Racial differences in cardiovascular and sympathetic reactivity to dynamic exercise

The purpose of this study was to assess possible racial differences in cardiovascular (CV) and sympathetic nervous system (SNS) responses to a graded exercise test. A biracial group of normotensive college-age males (15 blacks, 15 whites) were tested for maximal oxygen uptake (VO_2max), resting blood pressure (BP) and heart rate (HR). Subjects performed graded exercise on a cycle ergometer at 25, 50 and 75% of VO_2max (6 min at each stage). BP and HR were measured during supine rest, bike rest, and at each stage using a Colin STBP 780 blood pressure monitor. Cardiac output was measured using the C_O2 rebreathing technique, and expressed as cardiac index (Cl). At each stage, venous blood was sampled to allow determination of plasma norepinephrine (NE) and epinephrine (E). The results indicated that resting BP was similar for blacks and whites (114/68 vs. 115/68, respectively). However, blacks had a greater BP response to exercise, evidenced by higher systolic blood pressure (SBP) and diastolic blood pressure (DBP) at 50 and 75 % VO_2max. Racial differences did not exist for HR, but blacks had higher values for systemic vascular resistance (SVR), while whites had higher Cl values, across all conditions. Though no overall racial differences were seen for plasma catecholamine concentrations at rest, blacks had significantly lower levels of NE (1275.6 vs. 1556.0 pg/ml) and higher levels of E (306.9 vs. 216.9 pg/ml) than whites at 75% VO_2max. The present study confirms previous findings of an increased BP response to exercise in normotensive blacks, due to an elevation in SVR. However, the results of the plasma catecholamine analysis failed to provide clear evidence of a racial difference in sympathic drive.