Influence of spontaneous bursts of muscle sympathetic nerve activity on superficial femoral artery and femoral vein flow at rest and during slow deep breathing

The effect of slow deep breathing (SDB) on the dynamic transduction of sympathetic nerve activity to the superficial femoral artery (SFA), femoral vein (FV) and blood pressure was determined. In twelve healthy volunteers (5 women, 25±7 years, mean±SD) simultaneous imaging of the SFA and FV, along with contemporary measures of muscle sympathetic nerve activity (MSNA), were obtained and signal-averaging techniques used to quantify sympathetic neurovascular transduction at rest (baseline) and during 5 min SDB at 6 breaths/min. At baseline, MSNA bursts were followed by transient increases in mean arterial pressure (MAP; peak +3.0±1.2 mmHg), decreases in SFA flow (nadir -6.3±4.5 ml/min), and small, inconsistent increases in FV flow (peak +4.3±6.7 ml/min). SDB decreased MSNA burst frequency and burst incidence by ~30% while MAP was unchanged. During SDB, MSNA bursts were followed by greater increases in MAP (peak +6.0±2.4 mmHg, P<0.001 vs. baseline), greater decreases in SFA flow (nadir -9.8±4.0 ml/min, P=0.002 vs. baseline), and a tendency for a greater increase in FV flow (peak +20.6±21.0 ml/min, P=0.051). Therefore, while SDB reduces MSNA, the augmented MSNA transduction to blood pressure may help to preserve MAP. SDB evoked greater reductions in SFA flow and increases in FV flow following a MSNA burst, which may work synergistically with the respiratory muscle pump to facilitate venous return. Collectively, these findings highlight the important role played by MSNA in the dynamic regulation of peripheral blood flow, venous return and blood pressure.