Maximal inspiratory and expiratory pressures in men with chronic obstructive pulmonary disease: A cross-sectional study

Abstract

Introduction: Respiratory muscle dysfunction is a cardinal feature in chronic obstructive pulmonary disease (COPD) contributing to decreased exercise capacity and pulmonary function test (PFT) limitation with progression of the disease. Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) are reliable parameters for assessing the respiratory muscle strength. Aims: This study aims to measure maximal inspiratory and expiratory pressures in male COPD patients, to determine their correlates, and to study the relationship between the severity of COPD and respiratory muscle strength. Patients and Methods: This was an observational, cross-sectional study. A total of 100 males, who were known COPD patients and who were clinically stable, were recruited. Both inpatients and outpatients were studied. Spirometric PFT test was done, and MIP and MEP were measured using respiratory pressure meter. Descriptive statistics and Pearson's correlation were used. Results: The mean (± standard deviation) MIP and MEP were 47.73 (±19.6) cm H2O and 60.76 (±11.6) cm H2O, respectively. MIP and MEP showed a highly significant correlation (P < 0.001) with forced expiratory volume at 1 s (FEV1) and forced vital capacity. The correlation of MIP and MEP with FEV1shows a positive linear trend, and the MEP values were higher than MIP values. There was a decrease in MIP and MEP with increasing severity of COPD. Conclusion: MIP decreases with progression of the disease, and thus, inspiratory muscle training should be included in a pulmonary rehabilitation program.

Full text

© 2018 Indian Journal of Respiratory Care | Published by Wolters Kluwer ‑ Medknow
88
Original Article
IntroductIon
According to the World Health Organization, it is estimated
that chronic obstructive pulmonary disease (COPD) will
be the third‑most common cause of death and fth‑most
common cause of disability in the world by 2020.[1] COPD
is considered as a respiratory disease with multiple systemic
pathological components. Musculoskeletal system is often
involved in patients with COPD, contributing to decrease in
effort capacity and quality of life.[2] In this context, inspiratory
muscle function is frequently affected. This may be due to
chronic systemic inammation inducing pathological changes
in the thoracic cage or producing structural alteration in
the respiratory muscles.[3‑5] Decrease in inspiratory muscle
function represents an important prediction factor for the
survival rate in COPD patients.[6]
The imbalance between respiratory muscle function and load is
an important determinant of dyspnea and hypercapnia.[7] While
inspiratory muscles reach their optimal force‑length relationship
at low pulmonary volumes, the expiratory muscles reach it at
high lung volumes.[8] Respiratory muscle dysfunction is a cardinal
feature of acute and chronic respiratory failure in COPD.[9]
Hypercapneic respiratory failure following inspiratory muscle
weakness is found to be the leading cause of death in COPD
patients.[10,11] As the most of the lung and airway derangements
are irreversible in COPD, all therapeutic interventions must be
aimed at strengthening the respiratory muscles.[7]
The respiratory muscle strength is best assessed regarding
maximal inspiratory pressure (MIP) and maximal expiratory
Maximal Inspiratory and Expiratory Pressures in Men with
Chronic Obstructive Pulmonary Disease: A Cross‑Sectional
Study
Veena Kiran Nambiar, Savita Ravindra, B. S. Nanda Kumar1
Departments of Physiotherapy and 1Community Medicine, Ramaiah Medical College and Hospitals, Bengaluru, Karnataka, India
Introduction: Respiratory muscle dysfunction is a cardinal feature in chronic obstructive pulmonary disease (COPD) contributing to decreased
exercise capacity and pulmonary function test (PFT) limitation with progression of the disease. Maximal inspiratory pressure (MIP) and maximal
expiratory pressure (MEP) are reliable parameters for assessing the respiratory muscle strength. Aims: This study aims to measure maximal
inspiratory and expiratory pressures in male COPD patients, to determine their correlates, and to study the relationship between the severity
of COPD and respiratory muscle strength. Patients and Methods: This was an observational, cross‑sectional study. A total of 100 males, who
were known COPD patients and who were clinically stable, were recruited. Both inpatients and outpatients were studied. Spirometric PFT
test was done, and MIP and MEP were measured using respiratory pressure meter. Descriptive statistics and Pearson’s correlation were used.
Results: The mean (± standard deviation) MIP and MEP were 47.73 (±19.6) cm H2O and 60.76 (±11.6) cm H2O, respectively. MIP and MEP
showed a highly signicant correlation (P < 0.001) with forced expiratory volume at 1 s (FEV1) and forced vital capacity. The correlation of
MIP and MEP with FEV1 shows a positive linear trend, and the MEP values were higher than MIP values. There was a decrease in MIP and
MEP with increasing severity of COPD. Conclusion: MIP decreases with progression of the disease, and thus, inspiratory muscle training
should be included in a pulmonary rehabilitation program.
Keywords: Chronic obstructive pulmonary disease, maximal expiratory pressure, maximal inspiratory pressure, pulmonary function test
Address for correspondence: Dr. Veena Kiran Nambiar,
Department of Physiotherapy, Ramaiah Medical College and Hospitals,
Bengaluru ‑ 560 054, Karnataka, India.
E‑mail: veenakiran_nambiar@yahoo.co.in
Access this article online
Quick Response Code:
Website:
www.ijrconline.org
DOI:
10.4103/ijrc.ijrc_5_18
How to cite this article: Nambiar VK, Ravindra S, Kumar BS. Maximal
inspiratory and expiratory pressures in men with chronic obstructive
pulmonary disease: A cross‑sectional study. Indian J Respir Care
2018;7:88‑92.
Abstract
This is an open access journal, and arcles are distributed under the terms of the
Creave Commons Aribuon-NonCommercial-ShareAlike 4.0 License, which
allows others to remix, tweak, and build upon the work non-commercially, as long
as appropriate credit is given and the new creaons are licensed under the idencal
terms.
For reprints contact: reprints@medknow.com
[Downloaded free from http://www.ijrconline.org on Tuesday, July 3, 2018, IP: 10.232.74.27]

Nambiar, et al.: Respiratory muscle pressures in male COPD patients
Indian Journal of Respiratory Care ¦ Volume 7 ¦ Issue 2 ¦ July-December 2018 89
pressure (MEP). MIP is the maximum negative pressure that
can be generated from one inspiratory effort starting from
functional residual capacity (FRC) or residual volume (RV).
MEP measures the maximum positive pressure that can be
generated from one expiratory effort starting from total lung
capacity (TLC) or FRC.
This study aimed to measure the respiratory muscle strength
using MIP and MEP in clinically stable male COPD patients,
to determine the correlates for MIP and MEP, and to study the
relationship between severity of COPD (GOLD Criteria) and
respiratory muscle strength.
PatIents and Methods
This was a cross‑sectional, observational study. Convenience
sampling was used. Participation was purely on voluntary basis.
After obtaining informed consent, 100 males, who were known
COPD patients, both inpatients and outpatients, and who were
clinically stable, were recruited. Ethical clearance was obtained
from the Ethical Review Board of the Institution. This study
was conducted on male patients only to avoid intergender
differences in MIP and MEP. A total of 99 patients completed
the MIP and MEP assessment phase. There was a dropout of
one patient due to noncompliance and thus incomplete data.
Patients with primary muscular/neuromuscular diseases and
clinically signicant comorbidities that could affect the test
results and COPD patients in acute exacerbation were excluded
from the study.
For all patients, demographic data were obtained. Spirometric
pulmonary function (PFT) was done using Schiller machine.
Best of the three successive test readings were taken as a nal
result, and the primary values, i.e., forced vital capacity (FVC),
forced expiratory volume in the 1 s (FEV1), and FEV1/FVC
ratios were recorded. Anthropometry was done by measuring
weight in kilogram (kg) and height with a stadiometer and body
mass index (BMI) was calculated according to the formula
kg/m2. MIP and MEP were determined using portable pressure
meter (Micro respiratory pressure meter). MIP was measured
from FRC or RV, and MEP was measured starting from TLC. All
recordings were taken in the sitting posture. Maximum of three
trials were given with an interval of 1 min between the trials for
each subject. The highest value was accepted for computation.
The collected data were coded, tabulated, and introduced to
PC using SPSS 16 (SPSS Inc., SPSS for Windows, Chicago).
Descriptive statistics were used to obtain mean and standard
deviation (±SD) for parametric numerical data, namely, age,
height, weight, BMI, FEV1, FVC, FEVI/FVC, MIP, and MEP.
Pearson’s correlation was used to assess the relation between
MIP and MEP with independent variables such as age, height,
weight, BMI, FEV1%, FVC%, and FEVI/FVC%.
results
A total of 99 known COPD male patients, who were clinically
stable, completed the measurement process in this study. The
mean age of the COPD population studied was 62.90 ± 6.23 years.
PFT measured by spirometry showed a mean (±SD) FEV1%
of 47.81 ± 23.9, mean (±SD) FVC% of 63.99 ± 22.08, and
mean (±SD) FEV1/FVC% of 67.60 ± 21.99. Maximum
inspiratory and expiratory pressures were a mean (±SD)
47.73 ± 19.6 and 60.76 ± 11.6 cm H2O, respectively, [Table 1].
Pearson’s correlation‑coefficient was used to assess the
relation between MIP and MEP with independent variables
such as age, height, weight, BMI, FEV1%, FVC%, and
FEVI/FVC% [Tables 2 and 3]. It was seen that MIP showed
a highly signicant correlation (P < 0.001) with both FEV1%
and FVC%. The correlation between MIP and FEV1 shows a
positive linear trend and more clustering of MIP toward FEV1
at 25%–75% [Figure 1]. MEP showed a highly signicant
correlation (P < 0.001) with weight, FEV1%, and FVC% and a
moderately signicant correlation (P < 0.05) with BMI [Table 3].
A positive linear correlation was seen between MEP
and FEV1, and the MEP P values were higher than MIP
P values [Figure 2]. A negative correlation existed between
MIP and MEP with age [Figures 3 and 4]. With increase in
age, there was a decrease in both MIP and MEP. According to
Table 1: Descriptive statistics (n=99)
Mean±SD Minimum Maximum
Age (years) 62.90±6.23 50 85
Height (cm) 165.74±6 140 177
Weight (kg) 61.60±11 30 120
FEV1 (%) 47.81±24 20 127
FVC (%) 63.99±22 28 135
FEV1/FVC (%) 67.60±22 20 114
MIP (cm H2O) 47.73±19.62 18 127
MEP (cm H2O) 60.76±11.64 40 128
BMI (kg/m2) 22.4±3.55 10.73 41.52
FEV1: Forced expiratory volume in the 1 s, FVC: Forced vital capacity,
MIP: Maximum inspiratory pressure, MEP: Maximum expiratory
pressure, BMI: Body mass index, SD: Standard deviation
Table 2: Correlation between maximum inspiratory
pressure and age, height, weight, body mass index,
forced expiratory volume in the 1 s percentage, forced
vital capacity percentage, and forced expiratory volume
in the 1 s/forced vital capacity percentage
Variable MIP (cm H2O)
r P
Age (years) −0.051 0.613
Height (cm) 0.194 0.054
Weight (kg) 0.151 0.137
BMI (kg/m2) 0.101 0.318
FEV1 (%) 0.616 <0.001*
FVC (%) 0.535 <0.001*
FEV1/FVC (%) 0.128 0.207
* Level of signicance set at P < 0.05. BMI: Body mass index, FEV1: Forced
expiratory volume in the 1 s, FVC: Forced vital capacity, MIP: Maximum
inspiratory pressure
[Downloaded free from http://www.ijrconline.org on Tuesday, July 3, 2018, IP: 10.232.74.27]

Nambiar, et al.: Respiratory muscle pressures in male COPD patients
Indian Journal of Respiratory Care ¦ Volume 7 ¦ Issue 2 ¦ July-December 2018
90
the value of FEV1%, the results revealed that 30% of COPD
patients had very severe airow obstruction (FEV1 <30%),
35% had severe airow obstruction (FEV1 30%–50%), 25%
had moderate airow obstruction (FEV1 50%–80%), and 9% of
patients had mild airow obstruction (FEV1 >80%) [Table 4].
As the severity of airow obstruction is progressively increasing,
the value of MIP and MEP were signicantly lowered in
patients with severe and very severe airway obstruction with a
statistically signicant difference between the levels of airway
obstruction concerning MIP value (F‑test‑29.31, P < 0.001)
and MEP value (F‑test‑15.67, P < 0.001) [Table 5].
It is seen from the box and error plot that there was a
decrease in MIP and MEP with increasing severity of COPD
[Figures 5 and 6]. There is a positive correlation between MIP
and MEP [Figure 7].
dIscussIon
The results show that the MIP values among male COPD
patients were much lower than their age‑matched controls.[12]
The MIP (inspiratory muscle strength) values were more
affected when compared to MEP (expiratory muscle strength)
Figure 4: Scatter plot depicting the correlation between maximal expiratory
pressure and age
Figure 3: The correlation between maximal inspiratory pressure and age
Table 3: Correlation between maximum expiratory
pressure and age, height, weight, body mass index,
forced expiratory volume in the 1 s percentage, forced
vital capacity percentage, and forced expiratory volume
in the 1 s/forced vital capacity percentage
Variable MEP (cm H2O)
r P
Age (years) −0.190 0.059
Height (cm) 0.172 0.089
Weight (kg) 0.273** <0.006
BMI 0.233* <0.020
FEV1 (%) 0.505** <0.001
FVC (%) 0.379** <0.001
FEV1/FVC (%) 0.222 0.027
**P<0.001, *P<0.05. BMI: Body mass index, FEV1: Forced expiratory
volume in the 1 s, FVC: Forced vital capacity, MEP: Maximum
expiratory pressure
Figure 1: Scatter plot depicting the correlation between maximal
inspiratory pressure and FEV1
Figure 2: Scatter plot depicting the correlation between Maximal expiratory
pressure and FEV1
[Downloaded free from http://www.ijrconline.org on Tuesday, July 3, 2018, IP: 10.232.74.27]

Nambiar, et al.: Respiratory muscle pressures in male COPD patients
Indian Journal of Respiratory Care ¦ Volume 7 ¦ Issue 2 ¦ July-December 2018 91
values in COPD patients. There was a decline in MIP and MEP
with increase in age.
MIP and MEP correlated with FEV1, i.e., when FEV1 reduced,
MIP and MEP also reduced signicantly. The results obtained
in the present study were in parallel with some of the recent
literature. In addition, it was seen that respiratory muscle
weakness occurs early in COPD with a decline in MIP and
MEP as the severity of the disease (GOLD Criteria) progressed.
The results show that the MIP values among COPD patients
were much lower than their age‑matched normal people.
However, the MEP values did not show much of a difference
in the (60–70) years of age group. The MIP (inspiratory
muscle strength) values were more affected when compared
to MEP (expiratory muscle strength) values in COPD
patients. According to a study done by Voicu et al., MIP was
signicantly decreased in moderate to severe stages of COPD
which correlated with decreased effort capacity as measured
by 6‑min walk distance.
The lean body mass decreases with increase in the severity
of the disease. Thus, there is decreased muscle strength
which is induced by various factors such as oxidative stress,
inammatory status, metabolic and nutritional dysfunction,
bed rest, and prolonged steroid treatment.[13] MIP and MEP
indicate the state of respiratory muscle strength and is related
to the severity of COPD and spirometric indices.
MIP negatively correlated with age. Due to the aging process,
there is a reduction in the diaphragm and respiratory muscle
mass. Therefore, MIP was further compromised in COPD
patients.[14] Khalil et al. studied MIP and MEP in patients with
COPD being 43.6% ± 26.9% and 46.8% ± 26%, respectively,
which was similar to this present study.[15] It was concluded in
a study done by Hans‑Joachim Kabitz that inspiratory muscle
strength decreases in COPD patients with increasing disease
severity. This could be attributed to two factors: compromised
diaphragmatic contractility in the early stages and further
reduction in inspiratory muscle strength following hyperination
in advanced COPD. All these lead to decreased exercise capacity,
impaired gas exchange, and increased dyspnea. Thus, the two
mechanisms responsible for decreased MIP in COPD are
decreased diaphragmatic contractility which begins in the early
stages of the disease, which is independent of hyperination,
and second, decreased diaphragmatic force generation due to
hyperination in severe to very severe stages of the disease.[16]
Limitations of the study
In this study, other factors, such as smoking, medication
compliance, and comorbidities were not considered, which
probably could have an inuence on MIP and MEP.
conclusIon
COPD is a cause of respiratory muscle weakness and it occurs
early in the disease. There is a decrease in respiratory muscle
strength, especially inspiratory muscle strength (MIP) with
progression of the disease.
Table 4: The degree of airflow obstruction in the study
population
Degree of airflow obstruction (n=99) Frequency, n (%)
Mild (FEV1% >80) 9 (9.1)
Moderate (FEV1% [50‑80]) 25 (25.3)
Severe (FEV1% [30‑50]) 35 (35.4)
Very severe (FEV1% <30) 30 (30.3)
FEV1: Forced expiratory volume in the 1 s
Table 5: Comparison between the chronic obstructive pulmonary disease subjects according to the level of severity
concerning the maximum inspiratory pressure and maximum expiratory pressure (cm H2O)
COPD stage (GOLD criteria)
Mild Moderate Severe Very severe
MIP
Range (mean±SD)* 69.54‑110.46 (90±26.6) 41.27‑50.89 (46.08±11.64) 42.1‑46.0 (44.09±5.7) 33.89‑47.45 (40.67±18.1)
MEP
Range (mean±SD)* 62.7‑100.14 (81.44±24.3) 57.45‑62.5 (60±6.1) 56.9‑61.7 (59.3±6.8) 54.03‑59.64 (56.83±7.5)
* Compared using ANOVA and the difference was found to be signicant with P<0.001. SD: Standard deviation, COPD: Chronic obstructive pulmonary
disease, MIP: Maximum inspiratory pressure, MEP: Maximum expiratory pressure
Figure 5: Box error plot showing the correlation between maximal
inspiratory pressure and different stages of chronic obstructive pulmonar y
disease severity (GOLD criteria). 1 ‑ Mild, 2 ‑ Moderate, 3 ‑ Severe,
4 ‑ Very Severe
[Downloaded free from http://www.ijrconline.org on Tuesday, July 3, 2018, IP: 10.232.74.27]

Nambiar, et al.: Respiratory muscle pressures in male COPD patients
Indian Journal of Respiratory Care ¦ Volume 7 ¦ Issue 2 ¦ July-December 2018
92
Implications
Respiratory muscle strength assessment in the form of MIP
and MEP should be carried out in a COPD patient, and thus,
respiratory muscle training should be included in a pulmonary
rehabilitation program.
Figure 7: Scatter plot depicting the correlation between Maximal
inspiratory pressure and Maximal expiratory pressure
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conicts of interest.
references
1. Barnes PJ. Chronic obstructive pulmonary disease. N Engl J Med
2000;343:269‑80.
2. Skeletal muscle dysfunction in chronic obstructive pulmonary disease.
A statement of the American thoracic society and European respiratory
society. Am J Respir Crit Care Med 1999;159:S1‑40.
3. Gosselink R, Troosters T, Decramer M. Distribution of muscle
weakness in patients with stable chronic obstructive pulmonary disease.
J Cardiopulm Rehabil 2000;20:353‑60.
4. Troosters T, Pitta F, Decramer M. Respiratory muscle assessment
in pulmonary rehabilitation. In: Donner CF, editor. Pulmonary
Rehabilitation. London: Hodder Arnold; 2005. p. 69‑79.
5. Orozco‑Levi M. Structure and function of the respiratory muscles in patients
with COPD: Impairment or adaptation? Eur Respir J Suppl 2003;46:41s‑51s.
6. Celli BR, Cote CG, Marin JM, Casanova C, Montes de Oca M,
Mendez RA, et al. The body‑mass index, airow obstruction, dyspnea,
and exercise capacity index in chronic obstructive pulmonary disease.
N Engl J Med 2004;350:1005‑12.
7. Marchand E, Decramer M. Respiratory muscle function and
drive in chronic obstructive pulmonary disease. Clin Chest Med
2000;21:679‑92.
8. Terzano C, Ceccarelli D, Conti V, Graziani E, Ricci A, Petroianni A,
et al. Maximal respiratory static pressures in patients with different
stages of COPD severity. Respir Res 2008;9:8.
9. Klimathianaki M, Vaporidi K, Georgopoulos D. Respiratory muscle dysfunction
in COPD: From muscles to cell. Curr Drug Targets 2011;12:478‑88.
10. Bégin P, Grassino A. Inspiratory muscle dysfunction and chronic
hypercapnia in chronic obstructive pulmonary disease. Am Rev Respir
Dis 1991;143:905‑12.
11. Zielinski J, MacNee W, Wedzicha J, Ambrosino N, Braghiroli A,
Dolensky J, et al. Causes of death in patients with COPD and chronic
respiratory failure. Monaldi Arch Chest Dis 1997;52:43‑7.
12. Nambiar VK, Ravindra S. Maximal respiratory pressures and their
correlates in normal Indian adult population: A cross‑sectional study. Int
J Physiother Res 2015;3:1188‑96.
13. Tudorache V, Oancea C, Mlădinescu OF. Clinical relevance of maximal
inspiratory pressure: Determination in COPD exacerbation. Int J Chron
Obstruct Pulmon Dis 2010;5:119‑23.
14. Hafez MR, Eisheikh RM. Assessment of the respiratory muscles
function in COPD patients. Egypt J Hosp Med 2012;49:661‑71.
15. Khalil M, Wagih K, Mahmoud O. Evaluation of maximum inspiratory
and expiratory pressure in patients with chronic obstructive pulmonary
disease. Egypt J Chest Dis Tuberculosis 2014;63:329‑35.
16. Kabitz HJ, Walterspacher S, Walker D, Windisch W. Inspiratory muscle
strength in chronic obstructive pulmonary disease depending on disease
severity. Clin Sci (Lond) 2007;113:243‑9.
Figure 6: Box error plot showing the correlation between Maximal
expiratory pressure and different stages of chronic obstructive pulmonar y
disease severity (GOLD criteria). 1 ‑ Mild, 2 ‑ Moderate, 3 ‑ Severe,
4 ‑ Very Severe
[Downloaded free from http://www.ijrconline.org on Tuesday, July 3, 2018, IP: 10.232.74.27]