The autonomic nervous activity of hypertension

Autonomic nervous function was evaluated by means of power spectral analysis of heart rate variability in hospitalized patients with different circadian blood pressure(BP) variation, i.e., dipper(n = 33), non-dipper(n = 37), extreme dipper(n = 26) and riser(n = 20). Ambulatory BP monitoring was performed by A & D TM2425 based on a cuff-oscillometric method. Circadian BP variation was defined in these subjects. The non-dipper, extreme dipper and riser subjects were defined as those whose nocturnal decrease in systolic BP was less than 10%, more than 20% and elevation of BP, as compared to the daytime BP, respectively. Power spectral analysis of hourly R-R intervals for 24 hours was done to obtain the low frequency power(LF, 0.04 to 0.15 Hz) and high frequency power(HF, 0.15 to 0.40 Hz). LF/HF ratio was considered to be an index of sympathetic nervous activity, and HF parasympathetic nervous activity, respectively. LF/HF was significantly lower in both riser and non-dipper than that in dipper subjects throughout the day. In non-dipper day-night difference of HF was smaller than in dipper and extreme dipper groups. These findings indicated that riser and non-dipper hypertensives were characterized by decreased physiological circadian fluctuation of autonomic functions when compared to dipper subjects. The circadian variation of BP may be mediated at least in part by circadian variation of autonomic nervous system activity.