POTASSIUM AND VENTILATION DURING POSITIVE AND NEGATIVE WORK IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

In patients with chronic obstructive pulmonary disease (COPD), reduced ventilatory reserves limit exercise tolerance. In these patients, the ventilatory requirements of eccentric exercise (negative work, W-neg) are lower than those of concentric exercise (positive work, W-pos) at similar workloads. In this study, we investigated the relationship be tween plasma potassium levels and ventilation during W-pos and W-neg i n these patients. Twelve patients with stable COPD [mean (SD) FEV1 46% (16) of predicted] performed W-pos and W-neg on a cycle ergometer (6 min of exercise; interval greater than or equal to 1 h) in a randomize d order at a constant workload of 50% of the individual maximum (posit ive) work capacity. Minute ventilation (V-E) and arterial plasma potas sium concentration ([K+](a)) were measured at rest, and at 1-min inter vals during exercise and during 3 min of recovery. V-E increased less during W-neg than during W-pos [6 (range 3-26) vs. 18 (range 8-28) 1 m in(-1); P<0.01]. V-E during W-neg was reduced in proportion to VCO2. T he increase in [K+](a) during W-pos and W-neg [0.45 (range 0.26-0.75) and 0.34 (range 0.1-0.97) mM] did not differ significantly. V-E was cl osely correlated with VCO2 during both types of exercise. V-E was also closely correlated with [K+](a), but the slope of the relationship be tween [K+](a) and V-E was steeper during W-pos than during W-neg [39.1 (range 15.2-88.6) vs. 18.3 (range 7.2-37.3) 1 min(-1) mM(-1); P= 0.01 2]. In contrast, the slope of the relationship between VCO2 and V-E wa s similar during both types of exercise [27.8 (range 19.2-37.1) vs. 32 .1 (range 19.8-48.4)]. Thus, for a given increase in [K+](a), the incr ease in V-E was significantly less during W-neg. In patients with COPD , potassium did not explain the difference in exercise ventilation bet ween W-neg and W-pos, and may not play a significant role in the contr ol of breathing during low-intensity exercise.