The Hot-Film Anemometer – a Method for Blood Velocity Determination

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Abstract
In an in vitro flowmodel a constant temperature hot-film anemometer was tested, using conical needle and catheter-mounted probes. Calibration, linearization and zero-point determination as well as sensitivity change with hematocrit, angulation, flow direction and dirt deposits on the film are described. Curves were compared with those obtained simultaneously from an electromagnetic flowmeter. The hot-film anemometer was direction-insensitive and signals were seen 0.01—0.03 sec before the flowmeter signals. The frequency response of the anemometer was sufficiently high to register turbulent flow. In 27 simultaneous measurements the mean anemometer results were 6 ± 8% ( ± SD) higher than the flowmeter results and the peak results correspondingly 16 ± 6%. Both differences were significant (p < 0.001). Qualitatively hot-film anemometer curves were comparable to electromagnetic flowmeter curves. However, certain differences were demonstrated.