Heart rate of black and white youths aged 12-17 years: associations with blood pressure and other cardiovascular risk factors.

Correlates of heart rate were investigated in youths aged 12 to 17 years examined in the United States National Health Examination Survey. Heart rate decreased with age in boys but no consistent trend appeared in girls. Girls had higher heart rates than boys. Blacks had heart rates 6 to 12 beats per minute lower than whites of the same age and sex.Multiple regression analysis showed the effect of race to be independent of multiple other variables. Regression analyses within sex-race groups identified the following independent correlates of heart rate: white boys, age, systolic blood pressure, and body temperature; black boys, age, body temperature, subscapular skinfold, and systolic blood pressure; white girls, systolic blood pressure, body temperature, cigarette smoking; black girls, body temperature. Correlations of two heart rate measurements 28 to 53 months apart (median 44 months) ranged from r = 0.21 to r = 0.30.Although expanded blood volume and lower sympathetic tone in blacks have been hypothesized, further longitudinal studies are needed to explain the differences in heart rates between races and sexes and their relationship to hypertension in adulthood.