Growing evidence suggests that the larger conducting airways are smaller in women than men; however, evidence of this sex-difference in airway geometry is yet to be demonstrated in a large cohort of adult, healthy non-smokers. Furthermore, it is not known whether these sex differences persist after airway size is adjusted for its allometric relationship with absolute lung size.

Purpose We examined the effect of sex on airway size in a large cohort of non-smoking healthy adults after adjusting for the possible confounding effect of absolute lung size.

Methods A total of 133 (75 men; 58 women) non-smoking adults (50 ± 18 yrs) with normal pulmonary function (>80% pred.) participated in this study. Full thoracic CT scans were obtained in each participant during a breath-hold at full inflation. Commercial software was used to automatically segment airways and assign 32 anatomical labels ranging from the 0th to the 5th generation. Intraluminal hydraulic diameters (Dh) were obtained for each airway. An allometric relationship was assumed between Dh and absolute lung size, as given by: Dh = TLVβ·ek, where TLV is the total lung volume at full inflation, β is the allometric scaling exponent, and k allowed for proportional effects of confounding variables. This allometric equation was log-log transformed such that it could be examined using linear regression: e.g., ln(Dh) = β·ln(TLV) + k. Sex, age and their interaction were allowed to contribute to both β and k as covariates. The model also included a term for reconstructed voxel size. Model averaging was used to provide parameter estimates of the log-log transformed allometric equation.

Results The allometric exponent, β, assigned to TLV was significant for all 32 anatomically labelled airways (P < 0.05); neither sex nor age affected β. On the other hand, sex and age were significant mediators of k for the extra-parenchymal airways only (Trachea, RMB, LMB, BronInt, see Figure 1, P < 0.05).

Conclusions Our findings indicate that sex differences in Dh remain present despite accounting for the allometric relationship between airway and lung size (see Figure 1). Importantly, however, this sex-difference in airway size is seemingly confined to the extra-parenchymal airways.

Support or Funding Information

This work was supported by NIH Grant HL71478.

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.