selected reports
Peak Expiratory Flow With or
Without a Brief Postinspiratory
Pause*
Tariq Omar, MD; Husain Alawadhi, MD;
Ayman O. Soubani, MD, FCCP; and
George E. Tzelepis, MD, FCCP
Background: The duration of postinspiratory pause
prior to forced expiration may significantly influence
the peak expiratory flow (PEF) measured during maximal forceful expirations. In comparison with maneuvers without a postinspiratory pause, maneuvers with 4
to 6-s pause at total lung capacity (TLC) result in
decreased PEF values. The extent to which brief
pauses (< 2 s) similarly affect PEF values is unknown.
Methods: Thirty-six healthy volunteers (mean [ⴞSD]
age, 35 ⴞ 8 years; 18 men) performed a series of
maximal forceful expirations with two different types of
maneuvers. One maneuver (NP) included no inspiratory pause at TLC prior to forceful expiration, whereas
the second (P) included a brief pause (< 2 s). The speed
of inhalation to TLC was rapid and similar for both
maneuvers. The highest PEF for each maneuver was
used for analysis.
Results: The maximal PEF did not differ (p > 0.05)
between the P and NP maneuvers (7.78 ⴞ 1.45 vs
7.83 ⴞ 1.45 L/s, respectively). Comparison of the intermaneuver differences showed a bias of 0.05 L/s and
95% confidence interval in the range of ⴚ0.9 to 1.0 L/s.
Conclusions: Forceful expiratory maneuvers with or
without postinspiratory pauses of < 2 s produce identical maximal PEF values and, therefore, can be used
interchangeably for the spirometric measurement of
PEF in healthy subjects.
(CHEST 2005; 128:442– 445)
Key words: peak expiratory flow; postinspiratory pause; pulmonary function testing; spirometry
Abbreviations: NP ⫽ maneuver type with no inspiratory pause
*From the Wayne State University School of Medicine (Drs.
Omar, Alawadhi, Soubani, and Tzelepis), Detroit, MI; and
University of Athens Medical School (Dr. Tzelepis), Athens,
Greece.
Manuscript received September 15, 2004; revision accepted
January 19, 2005.
Reproduction of this article is prohibited without written permission
from the American College of Chest Physicians (www.chestjournal.
org/misc/reprints.shtml).
Correspondence to: George E. Tzelepis, MD, FCCP, Department of Pathophysiology, University of Athens Medical School,
75 M Asias St, 11527 Athens, Greece; e-mail:gtzelep@med.
uoa.gr
at total lung capacity prior to forceful expiration; P ⫽ maneuver
type with an inspiratory pause at total lung capacity prior to
forceful expiration; PEF ⫽ peak expiratory flow; TLC ⫽ total
lung capacity.
eak expiratory flow (PEF), the maximal flow that can be
P achieved
during a forceful expiration at total lung capac-
ity (TLC), is an important parameter that is used to monitor
airway obstruction. PEF is determined in large part by the
lung volume, lung elastic recoil, and muscular effort.1 Studies
in healthy volunteers2,3 and patients with lung diseases4 –7
showed that the type of inspiratory maneuver preceding
forceful expiration could affect the magnitude of PEF. The
values of PEF are significantly higher if the FVC maneuver
is preceded by fast inspiration without a postinspiratory pause
than when it is preceded by a slow inspiration with a 4 to 6-s
postinspiratory pause. This dependence of PEF on the
length of postinspiratory duration is best explained on the
basis of the lung elastic recoil pressure, which is timedependent, and, therefore, the longer pause will result in
lower effective lung elastic recoil pressure prior to expiration and, thus, lower PEF.2,3 An additional mechanism
that could also lead to greater PEF values with the fast
inspirations is related to enhancements of expiratory muscle force output because of the stretch-shorten cycle.3,8
Currently, the published guidelines9,10 for measuring
PEF provide no precise recommendations about the
speed of inspiration preceding expiration and the appropriate duration of the postinspiratory pause. Although long
postinspiratory pauses (ie, ⬎ 3 s) are generally not used,
pauses of ⱕ 2 s are often allowed prior to expiration in
most pulmonary laboratories. The extent to which these
brief pauses may similarly affect measurements of PEF is
unknown.
This study was undertaken in a group of healthy
volunteers with the objective to compare PEF values
obtained spirometrically during FVC maneuvers that included an inspiratory pause at TLC prior to forceful
expiration (P) [about 2 s] with PEF measured with
maneuvers that included no inspiratory pause at TLC
prior to forceful expiration (NP). The speed of inspiration
to TLC prior to forced expiration was similar (about 1 to
2 s) for both maneuvers.
Materials and Methods
Thirty-six healthy volunteers (mean age, 36 ⫾ 8; 18 men)
participated in the study. All of the subjects were nonsmokers;
had no history of asthma, cough, or recent respiratory infection;
and were not taking medications during the study. The subjects
were naı̈ve to the purpose of the study and all but two had never
performed spirometry before. The research was approved by the
institutional ethics committee, and informed consent was obtained from all of the subjects.
Respiratory flow was measured with a pneumotachograph
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Selected Reports
(model 3813; Hans Rudolph; Kansas City, MO) that was linear
ⱕ 13.6 L/s and a differential pressure transducer (MP-45, ⫾2 cm
H2O; Validyne; Northridge, CA). The volume was obtained by
digitally integrating (PowerLab; ADInstruments; Castle Hill,
NSW, Australia) the flow signal. A 3-L super-syringe was used to
calibrate the volume signal at different flow rates, and the
calibration was frequently checked. Flow and volume signals
were sampled online (PowerLab; ADInstruments) and recorded
on a computer disk for later analysis.
The subjects were tested in two sessions, approximately 2 to 3
weeks apart. In each session, they performed a series of forced
expirations using two different types of maneuvers. These two
types of maneuvers were the NP maneuver and the P maneuver.
With the NP maneuver, the subjects inhaled rapidly to TLC and
immediately performed the forced expiration, whereas with the P
maneuver the subjects inhaled rapidly to TLC and after a brief
pause (about 2 s) performed the forceful expiration. All of the
subjects were instructed to exhale as fast and as hard as possible,
focusing on the initial split seconds of expiration. The neck was
kept in a neutral position in order to reduce PEF variability
related to the tracheal shape.11 During these maneuvers, all of
the subjects were coached by the same operator.
All of the subjects initially practiced both expiratory maneuvers. Following familiarization with the two types of maneuvers,
they performed a total of eight forced expirations, four with each
type of maneuver in an alternate fashion. Ample time was allowed
for rest between trials. Of the 36 subjects who completed
measurements in the first session, 33 returned to the laboratory
for the second session of measurements. With these two sessions,
the subjects generated a series of individual forced expirations.
For each session, the largest PEF and the average for each
maneuver and subject were chosen for analysis.
Data are presented as mean (⫾ SD). A paired t test was used
to compare the intermaneuver differences in PEF. The agreement between the two maneuvers was analyzed with the method
of Bland and Altman12 in which agreement between the two
maneuvers was expressed in a diagram showing the differences
between maneuvers plotted against the mean of the two. All of
the statistical analyses were performed with computer software
(Analyze-It with Microsoft Excel for Windows; Analyze-It Software Ltd; Leeds, UK).
Results
Figure 1 shows the typical volume and flow tracings
with each expiratory maneuver. There were no differences
in the best PEF or average PEF between the two
maneuvers (Table 1). With the P maneuver, the best PEF
was achieved with the first three trials in 78% of the
individual blows, whereas with the NP, the best PEF was
achieved with the first three trials in 75% of the individual
blows. In 52% of the individual blows, the best PEF was
achieved with the NP maneuver and in 45% of the
individual blows with the P maneuver (p ⬎ 0.05 [␹2 test]).
Figure 2 shows the Bland and Altman12 analysis for the
intermaneuver differences in PEF. The bias was 0.05 L/s
with 95% confidence intervals from ⫺0.069 to 0.171 L/s.
The lower and upper 95% limits of agreement were
⫺0.929 and 1.031 L/s, respectively.
Discussion
The two maneuvers differed only in the duration of
inspiration, with the NP maneuver containing essentially
no inspiratory pause. The subjects were asked to inhale
rapidly to TLC, but no other instructions were given about
www.chestjournal.org
Figure 1. Representative tracings of flow and lung volume
during forceful expirations in a volunteer with two different
maneuvers. Note that with the P maneuver there is about a 2-s
breathhold at TLC prior to forceful expiration, whereas with the
NP maneuver there is essentially no postinspiratory pause.
the vigor of inspiration. With regard to breathhold at TLC,
the subjects were simply instructed to pause until they
heard the cue for forceful expiration.
Agreement of the maneuvers was analyzed with the
method by Bland and Altman,12 which showed that the
mean intermaneuver difference (bias) was negligible. Also,
the differences appeared to be uniform through the range
of PEF measurements following a normal distribution (Fig
2, right). The 95% limits of agreement, however, ranged
from ⫺0.9 to 1.0 L/s. This range of dispersion is relatively
large and is most likely related to the intraindividual
variability of PEF.7,13–15
In several previous studies, fast inspiratory maneuvers
with no breathhold were associated with greater PEF
values in healthy volunteers,2,3,7 as well as patients with
asthma,7,16 COPD,5 cystic fibrosis,4 or restrictive diseases6
when compared with maneuvers that included a breathhold of about 4 to 6 s. In certain patients, particularly
COPD and cystic fibrosis,4,5 the differences in PEF and
other spirometric parameters were much greater, probably reflecting the lung viscoelastic properties of these
patients. In view of these findings, several authors2,4 –7
Table 1—Data Obtained With the Two Maneuvers*
Variables
P Maneuver
NP Maneuver
p Value
PEF, L/s
Best
Average
Pause, s
Vinsp, L/s
FEV1 best, L
7.78 ⫾ 1.45
7.44 ⫾ 1.43
1.63 ⫾ 0.3
4.03 ⫾ 1.3
3.16 ⫾ 0.62
7.83 ⫾ 1.45
7.48 ⫾ 1.37
NS
NS
4.40 ⫾ 1.4
3.19 ⫾ 0.62
0.002
NS
*Values given as mean ⫾ SD, unless otherwise indicated. NS ⫽ not
significant; Vinsp ⫽ inspiratory flow.
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443
Figure 2. Bland and Altman12 analysis of differences in PEF between the two maneuvers vs average
PEF values.
emphasized the need to standardize the duration and type
of inspiration preceding forceful expiration. They argued
that rapid inspiratory efforts to TLC followed immediately
by forceful expiration should be used for the spirometric
measurements of FVC. In the absence of data, the
American Thoracic Society9 and the European Respiratory Society10 in their most recent statements provided no
detailed recommendations about the duration of inspiration. Although the American Thoracic Society guidelines9
recommend avoidance of excessive pauses at TLC, the
European Respiratory Society guidelines10 suggest a maximum postinspiratory pause of about 2 s.10
The speed of inspiration may influence the magnitude
of PEF measured during the subsequent expiration
through its effects on the elastic recoil pressure of the
lungs and chest wall and through its effects on the
respiratory muscle force. Fast inspirations produce greater
increases in the elastic recoil of the lung and chest wall
and, therefore, result in greater PEF values. Fast inspirations can also enhance expiratory muscle pressure during
the subsequent expiration via the stretch-shorten cycle.3,8
With fast inspirations, the expiratory muscles are actively
stretched and are then shortened during the subsequent
expiration. As in peripheral muscles,17 the transition from
an activated stretched muscle (eccentric contraction) to
one that is now shortening can augment respiratory muscle force output. In some studies,3,8 forceful inspirations
that were immediately followed by forced expirations
produced greater increases in the expiratory pressures (by
approximately 10 to 15%) when compared with maneuvers
characterized by slow inspirations and postinspiratory
pauses at TLC. To the extent that PEF is flow-limited in
most healthy subjects,18,19 greater expiratory pressures in
the setting of an optimally performed forced expiratory
maneuver will not result in an additional increase in PEF.
The length of postinspiratory pause may neutralize the
inspiratory maneuver effects on PEF. A breathhold at
TLC allows stress relaxation in both the airway wall and
lung parenchyma to occur and, thus, increases the airway
compliance and decreases the effective elastic recoil pressure. In previous studies,20 long pauses (⬎ 10) were
invariably associated with decreases in PEF. Pauses of
about 4 to 6 s were also associated with decreases in PEF
in the range of 6 to 13%, especially when comparisons
were made between maneuvers with fast inspirations and
those with slow inspirations.2,3,7 For maneuvers in which
inspiratory speed was relatively slow, the effect of a
breathhold on PEF was less pronounced in healthy volunteers. As suggested by studies in peripheral muscles,21
long postinspiratory pauses may also offset the enhancement of expiratory muscle force related to the stretchshorten cycle.
There may be several explanations for the lack of
differences in PEF between the two maneuvers. First,
intervals of ⱕ 2 s are probably too short for significant
changes in the airway wall and the lung parenchyma to
take place, especially when subjects do not relax their
respiratory muscles during the breathhold. In healthy
volunteers, the decreases in PEF with longer pauses (ie, 4
to 6 s) were found to be in the range of about 6 to 8% and
occurred in some but not all of the subjects.3,7 Therefore,
it is highly likely that the changes in the PEF induced by
periods of 2 s are relatively small and perhaps smaller than
the changes related to the PEF variability.13–15
A study in healthy volunteers22 found that maneuvers
with a postinspiratory pause of 2 s at TLC decreased PEF
by about 10% when compared with maneuvers without a
pause. However, this study is not directly comparable to
our study because of methodologic differences; the study
included only five volunteers in whom the analysis of
intermaneuver differences in PEF was based, not on the
highest PEF, but on matched effort as assessed by the
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esophageal pressure. Furthermore, unlike our study, the
subjects were asked to relax the respiratory muscles during
breathhold, which most likely caused a relatively greater
increase in the compliance of the airway wall.
The inspiratory flow was slightly greater with the NP
maneuver, perhaps because of the overall faster character
of the NP maneuver in comparison with the P maneuver.
However, this difference in inspiratory speed is very
unlikely to have systematically biased our data for several
reasons. First, the 10% difference in inspiratory speed
between the two types of maneuvers is relatively small. In
previous studies in which inspiratory speed with the NP
maneuvers accounted for the intermaneuver differences
in PEF, the inspiratory flow was several-fold greater than
that of the pause maneuvers.2– 4,7 Furthermore, to the
extent that NP maneuvers are more likely to produce
greater PEF, if there was any inspiratory speed-related
bias, this would have led to greater PEF values with the
NP than with the P maneuver. However, the finding of
similar PEF values for the two types of maneuvers argues
against it. In general, the inspiratory speed was in the same
range as that used in previous studies2 examining the
effect of fast inspirations on PEF.
Our data apply to healthy volunteers and may not be
extrapolated to patients without caution. In COPD patients, fast maneuvers with no inspiratory pause produced
relatively greater increases in PEF than maneuvers incorporating postinspiratory pauses.5 This may be related to
several factors including time-constant inequality within
the lung in these patients. Because maneuvers with a brief
postinspiratory pause allow coaching in a stepwise manner,
they might be easier to perform in the pulmonary function
laboratory, especially by the poorly cooperative patient. In
conclusion, we found that forceful expiratory maneuvers
with or without postinspiratory pauses of ⱕ2 s produce
identical maximal PEF values and, therefore, can be used
interchangeably for the spirometric measurement of PEF
in healthy subjects.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
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␣1-Antitrypsin and Neutrophil
Elastase Imbalance and Lung
Cancer Risk*
Ping Yang, MD, PhD; William R. Bamlet, MS;
Zhifu Sun, MD, PhD; Jon O. Ebbert, MD;
Marie-Christine Aubry, MD; William R. Taylor, MS;
Randolph S. Marks, MD; Claude Deschamps, MD, TS;
Stephen J. Swensen, MD; Eric D. Wieben, PhD;
Julie M. Cunningham, PhD; Lee Joseph Melton, MD; and
Mariza de Andrade, PhD
Objective: Imbalance between ␣1-antitrypsin and
neutrophil elastase is an underlying cause of lung
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