An evaluation of methods for measuring cardiac output with volumetric heating

Bolus thermodilution is presently the accepted method for measuring cardiac output, but bolus thermodilution suffers from various sources of measurement error and, due to fluid loading, can only supply periodic measurements. Cardiac output measurement using resistive heating overcomes some sources of measurement error and allows continuous monitoring of cardiac output. However, because the maximum safe power input is limited with surface heating, cardiac output measurements made using resistive heating are less accurate than those made using bolus thermodilution. The authors have investigated 3 methods for measuring cardiac output using volumetric heating: RF, microwave, and laser. Given the design constraints of a catheter device, volumetric heating allows a higher maximum safe power input than surface heating. The authors have demonstrated that, under realistic thermal noise conditions, all 3 volumetric heating methods are more accurate and reliable than resistive heating. The laser heating method seems to be the most practical to implement.