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     

旋转床模拟推拉动作的心血管效应

目的　使用旋转床模拟推拉动作 ,观察推拉动作时人体的生理反应 ,探讨推拉效应的发生机理。　方法　 11名受试者在旋转床上经受“直立位 ( 1GZ)→倒立位 ( - 1GZ)→直立位 ( 1GZ)”的模拟推拉动作 ,测定心率 ( HR)、血压 ( BP)、基础阻抗 ( Z0 )、每搏心输出量 ( SV)及总外周阻力( TPR)等生理指标。　结果　在倒立位时 HR、平均动脉压 ( MAP)、舒张压 ( DBP)、Z0 及 TPR较对照降低均有显著性意义 [HR分别为 ( 6 0 .8± 7.9)次 / min与 ( 87.8± 7.4)次 / min,P<0 .0 1;MAP分别为( 83.8± 8.2 ) m m Hg与 ( 91.8± 15 .0 ) mm Hg,P<0 .0 5 ;DBP分别为 ( 6 7.3± 8.3) mm Hg与 ( 77.0±15 .6 ) m m Hg,P<0 .0 5 ;Z0 分别为 ( 2 7.0± 2 .8) Ω 与 ( 2 9.1± 3.3) Ω,P<0 .0 1;TPR分别为 ( 73.15±12 .12 ) k Pa· s· L- 1 与 ( 113.3± 36 .4) k Pa· s· L- 1 ,P<0 .0 1],SV升高有显著性意义 [分别为 ( 15 5 .0± 2 6 .1) m l与 ( 78.7± 19.5 ) ml,P<0 .0 1],SBP有降低趋势 ,但未达显著水平。在再次直立位时 ,HR、MAP、DBP、Z0 及 TPR较对照降低均有显著性意义 [HR分别为 ( 81.9± 8.9)次 / min与 ( 87.8± 7.4)次 / m in,P<0 .0 5 ;MAP分别为 ( 88.1± 13.6 ) mm Hg与 ( 91.8± 15 .0 ) m m Hg,P<0     

头低位暴露后直立位下体负压作用的耐力变化和心血管反应

目的观察头低位后直立位下体负压暴露的耐力和心血管反应。方法8名被试者在下体负压倾斜床上进行“直立位-倒立位30s-直立位联合下体负压(-60mmHg)致晕厥前症状”的模拟推拉效应试验及单纯直立位 下体负压(-60mmHg)致晕厥前症状的对照试验,用阻抗法测量了试验过程中心血管功能指标的变化。结果在模拟推拉效应试验中,8名被试者出现晕厥前症状的平均耐受时间为4.5±2.4min,显著低于对照试验时的8.4±2.1min(P<0.01)。在倒立位,被试者HR较直立位基础值降低,SV和CO较直立位基础值升高,均有显著性意义。和基础值相比,直立位下体负压时HR增加的百分比显著低于对照试验(P<0.05),而直立位下体负压时SV和CO降低的百分比均显著高于对照试验时SV和CO降低的百分比(P<0.05)。在直立位下体负压暴露时,对照试验的PP和基础值比较显著降低(P<0.05),TPR比基础值显著增加(P<0.05)。结论倒立位后,再进行直立位下体负压作用,出现晕厥前症状的平均耐受时间缩短,心血管反应降低。     

倾斜床模拟推拉动作下心率和血压变化

目的建立倾斜床模拟推拉动作模型 ,并观察其引发的心血管反应性特点。方法以 1 0名健康歼击机飞行员为被试者 ,随机进行 3次 90°立位 (HUT)和 90°倒立位 (HDT)体位转换试验 ,HUT 1min→HDT 1 0s→HUT 1min ,第 2、3次体位转换时HDT的持续时间分别为 1 5s和 2 0s。床体旋转速度为45°/s。间隔 4s监测一次血压 ,连续记录心电图。结果在HDT期间 ,各时间心率和血压较基础HUT明显下降。随后HUT时 ,除 1 1～ 1 5s血压外 ,其余各时间心率和血压较基础HUT明显下降。结论采用倾斜床可以模拟推拉动作所引起的心血管的反应 ,故其可作为推拉动作的模型     

下体负压联合旋转床模拟推拉效应的心率变化特征

目的 建立下体负压联合旋转床模拟推拉效应的方法,观察不同预先-Gz作用后Gz时心率反应的变化特征.方法 8名健康男性志愿者,利用旋转床或联合下体负压随机暴露于预先0°(0 Gz)、-30°(-0.5 Gz)和-90°(-1 Gz),分析在模拟推拉动作时-Gz或0 Gz、"拉"时相及与单纯+1 Gz时相同时间段的平均心率,比较在不同倾斜角度即不同预先-Gz作用或联合下体负压模拟推拉动作时"拉"时相的心率反应.结果 利用旋转床模拟推拉动作时,在"推"时相即头低位时心率显著降低,随倾斜角度的增大降低更加显著,"拉"时相的心率随预先倾斜角度增大回升更明显.下体负压联合旋转床模拟推拉动作时,心率变化与单纯旋转床模拟推拉动作时基本一致.后者在"拉"时相与单纯+1 Gz作用时相比心率变化更大,提示心率回升更加缓慢.结论 旋转床或联合下体负压可以模拟推拉效应,其心率反应随预先-Gz值的增大在"拉"时相回升明显,并且受随后模拟+Gz负荷大小的影响.     

下体负压与下肢局部加压对模拟推拉动作时脑血流的保护作用研究

目的:对比下体负压（lower body negative pressure,LBNP）策略与下肢局部加压策略对模拟推拉动作时脑血流的保护作用。方法:研究采用重复交叉设计。15名健康成年男性为受试者。所有受试者均经历无干预模拟推拉动作测试（对照轮）、带LBNP的模拟推拉动作测试（LBNP轮）、带下肢局部加压的模拟推拉动...     

高性能战斗机空战训练课目推拉效应动作发生频率调查

目的 了解某型高性能战斗机在空战训练课目中推拉效应动作发生的频率和强度。方法 回顾分析某型单座高性能战斗机单机战斗特技和双机空战截击课目飞行参数记录中的加速度数据,统计导致推拉效应的飞行动作的频数及该动作G负荷的变化幅度。结果 这两个飞行课目中,34.1％的起落有推拉效应动作。单机战斗特技比双机空战截击出现推拉效应动作的频率高,G值变化幅度也大。结论 某型高性能战斗机空战训练飞行中存在可以导致推拉效应的飞行动作,这是一种危险因素,应予以预防。     

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.     

下体正压模拟推拉动作对＋GZ耐力的影响

目的 用单轴向离心机和下体正压模拟推拉动作,研究推拉动作对＋Ｇｚ耐力的影响。方法 ６名受试者着ＫＨ－３抗荷服充气３００ｍｍＨｇ（１ｍｍＨｇ＝０．１３３ｋＰａ）１ｍｉｎ,测定下体正压前、中、后血压（ＢＰ）、心率（ＨＲ）变化。在离心机上测基础耐力后,向抗荷服充气３００ｍｍ Ｈｇ、１ｍｉｎ放气后立即转动离心机,测松弛Ｇ耐力。结果 收缩压（ＳＢＰ）在下体正压中与下体正压前相比升高有显著性意义（Ｐ〈０．０１     

推拉动作对大鼠脑组织NO含量及DNA分布图的影响

目的 探讨推拉动作对大鼠脑组织中NO含量及细胞凋亡的影响。方法 90只雄性Wistar大鼠随机分成对照组、 Gz暴露组、推拉组，在 Gz暴露后30min、3h、12h、24h和48h 5个时间点处死大鼠取脑。用硝酸还原酶化学比色法检测：NO含量的变化。并用流式细胞仪检测皮层和海马细胞DNA分布图，测定AO峰所占的百分比，表示细胞凋亡程度。结果 脑组织一氧化氮含量，在30min、3h和12h时， Gz暴露组和推拉组与对照组比较有显著差异，推拉组与 Gz暴露组相比较也有差异性，24h和48h组间比较无显著性差异。皮层、海马细胞在3h、12h和24h时两实验组与对照组相比较细胞凋亡百分比明显增多，24h达高峰，48h无显著性差异。推拉组与 Gz暴露组细胞凋亡百分比在3h和24h有差异，12h差异显著。结论 高 Gz及推拉动作可引起大鼠脑组织：NO含量和细胞凋亡百分比增加；推拉组比单纯 Gz暴露所造成的NO含量及脑细胞凋亡百分比多，但这种对神经元的损害是可逆性的.     

Cerebral blood flow velocity by transcranial Doppler during a vertical-rotating table simulation of the push-pull effect

BACKGROUND: The push-pull effect (PPE) has been suspected of causing many aircraft accidents. The perfusion and then withdrawal of cerebral blood during the PPE may change the state of the cerebral blood vessel. HYPOTHESIS: During head-down tilt (HDT) cerebral vasoconstriction occurs in response to the elevated perfusion pressure to maintain cerebral blood flow, and during subsequent head-up tilt (HUT) the increased resistance of the cerebral blood vessel recovers slowly. METHODS: Ten healthy male non-pilots were exposed to the following protocol using a rotating-table to simulate the push-pull maneuver: HUT (+1 Gz) for 1 min followed by transition to HDT (-1 Gz) 10 s followed by transition to HUT (+1 Gz) 1 min. Cerebral blood flow velocity and pulsatility indices in the left middle cerebral artery were continually measured with a transcranial Doppler (TCD) instrument. RESULTS: Mean blood flow velocity (Vm) increased significantly by 10%, during the first 5 s of HDT, recovered to baseline during HDT 5 10 s, and remained unchanged during subsequent HUT. Systolic blood flow velocity (Vs) increased by 9% during HDT 5-10 s and 11% during HUT 0-5 s. Diastolic blood flow velocity (Vd) decreased by -9% during HDT 5-10 s, and -22% during HUT 0-5 s. Vs-Vd increased by 26% during HDT 5 10 s, and 41%, during HUT 0-5 s. Pulsatile indices (PI) and resistance index (RI) increased by 26%) and 15% during HDT 5-10 s, and by 40% and 27% during HUT 0-5 s, respectively. Vs, Vs-Vd, PI, and RI remained at the higher level, and Vd remained at the lower level to HDT 15-20 s. CONCLUSIONS: The results indicate that cerebral vasoconstriction occurred to prevent brain over-perfusion during HDT. During HUT, the elevated resistance of the cerebral vessel remained at the higher level for about 20 s, and may have worsened the cerebral perfusion from exposure to +Gz. This may be one of the mechanisms of PPE.     

Brief exposure to -Gz reduces cerebral perfusion pressure during subsequent +Gz stress in rats

INTRODUCTION: In humans, +Gz exposure immediately preceded by exposure to zero or -Gz can result in unexpected incapacitation ("push-pull" effect). Our goals were to establish whether this phenomenon exists in rats and to evaluate the importance of varying the duration of -Gz exposure on magnitude of the push-pull effect on cerebral perfusion pressure. METHODS: Eight conscious male rats were studied in the transition from +5 Gz to +10 Gz imposed by centrifugation. This was done with (push-pull) or without (control) 2 s exposure to -5 Gz applied using a counterbalanced design. Seven isoflurane anesthetized rats were studied in the transition from 0Gz (+1Gy) to + 1Gz imposed by tilting. This was done with (push-pull) or without (control) 0.5, 1, 3, or 9 s exposure to -1Gz imposed immediately prior to the transition applied using a counterbalanced designed. RESULTS: Exposure to 2 s of -5 Gz significantly (p < 0.01) reduced carotid artery pressure in the 4th through 8th s of exposure to +10 Gz by an average of 15 mmHg compared with control. In the tilt experiments, a push-pull effect was found with mild Gz exposure (+/-1Gz) with as little as 0.5 s -Gz exposure. Varying the head-down dwell time did not alter the magnitude of the exaggerated hypotension induced by "push-pull" (p = 0.90). CONCLUSIONS: We conclude that rats express a "push-pull" effect similar to that observed in humans but that altering the duration of exposure to -Gz does not influence the magnitude of the "push-pull" effect.     

脑血氧饱和度的近红外光谱测量技术及其在超重条件下的应用

目的：用近红外光谱技术对加速度作用后(超重条件下)的大鼠进行脑血氧饱和度(％SaO2)的无损监测。方法：制作头部不同程度缺血缺氧模型，抽血测量其血氧饱和度，并计算出与正常组之间的差值。同时测定出在850nm和760nm波长处缺血缺氧模型的光谱吸收强度，计算出与正常组之间的差值，并绘制出两者之间的关系曲线。根据关系曲线，通过用近红外光谱仪监测高 Gz和推拉动作后的光谱吸收强度，计算出与0 Gz组差值，推测出加速度作用后脑血氧饱和度。结果：由关系曲线推测出加速度作用后，大鼠脑血氧饱和度降低；推拉动作后，脑血氧饱和度降低更为明显。结论：根据关系曲线，用近红外光谱技术可以无损监测脑血氧饱和度的变化。     

Impairment of cardiovascular and vasomotor responses during tilt table simulation of "push-pull' maneuvers

BACKGROUND: Numerous studies have shown that tolerance to positive acceleration (+Gz) is impaired subsequent to an exposure of less than +1 Gz. HYPOTHESIS: Vasodilation induced by antecedent negative Gz (-Gz) exposure delays sympathetic vasoconstriction during subsequent +Gz, further reducing G-tolerance. METHODS: There were 20 subjects tested on an electronic tilt table, and exposed to the following randomized head-up tilt (HUT) and head-down tilt (HDT) conditions: +75 degrees HUT for 60 s, followed by transition to either 0 degrees (supine) HDT, or -25 degrees HDT, or -45 degrees HDT for 7 or 15 s at tilt rate of 45 degrees x s(-1). This was followed by HUT, divided into three periods: HUT1 (approximately 3-10 s), HUT2 (approximately 15-22 s), and HUT3 (approximately 27-35 s). Systolic blood pressure (SBP) was normalized to heart and head-levels. Stroke volume (SV) was estimated using impedance cardiography; forearm blood flow (FBF) estimated by venous occlusion plethysmography and forearm vascular resistance (FVR) was calculated from FBF and SBP. Total peripheral resistance (TPR) was estimated by MAP/(SV*HR). RESULTS: Heart-level SBP decreased significantly during HDT for both HDT durations (p < 0.01). SBP increased significantly at head-level during HDT (p < 0.001). During HUT1 heart and head-level SBP decreased for all conditions (p < 0.001), recovering to baseline levels by HUT2. TPR decreased significantly for all HDT conditions (p < 0.001), with this decrease related to the degree of HDT angle (p < 0.05). During HUT1, TPR remained depressed below baseline. At HUT2, TPR remained decreased for the -45 degrees/7-s condition only (p < 0.01). FBF decreased significantly during HDT (p < 0.02), with the magnitude related to the HDT angle. FBF remained elevated during HUT1 (p < 0.01). FVR decreased as a function of HDT angle during HDT (p < 0.001), with the decrease persisting into the HUT1 phase (p < 0.01). By the HUT2 and HUT3 periods, FVR were above baseline levels for the -45 degrees HDT condition (p < 0.01). CONCLUSION: These results confirm in humans the delayed recovery of peripheral vascular resistance observed in animal studies when -Gz precedes +Gz. Since SV recovered to baseline levels during the "pull" phase (HUT1-3), with TPR and forearm vascular resistance remaining depressed, baroreflex-mediated peripheral vascular control is delayed. This delay at higher subsequent +Gz levels is dangerous for the military pilot, since symptoms of G-intolerance due to delay in head-level BP recovery will ensue at lower absolute +Gz levels during push-pull type maneuvers.     

Centrifuge training program with "push-pull" elements

INTRODUCTION: Pilots of fighter aircraft are often exposed to maneuvers that produce negative acceleration (-Gz) immediately followed by positive acceleration (+Gz). This sequence has been found to reduce tolerance to +Gz, a phenomenon known as the "push-pull" effect. We devised a centrifuge training program to demonstrate this phenomenon to pilots. METHODS: The centrifuge of the Military Institute of Aviation Medicine in Warsaw, Poland, was modified in 1996 to allow active positioning of the gondola during rotation. Head-down position of -6 degrees to -40 degrees were used to produce relative -Gz (r-Gz) in a range down to 0.2. As a side effect, this produces Gy acceleration between -1.3 Gy and -1.6 Gy. Pilots completed normal centrifuge training, including a relaxed, gradual-onset run and three rapid-onset runs. They were then exposed to a profile that included a series of push-pull exposures where r-Gz was followed by +Gz with stepwise increases in the latter from +2.5 to +5 Gz. The final profile was a simulated aerial combat maneuver with push-pull elements. RESULTS: The trainees expressed surprise at the push-pull effect, which forced them to begin an anti-G straining maneuver at lower levels than normal. They complained about the presence of the Gy, which rarely occurs in aircraft. DISCUSSION: This type of profile appears useful for training pilots about the push-pull phenomenon. After collection of additional data, the profiles may be refined.     

不同强度的模拟推拉动作致大鼠海马神经元损伤的实验研究

目的探讨不同强度的推拉动作所致的推拉效应对大鼠海马神经元损伤的程度和时相性。方法应用动物模型评分、病理、电镜技术分别对不同强度模拟推拉动作后大鼠海马各区神经元损伤情况进行检测。结果 1 )动物模型评分 :随着推拉动作强度的加大 ,卒中指数和神经症状评分逐渐增高。 2 )HE染色 :对照组和± 2Gz暴露后各组及± 6Gz、± 8Gz暴露后的 30min组海马各区神经元形态及分布未见异常。± 6Gz、± 8Gz暴露后的 6h和 2 4h组可见轻重不等的神经元变性。 3)电镜超微结构检查 :± 2Gz暴露后 30min和 2 4h组 ,海马CA1区神经元与正常对照组比较无明显改变。± 2Gz暴露后 6h组及± 6Gz、± 8Gz暴露后的 6h和 2 4h实验组可见大鼠海马CA1区部分神经元出现程度不等的变性。结论± 6Gz和± 8Gz暴露后可引起大鼠海马神经元损伤 ,且以± 8Gz暴露后 6h损伤程度最重。     

推拉动作对大鼠脑GFAP表达的影响

目的 观察推拉动作后大鼠脑星形胶质细胞中胶质纤维酸性蛋白(GFAP)表达的改变.方法 雄性SD大鼠44只,随机分为对照组、 10 Gz暴露组、推拉动作组,分别于暴露后不同时间灌注取脑,免疫组织化学染色观察脑GFAP的表达情况.结果 10 Gz暴露后6 h,顶叶皮层、海马、丘脑可见GFAP呈中等强度的阳性反应,阳性细胞数较对照组显著增多(P＜0.01),多为中等阳性细小型;暴露后1 d、2 d、4 d和6 d,GFAP阳性反应程度进一步增强,阳性细胞数进一步增多.推拉动作组暴露后各时间点,顶叶皮层、海马、丘脑GFAP呈较强的阳性反应,阳性细胞数较 10 Gz暴露组显著增多(P＜0.01),以强阳性肥大型为主.结论 10 Gz/3 min 暴露可引起大鼠顶叶皮层、海马、丘脑GFAP表达显著增加,而推拉动作组比 10 Gz暴露组引起脑组织GFAP的表达增加更明显.