Effects of Vestibular Stimulation on Cardiovascular Autonomic Nerve Regulation and Orthostatic Ttolerance

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.     

有氧锻炼对心血管自主神经调节的影响

为研究有氧锻炼对心血管自主神经调节的影响,采用动态心电、血压监测技术,对6名男性中长跑运动员和7名健康男性大学生6个月长跑训练(20～25km/周)前后的下体负压(LBNP)耐力,Valsalva动作的心率、血压反应,心率变异性(HRV),血压变异性(SBPV)以及自发性压力感受器-心率反射反应的斜率(BRS)进行了测量.结果表明,有氧锻炼可以导致LBNP耐力降低,Valsalva动作Ⅱ期舒张压恢复幅度与最大心率值显著减小,平卧位HRV谱总功率(TP)、低频(LF)与高频(HF)成分功率呈减小变化,平卧位SBPV谱TP、LF成分功率与平均自发性BRS值减小,LBNP作用下HRV谱LF/HF值明显增大.说明有氧锻炼可导致心血管自主神经调节功能下降,可考虑将上述有关指标变化用于监测有氧锻炼强度以及个体敏感性,更科学地对有氧锻炼进行卫生指导.     

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     

压力感受器反射敏感性的测量方法与应用研究进展

目的 回顾分析压力感受器反射敏感性的理论机制、方法学与应用研究方面的最新进展,探讨其在航空航天医学研究中的应用价值.资料来源与选择 该领域的研究论文和专著.资料引用引用国内外相关文献资料45篇.资料综合 压力感受性反射在体位变化引起的血压调节过程中起着重要的作用,可以独立预测心血管疾病的危险性及直立位耐力不良,通过科学适宜的有氧运动锻炼可以提高压力感受器反射敏感性.结论 压力感受器反射敏感性测试与评价在航空航天医学、心血管病风险预测预警方面有实际应用价值.     

压力感受器反射敏感性的测量方法与应用研究进展

目的 回顾分析压力感受器反射敏感性的理论机制、方法学与应用研究方面的最新进展,探讨其在航空航天医学研究中的应用价值.资料来源与选择 该领域的研究论文和专著.资料引用引用国内外相关文献资料45篇.资料综合 压力感受性反射在体位变化引起的血压调节过程中起着重要的作用,可以独立预测心血管疾病的危险性及直立位耐力不良,通过科学适宜的有氧运动锻炼可以提高压力感受器反射敏感性.结论 压力感受器反射敏感性测试与评价在航空航天医学、心血管病风险预测预警方面有实际应用价值.     

飞行学员入校前后压力感受器敏感性的变化分析（摘要）

目的本研究通过对飞行学员入校时及入校6个月后BRS的检测,客观地评判飞行学员运动锻炼对压力感受器敏感性的影响。方法（1）调查问卷：主要收集飞行学员体育锻炼情况;（2）检测仪器：Portapres逐跳血压记录仪;（3）检测流程：采用主动立位耐力检查方法（即平卧10min后主动直立20min,再平卧10min）,全程监测左手中指逐跳血压;     

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     

抗荷服对颈动脉-心压力反射功能的保护作用

前言 由于血液重新分布到下肢,使心率对动脉压力感受器刺激的反应下降。这可损害G增加时的血压调节,进而降低立位耐力。除了降低血液下肢回到心脏的流体静压效应外,抗G服充气能增加心脏对压力感受器刺激的时间变化反应和增强缓冲血压的压力反射。方法 为检验这个假设,以两个水平的下体负压     

麻醉大鼠冰水灌耳交感神经响应在心血管调节中的作用

目的研究冰水灌耳刺激引起的交感神经响应、心率以及血压调节之间的内在联系,探讨前庭刺激在心血管调节中的作用。方法记录正常麻醉（CON）大鼠（n=5）、压力反射去除（SAD）大鼠（n=5）和迷路毁损（VD）大鼠（n=5）在冰水灌耳时内脏大神经传出放电及血压和心率的变化。结果正常麻醉大鼠灌耳后,血压、心率降低,内脏大神经反应由增强到减弱。压力反射去除大鼠灌耳后内脏大神经活动显著高于迷路毁损大鼠,且两组动物血压呈相反方向变化。内脏大神经放电与呼吸的耦合形式受到灌耳刺激的影响。结论半规管输入至少参与了血压的短时调节机制,其作用途径可能涉及呼吸运动的调节机制,在血压调节中压力反射和前庭输入两者作用不同,在某些生理调节过程中可能有协同作用。     

重力应激下自发性压力感受器-心率反射反应性的评定

为探讨重力应激下自发性压力感受器 -心率反射反应性的评定方法 ,观察了 1 0人 65°头高位倾斜 (HUT)与 8人 -6.67kPa下体负压 (LBNP)作用下 ,以及 1 5人 1 6d-6°头低位卧床期间BRS的变化。结果表明 ,在HUT与LBNP作用期间 ,尽管血压反应有所不同 ,但自发性BRS值均显著减小 (P <0 .0 1 ) ,卧床第 1 6d时平均自发性BRS值也显著减小 (P <0 .0 5)。说明该方法可用于评定重力应激下压力感受器 -心率反射反应性的变化。     

Characteristics of the reactions to active orthostatic and water loading tests in persons with varying resistance to +Gz loads

Thirty-seven healthy male test subjects, aged 19-21, with different +Gz acceleration tolerance were examined. Their blood pressure (BP) and heart rate (HR) during 5-min tilt tests and 2% water loading tests were measured 2-3 weeks prior to centrifugation. Quantitative evaluation of orthostatic tolerance using an orthostatic index and BP and HR responses to tilt tests before and after water loading revealed specific features of cardiovascular regulation in the subjects with high and low +Gz acceleration tolerance. The negative predictive indicators include: decreased BP, HR and cardiac index in the supine position in combination with high orthostatic tolerance, as well as decreased orthostatic tolerance in combination with a lower function of vasoconstrictor mechanisms in the upright position and a lower sensitivity of carotid sinus reflexes to blood volume changes during tilt and water loading tests. When examining test subjects with high +Gz tolerance, preference should be given to those who can well tolerate tilt tests and show moderately high BP and HR in the supine position, as well as to those who exhibit a noticeable increment of diastolic BP during 5-min tilt tests.     

Cerebrovascular responses during lower body negative pressure-induced presyncope

BACKGROUND: Reduced orthostatic tolerance is commonly observed after spaceflight, occasionally causing presyncopal symptoms which may be due to low cerebral blood flow (CBF). It has been suggested that CBF decreases in early stages of exposure to orthostatic stress. The purpose of this study was to investigate cerebrovascular responses during presyncope induced by lower body negative pressure (LBNP). HYPOTHESIS: Although CBF decreases during LBNP exposure, blood pressure (BP) or heart rate (HR) contributes more to induce presyncopal conditions. METHODS: Eight healthy male volunteers were exposed to LBNP in steps of 10 mm Hg every 3 min until presyncopal symptoms were detected. Electrocardiogram (ECG) was monitored continuously and arterial BP was measured by arterial tonometry. CBF velocity at the middle cerebral artery was measured by transcranial Doppler sonography (TCD). Cerebral tissue oxygenation was detected using near-infrared spectroscopy (NIRS). We focused our investigation on the data obtained during the final 2 min before the presyncopal endpoint. RESULTS: BP gradually decreased from 2 min to 10 s before the endpoint, and fell more rapidly during the final 10 s. HR did not change significantly during presyncope. CBF velocity did not change significantly, while cerebral tissue oxygenation decreased prior to the presyncopal endpoint in concert with BP. Our results suggest that CBF is maintained in the middle cerebral artery during presyncope, while BP decreases rapidly. CONCLUSIONS: Cerebrovascular hemodynamics are relatively well maintained while arterial hypotension occurs just prior to syncope.     

Baroreflex sensitivity during static exercise in individuals with Down Syndrome

INTRODUCTION: Individuals with Down syndrome (DS) have altered heart rate (HR) and blood pressure (BP) responses to orthostatic challenges and isometric handgrip (IHG) exercise, suggesting possible alteration in baroreflex sensitivity. PURPOSE: This study investigated baroreflex sensitivity (BRS) as a potential mechanism contributing to chronotropic incompetence during IHG in persons with DS. METHODS: Heart rate and BP were continually recorded in 12 individuals with DS and 10 controls, at rest and during 2 min of IHG, at 30% of maximal voluntary contraction (MVC). Spontaneous BRS was derived via the sequence method. RESULTS: No differences were seen in HR at rest between groups. Systolic BP (SBP) was significantly lower in the DS group at rest (106.1+/- 2.9 vs 116.5+/- 3.9 mm Hg, P < 0.05) and during IHG (123.9+/- 4.6 vs 150.1+/- 5.3 mm Hg, P<0.001). A significant group-by-task interaction was found for both change in HR and change in SBP with IHG, because of an attenuated HR and SBP response to IHG in participants with DS (P<0.05). When controlling for resting SBP, the DS group had a lower BRS at rest (16.0+/-1.7 vs 21.2+/-4.2 ms.mm Hg, P< 0.05) and during IHG (7.8 +/-1.0 vs 12.1+/- 2.6 ms.mm Hg, P< 0.05). CONCLUSIONS: Individuals with DS have lower BRS at rest and during IHG than controls and this may be related to their attenuated HR response during perturbation.     

Baroreflex control of heart rate during heating in subjects with low orthostatic tolerance

BACKGROUND: Heat stress induces a reduction of orthostatic tolerance. The cardiovascular responses, including the cardiac baroreflex response to heat stress, were examined to test the hypothesis that subjects with orthostatically low tolerance demonstrate an impaired baroreflex control of heart rate (HR) during heat stress. METHODS: There were 44 healthy young volunteers who underwent whole body heat stress produced by a hot-water-perfused suit during supine rest for 45 min and 75 degrees head-up tilt (HUT) for 6 min. Esophageal temperature, HR, arterial pressure, and skin blood flow in the forearm and palm were measured continuously throughout the experiment. The sensitivity of the arterial baroreflex control of HR was calculated from the spontaneous changes in beat-to-beat arterial pressure and HR. RESULTS: The HUT was uneventful for 22 volunteers (higher tolerance group), but 22 volunteers (lower tolerance group) reached presyncope after 195 +/- 19 s. Esophageal temperature, HR, arterial pressure, and skin blood flow changed similarly in the two groups during heating. In the preheating condition, the sensitivity of the baroreflex control of HR did not differ significantly between the two groups. Heating did not alter the sensitivity of baroreflex control of HR in the higher tolerance group, but decreased it significantly in the lower tolerance group. Heating increased the number of heartbeats used for analysis of the baroreflex sensitivity in the higher tolerance group, but did not change it in the lower tolerance group. CONCLUSIONS: These results suggest that the impairment of vagal baroreflex control of HR during heat exposure aggravates the orthostatic intolerance in heat-stressed humans.     

立位耐力监测系统与常规立位耐力试验的对比研究

目的 对自行研制的立位耐力监测系统的稳定性和可行性进行评价。方法 试验对象为６１名健康飞行人员,以常规立主动立位耐力试验为标准方法,应用立位耐力监测系统与常规主动立位耐力试验进行心率、收缩率、压缩压和平均动脉压监测,对各生理参数进行对比分析。立位耐力监测系统是由控制监测台和自动记录包括有１０余项生理参数和图形的立位耐力评价系统。结果 经校正后,两种方法在立位即刻心率分别为,立位耐力监测系统７６．６     

21天头低位(-6°)卧床前后下体负压和头高位倾斜暴露时的心血管反应

目的探讨２１天头低位（ＨＤＴ）卧床对人体立位应激下心血管反应的影响,以及比较下体负压（ＬＢＮＰ）和头高位倾斜（ＨＵＴ）两种立位应激下心血管反应的差异。方法６名受试者在２１天ＨＤＴ前、后分别进行ＬＢＮＰ（－４．００ｋＰａ／３ｍｉｎ、－６．６７ｋＰａ／３ｍｉｎ及－９．３３ｋＰａ／３ｍｉｎ）和ＨＵＴ试验（３０°／３ｍｉｎ、４５°／３ｍｉｎ、６０°／３ｍｉｎ及７５°／３ｍｉｎ）,以比较两种检测方法的血压（ＢＰ）和心率（ＨＲ）的变化情况。结果与ＬＢＮＰ（或ＨＵＴ）前相比：①ＬＢＮＰ（ＨＵＴ）时ＨＲ显著增加（Ｐ＜０．０１）,ＳＢＰ显著降低（Ｐ＜０．０５）;卧床后相应的变化量增加。②ＬＢＮＰ时ＤＢＰ降低（卧床后达显著,Ｐ＜０．０５）;而ＨＵＴ时ＤＢＰ增加（卧床后达显著,Ｐ＜０．０５）。③ＬＢＮＰ时ＭＡＰ均显著降低（Ｐ＜０．０５）;而ＨＵＴ时在卧床前无变化（Ｐ＞０．０５）,在卧床后显著增加（Ｐ＜０．０５）。结论ＬＢＮＰ和ＨＵＴ引起的ＣＶＳ反应并不相同。笔者认为,ＨＵＴ更能促进心血管系统对立位应激的调节作用。     

血容量减少对立位应激反应影响的仿真研究

目的 研究不同程度的血容量减少对心血管系统立位应激反应的影响,探讨血容量降低在航天失重后心血管失调和立位耐力降低机理中的意义。方法 在仿真下体负压（LBNP）暴露时心血管系统反应模型的血液重新分配子模型中引入血容量减少因素,仿真血容量减少0－25％后LBNP时心率（HR）和血压BP变化,结果 血容量减少低于总血量的5％条件下,心血管系统可以通过压力反射调节作用维持LBNP时政党的HR和BP;血容量减少超过约15％,在安静仰卧位时,HR和BP正常,但LBNP时BP迅速降低,系统可失去稳定性。结论 血容量减少将导致心血管系统对立位应激反应的改变。     

不同体位短臂离心机暴露时心血管及前庭功能的改变

目的 通过观察和比较不同体位下短臂离心机暴露所引起的心血管及前庭功能反应,进一步明确短臂离心机暴露下体位因素对心血管和前庭功能的影响. 方法 10名健康男性,依次进行75°、45°、15°后倾体位的短臂离心机暴露,且每体位先后进行2 G、3 G(足水平)人工重力暴露;采用便携式无创逐跳血压监测仪(Portapres)全程监测,并记录受试者血压、心率,通过Beatscope分析软件计算心脏泵血功能和总外周阻力;同时进行前庭功能评价,比较不同体位短臂离心机暴露对心血管、前庭系统的影响. 结果 2 G、3 G短臂离心机分别暴露时,15°体位下6名受试者出现严重运动病症状被迫终止试验;75°和45°两种体位下受试者血压、心率较基础值增高(F=2.79～16.44,P<0.05);心输出量则无显著变化.3 G暴露75°和45°两种体位时,每搏量显著降低(F=2.25、8.35,P<0.05).3 G暴露45°体位时总外周阻力较基础值增高(F=2.61,P<0.05);相同G值短臂离心机暴露时,75°体位下心血管功能变化较45°体位差异无统计学意义,而前庭功能评分则随着体位角度的减小而逐渐增高,15°体位下评分较45°和75°体位增高,差异有统计学意义(P<0.05). 结论 短臂离心机暴露时,45°和75°两种体位对心血管功能的影响无统计学意义,但不同体位对前庭功能的影响却差异较大.暴露体位越趋近于坐位,引起的运动病程度越重. Abstract： Objective To investigate the changes of human cardiovascular and vestibular functions when exposed to the artificiaI gravity generated by short-arm centrifuge with different body positions.Methods Ten healthy male volunteers were exposed to the artificial gravity at three different body positions:foot towards to the radial direction off the rotation center respectively with 75°,45°and 15°back tilting.Each position underwent on short-arm centrifuge with two sessions that were at 2 G and 3 G (at foot level) respectively.Beat-by-beat arterial blood pressure (BP) and heart rate (HR) were measured before and during the experiment by means of Portapres and calculated parameters,such as stroke volume (SV),cardiac output (CO) and total peripheral resistance (TPR),were obtained by Beatscope software.A subjective scoring was taken for assessing vestibular sensations. Results Six of 10 subjects with 15°posture were terminated both in 2 G and 3 G exposure due to their serious motion sickness symptoms.Comparing to the measurements before exposure,subjects with 45°and 75°posture showed significant increased BP and HR (F=2.79 to 16.44,P<0.05) but SV (F=2.25 or 8.35,P<0.05) while CO had no obvious change.Comparing to the measurements before exposure,subjects with 3 G (45°posture) showed significant incleased TPR (F=2.61,P<0.05).3 G exposure resulted in higher HR than that in 2 G.No significant changes of BP,HR,CO,SV and TPR were found between 45°and 75°postures under same exposure.The scores of vestibular assessment showed increased tendency with the decreased tilt angle.Significantly higher scores were got for 15°posture exposures comparing to others and indicated stronger vestibular stimuli.Conclusions The results suggested that the smaller tilted angle posture would result in mole serious vestibular symptoms.     

Maximal exercise as a countermeasure to orthostatic intolerance after spaceflight

Previous investigators have suggested that maximal exercise performed 24 h before the end of bed rest, a spaceflight analog, restores prebed rest plasma volume, baroreflex responses, and orthostatic tolerance. PURPOSE: In this case report, we examined the effect of a similar exercise protocol 24 h before a Shuttle landing on the orthostatic responses of four crewmembers (EX) after spaceflights of 8-14 d. Four additional crewmembers (CON) served as controls and did not perform exercise during the final day of the flight. METHODS: Each crewmember performed a 10-min stand test approximately 10 d before launch (L-10) and within 1-2 h of landing (R+0). Cardiac stroke volume was measured (Doppler ultrasound) supine and during each min of standing for three EX and three CON subjects. RESULTS: Preflight, all crewmembers completed the stand test and each group had similar heart rate and blood pressure responses. Postflight, all subjects also completed the 10-min stand test. Each group had similarly elevated supine and standing heart rates, elevated diastolic and mean arterial blood pressures, and reduced pulse pressures compared to L-10. However, postflight cardiac output, mean +/- SEM, (EX: 4.5+/-0.6 L x min(-1); CON: 3.1+/-0.3 L x min(-1)) and stroke volume (EX: 43+/-7 mL x beat; CON: 30+/-6 mL x beat) were higher after 10 min standing in the EX subjects compared to CON subjects. CONCLUSIONS: For these four crewmembers, maximal exercise performed 24 h before landing may have helped maintain stroke volume but did not maintain heart rate and blood pressure responses during standing compared to preflight.     

Leg vascular responsiveness during acute orthostasis following simulated weightlessness

Ten men (35-49 years old) underwent lower body negative pressure (LBNP) exposures before and after 10 d of continuous 6 degrees head-down bedrest in order to predict the effect of weightlessness on the responsiveness of leg vasculature to an orthostatic stress. Heart rate (HR), mean arterial blood pressure (MAP), and impedance rheographic indices of arterial pulse volume (APV) of the legs were measured during rest and at 1 min of -30 mm Hg LBNP. Bedrest-induced deconditioning was manifested by decreases (p less than 0.05) in plasma volume (17%), peak oxygen uptake (16%), and LBNP tolerance (17%). Resting HR was unchanged after bedrest, but HR was higher (p less than 0.05) at 1 min of -30 mm Hg LBNP after, compared with before, bedrest. Responses of MAP to -30 mm Hg LBNP were not altered by bedrest. Resting APV was decreased (p less than 0.05) by simulated weightlessness. However, APV was reduced (p less than 0.05) from rest to 1 min -30 mm Hg LBNP by the same relative magnitude before and after bedrest (-21.4 +/- 3.4% and -20.5 +/- 2.7%, respectively). We conclude that peripheral arterial vasoconstriction, as indicated by reductions in APV during LBNP, was not affected by bedrest. These results suggest that there was no apparent alteration in responsiveness of the leg vasculature following simulated weightlessness. Therefore, it appears unlikely that control mechanisms of peripheral resistance contribute significantly to reduced orthostatic tolerance following spaceflight.