94 SYSTOLIC LEFT VENTRICULAR AND AORTIC BLOOD FLOW RE-Q4 SPONSE TO INCREASING SYSTEMIC VASCULAR RESISTANCE

Abstract

Classical indices of myocardial performance may be insensitive to changes in myocardial reserve when native afterload is reduced The objective of this study was to examine the response of left ventricular and regional aortic blood flow to changes in systemic vascular resistance(SVR) in a canine model using combined gated pulsed doppler echocardiography(GPDE) and a non-imaging cardiac probe(NICP). SVR was augmented by continuous methoxamine infusion and calculated by standard thermodilution techniques in 5 animals (3-5kg). Aortic blood flow was evaluated by GPDE interrogation of the thoracic aorta. Systolic aortic blood flow was described by the mean velocity and the frequency time integral partitioned into the first and latter two-thirds of systole. The left ventricular ejection rate and stroke volume were measured simultaneously by NICP. Increasing SVR resulted in a pansystolic reduction in the mean ejection rate of the left ventricle and mean systolic aortic flow velocity. A normal reciprocal relationship was present for the first and latter two-thirds of left ventricular and aortic systolic blood flow as measured by percent change of stroke volume. This baseline relationship persisted with increasing SVR. In conclusion, combined GPDE and NICP can provide an effective means to noninvasively evaluate left ventricular performance and regional aortic blood flow changes with augmentation of afterload.