title: Characterizing sympathetic neurovascular transduction in humans.
abstract: Despite its critical role for cardiovascular homeostasis in humans, only a few studies have directly probed the transduction of sympathetic nerve activity to regional vascular responses--sympathetic neurovascular transduction. Those that have variably relied on either vascular resistance or vascular conductance to quantify the responses. However, it remains unclear which approach would better reflect the physiology. We assessed the utility of both of these as well as an alternative approach in 21 healthy men. We recorded arterial pressure (Finapres), peroneal sympathetic nerve activity (microneurography), and popliteal blood flow (Doppler) during isometric handgrip exercise to fatigue. We quantified and compared transduction via the relation of sympathetic activity to resistance and to conductance and via an adaptation of Poiseuille's relation including pressure, sympathetic activity, and flow. The average relationship between sympathetic activity and resistance (or conductance) was good when assessed over 30-second averages (mean R(2) = 0.49±0.07) but lesser when incorporating beat-by-beat time lags (R(2) = 0.37±0.06). However, in a third of the subjects, these relations provided relatively weak estimates (R(2)<0.33). In contrast, the Poiseuille relation reflected vascular responses more accurately (R(2) = 0.77±0.03, >0.50 in 20 of 21 individuals), and provided reproducible estimates of transduction. The gain derived from the relation of resistance (but not conductance) was inversely related to transduction (R(2) = 0.37, p<0.05), but with a proportional bias. Thus, vascular resistance and conductance may not always be reliable surrogates for regional sympathetic neurovascular transduction, and assessment from a Poiseuille relation between pressure, sympathetic nerve activity, and flow may provide a better foundation to further explore differences in transduction in humans.
authors: Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, Boston, Massachusetts, United States of America. cotan@partners.org
authors: Can Ozan
authors: CO
authors: Tan
authors: Renaud
authors: R
authors: Tamisier
authors: J W
authors: JW
authors: Hamner
authors: J Andrew
authors: JA
authors: Taylor
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000502:physiology; D015444:Exercise / Q000502:physiology; D018737:Hand Strength / Q000502:physiology; D006439:Hemodynamics; D006801:Humans; D007866:Leg / Q000098:blood supply / Q000502:physiology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D013564:Sympathetic Nervous System / Q000098:blood supply / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology*