Blood gases and cardiovascular shunt in the South American lungfish (Lepidosiren paradoxa) during normoxia and hyperoxia

The South American lungfish (Lepidosiren paradoxa  ) has an arterial PO2PO2 (PaO2PaO2) as high as 70–100 mm Hg, corresponding to Hb–O2 saturations from 90% to 95%, which indicates a moderate cardiovascular right to left (R–L) shunt. In hyperoxia (50% O2), we studied animals in: (1) aerated water combined with aerial hyperoxia, which increased PaO2PaO2 from 78 ± 2 to 114 ± 3 mm Hg and (2) and aquatic hyperoxia (50% O2) combined room air, which gradually increased PaO2PaO2 from 75 ± 4 mm Hg to as much as 146 ± 10 mm Hg. Further, the hyperoxia (50%) depressed pulmonary ventilation from 58 ± 13 to 5.5 ± 3.0 mL BTPS kg h−1, and PaCO2PaCO2 increased from 20 ± 2 to 31 ± 4 mm Hg, while pHa became reduced from 7.56 ± 0.03 to 7.31 ± 0.09. At the same time, venous PO2PO2 (PvO2PvO2) rose from 40.0 ± 2.3 to 46.4 ± 1.2 mm Hg and, concomitantly, PvCO2PvCO2 increased from 23.2 ± 1.1 to 32.2 ± 0.5 mm Hg. R–L shunts were estimated to about 19%, which is moderate when compared to most amphibians.