Exercise dynamics at submaximal workloads in patients with chronic heart failure

Abstract

Background: The aims of this study were to analyze the relationship between exercise at self-selected work loads and peak exercise performance in patients with chronic heart failure and to analyze possible relationships between gait pattern and exercise performance and ventilatory response to exercise in chronic heart failure. Methods and Results. Twelve patients with stable chronic heart failure and 10 age- and build-matched control subjects undertook symptom-limited maximal exercise testing with metabolic gas exchange measurements to determine peak oxygen consumption (V̇o> 2) and the slope of the relationship between ventilation and carbon dioxide production (V̇e/V̇co 2 slope). Respiratory rate was also determined. Self-selected walking pace and cadence (steps per minute) were determined. Metabolic gas exchange analysis was repeated at matched low-level exercise and at self-selected walking pace. Self-selected exercise was at a lower speed for patients than control subjects (1.28 [0.22] vs 1.43 [0.19] m s −1), representing a similar proportion of peak oxygen consumption (63.6 [19.3]% vs 56.7 [25.4]%). There was a relationship between peak Vo 2 and Vo 2 at self-selected workload ( r = .55, P < .001) and self-selected walking velocity ( r = .58, P < .005). Gait analysis demonstrated that the reduction in self-selected velocity in heart failure patients was due to a reduced cadence (101.5 [8.7] steps/min vs 110.2 [9.1] steps/min, P < .01), not a reduction in stride length. There was a negative relationship between V̇e/V̇co 2 slope and self-selected cadence ( r = −.68, P < .001) and a negative correlation between respiratory rate and cadence at self-selected workload ( r = −.6, P < .005). Conclusions: Self-selected walking speed is at the same proportion of peak oxygen consumption in patients with heart failure as compared with control subjects, but a lower absolute level. Patients have the same stride length as normal control subjects. Ventilation is increased in patients, but there is no direct relationship between ventilation and gait.