Validation of the acetylene rebreathing method for measurement of cardiac output at rest and during high-intensity exercise.

The use of the acetylene rebreathing method to estimate cardiac output (CO) during high-intensity exercise, which may be influenced by recirculation of acetylene, has not been validated. This study was designed to validate the acetylene rebreathing method to measure CO during high-intensity exercise using the direct Fick method. CO was measured at rest and during exercise at 25%, 50%, 75% and 90% of the nine subjects' maximum oxygen uptake (VO2max) by the direct Fick and acetylene rebreathing method. CO measured by the acetylene rebreathing method correlated with work rate (r = 0.90, P < 0.01) and with oxygen uptake (r = 0.94, P < 0.01). The correlation coefficient of CO between both methods was r = 0.91 (P < 0.01). There was no significant difference in CO measured by each method at rest as well as at each work rate. The difference in CO between each method was greater at lower CO than at higher CO. At 90% of VO2max, the CO measured by acetylene rebreathing was nearly identical to that measured by the Fick method. It can be concluded that acetylene rebreathing for measurement of CO is valid not only at rest but also during exercise, especially during high-intensity exercise.