Constant infusion transpulmonary thermodilution for the assessment of cardiac output in exercising humans

To determine the accuracy and precision of constant infusion transpulmonary thermodilution cardiac output (CITT-Q) assessment during exercise in humans, using indocyanine green (ICG) dilution and bolus transpulmonary thermodilution (BTD) as reference methods, cardiac output (Q) was determined at rest and during incremental one- and two-legged pedaling on a cycle ergometer, and combined arm cranking with leg pedaling to exhaustion in 15 healthy men. Continuous infusions of iced saline in the femoral vein (n=41) or simultaneously in the femoral and axillary (n=66) veins with determination of temperature in the femoral artery were used for CITT-Q assessment. CITT-Q was linearly related to ICG-Q (r=0.82, CITT-Q=0.876xICG-Q+3.638, P<0.001; limits of agreement ranging from -1.43 to 3.07L/min) and BTD-Q (r=0.91, CITT-Q=0.822xBTD+4.481L/min, P<0.001; limits of agreement ranging from -1.01 to 2.63L/min). Compared with ICG-Q and BTD-Q, CITT-Q overestimated cardiac output by 1.6L/min (approximate to 10% of the mean ICG and BTD-Q values, P<0.05). For Q between 20 and 28L/min, we estimated an overestimation <5%. The coefficient of variation of 23 repeated CITT-Q measurements was 6.0% (CI: 6.1-11.1%). In conclusion, cardiac output can be precisely and accurately determined with constant infusion transpulmonary thermodilution in exercising humans.