INFLUENCE OF CARDIAC MOTION ON DOPPLER MEASUREMENTS USING IN-VITRO AND IN-VIVO MODELS

Objectives. Using both in vitro and in vivo techniques, we investigate d the extent to which cardiac motion alters Doppler-measured blood flo w velocity and thus potentially can alter the calculation of valve are as or pressure gradients. Background. Blood flow velocity measured by Doppler ultrasound represents the net motion of the blood relative to the transducer. It is widely assumed that the measured velocity repres ents the actual flow. It has been demonstrated that cardiac motion gen erates regularly occurring low velocity Doppler signals that are commo nly treated as artifact. Methods. We used an in vitro model that allow ed us to measure and independently control the flow of a liquid throug h a chamber and the motion of the chamber relative to the Doppler beam . A cornstarch-water slurry was driven by a pulsatile pump through tub ing to simulate the blood flow within the heart, and the tubing was cy clically moved by a piston to simulate the heart motion. We also measu red cardiac motion using M-mode and two-dimensional echocardiography a nd compared the results with the Doppler signal derived from cardiac m otion in subjects without cardiac disease. Results. In the in vitro mo del, alteration in the motion of the tubing resulted in apparent chang es in the measured maximal velocity of the fluid. The Doppler spectrum of the combined motion of the tubing and the fluid was the algebraic sum of their Doppler signals. In human subjects, the maximal slope of the M-mode tracing of the aortic annular motion and the peak Doppler s ignal due to cardiac motion were compared and were highly correlated. Conclusions. Cardiac motion alters the Doppler signal derived from blo od flow. This effect can be demonstrated in vitro and in vivo.