Evaluation of precordial detection and arterial sampling for the measurement of cardiac output using the indicator dilution principle

The external detection method for measuring cardiac output has been compared with the conventional arterial sampling technique to determine the relative accuracy of these techniques. Refinements in the external detection method have included more sensitive precordial detection equipment, focusing collimation and a simplified method for standardization of the counting equipment. Observations were made in human volunteers and dogs. The results indicate that with the equipment and methods used in this study, the systematic error of external detection compared to the cannulation method is approximately plus 3 per cent in human volunteers and plus 5 per cent in dogs, with a standard deviation of 16 and 13 per cent respectively. It would appear from this study that the external detection method is a simple technique for measuring cardiac output and gives results which are within the range of accuracy to make it a useful clinical procedure.