Ventilatory response to positive and negative work in patients with chronic obstructive pulmonary disease

In healthy subjects, oxygen consumption and cardiorespiratory responses are lower during eccentric exercise (negative work, Wneg) than during concentric exercise (positive work, Wpos) at the same work load. The aim of the present study was to investigate the ventilatory response to Wneg in patients with chronic obstructive pulmonary disease (COPD). The study population consisted of 12 subjects with COPD [forced expiratory volume in 1 s (FEV1) mean (SD): 1.5 (0.4) 1, 46 (16)% of predicted]. Concentric and eccentric exercise tests (6 min exercise; interval > or = 1 h) were performed in random order at constant work loads of 25 and 50% of the individual maximal (positive) work capacity. Expired ventilation per minute (VE), oxygen consumption (VO2) and carbon dioxide production (VCO2) were 30% lower during Wneg than during Wpos for both work intensities. The breathing reserve during 25% Wneg was 11 (8)% and during 50% Wneg was 18 (14)% higher than during Wpos at corresponding work loads (P < 0.01). VE/VO2 and VE/VCO2 were similar during Wpos and Wneg. Arterial carbon dioxide tension (PaCO2) increased by 0.1 (0.4) kPa during 50% Wneg and by 0.7 (0.5) kPa during 50% Wpos (P < 0.01). During 50% Wneg' perceived leg effort (modified Borg scale) tended to be higher than perceived breathlessness (2.4 (1.2) vs. 2.0 (1.1). It was concluded that in subjects with COPD, the ventilatory requirements of Wneg were considerably lower than those of Wpos at similar work loads up to 50% of maximal work capacity. During Wneg, the ventilatory reserve was higher and gas exchange was less disturbed as a result of a lower VO2 and VCO2.