Cardiac output measured by thermal dilution of room temperature injectate

¹ Department of Physiology, College of Medicine, State University of Iowa, Iowa City, Iowa

A technique is described for recording time concentration curves utilizing the thermal dilution method using normal room-temperature isotonic saline as the dilution indicator. This technique was compared with the dye dilution method by simultaneously recording the left heart output with each of the methods. The coefficient of correlation between these simultaneous measurements was 0.962. Paired analysis showed the thermal measurements to be 4% greater than dye measurements. However, their reproducibilities and sensitivities were comparable. Simultaneous thermal measurements for both sides of the heart resulted in a slightly higher reading (2%) from the left side. In spite of this small difference the reproducibilities with either side were comparable. The coefficient of correlation between the two was 0.96. A formula is advanced for calculating cardiac output from thermal dilution curves. The thermal dilution technique described provides a satisfactory method for estimating either right or left heart outputs.