Intra- and inter-day reliability of sympathetic transduction to blood pressure in young, healthy adults.

Microneurographic recordings of muscle sympathetic nerve activity (MSNA) and the succeeding changes in beat-to-beat blood pressure (i.e., sympathetic transduction) provide important insights into the neural control of the circulation in humans. Despite its widespread use, the reliability of this technique remains unknown. Herein, we assessed the intra- and inter-day test-retest reliability of signal-averaging sympathetic transduction to blood pressure. Data were analyzed from 15 (9M/6F) young, healthy participants who completed two baseline recordings of fibular nerve MSNA separated by 60 minutes (intra-day). The inter-day reliability was obtained in a subset of participants ( n =13, 9M/4F) who completed a follow-up MSNA study. Signal-averaging sympathetic transduction was quantified as peak change in diastolic (DBP) and mean arterial pressure (MAP) following a burst of MSNA. Analyses were also computed considering different MSNA burst sizes (quartiles of normalized MSNA), and burst patterns (singlets, couplets, triplets, and quadruplets+), as well as non-burst responses. Intraclass-correlation coefficients (ICC) were used as the main reliability measure. Peak changes in MAP [intra-day: ICC=0.76(0.30-0.92), P =0.006; inter-day: ICC=0.91(0.63-0.97), P <0.001] demonstrated very good to excellent reliability. Sympathetic transduction of MSNA burst size displayed moderate to very good reliability, though the reliability of MSNA burst pattern was poor to very good. Non-burst responses revealed poor intra-day [ICC=0.37(-1.05-0.80), P =0.21], but very good inter-day [ICC=0.76(0.18-0.93), P =0.01] reliability. Intra-day reliability measures were consistently lower than inter-day. Similar results were obtained using DBP. Collectively, these findings provide evidence that the burst-triggering signal-averaging technique is a reliable measure of sympathetic transduction to blood pressure in young, healthy adults.