Heightened Parasympathetic Activity to Stressors in African American Male Juveniles before the Onset of Clinical Hypertension

Abstract

Factors, such as race, family history, and stress, may produce cardiovascular and autonomic differences responsible for the prevalence of hypertension in African Americans. We used non-invasive measurements of cardiovascular and autonomic activity in black and white normotensive male juveniles with (+FH) and without (−FH) a family history of hypertension in response to stress, with the goal of identifying markers for development of adult hypertension. (+FH) required one hypertensive parent. Forty juveniles (12–19 years) divided into 4 equal groups, (+FH) and (−FH) black and white subjects, underwent three stress tests: orthostatic stress (70° head-up-tilt), mental stress (Stroop color word, CWT) and physical stress (cold pressor). Repeated ANOVA was used to determine significant (P<0.05) differences. Blood pressure (BP) analyses revealed lower mean arterial pressure, diastolic pressure and peripheral vascular resistance in (+FH) subjects compared with (−FH) subjects during the CWT, independent of race. During tilt, racial differences were found in heart rate (HR) with black males having lower values, independent of family history. Frequency analyses of HR and BP variability showed that black malesproduced lower sympathetic activity during control CWT, independent of family history. During tilt, sympathetic modulation was lower and parasympathetic modulation was greater in (+FH) subjects, independent of race. Augmentation of parasympathetic modulation and loss of sympathetic modulation were opposite to the behavior often observed in adult hypertensive subjects. Supported by a Southern Regional Education Board (SREB) fellowship.