Ventilation, cardiac output and blood respiratory parameters in the carp, Cyprinus carpio, during hyperoxia

The specific ventilatory flow rate (Vw), cardiac output (Vb) and blood respiratory parameters were determined in the carp (Cyprinus carpio) during hyperoxia. Vb changed little during moderate hyperoxia (240-330 Torr) but slightly increased during extreme hyperoxia (430-490 Torr) while Vw decreased. This means that the ventilation-perfusion ratio considerably decreased during hyperoxia. The CO2 tension (PCO2) of blood rose, causing a corresponding decrease in blood pH. The O2 tensions (PO2) of arterial and mixed venous blood increased but remained low (about 40 Torr and 15 Torr, respectively). Consequently, the hemoglobin in the arterial and mixed venous blood was not saturated with O2 (about 80 and 55%, respectively) even during extreme hyperoxia. This indicates that most of the O2 which is consumed by the fish remains transported in a combined form during hyperoxia. During hyperoxia, when the decreased Vw was artificially elevated to the normoxic level, the PO2 of arterial blood (PaO2) rose further and the PCO2 and pH of arterial blood became restored to the normoxic levels. This suggests that the CO2 retention and the depressed increase in PaO2 during hyperoxia are mainly due to the decrease in Vw in the carp.