Evaluation of the continuous thermal dilution technique for measurement of coronary blood flow

A continuous thermodilution technique has been used in a flow model. It has been difficult to determine the exact flow, but alterations of the flow have been reliably determined. For in vivo measurement the catheter is inserted into the vein of the actual organ. The indicator is injected against the bloodstream with a constant speed. The temperature of the indicator and the fall of blood temperature during the injection of indicator are measured with thermistors located at the catheter. The inability to measure the exact flow was mainly due to three factors; it turned out to be difficult to obtain the total and uniform mixing between the "blood" of the flow model and the indicator. Heat leakage occurs within the catheter as well as to ambient structures. The Wheatstone bridge was found not to be suitable, and a new type of instrument for determination of changes of resistance in the thermistors was used.