Author(s): TAYLOR, J., FORBES-SCHNICK, A.E., FLEMING, E.C., MATHEWS, C.A., KORPACH, S.G.C., LINGAPPA, K.L., BUSCH, S.A., SHIFFMAN, V.J., ARN, S.R., BOUSHEL, R., STÖHR, E.J., SHEEL, A.W., Institution: UNIVERSITY OF BRITISH COLUMBIA, Country: CANADA, Abstract-ID: 1160

INTRODUCTION:
Females have a disproportionately greater work of breathing (Ẇb) when minute ventilation exceeds 60 L/min. This phenomenon is thought to be associated with narrower conducting airways (generations 4-6) in females vs. males. However, it is unknown if differences in Ẇb related to airway size may cause sex differences in exercise capacity. We hypothesised that females would experience a larger improvement in exercise capacity when Ẇb is lowered.
METHODS:
Healthy participants (5M, 5F, 25±4 yrs) underwent an incremental ramp cycle test to volitional fatigue, and the wattage at the respiratory compensation point (RCP) was determined for subsequent testing. Six constant load time-to-exhaustion (TTE) tests at an exercise intensity equivalent to RCP (M:255±75W, F:192±21W). A randomised crossover single-blind design between three breathing conditions was performed twice each: (i) room air (CON), (ii) heliox (FiO_2=0.21, FiHe=0.79) (HEL), and (iii) hyperoxic-heliox (FiO_2=0.26, FiHe=0.74) (HYP-HEL). Relative to CON, Ẇb was lowered in HEL (59±11%) and HYP-HEL (53±10%), across all trials in both sexes (p<0.05).
RESULTS:
We found a main effect of gas condition on TTE (mean of 2 trials/condition) (F=10.3, p=0.012). Pairwise comparisons revealed that HYP-HEL (523±163s) was significantly greater than CON (447±151) (p=0.008). There was no significant difference between CON and HEL (455±104s) (p=0.74), or HEL and HYP-HEL (523±163s) (p=0.075). TTE was not significantly different between sexes (F=1.1, p=0.319). However, there was a non-significant trend of ∆19s (∆5%, range: 3-57s) in females between TTE in CON (F:397±97s) and HEL (F:416±96s). While no difference was seen between CON (M:496±190s) and HEL (M:495±106s) in males. There was no interaction effect for gas condition and sex (F=0.5, p=0.829). ∆Ẇb was not associated with ∆TTE in CON to HEL (r=0.478, p=0.193) but was significantly correlated between CON and HYP-HEL (r=0.675, p=0.046).
CONCLUSION:
These preliminary data suggest that inspiring a mildly hyperoxic and helium-backed gas reduces the Ẇb and improves exercise capacity. Further study is required to determine if Ẇb and exercise capacity differ on the basis of sex.