Increased exercise ventilation in patients with chronic heart failure: intact ventilatory control despite hemodynamic and pulmonary abnormalities

Abstract

This study was designed to determine the pathophysiologic basis of increased exercise ventilation in the presence of chronic heart failure. Sixty-four ambulatory patients with chronic heart failure and 38 age-matched normal control subjects performed exercise according to identical staged, symptom-limited bicycle exercise protocols with measurement of hemodynamic, ventilatory, and metabolic responses. Compared with normal subjects, ventilation and the ratio of ventilation to CO2 production (Ve/VCO2), and pulmonary capillary wedge pressure were elevated in patients at rest and during exercise. The ratio of pulmonary dead space to tidal volume (Vd/Vt) also was elevated in the heart failure group at rest and during exercise and was closely related to Ve/VCO2 (all r greater than .72, p less than .001). Rest and exercise arterial PCO2 regulation was normal in patients. Peak exercise Ve/VCO2 did not correlate with pulmonary vascular pressures, but was inversely related to cardiac output (r = -.49, p less than .001). Thus, neurohumoral ventilatory control mechanisms are intact in patients with chronic heart failure and act to maintain normal PaCO2 levels in the face of increased pulmonary dead space. Activation of abnormal reflexes due to hemodynamic derangements during exercise are not important in determining ventilation in the presence of chronic heart failure. The demonstration of a correlation between decreased cardiac output and increased ventilation in the patient group suggests that attenuated pulmonary perfusion may play a role in causing exercise hyperpnea in the presence of chronic heart failure by producing ventilation perfusion abnormalities and thereby increasing physiologic pulmonary dead space.