AORTIC PEAK FLOW VELOCITY AS AN INDEX OF MYOCARDIAL-CONTRACTILITY IN THE CONSCIOUS RAT

The present studies were conducted in conscious, instrumented rats to evaluate measurements of aortic peak flow velocity (PFV) as an index o f myocardial contractility. Because our previous studies had character ized/verified procedures to determine pressure-derived indices of cont ractile function in the anesthetized, ventilated, open-chest rat, we f irst correlated PFV with (a) maximum rate of left ventricular pressure development (max + dP/dt) and (b) a contractility index derived by di viding max + dP/dt by left ventricular pressure at max + dP/dt [(dP/dt )/P] in anesthetized rats (n = 5). The positive inotropic agent, isopr oterenol, given by bolus intravenous injection (0.2 mu g), significant ly and concurrently increased dP/dt, (dP/dt)/P, and PFV. The negative inotropic agent, propranolol, given by bolus intravenous injection (2 mg/kg), significantly and concurrently attenuated all of the above mea surements. When control, isoproterenol, and propranolol responses were used to calculate multivariate correlation coefficients among dP/dt, (dP/dt)/P, and PFV, r values ranged from 0.74 (PFV vs. dP/dt) to 0.84 (dP/dt) vs (dP/dt)/P) to 0.91 (PFV vs. (dP/dt)/P). A separate group of rats (n = 4) was surgically implanted with ascending aortic blood flo w sensors, carotid artery and jugular vein catheters. Intravenous isop roterenol (0.2 mu g, bolus) elicited increased cardiac (heart rate and cardiac output) and decreased peripheral vascular resistance (mean ar terial blood pressure) beta-adrenergic receptor agonist effects. Propr anolol (2 mg/kg, i.v. bolus) produced hemodynamic effects consistent w ith cardiovascular beta-adrenergic receptor blockade. Isoproterenol an d propranolol had directionally appropriate, and significant effects o n PFV in the conscious rat. When compared with PFV values under contro l conditions in the anesthetized rat, conscious rat values are approxi mately double those observed under anesthesia; however, the relative P FV responses to isoproterenol and propranolol were not affected. There fore, the present studies provide evidence that aortic PFV can be util ized as an estimate of heart contractile performance, i.e., myocardial contractility, in the conscious, instrumented rat.