title: 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.
authors.affiliation: 247 Forker Building, Dept. of Health and Human Performance, Iowa State University, Ames, IA 50011, USA. wfranke@iastate.edu
authors.forename: Warren D
authors.initials: WD
authors.lastname: Franke
authors.forename: Kichang
authors.initials: K
authors.lastname: Lee
authors.forename: Dwayne B
authors.initials: DB
authors.lastname: Buchanan
authors.forename: Juliane P
authors.initials: JP
authors.lastname: Hernandez
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D017704:Baroreflex; D044383:Black People; D002302:Cardiac Output; D002319:Cardiovascular System / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D007024:Hypotension, Orthostatic / Q000208:ethnology / Q000209:etiology / Q000503:physiopathology*; D008150:Lower Body Negative Pressure; D008297:Male; D014655:Vascular Resistance; D044465:White People