Nuckols M L
Department of Naval Architecture, Ocean and Marine Engineering, U.S. Naval Academy, Annapolis, MD 21402, USA.
Life Support Biosph Sci. 1996 Winter;2(3-4):117-24.
Closed circuit rebreathers used by divers recirculate the respiratory gases through a scrubber to remove exhaled carbon dioxide. For systems used in deep diving applications, oxygen is mixed with a diluent gas to maintain a preset partial pressure of oxygen (PO2) that is within the physiologically acceptable limits for the diver. These systems accurately maintain the oxygen set point while the diver swims at constant depth. However, as a diver increases depth, the gas volume in his lungs and his underwater breathing apparatus (UBA) will be compressed. To avoid damage, a diluent gas, a breathable mixture of oxygen and some inert component such as nitrogen or helium, must be supplied to the breathing circuit to maintain constant volume. Because the composition of this diluent will normally be different from the desired circuit breathing mixture, it is important that the addition of this diluent will not have harmful physiological effects on the diver. The effects of UBA circuit volume, diver descent rate, oxygen consumption rate, and diluent composition on the oxygen partial pressures within the breathing circuit during descent are investigated in this article. Exposures to oxygen partial pressures in excess of 2.0 atmospheres absolute (ata) are shown to be possible during dives when using closed circuit UBAs with present PO2 levels of 0.7 ata. These elevated oxygen exposures are shown to diminish when a diver reaches depth, but could last in excess of 18 min during a dive to 200 ft of seawater.
潜水员使用的闭路循环呼吸器通过洗涤器使呼吸气体再循环，以去除呼出的二氧化碳。对于深潜应用中使用的系统，氧气与稀释气体混合，以维持预设的氧分压（PO2），该氧分压在潜水员生理可接受的限度内。当潜水员在恒定深度游泳时，这些系统能精确维持氧气设定点。然而，随着潜水员深度增加，其肺部和水下呼吸装置（UBA）中的气体体积会被压缩。为避免损坏，必须向呼吸回路供应稀释气体，即氧气与一些惰性成分（如氮气或氦气）的可呼吸混合物，以维持恒定体积。由于这种稀释剂的成分通常与所需的回路呼吸混合物不同，因此添加这种稀释剂不会对潜水员产生有害的生理影响非常重要。本文研究了UBA回路体积、潜水员下降速率、氧气消耗速率和稀释剂成分对下降过程中呼吸回路内氧分压的影响。研究表明，当使用当前PO2水平为0.7绝对大气压（ata）的闭路UBA时，潜水过程中氧分压可能会超过2.0绝对大气压（ata）。当潜水员到达一定深度时，这些升高的氧气暴露情况会减弱，但在潜入200英尺海水深度的潜水过程中，可能会持续超过18分钟。
