SA NODAL PARASYMPATHECTOMY DELINEATES AUTONOMIC CONTROL OF HEART-RATE POWER SPECTRUM

The purpose of this study was to quantify the relative roles of the canine cardiac parasympathetic and sympathetic nerves in controlling the distribution of power within the heart rate (HR) power spectrum using a highly selective surgical technique to parasympathectomize the SA node. Data were recorded in awake dogs (n = 6) before and after the selective denervation; the animals were isolated from human contact and their behavior carefully monitored during the measurements. The average amplitude in the high-frequency (almost-equal-to 0.32 Hz) peak in the HR power spectrum decreased from a predenervation control of 2.68 +/- 1.54 (mean +/- SD, arbitrary units) to 0.07 +/- 0.06 (P < 0.05). Corresponding resting HR increased from 80 +/- 9 to 106 +/- 16 beats/min (P < 0.05). The low-frequency peak (almost-equal-to 0.02 Hz) also decreased from a control of 2.45 +/- 1.18 to a postparasympathectomy value of 1.25 +/- 0.92 (P < 0.05). beta-Adrenergic blockade (propranolol, 1 mg/kg) further decreased the latter peak to 0.59 +/- 0.52 (P < 0.05). These data directly demonstrate that the high-frequency peak of the HR power spectrum 1) results from parasympathetic control of SA nodal automaticity, while 2) the low-frequency peak reflects activity in both divisions of the autonomic nervous system.