下体负压旋转床模拟航空推拉效应对心血管功能的影响

目的探讨下体负压旋转床模拟航空推拉效应的效果 ,观察推拉动作对心血管功能的影响。方法 8名被试者在下体负压旋转床上进行“直立位 (HUT ,+1Gz) -倒立位 -直立位 +下体负压 (LBNP ,- 5 0mmHg) 1 0min”的模拟推拉效应试验及单纯直立位 +下体负压 (- 5 0mmHg) 1 0min的对照试验 ,用阻抗法测量了试验过程中心率 (HR)、血压 (BP)、基础阻抗 (Z0 )、每搏心输出量 (SV)、心输出量 (CO)及总外周阻力 (TPR)等心血管功能指标的变化。结果在模拟推拉效应试验中 ,有 3名被试者没有完成直立位 +LB NP作用 1 0min的试验 ,出现晕厥前症状 ,8名被试者平均耐受时间为 8.99± 1 .47min。而对照试验时 ,被试者均完成了 1 0min的直立 +LBNP试验。模拟推拉效应试验时 ,在倒立位 ,被试者HR、Z0 较直立位对照值降低 ,SV和CO较直立位对照值升高 ,均有显著性意义 ;直立位 +LBNP过程中 ,HR、Z0 、TPR较对照和倒立位值显著增高 ,SV和CO较对照和倒立位值显著降低 ,SBP在HUT即刻较对照值显著性增高 ,在HUT +LBNP过程中显著性降低。在对照试验时 ,上述指标呈现出相同的变化 ,但增高或降低的百分比 (% )低于模拟推拉效应试验 (HR除外 )。结论倒立位后 ,再直立 +LBNP作用 ,心血管功能下降程度大于单纯直立 +LBNP作用 ,下体负压旋转床     

自行下体负压训练器训练对推拉效应的影响

目的 探讨利用自行下体负压训练器训练后的心血管反应改变及其在推拉效应中的作用,为其在推拉效应的地面防护中提供实验依据.方法 8名男性被试者进行一定方式的自行下体负压训练器训练,每天1次,连续10 d.在训练前、训练5 d及训练10 d后测量平卧位心脏泵血功能,进行心率变异性(HRV)、血压变异性(SBPV)及压力反射敏感性(BRS)分析和推拉动作、头高位倾斜(HUT)测试.结果 训练10 d后,平卧位血压及心脏泵血功能较训练前显著升高(P<0.05).HRV分析的HFn降低.而LFn升高,但未达到显著水平.SBPV分析及BRS在训练后无明显改变.训练后的模拟推拉动作HUT阶段及HUT实验中,SBP、DBP、SV及CO较训练前显著升高(P<0.05).结论 自行下体负压训练器训练可以提高被试者的基础心血管水平,增强其对立位应激的调节能力,可能对推拉效应的防护具有一定的作用,可用于战斗机飞行员进行地面抗荷生理训练.     

提踵动作对下体负压耐力的影响

目的验证提踵动作对提高下体负压耐力的有效性,并探讨其可能的作用机制。方法健康男性志愿者10名,在下体负压(LBNP)条件下分别随机进行2次头高位倾斜检查(HUT)测定其下体负压耐力。一次为志愿者的基础下体负压耐力(对照组),另外一次要求志愿者在LBNP条件下做提踵动作,直至耐力终点(提踵组)。结果提踵组下体负压耐受时间(DNP)和累计应激指数(CSI)均显著增加(P<0.05)。在下体负压过程中,提踵组平均动脉压呈升高趋势,心率增加呈降低趋势,每搏量增加,且均在-40 mmHg及-50 mmHg时达到显著水平(P<0.05)。结论提踵动作可以提高下体负压耐力,可望作为航天员在长期太空飞行后引起立位耐力不良时的应对措施,也可作为血管迷走性晕厥患者的预防措施和治疗手段。     

心血管系统对下体负压及立位应激反应的比较

为了比较人体心血管系统在下体负压和立位耐力试验中的变化，本实验观察了１１名男性青年被试者，在阶梯式卧位下体负压（一２．７ｋＰａ、２ｍｉｎ；一４．０ｋＰａ、３ｍｉｎ，一５．３ｋＰａ、５ｍｉｎ和一６．７ｋＰａ、１０ｍｉｎ）试验和２０ｍｉｎ的立位耐力试验时的心率、血压、外周阻力、终末舒张容积、心搏量、心输出量和脑血流图等指标的变化。结果表明，两种应激试验均使回心血量减少，终末舒张容积降低，心脏处于低泵血状态，心率随负荷量增加而增加。在立位试验中，心率只在由卧位变为立位时发生一次性的明显增加，舒张压和平均动脉压的变化明显高于下体负压试验中的变化。脑血流图在两种试验中呈现相反趋势的变化。     

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。     

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。     

坐位下体负压下人体大脑中动脉血流速度及血氧饱和度的改变

目的探讨坐位下体负压对人体大脑中动脉血流速度、心率和血氧饱和度的影响。方法 15名健康青年男性在坐位下体负压 - 4.0 0kPa、 - 6.67kPa条件下 ,分别测试负压前、下体负压暴露 0 .5、1、2、3、4、5min和卸压后 1、3、5min的大脑中动脉血流速度、心率和血氧饱和度。结果在 - 4.0kPa下体负压作用 4、5min时 ,脑血流速度减慢 (P <0 .0 5 ) ;负压作用 3、4、5min时心率增快 (P <0 .0 5 ) ;血氧饱和度无明显改变。在 - 6.67kPa下体负压作用 2、3min时 ,脑血流速度减慢 (P <0 .0 5 ) ,在 4min和 5min时显著减慢 (P <0 .0 1) ,卸压后 1min尚未恢复 (P <0 .0 5 ) ,随后恢复至对照水平 ;负压作用后各时间点心率均显著增快 (P <0 .0 1) ;血氧饱和度在负压暴露 5min时显著下降 (P <0 .0 5 )。结论坐位下体负压造成血液在下肢淤积 ,大脑中动脉血流速度减慢 ,引起大脑血供减少 ,为空中晕厥和立位耐力不良的医学鉴定提供了人体实验依据     

下体负压锻炼提高战斗机飞行员加速度耐力（摘要）

目的探讨下体负压锻炼提高加速度耐力可行性。方法针对3名未通过离心机检查的加速度耐力不良战斗机飞行员,给予下体负压锻炼1周,每天1h左右。负压自-50mmHg开始,锻炼5～10min,如果能耐受,逐渐增加负压,每次增加-10mmHg,最大不超过-80mmHg。记录心率、血压、呼吸频率、血氧饱和度、耳脉搏及主观症状。     

21d头低位卧床期间第一周和最后一周下体负压锻炼对立位耐力和心功能的影响

目的观察在 2 1d头低位卧床的第一周和最后一周进行下体负压锻炼对立位耐力和心功能的影响。方法 1 2名健康男性志愿者 ,随机分为对照组和LBNP组 ,每组 6人 ,均参加 - 6°头低位倾斜卧床实验。对照组在卧床期间不做任何处理 ,LBNP组在卧床第一周和最后一周 ,每天进行 1h、- 30mmHg的下体负压锻炼。卧床前和卧床第 1 0、2 1天在倾斜床上进行 3次立位耐力检查 ,卧床期间测量心脏泵血和收缩功能等指标。结果卧床前两组 1 2名被试者均顺利通过立位耐力检查。卧床第 1 0和 2 1天 ,对照组所有被试者均不能通过立位耐力检查 ,而下体负压组仅有 1人未通过 ,卧床第 2 1天下体负压组( 1 9.7± 0 .9min)平均耐受时间较对照组 ( 1 5 .0± 3.2min)显著延长 (P <0 .0 5 )。对照组每搏输出量(SV)及心输出量 (CO)在卧床第 3、1 0天较卧床前显著降低 (P <0 .0 5 ) ,而LBNP组SV及CO在卧床期间均无显著性变化 ;两组的射血前期 (PEP) /左室射血时间 (LVET)在卧床第 3、1 4天均显著升高 (P <0 .0 5 )。两组间比较 ,LBNP组PEP/LVET在卧床第 3天较对照组显著降低 (P <0 .0 5 ) ,LVET在卧床第 3、7和 1 4天较对照组显著升高 (P <0 .0 5 )。结论 2 1d头低位卧床可引起立位耐力、心脏泵血和收缩功能显著降低 ;在 2 1d头低位卧床的     

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。     

下体负压对男女飞行学员心血管调节功能的影响

观察男女飞行学员在下体负压条件下各项生理指标的变化差异，男女两组受试者分别下体负压裤，在－50mmHg负压下持续暴露8min。在下体负压（LBNP）作用时，同步记录心电图、心率、血压、脑血流量、负压暴露时间。结果显示，在LBNP作用下，随着负压暴露时间的增加，所有受试者均出现心率增快，收缩压降低、脑血流量下降。研究表明，下体负压所产生的生理学效应在男女飞行学员间相似。     

Oxygen status and regional blood flow in the gingival mucosa as affected by lower body negative pressure

Five test subjects were exposed to lower body negative pressure (LBNP). During exposure their regional circulation and oxygen balance of the gingival mucosa were measured and electrocardiography and kinetocardiography were performed to calculate parameters of the left heart function. The study showed a distinct correlation between LBNP tolerance and the level of compensatory reactions of the gingival mucosa blood flow and the cardiovascular system as a whole. The subjects with a high LBNP tolerance showed well pronounced regional compensatory reactions of the gingival mucosa that were not accompanied by significant changes in the left heart function. The subjects with a moderate tolerance exhibited either weak or no regional compensatory reactions of the gingival mucosa and significant changes in the left heart function.     

急性缺氧条件下的心率变异性分析

目的 以心率变异性（HRV）为定量评价心血管自主神经调节变化的指标,观察模拟5000m急性缺氧条件下,自主神经变化特点,并探讨预测缺氧耐力不良的方法。方法 被试者为11名18－30岁的健康男性,以呼吸10．5％的低氧混合气30min模拟5000m急性缺氧,以时域和频域（粗粒化谱分析,CGSA）方法进行HRV分析。并根据是否完成实验过程将被试者分为耐力良好组（A组）和耐力不良组（B组）。结果 耐力良好组在缺氧时心率显著增快,相邻RR间期之差的均方根值（RMSSD）显著减小,LFn.u(LF的标准单位）和LF／HF显著增大,HF和HFn.u.(HF的标准化单位）显著减小。两组比较,缺氧5－10min时,LFn.u.和LF／HF在B组显著大于A组,缺氧10－15min时,RMSSD在B组显著小于A组。结论 在模拟5000m急性缺氧条件下,交感神经活动增强,迷走神经活动减弱;HRV分析对评价缺氧耐力有一定的预测性。     

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.     

用脉图方法观察2.5h头低位15°倾斜期间心血管系统的变化

为了解航天员航天初期心血管功能的动态变化，用脉图方法观察了１９名被试者在２．５ｈ头低位１５°倾斜期间的心血管功能。结果表明，ＨＤＴ期间心血管指标变化可分为现时期：急性反应期和反应期。     

Physiologic study of pressure point techniques used in the martial arts

BACKGROUND: Study physiologic changes occurring during "knockouts" produced by application of pressure point techniques during martial arts demonstrations. METHODS: Experimental design: prospective analysis of physiologic variables during and immediately following an acute event. Setting: martial arts demonstration carried out at a medical center hospital. Subjects: 12 normal volunteers participating in a martial arts demonstration. Interventions: application of various pressure point techniques that have been observed to produce states of unresponsiveness in volunteers. Measures: continuous ECG and video/EEG monitoring with measurements of blood pressure and oxygen saturation. Qualitative analysis of EEG and ECG recordings and quantitative comparison of heart rate, blood pressure, and oxygen saturation measurements before during and after the period of induced unconsciousness. RESULTS: No significant changes in blood pressure, oxygen saturation, cardiac rate or rhythm, or electroencephalogram are noted during the knockouts produced by application of pressure point techniques. There was only variable inability for subjects to remember words spoken to them during the episode of apparent unresponsiveness. CONCLUSIONS: The mechanism for the state of unresponsiveness produced by application of pressure point techniques is not related to a significant cardiac or pulmonary process. There is no evidence of reduced cerebral blood flow during this time or of other dangerous physiologic changes. The exact mechanism for this phenomenon remains uncertain.     

Cardiovascular dynamics associated with tolerance to lower body negative pressure

The purpose of this investigation was to identify cardiovascular responses associated with tolerance to lower body negative pressure (LBNP). In this study, 18 men, ages 29-51 years, were categorized as high (HT) or low (LT) LBNP tolerant based on a graded presyncopal-limited LBNP exposure criterion of -60 mm Hg relative to ambient pressure. Groups were matched for physical characteristics and preLBNP cardiovascular measurements, with the exceptions of greater (p less than 0.05) end-diastolic volume and cardiac output in the HT group. During peak LBNP, cardiac output was similar (NS) in both groups, although the HT group displayed a greater heart rate (p less than 0.05). In both groups, venous return appeared to limit cardiac output resulting in decreased arterial pressure. Tolerance to LBNP did not appear solely dependent on the absolute amount of blood pooled in the legs since the HT group demonstrated a greater (p less than 0.05) peak LBNP-induced increase in midthigh-leg volume. Greater tolerance to LBNP was associated with a larger preLBNP cardiac output reserve and higher compensatory increases in heart rate and peripheral resistance.     

下体负压作用下脑氧饱和度的变化

The purpose of this study was to observe and analyse the changes of regional cerebral oxygen saturation (SrO2) under lower body negative pressure (LBNP). 12 healthy young subjects were tested in an LBNP chamber in sitting position. Incremental negative pressure was used and end points of test were onset of presyncopal symptoms or completion of the 15min test. The results were: (1) SrO2 showed a significant decrease under LBNP; (2) The magnitude of decrease of SaO2 showed significant differences among subjects with different reactions at the termination of LBNP; (3) Under LBNP the arterial oxygen saturation (SrO2) kept constant. The changes of SrO2 correlated strongly with the percentage changes of superaorbitalis arterial blood flow (r = 0.59-0.86, P < 0.05 or 0.01). It was suggested that the changes of SrO2 were related to the decrease of cerebral blood flow under LBNP. It was possible to use SrO2 to detect presyncopal and syncopal symptoms. So the monitoring of SrO2 could be used in studies of G-LOC.     

预测下体负压耐力方法初探

为探讨预测下体负压耐力的方法，对１１名被试者进行了－４．００ｋＰａ，－５．３３ｋＰａ，－６．６７ｋＰａ各５ｍｉｎ的阶梯式坐位下体负压耐力检查，以晕厥前症状或持续１５ｍｉｎ为终止指征。检查结果将被试者分为耐力良好组（Ａ组，ｎ＝５）和耐力不良组（Ｂ组，ｎ＝６）；组间比较时发现负压作用第１１ｍｉｎ时的ＭＡＰ、△ＳｒＯ２和△ＣＯ（％）判别显著（Ｐ〈０．０５）；用这一时刻的ＭＡＰ和△ＳｒＯ２建立的回归方程对