Maximal Respiratory Pressures and Exercise Tolerance in Patients with COPD

Many authors reported respiratory muscle function impairment in patients with chronic obstructive pulmonary disease (COPD). Impaired respiratory muscle function may contribute exercise intolerance which is frequently observed in this disease. Aim of the study: was to determine the influence of respiratory muscle function on exercise capacity in patients with COPD. Methods: 23 patients with stable COPD aged 62.7 ± 9.3 years (6F, 17M; mean post-bronchodilator FEV₁ = 47.9 ± 12.4% value predicted) participated in the study. Exercise capacity was assessed by the six-minute walk test and the incremental cardiopulmonary exercise test (CPET) on a treadmill. Maximal respiratory pressures (PI_max, PE_max) were evaluated before and directly after CPET. Results: The mean peak oxygen uptake (VO₂max) was 27.2 ± 6.1 mlO₂/min/kg and the mean distance walked during the 6 MWT was 569.4 ± 101.7 m. Both PImax and PEmax decreased significantly after maximal exercise (71.4 ± 23.0 vs. 63.6 ± 22.2 cm H₂O, p = 0.001 and 124.9 ± 46.5 vs. 112.3 ± 46.6 cm H₂O, p = 0.02 respectively). No correlation between VO₂max and the 6-minute walk distance and the maximal respiratory pressures was found. We observed a negative correlation between the 6-minute walk distance and the difference between the pre- and post CPET maximal inspiratory pressure. Conclusions: respiratory muscle function is impaired in patients with COPD but this does not affect exercise performance. Exercise causes a decrease of the respiratory muscle strength.