Continuous Registration of Blood Velocity and Cardiac Output with a Hot-Film Anemometer Probe, Mounted on a Swan-Ganz Thermodilution Catheter

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Abstract
In order to construct a catheter, capable of monitoring cardiac output, a specially designed double-conical hot-film anemometer probe was fastened at the tip of a Swan-Ganz thermodilution catheter. Common sources of error for most catheter velocity probes include difficult calibration, unknown velocity profile at the point of measurement and unknown position of the probe in this profile. By using mongrel dogs and in order to exclude these sources of error, the intermittent thermodilution method was used to in vitro calibrate the hot-film anemometer, which registered velocity continuously. A mean correlation coefficient between these two methods was found to be 0.886. A mean line of regression between thermodilution (abscissa) and anemometer (ordinate) had a slope of 0.796 ± 0.223 (±SD) and a y-intercept of 24 ± 14 ml/min/kg. The slope was significantly lower than one (t test, p < 0.05) and the y-intercept significantly larger than zero (t test, p < 0.02). As a control of the thermodilution method, electromagnetic flow in the ascending aorta was registered and a mean correlation coefficient of 0.967 found. The hot-film sensor itself can be used as thermodilution thermistor intermittently and this new catheter combines thus the advantages of the thermodilution method with the hot-film anemometer’s continuous registration of velocity.

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