Regional Gas Exchange Measured by Xe Magnetic Resonance Imaging Before and After Combination Bronchodilators Treatment in Chronic Obstructive Pulmonary Disease.

Background: Hyperpolarized Xe magnetic resonance imaging (MRI) provides a non-invasive assessment of regional pulmonary gas exchange function. This technique has demonstrated that chronic obstructive pulmonary disease (COPD) patients exhibit ventilation defects, reduced interstitial barrier tissue uptake, and poor transfer to capillary red blood cells (RBCs). However, the behavior of these measurements following therapeutic intervention is unknown.

Purpose: To characterize changes in Xe gas transfer function following administration of an inhaled long-acting beta-agonist/long-acting muscarinic receptor antagonist (LABA/LAMA) bronchodilator.

Study Type: Prospective.

Population: Seventeen COPD subjects (GOLD II/III classification per Global Initiative for Chronic Obstructive Lung Disease criteria) were imaged before and after 2 weeks of LABA/LAMA therapy.

Field Strength/sequences: Dedicated ventilation imaging used a multi-slice 2D gradient echo sequence. Three-dimensional images of ventilation, barrier uptake, and RBC transfer used an interleaved, radial, 1-point Dixon sequence. Imaging was acquired at 3 T.

Assessment: Xe measurements were quantified before and after LABA/LAMA treatment by ventilation defect + low percent (ven ) and by barrier uptake and RBC transfer relative to a healthy reference population (bar and RBC ). Pulmonary function tests, including diffusing capacity of the lung for carbon monoxide (DL ), were also performed before and after treatment.

Statistical Tests: Paired t-test, Pearson correlation coefficient (r).

Results: Baseline ven was 57.8 ± 8.4%, bar was 73.2 ± 19.6%, and RBC was 36.5 ± 13.6%. Following treatment, ven decreased to 52.5 ± 10.6% (P < 0.05), and improved in 14/17 (82.4%) of subjects. However, RBC decreased in 10/17 (58.8%) of subjects. Baseline measurements of bar and DL were correlated with the degree of post-treatment change in ven (r = -0.49, P < 0.05 and r = -0.52, P < 0.05, respectively).

Conclusion: LABA/LAMA therapy tended to preferentially improve ventilation in subjects whose Xe barrier uptake and DL were relatively preserved. However, newly ventilated regions often revealed RBC transfer defects, an aspect of lung function opaque to spirometry. These microvasculature abnormalities must be accounted for when assessing the effects of LABA/LAMA therapy.

Level Of Evidence: 1 TECHNICAL EFFICACY STAGE: 4.