Mechanisms of respiratory sinus arrhythmia in patients with mild heart failure

The high-frequency (HF) component of the heart rate variability (HRV) is re garded as an index of cardiac vagal responsiveness. However, when vagal ton e is decreased, nonneural mechanisms could account for a significant propor tion of the HF component. To test this hypothesis, we examined the HRV spec tral power in 20 patients with mild chronic heart failure (CHF) and 11 cont rols before and during ganglion blockade with trimethaphan camsylate (3-6 m g/min iv). A small HF component was still present during ganglion blockade, and its amplitude did not differ between CHF patients and controls. The av erage contribution of nonneural oscillations to the HF component was 15% (r ange 1-77%) in patients with CHF and 3% (range 0.7-30%) in healthy controls (P< 0.005). During controlled breathing at 0.16 Hz, however, it decreased to 1% (range 0.2-13%) in healthy controls and 5% (range 1-44%) in CHF patie nts. Our results indicate that the HF component can significantly overestim ate cardiac vagal responsiveness in patients with mild CHF. This bias is im proved by controlled breathing, since this maneuver increases the vagal con tribution to HF without affecting its nonneural component.