Evidence for differential control of muscle sympathetic single units during mild sympathoexcitation in young, healthy humans

摘要

Two subpopulations of muscle sympathetic single units with opposite discharge characteristics have been identified during low-level cardiopulmonary baroreflex loading and unloading in middle-aged adults and patients with heart failure. The present study sought to determine whether similar subpopulations are present in young healthy adults during cardiopulmonary baroreflex unloading (study 1) and rhythmic handgrip exercise (study 2). Continuous hemodynamic and multiunit and single unit muscle sympathetic nerve activity (MSNA) data were collected at baseline and during nonhypotensive lower body negative pressure (LBNP; n = 12) and 40 maximal voluntary contraction rhythmic handgrip exercise (RHG; n = 24). Single unit MSNA responses were classified as anticipated or paradoxical based on whether changes were concordant or discordant with the multiunit MSNA response, respectively. LBNP and RHG both increased multiunit MSNA burst frequency (A5 ± 3 bursts/min, P < 0.001; A5 ± 8 bursts/min, P = 0.005), burst amplitude (A5 ± 7, P = 0.04; A13 ± 14, P < 0.001), and total MSNA (A302 ± 191 AU/min, P = 0.001; A585 ± 556 AU/min, P < 0.001).