DETERMINANTS OF PULMONARY ARTERY BLOOD VELOCITY PROFILE

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Current methodologies for 1) quantifying pulmonary blood flow noninvasively with ultrasound and 2) estimating pulmonary input impedance with intraluminal velocity catheters rely heavily on the assumption that the velocity profile in the main pulmonary artery is flat. However, recent studies in humans and animals indicate that the mean profile along the long axis may be skewed toward the anterior wall. This skew has been attributed to flow reversals near the posterior wall during diastole and late systole which become accentuated and extend over a larger portion of the cross sectional area in the presence of pulmonary hypertension. Though attempts to correlate the magnitude and/or duration of flow reversal with pulmonary artery pressure have been made, little is known about 1) the source of the apparent backflow, 2) the effects of elevated flow on the velocity profile, or 3) discrepancies which may occur in impedance related parameters such as characteristic impedance and frequency of the first modulus minimum as a result of intraluminal catheter position. This study will address these issues by evaluating the relationships between velocity profiles and abnormal pulmonary hemodynamics in animal models using an intraluminal 20 MHz pulsed Doppler device. Profiles will be obtained along the long and short axes to create a two-dimensional profile which will be correlated with electromagnetically measured blood flow. Studies performed on the main pulmonary artery will be duplicated on the right pulmonary artery to determine the extent of the flow reversal phenomena as well as the feasibility of using the input impedance of the right rather than the main pulmonary artery to assess pulmonary vascular impairment. Chronic pulmonary hypertension and/or elevated pulmonary blood flow will be created in dogs and lambs. Once control profiles are obtained, the effects of 100% oxygen inhalation and hydralazine will be evaluated. Efforts will be made to improve current methods of measurement by reducing intraluminal probe size and time needed to complete a profile. Findings in the animal models will be compared to patient data. The spectra in the main pulmonary artery, currently being obtained intraoperatively using electromagnetic flow probes, will be compared to the spectra obtained by measuring velocity in the main and right pulmonary artery with a hand-held extraluminal pulsed Doppler probe. Finally, efforts will be made to obtain spectra in the right pulmonary artery whenever studies of the effects of oxygen inhalation are done in the catheterization laboratory to assess vascular tone in patients with abnormal pulmonary hemodynamics.