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Journal of Ultrasound in Medicine, Vol 10, Issue 6 305-308, Copyright © 1991 by American Institute of Ultrasound in Medicine
In vitro validation of Doppler indices using blood and water
J. A. Spencer, D. A. Giussani, P. J. Moore and M. A. Hanson
Department of Physiology, University of Reading, Berkshire, UK.
Using an in vitro flow model, volume flow and pressure were measured to
compare calculated resistance with simultaneously measured continuous-wave
Doppler indices during imposed changes in downstream resistance to
pulsatile flow. With stepwise reductions in flow, the peak (S) and trough
(D) points of the maximum shifted-frequency envelope fell in parallel in a
linear fashion until D reached zero. Pressure remained constant, and the
pressure waveform remained unchanged. As calculated resistance increased,
resistance index (RI) and pulsatility index (PI) both increased in a linear
fashion until the point at which D became zero. However, S/D ratio was not
linear, and the slope increased as resistance increased. The results
obtained from microspheres suspended in water and with heparinized sheep's
blood were similar. The results indicate that, with reductions in flow at
constant pressure in vitro, S/D ratio does not relate to calculated
resistance in the same linear manner as PI and RI.
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