Rt. Dowell et Aa. Houdi, AORTIC PEAK FLOW VELOCITY AS AN INDEX OF MYOCARDIAL-CONTRACTILITY IN THE CONSCIOUS RAT, Methods and findings in experimental and clinical pharmacology, 19(8), 1997, pp. 533-539
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.