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Heart rate variability (HRV) is used to study autonomic effects on the heart. The time domain PNN50 (percentage of consecutive RR intervals differing by &gt; 50%) measures high frequency in HRV primarily reflecting parasympathetic activity. The ratio of low to high frequency power (LF/HF) measured by fast Fourier analysis is used to measure sympathetic to parasympathetic balance. In adults, increased sympathetic tone has been found in hypertensive individuals. The present study was performed to look for differences in HRV by race and between subjects with high and low blood pressure (BP). Heart rate variability data was analyzed from Holter monitor recordings in 39 healthy male subjects aged 13 to 17 years (50% white). Half were selected with Korotkoff fourth sound (K4) DBP &gt; 85th percentile for height measured twice, 3 to 5 years apart (average 116/75 mm Hg). Half had DBP &lt; 15th percentile for height (average 101/57 mm Hg). Subjects underwent a physical examination including 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 higher and the PNN50 was significantly lower in whites compared with ratios for blacks during all CV reactivity tests (all P &lt; .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 significance. It was concluded that healthy white adolescents exhibit increased sympathetic tone compared with that of blacks during CV reactivity tests. A trend towards sympathetic predominance during reactivity testing was demonstrated in children with higher levels of DBP.

american journal of hypertension

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