Van Liew H D, Burkard M E
Department of Physiology, University of Buffalo, SUNY 14214.
Aviat Space Environ Med. 1995 Jan;66(1):50-5.
To gain insight into the special features of bubbles that may form in aviators and astronauts, we simulated the growth and decay of bubbles in two hypobaric decompressions and a hyperbaric one, all with the same tissue ratio (TR), where TR is defined as tissue PN2 before decompression divided by barometric pressure after. We used an equation system which is solved by numerical methods and accounts for simultaneous diffusion of any number of gases as well as other major determinants of bubble growth and absorption. We also considered two extremes of the number of bubbles which form per unit of tissue.
A) Because physiological mechanisms keep the partial pressures of the "metabolic" gases (O2, CO2, and H2O) nearly constant over a range of hypobaric pressures, their fractions in bubbles are inversely proportional to pressure and their large volumes at low pressure add to bubble size. B) In addition, the large fractions facilitate the entry of N2 into bubbles, and when bubble density is low, enhance an autocatalytic feedback on bubble growth due to increasing surface area. C) The TR is not closely related to bubble size; that is when two different decompressions have the same TR, metabolic gases cause bubbles to grow larger at lower hypobaric pressures. We conclude that the constancy of partial pressures of metabolic gases, unimportant in hyperbaric decompressions, affects bubble size in hypobaric decompressions in inverse relation to the exposure pressure.
为深入了解可能在飞行员和宇航员体内形成的气泡的特殊特征，我们模拟了两次低压减压和一次高压减压过程中气泡的生长和衰减，所有过程的组织比率（TR）相同，其中TR定义为减压前组织中的氮气分压除以减压后的气压。我们使用了一个通过数值方法求解的方程组，该方程组考虑了任意数量气体的同时扩散以及气泡生长和吸收的其他主要决定因素。我们还考虑了每单位组织中形成的气泡数量的两个极端情况。
A）由于生理机制使“代谢”气体（氧气、二氧化碳和水蒸气）的分压在一定范围的低压压力下几乎保持恒定，它们在气泡中的比例与压力成反比，并且它们在低压下的大体积会增加气泡大小。B）此外，这些大比例有助于氮气进入气泡，并且当气泡密度较低时，由于表面积增加，会增强对气泡生长的自催化反馈。C）TR与气泡大小没有密切关系；也就是说，当两次不同的减压具有相同的TR时，代谢气体会使气泡在较低的低压压力下生长得更大。我们得出结论，代谢气体分压的恒定性在高压减压中不重要，但在低压减压中与暴露压力成反比地影响气泡大小。
