Reproducibility of the acetylene rebreathe technique for determining cardiac output

Reproducibility of the acetylene rebreathe technique for determining cardiac output. Med. Sci. Sports Exerc., Vol. 30, No. 6. pp. 952-957, 1998. Purpose: The acetylene rebreathe technique is a well established method for the determination of cardiac output (Q˙) at rest and during exercise. We sought to demonstrate that the acetylene rebreathe technique allows for highly reproducible determinations of Q˙. Methods: Nine elite male endurance cyclists (V˙O2max = 68.9 ± 0.6 mL·kg−1·min−1) performed a modified acetylene rebreathe maneuver during incremental exercise on four repeat test days. A key modification to the method originally described by Grollman was the maintenance of a positive filling pressure during the inhalation portion of the procedure. Results: There were no significant differences in determinations of Q˙ at the same submaximal heart rates on four separate test days. The coefficient of variation for repeat determinations of maximal Q˙ during the same work rate, expressed as the standard deviation of the difference between duplicate measurements, is 4.8%. The coefficient of variation for determinations of maximal Q˙ at the same heart rate on different days, expressed as the standard deviation of the difference between four test days, is 2.6%. Conclusion: These findings illustrate that the acetylene rebreathe technique can be used with confidence to assess Q˙ across repeated experimental days.