In vivo imaging of the airway wall in asthma: fibered confocal fluorescence microscopy in relation to histology and lung function

Abstract

Background: Airway remodelling is a feature of asthma including fragmentation of elastic fibres observed in the superficial elastin network of the airway wall. Fibered confocal fluorescence microscopy (FCFM) is a new and non-invasive imaging technique performed during bronchoscopy that may visualize elastic fibres, as shown by in vitro spectral analysis of elastin powder. We hypothesized that FCFM images capture in vivo elastic fibre patterns within the airway wall and that such patterns correspond with airway histology. We aimed to establish the concordance between the bronchial elastic fibre pattern in histology and FCFM. Second, we examined whether elastic fibre patterns in histology and FCFM were different between asthmatic subjects and healthy controls. Finally, the association between these patterns and lung function parameters was investigated.

Methods: In a cross-sectional study comprising 16 subjects (8 atopic asthmatic patients with controlled disease and 8 healthy controls) spirometry and bronchoscopy were performed, with recording of FCFM images followed by endobronchial biopsy at the airway main carina. Elastic fibre patterns in histological sections and FCFM images were scored semi-quantitatively. Agreement between histology and FCFM was analysed using linearly weighted kappa κw.

Results: The patterns observed in histological sections and FCFM images could be divided into 3 distinct groups. There was good agreement between elastic fibre patterns in histology and FCFM patterns (κw 0.744). The semi-quantitative pattern scores were not different between asthmatic patients and controls. Notably, there was a significant difference in post-bronchodilator FEV1 %predicted between the different patterns by histology (p = 0.001) and FCFM (p = 0.048), regardless of asthma or atopy.

Conclusion: FCFM captures the elastic fibre pattern within the airway wall in humans in vivo. The association between post-bronchodilator FEV1 %predicted and both histological and FCFM elastic fibre patterns points towards a structure-function relationship between extracellular matrix in the airway wall and lung function.

Trial registration: Netherlands Trial Register NTR1306.

Figures

Figure 1

FCFM and biopsy during bronchoscopy. The FCFM probe was placed perpendicularly to the surface of the main carina (a) followed by endobronchial biopsy at the same location (b). Figure 1c and 1d gives a lateral view of the probe and biopsy location respectively. * = main carina.

Figure 2

Representative histological sections (20 × magnification) and corresponding FCFM images. Fibres were thin and loosely organized in the 'wispy' group (a), whereas these were thick and linearly organized into a layer in the 'lamellar' group (c). No specific pattern was present in the FCFM images of the 'wispy' group (d). Individual thick lines in layer-form were observed in FCFM images of the 'lamellar' group (f). Patterns of the 'mixed' group were a combination of those seen in the 'wispy' and 'lamellar' groups (b, e).

Figure 3

Pattern grading by histology (a) and FCFM (b). A = asthma; Total = all healthy control subjects; HA = healthy, atopic; HNA = healthy, non-atopic. Chi-square test: p > 0.05.

Figure 4

Post-bronchodilator FEV1 %predicted of the three classification scores in histology (a) and FCFM (b). Data presented as post-bronchodilator FEV1 %predicted of individual subjects and the mean per classification score. ● = asthma, ■ = healthy.