Blacks and whites differ in responses, but not tolerance, to orthostatic stress

Abstract

This study tested the hypothesis that normotensive black males differ from white males in their autonomic and cardiovascular responses to severe orthostatic stress. College age men (9 blacks, 9 whites) underwent graded lower body negative pressure (LBNP; 10 mmHg steps of 6 min each) to either -100 mmHg or presyncope. LBNP tolerance between the two groups did not differ (LBNP tolerance index: 378 +/- 34 vs 404 +/- 1 9mmHg.min, blacks vs whites). Responses to LBNP common to all subjects (< or = -40 mmHg), including spontaneous baroreflex sensitivity (sequence technique), did not differ between groups except whites experienced an earlier and more pronounced decline in total peripheral conductance than blacks (P < 0.01). At test termination, the heart rate variability measure of low frequency/high frequency ratio increased more in blacks than whites (5.2 +/- 1.1 vs 2.7 +/- 0.7 units; P < 0.05) while cardiac output and total peripheral conductance were lower in whites (both P < 0.05). These data suggest that blacks and whites have similar LBNP tolerances. They maintain blood pressure equally well when exposed to graded LBNP to presyncope, yet they differ in their mechanisms for doing so.

The circadian pattern of cardiac autonomic modulation and obesity in adolescents

“…We did not find significant ethnic effects on the cosine parameters; however, θ for SDNN was significantly delayed by 1-hour in non-Hispanic whites as compared to non-whites. The influence of ethnicity on HRV in children have been inconsistent [23,24,26], with studies reporting that African American youth have lower HRV [23], Asian have higher LF/HF [26], or that there are no significant ethnic differences [27]. Although we weren’t able to find any significant ethnic differences on  and θ, we are the first group analyzing the ethnicity and these parameters on adolescents.…”

C-reactive protein and cardiac vagal activity following resistance exercise training in young African-American and white men

“…We noted no racial differences in baseline heart rate variability or BRS. Although some studies have shown reduced high-frequency power of heart rate variability and lower BRS in African Americans (58), this is not a universal finding, with several studies noting no racial differences (14,30,47). Since within single individual markers of tonic vs. reflex vagal activity could have variable predictive power, Vanoli et al (52) have recently proposed a composite index derived from heart rate variability and BRS that gives equal weight to both the tonic and reflexive nature of cardiac autonomic physiology.…”

Greater Orthostatic Tolerance in Young Black Compared With White Women

“…Moreover, hypertension manifests at a younger age in black compared to white people and there are racial differences in the mechanisms that regulate blood pressure 4,5. With regard to orthostatic tolerance, in response to a 3.75 min standing test mean arterial pressure (MAP) increased in black subjects but fell in white and Asian subjects indicating differences in response to postural challenges across the three races 6.…”

“…With regard to orthostatic tolerance, in response to a 3.75 min standing test mean arterial pressure (MAP) increased in black subjects but fell in white and Asian subjects indicating differences in response to postural challenges across the three races 6. Finally, although black subjects display smaller increases in muscle sympathetic nerve activity (MSNA) during baroreceptor unloading compared to white subjects 4, forearm vasoconstriction is greater in black subjects, which would suggest enhanced sympathetic vascular transduction 4,5.…”

“…Even though orthostatic intolerance disproportionally affects women, studies that have addressed racial differences in cardiovascular responses to maximal lower body negative pressure have focused on men 4 or have not determined sex differences if women were included in the study 5. In light of the documented sex differences in orthostatic tolerance and racial differences in blood pressure regulation, we speculated that black and white women would respond differently to orthostatic stress induced by LBNP.…”