Simultaneous measurement of velocity, diameter, flow and pressure in the ascending aorta of cats. Evaluation of an extractable Doppler ultrasound probe for continuous monitoring of aortic blood flow.

To evaluate an extractable Doppler ultrasound probe designed for monitoring postoperative aortic flow in infants, simultaneous measurements of velocity, diameter, electromagnetic flow estimates, and pressure in the ascending aorta were recorded in cats. Doppler flow calculators were designed to provide flow estimates based on preset constant or measured instantaneous aortic diameter. Doppler sample volume was extended to about 1.2 X 1.6 X 4.0 mm. By pharmacological interventions, a wide range of flow rates and pressures were obtained, some of which were outside physiological values. The prototype probe described here was well suited for implantation in aortas with outer diameter 8-12 mm. Correlation coefficients between Doppler and electromagnetic estimated flow for 140 samples were 0.908 and 0.959 for constant and instantaneous diameter, respectively. Mean difference between the two methods was calculated, as well as the 95% confidence limits (2SD) of the differences. Limits of agreement, in stable haemodynamic situations without drugs, were -20.0 and 22.4% of mean average flow for constant diameter Doppler flow estimates, and -14.5 and 15.1% of electromagnetic flow values for instantaneous diameter estimates. These limits increased when all samples were taken into account, but the limits for instantaneous diameter estimates were reduced from -33.1 and 32.4 to -23.9 and 19.3% after removal of data obtained during isoprenaline infusion, which introduced extreme high flow/low pressure situations. This Doppler method seems well suited for postoperative monitoring of aortic flow in infants. Errors observed in larger aortas with an asymmetric flow profile do not seem to be present in smaller vessels within normal values of flow and pressure.(ABSTRACT TRUNCATED AT 250 WORDS)