Oxygen cost of exercise hyperpnoea is greater in women compared with men

Abstract

We compared the oxygen cost of breathing (V˙ O2RM) in healthy men and women over a wide range of exercise ventilations (V˙ E). Eighteen subjects (9 women) completed four days of testing. First, a step-wise maximal cycle exercise test was completed for the assessment of spontaneous breathing patterns. Next, subjects were familiarized with the voluntary hyperpnoea protocol used to estimate V˙ O2RM. During the final two visits, subjects mimicked multiple times (4-6) the breathing patterns associated with 5-6 different exercise stages. Each trial lasted 5 min and on-line pressure- and flow-volume loops were superimposed on target loops obtained during exercise to accurately replicate the work of breathing. At ~55 l min-1 V˙ E, V˙ O2RM was significantly greater in women. At maximum ventilation, the absolute V˙ O2RM was not different (P>0.05) between the sexes, but represented a significantly greater fraction of whole-body V˙ O2 in women (13.8±1.5 vs. 9.4±1.1% V˙ O2). During heavy exercise at 92 and 100% V˙ O2max, the unit cost of V˙ E was +0.7 and +1.1 mlO2 l-1 greater in women (P<0.05). At V˙ O2max, men and women who developed expiratory flow limitation had a significantly greater V˙ O2RM than those who did not (435±44 vs. 331±30 mlO2 min-1). In conclusion, women have a greater V˙ O2RM for a given V˙ E and this represents a greater fraction of whole-body V˙ O2. The greater V˙ O2RM in women may have implications for the integrated physiological response to exercise.