Glass M L, Soncini R
Departamento de Fisiologia, Universidade de São Paulo, Brasil.
Braz J Med Biol Res. 1995 Nov-Dec;28(11-12):1161-6.
Extensive literature reports a negative delta pHa/delta t in ectothermic vertebrates, but data are scarce as to its consequences for O2 transport. In reptiles, the negative delta pHa/delta t results from an elevated lung gas PCO2 (PACO2) at higher temperatures, implying a corresponding fall of PAO2. In parallel, arterial PO2 rises with temperature, due to a combination of central vascular shunt and decreasing Hb.O2 affinity. As a result, the PO2 gradient between lung gas and blood (PA-aO2) becomes reduced at higher temperatures. In amphibians, the negative delta pHa/delta t results from combined cutaneous and pulmonary CO2 elimination. We propose that this leads to a rather temperature-independent lung gas PO2. Moreover, our calculations suggest that resting reptiles and amphibians maintain a relatively large PA-aO2 also at high temperatures. The negative delta pHa/delta t in teleost fish is generally considered to be a result of modulated plasma [HCO3-]. Recent data from our laboratory suggest that acute pH adjustments at high temperatures may involve alterations of PaCO2 through gill ventilation, leading to a decrease of PaO2 with rising temperature.
大量文献报道变温脊椎动物中存在负的ΔpHa/Δt，但关于其对氧气运输的影响的数据却很稀少。在爬行动物中，负的ΔpHa/Δt是由于较高温度下肺气体PCO2（PACO2）升高导致的，这意味着PAO2相应下降。与此同时，由于中央血管分流和血红蛋白 - 氧亲和力降低的共同作用，动脉血氧分压随温度升高而升高。结果，在较高温度下肺气体与血液之间的PO2梯度（PA - aO2）减小。在两栖动物中，负的ΔpHa/Δt是皮肤和肺共同排出二氧化碳的结果。我们认为这导致肺气体PO2相对不依赖于温度。此外，我们的计算表明，静止的爬行动物和两栖动物在高温下也能维持相对较大的PA - aO2。硬骨鱼类中的负ΔpHa/Δt通常被认为是血浆[HCO3-]调节的结果。我们实验室最近的数据表明，高温下的急性pH调节可能涉及通过鳃通气改变PaCO2，导致PaO2随温度升高而降低。
