RESPIRATORY PROPERTIES OF BLOOD AND PATTERN OF GAS EXCHANGE IN THE LUNGFISH

Abstract. Blood respiratory properties and gas exchange patterns have been studied in the lungfish Neoceratodus. O2- Hb dissociation curve reveals a high affinity for O2 (P50 of 11 mm Hg at PCO2 3.5 mm Hg). No Root effect but a pronounced Bohr effect was discernible. Temperature exerted only a minor influence on the affinity for O2. The CO2 dissociation curves conform to the shape observed in other classes of vertebrates and show a steep initial portion. The buffering capacity of the blood was low being 13.3 mMol/1/pH. An increased buffering power upon reduction of Hb was apparent. During rest in well oxygenated water, gill breathing prevailed entirely. Pulmonary arterial blood assumed to represent mixed arterial blood characteristically showed a Pco2 averaging 3.5 mm Hg. PaO2 was 40 mm Hg corresponding to an O2 saturation of 95 %. The pulmonary venous blood showed gas partial pressures in equilibrium with those in pulmonary arterial blood and air, documenting the minor importance of the lung as a gas exchanger during these conditions. When the fish was artificially exposed to air PaO2 diminished to 10-15 mm Hg with a concurrent increase in PaCO2 to 20 mm Hg in 30 min. While the lung performed well as an O2 absorber during air exposure it was totally inefficient in eliminating CO2. The data indicate that Neoceratodus is unfit to live out of water for any length of time