Associations of Maximal Inspiratory Pressure With Lung Hyperinflation, Functional Capacity, and Muscle Strength in Patients With Chronic Obstructive Pulmonary Disease.
Abstract
Background
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Purpose
In patients with chronic obstructive pulmonary disease (COPD), the correlations between inspiratory muscle weakness and some physiological factors were inconclusive. Understanding the relationship between these parameters may potentially be a screening tool for inspiratory muscle weakness. The purpose of this study was to evaluate the association between inspiratory muscle strength and functional capacity, dyspnea sensation, airway obstruction, lung hyperinflation, and peripheral muscle strength in patients with COPD.
Methods
A cross-sectional analytical study evaluated 40 patients with stable COPD. Patients underwent pulmonary function tests, maximal inspiratory and expiratory pressure (MIP, MEP) tests, handgrip strength measurement, and a six-minute walk test.
Results
Forty male patients were included. Fifteen patients (37.5%) had inspiratory muscle weakness when using a cut-off point of 60 cmH2O. Positive correlations were found between MIP and MEP (Pearson's correlation coefficient [r] = 0.489), six-minute walk distance (r = 0.504), and relative handgrip strength (r = 0.347). There was a negative correlation between MIP and residual volume/total lung capacity (RV/TLC) (r = -0.459). Regression analyses were performed after adjustment for age and forced expiratory volume in the first second (FEV1) % predicted. Linear regression showed that MIP was associated with MEP (coefficient [β] = 0.37; 95% confidence interval [CI], 0.12-0.62) and peak expiratory flow (PEF) (β = 7.68; 95% CI, 2.50-12.81). Exploratory logistic regression showed an association between PEF and inspiratory muscle weakness (OR = 0.36; 95% CI 0.14-0.93); exploratory ROC analysis yielded an AUC of 0.81 (95% CI, 0.68-0.95).
Discussion
A reduction in inspiratory muscle strength is related to lung hyperinflation, functional capacity, and peripheral muscle strength. Higher MIP was independently associated with higher MEP and PEF. After adjustment for age and FEV1% predicted, PEF was significantly associated with inspiratory muscle weakness.