Peripheral and proximal lung ventilation in asthma; short-term variation and response to bronchodilator

Background

The relative involvement of the large and small airways in asthma is not clear. Hyperpolarised gas MRI provides high resolution three-dimensional images of ventilation distribution which can be quantified by the ventilated volume percentage of the lungs (VV%).

Objective

To (1) quantify the baseline reproducibility of VV%, (2) assess the ventilation distribution between the proximal and peripheral lungs and (3) investigate regional ventilation response to bronchodilator inhalation in a cohort of patients with asthma.

Methods

33 patients with poorly controlled, moderate-to-severe asthma were scanned with hyperpolarised 3He MRI. Two image datasets were acquired at baseline, and one image dataset was acquired after bronchodilator inhalation. Images were divided into proximal and peripheral regions for analysis.

Results

Bland-Altman analysis showed strong reproducibility of VV% (bias = 0.12%, LOA = -1.86, 2.10%). VV% variation at baseline was greater in the periphery than in the proximal lung. The proximal lung was better ventilated than the peripheral lung. Ventilation increased significantly in response to bronchodilator, globally and regionally, and the ventilation increase in response to bronchodilator was greater in the peripheral lung than in the proximal lung. Hyperpolarised gas MRI was more sensitive to changes in response to bronchodilator (58%) than spirometry (33%).

Conclusion

The peripheral lung showed reduced ventilation and a greater response to bronchodilator than the proximal lung. The high level of baseline reproducibility and sensitivity of hyperpolarised gas MRI to bronchodilator reversibility suggests that it is suitable for low subject number studies of therapy response.