Mechanisms of Right Ventricular Oxygen Supply/Demand Balance in the Concious Dog

Abstract

Hart, Bradley Joe. Mechanisms of Right Ventricular Oxygen Supply/Demand Balance in the Conscious Dog Doctor of Philosophy (Biomedical Sciences), August,2000, 119 pp, 4 tables, 13 figures, references, 79 titles. No data exist in the literature describing the myocardial oxygen supply/demand relationship of the right ventricle in a conscious, anaesthetized animal. A novel technique developed in our laboratory enables us to collect right ventricular (RV) venous blood samples from conscious dogs to determine RV myocardial oxygen consumption (MVO2). RV oxygen supply/demand balance was examined in conscious dogs, chronically instrumented to measure right coronary blood flow (RCBF), segmental shortening (%SS) and RV pressure (RVP) during increases and decreases in RV myocardial oxygen demand. Right ventricular MVO2 and O2 extraction (O2E2) were determined; RCBF, RVP, dP/dt, and %SS were recorded concomitantly. Acute increases in RV MVO2 were accomplished by atrial pacing (200 beats/min), increasing RV afterload by 65%, infusion of isoproterenol (0.1 μg/kg/min, i.v.), and by conducting a submaximal exercise routine (70-75% of maximum VO2). An acute decrease in RV MVO2 was created by propranolol administration (1 mg bolus, i.c.). During acute increases in RV MVO2, the extraction reserve is utilized primarily; flow is not affected in the absence of direct vasodilatory effects of the intervention. A decrease in RV oxygen demand is associated with a further increase in the RV extraction reserve. Since RV O2E increases linearly with increases in RV MVO2, these data show that changes in RV venous O2 tension can occur with little or no change in RCBF. LC resistance is very sensitive to alterations in LC venous pO2; therefore, there appear to be significant differences between the left and right ventricles concerning the matching of oxygen supply with myocardial oxygen demand.