EVALUATION OF THE CO2 REBREATHING METHOD FOR THE NONINVASIVE MEASUREMENT OF RESTING CARDIAC OUTPUT IN MAN

Abstract

1. We have compared the indirect Fick, a non‐invasive CO2 rebreathing method for measuring resting cardiac output, with the thermodilution method in eleven subjects including some with cardiac and pulmonary disease. Three alternative methods for calculating veno‐arterial CO2 content difference were used: (i) from end‐tidal and rebreathing bag equilibrium Pco2 modified from the equations developed for use during exercise by Jones et al. (1975); (ii) by using the uncorrected difference between end‐tidal and equilibrium Pco2 and the standard CO2 dissociation curve; (iii) by direct measurement of arterial Pco2. 2. Each method was satisfactory in that reproducibility was similar to thermodilution..