Autoregulation of myocardial blood flow under controlled hypotension in the dog

The autoregulation of myocardial blood flow was studied under: (a) haemorrhagic hypotension (mean pressure decrease 40% from baseline); (b) drug-induced hypotension with sodium nitroprusside or trimetaphan (40% pressure decrease); (c) drug-induced hypotension (40% pressure decrease) after moderate blood loss of 20%. Dogs were used in experiments under general anaesthesia with sodium thiopentone and artificially ventilated with N2O/O2 (70%, 30%) and pancuronium. Under haemorrhagic hypotension, the flow was pressure-dependent from the beginning. During nitroprusside hypotension, there was autoregulation of coronary flow to the level of mean pressure decrease 30% from control. Under trimetaphan, a constant flow persisted to the level of mean pressure decrease 20% from the baseline. Identical changes were seen during drug-induced hypotension after moderate blood loss (20%). Central venous pressure, cardiac output, left ventricular stroke work and minute work changes are demonstrated. Blood gas data pH, PO2, PCO2 in the aortic and coronary sinus under drug-induced hypotension are compared with control groups. There is a level of autoregulation of myocardial blood flow under hypotension. This level can be unfavourably changed in cases with hypertension and coronary obstructive diseases.