A validation study of aortic stroke volume using dynamic 4-dimensional color Doppler: An in vivo study

Objective: To explore the feasibility of directly quantifying transaortic stroke volume with a newly developed dynamic 3-dimensional (3D) color Doppler flow measurement technique, an in vivo experimental study was performed. Background: Traditional methods for flow quantification require geometric assumptions about flow area and flow profiles. Accurate quantification of flow across the aortic valve is clinically important as a means of estimating cardiac output. Methods: Eight open-chest sheep were scanned with apical epicardial placement of a 7 to 4 MHz multiplane transesophageal probe scanning parallel to aortic flow and running on an ATL HDI 5000 system. An electromagnetic flow meter implanted on the ascending aorta was used as reference. Thirty different hemodynamic conditions were studied after steady states were obtained in the animals by administration of blood, angiotensin, and sodium nitroprusside. Electrocardiogram-gated digital color 3D velocity data were acquired for each of the 30 steady states. The aortic stroke volumes were computed by temporal and spatial integration of flow areas and actual velocities across a projected surface perpendicular to the direction of flow, at a level just below the aortic valve. Results: There was close correlation between the 3D color Doppler calculated aortic stroke volumes and the electromagnetic data (r = 0.91, y = 0.96x + 1.01, standard error of the estimate = 2.6 mL/beat). Conclusion: Our results showed that dynamic 3D color Doppler measurements obtained in an openchest animals provide the basis for accurate, geometry-independent quantitative evaluation of the aortic flow. Therefore, 3D digital color Doppler flow computation could potentially represent an important method for noninvasively determining cardiac output in patients.