Injectateless thermal cardiac output determination method and apparatus

Abstract

The method and system use a catheter that is configured such that a fluid may circulate within it. With the catheter in position, the fluid may circulate down one lumen as far as the RA or RV, over to another lumen and back up and out of the catheter. Nothing is injected into the bloodstream. On this or another catheter, a temperature sensor is positioned in the PA to monitor mixed venous blood temperature. Temperature sensor devices monitor the fluid temperature at the inlet to and outlet from the catheter. The flowrate of fluid circulation is controlled at a known value or monitored. The circulating fluid is preferably cooled to near ice temperature prior to input into the catheter. This fluid temperature and flow rate are preferably held relatively constant. Soon after fluid circulation is initiated a relatively steady state heat transfer system is attained. The circulating fluid cools the blood through the lumen walls. It also cools any adjacent fluid lumens which also cool the blood through their lumen walls and through dilution, if the lumen is used to introduce an IV solution. An appropriate heat balance equation allows cardiac output to be calculated. After an appropriate amount of data is collected, fluid circulation is discontinued, allowing the system to re-equilibrate. Once equilibrium is reestablished, another measurement cycle may be initiated.