Journal of Ultrasound in Medicine, Vol 2, Issue 8 357-362, Copyright © 1983 by American Institute of Ultrasound in Medicine
A removable extraluminal Doppler probe for continuous monitoring of changes in cardiac output
B. A. Keagy, C. L. Lucas, H. S. Hsiao and B. R. Wilcox
To address the problem of monitoring cardiac output in postoperative
cardiac patients, a removable, extraluminal pulsed Doppler probe has been
constructed which continuously reflects changes in cardiac output by
monitoring blood velocity in the ascending aorta. Velocity is related to
the frequency of the Doppler shift and the angle at which the ultrasound
beam intersects the vessel. A 1 mm2 piezoelectric crystal mounted at a 45
degree angle on the tip of the probe is activated with a 20-MHz range-gated
pulsed Doppler, and velocity is determined from Fourier analysis of
quadrature data using computer software with a 50-KHz processing range. The
device is designed for application to the ascending aorta at the conclusion
of a cardiac surgical procedure; and, since mean diameter changes in the
ascending aorta have been shown to be very small over a wide range of mean
aortic pressures, cardiac output is linearly related to velocity. To test
this technique, simultaneous recordings were made from the pulsed Doppler
probe and an electromagnetic flow probe in five mongrel dogs over a range
of cardiac outputs from 0.5 to 6 l/min for a total of 136 data points.
Excellent correlation was found between the electromagnetic flow probe and
pulsed Doppler probe data (average r = .98 +/- .006). Average slope between
the two was 1.004 and average zero intercept was -0.025 l/min. The catheter
is small, stable, has no baseline drift, and continuously and accurately
reflects pulsatile changes at high and low flows.
