Changes in elastic fibres in the small airways and alveoli in COPD

¹ Depts of Pharmacology & Clinical Pharmacology
² Anatomy with Radiology, University of Auckland and
³ Dept of Histopathology, Auckland Hospital, New Zealand

^* To whom correspondence should be addressed. E-mail: pn.black{at}auckland.ac.nz.

	Abstract

Small airways are the major site of airflow obstruction in COPD. This is attributed to loss of elastin in alveoli and fibrosis in small airways. We hypothesized that changes to elastic fibres in alveoli might be paralleled by a similar reduction in elastic fibres in small airways.

We studied tissue blocks from patients who had lobectomy for bronchial carcinoma. Patients were classified as COPD (FEV₁ <80% predicted, FEV₁/VC<0.7) or controls (FEV₁ 80% predicted, FEV₁/FVC 0.7). Elastic fibres were visualised using Elastic van Gieson staining and the volume/fraction (v/f) of elastic fibres determined as percentage of tissue volume using point counting. Elastic fibre networks were also visualised by confocal microscopy.

The v/f for elastic fibres in alveoli was 18.6% for COPD and 32.8% in controls. In the airways v/f was 14.6% for COPD and 25.5% in controls. FEV₁% predicted was correlated with v/f in both alveoli (r=0.66) and small airways (r=0.73).

The volume fraction of elastic fibres is reduced to a similar extent in small airways and alveoli in COPD and both are correlated with the extent of airflow obstruction. Loss of elastic fibres in small airways may contribute to the development of airflow obstruction in COPD.

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