CARDIOVASCULAR FLOW DYNAMICS--IN VIVO STUDIES

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The current year's efforts on this project have emphasized studies of intracardiac flow dynamics using flow imaging with two-dimensional color Doppler ultrasound for quantifying pathophysiologic hemodynamic abnormalities. Quantitative techniques have been applied to: 1) mitral regurgitation in native valves, 2) stenotic lesions in prosthetic valves and 3) stenotic lesions in small caliber arteries and vascular grafts. In animals with experimentally produced mitral regurgitation, digitally analyzed color Doppler flow data validated the use of proximal acceleration profiles for non invasively quantitating regurgitant volume and regurgitant fraction. On the other hand, studies performed under similar conditions demonstrated the limited utility of color jet area measurements for evaluating the severity of mitral regurgitation. In animals with bileaflet prosthetic mitral valves, the rate of change (spatial derivative) of the centerline acceleration profile was used to determine instantaneous flow rates through each of the valves' three orifices. the pathological flow disturbances associated with stenotic lesions in small caliber arteries and vascular grafts have been characterized. These studies demonstrate: 1) that proximal flow convergence observations using principles of momentum continuity preservation may be used to evaluate intracardiac hemodynamic pathophysiology; and 2) that principles of free jet flux are not readily applied to bounded jets associated with abnormal lows within cardiac chambers. Quantitative studies of vascular lesions have been initiated. these studies based on fundamental physical principles explore methodology, illustrate principles, validate techniques and demonstrate the utility of non invasive Doppler flow imaging to obtain clinically relevant quantitative information.