Myocardial blood flow in the diving seal.

Grey seals exhibit a marked drop in heart rate, a slight decrease in ventricular contractility, and an essentially unchanged stroke volume upon diving. In the present study, we have demonstrated that the resulting drop in cardiac output is associated with a 90% reduction of coronary blood flow. Such reduction of myocardial blood flow takes place despite a significant increase in effective coronary driving pressure, and is indicative of a 800% increase in coronary vascular resistance. This means that the circulatory adjustments displayed by the diving seal (i.e. a reduction of the workload on the heart) are so effective that myocardial blood flow can be reduced to 10% of the pre-dive value without loss of cardiac function and blood pressure. It is suggested that even partial simulation of such a circulatory state might be a successful approach in the treatment of ischemic injuries in the heart of man.