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Background: The aim of our study was to quantitatively compare the changes and correlations between pulmonary venous flow variables and mean left atrial pressure (mLAP) under different loading conditions in animals with chronic mitral regurgitation (MR) and without MR., Methods: A total of 85 hemodynamic conditions were studied in 22 sheep, 12 without MR as control (NO-MR group) and 10 with MR (MR group). We obtained pulmonary venous flow systolic velocity (Sv) and diastolic velocity (Dv), Sv and Dv time integrals, their ratios (Sv/Dv and Sv/Dv time integral), mLAP, left ventricular end-diastolic pressure, and MR stroke volume. We also measured left atrial a, x, v, and y pressures and calculated the difference between v and y pressures., Results: Average MR stroke volume was 10.6 +/- 4.3 mL/beat. There were good correlations between Sv (r = -0.64 and r = -0.59, P <.01), Sv/Dv (r = -0.62 and r = -0.74, P <.01), and mLAP in the MR and NO-MR groups, respectively. Correlations were also observed between Dv time integral (r = 0.61 and r = 0.57, P <.01) and left ventricular end-diastolic pressure in the MR and NO-MR groups. In velocity variables, Sv (r = -0.79, P <.001) was the best predictor of mLAP in both groups. The sensitivity and specificity of Sv = 0 in predicting mLAP 15 mm Hg or greater were 86% and 85%, respectively., Conclusion: Pulmonary venous flow variables correlated well with mLAP under altered loading conditions in the MR and NO-MR groups. They may be applied clinically as substitutes for invasively acquired indexes of mLAP to assess left atrial and left ventricular functional status.

Accurately quantifying transmitral flow volume is clinically important not only as a measure of cardiac output, but also as a value from which to subtract aortic flow, for determining the severity of mitral regurgitation. However, controversy exists over the accuracy of pulsed Doppler for mitral flow quantification because of the complexity of mitral flow geometry and dynamic changes in flow profile and flow area. To explore the feasibility of directly quantifying transmitral flow volume with a newly developed dynamic 3-dimensional digital color Doppler technique, this in vivo experimental study was conducted to validate the method. Eight open chest sheep were imaged with a multiplane transesophageal (TEE) probe placed on the heart for digital 3-dimensional gated acquisition of mitral inflow over a 180-degree acquisition. The digital velocity data were contour detected for flow area after computing the velocity vectors and flow profile perpendicular to a spherical 3-dimensional surface across the mitral annulus. Flow areas and actual velocities were then integrated in time and space and the resulting flow volumes were compared with those obtained by a reference electromagnetic flowmeter on the aorta for 26 steady hemodynamic states. The flow volumes correlated closely to the electromagnetic references (y = 0.87x + 2.49, r = 0.92, SEE = 1.9 Ml per beat). Our study shows that transmitral flow volume can be accurately determined in vivo by this dynamic 3-dimensional digital color Doppler flow quantification method.