Airway length per generation in the human healthy lung and the impact of COPD

Abstract

Within the human lung, the airway length gradually declines per generation which is dependent on the distance of the alveolar units to the main bronchus. How this complex hierarchical system is affected by chronic lung diseases like COPD remains unknown.

We aimed to investigate the airway length per generation of air-inflated (TLC) control and end-stage COPD whole lungs using microCT (155µM resolution). Our analysis was restricted to the longest airway tree from the main bronchus to the basal segment of the lower lobe as uniform simplified conceptual design. We hypothesized that hyperinflation in COPD stretches the airways and this is more pronounced in the more distal generations.

We assessed lower lobe volume, length of the longest airway branch and airway length per generation in 6 control (non-used donors) and 4 COPD (end-stage) explant lungs, matched for age and length.

In COPD, lower lobe volume increased with 68% (p=0.004, fig. 1.a) and total airway branch length with 14% (p=0.028, fig. 1.b). Linear regression of consecutive airway length per generation showed a progressive decline of -0.54mm/generation in normal lungs, which is not the case in COPD due to the elongation of the more distal airways (-0.0029mm/generation; p=0.013 compared to donor) (fig. 1.c).

Our results show an elongation of the more distal airway in COPD, corresponding with lung hyperinflation. Potentially, this impacts the airflow and function of the lung.

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