THE EFFECT OF PROLONGED HYPEROXIA ON THE CARDIOVASCULAR SYSTEM OF ANAESTHETIZED DOGS

Six dogs have been anaesthetized with trichloroethylene and ventilated with 100% oxygen at 2 atmospheres absolute for 8 hours followed by a 2-hour period of ventilation with 15% oxygen/85% nitrogen. A fall in cardiac output of approximately 30% occurred within 4 hours of commencing 100% oxygen ventilation, accompanied by a fall in left ventricular dp/dt(max), a 70% increase in systemic vascular resistance and a rise in left ventricular end-diastolic pressure. On resumption of oxygen/nitrogen at the end of 8 hours, there was a rapid restoration of all parameters towards the initial values. It would appear that the changes in cardiac output and vascular resistance with oxygen are not progressive within an 8-hour period and that myocardial oxygen toxicity is reversible in this time.