Intravascular and Intracardiac Blood Velocity Patterns recorded by means of NTC Resistors

Abstract

NTC resistors (‘thermistors’) can be used for measuring intravascular blood flow^1,2. The thermistor is heated by an electric current and cooled by the flowing blood. So its temperature is a function of the blood flow rate in its immediate environment, and since the thermistor's electric resistance increases some 5 per cent for a temperature drop of 1°C., resistance measurement provides a fairly sensitive method for the determination of flow. Mounting very small NTC beads in a cardiac catheter, Delaunois³ succeeded in recording the blood flow in the large vessels without opening the thorax. An NTC bead, having a diameter of 0.5 mm. was placed in a small cavity made in the side wall of a catheter near the tip and fixed with a plastic cement. The quantitative determination of flow rates by this method has not yet been entirely successful because of several difficulties, such as the large influence of small blood temperature variations and the complicated calibration procedure.