Although the present study demonstrated that a nondirectional Doppler catheter probe accurately measures unidirectional pulsatile flow velocity, the in vivo evaluation reveals several significant discrepancies. When positioned in the ascending aorta of dogs, the Doppler transducer underestimated changes in blood flow velocity and the degree of underestimation varied significantly between animals. Under these conditions the Doppler-recorded signal indicated nearly continuous aortic flow and a zero-flow reference level was not present in late diastole. The extent of apparent diastolic flow was greater at higher flow rates. These findings indicate that the nondirectional Doppler catheter tip velocity transducer in its present form is not suitable for accurately measuring changes in aortic blood flow velocity.
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