In vivo characterization of the transitional bronchioles by aerosol-derived airway morphometry

Effective airway dimensions (EADs) were determined in vivo by aerosol-deriv ed airway morphometry as a function of volumetric lung depth (VLD) to ident ify and characterize, noninvasively, the caliber of the transitional bronch iole region of the human lung and to compare the EADs by age, gender, and d isease. By logarithmically plotting EAD vs. VLD, two distinct regions of th e lung emerged that were identified by characteristic Line slopes. The inte rsection of proximal and distal segments was defined as VLDtrans, and assoc iated EAD(trans). In our normal subjects (n = 20), VLDtrans, [345 +/- 83 (S D) ml] correlated significantly with anatomic dead space (224 +/- 34 ml) an d end of phase II of single-breath nitrogen washout (360 +/- 53 ml). The co rresponding EAD(trans) was 0.42 +/- 0.07 mm, in agreement with other ex viv o measurements of the transitional bronchioles. VLDtrans, was smaller (216 +/- 64 mi) and EAD(trans), was larger (0.83 +/- 0.04 mm) in our patients wi th chronic obstructive pulmonary disease (n. = 13). VLDtrans increased with age for children (age 8-18 yr; P = 0.006, n = 26) and with total lung capa city for age 8-81 yr (P < 0.001, n = 61). This study extends the usefulness of aerosol-derived airway morphometry to in vivo measurements of the trans itional bronchioles.