Functional Ct Imaging For Identification Of The Spatial Determinants Of Small Airways Disease In Adult Asthma

Publication date: Available online 22 January 2019

Source: Journal of Allergy and Clinical Immunology

Author(s): Alex J. Bell, Brody H. Foy, Matthew Richardson, Amisha Singapuri, Evgeny Mirkes, Maarten van den Berge, David Kay, Chris Brightling, Alexander N. Gorban, Craig J. Galbán, Salman Siddiqui

abstract

Background

Asthma is a disease characterised by ventilation heterogeneity (VH). A number of studies have demonstrated that VH markers derived using impulse oscillometry (IOS) or multiple breath washout (MBW) are associated with key asthma patient related outcome measures and airways hyper responsiveness. However the topographical mechanisms of VH in the lung remain poorly understood.

Objectives

We hypothesised that specific regionalisation of topographical small airway disease would best account for IOS and MBW measured indices in patients.

METHODS

We evaluated paired expiratory/inspiratory computed tomography in a cohort of asthmatic (n=41) and healthy volunteers (n=11) to understand the determinants of clinical VH indices commonly reported using IOS and MBW. Parametric response mapping (PRM) was utilised to calculate functional small airways disease marker PRM^fSAD and Hounsfield unit (HU) based density change from total lung capacity to functional residual capacity (ΔHU); gradients of ΔHU, in gravitationally perpendicular (parallel), inferior-superior (anterior-posterior) axes, were quantified.

Results

ΔHU gradient in the inferior-superior axis provided the highest level of discrimination of both S_acin and R5-20. Patients with a high inferior-superior ΔHU gradient demonstrated evidence of reduced specific ventilation in the lower lobes of the lungs and high levels of PRM^fSAD. A computational small airway tree model confirmed that constriction of gravitationally dependant lower zone small airway branches would promote the largest increases in R5-R20. Ventilation gradients correlated with asthma control and quality of life but not with exacerbation frequency.

Conclusions

Lower lobe predominant small airways disease is a major driver of clinically measured VH in adult asthma.

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