Quantifying sympathetic neuro-haemodynamic transduction at rest in humans: insights into sex, ageing and blood pressure control

Sex and age differences in the sympathetic control of resting blood pressure (BP) may be due to differences in the transduction of sympathetic nerve activity (SNA) into vascular tone. Current methods for dynamically quantifying transduction focus on the relationship between SNA and vasoconstriction during a pressor stimulus, which increases BP and may be contra-indicated in patients. We describe a simple analytical method for quantifying transduction under resting conditions. We performed linear regression analysis of binned muscle SNA burst areas against diastolic BP (DBP). We assessed whether the slope of this relationship reflects the transduction of SNA into DBP. To evaluate this, we investigated whether this measure captures differences in transduction in different populations. Specifically, we (1) quantified transduction in young men (YM), young women (YW), older men (OM) and postmenopausal women (PMW); and (2) measured changes in transduction during beta-blockade using propranolol in YW, YM and PMW. YM had a greater transduction vs. OM(0.10 +/- 0.01 mmHg(%s)(-1), n = 23 vs. 0.06 +/- 0.01 mmHg (% s)(-1), n = 18; P = 0.003). Transduction was lowest in YW(0.02 +/- 0.01 mmHg (% s)(-1), n = 23) and increased during beta-blockade (0.11 +/- 0.01 mmHg(% s)(-1); P<0.001). Transduction in PMW (0.07 +/- 0.01mmHg(% s)(-1), n = 23) was greater compared to YW(P = 0.001), and was not altered during beta-blockade (0.06 +/- 0.01 mmHg (%s)(-1); P = 0.98). Importantly, transduction increased in women with age, but decreased in men. Transduction in women intersected that in men at 55 +/- 1.5 years. This measure of transduction captures age- and sex-differences in the sympathetic regulation of DBP and may be valuable in quantifying transduction in disease. In particular, this measure may help target treatment strategies in specific hypertensive subpopulations.