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

Abstract

In healthy subjects, oxygen consumption and cardiorespiratory responses are lower during eccentric exercise (negative work, W neg ) than during concentric exercise (positive work, W pos ) at the same work load. The aim of the present study was to investigate the ventilatory response to W neg in patients with chronic obstructive pulmonary disease (COPD). The study population consisted of 12 subjects with COPD [forced expiratory volume in 1 s (FEV 1) mean ( SD): 1·5 (0·4) 1, 46 (16) % of predicted]. Concentric and eccentric exercise tests (6 min exercise; interval ≥ 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 (V̇ E), oxygen consumption ( V ̇ O 2 ) and carbon dioxide production ( V ̇ CO 2 ) were 30% lower during W neg than during W pos for both work intensities. The breathing reserve during 25% W neg was 11 (8) % and during 50% W neg was 18 (14)% higher than during W pos at corresponding work loads ( P<0·01). V̇ E/V̇O 2 and V̇ E/V̇CO 2 were similar during W pos and W neg . Arterial carbon dioxide tension ( PaCO 2) increased by 0·1 (0·4) kPa during 50% W neg and by 0·7 (0·5) kPa during 50% W pos ( P<0·01). During 50% W neg , 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 W neg were considerably lower than those of W pos at similar work loads up to 50% of maximal work capacity. During W neg , the ventilatory reserve was higher and gas exchange was less disturbed as a result of a lower V ̇ O 2 and V ̇ CO 2 .