Background: Growing evidence suggests that the larger conducting airways are smaller in women than men, even when matched for age and lung size. The most convincing evidence in favour of this point was provided by Sheel et al. (J Appl Physiol 2009 107(5): 1622-1628) who examined airway size in older (>50 years) adults with a positive smoking history (>10 pack years). However, given that sex is known to modify the progression of smoking-related lung disease (i.e., emphysema), a similar examination of airway size in non-smoking adults is warranted.

Aims: We sought to determine the effect of sex on airway size in a cohort of non-smoking middle-aged adults.

Methods: A total 52 (33 men; 19 women) non-smoking adults (45±17 yr) with normal pulmonary function (>80% pred.) participated in this study. Chest computed tomography was used to quantify intraluminal airway size (Ai), perimeter (Pi) and hydraulic diameter (Dh) over generations 0 to 5 of the tracheobronchial tree. Data were analysed using a mixed-effects approach, wherein airway generation was treated as a random effect, and age, sex, and total lung capacity (TLC) were used as subject-level covariates.

Results: The mixed-effects model revealed that Ai, Pi and Dh were smaller in women from the 0th (trachea) to the 3rd generation of the tracheobronchial tree (P<0.05). Importantly, when the marginal effect of sex was evaluated holding age and TLC constant, Ai, Pi and Dh were systematically lower in women only up to generation 2 (P<0.05).

Conclusions: Our findings contribute to the growing impetus of research demonstrating that a sexual dimorphism of the central airways does indeed exist between non-smoking men and women.