Measurement of cardiac output during exercise by the thermodilution and direct Fick techniques in patients with chronic congestive heart failure.

Nine men with chronic stable congestive heart failure (New York Heart Association class II or III) were studied. Oxygen consumption was measured continuously and cardiac output (CO) determined by thermodilution and from the Fick equation at the end of each stage of treadmill exercise. CO measured by the 2 techniques was similar (r = 0.98) over the range of 2.5 to 13 liters/min (43 separate estimations). Tricuspid regurgitation developed in 2 patients during exercise, which resulted in unphysiologic estimates of CO (more than 30 liters/min) by thermodilution. In these circumstances estimation of CO by the direct Fick technique is superior. With this exception, CO measured by thermodilution was accurate even during exercise and provided results similar to those using the direct Fick technique.