The impact of idiopathic pulmonary fibrosis on the airway length per generation in the human lung

Abstract

In IPF, interstitial fibrosis restrains the secondary pulmonary unit to fully expand leading to a decrease in volume. The impact of this reduced lung volume on airway length is unknown.

We assessed differences in airway length in air-inflated (TLC) control and end-stage IPF lungs using whole lung microCT (155µM resolution). Our analysis was restricted to the longest airway from the main bronchus to the basal segment of the lower lobe as uniform simplified conceptual design. We hypothesized that decreased lung volume alters and reduces the airway length.

We measured lower lobe volume, length of the longest airway branch and airway length per generation in 6 control (non-used donors) and 6 IPF (end-stage) explant lungs, matched for age, gender and length.

In IPF, lower lobe volume decreased with 70% (p<0.0001, fig. 1.a), while total airway branch length did not change (p=0.53, fig. 1.b). Linear regression showed that consecutive branching length progressively decreases with increasing generation almost equally in normal and IPF lungs (-0.54 mm/generation, p=0.98, fig. 1.c). However, the (mainly small) airways in IPF appeared not straight but folded (fig. 1.e, f compared to control fig 1.d).

Our results show that the airways in IPF are bended in a “meandering” pattern to fit in the reduced lung volume, which will most certainly impact the airflow and pulmonary function.

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