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

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.

Reproducibility of the heart rate variability responses to graded lower body negative pressure.

The reproducibility of heart rate variability (HRV) measures during graded lower body negative pressure (LBNP) have not been studied in sufficient detail. Active college age men (n=14) underwent an orientation exposure and two trials of graded LBNP to presyncope or -100 mmHg, separated by 1 week. Heart rate, stroke volume (impedance cardiography), blood pressure (Finapres), and forearm blood flow were assessed, as was HRV in both time and frequency domains.