Wood E H
Mayo Medical School, Rochester, MN 55905.
Aviat Space Environ Med. 1990 Apr;61(4):366-73.
The G tolerance of internal organs depends on how closely force environments in body cavities mimic an aqueous system. Hydrostatic gradients in peritoneal and pericardial cavities sustain venous return and uniform transmyocardial pressures so that normotensive arterial pressures at heart level persist during initial (about 7 s) sudden sustained exposures to Gz acceleration followed by a compensatory baroreceptor-mediated hypertension. Further, cerebrospinal fluid hydrostatics-mediated negative intracranial pressures sustain cerebral perfusion and cognition in spite of Gz-produced zero or near zero systolic pressures at head level. Differences in the approximately 0 and 1.0 specific gravities of intra-alveolar gases and surrounding blood and tissues, respectively, render lung anatomy and functions highly susceptible to the force environment. Hydrostatic gradients in dependent regions, simultaneously with small gradients in superior regions, appear to be nature's method for decreasing force environment-mediated regional ventilation and perfusion inequalities within the thorax.
内脏的重力耐受性取决于体腔内的力环境与水性系统的相似程度。腹膜腔和心包腔内的流体静力梯度维持静脉回流和均匀的跨心肌压力，使得在最初（约7秒）突然持续暴露于Gz加速度期间，心脏水平的正常血压动脉压得以维持，随后出现压力感受器介导的代偿性高血压。此外，尽管在头部水平Gz产生的收缩压为零或接近零，但脑脊液静力学介导的颅内负压仍能维持脑灌注和认知功能。肺泡内气体与周围血液和组织的比重分别约为0和1.0，这使得肺部解剖结构和功能对力环境高度敏感。下垂区域的流体静力梯度与上部区域的小梯度同时存在，似乎是自然界减少力环境介导的胸部区域通气和灌注不均的方式。
