Skeletal muscle ergoreflex overactivity is not related to exercise ventilatory inefficiency in non-hypoxaemic patients with COPD

Abstract

Increased ventilatory response to the metabolic demand (“ventilatory inefficiency”) is commonly found during dynamic exercise in patients with chronic obstructive pulmonary disease (COPD). However, the role of enhanced muscle ergoreflex activity on this phenomenon is yet unknown. Ten non-hypoxaemic patients with varying degrees of disease severity (median and range of post-bronchodilator FEV₁ = 37.5 (27 to 70%) predicted) and 7 age- and gender-matched controls were studied. Subjects were submitted to wrist flexion tests to the limit of tolerance (Tlim) with and without post-exercise regional circulatory occlusion (PE-RCO) for 3 min. The muscle ergoreflex activity was quantified as the difference in ventilation between PE-RCO and control recovery periods corrected for the resting values (ergoreflex Δ). In addition, the area under the ventilatory curve in the recovery period was calculated in both conditions. We found that Tlim and the physiological stress associated with localized exercise did not differ between patients and controls. However, patients had increased ventilatory response to a given metabolic demand $({\dot{\rm V}}\hbox{CO}_2),$ either at rest or during exercise (P < 0.05). There were no significant differences in ergoreflex Δ in patients and controls (−2.2 to 2.4 (0.2) vs. −0.6 to 1.8 (0.3) l/min, respectively). In addition, the area under the ventilatory curve in the recovery period did not differ between control and PE-RCO tests in patients and healthy subjects (P > 0.05). We conclude that increased muscle ergoreflex activity did not contribute to an excessive ventilatory response to exercise in patients with COPD—at least in non-hypoxaemic and non-cachetic subjects.