Improvements in determination of cardiac output with a Swan-Ganz catheter.

The time constant for heat transfer may affect exact determination of cardiac output with Swan-Ganz catheters. Commercially available Swan-Ganz catheters are provided with thermistors with varying time constants. Current monitoring of cardiac output is not corrected for these time constants, so the conventional method of determining cardiac output using the equation of Stewart-Hamilton produces marked errors. The authors propose a new method of determining cardiac output with Swan-Ganz catheters with varying time constants from thermal dilution curve data based on Newton's cooling law. Values for blood flow rate determined by the new method using a completely stirred tank of original design, mimicking the natural heart and using bovine blood, are almost the same as values observed at varying saline infusion volumes, saline temperatures, and saline infusion times.