Microneurographic analysis of sympathetic nerve activity under weightlessness simulated by water immersion

本研究项目的目的是通过对人体的脆弱性进行模拟来澄清人体的神经控制机制。主题在18岁和62岁之间有30名健康志愿者。分级热中性水的影响，对对称神经活动、腿体积、心血管和激素功能的临界水平进行了分析。Muscle and skin sympathetic nerve activities （MSNA and SSNA） were recorded microneurographically from the tibial nerve。腿体积是由橡胶应变高等离子体造影测量的。心率、中风量、心脏输出、血液压力和总的外围抵抗力被测量为心血管功能。Plasma catechoamines （epinephrine and norepinephrine）、antidiuretic hormone（ADH）、aldosterone、renin activity、angiotensin I· II、atrial natriuretic polypeptide （ANP） were measured as homonal functions。1. MSNA是一种强烈的压抑，被头部流出的水淹没。However，MSNA的这种抑制性反应比年轻人中的加载者主题要少。2. SSNA也被头部流出的水淹没了。但这一反应比MSNA更弱。3.腿部体积、心脏速率和总的外围抵抗力降低了，而中风体积和心脏输出则因头部流出水的浸入而增加。血液压力在相同的条件下没有明显的变化。4.等离子体儿茶素， ADH，阿尔多司酮，肾上腺素活性，血管紧张素I和II减少，而ANP则被从头入水浸泡标记地增加。基于这些发现，它包含了MSNA的抑制性反应在协作中发挥了一个重要的作用，以补偿荷尔蒙反应，并通过水沉浸和维护血红蛋白同源物来补偿Sephalad流体移位。这对MSNA的抑制性反应似乎受到老龄化的影响，成为较老主题中的不重要的可能性。

The purpose of this research project was to clarify the neural controlling mechanisms of human body under weihjtlessness simulated by head-out water immersion. Subjects were 30 healthy volunteers ranging in age between 18 and 62. Effects of graded thermo-neutral water innersion up to the level of the neck of standing subject on sympathetic nerve activity, leg volume, cardiovascular and hormonal functions were analyzed. Muscle and skin sympathetic nerve activities (MSNA and SSNA) were recorded microneurographically from the tibial nerve. Leg volume was measured by rubber strain gauge plethysomgraphy. Heart rate, stroke volume, cardiac output, blood pressure and total peripheral resistance were measured as cardiovascular functions. Plasma catechoamines (epinephrine and norepinephrine), antidiuretic hormone(ADH), aldosterone, renin activity, angiotensin I・ II, atrial natriuretic polypeptide (ANP) were measured as homonal functions. 1. MSNA was strongly suppressed by head-out water immersion. However, this suppressive response of MSNA was less prominent in loder subjects than in younger ones. 2. SSNA was also suppressed by head-out water immersion. But this response was much weaker than that of MSNA. 3. Leg volume, heart rate and total peripheral resistance were reduced, while stroke volume and cardiac output were increased by head-out water immersion. Blood pressure was not significanty changed under the same condition. 4. Plasma catecholamines, ADH, aldosterone, renin activity, angiotensin I・ II were reduced, while ANP was markedly increased by head-out water immersion. Based on these findings, it is concluded that the suppressive response of MSNA plays an important role in cooperation with the hormonal responses to compensate cephalad fluid shift under weightlessness simulated by water immersion and to maintain hemodynamic homeostasis. This suppressive response of MSNA seems to be influenced by aging, becoming presumably less important in older subjects.