Fuster J F, Pagés T, Palacios L
Departamento de Bioquímica y Fisiología, Universidad de Barcelona, Spain.
Physiol Zool. 1997 Jan-Feb;70(1):7-18. doi: 10.1086/639531.
Oxygen stores available for aerobic diving were studied in the freshwater turtle (Mauremys caspica leprosa) at three constant body temperatures (15 degrees, 25 degrees, and 35 degrees C) and during the thermal transient (30 degrees-15 degrees C) induced by immersion in cold water. The term "aerobic dive limit" has been defined as the maximal duration of the dive before lactate increases. This increase occurs when a critical PO2 value is reached, and it is well characterized at lung level by a sharp increase in the lung apnoeic respiratory quotient. Kinetic analysis of lung gas composition during forced dives at fixed body temperature shows that critical PO2 values rise with temperature and that the postventilatory PO2 at the beginning of a dive decreases, so that the two temperature-dependent factors lead to a significant decrease with temperature in the lung O2 stores available for aerobic diving. During dives with transient body cooling, a natural condition in M. caspica leprosa, temperature equilibration occurs fast enough to expand aerobic scope by bearing the critical PO2 to the same value obtained at a fixed temperature of 15 degrees C. These dives are characterized by reversed CO2 transport (from lung to tissues) and therefore by negative values of the lung respiratory quotient; a decrease in temperature increases CO2 capacitance of tissues, resulting in a fall in PCO2 at constant CO2 content. Because this does not occur in the gas phase, PCO2 difference can lead to diffusion in the direction opposite from normal. This pattern may favour lung-to-tissue O2 transfer, through the Bohr effect. Therefore, the aerobic dive limit is reduced at high temperature not only through a metabolic rate effect but also through a marked decrease in the available O2 stores; fast body cooling (30 degrees-15 degrees C) associated with immersion in cold water extends the O2 stores available for aerobic diving to a level similar to that of immersions at constant body temperatures that are in equilibrium with water temperature.
在三种恒定体温（15摄氏度、25摄氏度和35摄氏度）下以及在冷水浸泡引起的热瞬变（30摄氏度 - 15摄氏度）期间，对淡水龟（地中海池龟麻风亚种）可用于有氧潜水的氧气储备进行了研究。“有氧潜水极限”一词被定义为乳酸增加前潜水的最大持续时间。当达到临界氧分压值时会发生这种增加，并且在肺部水平通过肺窒息呼吸商的急剧增加得到很好的表征。在固定体温下强制潜水期间对肺气体成分的动力学分析表明，临界氧分压值随温度升高，并且潜水开始时的通气后氧分压降低，因此这两个与温度相关的因素导致可用于有氧潜水的肺氧储备随温度显著降低。在身体短暂冷却的潜水过程中，这是地中海池龟麻风亚种的自然状态，温度平衡发生得足够快，通过将临界氧分压维持在固定温度15摄氏度时获得的相同值来扩大有氧范围。这些潜水的特征是二氧化碳逆向运输（从肺到组织），因此肺呼吸商为负值；温度降低会增加组织的二氧化碳容量，导致在二氧化碳含量恒定的情况下二氧化碳分压下降。因为在气相中不会发生这种情况,二氧化碳分压差异会导致扩散方向与正常情况相反。这种模式可能通过波尔效应有利于肺到组织的氧气转移。因此，有氧潜水极限在高温下降低不仅是由于代谢率的影响，还由于可用氧气储备的显著减少；与冷水浸泡相关的快速身体冷却（30摄氏度 - 15摄氏度）将可用于有氧潜水的氧气储备扩展到与在与水温平衡的恒定体温下浸泡时相似的水平。
