Cardiovascular reactivity and autonomic activity to stressors in African American and Caucasian normotensive adolescents with a family background of hypertension

Hypertension is a common cardiovascular disease that strikes many Americans. Specifically, African (black) Americans suffer from hypertension (high blood pressure) at a rate nearly twice that of white Americans and experience higher rates of associated morbidity and mortality. In particular, black males disproportionately suffer from essential hypertension more than any race/gender group in the United States. Previous studies have reported that if one or both parents were hypertensive it was expected that offspring would develop high blood pressure. Thus, a family history of hypertension may play a role in the likely development of hypertension in future generations.;Accordingly, this study sought to non-invasively define possible differences in cardiovascular and autonomic activity that occurred between black and white subjects and between subjects with a family history (+FH) of hypertension and subjects without a (-FH) family history of hypertension when exposed to various stressors. All four groups of black and white (+FH) and (-FH) subjects consisted of normotensive male teenagers in the age group 12--19 years. The stress tests consisted of an orthostatic stress (70° head-up tilt test), a mental stress (Stroop (CWT) color word test), and a physical stress (cold pressor test). Cardiovascular variables measured were mean arterial blood pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), cardiac index (CI), stroke index (SI), end diastolic index (EDI), and total peripheral resistance index (TPRI).;Statistical analyses of the CWT using repeated ANOVA revealed significantly (P < 0.05) lower values of MAP, DBP, TPRI in the (+FH) subjects compared with the (-FH) subjects, independent of race. A racial difference was observed only in the tilt test with the black subjects having a lower heart rate and stroke index than the white subjects. Both black and white subjects with (+FH) and without a (-FH) family history of hypertension responded similarly during stress with a blunting of the baroreflex sensitivity measured by a time domain analysis. A frequency analysis of heart rate and blood pressure variability showed that the black subjects produced lower parasympathetic (vagal) activity and lower sympathetic activity than the white subjects during control CWT and control tilt. During tilt, sympathetic modulation was lower and parasympathetic modulation was greater in the (+FH) subjects than in the (-FH) subjects, irrespective of race. The tilt induced augmentation of parasympathetic modulation and loss of sympathetic modulation were opposite to the behavior often observed in adult hypertensive subjects. This might point to a defense mechanism in the parasympathetic nervous system of teenagers that increases its activity before the onset of hyperreactivity of the sympathetic nervous system with development to adulthood.