21d头低位卧床期间心功能的变化及最后一周下体负压锻炼的影响

目的 观察21d头低位卧床期间被试者心功能的变化及最后一周下体负压锻炼（LBNP）的影响。方法 12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组在卧床最后一周，每天进行1h、－4．0kPa的下体负压锻炼。测量心脏收缩和泵血功能等指标。结果 在卧床期间，两组的心输出量、心指数及每搏输出量较卧床前均显著降低或有降低趋势，射血前期（PEP）均显著延长，总外周阻力、等容收缩时间／左室射血时间（LVET）、PEP／LVET均显著升高而有升高趋势，起床后第2天基本恢复。LBNP组PEP和PEP／LVET在第21天及起床后第2天较对照组显著升高。结论 21d头低位卧床可引起心脏泵血和收缩功能显著降低；在21d头低位卧床的最后一周进行下体负压锻炼，不能有效对抗头低位卧床模拟失重引起的心脏泵血和收缩功能的降低，但对提高立位耐力有利。

Changes of Cardiac Function during 21 d Head-down Tilt Bed Rest and the Effect of Lower Body Negative Pressure in the Last Week

Objective: To investigate the change of cardiac function during 21 d head-down tilt (HDT) bed rest and the effect of lower body negative pressure (LBNP) in the last week in human. Method: 12 healthy male served as subjects which were randomly divided into control and LBNP groups, with 6 in each group. All of them were exposed to -6 degrees HDT for 21 d. The LBNP group received -4.0 kPa LBNP training 1 h/d in the last week of the test. The cardiac pump function and cardiac systole function were measured before, during and after HDT. Result: Cardiac output, cardiac index and stroke volume decreased significantly, whereas total peripheral resistance, pre-ejection period (PEP), isovolumetric contraction time/left ventricular ejection time (LVET) and PEP/LVET increased significantly during HDT in both control and LBNP groups, compared to pre-HDT values, and they returned to normal level on day 2 post HDT. PEP and PEP/LVET in LBNP group were significantly higher than those in control group on day 21 of HDT and day 2 post HDT. Conclusion: The reduction of cardiac pump function and cardiac systole function induced by 21 d HDT could not be prevented by LBNP training in the last week of 21 d HDT.