SHORT-TERM VARIABILITY OF BLOOD-PRESSURE AND HEART-RATE IN BORDERLINEAND MILDLY HYPERTENSIVE SUBJECTS

Electrocardiogram and intra-arterial blood pressure were recorded in 9 6 men (aged 35 to 45 years) by the Oxford method over a 30-hour period . The study involved 33 normotensive, 29 borderline hypertensive, and 34 mildly hypertensive individuals, as assessed by the cuff method. Fi ve-minute periods during sleep and with subjects in supine, sitting, a nd standing positions were extracted from the recordings for frequency domain analysis. Power spectrum density estimates of systolic blood p ressure, diastolic blood pressure, and heart rate were calculated by a n autoregressive method over the bandwidths of 0.02 to 0.075 (low-freq uency), 0.075 to 0.15 (midfrequency), and 0.15 to 0.35 Hz (high-freque ncy), attributable to thermoregulatory, baroreceptor, and respiratory activity. No significant intergroup differences were observed at night time, but in different body positions the borderline hypertensive subj ects frequently had either greater low-frequency variability or smalle r midfrequency variability than the other groups. In this respect, the power spectra for systolic and diastolic blood pressures provided bet ter statistical differentiation between the groups than those for hear t rate. Furthermore, the borderline hypertensive subjects exhibited at tenuated night-day changes in the low-frequency band for all time seri es. The results suggest that in borderline hypertension the barorecept or oscillations are shifted to lower frequencies, presumably reflectin g altered function of the sympathetic nervous system. In conclusion, s pectral analysis of blood pressure variability for controlled test sit uations made it possible to detect differences in the cardiovascular r egulatory systems between normotensive, borderline hypertensive, and m ildly hypertensive individuals.