Modelling the effects of age and sex on the resistive and viscoelastic components of the work of breathing during exercise

New findings: What is the central question of this study? What is the effect of age and sex on the resistive and viscoelastic components of work of breathing (W_b ) during exercise? What is the main finding and its importance? The resistive and viscoelastic components of W_b were higher in older adults, regardless of sex. The resistive, but not viscoelastic, component of W_b was higher in females than in males, regardless of age. These findings contribute to improving our understanding of the effects of ageing and sex on the mechanical ventilatory response to exercise.

Abstract: Healthy ageing and biological sex each affect the work of breathing (W_b ) for a given minute ventilation ( ${\dot{V}}_E$ ). Age-related structural changes to the respiratory system lead to an increase in both the resistive and viscoelastic components of W_b ; however, it is unclear whether healthy ageing differentially alters the mechanics of breathing in males and females. We analysed data from 22 older (60-80 years, n = 12 females) and 22 younger (20-30 years, n = 11 females) males and females that underwent an incremental cycle exercise test to exhaustion. ${\dot{V}}_E$ and W_b were assessed at rest and throughout exercise. W_b - ${\dot{V}}_E$ data for each participant were fitted to a non-linear equation (i.e. W_b = a ${\dot{V}}_E$³ + b ${\dot{V}}_E$² ) that partitions W_b into resistive (i.e. a ${\dot{V}}_E$³ ) and viscoelastic (i.e. b ${\dot{V}}_E$² ) components. We then modelled the effects of healthy ageing and biological sex on each component of W_b . Overall, the model fit was excellent (r² : 0.99 ± 0.01). There was a significant main effect of age and sex on the resistive component of W_b (both P < 0.05), and a significant main effect of age (P < 0.001), but not sex (P = 0.309), on the viscoelastic component of W_b . No significant interactions between age and sex on a ${\dot{V}}_E$³ or b ${\dot{V}}_E$² were noted (both P > 0.05). Our findings indicate that during exercise: (i) the higher total W_b in females relative to males is due to a higher resistive, but not viscoelastic, component of W_b , and (ii) regardless of sex, the higher W_b in older adults relative to younger adults is due to higher resistive and viscoelastic components of W_b .