Original Research—Otology and Neurotology
Effects of Continuous Positive Airway
Pressure on Middle Ear Pressure and
Acoustic Stapedial Reflex
Otolaryngology–
Head and Neck Surgery
2016, Vol. 155(2) 307–311
Ó American Academy of
Otolaryngology—Head and Neck
Surgery Foundation 2016
Reprints and permission:
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DOI: 10.1177/0194599816643706
http://otojournal.org
Jinrang Li, MD1, and Keliang Li, MS1,2
No sponsorships or competing interests have been disclosed for this article.
Abstract
Objective. This study investigated the effects of continuous
positive airway pressure (CPAP) on middle ear pressure and
acoustic stapedial reflex and the correlation between CPAP
and middle ear pressure.
Study Design. Prospective cohort study.
Setting. Tertiary hospitals.
Subjects and Methods. Fifty patients with obstructive sleep
apnea-hypopnea syndrome were assigned to the study
group, and 50 healthy volunteers were assigned to the control group. The subjects underwent standard tympanometry
while wearing a CPAP device (ie, simulated CPAP treatment), which was set to 0, 5, 10, and 15 cm H2O, respectively. Tympanometry was performed before and after
swallowing at each pressure of CPAP treatment.
Results. The mean middle ear pressures were 21.2, 22.6,
22.7, and 23.4 daPa (before swallowing) and 21.6, 42.6, 81.4,
and 118.6 daPa (after swallowing) in the study group and
17.6, 18.7, 19.5, and 20.8 daPa (before swallowing) and 17.7,
44.2, 85.6, and 120.5 daPa (after swallowing) in the control
group at the CPAPs of 0, 5, 10, and 15 cm H2O, respectively.
While the CPAPs were at 0 and 15 cm H2O, the stapedial
muscle reflex at 1.0 kHz did not have a significant difference
between the 2 groups (x2 = 0.521, P = .470). The Pearson
correlation coefficient of the CPAP pressure and the middle
ear pressure after swallowing was 0.812 (P \.001).
Conclusion. CPAP affected middle ear pressure and was
directly proportional to the pressure of the CPAP. However,
CPAP treatment had no significant effect on stapedial
muscle reflex.
O
bstructive sleep apnea-hypopnea syndrome (OSAHS)
is characterized by episodes of airflow reduction
(hypopnea) or cessation (apnea) due to the collapse
and obstruction of the upper airway during sleep. It is often
accompanied by symptoms such as snoring, frequent reductions in blood oxygen saturation, and excessive daytime sleepiness. The literature indicates that the incidence of OSAHS
is about 4% and can even reach .15% among the middleaged and aged populations.1 In addition, the occurrence of
OSAHS is closely correlated with the occurrence and development of hypertension, arrhythmia, diabetes, and other diseases of aging.2
Continuous positive airway pressure (CPAP) therapy
involves the use of a nasal mask connected to a positive
pressure respirator, which ensures continuous pressure
during sleeping to maintain an open upper airway, relieve
apnea, and improve anoxia. As the first choice of conservative therapy for OSAHS,3 CPAP has been widely accepted
by physicians and patients. Although CPAP is a noninvasive
therapy, long-term CPAP treatment will nevertheless result
in various complications, including discomfort in the upper
airway, facial skin rashes, nasal congestion, and otalgia.4
Some studies showed that ear pain was an uncommon complication of CPAP and that CPAP therapy had no effect on
the eustachian tube function of patients who had received
such therapy for a minimum of 6 months.5-7 No study documented hearing loss over time with CPAP use; however,
CPAP therapy has been shown to have effects on middle
ear cavity pressure. As early as 2012, Lin et al8 conducted
follow-up research on 10 healthy volunteers and found that
when the subjects received CPAP treatment at a certain
pressure, their middle ear pressures also increased. The
research conducted by Sivri et al9 in 2013 showed that after
CPAP treatment for half a year, healthy volunteers and
1
Keywords
obstructive sleep apnea-hypopnea syndrome, continuous
positive airway pressure, middle ear pressure, tympanometry, stapedial muscle reflex
Received December 13, 2015; revised March 10, 2016; accepted March
18, 2016.
Department of Otorhinolaryngology–Head and Neck Surgery, Navy
General Hospital, Beijing, China
2
Anhui Medical University, Clinical College of Navy General Hospital,
Beijing, China
Corresponding Author:
Jinrang Li, MD, Department of Otorhinolaryngology–Head and Neck
Surgery, Navy General Hospital, Beijing, 100048, China.
Email: [email protected]
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308
Otolaryngology–Head and Neck Surgery 155(2)
Table 1. Comparison of Clinical Data between the 2 Groups.
Item
Age, y
Height, cm
Weight, kg
Body mass index
Neck circumference, cm
Heart rate, beats/min
Control Group
24.4 6
169.2 6
69.3 6
24.7 6
35.8 6
69.5 6
2.5
3.6
6.3
1.3
3.2
8.4
OSAHS patients both had a significant increase in their
middle ear pressures.
Compared with the 2 above-mentioned studies, this
research not only included a larger sample size but also
used different pressure settings for CPAP therapy to further
evaluate the correlation between CPAP and middle ear pressure. By using voluntary swallowing to mimic involuntary
swallowing during sleeping, the actual pressure in the
middle ear cavity after the opening of the eustachian tube
was determined, and the effects of the opening/closing of
the eustachian tube at the time of swallowing on middle ear
pressure were further analyzed. In addition, middle ear pressure and acoustic stapedial reflex were examined in healthy
volunteers and OSAHS patients while they were receiving
CPAP treatment at different pressures to evaluate the effects
of CPAP on the acoustic stapedial reflex.
Materials and Methods
General Data
This study was approval by the Institutional Review Board
of the Navy General Hospital. Male patients who received a
definite diagnosis of OSAHS via polysomnographic monitoring in our department between October 2014 and April
2015 underwent tympanometry. Patients with eustachian
tube dysfunction, other ear diseases, and absence of acoustic
stapedial reflex were excluded. Fifty OSAHS patients were
assigned to the study group. In addition, healthy male adults
were publicly recruited, and 50 volunteers without OSAHS
who were selected in the same manner were assigned to
control group. All the subjects in control group had no history of snoring and a normal body mass index. Patients with
hypertension, diabetes, and other diseases were excluded.
OSAHS was diagnosed according to criteria of the Chinese
Medical Association of Otorhinolaryngology10: when the
apnea hypopnea index in a patient with OSAHS is 5 to 15,
it is considered mild; 15 to 30, moderate; and .30, severe.
The index of the OSAHS patients ranged from 30.6 to
104.5, with an average of 58.22 6 24.35. The clinical data
of the 2 groups are listed in Table 1.
Methods
The subjects in both groups were kept in a tranquil and
conscious state during the tympanometry test, which was
Study Group
t
P Value
45.4 6 6.4
168.7 6 4.2
85.2 6 4.5
29.5 6 2.4
41.64 6 4.1
70.1 6 9.5
3.24
0.67
4.92
3.81
3.24
0.71
.002
.505
\.001
\.001
.002
.481
performed with a middle ear analyzer (OTOflex 100;
Otometrics, Taastrup, Denmark). First, the middle ear pressures on both sides were measured when the CPAP was set
at zero; then, the pressures were measured after swallowing;
last, the acoustic stapedial reflex of both ears was examined
at 1 kHz. Subsequently, CPAP was applied via a face mask,
and the tympanometry test was conducted with CPAPs at 5,
10, and 15 cm H2O. The middle ear pressures of both sides
after and before swallowing were measured again. When
the pressure was set at 15 cm H2O, the acoustic stapedial
reflexes of both ears after swallowing were examined.
While the subjects received 15 cm H2O, if the decibels
required for triggering the acoustic stapedial reflex increased
or if the acoustic stapedial reflex could not be triggered,
CPAP was considered to exert a negative effect and reduce
the sensitivity of the reflex. Finally, the total number of negative events in the 2 groups was recorded, and the incidence
of negative events was further compared between the 2
groups. Measurements at an adjusted pressure were conducted 3 to 5 minutes after the previous measurement, which
allows the middle ear pressure to return to the baseline.
Statistical Analysis
Data were analyzed with SPSS 21.0. The measurement
results were presented as mean 6 SD. The differences
between the 2 groups were determined with a t test, and the
count data were analyzed by a chi-square test. P \ .05 was
considered statistically significant.
Results
We obtained 1600 tympanometry charts. The mean middle
ear pressure was 19.36 daPa when the subjects were in a
tranquil state and the CPAP was set at 0 cm H2O before
swallowing. Among the measured middle ear pressure
values, the maximum and minimum values were 145 and
274 daPa, respectively. The changes in middle ear pressure
in the study and control groups are shown in Table 2. The
results showed that with the increase of the pressure in
CPAP, the middle ear pressure of the subjects in both
groups increased, with the increase being more significant
after swallowing. Middle ear pressure positively correlated
with the pressure of CPAP, with a Pearson correlation coefficient of 0.812. At CPAPs of 5, 10, and 15 cm H2O, the
middle ear pressures in both groups after swallowing were
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Li and Li
309
Table 2. Comparison of Middle Ear Pressure between the OSAHS and Healthy Volunteer Groups before and after Swallowing.a
OSAHS Group, daPa
CPAP, cmH2O
Before
Swallowing
0
5
10
15
21.2
22.6
22.7
23.4
6 6.1
6 7.2
6 7.3
6 7.4
After
Swallowing
21.6 6
42.6 6
81.4 6
118.6 6
7.2
8.1
11.7
15.2
Control Group, daPa
t1
P1
0.238
3.624
5.334
9.154
.812
.004
\.001
\.001
Before
Swallowing
17.6 6
18.7 6
19.5 6
20.8 6
7.2
7.6
7.2
8.4
After
Swallowing
t2
P2
t3
P3
t4
P4
17.7 6 6.7
44.2 6 8.2
85.6 6 15.4
120.5 6 16.2
0.334
3.718
6.512
9.425
.739
.003
\.001
\.001
2.364
2.276
2.204
2.251
.020
.024
.029
.026
2.357
2.319
2.506
2.314
.020
.022
.014
.227
Abbreviations: CPAP, continuous positive airway pressure; OSAHS, obstructive sleep apnea-hypopnea syndrome.
a
P1, comparison before and after swallowing in the study group; P2, comparison before and after swallowing in the control group; P3, comparison between
study and control groups before swallowing; P4, comparison between study and control groups after swallowing.
obviously higher than those before swallowing. The difference between them was statistically significant (P \ .05).
At the same pressure of the CPAP, the middle ear pressure
in the study group was always greater than that in the control group regardless of swallowing, with a statistically significant difference (P \ .05; see Table 2). The negative
events of acoustic stapedial reflex between the study and
control groups at a frequency of 1 kHz and at a CPAP of 15
cm H2O were also compared. After short-term CPAP therapy, the incidence rates of reduction in the sensitivity of the
acoustic stapedial reflex were 3% and 5% in the OSAHS
and healthy volunteer groups, respectively. The differences
between them were not statistically significant (x2 = 0.521,
P = .470).
Discussion
With the improvement of people’s standard of living, the
incidence of OSAHS has tended to increase in recent years.
As the first choice of conservative therapy for OSAHS,
CPAP is widely accepted by an increasing number of physicians and patients. The working mechanism of CPAP is to
provide a continuous physiologic pressure to keep the upper
airway open during sleep. The key to CPAP treatment is the
pressure adjustment.11 The ideal pressure level is the minimum pressure required for preventing apnea at different
sleep phases and postures. The ideal pressure can not only
eliminate snoring but also maintain blood oxygen saturation
at a normal level (.90%) during sleep. In clinical practice,
the final pressure used for treatment is usually much higher
than the normal range of middle ear pressure.11 Long-term
CPAP therapy administered via a face mask during sleep
may lead to the pressure transmission to the middle ear
through the opening of the eustachian tube, thus affecting
the pressure in the middle ear.
As an important protective mechanism for the human
body, swallowing facilitates the removal of saliva and fluid
secreted by salivary glands that are retained in the pharynx,
and it protects the lung and airway.12,13 However, swallowing does not only occur in a conscious state. Regular swallowing action also occurs during sleeping, especially during
deep sleep.14,15 Studies in the literature have reported that
OSAHS patients swallow less frequently during sleep than
healthy people do. However, some studies also showed that
swallowing often occurs after apnea or hypopnea in OSAHS
patients. In 2011, Sato et al14 proved that when OSAHS
patients were receiving CPAP treatment, the frequency of
their swallowing during sleep did not significantly differ
from that in healthy people. Therefore, we speculate that in
OSAHS patients who are receiving CPAP treatment, normal
swallowing occurs during sleep, which is accompanied by
opening of the eustachian tube, through which the pressure
of the CPAP can be continuously transmitted to the middle
ear cavity.
In this study, the middle ear pressures of the OSAHS
patients and healthy volunteers were measured at different
pressures of the CPAP before and after swallowing. The
results showed that for both the OSAHS patients and the
healthy subjects, middle ear pressure increased with the
increase pressure of the CPAP. In particular, the middle ear
pressure after swallowing almost linearly correlated with the
pressure of the CPAP, with a Pearson correlation coefficient
of 0.812. The differences of the middle ear pressure before
and after swallowing at CPAPs of 5, 10, and 15 cm H2O
were statistically significant (P \ .05). At the same pressure
of the CPAP, regardless of swallowing, the middle ear pressure in the study group was always slightly higher than that
in the control group, with a statistically significant difference (P \ .05). Therefore, we propose that the key influencing factors of middle ear pressure are CPAP and the
swallowing action during CPAP treatment. CPAP is the fundamental factor that affects middle ear pressure. At the time
of swallowing, the transmission of CPAP to the middle ear
cavity via the eustachian tube is the determining factor of
whether the middle ear pressure increases proportionally.
Other influencing factors include the time and degree of the
opening of the eustachian tube during swallowing and
the contraction or relaxation of surrounding structures after
the closing of the eustachian tube. At the same pressure
of the CPAP, the middle ear pressure in the OSAHS group
was slightly higher than that in the healthy group, regardless
of the swallowing action. Given that most OSAHS patients
are overweight, local fat accumulation and extrusion of soft
tissues may cause a further increase in middle ear pressure.
At a CPAP of 15 cm H2O, the 2 groups had no obvious
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Otolaryngology–Head and Neck Surgery 155(2)
difference in acoustic stapedial reflex. The incidence rates
of the reduction in the sensitivity of the acoustic stapedial
reflex in the 2 groups were only 3% (OSAHS) and 5%
(healthy), indicating that short-term CPAP does not exert
negative effects on the stapedius muscle or that the negative
effects caused by the short-term pressure change are not sufficient to affect the sensitivity of the acoustic stapedial
reflex.
Normally, middle ear pressure can rarely reach 40
daPa,16 whereas during this experiment, the mean middle
ear pressure reached 40 daPa at a CPAP of 5 cm H2O.
When OSAHS patients receive CPAP treatment, their
middle ears are also subjected to long-term pressure that
exceeds the physiologic level. Long-term positive pressure
may exert negative effects on the neural reflex and muscular
functions in the middle ear and eventually affect the hearing
of OSAHS patients.17,18 Before prescribing long-term CPAP
treatment for OSAHS patients, physicians should be vigilant
of potential auditory problems—especially for OSAHS
patients with hearing impairment or other ear diseases—and
deliberately consider the possible long-term effects of
CPAP treatment for OSAHS patients who need to receive
ear surgery (eg, tympanoplasty, ossiculoplasty, or stapedectomy). Whether CPAP treatment should be administered
immediately after surgery or when to receive the CPAP
treatment needs to be further studied.
In addition, all the subjects in this study were tested in a
conscious state, but in clinical practice, most OSAHS patients
receive CPAP treatment during sleep. Certain errors may
exist between the measured and actual values. However, in
this study, the subjects were instructed to swallow voluntarily
to mimic involuntary swallowing during sleep. Therefore, the
changes in middle year pressure should be similar to the
actual values. Moreover, as all subjects received short-term
CPAP therapy, the possible reduction in the sensitivity of the
acoustic stapedial reflex caused by long-term CPAP treatment
cannot be excluded. Owing to the limited number of cases in
this study, errors might exist between the final statistical
results and the actual values.
Conclusions
CPAP affected the middle ear pressures of both the OSAHS
patients and the healthy subjects and positively correlated
with middle ear pressure after swallowing. In addition,
short-term CPAP treatment did not affect the acoustic stapedial reflex of the OSAHS patients and healthy subjects, but
the possible effect of long-term CPAP treatment in reducing
the sensitivity of the acoustic stapedial reflex cannot be
excluded.
Author Contributions
Jinrang Li, design the study, revised the article, final approval,
accountability for all aspects of the work; Keliang Li, collected
data, analyzed the data, drafting the paper.
Disclosures
Competing interests: None.
Sponsorships: None.
Funding source: None.
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