University Health Network and Mount Sinai Hospital Division of Cardiology, University of Toronto, Toronto, Ontario, Canada.
Am J Physiol Heart Circ Physiol. 2013 Sep 15;305(6):H931-8. doi: 10.1152/ajpheart.00375.2013. Epub 2013 Jul 12.
Atrial mechanoreceptors, stimulated by increased pressure or volume, elicit in healthy humans a net sympathoinhibitory response. The co-existence of an atrial reflex eliciting muscle sympathoexcitation has been postulated but undetected by conventional multi-unit muscle sympathetic nerve activity (MSNA). We hypothesized that in response to a selective increase in atrial pressure, single-unit MSNA would reveal a subpopulation of efferent sympathetic neurons with firing patterns opposite to the integrated multi-unit MSNA envelope. Multi- and single-unit MSNA recordings were acquired in eight healthy middle-aged subjects (age, 57 ± 8 years; body mass index, 25 ± 2 kg/m(2)) submitted to selective decreases or increases in atrial pressure by nonhypotensive lower body negative pressure (LBNP; -10 mmHg) or nonhypertensive lower body positive pressure (LBPP; +10 mmHg), respectively. Single-unit MSNA firing responses were classified as anticipated if spike frequency and incidence increased with LBNP or decreased with LBPP and paradoxical if they decreased with LBNP or increased with LBPP. LBNP decreased (3.2 ± 2.8 to 1.4 ± 3.1 mmHg, P < 0.01) and LBPP increased (3.3 ± 2.7 to 4.9 ± 2.8 mmHg, P < 0.01) estimated central venous pressure without affecting stroke volume, systemic pressure, or resistance. Multi-unit MSNA increased with LBNP (31 ± 17 to 38 ± 19 bursts/min, P < 0.01) and diminished with LBPP (33 ± 15 to 28 ± 15 bursts/min, P < 0.01). Of 21 single-units identified, 76% exhibited firing responses to both LBNP and LBPP concordant with multi-unit MSNA, whereas 24% demonstrated discordant or paradoxical responses. The detection of two subpopulations of single-units within the multi-unit MSNA recording, exhibiting opposite firing characteristics, establishes the first evidence in humans for the existence of an excitatory cardiac-muscle sympathetic reflex activated by increasing atrial pressure.
在健康人群中，心房机械感受器受到压力或容量增加的刺激，会引起净交感抑制反应。已经推测出存在一种心房反射，该反射会引起肌肉交感神经兴奋，但常规的多单位肌肉交感神经活动（MSNA）并未检测到。我们假设，在对心房压力的选择性增加作出反应时，单单位 MSNA 将揭示一个传出交感神经元亚群，其放电模式与综合多单位 MSNA 包络相反。在 8 名健康中年受试者（年龄 57 ± 8 岁；体重指数 25 ± 2 kg/m²）中，通过非低血压性下体负压（-10 mmHg）或非高血压下体正压（+10 mmHg）分别选择性地降低或增加心房压力，以采集多单位和单单位 MSNA 记录。如果单个单位 MSNA 放电反应的频率和发生率随着 LBNP 的增加而增加，或者随着 LBPP 的增加而减少，则将其归类为预期；如果它们随着 LBNP 的减少或随着 LBPP 的增加而减少，则将其归类为反常。LBNP 降低（从 3.2 ± 2.8 降至 1.4 ± 3.1 mmHg，P < 0.01），LBPP 升高（从 3.3 ± 2.7 增至 4.9 ± 2.8 mmHg，P < 0.01），而中心静脉压升高而不影响心输出量、全身血压或阻力。随着 LBNP 的增加，多单位 MSNA 增加（从 31 ± 17 增加至 38 ± 19 次/分，P < 0.01），随着 LBPP 的增加，MSNA 减少（从 33 ± 15 减少至 28 ± 15 次/分，P < 0.01）。在鉴定的 21 个单单位中，76%对 LBNP 和 LBPP 的放电反应与多单位 MSNA 一致，而 24%则表现出不一致或反常的反应。在多单位 MSNA 记录中发现两个单单位亚群，它们具有相反的放电特征，这首次在人体中证实了一种通过增加心房压力激活的兴奋性心脏-肌肉交感反射的存在。
