Precise mimicking of exercise hyperpnea to investigate the oxygen cost of breathing

• Quantification of respiratory muscle oxygen consumption is highly variable in the literature.
• Repeated measures and biofeedback consistently determine respiratory muscle oxygen consumption.
• The work of breathing must be measured when determining respiratory muscle oxygen consumption.

The oxygen cost of exercise hyperpnea (V⋅o2RM) has been quantified using a variety of techniques with inconsistent findings. Between-study variation relates to poor control of breathing patterns and lung mechanics. We developed a methodology allowing precise matching of exercising WOB in order to estimate V⋅o2RM. Thirteen healthy young subjects (7 male) completed an incremental cycle exercise test, familiarization and experimental days where exercise hyperpnea was mimicked. On experimental days, feedback of exercise flow, volume and the respiratory pressures were provided while end-tidal CO2 was kept at exercise levels during each 5-min trial. Minute ventilation levels between 50 and 100% maximum were mimicked 3–5 times. The r2 between exercise and mimic trails was 0.99 for frequency, tidal volume and minute ventilation; 0.86 for esophageal pressure swings and 0.93 for WOB. The coefficient of variation for (V⋅o2) averaged 4.3, 4.4 and 5.7% for 50, 75 and 100% ventilation trials. When WOB and other respiratory parameters are tightly controlled, the V⋅o2RM can be consistently estimated.