模拟微重力期间心血管系统的适应性——下身负压在对抗立位性低血压中的作用

人进入微重力环境后,约有1500ml～2000ml血液由下身向头一胸部转移,这是引起失重时心血管系统适应性综合症的主要起因。这种综合症的表现之一,就是返回地球后航天员的立位耐力降低。航天员在返回过程中需要耐受+Gz力的作用,它对心血管系统是一个很大的刺激,在心血管系统调节能力下降的情况下,有可能产生晕厥。因此,防止航天员引起的立位性低血压是一项重要的课题。目前已采用运动、穿抗荷服、电刺激肌     

失重对人的压力感受反射功能的影响

失重可引起航天员心血管功能失调,表现为返回后立位时血压的降低、心率的异常及运动耐力下降。由于压力突然改变时压力感受器反射功能在调节血液动力学上起主要作用,因此在研究失重心血管系统失调的起因时,必须了解失重对压力感受器反射功能的影响。本实验观察了7名SLS-1航天飞机飞行员在飞行前、中、后时压力感受器反射功能的变化。具体的测量时     

失重或模拟失重对人体交感肾上腺活动的影响

失重或模拟失重对人体交感肾上腺活动的影响杨玉华高淳航天时航天员的体液头向转移，使机体产生一系列的生理、生化变化。心血管功能失调是航天员返回地面时超重耐力和立位耐力下降的主要原因。因此失重对心血管系统的影响、失重时心血管系统的适应性变化过程，一直是航天...     

失重对人压力感受器反射功能的影响

失重可引起航天员心血管功能失调,表现为返回后立位时血压的降低和心率的异常升高及运动耐力下降。由于压力突然改变时压力感受器反射功能在调节血液动力学上起主要作用,因此,在研究失重心血管系统失调的起因时,必须了解失重对压力感受器反射功能的影响。本实验观察了7名SLS-1航天飞机飞行员在飞行前、中、后时压力感受器反射功能的变化。具体的测量时间是,飞行前第105、75、45、15天,飞行中第2、4、6、8天     

空间环境诱导心血管功能失调的细胞学机制研究进展

人体心血管系统对空间环境的不良反应是引起航天员飞行中和飞行后出现航天运动病和立位耐力不良的主要原因。回顾了近些年关于失重、空间辐射和亚磁场等太空环境对心血管系统不良影响的相关研究进展,首先从细胞层面分析空间环境对心肌细胞、内皮细胞、成纤维细胞和平滑肌细胞4种心脏细胞的影响。然后由细胞到组织和器官,就空间环境诱导心血管功能失调的细胞学机制和分子学机制进行归纳总结。最后提出了目前空间环境对心血管系统影响研究所面临的障碍及解决方案,以期为相关机制的探索提供思路。     

立位-下体负压时心血管指标的变化

目的了解立位 -下体负压 (HUT +LBNP)期间心血管系统的变化 ,确定心律变异和脉图两种方法在评价心血管调节功能中的作用。方法观察 1 6名被试者在 75°头高位倾斜加 - 4kPa下体负压 2 0min期间血压、脉图、心律变异和脑血氧饱和度的变化。结果 ( 1 )HUT +LBNP可引起被试者出现明显的心率、血压、规 -化低频峰功率 (LFn)、LFn/HFn增加 ,脑血氧饱和度、心电T波和规 -化高频峰功率(HFn)下降 ;( 2 )晕厥前出现明显的血压、心率和脑血氧饱和度下降 ;( 3)低耐力组在HUT +LBNP初期的心率明显高于高耐力组 ;( 4 )HUT +LBNP时脉搏波波形发生很大变化 ,无法进行分析。结论HUT +LBNP是一种负荷量较高的立位耐力检查方法 ,可充分暴露被检者在立位中的心血管调节功能 ;脉图检测方法不能作为评价被试者HUT +LBNP耐力的方法。     

头低位卧床7d对立位心肺循环功能的影响

目的观察短期模拟失重对立位心肺循环功能的影响,为进一步研究失重时心血管功能下降机理积累资料。方法６名健康男性被试者,头低位６°卧床７ｄ。分别观察卧床前、后立位心肺循环功能的变化。心肺循环功能检测选用ＸＸＨ－２０００型小循环心功能检测仪。结果头低位卧床７ｄ致被试者立位耐力降低,卧床后右心室射血期（ｊ－ｚ）缩短,右心室排血效率降低（Ｑ－ｊ／ｊ－ｚ升高）,提示右心功能减退。心血管调节适应性反应减弱,右心功能储备降低。结论ｃ波高度（ｈｃ）、ｃ波高度与Ｚ波高度的比值（ｈｃ／ｈｚ）可作为评价立位耐力或预测立位晕厥的指标;小循环心功能检测法评价立位心肺循环功能的变化有一定的前景。     

人工重力联合有氧锻炼可以有效对抗4d头低位卧床所致立位耐力不良

目的探讨人工重力联合运动锻炼对模拟失重引起的心血管功能失调的对抗效果。方法 12名男性志愿者随机分为对照组和锻炼组。对照组仅进行4天头低位卧床,锻炼组在卧床期间每天进行60min的2 G人工重力联合80%~95%无氧阈强度的有氧锻炼。卧床前后测量立位耐力、运动能力、心脏收缩功能、血浆容量、腘静脉顺应性等。结果与卧床前相比,对照组卧床后立位耐力、运动耐力及心脏泵血与收缩功能明显下降(P0.05),腘静脉横截面积及顺应性显著增加(P0.05),而锻炼组志愿者卧床后上述参数无明显变化。结论 4 d头低位卧床可导致心脏收缩功能降低,血浆容量减少以及下肢静脉顺应性升高,立位耐力及运动耐力下降。每天60 min的2 G人工重力联合80%~95%无氧阈运动强度的锻炼可有效维持卧床期间心脏收缩功能、血浆容量以及下肢静脉顺应性,从而对抗模拟失重引起的立位耐力和运动耐力的下降。     

失重对压力感受器反射功能的影响

压力感受器反射功能下降是引起飞行后航天员立位耐力下降的重要起因之一。本文综述了失重和模拟失重时压力感受器反射功能的变化及失重引起的上身压力增高和血液中离子改变对压力感受器反射功能的影响。     

前庭刺激对心血管自主神经调节及立位耐力的影响

目的观察前庭刺激前后被动直立位耐力试验心率、血压和压力感受器敏感性等指标的变化,了解前庭刺激对心血管自主神经调节功能及直立位耐力的影响。方法对15名男性健康志愿者在转椅刺激前、后进行被动直立位耐力检查。被动直立位耐力实验全程监测心电图和左手中指逐跳血压,在试验的第20,21,23,25,30,35,40,41,45 min测量常规血压、心率和压力感受器反射敏感性指标(BRS)。结果前庭刺激前直立位耐力检查结果均正常,刺激后有两人发生晕厥前症状;常规血压(SBP、DBP)检查在大部分实验时间无统计学差异,心率在检测的大部分时间点有统计学差异;BRS指标仅在直立位25～min段、30～min段有统计学差异,其余检测时间段没有统计学差异。结论前庭刺激可能会削弱机体心血管压力感受器反射调节功能的稳定性,造成部分志愿者直立位耐力的降低。     

失重∕模拟失重与血管重塑

航天中航天员不可避免地处于失重环境中，重力的消失将引起人体生理系统的明显变化，血管重塑是失重或模拟失重下机体心血管系统所发生的重要变化之一。本文回顾近年来有关失重／模拟失重对机体血管重塑影响的研究进展，综述了血管重塑概念的产生、发展，扼要论述了近年来有关血管重塑的研究进展，重点阐述了失重／模拟失重对心血管系统重塑的影响及其机理，提出血管重塑对研究飞行后立位耐力的下降有重要意义。     

模拟失重对心血管功能的影响及下体负压的对抗作用

总结了近年来本实验室有关模拟失重对心血管功能影响及下体负压对抗作用的研究，讨论了模拟失重致立位耐力不良的机理可能与心血管功能降低，脑血流降低及内分泌改变等有关，以及采用数学模型方法探讨失重致立位耐力降低机制的作用意义，重点论述了下体负压对抗方案问题。     

Evaluation of cardiovascular risks of spaceflight does not support the NASA bioastronautics critical path roadmap

INTRODUCTION: Occurrence of serious cardiac dysrhythmias and diminished cardiac and vascular function are the primary cardiovascular risks of spaceflight identified in the 2005 NASA Bioastronautics Critical Path Roadmap. METHODS: A review of the literature was conducted on experimental results and observational data obtained from spaceflight and relevant ground simulation studies that addressed occurrence of cardiac dysrhythmias, cardiac contractile and vascular function, manifestation of asymptomatic cardiovascular disease, orthostatic intolerance, and response to exercise stress. RESULTS: Based on data from astronauts who have flown in space, there is no compelling experimental evidence to support significant occurrence of cardiac dysrhythmias, manifestation of asymptomatic cardiovascular disease, or reduction in myocardial contractile function. Although there are post-spaceflight data that demonstrate lower peripheral resistance in astronauts who become presyncopal compared with non-presyncopal astronauts, it is not clear that these differences are the result of decreased vascular function. However, the evidence of postflight orthostatic intolerance and reduced exercise capacity is well substantiated by both spaceflight and ground experiments. Although attenuation of baroreflex function(s) may contribute to postflight orthostatic instability, a primary mechanism of orthostatic intolerance and reduced exercise capacity is reduced end-diastolic and stroke volume associated with lower blood volumes and consequent cardiac remodeling. CONCLUSION: Data from the literature on the current population of astronauts support the notion that the primary cardiovascular risks of spaceflight are compromised hemodynamic responses to central hypovolemia resulting in reduced orthostatic tolerance and exercise capacity rather than occurrence of cardiac dysrhythmias, reduced cardiac contractile and vascular function, or manifestation of asymptomatic cardiovascular disease. These observations warrant a critical review and revision of the 2005 Bioastronautics Critical Path Roadmap.     

模拟微重力或微重力时血容量减少对立位耐力影响的研究进展

航天后立位耐力降低普遍存在,其机理仍不清楚。一般认为血容量减少是航天后立位耐力降低的一个重要因素。现有对抗航天后一耐力降低的措施均与血容量有关。微重力（μＧ）和模拟μＧ时研究表明：μＧ与现有模拟μＧ模型时人体生理学变化的主要差异表现在低压区循环和体液、电解质代谢。细胞外体液主要受心肺反射和适当的模拟μＧ模型研究低压区循环、心肺反射变化的时间过程,对认为立位耐力降低机理和制定更有效的对抗立位耐力降低     

航天中各阶段心脏动力学变化

人体正常动脉血压的维持依赖于心功能正常。国外载人航天活动各阶段心脏动力学参数是检测的重点之一。虽然航天中有关心脏动力学参数的报道不尽一致，但一般都观察到航天后立位应激时心脏动力学参数有较大变化，立位耐力降低的机理尚不清楚，心脏动力学变化对立位耐力的影响也有待探讨。本文对国外载人航天活动各阶段有关心脏动力学的变化及变化机理作一简要概述。     

Hypovolemic intolerance to lower body negative pressure in female runners.

PURPOSE: An attenuated baroreflex response and orthostatic intolerance have been reported in endurance-trained male athletes; however, it is still unknown whether this occurs also in females. The purpose of the present study was to examine whether endurance exercise-trained women had a predisposition to orthostatic compromise, and if so, what causative factor(s) may induce orthostatic intolerance. METHODS: We studied cardiovascular and hormonal responses to graded lower body negative pressure (LBNP) (0 to -60 mm Hg) in 26 middle-distance female runners (18.6 +/- 0.1 yr) as the exercise-trained (ET) subjects and 23 age-matched untrained (UT) control subjects. On the basis of the occurrence of syncope episodes during LBNP, ET and UT subjects were further allocated to two groups; ET with presyncope (ET+syncope) and without presyncope (ET-syncope) and UT with presyncope (UT+syncope) and without presyncope (UT-syncope). RESULTS: Occurrence of presyncope episodes during LBNP was higher in ET (65.4%, P < 0.05) than that for UT (34.8%). Leg compliance was higher (P < 0.05) in ET than in UT. LBNP reduced stroke volume (SV) more (P < 0.05), increased heart rate (HR) higher (P < 0.05), and increased forearm vascular resistance (FVR) more in ET+syncope as compared with the other groups. Response of vasoactive hormones to LBNP was higher in ET+syncope (P < 0.05) than that of the other groups except for norepinephrine (NE); high in both ET+syncope and UT+syncope. The relationship between SV and NE, an index of sympathetic neuronal response, had no training-related changes during LBNP. CONCLUSION: We conclude that exercise-trained females have a high incidence of orthostatic intolerance during LBNP, with a greater reduction of SV independent of changes in baroreflex and neurohumoral function. A lower incidence of LBNP intolerance in UT may be accounted for by a lower reduction of SV during LBNP. An increase in leg compliance in the exercise-trained females may play an important role in inducing pronounced reduction of SV and hence the intolerance to LBNP.     

Considerations in prescribing preflight aerobic exercise for astronauts

Many human responses to the weightless environment have been documented from actual spaceflights. These include physiological effects on the nervous system, cardiovascular system and fluid balance, and the musculoskeletal system, as well as psychological effects. Simulations on Earth have added to our knowledge about the physiology of weightlessness. Early data on orthostatic intolerance after real and simulated spaceflight led some scientists to discourage a high level of aerobic fitness for astronauts. They believed it was detrimental to orthostatic tolerance on return to Earth. However, most of the data available today do not support this contention. Furthermore, aerobic fitness is beneficial to cardiovascular function and mental performance. Therefore, it may be important in performing extra-vehicular activities during flight. Some astronauts claim exercise enhances their feeling of well-being and self image. And, although the cardiovascular system and exercise performance may recover more slowly after flight to preflight levels when fitness level prior to flight is high, the musculoskeletal system may recover more rapidly. Research is needed to determine optimal levels of aerobic training for performing tasks in flight, maintaining health and well-being during flight, and assuring satisfactory recovery on return to Earth.     

心肌收缩功能降低对下体负压效应影响的仿真研究

目的：研究不同程度心肌收缩功能降低对心血管系统立位应激反应的影响，探讨心肌收缩功能改变在航天失重心后心血管失调和立位耐力降低机理中的意义。方法：以我们原有仿真血量减少后下体负压（LBNP）暴露时心血管系统反应的模型为基础，对其心脏工作子模型中最大弹性系数（maximum elastance)乘以一个反映心肌收缩功能改变的系数。然后逐渐降低收缩功能改变系，仿真血容量减少12％后，心肌收缩功能降低0－305后LBNP时心率（HR）、血压（BP）和心输出量（CO）的变化。结果：心肌收缩功能降低将使LBNP时，HR加快，BP降低和CO减小。结论：心肌收缩功能降低导致心血管系统对立位应激的调节能力降低。     

Cardiovascular deconditioning during space flight and the use of saline as a countermeasure to orthostatic intolerance

Alterations in the physiology of the cardiovascular system have been noted during all exposures to the microgravity experienced in space flight. Of most importance to the operational function of Space Shuttle crewmembers is orthostatic intolerance. Although complex changes occur as a result of adaptation to weightlessness, the redistribution and loss of body fluid apparently plays a substantial role. Utilizing ground-based bed rest data as an analog to the absence of gravitational force encountered in orbital flight, a saline loading countermeasure was developed. In this study, 17 crewmembers consumed various amounts of salt and fluid prior to the reentry phase of Space Shuttle flights; 9 other astronauts served as control subjects. The countermeasure reduced the heart rate response to orthostatic stress 29% and reversed the fall in mean blood pressure. A Cardiovascular Index of Deconditioning (defined as CID = delta HR - delta SBP + delta DBP) equalled 21 in those who utilized the countermeasure, a significant improvement toward baseline (p less than 0.003) when compared to the control group CID = 49. The encouraging results of these investigations have led to the adoption of the countermeasure as an operational procedure by Shuttle crewmembers.