Assessing sympathetic vascular transduction in humans: Beat‐to‐beat considerations

Measures of sympathetic vascular transduction attempt to quantify peripheral vasoconstrictor responses to sympathetic nerve activity (SNA). Previous studies have assessed sympathetic transduction by quantifying the mean vascular conductance and SNA over periods ranging from 30s to 2 min. However, the temporal resolution of these analyses may minimize important information on the ability of SNA to dynamically control vascular function on a beat‐to‐beat basis. To begin to address this, forearm blood flow (Doppler ultrasound), muscle SNA (microneurography) and blood pressure were measured in six subjects during supine rest and −15 and −30 Torr lower body negative pressure (LBNP). Transduction was assessed by identifying the peak of the beat‐to‐beat fall in forearm vascular conductance (FVC) following each muscle SNA burst and compared to time averaged measures, calculated as FVC/muscle SNA. Muscle SNA was significantly increased with LBNP, and FVC decreased accordingly. This translated to an elevated time averaged sympathetic transduction during −15 and −30 LBNP. Interestingly, beat‐to‐beat FVC reductions following a burst were unchanged from rest (−15 ± 3%) to −15 and −30 LBNP (−12 ± 1% and −12 ± 2%, respectively; P > 0.05). These preliminary results suggest that sympathetically mediated beat‐to‐beat fluctuations in FVC provide distinct information from the cumulative vascular response to SNA over time. Supported by: RO1HL093167