Race (black-white) differences in heart rate variability measured during cardiovascular stress testing in healthy male adolescents: the bogalusa heart study

Heart rate variability (HRV) is used to study autonomic effects on the heart. The time domain PNN50, (% of consecutive RR intervals differing by > 50 %) measures high frequency in HRV primarily reflecting parasympathetic activity. The ratio of low to high frequency power ( ) 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. HRV data was analyzed from Holter monitor recordings in 39 healthy males age 13-17 yrs (50 % white). Half were selected with K4 diastolic BP > 85th % for height measured twice, 3-5 yrs apart (avg mmHg). Half had diastolic BP < 15th % for height (avg mmHg). Subjects underwent a physical examination including BP, height, and weight prior to cardiovascular stress testing including measurements taken supine, standing, and during 20 % maximal isometric hand grip, Valsalva, and immersion of hand in water at 4°C. The ratio was significantly higher and the PNN50 was significantly lower in whites compared to blacks during all stress tests (all p<0.05). No consistent differences were found between groups with high vs. normal BP. Sympathetic predominance was not demonstrated in children with higher levels of diastolic BP. However, healthy white adolescents exhibit increased sympathetic tone compared to blacks during CV stress tests.