21天头低位卧床期间脑血流的变化及其与立位耐力的关系

Changes of human cerebral blood flow during 21 days -6° head down tilt bed rest and the relationship with orthostatic tolerance

目的建立３周头低位倾斜（ＨＤＴ）－６°人体实验模型，观察卧床模拟失重期间脑血流变化及其与立位耐力的关系。方法６名健康男性志愿者进行了２１天ＨＤＴ－６°卧床试验。受试者年龄２３．８±６．１岁。ＨＤＴ前、ＨＤＴ第１０天及卧床结束时进行了３次立位耐力检查。ＨＤＴ前、ＨＤＴ第３天、第１０天、第２１天用ＫＹＥＮＧ－Ⅰ导纳式双侧脑血流自动检测仪测量脑血流量。结果卧床第１０天和卧床结束时，受试者立位耐力平均立位时间比卧床前显著降低（Ｐ＜０．０５）。卧床期间，左右侧大脑血流主峰高度和Ⅰ相面积较卧床前显著降低（Ｐ＜０．０５或Ｐ＜０．０１）；卧床第３天和第２１天的左侧大脑阻力指数较卧床前显著增高（Ｐ＜０．０５），卧床第１０天、第２１天的左侧大脑血液流入时间较卧床前显著延长（Ｐ＜０．０５），卧床期间左侧大脑血液流入速度比卧床前显著降低（Ｐ＜０．０５或Ｐ＜０．０１）；卧床期间受试者左侧大脑Ⅰ相面积、左侧主峰高度、左侧大脑血液流入速度均和立位耐力时间呈显著正相关（Ｐ＜０．０１或Ｐ＜０．０５）。结论２１天头低位卧床使立位耐力显著降低；ＨＤＴ卧床期间，脑血管阻力增加，脑血流量减少，可能是导致立位耐力降低的原因之一。

Objective To investigate the change of human cerebral blood flow(CBF) and its relation to orthostatic tolerance during 21 days of -6° head down tilt (HDT) bed rest. Methods Twenty one days -6° head down tilt bed rest were used to simulate weightlessness. Subjects were 6 healthy male, aged 23.8±6.1. CBF and cerebral vascular resistance (CVR) were measured by rheoencephalogram in day 1,3,10,21 of HDT. Head up tilt(HUT) +75° 20 min orthostatic tolerance tests were done on day 1,10, and 21 of HDT. Results During HUT +75° 20 min orthostatic tolerance test on day 10 and 21 of HDT, the average tolerance time were 13.06±4.91 min and 12.99±4.01 min respectively, both of them were lower than that of the pre HDT 20 min( P <0.05). Cerebral Ⅰ quadrant area and cerebral Δy wave crest height during HDT were significantly less than those of pre HDT ( P <0.05 or P <0.01). On day 3 and 21 of HDT left cerebral resistance index were significantly higher than those of pre HDT ( P <0.05). On day 10 and 21 of HDT left cerebral inrush time were longer than that of pre HDT ( P <0.05). Left cerebral inrush velocity during HDT were significantly lower than that of pre HDT ( P <0.05 or P <0.01). Left cerebral Ⅰ quadrant area, left cerebral Δy wave crest height and left cerebral inrush velocity were positively correlated with orthostatic tolerance( P <0.01 or 0.05). Conclusions The current study clearly shows that 21 d HDT bed rest may induce orthostatic intolerance. During 21 d HDT, cerebral blood flow become lower and cerebral vascular resistance higher than that before HDT. The changes of human CBF and CVR may be the reason of orthostatic intolerance.