Ineffective ventilation during exercise in patients with chronic congestive heart failure.

The pathophysiologic mechanisms causing exertional breathlessness in patients with chronic congestive heart failure (CHF) are not fully understood. Therefore, we have studied whether the ventilation in such patients is ineffective during exercise. Thirteen patients with treated chronic CHF (New York Heart Association class II-IV) and eight healthy controls underwent a maximal bicycle ergometer test with continuous analysis of expired air and frequent arterial blood sampling for gas and lactate analysis. All subjects were non-smokers and none had any signs of a pulmonary disease. Peak O2 consumption of the patients was 14.9 +/- 5.3 ml min-1 kg-1 and that of controls 33.6 +/- 7.5 ml min-1 kg-1. In patients with CHF the ratio of pulmonary dead space to tidal volume was significantly elevated at peak exercise compared with that of the controls (0.36 +/- 0.08 vs. 0.20 +/- 0.07, P less than 0.05). The ventilatory equivalent for CO2 (VE:VCO2) was also significantly higher in patients than in controls during exercise (P less than 0.05). Furthermore, both the ventilatory equivalents for CO2 and O2 (VE:VO2) had a significant inverse correlation with peak O2 consumption (P less than 0.001 for VE:VCO2 and P less than 0.05 for VE:VO2), O2 consumption at anaerobic threshold (P less than 0.01) and O2-pulse (P less than 0.001) among the patients. During exercise the arterial PO2 and PCO2 remained normal in patients and controls. These data indicate that in patients with chronic CHF wasted ventilation is pathologically increased during exercise, and this is related to the severity of the disease. Chronic CHF is not associated with decreased ventilatory reserve, hypoxaemia or alveolar hyperventilation. The ineffectiveness of ventilation is probably an important cause of exertional breathlessness in patients with CHF.