ETHNIC (BLACK-WHITE) CONTRASTS IN HEART-RATE-VARIABILITY DURING CARDIOVASCULAR REACTIVITY TESTING IN MALE-ADOLESCENTS WITH HIGH AND LOW BLOOD-PRESSURE - THE BOGALUSA HEART-STUDY

Heart rate variability (HRV) is used to study autonomic effects on the heart. The time domain PNN50 (percentage of consecutive RR intervals differing by > 50%) measures high frequency in HRV primarily reflectin g parasympathetic activity. The ratio of low to high frequency power ( LF/HF) measured by fast Fourier analysis is used to measure sympatheti c to parasympathetic balance. In adults, increased sympathetic tone ha s been found in hypertensive individuals. The present study was perfor med to look for differences in HRV by race and between subjects with h igh and low blood pressure (BP). Heart rate variability data was analy zed from Holter monitor recordings in 39 healthy male subjects aged 13 to 17 years (50% white). Half were selected with Korotkoff fourth sou nd (K4) DBP > 85th percentile for height measured twice,3 to 5 years a part (average 116/75 mm Hg). Half had DBP < 15th percentile for height (average 101/57 mm Hg). Subjects underwent a physical examination inc luding BP, height, and weight before cardiovascular reactivity testing including measurements taken while supine and standing, and during 20 % maximal isometric hand grip, Valsalva maneuver, and immersion of the hand in water at 4 degrees C. The LF/HF ratio was significantly highe r and the PNN50 was significantly lower in whites compared with ratios for blacks during all CV reactivity tests (all P < .05). There was a trend for higher LF/HF ratio and lower PNN50 in blacks and whites with higher levels of BP, although this did not reach statistical signific ance. It was concluded that healthy white adolescents exhibit increase d sympathetic tone compared with that of blacks during CV reactivity t ests. A trend towards sympathetic predominance during reactivity testi ng was demonstrated in children with higher levels of DBP. (C) 1998 Am erican Journal of Hypertension, Ltd.