AUTONOMIC NERVOUS FUNCTION IN NON-DIPPER ESSENTIAL HYPERTENSIVE SUBJECTS - EVALUATION BY POWER SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY

Autonomic nervous function was evaluated by means of power spectral an alysis of heart rate variability in hospitalized dipper (n=31) and non -dipper (n=31) essential hypertensive subjects. Twenty-four-hour blood pressure (BP) measurement was performed by the cuff-oscillometric met hod to evaluate the nocturnal decrease of BP. The non-dipper subjects were defined as those whose nocturnal decrease of systolic BP was <10% of daytime BP. Power spectral analysis of RR interval was performed f rom Holter ECG every 10 minutes by the maximum entropy method to obtai n the low-frequency band (LFB, 0.04 to 0.15 Hz), which is an index of both parasympathetic and sympathetic nervous activities, and the high- frequency band (HFB, 0.15 to 0.4 Hz), which reflects parasympathetic n ervous activity. LFB and HFB were averaged every hour to obtain hourly LFB and HFB values. Total LFB total HFB were calculated as the mean v alues of 24 hourly averaged LFBs and HFBs. Both LFB and HFB were signi ficantly lower in non-dipper hypertensives than in dipper subjects thr oughout the day. In dipper hypertensives, LFB showed a nocturnal decre ase, whereas HFB was significantly increased during the nighttime. How ever, these diurnal changes in LFB and HFB were significantly blunted in non-dipper subjects. These findings indicate that non-dipper hypert ensive subjects were characterized with a decreased physiological circ adian fluctuation on autonomic functions compared with dipper subjects . This alteration in the autonomic nervous function may explain the no n-dipper phenomenon in essential hypertension.