坐位下体负压对人体心脑血管系统的影响

Effects of lower body negative pressure in upright seated position on human cardiovascular system and cerebrovascular system

目的探讨坐位下体负压对人体心脑血管系统的影响。方法15名健康青年男性在-4.00 kPa、-6.67 kPa坐位下体负压下,分别测试负压前、负压暴露0.5、1、2、3、4、5 m in和卸压后1、3、5 m in的大脑中动脉的搏动指数(PI)、阻力指数(R I)、血流速度(VMCA),心率(HR),血氧饱和度(SaO2),血压(BP)及主观症状和客观体征。结果在-4.00 kPa下体负压作用下,PI、R I、BP、SaO2无明显改变,VMCA在负压作用4、5 m in时减慢(P<0.05);HR在负压作用3、4、5 m in时增快(P<0.05)。在-6.67 kPa下体负压作用下,PI、R I在负压作用4、5 m in时增大(P<0.05);VMCA在负压作用2、3 m in时显著减慢(P<0.05),在4、5 m in时非常显著减慢(P<0.01),卸压后1 m in尚未恢复(P<0.05),随后恢复至对照水平;负压作用各时间点HR均显著增快(P<0.01);SaO2在负压暴露5 m in时显著下降(P<0.05);收缩压与负压前无明显变化,舒张压显著升高(P<0.05)。结论坐位下体负压造成血液在下肢淤积,搏动指数和阻力指数升高,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。

AIM To investigate the effects of lower body negative pressure （LBNP） in the upright seated position on the human cardiovascular system and cerebrovascular system METHODS Fifteen healthy males were included as subjects. The pulsatility index （PI）, resistance index （RI）, blood flow velocity in middle cerebral （ VMCA ）, pulse rate, blood oxygen saturation （ SaO2 ） and blood pressure （BP） of middie cerebral artery with their subjective symptoms and objective physical signs were measured at 0.5,1 , 2, 3, 4 and 5 min during LBNP and 1,3 and 5 min after - 4.00 kPa and - 6.67 kPa LBNP respectively in upright seated position. RESULTS Under - 4.00 kPa LBNP, VMCA slowed down at 4 and 5 min during LBNP （ P 〈 0.05 ） and pulse rate speeded up at 3,4 and 5 min during LBNP （ P 〈 0.05 ）. There were no significant changes of PI, RI, BP and SaO2. Under - 6.67 kPa LBNP, PI and RI augmented at 4 and 5 rain during LBNP （ P 〈 0.05 ）. VMCA slowed down at 2 and 3 min during LBNP （ P 〈 0.05 ）, and at 4 to 5 min VMCA decelerated more significantly during LBNP （P 〈0.01 ）. At 1 min after the release of LBNP, VMCA did not recover （ P 〈 0.05 ） , after which it recovered to control level. The pulse rates significantly increased during LBNP at every time point （ P 〈 0.01 ） and SaO2 decreased move obviously at 5 min during LBNP （ P 〈 0.01 ）. Systolic pressure had no great change but diastolic pressure notably stepped up during LBNP （ P 〈 0.05 ）. CONCLUSION LBNP causes blood to be silted up in lower body so that PI and RI increase while VMCA decreases, thus causing loss of brain blood volume. The resuits of this experiment provide some experimental data for the diagnosis of presyncope syndrome and orthostatic intolerance.