INFLUENCE OF SLEEP ON SYSTEMIC AND CORONARY HEMODYNAMICS IN LAMBS

Experiments were done on seven lambs between the ages of 18 and 24 days to investigate the effects of sleep on systemic and coronary hemodynamics. Each lamb was anesthetized and instrumented for recordings of electrocorticogram, electro-oculogram and nuchal electromyograms, and for measurements of cardiac output and coronary blood flow as well as systemic arterial blood pressure and arterial-, mixed-venous- and coronary-sinus- hemoglobin oxygen saturations. No sooner than three days after surgery, measurements were made during periods of quiet wakefulness (QW), quiet sleep (QS) and active sleep (AS) at an ambient temperature of 25-degrees-C. Cardiac output and heart rate were decreased during AS compared to QW and QS. A significant increase in systemic vascular resistance during AS prevented more than a slight decrease in systemic arterial blood pressure. Coronary blood flow decreased during AS compared to QW and QS. Furthermore, myocardial work as estimated from the product of systolic blood pressure and heart rate decreased during AS compared to QW and QS as did myocardial oxygen consumption and myocardial oxygen transport. Transient hypertensive phases - defined as transient increases in mean blood pressure of greater than 15 mmHg above the mean blood pressure for a period of AS - occurred during eight of 13 periods of AS in four of the seven animals. These transient hypertensive phases were caused primarily by an increase in systemic vascular resistance; surprisingly, coronary vascular resistance also increased at this time when estimated myocardial work was increased. The possible consequences of this increase in coronary vascular resistance in the face of an increase in myocardial work during physiological conditions and during pathophysiological conditions of altered systemic and myocardial oxygen supply and demand are of interest and should be investigated.