[Peripheral muscle fatigue and ventilatory response to effort in chronic airflow limitation]

We aimed to analyze peripheral muscle fatigue and ventilatory pattern in a group of 28 individuals (12 health and 16 with chronic air flow limitation) performing incremental exercise. The level of exercise reached was significantly less for patients than for healthy subjects (107 +/- 30 W vs. 234 +/- 44 W). Minute ventilation (VE) was 54 +/- 15 l/min evolving linearly with no breaking pint, and the respiration pattern was tachypneic with high frequency (f) and low circulating volumen (VT) in patients. The ration Ti/Ttot did not change during exercise in either of the groups. Occlusion pressure (P0.1) was always higher in the patient group (p < 0.001) while mean inspiratory flow was higher at rest and at moderate levels of exercise (P < 0.05) but significantly lower at high levels (1.95 +/- 0.6 vs. 3.98 +/- 1 l.s-1). Muscle fatigue, defined as the fall in the H/L index in the electromyogram, appeared in 11/12 healthy subjects (H/L: 71 +/- 11%) and in 9/16 patients (H/L: 67 +/- 17%). There were no physical differences between the 2 groups of patients (those with and without fatigue). Patients with fatigue showed a more moderate degree of obstruction (FEV1 68 +/- 12% vs. 42 +/- 13% v. ref) with less airways impedance (p < 0.001) and hypoxia (SaO2 91.3% vs. 87%), and a better ventilatory response to exercise (VE 61 +/- 14 vs. 45 +/- 10 l/min) with a higher mean inspiratory flow (2.25 +/- 0.54 vs. 1.57 +/- 0.54 l.s-1) in spite of there being no differences in P0.1. The restricting factor was ventilatory limitation, although muscle fatigue appeared in 53% of the patients. Patients who experienced muscle fatigue had less obstruction and better ventilatory response to exercise.