Doppler flow velocity measurement to assess changes in inotropy and afterload: a study in healthy dogs

Myocardial contractility and afterload are important factors for adequate circulation. To noninvasively assess changes in inotropy and afterload, ascending aortic blood flow was measured by continuous-wave Doppler echocardiography before and after the administration of an inotrope and a vasodilator in eight open chest dogs. Data were collected in the baseline, at three different doses of epinephrine (0.1, 0.5, and 1 microg/kg/min) and nitroprusside (1, 4, and 8 microg/kg/min) administration, and after a simultaneous infusion of both drugs in various combinations. Epinephrine infusion caused increases in peak velocity (PV), mean acceleration (MA), velocity time integral (VTI), and minute distance without a significant change in afterload. Acceleration time (AT) and ejection time (ET) showed a slight tendency to decrease with an increase in inotropy, but with no significance. Nitroprusside infusion produced dose-dependent decreases in blood pressure and index of systemic vascular resistance (ISVR), which was associated with increases in PV, MA, and minute distance, and with a decrease in AT. The combined infusion of nitroprusside and epinephrine, unless ISVR was elevated, produced synergistic effects on PV, MA, VTI, and minute distance. However, these Doppler parameters tended to diminish with an elevation in afterload. ISVR obtained during nitroprusside infusion had a better correlation with both PV and MA than with VTI or the Doppler time intervals. Our study suggests that Doppler measurement of aortic blood flow velocity and acceleration can be used for the noninvasive assessment of changes in inotropy and afterload.