Heterogeneity in arm and leg vasoconstrictor responses to spontaneous bursts of resting muscle sympathetic nerve activity in humans

Abstract

Sympathetic vascular regulation depends on the effectiveness of peripheral vessels to respond to muscle sympathetic nerve activity (MSNA). Greater α1‐adrenoceptor responsiveness has been reported in the human leg compared to the arm. However, whether these underlying receptor differences alter limb vascular responsiveness to MSNA is unknown. To begin to address this, we examined arm and leg vascular conductance responses to spontaneous MSNA bursts. Arterial pressure (Finapres), MSNA (microneurography) and simultaneous blood flows in the brachial (BA) and common femoral (CFA) arteries (duplex Doppler ultrasound) were continuously measured during 20 minutes of supine rest in 8 young men. Beat‐by‐beat changes in conductance for each vessel were characterized for 15 cardiac cycles following each individual MSNA burst using signal averaging to identify the temporal conductance pattern and a peak response was calculated. CFA conductance significantly decreased following MSNA bursts, reaching a nadir (−7.6±1.7%, p<0.05 vs. baseline) in ~8 cardiac cycles. In contrast, BA conductance initially increased (peak: +7.0±1%, p<0.05) and subsequently decreased (nadir: −1.4±1.3%, p>0.05) after ~8 cardiac cycles. These preliminary findings suggest heterogeneity between the arm and leg in the acute vascular responses following individual bursts of MSNA. Supported by RO1 HL093167