Reproducibility of the acetylene rebreathe technique for determining cardiac output

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 (VO2max = 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.