Systemic hemodynamics during hyperbaric oxygen exposure in rats

The effect of 1-5 bar O2 on left ventricular pressure (LVP), maximal velocity of LVP rise (+dP/dt) and fall (-dP/dt), systolic arterial pressure (APsys), pulse pressure (delta AP), heart rate (HR), and respiratory frequency (RF) was studied in anesthetized and conscious rats. At 1 bar O2, all blood pressure parameters increased significantly (9-56%) in both groups of rats, while RF fell (11-12%). HR fell only in conscious rats, while arrhythmias occurred in both groups. Compression to 5 bar O2 induced a significant further increase in all blood pressure parameters. HR fell further in the conscious rats. Arrhythmias were observed in increasing number during compression and at 5 bar O2. Elevation in estimated oxygen-consumption of the heart was found both during compression and at 5 bar O2. We conclude that O2 exposure markedly stimulates the myocardium by elevating the LVP, +dP/dt, and -dP/dt, thus elevating APsys and delta AP. Arrhythmias developed in both groups, while bradycardia occurred only in conscious rats.