Heliox breathing equally influences respiratory mechanics and cycling performance in trained males and females

Abstract

In this study we tested the hypothesis that inspiring a low-density gas mixture (helium-oxygen; HeO2) would minimize mechanical ventilatory constraints and preferentially increase exercise performance in females relative to males. Trained male (n = 11, 31 yr) and female (n = 10, 26 yr) cyclists performed an incremental cycle test to exhaustion to determine maximal aerobic capacity (V̇o2max; male = 61, female = 56 ml·kg(-1)·min(-1)). A randomized, single-blinded crossover design was used for two experimental days where subjects completed a 5-km cycling time trial breathing humidified compressed room air or HeO2 (21% O2:balance He). Subjects were instrumented with an esophageal balloon for the assessment of respiratory mechanics. During the time trial, we assessed the ability of HeO2 to alleviate mechanical ventilatory constraints in three ways: 1) expiratory flow limitation, 2) utilization of ventilatory capacity, and 3) the work of breathing. We found that HeO2 significantly reduced the work of breathing, increased the size of the maximal flow-volume envelope, and reduced the fractional utilization of the maximal ventilatory capacity equally between men and women. The primary finding of this study was that inspiring HeO2 was associated with a statistically significant performance improvement of 0.7% (3.2 s) for males and 1.5% (8.1 s) for females (P < 0.05); however, there were no sex differences with respect to improvement in time trial performance (P > 0.05). Our results suggest that the extent of sex-based differences in airway anatomy, work of breathing, and expiratory flow limitation is not great enough to differentially affect whole body exercise performance.

Keywords: exercise; expiratory flow limitation; sex differences; ventilatory limitations to exercise.

Fig. 1.

Flow-volume and pressure-volume loops during time trial exercise in representative male subject. A and B: tidal loops obtained at rest and at 1, 3, and 5 km positioned within the maximal expiratory flow volume curve (MEFV) breathing room air (A) or HeO₂ (B). Note that with each successive kilometer, end-expiratory lung volume increased towards resting values. C and D: pressure-volume loops obtained at rest and at 1, 3, and 5 km while breathing room air (C) or HeO₂ (D). Note the reduction in size of the transpulmonary loop when breathing HeO₂ (i.e., a reduced work of breathing) despite a larger flow-volume loop.

Fig. 2.

Flow-volume and pressure-volume loops during time trial exercise in representative female subject. A and B: tidal loops obtained at rest and at 1, 3, and 5 km positioned within the maximal expiratory flow volume curve (MEFV) breathing room air (A) or HeO₂ (B). Note that with each successive kilometer, end-expiratory lung volume increased towards resting values. C and D: pressure-volume loops obtained at rest and at 1, 3, and 5 km while breathing room air (C) or HeO₂ (D). Note the reduction in size of the transpulmonary loop when breathing HeO₂ (i.e., a reduced work of breathing) despite a larger flow-volume loop. See Fig. 1 for description of individual lines.

Fig. 3.

Change in minute ventilation/ventilatory capacity (V̇e/V̇e_cap) when breathing HeO₂ relative to room air. Shown are mean values for the inspired gas conditions with male and female values combined. No statistical differences were detected between males and females (P > 0.05). Inspiring HeO₂ reduced V̇e/V̇e_cap at each kilometer (*P < 0.05) indicating a reduced fractional usage of the maximal ventilatory capacity and a minimization of mechanical constraints.

Fig. 4.

Individual and group mean time trial (TT) performance times relative to the line of identity. Triangles are means ± SE. HeO₂, helium oxygen; RA, room air; TT, time trial.