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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 7  |  Issue : 2  |  Page : 88-92

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


1 Department of Physiotherapy, Ramaiah Medical College and Hospitals, Bengaluru, Karnataka, India
2 Department of Community Medicine, Ramaiah Medical College and Hospitals, Bengaluru, Karnataka, India

Date of Web Publication28-Jun-2018

Correspondence Address:
Dr. Veena Kiran Nambiar
Department of Physiotherapy, Ramaiah Medical College and Hospitals, Bengaluru - 560 054, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijrc.ijrc_5_18

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  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.

Keywords: Chronic obstructive pulmonary disease, maximal expiratory pressure, maximal inspiratory pressure, pulmonary function test


How to cite this article:
Nambiar VK, Ravindra S, Kumar B S. Maximal inspiratory and expiratory pressures in men with chronic obstructive pulmonary disease: A cross-sectional study. Indian J Respir Care 2018;7:88-92

How to cite this URL:
Nambiar VK, Ravindra S, Kumar B S. Maximal inspiratory and expiratory pressures in men with chronic obstructive pulmonary disease: A cross-sectional study. Indian J Respir Care [serial online] 2018 [cited 2018 Dec 14];7:88-92. Available from: http://www.ijrconline.org/text.asp?2018/7/2/88/235523




  Introduction Top


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 fifth-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 inflammation inducing pathological changes in the thoracic cage or producing structural alteration in the respiratory muscles.[3],[4],[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 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 Top


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 significant 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 final 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/m 2. 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 Top


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].
Table 1: Descriptive statistics (n=99)

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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% [Table 2] and [Table 3]. It was seen that MIP showed a highly significant 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 significant correlation (P < 0.001) with weight, FEV1%, and FVC% and a moderately significant correlation (P < 0.05) with BMI [Table 3].
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

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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

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Figure 1: Scatter plot depicting the correlation between maximal inspiratory pressure and FEV1

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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 [Figure 3] and [Figure 4]. With increase in age, there was a decrease in both MIP and MEP. According to the value of FEV1%, the results revealed that 30% of COPD patients had very severe airflow obstruction (FEV1 <30%), 35% had severe airflow obstruction (FEV1 30%–50%), 25% had moderate airflow obstruction (FEV1 50%–80%), and 9% of patients had mild airflow obstruction (FEV1 >80%) [Table 4].
Figure 2: Scatter plot depicting the correlation between Maximal expiratory pressure and FEV1

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Figure 3: The correlation between maximal inspiratory pressure and age

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Figure 4: Scatter plot depicting the correlation between maximal expiratory pressure and age

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Table 4: The degree of airflow obstruction in the study population

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As the severity of airflow obstruction is progressively increasing, the value of MIP and MEP were significantly lowered in patients with severe and very severe airway obstruction with a statistically significant 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].
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)

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It is seen from the box and error plot that there was a decrease in MIP and MEP with increasing severity of COPD [Figure 5] and [Figure 6]. There is a positive correlation between MIP and MEP [Figure 7].
Figure 5: Box error plot showing the correlation between maximal inspiratory pressure and different stages of chronic obstructive pulmonary disease severity (GOLD criteria). 1 - Mild, 2 - Moderate, 3 - Severe, 4 - Very Severe

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Figure 6: Box error plot showing the correlation between Maximal expiratory pressure and different stages of chronic obstructive pulmonary disease severity (GOLD criteria). 1 - Mild, 2 - Moderate, 3 - Severe, 4 - Very Severe

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Figure 7: Scatter plot depicting the correlation between Maximal inspiratory pressure and Maximal expiratory pressure

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  Discussion Top


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) 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 significantly. 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 significantly 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, inflammatory 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 hyperinflation 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 hyperinflation, and second, decreased diaphragmatic force generation due to hyperinflation 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 influence on MIP and MEP.


  Conclusion Top


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.

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.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Hafez MR, Eisheikh RM. Assessment of the respiratory muscles function in COPD patients. Egypt J Hosp Med 2012;49:661-71.  Back to cited text no. 14
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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