Exaggerated Vasoconstriction to Spontaneous Bursts of Muscle Sympathetic Nerve Activity in Healthy Young Black Men

Abstract

Blacks have the highest prevalence of hypertension, putting them at greater risk of cardiovascular disease and death. Previous studies have reported that, relative to whites, healthy black men have augmented pressor responses to sympathoexcitatory stressors. Although important, these studies do not inform about the resting state and the influence of spontaneous changes in resting muscle sympathetic nerve activity (MSNA). Likewise, little is known about the transduction of MSNA into a vascular response at rest on a beat-to-beat basis. Accordingly, we tested the hypothesis that relative to whites, blacks would exhibit greater vasoconstriction and pressor responses following spontaneous bursts of MSNA. Mean arterial pressure, common femoral artery blood flow, and MSNA were continuously recorded during 20 minutes of supine rest in 35 young healthy men (17 blacks and 18 whites). Signal averaging was used to characterize changes in leg vascular conductance, total vascular conductance, and mean arterial pressure following spontaneous MSNA bursts. Blacks demonstrated significantly greater decreases in leg vascular conductance (blacks: -15.0±1.0%; whites: -11.5±1.2%; P=0.042) and total vascular conductance (blacks: -8.6±0.9%; whites: -5.1±0.4%; P=0.001) following MSNA bursts, which resulted in greater mean arterial pressure increases (blacks: +5.2±0.6 mm Hg; whites: +3.9±0.3 mm Hg; P=0.04). These exaggerated responses in blacks compared with whites were present whether MSNA bursts occurred in isolation (singles) or in combination (multiples) and were graded with increases in burst height. Collectively, these findings suggest that healthy young black men exhibit augmented sympathetic vascular transduction at rest and provide novel insight into potential mechanism(s) by which this population may develop hypertension later in life.

Keywords: blood pressure; femoral artery; muscle sympathetic nerve activity; prevalence; race; vascular conductance; vasoconstriction.

Figure 1

A) Percent decreases in leg vascular conductance (LVC) over the 10 cardiac cycles immediately following spontaneous MSNA bursts. B) Peak decreases in LVC following spontaneous MSNA bursts. AA = African American, denoted by filled symbols & bars; CA = Caucasian American, denoted by open symbols & bars; *P < 0.05, AA versus CA.

Figure 2

A) Percent decreases in total vascular conductance (TVC) over the 10 cardiac cycles immediately following spontaneous MSNA bursts. B) Peak decreases in TVC following spontaneous MSNA bursts. AA = African American, denoted by filled symbols & bars; CA = Caucasian American, denoted by open symbols & bars; *P < 0.05, AA versus CA.

Figure 3

A) Absolute increases in mean arterial pressure (MAP) over the 10 cardiac cycles immediately following spontaneous MSNA bursts. B) Peak increase in MAP following spontaneous MSNA bursts. AA = African American, denoted by filled symbols & bars; CA = Caucasian American, denoted by open symbols & bars; *P < 0.05, AA versus CA.

Figure 4

Peak changes in A) LVC, B) TVC, and C) MAP following spontaneous MSNA bursts which occur in isolation (Singles) or adjacent to other MSNA bursts (Multiples). AA = African American, denoted by filled bars; CA = Caucasian American, denoted by open bars.

Figure 5

Peak changes in A) LVC, B) TVC, and C) MAP following spontaneous MSNA bursts from the smallest height quartile (Q1) to the largest (Q4). AA = African American, denoted by filled bars; CA = Caucasian American, denoted by open bars; *P < 0.05, AA versus CA.