Quantitative ultrasonic blood flow measurement in Dacron grafts

A quantitative directional Doppler system was used to determine blood flow in 8 mm. aortoaortic Dacron grafts in dogs. The Doppler was calibrated with frequency standards and the output was integrated for one minute intervals. With the probe held at an angle of 60 degrees to the flow axis, the average frequency of the Doppler shift was determined. Frequency was converted to velocity with the Doppler equation. Volume flow was calculated from the product of velocity and cross-sectional area of the graft. When compared with an electromagnetic flowmeter, the Doppler system was highly accurate with flow rates up to 900 c.c per minute. At flow rates above 900 c.c. per minute, there was a significant decrease in Doppler output which probably is due to the effects of turbulence and background noise on the Doppler signal.