The metabolic cost of breathing for exercise ventilations : Effects of age and sex

Given there are both sex-based structural differences in the respiratory system and age-associated declines in pulmonary function, the purpose of this study was to assess the effects of age and sex on the metabolic cost of breathing (VO2RM) for exercise ventilations in healthy younger and older, males and females. Methods: Forty healthy participants (10 young males 23±3yrs; 10 young females 23±3yrs; 10 older males 63±3yrs, 10 older females 63±6yrs) mimicked their exercise breathing patterns (voluntary hyperpnea) in the absence of exercise across a range of exercise intensities. Results: At peak exercise, VO2RM represented a significantly greater fraction of peak oxygen consumption (V̇O2peak) in young females, 12.8±3.9%, compared to young males, 10.7±3.0% (P=0.027), while V̇O2RM represented 13.5±2.3% of V̇O2 peak in older females and 13.2±3.3% in older males. At relative ventilations, there was a main effect of age, with older males consuming a significantly greater fraction of V̇O2RM (6.6%±1.9) than the younger males (4.4%±1.3; P=0.012), and older females consuming a significantly greater fraction of V̇O2RM (6.9%±2.5) than the younger females (5.1%±1.4; P=0.004) at 65% V̇Emax. Furthermore, both younger and older males had significantly better respiratory muscle efficiency than their female counterparts at peak exercise (P=0.011; P=0.015). Similarly younger participants were significantly more efficient than older participants (6.5%±1.5% vs. 5.5±2.0%; P=0.001). Conclusion: Age-related changes in respiratory function, and sex-based differences in airway anatomy, influence the cost to breathe during exercise. It is possible the higher fraction of V̇O2RM during peak exercise predispose young females and older individuals to divert more blood flow to respiratory muscles at the expense of other muscles.