Pulmonary Oxygen Diffusing Capacity of the South American LungfishLepidosiren paradoxa: Physiological Values by the Bohr Method

Lungfish (Dipnoi) may represent the sister group to all land vertebrates and are therefore important for reconstructing the conquest of land by tetrapods. We determined venous and arterial blood gases, pulmonary O(2) uptake, and the form of the hemoglobin-O(2) dissociation curves in the South American lungfish Lepidosiren paradoxa. Measurements were performed at 25 degrees and 35 degrees C. Based on this information, we calculated its pulmonary O(2) diffusing capacity (D(L)O(2)), using the Bohr integration procedure. D(L)O(2) increased with temperature to reach about 0.04 mL stpd kg(-1) min(-1) mmHg(-1) at 35 degrees C. This value represents about 40% of the morphometric diffusing capacity and is similar to physiological values in some amphibians and reptiles.