Racial Differences In Exercising Limb Blood Flow During Elevated Sympathetic Activity

Abstract

PURPOSE: Young, healthy African Americans (AA) exhibit lower vascular conductance during an exercise bout compared to Caucasian Americans (CA). This disparity may be due to greater sympathetic vasoconstriction and an impairment in functional sympatholysis during exercise in AA. Thus, the purpose of this study is to examine racial differences in vascular conductance during lower limb exercise in the presence of elevated sympathetic activity administered via cold pressor test (CPT). METHODS: A total of 5 African American (AA) and 4 Caucasian (CA) young (24 ± 2 yrs), healthy males were recruited. Subjects then underwent 6 minutes of rhythmic plantar flexion (PF) exercise at 30% of their previously determine maximum voluntary contraction (MVC). Doppler ultrasonography was utilized to measure superficial femoral artery blood flow on the exercising leg while simultaneous measures of mean arterial pressure (MAP) were obtained via finger plethysmography. Subjects underwent the CPT (minutes 4-6) during which the hand was placed in cold water (4 °C) during PF exercise. Measures were obtained during steady state exercise blood flow (measured at minutes 3-4) and during the CPT (measured at minute 5-6) to determine differences in vascular conductance with and without the presence of elevated sympathetic activity. RESULTS: The CPT resulted in similar increases in MAP in both AA (+24.8 ± 3 mmHg) and CA (+25.56 ± 13 mmHg) (p = 0.95) when compared to PF exercise alone. Exercising leg blood flow [AA (-38.89 ± 62 mL/min); CA (+137.97 ± 62 mL/min) (p = .09)] or leg vascular conductance [AA (-1.00 ± .6 mL/min/mmHg); CA (-0.28 ± .4 ml/min/mmHg) (p = .35)] was not different between groups when evaluated during the CPT and expressed as change from PF exercise alone. CONCLUSIONS: This study suggests that during lower limb exercise, young AA males, when compared to CA, are similarly resistant to reductions in lower limb vascular conductance in response to elevated sympathetic activity.