Determinants of maximum exercise capacity in patients with chronic airflow obstruction

Patients with chronic airflow obstruction (CAO) often develop impairment of respiratory muscle function. We hypothesized that inspiratory muscle strength, as assessed by resting, peak inspiratory pressure (PIP) may be an important determinant of maximum exercise capacity in patients with CAO. Twenty ambulatory male patients (mean age, 56 ± 3 years [± SE]) with CAO (FEV₁, 1.72 ± 0.21 L) comprised the studied population. Oxygen consumption at incremental cycle ergometry to tolerance (V̇O₂max, 1.80 ± 0.20 L/min) served as the dependent variable for regression vs measures of resting pulmonary function. Significant correlations with V̇O₂max included power output in watts (r = 0.951), V̇Emax (r = 0.858), Dsb (r = 0.841), PIP (r = 0.816), age (r = -0.809), FEV₁ (r = 0.763), and FVC (r = 0.663). The FEV₁, Dsb, and PIP each entered into a multiple linear regression relationship describing V̇O₂max. Also, when paired with V̇Emax as independent variables in multiple regression, PIP and Dsb each improved description of V̇O₂max over V̇Emax alone (p < 0.05), whereas FEV₁ and FVC did not (p > 0.05). We conclude that factors other than ventilatory capacity also have a quantitative effect on V̇O₂max and that PIP constitutes a determinant of maximum exercise capacity in patients with CAO.