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 P(O(2)) (Pa(O(2))) as high as 70-100 mmHg, corresponding to Hb-O(2) saturations from 90% to 95%, which indicates a moderate cardiovascular right to left (R-L) shunt. In hyperoxia (50% O(2)), we studied animals in: (1) aerated water combined with aerial hyperoxia, which increased Pa(O(2)) from 78+/-2 to 114+/-3 mmHg and (2) and aquatic hyperoxia (50% O(2)) combined room air, which gradually increased Pa(O(2)) from 75+/-4 mmHg to as much as 146+/-10 mmHg. Further, the hyperoxia (50%) depressed pulmonary ventilation from 58+/-13 to 5.5+/-3.0 mLBTPSkgh(-1), and Pa(CO(2)) increased from 20+/-2 to 31+/-4 mmHg, while pHa became reduced from 7.56+/-0.03 to 7.31+/-0.09. At the same time, venous P(O(2)) (Pv(O(2))) rose from 40.0+/-2.3 to 46.4+/-1.2 mmHg and, concomitantly, Pv(CO(2)) increased from 23.2+/-1.1 to 32.2+/-0.5 mmHg. R-L shunts were estimated to about 19%, which is moderate when compared to most amphibians.