VENTILATORY AND GAS-EXCHANGE ABNORMALITIES ON EXERCISE IN CHRONIC HEART-FAILURE

The mechanism of breathlessness on exertion in patients with chronic h eart failure are still not fully understood. We therefore investigated the effects of ventilatory and gas exchange abnormalities on exercise capacity in chronic heart failure. Exercise testing was performed in 30 patients with exertional breathlessness due to chronic heart failur e and in 30 controls, using continuous transcutaneous blood gas monito ring. Maximal symptom-limited oxygen consumption as (V'O-2) as a perce ntage predicted was reduced in patients (45 +/- 10%; mean +/- SD) comp ared to controls (87 +/- 7). The ventilatory response (minute ventilat ion/carbon dioxide production (V'E/V'CO2)) was significantly increased in patients compared to controls (39.9 +/- 7.7 and 25.9 +/- 3.6, resp ectively). The dead space to tidal volume ratio (VD/VT) was raised in patients compared to controls at rest (0.45 +/- 0.04 vs 0.35 +/- 0.02, respectively) and this persisted on exertion (0.40 +/- 0.05 in patien ts and 0.20 +/- 0.05 in controls). At maximal symptom-limited exercise , V'E/V'CO2 was inversely related to the % predicted V'O-2 in patients , but not in controls (r = -0.62 and r = -0.24, respectively). In pati ents, V'E/V'CO2 was significantly correlated with VD/VT at maximum exe rcise (r = 0.82). Patients with chronic heart failure have a significa nt degree of ''wasted ventilation'' on exertion, which is associated w ith increased ventilatory response. The increased ventilatory response on exertion appears to contribute to exercise limitation in these pat ients.