Acute Effects of 6ﾟ Head Down Bed Rest on Carotid Baroreflex and Cerebrovascular Hemodynamic in Human

在进行了以下基础研究后，作者研究了4小时6头下床休息（6HDBR）和1小时水平床休息（OBR）对颈动脉压力反射功能和脑循环的急性影响。(1)为检验颈抽吸法评价颈动脉压力感受器功能的方法，通过测量颈抽吸法引起的心率和血压变化来评价颈动脉压力感受器反射敏感性（BRS），并将颈抽吸法评价的BRS与常规苯肾上腺素法评价的BRS进行比较。此外，为了揭示颈动脉窦压力（CSP）变化时的压力反射反应特征，我们使用NS方法评估BRS，并改变NS压力变化率（dp/dt）。NS法与常规的苯肾上腺素法同样有效。结果表明，脉压升高是刺激颈动脉压力感受器的一个因素。在NS法中可以观察到CSP对dp/dt变化的更大响应，从而观察到BRS与dp/dt之间的正相关。(2)为了研究晕厥发病过程中由倒压反射介导的自主神经机制，我们研究了鞍座支撑平顶倾斜直立负荷时的血流动力学变化。本研究表明，除了增强血管舒缩性肾上腺素能活性外，压力反射介导的自主神经机制可能对晕厥直立应激时血压的维持有更大的贡献。(3)为探讨压力反射介导的自主神经功能随体位变化的变化，采用心率和血压变异性谱分析方法研究了下体负压站立负荷时自主神经活动的变化。本研究推断，心脏迷走神经传出活动在早期通过抑制压力反射而受到抑制。反射控制导致血管舒缩交感神经活动的加剧，在3分钟的直立应激后达到峰值。观察6HDBR和OBR期间颈动脉压力反射功能和脑血管血流动力学的变化。(1)抗利尿激素和去甲肾上腺素在6HDBR和OBR期间均呈下降趋势。这些变化受卧床休息时间的影响。然而，在6HDBR期间BRS增加，并且在6HDBR后的OBR期间死亡，基线血压和心率没有变化。因此，在卧床休息急性期，气压反射对体位变化的反应相差6度。(2) 6HDBR和BR期间颈窦压力dp/dt变化的压力反射反应基本不变，交感神经活动减弱，副交感神经活动增强。(3) NS法颈动脉压力反射刺激的脑血管控制在6HDBR和OBR期间没有变化。在之前的研究中，我们报道了长时间6HDBR后，脑血管对颈动脉压力感受器刺激的反应取决于平均血压的变化。综上所述，6HDBRand OBR急性期心脑血管血流动力学神经控制存在差异。少

The authors studied acute effects of carotid baroreflex function and cerebral circulation during 4 hours 6 Head Down Bed Rest(6HDBR) and 1 hour horizontal bed rest(OBR) after the following basic studies. (1)To examine the neck suction (NS) method of evaluating carotid baroreceptor function, we evaluated carotid baroreceptor reflex sensitivity (BRS) by measuring changes in heart rate and blood pressure induced by the NS method, and compared BRS evaluated by NS method with BRS evaluated by the conventional phenylephrine method. In additon, to reveal the characteristica of baroreflex responce to change in carotid sinus pressure(CSP), we evaluated BRS using the NS method and varying the rate of change in NS pressure(dp/dt). The NS method was shown to be as effective in evaluating BRS as the conventional phenylephrine method. It was shown that an increase in pulse pressure was a factor in stimulating the carotid baroreceptor when the NS method was used. The characteristics of the baroreflex … More response to change in dp/dt of CSP could be observed in the NS method in order that a positive correlation was observed between BRS and dp/dt. (2)To investigated the baroreflex-mediated autonomic mechanisms involved in the pathogenesis of syncope, hemodynamic changes were examined during orthostatic stress loading by saddle support head-up tilt. This study indicated that baroreflex-mediated autonomic mechanisms other than enhancement of vasomotor aipha-adrenergic activity may make a greater contribution to the maintenance of blood pressure during orthostatic stress in syncope. (3)To investigated the changes of baroreflex-mediated autonomic function against posture change, the autonomic activity evaluated by spectral analysis of heart rate and blood pressure variability was examined during orthostatic stress loading by lower body negative pressure. In this study, it was inferred that cardiac vagal efferent activity is inhibited at early stage via inhibition of the baroreflex during. Reflex control results in an exacerbration of vasomotor sympathetic activity which reaches a peak after 3 minutes of orthostatic stress.The changes of carotid baroreflex function and cerebrovascular hemodynamic during 6HDBR and OBR evaluated by NS method were following.(1)The decreasing of vasopressin and norepinepfrine were observed during both 6HDBR and OBR.These changes were effected by term of bed rest. However, BRS was increased during 6HDBR, and was deceased during OBR after 6HDBR with no changes in base line blood pressure and heart rate. Therefore, baroreflex responces to posture chanege in differnce of 6 degrees in acute phase of bed rest. (2)The baroreflex responce to change in dp/dt of carotic sinus pressure unchanged during 6HDBR and BR with the decreasing of sympathetic activity and increasing of parasympathetic activity. (3)The cerebrovascular contol stimulated by carotid baroreflex using NS method unchanged during 6HDBR and OBR.In previous study, we reported that the cerebrovascular responce in stimulation of carotid baroreceptor depends on changing of mean blood pressure after prolonged 6HDBR.In conclusion, the neural controls of cardiovascular and cerebrovascular hemodynamic are different between 6HDBRand OBR in acute phase. Less