Gender differences in autonomic cardiovascular regulation: spectral, hormonal, and hemodynamic indexes

The autonomic nervous system drives variability in heart rate, vascular ton e, cardiac ejection, and arterial pressure, but gender differences in auton omic regulation of the latter three parameters are not well documented. In addition to mean values, we used spectral analysis to calculate variability in arterial pressure, heart rate (R-R interval, RRI), stroke volume, and t otal peripheral resistance (TPR) and measured circulating levels of catecho lamines and pancreatic polypeptide in two groups of 25 +/- 1.2-yr-old, heal thy men and healthy follicular-phase women (40 total subjects, 10 men and 1 0 women per group). Group 1 subjects were studied supine, before and after beta- and muscarinic autonomic blockades, administered singly and together on separate days of study. Group 2 subjects were studied supine and drug fr ee with the additional measurement of skin perfusion. In the unblocked stat e, we found that circulating levels of epinephrine and total spectral power of stroke volume, TPR, and skin perfusion ranged from two to six times gre ater in men than in women. The difference (men > women) in spectral power o f TPR was maintained after beta- and muscarinic blockades, suggesting that the greater oscillations of vascular resistance in men may be alpha -adrene rgically mediated. Men exhibited muscarinic buffering of mean TPR whereas w omen exhibited beta -adrenergic buffering of mean TPR as well as TPR and he art rate oscillations. Women had a greater distribution of RRI power in the breathing frequency range and a less negative slope of In RRI power vs. In frequency, both indicators that parasympathetic stimuli were the dominant influence on women's heart rate variability. The results of our study sugge st a predominance of sympathetic vascular regulation in men compared with a dominant parasympathetic influence on heart rate regulation in women.