Diaphragmatic fatigue and high-intensity exercise in patients with chronicobstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) are at a mechani cal disadvantage and should be predisposed to the development of diaphragma tic fatigue when the ventilatory system is stressed by exercise. The purpos e of this study was to determine whether patients with moderately severe CO PD develop contractile fatigue of the diaphragm after cycle exercise to the limits of tolerance. Twelve male patients with COPD, age 61.4 +/- 3.0 yr, participated. Their forced expiratory volume in 1 s (FEV1) was 1.79 +/- 0.1 4 L, 49.6 +/- 3.4% of predicted. Patients cycled at 60-70% of their predete rmined maximal work capacity until they had to stop because of intolerable symptoms. Twitch transdiaphragmatic pressure (Pdi,tw) was measured during c ervical magnetic stimulation before and 10, 30, and 60 min after exercise. A persistent fall in Pdi,tw postexercise of greater than or equal to 10% wa s considered potentially indicative of contractile fatigue of the diaphragm . Patients cycled for 10.2 +/- 2.0 min at a workload of 59.9 +/- 4.3 W. Pat ients exercised maximally relative to their capacity reaching a peak oxygen consumption (Vo(2)) of 108.1 +/- 2.8% of the peak Vo(2) obtained during a preliminary maximal incremental exercise test. Pdi,tw was not significantly different from baseline at any time postexercise. Pdi,tw was 19.9 +/- 1.6 cm H2O at baseline, 19.6 +/- 2.0 cm H2O at 10 min postexercise, 18.6 +/- 2. 0 cm H2O at 30 min postexercise, and 19.5 +/- 1.7 cm H2O at 60 min postexer cise. In the individual patients, two of the patients had a persistent grea ter than or equal to 10% fall in Pdi,tw postexercise, potentially indicativ e of contractile fatigue of the diaphragm. In conclusion, the majority of p atients with moderately severe COPD do not develop contractile fatigue of t he diaphragm after high-intensity constant workload cycle exercise to the l imits of tolerance.