Esophageal Doppler monitoring: Effects of preload, afterload, and contractility on peak velocity

S87 INTRODUCTION: We have recently demonstrated that Esophageal Doppler Monitor (EDM) measurements of cardiac output (COe) and preload (FTc) correlate with aortic flow probe and end-diastolic area (EDA) measurements respectively. [1] EDM also measures the maximal or peak velocity (PV) of blood ejected from the heart during systole. This study was designed to evaluate the influences of preload, afterload, and contractility on EDM-derived peak velocity (PV). METHODS: Following IRB approval and informed consent, we studied 34 patients undergoing surgery with cardiopulmonary bypass (CPB). Hemodynamic data were collected using an aortic flow probe, an esophageal doppler monitor (Deltex Medical, Irving, TX), a transesophageal echocardiography probe (TEE) and a pulmonary artery catheter (PAC). Data were collected at baseline, following each of two 300 mL volume challenges pre-CPB, and at 2 timepoints (5[prime] and 15[prime]) post-CPB. The aortic flow probe was our "gold standard" for cardiac output (CO), and the TEE end diastolic area (EDA) was used to assess preload. A contractility index was determined from Frank-Starling Response (FSR) curves for each patient by plotting CO vs. EDA for the three pre-CPB timepoints. [2] The slope of the FSR curves was used as an index of contractility. The afterload, or systemic vascular resistance (SVR), was calculated using CO (flow probe), mean systemic blood pressure and CVP (PAC). Standard linear regression analysis was performed for each variable with p < 0.05 considered significant. RESULTS: The EDM-derived PV directly correlated with the CO from the aortic flow probe (r = 0.585; p < 0.0001). The PV did not correlate with either preload, measured by EDV (Figure 1) or our contractility index (r = -0.3923, p = 0.1329). The PV had a strong inverse correlation with SVR (Figure 2).Figure 1: PV vs. End-Diastolic AreaFigure 2: PV vs. SVRCONCLUSION: These data suggest that peak velocity is most influenced by the afterload conditions imposed on the ejecting ventricle and thus may serve as an index of SVR. This correlation seems reasonable in that one would expect the velocity of blood flow to be higher when blood is ejected into a lower resistance system. This index, if validated, may provide information about SVR independent of other more invasive monitors.