INFLUENCE OF ATRIAL-NATRIURETIC-FACTOR ON HEART-RATE-VARIABILITY IN NORMAL MEN

To study the effects of atrial natriuretic factor (ANF) on sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) control of heart rate, we gave ANF (50 mu g over 3 min, then 50 ng.kg(-1).min(-1)) and saline (vehicle) to six normal men [age 22 +/- 2 (SE) yr] during supine rest on two separate study days according to a random double-blind design. R-R interval data were sampled at 1,000 Hz over 7-min time segments, then analyzed by coarse graining spectral analysis of heart rate variability (HRV) to yield indicators of PNS and SNS activity. From the harmonic component of HRV, the integrated power in the low-frequency region (0.0-0.15 Hz, FL) and in the high-frequency region (0.15-0.50 Hz, P-H) were calculated. Total spectral power (P-T) was obtained and used to normalize the PNS indicator as P-H/P-T The quantity P-L/P-H was taken as an indicator of SNS activity. By the 20th min of its infusion, ANF lowered PT, PH, and the SNS indicator (4.20 +/- 1.9 to 2.37 +/- 0.65; P < 0.05) but did not significantly change the PNS indicator (P-H/P-T) In contrast, 20-min saline infusion had no effect on these variables. These observations are consistent with our previous documentation of a relative sympathoinhibitory action of ANF on muscle sympathetic nerve activity and support the concept that ANF acts on the autonomic nervous system to decrease sympathetic outflow.