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.     

Cardiovascular training effects in fighter pilots induced by occupational high G exposure

INTRODUCTION: A fundamental difference in the cardiovascular response to acceleration between a group of fighter pilots (FP) and a group of non-pilots (NP) has been demonstrated previously. This study investigated the longitudinal effects of repetitive occupational +Gz exposure on the cardiovascular response to acceleration. METHODS: There were 6 FP and 6 NP subjects who underwent rapid +75 degrees head-up tilt (HUT) on two separate occasions. The FP group were tested after a non-flying period of 5 wk (Test 1), and tested again after a period of repetitive exposure to high +Gz missions (Test 2). The NP group did not fly at all between Test 1 and Test 2. Mean arterial pressure (MAP), heart rate (HR), stroke volume (SV), and total peripheral resistance (TPR) were all determined non-invasively. SV was determined using impedance cardiography and calculated via the Kubicek equation. For each variable, resting values and the response to tilt for both HUT tests within and between each group were compared. RESULTS: In the FP group, resting MAP was higher (86 mmHg) in Test 2 compared with Test 1 (78 mmHg). Between groups, FP resting MAP was only different from the NP resting MAP in Test 2. The FP HR response to HUT increased significantly between the two tests. CONCLUSIONS: These findings suggest a +Gz-induced cardiovascular training effect in the FP group. Repetitive exposure to +Gz results in an increased resting MAP and an elevated HR response to tilt, which may provide benefits to operational fighter pilots.     

Inspiratory impedance effects on hemodynamic responses to orthostasis in normal subjects

BACKGROUND: Breathing through an impedance threshold device (ITD) might prove effective as a countermeasure against post-spaceflight orthostatic hypotension since it increased blood pressure (BP) and cardiac output in supine human subjects. OBJECTIVE: We tested the hypothesis that spontaneous breathing through an ITD would attenuate the reduction in stroke volume and BP during orthostasis in human subjects. METHODS: There were 19 volunteers (10 men, 9 women) who completed two 80 degrees head-up tilt (HUT) protocols with (active) and without (sham control) an ITD set to open at -7 cm H2O pressure. Heart rate (HR), stroke volume (SV), cardiac output (CO), mean arterial pressure (MAP), and total peripheral resistance (TPR) were measured non-invasively during transition from supine to HUT. RESULTS: HUT caused significant elevation in HR and reductions in SV, CO, TPR, and MAP. Hemodynamic effects of HUT were similar for sham and active ITD. Further analysis revealed a subset (n = 11) of subjects who demonstrated a > 20% decrease in SV during HUT with the sham ITD. In this subset of subjects, the ITD attenuated (p = 0.004) the %deltaSV (-22.5 +/- 3.0%) during HUT compared with the sham ITD (%deltaSV = -37.4 +/- 2.6%). There was no statistical effect of ITD use in the subgroup who demonstrated < 20% reduction in SV (-16.6 +/- 0.4%). CONCLUSIONS: Use of an ITD may provide significant protection against orthostatic compromise in individuals with greater than 20% reductions in SV, such as astronauts returning from space.     

Cardiovascular responses to head-up tilt after an endurance exercise program

The cardiovascular responses to 10 min of orthostasis were assessed before and after an aerobic exercise program. Five men and five women (18-25 years old) exercised for 7 weeks, four times per week, for 50 min per session at 70% of maximal heart rate (HR). Before and after the exercise program, maximal aerobic power (VO2max) was determined, and HR, systolic (SBP), diastolic (DBP), and pulse (PP) blood pressures were measured each minute during 5 min of supine rest, 10 min of foot-supported 70 degree head-up tilt (HUT), and 5 min of supine rest. Orthostatic tolerance was not determined. Calf compliance was measured in five of the subjects before and after the program as the change in leg volume at occluding pressures of 20, 40, 60, 80, and 100 mm Hg. Following the program, VO2max increased by 8.7% (p = 0.012), while decreases were noted in resting HR (9.4%, p = 0.041), SBP (5.0%, p less than 0.0005), and DBP (14.2%, p less than 0.0005). Despite a greater HR increase during HUT (7.1 beat.min-1, p = 0.034), SBP decreased by 3.4 mm Hg during HUT after the exercise program (p = 0.008). No differences were noted in the changes in DBP, MAP, or PP upon tilting (p greater than 0.05). After the program, the amount of fluid pooled in the calf at high occluding pressures (80 and 100 mm Hg) increased by 0.96 +/- 0.24 and 1.10 +/- 0.33 ml.100 ml tissue-1 (X +/- S.E.M., p = 0.017 and p = 0.028, respectively). We suggest that control of blood pressure during 10 min of orthostasis may be altered by endurance exercise training.     

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。     

The effect of baroreflex adaptation on the dynamic cardiovascular response to head-up tilt

BACKGROUND: Baroreflex adaptation to repetitive +Gz has been reported previously. The underlying mechanism may involve different responses of stroke volume (SV) and total peripheral resistance (TPR) to +Gz. HYPOTHESIS: The previously observed enhanced mean arterial pressure (MAP) regulation in fighter pilots (FP) is mediated by increases in SV and/or TPR. METHODS: There were 8 pilots and 12 non-pilots who underwent head-up tilt. SV was determined using impedance cardiography. RESULTS: MAP increased significantly in FP, due to heart rate (HR) and TPR increasing more and SV decreasing less. CONCLUSION: Baroreflex adaptation results in better performance of HR, SV and TPR in response to +Gz.     

Squat-stand test response following 10 consecutive episodes of head-up tilt

INTRODUCTION: The cardiovascular system is adaptable to multiple exposures to gravity over several days, and to repeated exposures in a single day. This study aimed to investigate if the cardiovascular adaptation observed following 10 +75 degrees head-up tilts (HUT) would improve the responses to the squat-stand test (SST). METHODS: There were 16 subjects who were randomly allocated into either a tilting group that underwent 10 +75 degrees HUTs in 70 min (Tilting) or a control group that underwent 70 min of rest (Control). Before and after HUT or rest, subjects performed a SST (SST1 and SST2, respectively). Heart rate (HR), BP [systolic (SBP), diastolic (DBP), mean (MAP)], total peripheral resistance (TPR), stroke volume (SV), and cardiac output (CO) were determined during both SSTs. The final 30 s of squat and the first 30 s of stand (divided into three 10-s blocks termed Stand10, Stand20, and Stand30) were compared between SST1 and SST2. RESULTS: In the Tilting condition, during the squat phase of SST2, the following were significantly elevated: SBP (131 +/- 9 to 140 +/- 7.2 mmHg) and MAP (94 +/- 8.7 to 105 +/- 10.2 mmHg); DBP (76 +/- 9.4 to 87 +/- 11.9 mmHg); TPR (1197 +/- 524.6 to 229 +/- 610.5 dyn x s(-1) x cm(-5)) and HR were significantly decreased (78 +/- 6.9 to 73 +/- 7.5 bpm) compared with SST1. At Stand10, DBP and MAP were significantly increased (59 +/- 9.5 to 69 +/- 15.7 mmHg and 74 +/- 8.9 to 84 +/- 14.7 mmHg, respectively); at Stand20, SBP was increased (121 +/- 17 to 128 +/- 22 mmHg); and at Stand30 the following were increased: DBP (64 +/- 8.8 to 75 +/- 16.1 mmHg); SBP (127 +/- 9.2 to 139 +/- 15.8 mmHg); and MAP (79 +/- 8 to 90 +/- 14.9 mmHg). There were no differences observed between SST1 and SST2 in the Control group. DISCUSSION: Cardiovascular responses to the SST can be improved with 10 consecutive +75 degrees HUTs. This is predominantly due to an increase in DBP, indicative of a change in vascular resistance.     

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     

Hemodynamic responses to upright tilt at sea level and high altitude

Hemodynamic responses to upright tilt were studied in eight young men at sea level (SL); after 1 h at 4,300 m simulated altitude (SA); and at 18 h, 66 h and 114 h during residence at 4,300 m (HA). Heart rate (HR), stroke volume (SV), cardiac output (CO), calf blood flow (CBF), blood pressure (BP) and total peripheral resistance (TPR) were obtained during supine rest and after 13 min of 60 degrees head-up tilt using an impedance monitor and electrosphygmomanometer. SL to HA changes in blood volume (BV) were calculated from hematocrit and hemoglobin values. Plasma norepinephrine (Nor) was measured at SL and after 18 h and 66 h of HA. Supine HR, TPR and BP were increased while SV, CO and CBF were reduced SL to HA (p less than 0.05). HR and BP in the upright position were increased SL to HA (p less than 0.05). The responses to tilt (delta supine to upright) were unaltered SL vs SA. With prolonged exposure, SV, CO, TPR and CBF responses to tilt were reduced (p less than 0.05). The reduced responses to tilt at HA were associated with a 10% decline in BV (p less than 0.01) and a 40% increase in Nor (p less than 0.05). It was concluded that the reduction in SV during tilt at SL and SA was compensated for by increases in HR and TPR in order to maintain BP. After 18 h HA, BP in the upright position was maintained only by an increase in HR.     

24h头低位卧床对心血管功能及立位应激反应的影响

目的 观察２４ｈ头低位卧床对心血管系统功能和头高位倾斜心血管反应变化的影响。方法健康男性学员６名,年龄２２～２３岁,进行了２４ｈ头低位卧床实验,卧床期间用阻法测量了心脏泵血功能指标,并观测了卧床前后头高位倾斜时的心血管反应和卧床期间尿量的变化。结果 在卧床期间受试者心率较卧床前（立位）显著减慢,第６、１２、１８ｈ的心率较卧床开始时（０ｈ）显著降低。ＳＶ和ＳＩ在卧床０、６、１２和２４ｈ较卧床前显著增     

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。     

重力应激正自发性压力感受器—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１０人＋６５°头高位倾斜与８人－６．６７ｋＰａ下体负压作用下，以及１５人１６ｄ－６°头低位卧床期间ＢＲＳ的变化。     

Aerobatic flight effects on baroreflex sensitivity and sympathovagal balance in experienced pilots

BACKGROUND: Aerobatic flights subject pilots to accelerations and, therefore, to heavy physical workloads. OBJECTIVE: Our aim was to document changes in spontaneous baroreflex sensitivity and disturbances of sympathovagal balance after exposure to "push-pull" accelerations. METHODS: During 30-min flights, five aerobatic pilots performed five series of descending spirals: first, 30 s under negative (-3 Gz max), and then 30 s under positive (+4 Gz max) G loading, climbing between each series to regain altitude. A stand-test was performed before (T0), immediately postflight (PF), 1 h (PF1), and 2 h after (PF2) the flight. A Finapres apparatus recorded heart rate (HR) and BP during the stand-tests. RESULTS: Resting HR was higher at PF than T0 in supine (11.2 +/- 5.3%, p < 0.01) and standing (11.0 +/- 4.9%; p < 0.05) positions. Sequence analysis of spontaneous baroflex sensitivity (BRS) and spectral analysis of HR variability showed that: a) supine spontaneous BRS did not differ between preflight and postflight, while parasympathetic modulation of HR variability tended to increase; and b) supine spontaneous BRS was higher at PF1 than PF (PF: 0.011 +/- 0.0014 ms x mmHg(-1), PF1: 0.015 +/- 0.0012 ms x mmHg(-1); p < 0.05) and parasympathetic modulation of HR variability (high frequency component) was higher at PF2 than PF (PF: 0.014 +/- 0.007, PF2: 0.039 +/- 0.009; p < 0.001). CONCLUSIONS: These findings may reflect a change in the sympathovagal balance during the second hour of recovery from repeated push-pull maneuvers.     

The effect of caffeine on the cardiovascular responses to head-up tilt

BACKGROUND: Both caffeine and orthostasis have known cardiovascular effects. The possible interaction between these factors remains unknown. This study aimed to determine the effect of caffeine consumption on cardiovascular responses to head-up tilt. METHODS: Sixteen subjects underwent three +75 degree head-up tilts: i) control, ii) acute, after a dose of 5 mg x kg(-1) body mass of caffeine or placebo, and iii) chronic, following 7 d of caffeine or placebo consumption at a daily dose of 5 mg x kg(-1) body mass. Heart rate (HR), systolic BP (SBP), diastolic BP (DBP), and mean arterial pressure (MAP) were measured using a Portapres BP monitor. RESULTS: The overall pattern of heart rate (HR) response in both caffeine and placebo groups showed a significant increase in HR after tilting for each tilt. Acute caffeine consumption significantly decreased resting HR (p < 0.05). After chronic consumption, resting HR was no longer significantly different. In the control condition, the overall pattern of response to tilt for SBP, DBP, and MAP showed no significant differences in either group. An acute dose of caffeine caused a significant fall (p < 0.05) in all BP variables in response to tilt. This effect was also seen after chronic caffeine consumption in SBP and MAP, but not in DBP. CONCLUSIONS: The results of this study indicate that both acute and chronic consumption of caffeine can lead to impaired cardiovascular function after exposure to an orthostatic challenge. This impaired function, reflected in a decreased resting HR and an inability to maintain MAP, is potentially due to impaired baroreflex function.     

“神舟”7号飞行前后呼吸和应激测试中航天员血流动力学反应(英文)

目的本研究旨在探明3 d航天飞行是否会导致航天员的心脏-压力反射功能及血流动力学参数发生变化。方法在飞行前14 d及返回后第2天,采用SEVE系统以非介入式的逐搏测量技术连续监测航天员做呼吸动作及应激测试时的心电、血压和呼吸信号。通过分析这些生理信号,对航天员自发性压力反射敏感性(SBRs)、心输出量(CO)、每搏量(SV)及总外周血管阻力(TPR)变化进行评价。结果飞行后,航天员的立位耐力评分轻微下降;在基础状态下,飞行导致SBRs和TPR下降,SV和CO升高。在做呼吸动作及应激测试中发现,航天飞行导致收缩压、舒张压、心率(HR)、SV及CO对应激的反应能力下降,而SBRs对应激的反应能力却没有受到影响。结论短期航天飞行导致了基础状态下航天员的SBRs和TPR下降,SV和CO升高,抑制了应激状态下心血管系统的调节功能。     

Left ventricular volumes and hemodynamic responses to postexercise ischemia in healthy humans

PURPOSE: The purpose of this study was to determine the cardiac mechanisms involved in cardiovascular adjustments during postexercise circulatory occlusion (OCCL). METHOD: Heart rate (HR), mean arterial pressure (MAP), left ventricular end-diastolic (EDV) and end-systolic volumes (ESV), stroke volume (SV), cardiac output (CO), and total peripheral vascular resistance (total peripheral resistance (TPR)) were assessed in nine healthy volunteers during rest and static exercise at 30% of maximum voluntary contraction followed by either OCCL for 3 min or non-OCCL in a randomized crossover protocol. RESULTS: During handgrip, HR (+20%; P < 0.001), CO (+11%; P = 0.003), MAP (+18%; P = 0.001), and TPR (+6%; P = 0.004) increased, SV (-8%; P = 0.001) and EDV (-5%; P < 0.001) decreased, while ESV did not change (P > 0.05). These responses were similar between conditions (P > 0.05). During OCCL, HR, SV, and CO returned to baseline, whereas MAP (+19%; P < 0.001) and TPR (+9%; P = 0.004) remained elevated. EDV (+12%; P < 0.001) and ESV (+23%; P < 0.001) increased in parallel above resting values. CONCLUSION: Activation of muscle metaboreceptors during OCCL increased MAP by elevating TPR. Despite the higher afterload and increased ESV, CO and SV were kept similar to resting values because EDV also increased, implying the involvement of the Frank-Starling mechanism.     

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.     

累加角度头高斜位下心率、血压、心率变异性与脑血流变化的特征

目的探讨累加角度头高斜位暴露下 ,正常人体血压、心率、脑血流及心率变异性 (HRV)变化特征 ,为建立飞行员晕厥检查的方法学提供生理依据。方法采用自行研制的多功能双向式医用倾斜床 ,结合先进的十二导联同步心电图描记方法和经颅多普勒脑血流成像技术进行累加角度 ( + 4 5°→ 60°→75°)头高斜位 (HUT)暴露下的心率、血压、HRV和脑血流速率的测量与分析。结果 1 )随着倾斜角度加大 ,暴露时程延长 ,HR逐渐增快 ,SBP逐渐下降 ,DBP逐渐升高 ,PP逐渐缩小 ,与暴露前比较 ,HR、PP和DBP相差非常显著 (P <0 .0 5 ) ;脑血流速率 (包括 :Vs、Vm、Vd)逐渐下降 ,无论与暴露前比 ,或倾斜角度之间比 ,差异十分显著 (P <0 .0 1 ) ;mRR和sdRR逐渐减小。 2 )生理指标与技术指标直线相关分析发现 :在 1min时 ,SBP、DBP、MAP、Vd、sdRR与倾斜角度呈明显正相关 (P <0 .0 1 ) ;在 2 0min时 ,HR和sdRR与倾斜角度呈明显正相关 (P <0 .0 1 ) ,与SBP、PP、Vs、mRR明显负相关 (P <0 .0 1 ) ;暴露时程与HR呈明显正相关 (P <0 .0 1 ) ,与SBP、Vm、Vd、mRR呈明显负相关 (P <0 .0 1 )。 3)生理指标间相关分析发现 :HR与SBP、Vs、Vm、Vd 呈明显负相关 (P <0 .0 1 ) ;SBP与Vd 和mRR呈明显正相关 (P <0 .0 1 ) ;Vs、Vm、Vd 与mRR和sdR     

Inspiratory CO2 increases orthostatic tolerance during repeated tilt.

INTRODUCTION: The partial pressure of end tidal CO2 (PetCO2) is known to decrease with head-up tilt. Decreases in arterial CO2 reduce cerebral blood flow (CBF) and may increase the incidence of presyncope. We measured cerebral and central cardiovascular responses to repeated tilt where: 1) PetCO2 was allowed to change with tilt (eucapnic): and 2) PetCO2 was clamped at supine levels (isocapnic). METHODS: In eight healthy subjects breath-by-breath measurements were made of ventilation (VE) and PetCO2 along with beat-by-beat measurements of blood pressure (BP), heart rate (HR) and middle cerebral artery mean flow velocities (MFV). Following 30-min in the supine position, a series of six 10-min 90 degrees head-up tilts were performed, with 30-s of supine between each. Presyncopal subjects were returned immediately to the supine position. RESULTS: Statistical comparisons were made between the supine, and the first and last minute of the first tilt. BP, HR responses were not different between the eu- and isocapnic conditions; however, by the end of the first tilt VE was significantly higher than supine. MFV and BP at brain level decreased and HR increased from supine to tilt. MFV was higher in the isocapnic compared with the eucapnic condition but decreased from the beginning to the end of the first tilt in both conditions (i.e., tilt #1: eucap. 49.4 to 46.7; isocap. 65.0 to 59.6 cm s(-1); p < 0.05) while the BP remained constant. Five subjects were presyncopal in the study. With isocapnic tilt, presyncopal time was not reduced but was extended in four of the five subjects (2.2, 5.5, 6.3 and 31 min) yet at presyncope the values for MFV, BP and HR were the same in both conditions. CONCLUSIONS: Inspiratory CO2 contributed to increased MFV at the beginning of tilt and increased orthostatic tolerance.     

咪达唑仑和丙泊酚全身麻醉药物诱导对高龄患者心功能的影响

目的探讨咪达唑仑与丙泊酚全身麻醉药物诱导对高龄患者心功能的影响。方法将2009年8月—2012年10月期间在我院接受非心脏手术的156例高龄患者采用数字表法随机分为观察组(78例)与对照组(78例),前者接受咪达唑仑全身麻醉,后者接受丙泊酚全身麻醉。分别在麻醉诱导前(T0)、麻醉诱导插管前1 min(T1)、麻醉诱导插管后2 min(T2)、麻醉诱导插管后5 min(T3)、麻醉诱导插管后10 min(T4)等5个时间点监测患者的心率(HR)、每搏输出量(SV)、每分输出量(CO)、平均动脉压(MAP)、外周血管阻力(SVR)、峰值速度(VpK)、净射血时间百分比(ET%)等指标。结果两组患者T0时HR、SV、CO、MAP、SVR、VpK、ET%相比差异无统计学意义(P>0.05)。与对应的T0相比,两组患者在T1～T4时的HR、SV、CO、MAP、SVR、VpK均显著下降(P<0.05),ET%则显著升高(P<0.05)。观察组患者在T1～T4时的HR、SV、CO、MAP、SVR、VpK均显著高于对照组,ET%则显著低于对照组(P<0.05)。结论与丙泊酚相比,咪达唑仑更适用于高龄患者手术过程中的全身麻醉药物诱导。