EFFECT OF ACUTE BICARBONATE ADMINISTRATION ON EXERCISE RESPONSES OF COPD PATIENTS

Patients with severe chronic obstructive pulmonary disease (COPD) are limited in their exercise tolerance by the level of ventilation ((V) o ver dot (E)) they can sustain. We determined whether acutely increasin g blood bicarbonate levels decreased acid stimulation to the respirato ry chemoreceptors during exercise, thereby improving exercise toleranc e. Responses were compared with those obtained during 100% O-2 breathi ng (known to reduce (V) over dot (E) in these patients) and to the res ponses of healthy young subjects. Participants were six patients with severe COPD (forced expired volume in 1 s = 31 +/- 11% predicted) but without chronic CO2 retention and 5 healthy young subjects. Each subje ct performed three incremental cycle ergometer exercise tests: 1) cont rol, 2) after ingestion of 0.3 g . kg(-1) of sodium bicarbonate and 3) while breathing 100% O-2. During these tests (V) over dot (E) was mea sured continuously and arterialized venous blood (patients) or arteria l blood (healthy subjects) was sampled serially to assess acid base va riables. Bicarbonate loading increased standard bicarbonate by 4-6 mmo l . L-1 and this elevation persisted during exercise. In both groups, bicarbonate loading resulted in a substantially higher arterial pH; ar terial PCO2 was either unchanged (healthy subjects) or mildly (averagi ng 5 torr) higher (COPD patients). However, in neither group did bicar bonate loading result in an altered (V) over dot (E) response to exerc ise or an increase in exercise tolerance. In contrast, superimposing h yperoxia on bicarbonate ingestion yielded, on average, 24% reduction i n (V) over dot (E) and 50% increase in peak: work rate in the patients (but not in the healthy young subjects). We conclude that acute bicar bonate loading is not an ergogenic aid in patients with severe COPD.