Wide-band spectral analysis of blood pressure and RR interval variability in borderline and mild hypertension

The aim of this study was firstly to investigate whether indices of wide-ba nd spectral analysis in borderline hypertensive (BHT) or mildly hypertensiv e (HT) subjects differ from those in normotensive (NT) subjects, and second ly to assess the predictive value of these indices for future hypertension. Electrocardiogram and intra-arterial 24 h ambulatory blood pressure (BP) w ere recorded in 32 NT, 29 BHT and 30 HT middle-aged men. From the recording s, a 16 h period was extracted for wide-band spectral analysis. A single sp ectrum of BP and RR interval (RRI) variability was computed for each period by the fast Fourier transform method. The slopes of the spectra were asses sed on a log-log scale by linear fitting of the spectral values. Power spec tral densities were calculated over regions of 0-0.003, 0.003-0.04, 0.04-0. 15, 0.15-0.40 and 0-0.4 Hz. No between-group differences were found in the slopes of BP and RRI spectra. The between-group differences in spectral pow ers for BP variability were almost invariably significant. The spectral pow ers for RRI variability did not show between-group differences. Five years later, 22 NT, 22 BHT and 18 HT subjects were re-assessed using casual BP me asurements. In a logistic regression model for the combined group of NT and BHT subjects who became HT (22 of 44) during the five-year period, none of the parameters of wide-band spectrum predicted the development of hyperten sion. In conclusion, parameters of wide-band spectral analysis may not be u seful in predicting future hypertension in NT and BHT subjects. Because the BP level is a major factor influencing BP variability, the between-group d ifferences in wide-band spectral powers in BP may be due to differences in BP level rather than differences in cardiovascular regulatory mechanisms.