Neurovascular Transduction in Humans: New Insights from Multifiber Muscle Sympathetic Recordings

Abstract

Few studies have explored neurovascular transduction with sufficient time resolution to derive characteristic delays or without deriving indices of vasomotor responses (i.e., resistance or conductance) that may generate misleading nonlinearities. Our recently developed method to identify individual nerve firings was used to determine features of sympathetic activity that underlie neurovascular transduction. Sympathetic recordings, beat‐by‐beat arterial pressures, and popliteal blood flows were obtained in 11 volunteers during 15 min of rest (low tonic sympathetic activity), isometric handgrip to fatigue (increasing sympathetic activity), and 3 min of post‐handgrip ischemia (high tonic sympathetic activity). Each phase was analyzed separately to obtain lags between sympathetic firing and its cumulative effect on blood flow. Pressure was treated as a parameter directly relating to flow within a single beat. The delay between sympathetic firing and blood flow was approximately 5 sec at rest (5.1+/−1.7), was slightly increased with exercise (6.4+/−1.3), but was doubled during post‐exercise ischemia (10.2+/−1.6). Neurovascular transduction was slightly lower at rest than during exercise (−0.12+/−0.04 vs −0.14+/−0.06), but was markedly less during post‐exercise ischemia (−0.06+/−0.04). Thus, neurovascular transduction may not just differ across individuals, but also across conditions.