Effect of OPEP on Mucus Plugging and Airflow Obstruction in Patients with Moderate-to-severe Asthma

Inclusion Criteria: 1. Able and willing to provide written informed consent. 2. Able and willing to comply with the study protocol. 3. Males and females ≥ 18 years of age. 4. Asthma diagnosed by a respiratory physician ≥12 months prior to study enrolment based on the Global Initiative for Asthma (GINA) 2014 guidelines - GINA 4 or 5. 5. ICS dose ≥500 mcg of fluticasone equivalent/day. Patients on prednisone or biologic for ≥3 months would not be excluded as long as they meet the rest of the inclusion criteria. 6. ACQ ≥1.5 during the screening period. 7. CT mucus score ≥4 during the screening period. Exclusion Criteria: 1. Acute or chronic parasitic, bacterial, fungal or viral infections that required, or currently requires, hospitalization or antimicrobial treatment during the last four weeks. 2. Acute asthma exacerbation event treated with increased doses of oral, or any dose of intramuscular (IM) or intravenous (IV) corticosteroids within six weeks prior to screening. 3. Other relevant pulmonary diseases (e.g., chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, cystic fibrosis, pulmonary arterial hypertension, tuberculosis) requiring treatment within 12 months prior to screening. 4. Alcohol or substance abuse within 12 months prior to screening. 5. Current smoker defined as having smoked at least one cigarette (or pipe, cigar, or cannabis) per day for ≥ 30 days within the three months prior to screening. 6. Ex-smokers with ≥ 15 pack-year smoking history. 7. Patient has an implanted mechanically, electrically, or magnetically activated device or any metal in their body which cannot be removed, including but not limited to pacemakers, neurostimulators, biostimulators, implanted insulin pumps, aneurysm clips, bioprosthesis, artificial limb, metallic fragment or foreign body, shunt, surgical staples (including clips or metallic sutures and/or ear implants) (at the discretion of the MRI Technologist). 8. In the investigator's opinion, subject suffers from any physical, psychological, or other condition(s) that might prevent performance of the MRI, such as severe claustrophobia. 9. Pregnant or breastfeeding 10. Participation in any clinical trial of an investigational agent or procedure within three months prior to screening or during the study.