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

作者在基础研究的基础上，研究了4 h 6头低位卧床（6 HDBR）和1h水平卧床（OBR）对颈动脉压力感受性反射功能和脑循环的急性影响。(1)To探讨颈动脉压力感受器功能评价的颈吸法（NS），通过测量NS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NS法评价的BRS与传统苯肾上腺素法评价的BRS进行比较。此外，为了揭示压力反射对颈动脉窦压力（CSP）变化的反应特点，我们用NS方法和改变NS压力变化率（dp/dt）来评价BRS。NS方法被证明是有效的评价BRS作为传统的苯肾上腺素的方法。结果表明，当使用NS方法时，脉压的增加是刺激颈动脉压力感受器的一个因素。压力感受性反射的特点 关于我们 在NS方法中可以观察到CSP对dp/dt变化的响应，以便在BRS和dp/dt之间观察到正相关性。(2)To为探讨压力反射介导的自主神经机制在晕厥发病中的作用，研究了鞍支持头高位倾斜体位负荷时血流动力学的变化。这项研究表明，压力反射介导的自主机制，而不是增强血管aifa-肾上腺素能活性可能作出更大的贡献，维持血压在直立应激晕厥。(3)To研究体位变化对压力反射介导的自主神经功能的影响，通过对下体负压立位负荷时心率和血压变异性的频谱分析，检测体位变化对自主神经功能的影响。本研究推测心脏迷走神经传出活动在早期受到抑制，可能是通过抑制压力感受性反射而实现的。采用生理盐水法测定6个HDBR和OBR期间颈动脉压力感受性反射功能和脑血管血流动力学的变化。（1）6天卧床和OBR时，垂体后叶素和去甲肾上腺素均明显降低，且与卧床时间有关。6天后，BRS在OBR时下降，而基础血压和心率无明显变化。因此，在卧床休息的急性期，压力感受性反射对姿势改变的反应呈6度差。（2）在6 HDBR和BR期间，随着交感神经活动的减弱和副交感神经活动的增强，对颈动脉窦压力dp/dt变化的压力感受性反射反应无明显变化。（3）颈动脉压力感受器反射刺激脑血管的神经控制在6 HDBR和OBR期间无明显变化，我们以前的研究表明，刺激颈动脉压力感受器引起的脑血管反应依赖于延长6 HDBR后平均血压的变化，因此，6 HDBR和OBR急性期心脑血管血流动力学的神经控制是不同的。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