Assessment of Afterload by Doppler Aortic Flow Velocity Measur ement

Sohn, Se Jung; Han, Jae Jin

Abstract

BACKGROUND: Afterload as well as myocardial contractil ity is an important factor for the adequacy of circulation after cardiac surgery . To noninvasively assess alterations in afterload, we evaluated the changes in aortic blood velocity waveform. MATERIAL AND METHOD: Ascending aortic blood flow was measured by continuous wave Doppler echocardiography befo re and after afterload manipulation in eight open-chest dogs. Nitroprusside was administered singly and simultaneously with epinephrine in various combinations. Left atrial pressure as an index of preload was maintained by saline administra tion. RESULT: The infusion of nitrop russide produced dose-dependent decreases in blood pressure and index of systemi c vascular resistance(ISVR) (all p<0.05 vs baseline), which was associated with increases in peak velocity(PV), mean acceleration(MA) and minute distance, and w ith a decrease in acceleration time(all p<0.05 vs baseline). ISVR obtained durin g nitroprusside infusion had a better correlation with both PV(r=-0.60, p=0.001) and MA(r=-0.52, p=0.003) than with velocity time integral(VTI) or the Doppler t ime intervals. The combined infusion of nitroprusside and epinephrine, unless IS VR was elevated, produced synergistic effects on PV, MA and VTI, but these Doppl er indexes tended to diminish with an elevation in afterload.
CONCLUSION
Doppler measuremen t of PV and MA in the ascending aorta may be used to noninvasively assess change s in afterload.