neurons. It exhibits phasic contractions along respiration; in addition, it contracts reflexively with manoeuvres that increase
intra-abdominal pressure (18). Swallowing, transient LES relaxations, and
esophageal distension each induce the relaxation of the CD (19, 20).
Upper esophageal sphincter
The upper esophageal sphincter (UES) is a region of high pressure located
at the junction between the pharynx and the cervical esophagus. Tonic
contraction of the UES prevents air from entering the esophagus and
guards against aspiration of gastric reflux. The UES opens to allow the
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passage of swallowed food and relaxes or contracts during various reflexes
and physiological states. Of most relevance to the UES function are the
intrinsic cricopharyngeus muscle (CP) and the extrinsic suprahyoid muscles, which are all striated muscles mechanically coupled to the UES (21).
The highly elastic CP is attached to the cricoid cartilage and is the most
important contributor to the basal tone of the UES. The pharyngoesophageal nerve, which is a branch of the vagus nerve with motor neuron in the
nucleus ambiquus, is the main innervator of the CP. In contrast to many
other sphincters, the UES does not appear to exhibit a constant, active
tone. Indeed its tone falls to very low levels during anaesthesia or sleep
(21). However, changes in posture or arousal can cause very large increases in UES tone (21). The extrinsic suprahyoid muscles are the opening
muscles of the UES and are innervated by several cranial nerves and the
first cervical spinal nerves. The only neurotransmitter found to mediate
contraction of the UES is acetylcholine acting through nicotinic cholinergic
receptors, although several neuropeptides have been found in the CP (neuropeptide Y, calcitonin gene-related peptide, tyrosine hydroxylase, substance P, VIP, and galanin)(22).
Pharyngeal and laryngeal reflexes
Several pharyngeal and laryngeal reflexes protect the direct entrance to the
airway, with or without coincident swallowing. The pharyngoglottal closure reflex, pharyngo-UES contractile reflex, and reflexive pharyngeal
swallow are triggered by pharyngeal water stimulation and thought to
protect the airway during both anterograde and retrograde flow of fluids
through the pharynx (23, 24). The deglutitive glottic closure with vocal
cord closure, aryepiglottic adduction, and epiglottal descent are actions of
the intrinsic laryngeal muscles and provide a sealed barrier against laryngeal penetration of the bolus during swallowing (25). The pharyngeal
plexus, which is mainly formed by the glossopharyngeal and vagus nerves,
mediates the sensory innervation of the pharyngeal wall. Branches of the
vagus nerve also innervate the larynx. The Efferent motor supply to the
laryngeal and pharyngeal muscles originates from the vagus and accessory
nerves.
Swallowing
Swallowing is a complex process consisting of three stages (oral, pharyngeal, and esophageal) and employing several dozen paired muscle groups
and a neural control mechanism that extends from the cortex to the spinal
JOHANNA SAVILAMPI
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13
cord. A central pattern generator located within the medulla oblongata
directs the sequential and rhythmic patterns of swallowing. This pattern
generator is intimately associated with the nucleus tractus solitaries. The
motor neurons that control all stages of swallowing are located in the
brainstem and the cervical part of the spinal cord, according to their anatomical distribution within the swallowing apparatus (26). The oral stage
of swallowing is a voluntary action, while the pharyngeal and esophageal
stages are automatic.
Pharyngeal swallowing
All of the muscles involved in the oropharyngeal stage of swallowing are
striated muscle. After the initial oral preparation, delivery of the bolus to
the pharynx triggers the pharyngeal swallow reflex; the tongue base propels the bolus against the posterior pharyngeal wall and further backwards, the soft palate closes the nasopharynx, the larynx elevates, the
vocal folds close, and the UES relaxes and opens to allow the bolus to
pass. Simultaneously, the pharyngeal constrictor muscles begin to contract
in a descending manner, elevating and widening the pharynx to first engulf
the bolus and then clear the bolus residue from the pharynx in a typical
wave pattern. The neural control of pharyngeal swallowing involves five
major components: 1) sensory afferents contained in cranial nerves; 2)
input from cerebral and midbrain fibers; 3) swallowing centers in the
brainstem which relay these inputs; 4) motor efferents contained in cranial
nerves; and 5) muscles and other end organs.
Esophageal swallowing
The esophagus can be simply described as a hollow muscular tube closed
by the UES proximally and by the EGJ distally. The cervical esophagus is
composed of striated muscle and innervated by lower motor neurons carried within cranial nerves (mainly the vagus nerve). In contrast, the thoracic esophagus is smooth muscle innervated by preganglionic excitatory and
inhibitory efferents carried within the vagus nerve (27), as well as by intramural postganglionic neurons located in the myenteric plexus. Preganglionic transmission is mainly cholinergic nicotinic. Nitric oxide is the
predominant inhibitory neurotransmitter, and acetylcholine, acting on
muscarinic receptors, is the excitatory neurotransmitter in the myenteric
plexus. After the bolus has passed through the UES, it shuts rapidly and
the esophageal stage of swallowing commences. The peristalsis of the
esophagus is the result of sequential inhibition of the esophageal muscles,
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which disrupts all activity and finally results in the opening of the EGJ,
followed by the excitation and lumen-occluding contraction of the circular
muscles of the esophagus (28, 29). This inhibitory wave, also known as
deglutitive inhibition, progressively increases in duration distally along the
esophagus, and is followed by peristaltic contraction (30).
The impact of aging
The efficiency of swallowing and airway protection declines with age, even
in healthy older adults (31, 32). In the elderly, several aeroprotective reflexes are impaired (33, 34). Lingual propulsion during swallowing is
weakened, and duration of the oropharyngeal stage of swallowing is prolonged (35-39), increasing the time of exposure of the laryngeal vestibule.
These multiple subtle reductions in function result in a much smaller margin for error, and may lead to rapid decompensation in swallowing function during illness or during sedation/anaesthesia. For example, patients
aged 80 years or older have an almost 10-fold increased risk of pulmonary
aspiration compared with 20-year-olds (40). The function of esophageal
peristalsis appears to be more preserved with aging; duration may be prolonged and amplitude lessened, but the clinical significance of these findings remains unclear.
Opioids
Previous manometric studies investigating the effects of opioids on EGJ
pressure (41-48) have mainly focused on end-expiratory EGJ pressure, and
have revealed that decreased pressures are induced by opioids. However,
the inspiratory EGJ augmentation appears to be more important when
examining reflux barrier function of the EGJ (12). There are currently no
studies regarding the effects of opioids on inspiratory EGJ augmentation.
A few studies have investigated esophageal motility and opioids (44, 4951), and have found that opioids increase the velocity of esophageal peristalsis and decrease the swallow-induced relaxation of the EGJ. Regarding
the effects of opioids on pharyngeal function, case reports describe temporary dysphagia after intrathecal fentanyl (52-55), morphine (55), and
sufentanil (56). Furthermore, the impact of other anaesthetic agents on
pharyngeal function has been investigated as an indicator of increased
aspiration risk (57-60); however, to our knowledge no studies have
demonstrated that opioids or other anaesthetic agents directly induce aspiration when administrated at the doses used in sedation.
JOHANNA SAVILAMPI
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Remifentanil
The primary focus in this thesis was the effect of remifentanil on the risk
of aspiration and on different levels of defence against pulmonary aspiration. Remifentanil is suitable for spontaneously breathing patients in monitored anaesthesia care settings in spontaneously breathing patient because
its pharmacokinetic profile features an ultra-rapid onset time and short
duration of action. Remifentanil has recently gained field as pain relief
among women in labour (61, 62); notably, these patients are rarely fasting. The adverse effect profile of remifentanil is similar to those of other,
newer synthetic opioids, and includes muscle rigidity (63). The influence
of remifentanil on the risk of aspiration is still mostly unknown. In our
previous studies (46, 64), volunteers spontaneously reported subjective
swallowing difficulties when they received remifentanil. This possibly unknown side effect of remifentanil and the fact that remifentanil is now
widely used in a variety of anaesthesia settings inspired us to examine the
potential risks more closely.
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Aims
The overall aim of this thesis was to investigate the effects of remifentanil
on the physiological defence against pulmonary aspiration.
The specific aims were:
• To determine the effect of remifentanil on the function of the EGJ
as a reflux barrier by using the inspiratory EGJ augmentation as an
indicator, and to evaluate whether this possible effect is centrally or
peripherally mediated.
• To determine through a direct method whether remifentanil results
in pulmonary aspiration.
• To evaluate the impact of remifentanil on esophageal motility, and
to describe whether there is a dose response associated with remifentanil´s effects and whether they are counteracted by naloxone
and/or dopamine.
• To assess the effects of remifentanil on pharyngeal function and
UES relaxation during swallowing, to compare these effects with
those of morphine, and to describe the impact of age on these effects.
• To describe to what extent remifentanil induces subjective swallowing difficulties.
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Volunteers and Methods
Approvals
All studies were approved by the Regional Ethics Committee in Uppsala,
Sweden (Dnr 2009/219, Dnr 2011/017, Dnr 2010/220, Dnr 2013/251),
and by the Swedish Agency for drugs. All studies were conducted in accordance with the Declaration of Helsinki and Good Clinical Practise, and
registered in a central database, ClinicalTrials.gov.
Volunteers
After oral and written informed consent, a total of 67 healthy volunteers
were included (female: 28, male 39), 60 young (study I-VI) and 7 elderly
(study IV). The volunteers lacked any history of swallowing difficulties,
upper gastrointestinal conditions including gastro-esophageal reflux disease or previous gastrointestinal surgery. Young volunteers were medication-free and none of the elderly volunteers used any medication known to
affect gastrointestinal motility.
High resolution solid-state manometry
High resolution manometry (HRM) has its roots in conventional waterperfused systems and is the current gold standard technique to assess
esophageal motility. Its major advantage compared with earlier technologies is the vastly greater number of pressure sensors along the manometric
catheter and diminished space between them (65, 66). This feature enables
simultaneous dynamic recording of pressure morphology all the way from
the pharynx to the stomach without spatial gaps between recording sites
and with no need to compensate for the axial motion of (for example) the
esophageal sphincters during swallowing. Furthermore, compared with
water-perfused systems, solid-state HRM systems are free of hydrostatic
influences, consistently measure of rapidly changing pressures (pharynx,
UES) and are easily mobile because the pressure sensors are incorporated
into the catheter. Pressure transducers underlying the sensors within the
catheter convert tactile pressure on the catheter to an electrical signal that
is then amplified, and filtered, and then digitised using standard circuitry
connected to a personal computer (67).
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In this thesis, the HRM system used for pure manometric measurements
in studies I and II was the ManoScan 360 (Sierra Scientific Instruments,
Inc., Los Angeles, CA). This system uses a solid-state catheter (Ø 4.2 mm)
with circumferential pressure sensors at 1-cm intervals over a length of 36
cm.
Esophageal pressure topography
Esophageal pressure topography (EPT) (Fig 1 is a display method in which
pressure data acquired by HRM is plotted against both time and distance
along the esophagus. The resulting colour-coded topographs are also
called Clouse plots, in honour of key innovator Ray Clouse (65). EPT has
improved the accuracy and speed with which this form of data is interpreted, compared to conventional line plots. It also enables correct positioning of the manometric catheter and the resolution of technical problems at the time of the recording (67, 68).
The Chicago Classification (69) is a practical classification of esophageal motility disorders based on EPT metrics developed by the HRM Working Group and subsequently updated with intent of improving diagnostic
accuracy and clinical utility (70). At present, the Chicago Classification
defines swallow induced EGJ relaxation, esophageal contractile activity,
and esophageal pressurisation but does not include pharyngeal motility or
UES function.
Analysis procedures
Manoview analysis software (Sierra Scientific Instruments, Inc.) was used
to evaluate the effect of remifentanil on EGJ pressures in study I and on
esophageal motility in study III. In study I, in the manner of Pandolfino et
al. (12) after identification of the EGJ high pressure zone, inspiratory EGJ
pressure was defined as the maximal pressure that occured during a normal respiratory cycle, and expiratory EGJ pressure was defined as the
pressure at the midpoint between adjacent inspiratory EGJ pressures during a normal respiratory cycle. The inspiratory augmentation of the EGJ
pressure was the difference between the basal inspiratory pressure and the
basal expiratory pressure. In study III, each swallow was examined with
the tools provided by the software, and EPT metrics based on the Chicago
Classification characterizing the features of esophageal motility were defined (Table 1).
JOHANNA SAVILAMPI
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19
Figure 1. Esophageal pressure topography depicting one swallowing event. EGJ =
Esophagogastric junction, I = Inspiration, E = Expiration.
Metric
Description
Integrated
relaxation
pressure, 4-sIRP
(mmHg)
Intra bolus
pressure, IBP
(mmHg)
Mean lowest esophagogastric junction pressure for four continuous or
non-continuous seconds in the 10-s window following deglutitive upper
esophageal sphincter relaxation, indicative of deglutitive esophagogastric
junction relaxation
Contractile
deceleration
point, CDP
Distal latency,
DL (s)
Contractile front
velocity, CFV
(cm/s)
Distal contractile integral, DCI
(mmHg-s-cm)
Greatest pressure obtained for a continuous or non-continuous 3-s period within the same temporal boundaries used to calculate the 4-s IRP,
reflects the pressure within the fluid compartmentalised between the EGJ
and the esophageal contraction
The inflection point along the 30-mmHg isobaric contour where propagation velocity slows, demarcating the tubular esophagus from the
phrenic ampulla
The time interval between the opening of the upper esophageal sphincter
and the CDP
The slope of the best-fit tangent approximating the 30 mmHg isobaric
contour between the proximal trough and the CDP
Summarises the vigor of the distal esophageal contraction and is an
integral of amplitude, duration, and length of the distal propagation
wave from proximal to distal pressure troughs
Table 1. EPT metrics used to assess esophageal motility
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High resolution impedance manometry
High resolution impedance manometry (HRIM) combines impedance
monitoring segments in the manometric catheter, allowing the simultaneous measurement of impedance and pressures. Intraluminal impedance
monitoring is a recent technique to detect the flow of fluids and gases
through hollow viscera, such as the esophagus. The physical principle in
impedance monitoring is the measurement of resistance to electrical flow
in an alternating current circuit that is generated between two ring electrodes (impedance monitoring segments) separated by a nonconductive
catheter. Impedance is inversely related to the conductivity of the medium
surrounding the catheter: air has high impedance due to very low conductivity, and liquids such as saline or gastric juice have low impedance and
high conductivity. In HRIM, several impedance monitoring segments are
placed along the catheter to enable the evaluation of the direction and
velocity of the flow of medium (71). The method can be used to measure
the clearance of a swallowed bolus in the esophagus, to detect gastroesophageal reflux independent of its acidity, to determine the nature of
belches, and to assess pharyngeal swallowing, as described below.
As part of this thesis, a combined solid-state manometric and impedance catheter incorporating 36 circumferential pressure sensors spaced at
1-cm intervals and 18 impedance segments (each 2 cm long) was used to
acquire pressure and impedance data in study IV (Sierra Scientific Instruments, Inc., Los Angeles, CA).
Automated impedance manometry analysis
Automated impedance manometry analysis (AIM analysis, AIMplot software copyright, Taher Omari, Adelaide, Australia) is a MATLAB-based
analysis program (Mathworks, Natick, MA) that provides a novel technique to assess pharyngeal function (72, 73). Measurements using automated algorithms are derived from pressure and impedance waveforms.
These measurements quantify bolus flow, flow resistance, and contractile
strength during pharyngeal swallowing and provide objective numerical
values for physiological processes associated with pharyngeal swallowing.
Analysis procedure
In this thesis, AIM analysis was used in study IV to evaluate the effects of
remifentanil on pharyngeal swallowing. First, the pressure and impedance
data was exported from the HRIM recording system as text files, and then
the entire pharyngeal region to the proximal UES was displayed as presJOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
21
sure and impedance topographic plots (Fig. 2). Regions of interest encompassing the pharynx, distal pharynx, and UES in these plots were located
by placing specific time-space landmarks. Next, the swallow function variables were automatically derived, based on established methodology (7274) (Table 2).
Figure 2. A colour pressure topography plot of a 10ml swallow. The UES high
pressure zone (HPZ) is an easily recognisable region of tonic pressure. ROI =
region of interest.
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Variable
PeakP,mmHg
Description
Mean pressure of the entire pharyngeal stripping wave
Indicates
Contractile vigor of the pharyngeal stripping wave. Low = poor capacity to clear
bolus residue
PZn,mmHg
Mean pressure when the pharyngeal
impedance is at its nadir
Pharyngeal residual pressure during maximum bolus flow. High = poor compliance/obstruction
TZn-PeakP,ms
Mean time interval from nadir
impedance to peak pressure
Pharyngeal capacity to propel the bolus in
advance of the stripping wave. Short = poor
bolus propulsion
Flow Interval, ms
Time interval of the impedance drop
Bolus dwell time during swallow. Long =
delayed initiation of and/or failed clearance
of bolus residue
Swallow Risk Index
Flow Interval × PZn
PeakP × (TZn-PeakP + 1)
× 100
Global measure of swallow function. High
= swallow dysfunction predisposing to
aspiration risk
UES-Relaxation
Interval, s
UES relaxation time
Duration of UES pressure drop
UES nadir pressure,
mmHg
Minimum relaxation pressure
UES residual pressure
UES intrabolus
pressure, mmHg
Median intra-bolus pressure during
UES relaxation
UES bolus distension pressure
UES-Resistance,
mmHg/s
UES-IBP/RI
UES bolus distension pressure relative to
UES relaxation time
Ratio of nadir impedance to postswallow impedance
iZn/Z
Postswallow residue
Table 2. Pressure flow variables and UES relaxation variables derived by AIM
Analysis
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23
Radionuclide scans
In study II, a method previously described by Gleeson et al. (75) was used
to determine whether remifentanil results in aspiration. Radionuclide tracer solution (99mTc-labeled colloid albumin) was infused into the nasopharynx using a pliable plastic tube (10FR) during one hour parallel to intravenous remifentanil or placebo infusion. Eventually, aspirated tracer was
detected in subsequent lung scans. All images were reviewed by the same
nuclear medicine physician and scored as positive or negative for aspiration. Aspiration was diagnosed when activity was present in the lung fields
on either side of the midline structures, such as the esophagus and trachea
(Fig. 3).
Figure 3. Frontal lung scan image showing aspirated tracer in the right lung field.
24
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
Assessment of subjective swallowing difficulties
In all four studies, volunteers were asked to perform dry swallows (stydies
I and II) or wet swallows (studies III and IV) and assess subjective swallowing difficulties on a four-point scale (no difficulty, mild difficulty,
moderate difficulty, or severe difficulty).
Drug administration and monitoring
In all four studies, remifentanil was administered as a target controlled
intravenous infusion (TCI; Minto Model, Alaris PK syringe pump, Alaris
Medical Nordic AB, Sollentuna, Sweden). In studies I and II the effect site
target concentration was 3 ng/ml, in study III three target concentrations
were used (1, 2, and 3 ng/ml), and in study IV the target concentration
was 3 ng/ml for young volunteers and 2 ng/ml for elderly volunteers. In
study I, methylnaltrexone 0.15 mg/kg was administered as subcutaneous
injection In study III, naloxone was administered as an intravenous bolus
injection of 6 μg/kg with subsequent infusion of 0.1 μg · kg−1 · min−1 and
metoclopramide 0.2 mg/kg was given intravenously. In study IV, morphine was administered as a bolus injection of 0.1 mg/kg for young volunteers and 0.07 mg/kg for elderly volunteers. Saline was used as a placebo
comparator in equal amounts to respective drug in study I (methylnaltrexone), study II (remifentanil), and study II (naloxone). Grip strength was
measured using avJamar dynamometervin study II. Vital parameters were
continuously monitored and recorded in all studies.
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Effects of remifentanil on esophageal sphincters
25
Study protocols
Schematic pictures of study protocols used in studies I – IV are presented
in Fig. 4. In all studies, the volunteers were examined on two different
occasions according to crossover design, with intervals of approximately 1
to 2 weeks. Volunteers were placed in supine position in studies I – III and
had a 30° head-up tilt in study IV. Randomization was conducted using
sealed envelopes in study I, and a random number generator in studies II –
IV. In HRM and HRIM studies (studies I, III, and IV), after intravenous
access was obtained the manometric catheter was positioned transnasally,
with the catheter tip in the stomach and the measuring sensors straddling
the pharynx and the entire esophagus. Before and immediately after each
investigation, the catheter was calibrated outside the body using the calibration options provided by the software. In study II, the tube for infusion of radionuclide solution was placed in the nasopharynx, approximately 7 cm into the naris.
26
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Effects of remifentanil on esophageal sphincters
Figure 4. Schematic presentations of study protocols (Studies I – IV). EGJ =
esophagogastric junction; HRM = high resolution manometry; MNTX = methylnaltrexone; EPT = Esophageal pressure topography; HRIM = high resolution
impedance manometry.
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Effects of remifentanil on esophageal sphincters
27
Statistics
For all manometric and impedance parameters, a mean value based on
several measurements (study I: five consequent respiratory cycles; study
III: five swallows; study IV: ten swallows) was calculated for each volunteer and study condition (baseline or during exposure to drug). Data are
summarised as mean ± SD and treatment effects were presented together
with 95% confidence intervals (CI). Two-way repeated measures ANOVA
with one to two within-subject factors were used, followed by planned
comparisons between baseline and exposure to drug (factor time) and
between treatments (factor agent; e.g., remifentanil versus morphine in
study IV). In addition, the linear effect was evaluated for a possible doseresponse association of remifentanil in study II, and age was evaluated as a
between-subject factor in study IV. If violation from the normal distribution of the parameters was observed with the Shapiro-Wilk test, then it
was re-evaluated after logarithmic (log10) transformation. If the ShapiroWilk test still indicated non-normality after log transformation, then nonparametric methods were used for sensitivity analysis (study IV).
In all studies, for each study condition the most frequent answer regarding subjective swallowing difficulties was chosen from repeated assessments. The Wilcoxon paired signed-rank test was used to determine statistically significant differences in subjective swallowing experiences at baseline versus during exposure to drug.
In study II, the occurrence of aspiration with remifentanil versus placebo was compared using an exact test for paired proportions, and the results were presented as proportional differences with normalapproximated 95% confidence intervals (CIs). The x2 test was used to test
the association between swallowing difficulties and aspiration. Two-way
repeated measures ANOVA was used to evaluate grip strength in the same
way as manometric data in other studies.
Vital parameters were evaluated in the same way as manometric data.
P-values < 0.05 were considered statistically significant. All statistical
analyses were performed using SPSS version 19 to version 22 (IBM Corp,
Armonk, NY, USA) or STATA release 11 (STATACorp., College Station,
TX).
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Effects of remifentanil on esophageal sphincters
Results
Study I
In study I, we examined the effect of remifentanil on the EGJ and showed
that remifentanil significantly decreased the inspiratory EGJ augmentation
(P < 0.01) (Fig. 5). The decrease was not significant when the volunteers
received methylnaltrexone and remifentanil, nor were the differences between placebo/remifentanil and methylnaltrexone/remifentanil statistically
significant.
Figure 6 illustrates the swallowing difficulties experienced by volunteers
before, during, and after remifentanil infusion. The time during remifentanil infusion was divided into two 15-min periods. With both placebo
and methylnaltrexone, the same 7 volunteers reported more difficulty
swallowing during remifentanil infusion compared with both before infusion and 15 min after ending remifentanil infusion. Statistically significant
increases in swallowing difficulty were observed between pre-remifentanil
and the first 15 min of remifentanil infusion with both placebo (P = 0.02)
and methylnaltrexone (P = 0.03). Statistically significant differences were
also observed between pre-remifentanil and the second 15-min period of
remifentanil infusion. After remifentanil infusion was stopped, the swallowing difficulties gradually vanished as the target concentration of remifentanil diminished.
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
29
Figure 5. Boxplots showing the inspiratory EGJ augmentation over time in 10
volunteers randomly assigned to receive methylnaltrexone or placebo in addition
to remifentanil infusion in study I. T2 = 30 min after methylnaltrexone/placebo
injection, T3 = 15 min after remifentanil infusion was started, T4 = 30 min after
remifentanil infusion was started, T5 = 15 min after remifentanil infusion was
stopped. Boxplot showing the 25th and 75th percentiles as the top and bottom
edges of a box and the median as the line inside the box; whiskers represent the
minimum and maximum, if no outliers are present.
30
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Effects of remifentanil on esophageal sphincters
Figure 6. Subjective swallowing difficulties experienced by volunteers in study I.
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
31
Study II
In study II we investigated whether a 1-hour infusion of remifentanil at a
target controlled concentration of 3 ng/ml results in pulmonary aspiration.
Subjective swallowing difficulties and grip strength were recorded, and the
association between eventual aspiration and swallowing difficulties was
determined. The occurrence of aspiration in volunteers during the study is
presented in Table 3. Ten of 25 study subjects had evident radionuclide
tracer in their lung fields, indicating aspiration, after remifentanil treatment but not after placebo. Twelve subjects did not have apparent radionuclide tracer in the lungs after either treatment, two subjects had positive
lung scans after both treatments, and one subject had radionuclide in the
lungs only after placebo treatment. The difference between remifentanil
and placebo treatment was significant; 48% and 12% of volunteers aspirated after remifentanil and placebo, respectively (Difference: 36%;
95%CI 10% to 62%). The location of the tracer in the lung fields demonstrates that the majority of volunteers aspirated into the right lung field
(Table 4).
During remifentanil treatment, seven volunteers experienced moderate
swallowing difficulties and five volunteers experienced severe swallowing
difficulties. None of these 12 volunteers had swallowing difficulties before
the infusion, and all returned to normal swallowing after the infusion. The
remaining 13 volunteers experienced no difficulty swallowing before, during, or after the infusion. The difference in swallowing difficulty before
infusion (0%) versus during infusion (48%) was significant (p = 0.002).
None of the volunteers had difficulty swallowing before, during, or after
placebo treatment. The difference in swallowing difficulty among the placebo group (0%) versus the remifentanil group (48%) was significant (p =
0.002).
Swallowing difficulties were reported by seven of the 12 volunteers
(54%) who aspirated during remifentanil treatment compared with five of
the 13 (38%) who did not aspirate during remifentanil treatment. The
association between aspiration and swallowing difficulties was not significant (p = 0.32). None of the three volunteers who aspirated during placebo treatment had swallowing difficulties.
No differences in grip strength were observed between the remifentanil
and placebo groups.
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Effects of remifentanil on esophageal sphincters
PLACEBO n = 25
REMIFENTANIL
Aspiration
n = 25
No Aspiration
Total
Aspiration
No Aspiration
8% (2)
40% (10)
4% (1)
48% (12)
Total
48% (12)
12% (3)
Table 3. Aspiration in groups that received remifentanil versus placebo in study II.
Proportions are presented as percentages, with actual frequency counts in parentheses.
Subject No.
Remifentanil
Placebo
1
Right Lung
-
Right Lung
-
3
-
Right Lung
4
Right and Left Lung
-
5
Right Lung
-
6
Right Lung
-
7
Right and Left Lung
Left Lung
8
Right Lung
-
9
Right and Left Lung
-
10
Right and Left Lung
Right and Left Lung
11
Left Lung
-
12
Right Lung
-
13
Right Lung
-
”-” indicates no aspiration.
Table 4. Location of aspirated tracer in study II
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Effects of remifentanil on esophageal sphincters
33
Study III
In study III, the impact of remifentanil onesophageal motility was evaluated by analysing five specific EPT metrics based on the Chicago Classification. We also aimed to determine whether the effects of remifentanil were
subject to dose-response association and whether the effects could be
counteracted by naloxone or metoclopramide. The results are presented in
Table 5. The study showed that three of the EPT metrics that define primary esophageal motility were significantly influenced by remifentanil: the
latency time of distal swallow-evoked esophageal contraction was shortened, the swallow-induced EGJ relaxation was decreased, and the intrabolus pressure preceding the esophageal contraction was increased. There
was a negative association between the latency time of the distal esophageal contraction and the concentration of remifentanil. No statistically
significant differences were observed between occasions with or without
naloxone. Metoclopramide significantly increased the vigor of the swallow-evoked esophageal contraction on both occasions.
On the occasion without naloxone, 14% of volunteers experienced mild
or more-severe swallowing difficulties at baseline compared with 43%
when exposed to remifentanil (P = 0.096). On the occasion with naloxone,
43 % of volunteers experienced mild or more severe swallowing difficulties both at baseline and when exposed to remifentanil (P = 0.41).
34
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Effects of remifentanil on esophageal sphincters
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Effects of remifentanil on esophageal sphincters
35
Data are means ± SD. Each esophageal pressure topography metric was evaluated with ANOVA for repeated measures,
with difference from baseline (T0) as the outcome variable for the interaction P-values (agent × time). Linear doseresponse evaluation for remifentanil was done from T0 to T3. Paired t-test was used to compare T3 and T4 for each
agent, as well as with an ANOVA interaction test (time × agent) with only T3 and T4 as time factors (metoclopramide
effect). 4s-IRP = integrated EGJ relaxation pressure; IBP = intra bolus pressure; DL = distal latency; CFV = contractile
front velocity; DCI = distal contractile integral; Nalox = naloxone; T0 = baseline; T1 = 1 ng/ml remifentanil; T2 = 2
ng/ml remifentanil 2 ng/ml; T3 = 3 ng/ml remifentanil; T4 = after metoclopramide.
Table 5. Esophageal pressure topography metrics in 14 volunteers in study III
Study IV
In study IV, we evaluated the effects of remifentanil on pharyngeal swallowing. We employed HRIM combined with AIM analysis to derive pressure-flow and UES relaxation metrics. We also aimed to compare remifentanil with morphine, and both young and old volunteers were enrolled in
the study. The effects of each drug on different swallow function variables
are presented as effect ratios in Table 6. Comparisons of the two drugs are
presented in Table 7. Most of the pressure flow variables were influenced
by remifentanil: the peak pharyngeal pressure (PeakP) was decreased, the
time interval from the pharyngeal peak pressure to the nadir impedance
(TZn-PeakP) decreased, and the swallow risk index (SRI) was increased.
Furthermore, measures of UES flow resistance were increased.
Similar although smaller effects were observed with morphine. One variable in particular exibited a statistically significant difference between
treatments: TZn-PeakP was decreased only with remifentanil. When the
volunteers were stratified by age, two variables exhibited significant interaction effect: in young volunteers, pressures during UES relaxation (UESNad-P and UES-IBP) increased by a significantly greater degree with remifentanil than with morphine. No differences between remifentanil and
morphine were observed among the older volunteers.
At baseline, one subject reported swallowing difficulties with both
treatments (remifentanil: male aged 26 years; morphine: male aged 27
years). No subjects reported swallowing difficulties during morphine exposure, while two subjects (both males, aged 22 and 65 years) reported
swallowing difficulties during remifentanil exposure. This increase in proportion was not statistically significant (p=0.41).
Vital parameters exhibited some minor but statistically significant differences in studies II-IV during drug exposure compared with baseline or
between treatments; however, but no clinically relevant changes were observed.
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Effects of remifentanil on esophageal sphincters
Table 6. The effects of remifentanil and morphine on pressure flow variables in 18
volunteers in study IV. Each variable was evaluated with repeated measures
ANOVA. A mean ratio is a relative mean difference: a mean ratio of 1 indicates no
difference, and a mean ratio of 1.40 indicates a 40% greater mean level (at timepoints T1, T2) with a specific agent (remifentanil or morphine) versus T0. The Pvalue for age tests whether treatment effects differ in young versus old volunteers.
All = all 18 volunteers; Young = 11 < 30 years; Old = 7 > 65 years; PeakP = peak
pharyngeal pressure; Zn = nadir impedance; PZn = pressure at nadir impedance;
TZn–PeakP = time interval from nadir impedance to PeakP; UES = upper esophageal sphincter; Zn/Z = ratio of nadir impedance to post swallow impedance T0 =
baseline; T1 = 15 min after treatment start; T2 = 30 min after treatment start; CI =
confidence interval. Data for which P < 0.05 are presented in bold.
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Effects of remifentanil on esophageal sphincters
37
Table 7. The effects of remifentanil versus morphine on pressure flow variables in
18 volunteers in study IV. Each variable was evaluated with repeated measures
ANOVA with differences between T0 and mean (T1 T2) as outcomes. A mean
ratio is a relative mean difference: a mean ratio of 1 indicates no difference, and a
mean ratio of 1.40 indicates a 40% greater mean effect T1, T2 vs. T0 with remifentanil versus morphine. P-value for interaction (age*agent) tests whether the
agent effects differ in young versus old volunteers. All = all 18 volunteers: Young =
11 < 30 years, Old = 7 > 65 years; PeakP = peak pharyngeal pressure; Zn = nadir
impedance; PZn = pressure at nadir impedance; TZn–PeakP = time Zn to PeakP;
CI = Confidence Interval. Data for which P < 0.05 are presented in bold.
38
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Effects of remifentanil on esophageal sphincters
Discussion
In this thesis, we attempted to explore how drugs used in anaesthesia, and
remifentanil in particular, affect defence mechanisms against pulmonary
aspiration in individuals. We also surveyed subjective swallowing difficulties induced by remifentanil.
Aspiration induced by remifentanil
We demonstrated in study II that a 1-hour infusion of remifentanil at a
target-site concentration of 3 ng/ml resulted in aspiration in healthy volunteers. Aspiration of pharyngeal content mixed with radionuclide tracer
was directly demonstrated in scintigraphic lung images, in contrast to
other investigations that have used impaired pharyngeal function induced
by agents during anaesthesia as an indirect indicator of increased aspiration risk (57-60). No differences in grip strength, which was recorded as a
measure of general muscle strength, were observed between remifentanil
and placebo; however, the study did not determine the mechanisms underlying aspiration induced by remifentanil in this experimental setting. Several levels of defence against pulmonary aspiration can be impaired. The
volunteers might aspirate the tracer detected in lung scans directly after its
entrance into the pharynx from the nasopharynx (pharyngeal-topulmonary aspiration), or they might first swallow and thereafter regurgitate the tracer before aspiration (gastric-to-pulmonary aspiration). The
relevance of this framing of the question is that gastric-to-pulmonary aspiration has been implicated in the development of aspiration pneumonitis,
pneumonia, and acute respiratory distress syndrome (ARDS) (76), while
the aspiration of oropharyngeal secretions may contribute to the development of pneumonia, but not necessarily pneumonitis or ARDS (77). The
direct entrance to the airway is protected by several laryngeal and pharyngeal reflexes, with or without coincident swallowing (24), and disruption
of these complex motorsensory neural circuits is one possible cause. Furthermore, the competence of the esophageal sphincters and wellfunctioning esophageal motility prevent the retrograde regurgitation of
already swallowed material, and these mechanisms may also be affected
by remifentanil. The remaining studies aimed to investigate the impact of
remifentanil on these airway defense mechanisms.
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Effects of remifentanil on esophageal sphincters
39
Effects of remifentanil on the esophagogastric junction
In study I, we used HRM to show that remifentanil affected the barrier
function of the EGJ by decreasing augmentation of the inspiratory EGJ.
Pandolfino et al. reported that the inspiratory augmentation of EGJ pressure is significantly independently associated with gastro-esophageal reflux
disease (12). When they analysed inspiratory EGJ augmentation as a predictor of objective reflux disease, they determined an optimal cut-off value
of 10 mmHg, with lower values being indicative for reflux. In study I, the
inspiratory augmentation of EGJ pressure decreased to 6.0 mmHg with
remifentanil, suggesting a risk for reflux when remifentanil is administered.
The augmentation of the inspiratory EGJ is thought to reflect the respiratory function of the CD, which is innervated by the phrenic nerve, and
we detected no statistically significant effects of the peripheral opioid antagonist methylnaltrexone on remifentanil-induced changes. However,
because of the limited sample size, no conclusion can be made regarding
whether remifentanil’s effects on EGJ augmentation and swallowing are
centrally or peripherally mediated.
Effects of remifentanil on esophageal motility
In study III, we demonstrated that remifentanil influenced distal esophageal peristalsis by shortening the latency time of distal esophageal contraction, decreasing the swallow-evoked relaxation of the EGJ, and increasing
the pressure in the fluid bolus preceding the esophageal contraction. Furthermore, there was a clear negative dose-dependent association between
remifentanil and distal latency time. After a swallow, a wave of hyperpolarisation of the esophageal smooth muscle precedes the arrival of the
peristaltic contraction that relaxes and prepares the esophageal body to
receive the oncoming bolus and open the EGJ (28). This relaxation starts
simultaneously throughout the entire distal esophageal body, but lasts
progressively longer in progressively more distal segments of the esophagus. Normal esophageal peristalsis is produced by an aborally increasing
latency between swallowing and contraction, also called deglutitive inhibition of the esophaegeal body (28). Shortening of the distal latency time
and decreased swallow-evoked EGJ relaxation are both expressions of
dysfunctional deglutitive inhibition (28, 78), and the results of study III
indicate that remifentanil impairs of deglutitive inhibition of the smooth
muscle of the distal esophageal body and the EGJ. Morphine has been
40
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Effects of remifentanil on esophageal sphincters
suggested to have similar effects, although with older manometric methodology; this implies that both older and newer synthetic opioids have a
similar influence on esophageal motility. Furthermore, in patients, failing
deglutitive inhibition is often presented as diffuse esophageal spasm or
spastic achalasia (79), and it is suggested that esophageal motility abnormalities in patients on chronic opiate medication mimic these clinical conditions (51). The effects of remifentanil on esophageal motility could be
either centrally or peripherally mediated, given that both central inhibitory
vagal pathways and regional inhibitory myenteric nerves are involved in
esophageal deglutitive inhibition.
Naloxone, a competitive opioid receptor antagonist, did not counteract
the effects of remifentanil; however, because of the limited sample size, it
is unclear whether the effects of remifentanil on esophageal motility are
mediated through opioid receptors or whether other receptors are also
involved. The dopamine antagonist metoclopramide did not attenuate the
effects of remifentanil. On the contrary, there was a tendency toward amplification of these effects which suggests that metoclopramide cannot be
used to prevent remifentanil-induced esophageal dysmotility.
Effects of remifentanil on pharyngeal swallowing
In study IV, we evaluated the effects of remifentanil on pharyngeal swallowing using HRIM combined with AIM analysis to derive pressure flow
and UES relaxation metrics. Remifentanil in particular influenced most
pressure flow variables towards the direction that suggests greater swallow
dysfunction: vigor of the pharyngeal contraction was weakened, pharyngeal bolus propulsion was diminished, and UES flow resistance increased.
In this study, the effects of remifentanil on pharyngeal swallowing were
compared with the effects of morphine. Even morphine resulted in weaker
pharyngeal contraction, and SRI and UES resistance were increased; however, the remifentanil’s effects were greater overall. Furthermore, there
was a significant difference between drugs regarding one variable in particular. TZn-PeakP was shortened with remifentanil, while no differences
were observed with morphine. TZn-PeakP measures the time from bolus
passage into the pharynx from the oral cavity to pharyngeal contraction
and is thought to reflect the strength of lingual bolus propulsion and/or
whether the pharyngeal response (also called the pharyngeal swallow trigger) is coordinated and well timed with respect to the bolus transfer.
Many dysphagia patients demonstrate weak lingual bolus propulsion,
poor oral bolus containment, and/or delayed pharyngeal trigger, and TZnJOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
41
PeakP is shorter in relation to these particular modes of swallow defect
(80). As a corollary to these objective findings, we found in study I that
subjects who reported swallowing problems following remifentanil exposure reported the inability to initiate a swallow. Hence, we conclude that
remifentanil may have a greater effect on lingual bolus propulsion and/or
pharyngeal swallow trigger than morphine.
Oropharyngeal swallowing is a complex, stereotyped sequence of the
inhibition and activation of several pairs of muscles driven by several motor neuron pools located in various cranial motor nuclei in the brainstem
and the upper part of the cervical spinal cord (26), which in turn are triggered by both central and peripheral inputs. Consequently, several sites of
action for opioids, both peripheral and central, or muscle tone/rigidity, are
possible.
Both young and old volunteers were enrolled in study IV. Generally, the
older volunteers exhibited differences in pressure flow variables that suggest greater swallow dysfunction compared with young volunteers. These
findings are consistent with a previous report evaluating older adults with
AIM analysis (81). In addition, when stratified by age, pressures during
UES relaxation (UES nadir pressure and UES intrabolus pressure) exhibited a heterogeneous treatment effect, and UES resistance showed a similar
trend: these variables increased in young volunteers exposed to remifentanil in particular, while the old volunteers started from almost twofold
higher baseline values and were less influenced by the treatments. One
explanation may be that old volunteers already exhibit values near the
upper limit for a specific variable with no capacity for additional increase.
Another explanation may be that the lower drug dosages administered to
older subjects were insufficient to induce an effect in these variables. Other
variables in study IV did not exhibit differing effects caused by drugs when
volunteers were stratified by age, although this might be a power issue:
although twelve old volunteers were planned to participate in accordance
with power analysis, we managed to include only seven.
Subjective swallowing difficulties
In study I, we showed that remifentanil induced subjective swallowing
difficulties. Seven of ten volunteers reported more difficulty swallowing
during remifentanil infusion than either before infusion or 15 min after
ending remifentanil infusion. Most volunteers went from experiencing no
difficulty to severe swallowing difficulty immediately after the remifentanil
target concentration was achieved. A significant increase in subjective
42
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Effects of remifentanil on esophageal sphincters
swallowing difficulties during exposure to remifentanil was also observed
in study II, although we observed no association between pulmonary aspiration detected with lung scans and swallowing difficulties. However,
these findings could not be reproduced in studies III and IV. The manometric results in these studies suggest that remifentanil affects pharyngeal
and esophageal swallowing towards the direction of greater dysfunction
while the mean values of swallow metrics remained within the sub-clinical
normal range, and therefore did not lead to symptoms in the tested subjects. The volunteers performed dry swallows in studies I and II and swallowed liquid boluses in studies III and IV (study II: 2 mL water; study III:
10 mL saline). Wet swallows are easier to perform than dry swallows, and
swallowing liquid is probably sufficient to overcome the sensation of swallowing difficulty induced by remifentanil. It might be claimed that the
volunteers experienced swallowing difficulty when performing dry swallows because of a lack of saliva in studies I and II; however, when the
remifentanil infusion was stopped, the subjective swallowing difficulties
were reversed.
Limitations
The blood concentration of remifentanil was not measured in these studies. This data would have strengthened the studies the actual blood concentrations reached with TCI methodology vary considerably among individuals. However, most volunteers were relatively young and of normal
weight, which minimizes this variability.
The level of sedation was not monitored in these studies, and whether
eventual sedation induced by remifentanil contributed to the increased
incidence of aspiration and to the effects on pharyngeal swallowing and
esophageal motility cannot be addressed. A previous study using the modified observer’s assessment of the alertness-sedation scale showed that remifentanil infusion with a target concentration of 3 ng/ml, which was used
in all of the four studies presented here, does not induce deep sedation
(82). Furthermore, remifentanil alone in concentrations in the clinical
range is insufficient to induce loss of consciousness (83, 84). All volunteers
responded promptly to instructions during the experiments (e.g., when
liquid boluses were administered for swallow assessment), indicating that
volunteers were not deeply sedated.
In study IV, dosages of remifentanil and morphine aimed to represent
clinically relevant dosages. Owing to different pharmacokinetic profiles,
no actual eqiupotency was searched.
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Effects of remifentanil on esophageal sphincters
43
No power analysis was performed in studies I and III. Study I was the
first evaluation of whether methylnaltrexone was able to reverse remifentanil-induced effects on EGJ and swallowing. Twelve volunteers were recruited based on the results of a previous study that investigated methylnaltrexone’s influence on the effects of morphine on gastric emptying, in
which 11 volunteers were enough to ensure statistical significance (85). In
study III, we recruited 15 volunteers based on the results of two previous
studies that investigated the effects of morphine on esophageal motor response, in which eight and ten volunteers, respectively, were sufficient to
ensure statistical significance (49, 86). Furthermore, in study IV, in accordance with the power analysis, we planned to recruit 12 young volunteers and 12 old volunteers. However, only seven old volunteers were
included owing to poor interest, and the small number of old individuals
weakened the study’s statistical power to demonstrate differences between
age groups.
A manometric catheter can influence the experience of eventual swallowing difficulties. However, exposure to remifentanil was always compared with baseline, after the catheter had been placed and before remifentanil had been administered. Furthermore, volunteers were instructed to
ignore the sensation of the catheter in the pharynx.
Clinical implications
In this thesis, we have explored deficiencies in protection against pulmonary aspiration owing to drugs used in anaesthesia and remifentanil in
particular. These findings are relevant to perioperative anaesthesia in clinical practice, particularly in the context of monitored anaesthesia care and
during intensive care.
Remifentanil has gained wide acceptance in clinical settings and is used
not only as an adjuvant in general anesthesia, but also in monitored anesthesia care as a single infusion or in combination with hypnotics. Remifentanil is particularly suitable for use in conscious sedation during painful
but minor surgical procedures because of its rapid onset (1 – 2 min) and
short duration of action (5 – 7 min) (63). Moreover, remifentanil has recently become an alternative in labor analgesia when neuraxial analgesia is
contraindicated (61, 62). Furthermore, remifentanil use is not unusual in
the intensive care unit, and pharyngeal dysphagia (87, 88) and silent aspirations (89) are common after prolonged endotracheal intubation. Our
studies indicate that remifentanil impairs several levels of airway protec44
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
tion. And although effects on pharyngeal and esophageal swallowing remained within the sub-clinical range, we believe that a compound effect
induced by remifentanil alters airway protection towards greater dysfunction. These findings may improve clinical practice by encouraging that the
drug is used with caution. In circumstances in which the patient is spontaneously breathing, swallowing keeps the pharynx free of material that
might otherwise threaten the airway. Therefore, swallowing dysfunction
induced by remifentanil is an essential problem to take into account. Additionally, we found that even morphine influences pharyngeal swallowing,
although not to the same extent as remifentanil, and based on our results
we think morphine should be chosen as analgesia in susceptible patients.
We even confirmed the previous findings (31, 32, 81) that the functional
swallowing reserve declines in healthy older individuals, and drugs that
further deteriorate swallowing function should be used with great attention in the elderly. Furthermore, with regard to our findings, we believe
the fasting guidelines for women in labor receiving remifentanil should be
reviewed.
Future perspectives
This thesis presents insights into the effects of remifentanil on pharyngeal
and esophageal defence mechanisms against pulmonary aspiration. Remifentanil-induced aspiration was directly demonstrated using a scintigraphic method. However, there are still many questions to be answered. For
example, it would be of clinical value to visualise the precise route of the
aspirated material in order to differentiate between pharyngeal-topulmonary and gastric-to-pulmonary aspiration; it should be feasible,
although logistically and economically difficult, to implement the dynamic
collection of a series of lung scans by having the study subject in the gamma camera during the entire study session.
How different drugs used for sedation in monitored anaesthesia care
influence defences against pulmonary aspiration has not been completely
explored. More volunteer studies to evaluate the effects of for example,
propofol and dexmedetomidine are needed. Perioperative studies to assess
pharyngeal swallowing with focus on the immediate postoperative phase
would also be interesting; this period should be vulnerable considering
postoperative pulmonary complications such as pneumonia, as the patient
is spontaneously breathing, is exposed to residual effects of general anaesthesia, and the requirements of analgesia are usually high.
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
45
Outcome studies to determine to what extent pulmonary complications
emerge after monitored anaesthesia care in high-risk patients are also
needed. Another interesting area is that regarding patients in the intensive
care unit with tracheostomy or after prolonged endotracheal intubation.
These patients are often encouraged to undertake oral feeding soon after
extubation in order to fulfil the nutritional and psychological needs, and
studies that assess swallowing function and the impact of different sedative drugs on swallowing in these patients would be valuable.
46
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
Conclusions
Based on this thesis it is concluded that:
• Remifentanil may increase risk for gastro-esophageal reflux by decreasing the inspiratory EGJ augmentation, and thereby interfering
with the function of the crural diagphragm.
• Remifentanil induces dysfunction of esophageal motility by impairing the deglutitive inhibition of the distal esophageal body. This
may also contribute to elevated risk of regurgitation.
• Remifentanil infusion at concentrations used in monitored anesthesia care increases the incidence of aspiration.
• Remifentanil in particular influences pharyngeal swallowing towards greater dysfunction, as does morphine in relevant doses.
• Remifentanil affects several levels of defence against pulmonary aspiration. The risk of gastric-pulmonary aspiration is increased by
impaired protection against gastro-esophageal reflux and retrograde regurgitation of gastric contents. Pharyngeal-to-pulmonary
aspiration can occur owing to dysfunction of pharyngeal swallowing.
• Remifentanil induces subjective swallowing difficulties when subjects perform dry swallows, but not when liquid is swallowed.
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
47
Summary in Swedish
Postoperativa lungkomplikationer är vanliga och en möjlig bakomliggande
orsak kan vara tyst aspiration, det vill säga att svalg-och/eller maginnehållet hamnar i lungorna utan att det bevittnas som uppenbar händelse. Det
finns flera nivåer av fysiologiska skydd mot pulmonell aspiration, de viktigaste är kompetensen i nedre- och övre esofagussfinktern samt faryngeala och laryngeala försvarsmekanismer med eller utan samtidig
sväljning. Den potenta opiaten remifentanil används utbrett inom anestesioch intensivvård; dels som adjuvantia vid generell anestesi men även som
enskilt läkemedel för sedering vid kirurgiska ingrepp. Det är även vanligt
förekommande som smärtstillande medel vid behandling av intensivvårdspatienter.
I mina studier har vi dels använt manometriska mätningar för att undersöka effekten av remifentanil på esophagussfinktrarna, samt på esophageala och pharyngeala sväljningsfasen med fokus på skydd mot aspiration. Vi har även testat förekomsten av pulmonell aspiration i samband
med remifentanil administration med en röntgenologisk metod. Eftersom
försökspersoner i våra tidigare studier spontant rapporterade sväljningssvårigheter vid remifentanil infusion har vi även studerat huruvida remifentanil inducerar sväljningssvårigheter.
I första arbetet visades att remifentanil försämrar barriärfunktionen av
den nedre esofagussfinktern genom att sänka tryckaugmentationen i denna
högtryckszon under inspiration. I det andra arbetet påvisades förekomst
av pulmonell aspiration hos friska frivilliga försökspersoner efter 60 minuters remifentanil infusion. I tredje och fjärde studien studerades effekten av
remifentanil på den esophageala respektive pharyngeala sväljningen och
man såg att båda sväljningsfaserna påverkades negativt. Remifentanil
nducerade subjektiva sväljningssvårigheter i de första två arbetena då försökspersoner utförde torra sväljningar, dessa fynd kunde dock inte upprepas i de sista två arbetena, då försökspersoner svalde vätska.
Sammanfattningsvis, remifentanil försämrar skyddet mot pulmonell
aspiration genom en påverkan på flertal fysiologiska försvarsmekanismer
av luftvägen i såväl farynx som esophagus. Detta, tillsammans med det
faktum att vi kunde påvisa förekomst av aspiration i samband med remifentanil infusion bör leda till att större försiktighet iakttas vid remifentanil
infusion på vakna patienter.
48
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
Acknowledgements
I would like to thank:
All volunteers who contributed to this thesis.
Magnus Wattwil, my tutor, for your support, positivity, and encouragement. Thank you for helping me to achieve one of the greatest goals of my
life.
Rebecca Ahlstrand, my co-tutor, for constructive criticism in detail of
every manuscript.
Anette Dahlqvist, research nurse, for your careful assistance in collecting
data. And Ingrid Engström for collaboration in study IV.
Anders Magnuson, statistician and co-author, for patiently supporting me
in the statistical analysis of the studies.
Håkan Geijer, co-author, for collaboration in study II.
Taher Omari, co-author, for collaboration in study IV.
Anders Nydahl, head of the department, for prioritising research.
Stina Björeman-Gerdevåg, assistant head of the department and scheduler,
for making space in the schedule for my research during the last busy
weeks.
My colleagues at the department, who together have all created time for
my research.
Ing-Marie Dimgren, Git Welamsson, secretaries, for your support with
these papers.
Members of the stuff at the department, especially at the day-care surgery,
for borrowing your corridors for studies I, III, and IV.
JOHANNA SAVILAMPI
Effects of remifentanil on esophageal sphincters
49
Members of the stuff at the department of radiology, for your assistance in
collecting data in study II.
My parents, for believing in me.
Martin, for love and support.
Kajsa, for being my everything.
The work in this thesis was supported by funding from the Research
Committee of the Örebro County Council.
50
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Effects of remifentanil on esophageal sphincters
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57
Publications in the series
Örebro Studies in Medicine
1.
Bergemalm, Per-Olof (2004). Audiologic and cognitive long-term
sequelae from closed head injury.
2.
Jansson, Kjell (2004). Intraperitoneal Microdialysis.
Technique and Results.
3.
Windahl, Torgny (2004). Clinical aspects of laser treatment of
lichen sclerosus and squamous cell carcinoma of the penis.
4.
Carlsson, Per-Inge (2004). Hearing impairment and deafness.
Genetic and environmental factors – interactions – consequences.
A clinical audiological approach.
5.
Wågsäter, Dick (2005). CXCL16 and CD137 in Atherosclerosis.
6.
Jatta, Ken (2006). Inflammation in Atherosclerosis.
7.
Dreifaldt, Ann Charlotte (2006). Epidemiological Aspects on
Malignant Diseases in Childhood.
8.
Jurstrand, Margaretha (2006). Detection of Chlamydia trachomatis
and Mycoplasma genitalium by genetic and serological methods.
9.
Norén, Torbjörn (2006). Clostridium difficile, epidemiology and
antibiotic resistance.
10. Anderzén Carlsson, Agneta (2007). Children with Cancer – Focusing
on their Fear and on how their Fear is Handled.
11. Ocaya, Pauline (2007). Retinoid metabolism and signalling in
vascular smooth muscle cells.
12. Nilsson, Andreas (2008). Physical activity assessed by accelerometry
in children.
13. Eliasson, Henrik (2008). Tularemia – epidemiological, clinical and
diagnostic aspects.
14. Walldén, Jakob (2008). The influence of opioids on gastric function:
experimental and clinical studies.
15. Andrén, Ove (2008). Natural history and prognostic factors in
localized prostate cancer.
16. Svantesson, Mia (2008). Postpone death? Nurse-physician
perspectives and ethics rounds.
17. Björk, Tabita (2008). Measuring Eating Disorder Outcome
– Definitions, dropouts and patients’ perspectives.
18. Ahlsson, Anders (2008). Atrial Fibrillation in Cardiac Surgery.
19. Parihar, Vishal Singh (2008). Human Listeriosis – Sources and Routes.
20. Berglund, Carolina (2008). Molecular Epidemiology of MethicillinResistant Staphylococcus aureus. Epidemiological aspects of MRSA
and the dissemination in the community and in hospitals.
21. Nilsagård, Ylva (2008). Walking ability, balance and accidental falls in
persons with Multiple Sclerosis.
22. Johansson, Ann-Christin (2008). Psychosocial factors in patients
with lumbar disc herniation: Enhancing postoperative outcome by
the identification of predictive factors and optimised physiotherapy.
23. Larsson, Matz (2008). Secondary exposure to inhaled tobacco
products.
24. Hahn-Strömberg, Victoria (2008). Cell adhesion proteins in different
invasive patterns of colon carcinoma: A morphometric and molecular
genetic study.
25. Böttiger, Anna (2008). Genetic Variation in the Folate Receptor-α
and Methylenetetrahydrofolate Reductase Genes as Determinants
of Plasma Homocysteine Concentrations.
26. Andersson, Gunnel (2009). Urinary incontinence. Prevalence,
treatment seeking behaviour, experiences and perceptions among
persons with and without urinary leakage.
27. Elfström, Peter (2009). Associated disorders in celiac disease.
28. Skårberg, Kurt (2009). Anabolic-androgenic steroid users in treatment:
Social background, drug use patterns and criminality.
29. de Man Lapidoth, Joakim (2009). Binge Eating and Obesity Treatment
– Prevalence, Measurement and Long-term Outcome.
30. Vumma, Ravi (2009). Functional Characterization of Tyrosine
and Tryptophan Transport in Fibroblasts from Healthy Controls,
Patients with Schizophrenia and Bipolar Disorder.
31. Jacobsson, Susanne (2009). Characterisation of Neisseria meningitidis
from a virulence and immunogenic perspective that includes variations
in novel vaccine antigens.
32. Allvin, Renée (2009). Postoperative Recovery. Development of a
Multi-Dimensional Questionnaire for Assessment of Recovery.
33. Hagnelius, Nils-Olof (2009). Vascular Mechanisms in Dementia
with Special Reference to Folate and Fibrinolysis.
34. Duberg, Ann-Sofi (2009). Hepatitis C virus infection. A nationwide
study of assiciated morbidity and mortality.
35. Söderqvist, Fredrik (2009). Health symptoms and potential effects on
the blood-brain and blood-cerebrospinal fluid barriers associated with
use of wireless telephones.
36. Neander, Kerstin (2009). Indispensable Interaction. Parents’ perspectives
on parent–child interaction interventions and beneficial meetings.
37. Ekwall, Eva (2009). Women’s Experiences of Gynecological Cancer
and Interaction with the Health Care System through Different Phases
of the Disease.
38. Thulin Hedberg, Sara (2009). Antibiotic susceptibility and resistance
in Neisseria meningitidis – phenotypic and genotypic characteristics.
39. Hammer, Ann (2010). Forced use on arm function after stroke.
Clinically rated and self-reported outcome and measurement during
the sub-acute phase.
40. Westman, Anders (2010). Musculoskeletal pain in primary health
care: A biopsychosocial perspective for assessment and treatment.
41. Gustafsson, Sanna Aila (2010). The importance of being thin
– Perceived expectations from self and others and the effect on
self-evaluation in girls with disordered eating.
42. Johansson, Bengt (2010). Long-term outcome research on PDR
brachytherapy with focus on breast, base of tongue and lip cancer.
43. Tina, Elisabet (2010). Biological markers in breast cancer and acute
leukaemia with focus on drug resistance.
44. Overmeer, Thomas (2010). Implementing psychosocial factors in
physical therapy treatment for patients with musculoskeletal pain
in primary care.
45. Prenkert, Malin (2010). On mechanisms of drug resistance in
acute myloid leukemia.
46. de Leon, Alex (2010). Effects of Anesthesia on Esophageal
­Sphincters in Obese Patients.
47. Josefson, Anna (2010). Nickel allergy and hand eczema –
epidemiological aspects.
48. Almon, Ricardo (2010). Lactase Persistence and Lactase NonPersistence. Prevalence, influence on body fat, body height, and
relation to the metabolic syndrome.
49. Ohlin, Andreas (2010). Aspects on early diagnosis of neonatal sepsis.
50. Oliynyk, Igor (2010). Advances in Pharmacological Treatment of
Cystic Fibrosis.
51. Franzén, Karin (2011). Interventions for Urinary Incontinence in
Women. Survey and effects on population and patient level.
52. Loiske, Karin (2011). Echocardiographic measurements of the heart.
With focus on the right ventricle.
53. Hellmark, Bengt (2011). Genotypic and phenotypic characterisation of
Staphylococcus epidermidis isolated from prosthetic joint ­infections.
54. Eriksson Crommert, Martin (2011). On the role of transversus
­abdominis in trunk motor control.
55. Ahlstrand, Rebecca (2011). Effects of Anesthesia on Esophageal
Sphincters.
56. Holländare, Fredrik (2011). Managing Depression via the Internet
– self-report measures, treatment & relapse prevention.
57. Johansson, Jessica (2011). Amino Acid Transport and Receptor ­Binding
Properties in Neuropsychiatric Disorders using the Fibroblast Cell
Model.
58. Vidlund, Mårten (2011). Glutamate for Metabolic Intervention in
Coronary Surgery with special reference to the GLUTAMICS-trial.
59. Zakrisson, Ann-Britt (2011). Management of patients with Chronic
Obstructive Pulmonary Disease in Primary Health Care.
A study of a nurse-led multidisciplinary programme of pulmonary
rehabilitation.
60. Lindgren, Rickard (2011). Aspects of anastomotic leakage, anorectal
function and defunctioning stoma in Low Anterior Resection of the
rectum for cancer.
61. Karlsson, Christina (2011). Biomarkers in non-small cell lung
­c arcinoma. Methodological aspects and influence of gender,
­histology and smoking habits on estrogen receptor and epidermal
growth factor family receptor signalling.
62. Varelogianni, Georgia (2011). Chloride Transport and Inflammation
in Cystic Fibrosis Airways.
63. Makdoumi, Karim (2011). Ultraviolet Light A (UVA) Photoactivation
of Riboflavin as a Potential Therapy for Infectious Keratitis.
64. Nordin Olsson, Inger (2012). Rational drug treatment in the elderly:
”To treat or not to treat”.
65. Fadl, Helena (2012). Gestational diabetes mellitus in Sweden:
screening, outcomes, and consequences.
66. Essving, Per (2012). Local Infiltration Analgesia in Knee
­Arthroplasty.
67. Thuresson, Marie (2012). The Initial Phase of an Acute Coronary
Syndrome. Symptoms, patients’ response to symptoms and
­opportunity to reduce time to seek care and to increase ambulance use.
68. Mårild, Karl (2012). Risk Factors and Associated Disorders of
­C eliac Disease.
69. Fant, Federica (2012). Optimization of the Perioperative Anaesthetic
Care for Prostate Cancer Surgery. Clinical studies on Pain, Stress
Response and Immunomodulation.
70. Almroth, Henrik (2012). Atrial Fibrillation: Inflammatory and
pharmacological studies.
71. Elmabsout, Ali Ateia (2012). CYP26B1 as regulator of retinoic acid
in vascular cells and atherosclerotic lesions.
72. Stenberg, Reidun (2012). Dietary antibodies and gluten related
­seromarkers in children and young adults with cerebral palsy.
73. Skeppner, Elisabeth (2012). Penile Carcinoma: From First Symptom
to Sexual Function and Life Satisfaction. Following Organ-Sparing
Laser Treatment.
74. Carlsson, Jessica (2012). Identification of miRNA expression
­profiles for diagnosis and prognosis of prostate cancer.
75. Gustavsson, Anders (2012): Therapy in Inflammatory Bowel ­Disease.
76. Paulson Karlsson, Gunilla (2012): Anorexia nervosa – treatment
­expectations, outcome and satisfaction.
77. Larzon, Thomas (2012): Aspects of endovascular treatment of
­abdominal aortic aneurysms.
78. Magnusson, Niklas (2012): Postoperative aspects of inguinal hernia
surgery – pain and recurrences.
79. Khalili, Payam (2012): Risk factors for cardiovascular events and
incident hospital-treated diabetes in the population.
80. Gabrielson, Marike (2013): The mitochondrial protein SLC25A43
and its possible role in HER2-positive breast cancer.
81. Falck, Eva (2013): Genomic and genetic alterations in endometrial
adenocarcinoma.
82. Svensson, Maria A (2013): Assessing the ERG rearrangement for
clinical use in patients with prostate cancer.
83. Lönn, Johanna (2013): The role of periodontitis and hepatocyte
growth factor in systemic inflammation.
84. Kumawat, Ashok Kumar (2013): Adaptive Immune Responses in the
Intestinal Mucosa of Microscopic Colitis Patients.
85. Nordenskjöld, Axel (2013): Electroconvulsive therapy for
­depression.
86. Davidsson, Sabina (2013): Infection induced chronic inflammation
and its association with prostate cancer initiation and progression.
87. Johansson, Benny (2013): No touch vein harvesting technique in
coronary by-pass surgery. Impact on patency rate, development
of atherosclerosis, left ventricular function and clinical outcome
during 16 years follow-up.
88. Sahdo, Berolla (2013): Inflammasomes: defense guardians in
­host-microbe interactions.
89. Hörer, Tal (2013): Early detection of major surgical postoperative
complications evaluated by microdialysis.
90. Malakkaran Lindqvist, Breezy (2013): Biological signature of HER2positive breast cancer.
91. Lidén, Mats (2013): The stack mode review of volumetric datasets
– applications for urinary stone disease.
92. Emilsson, Louise (2013): Cardiac Complications in Celiac Disease.
93. Dreifaldt, Mats (2013): Conduits in coronary artery bypass grafting
surgery: Saphenous vein, radial and internal thoracic arteries.
94. Perniola, Andrea (2013): A new technique for postoperative pain
management with local anaesthetic after abdominal hysterectomy.
95. Ahlstrand, Erik (2013): Coagulase-negative Staphylococci in
Hematological Malignancy.
96. Sundh, Josefin (2013): Quality of life, mortality and exacerbations
in COPD.
97. Skoog, Per (2013): On the metabolic consequences of abdominal
compartment syndrome.
98. Palmetun Ekbäck, Maria (2013): Hirsutism and Quality of Life with
Aspects on Social Support, Anxiety and Depression.
99. Hussain, Rashida (2013): Cell Responses in Infected and Cystic
Fibrosis Respiratory Epithelium.
100. Farkas, Sanja (2014): DNA methylation in the placenta and in cancer
with special reference to folate transporting genes.
101. Jildenstål, Pether (2014): Influence of depth of anaesthesia on postoperative cognitive dysfunction (POCD) and inflammatory marker.
102. Söderström, Ulf (2014): Type 1 diabetes in children with non-Swedish
background – epidemiology and clinical outcome
103.Wilhelmsson Göstas, Mona (2014): Psychotherapy patients in
mental health care: Attachment styles, interpersonal problems and
therapy experiences
104. Jarl, Gustav (2014): The Orthotics and Prosthetics Users´ Survey:
Translation and validity evidence for the Swedish version
105.Demirel, Isak (2014): Uropathogenic Escherichia coli, multidrugresistance and induction of host defense mechanisms
106.Mohseni, Shahin (2014): The role of ß-blockade and anticoagulation therapy in traumatic brain injury
107.Bašić, Vladimir T. (2014): Molecular mechanisms mediating
development of pulmonary cachexia in COPD
108. Kirrander, Peter (2014): Penile Cancer: Studies on Prognostic Factors
109. Törös, Bianca (2014): Genome-based characterization of Neisseria
meningitidis with focus on the emergent serogroup Y disease
110. von Beckerath, Mathias (2014): Photodynamic therapy in the Head
and Neck
111. Waldenborg, Micael (2014): Echocardiographic measurements at
Takotsubo cardiomyopathy - transient left ventricular dysfunction.
112. Lillsunde Larsson, Gabriella (2014): Characterization of HPV-induced
vaginal and vulvar carcinoma.
113. Palm, Eleonor (2015): Inflammatory responses of gingival fibroblasts in
the interaction with the periodontal pathogen Porphyromonas gingivlis.
114. Sundin, Johanna (2015): Microbe-Host Interactions in Post-infectious
Irritable Bowel Syndrome.
115. Olsson, Lovisa (2015): Subjective well-being in old age and its association
with biochemical and genetic biomarkers and with physical activity.
116. Klarström Engström, Kristin (2015): Platelets as immune cells in sensing
bacterial infection.
117. Landström, Fredrik (2015): Curative Electrochemotherapy in the Head
and Neck Area.
118. Jurcevic, Sanja (2015): MicroRNA expression profiling in endometrial
adenocarcinoma.
119. Savilampi, Johanna (2015): Effects of Remifentanil on Esophageal
Sphincters and Swallowing Function.