Peak Cardiac Output Determined Using Inert Gas Rebreathing: A Comparison of two Exercise Protocols.

PURPOSE: To compare Q̇peak elicited by a constant load protocol (Q̇CL) and an incremental step protocol (Q̇step).

METHODS: A non-inferiority randomized crossover trial was used to compare Q̇peak between protocols using a non-inferiority margin of 0.5 L/min. Participants [n = 34 (19 females, 15 males); 25 ± 5 y] performed two baseline V̇O2peak tests to determine peak heart rate (HRpeak) and peak work rate (Wpeak). Participants then performed the Q̇CL and Q̇step protocols each on two separate occasions with the order of the four visits randomized. Q̇peak was measured using IGR (Innocor, COSMED, Italy). The Q̇CL protocol involved a VO2peak test followed 10-min later by cycling at 90% Wpeak, with IGR initiated after 2 min. Q̇step involved an incremental step test with IGR initiated when the participant's HR reached 5 bpm below their HRpeak. The first Q̇CL and Q̇step tests were compared for non-inferiority and the second series of tests was used to measure repeatability [typical error (TE)].

RESULTS: The Q̇CL protocol was non-inferior to Q̇step (Q̇CL = 17.1 ± 3.2, Q̇step = 16.8 ± 3.1 L/min; 95% CIs = -0.16-0.72 L/min). The baseline V̇O2peak (3.13 ± 0.83 L/min) was achieved during Q̇CL (3.12 ± 0.72, p = 0.87) and Q̇step (3.12 ± 0.80, p = 0.82). The TE for Q̇peak was 6.6% and 8.3% for Q̇CL and Q̇step, respectively.

CONCLUSIONS: The Q̇CL protocol was non-inferior to Q̇step and may be more convenient due to the reduced time commitment to perform the measurement.