Oxygen cost of exercise hyperpnea is greater in women compared to men (882.3)

We tested the hypothesis that the O2 cost of exercise hyperpnea is greater in women compared to men. Healthy subjects (8M, 7F) first performed a maximal step cycle exercise test with esophageal and gastric balloon instrumentation followed by a hyperpnea familiarization trial on a separate day. Cardiorespiratory parameters were measured and flow‐ and pressure‐volume loops were constructed from the same breaths (~n=10) for each exercise stage. Days 3 and 4 involved exercise hyperpnea mimicking over 5 ventilatory levels while in the cycling position. Mimicking trials were repeated (n=4) for each ventilatory level. End‐tidal CO2 was controlled to a level corresponding to each exercise stage. Respiratory muscle O2 uptake (VO2rm) was linearly related to work of breathing (WOB) in men (r=0.94, P<0.001) and women (r=0.88, P<0.001). The VO2rm to VE relationship was assessed by fitting a regression accounting for viscous and resistive work. There was no difference in viscous work (P=0.45); however, the resistive component was ~13x greater in women (P<0.05). At maximal ventilation the absolute VO2rm was similar between sexes (0.39 vs. 0.42 l min‐1, P=0.52) despite men having a greater VE (108 vs. 169 l min‐1); but the VO2rm represented a greater fraction of whole‐body VO2 in women (14.6 vs. 9.8%, P<0.05). In conclusion, the O2 cost of exercise hyperpnea is greater in women owing to a greater resistive WOB. Grant Funding Source : Natural Sciences and Engineering Research Council of Canada