981-53 Impaired Ventilatory Adaptations to Submaximal Exercise in Patients with Chronic Heart Failure

The physiologic determinants limiting maximal exercise performance in patients with congestive heart failure (CHF) have not been completely characterized. Cardiac, peripheral, and ventilatory responses to exercise are attenuated in patients with CHF. While ventilatory factors are not believed to limit maximal exercise, several abnormalities of pulmonary function have been documented. Maximal voluntary ventilation (MVV) is a brief hyperventilatory maneuver that is usually performed at rest. We hypothesized that this maneuver performed during exercise could further elucidate exercise-induced pulmonary abnormalities in patients with CHF. Accordingly, MVV (in L/min, determined by a 12-second maximal hyperventilatory effort) was measured at rest and during 10 minutes of submaximal bicycle exercise (at 55% of a previously determined maximal effort) in 9 normal subjects (NL) and 9 patients with CHF (mean EF 0.23). Results VO 2 max Peak V E Rest MVV Exercise MVV NL 38.3 ± 7.1 132 ± 32 175 ± 42 193 ± 36 CHF 15.4 ± 1.9 * 73 ± 13 * 143 ± 28 143 ± 25 * Peak V E  = peak ventilation during maximal exercise * P l 0.05. CHF vs normals Although ventilatory factors did not appear to limit exercise (since MVV gg peak V E in both NL and CHF), MVV increased during submaximal exercise only in normal subjects but not in patients with CHF (+ 11% vs +0%, P l 0.05). The exercise-induced increase in MW in normal subjects may represent an adaptive response to exercise related to exercise-induced bronchodilation or sympathetic stimulation of the diaphragm. These mechanisms may be attenuated in CHF secondary to bronchial edema from high left ventricular filling pressures, or due to intrinsic diaphragmatic muscle abnormalities. The absence of normal ventilatory adaptations to exercise may contribute to exercise intolerance in patients with CHF