The Role of Gas Flow in Transnasal Pulmonary Aerosol Delivery: A Double-blinded, Randomized Controlled Trial

Introduction Both in vitro and in vivo radiolabeled studies on nebulization via high flow nasal cannula (HFNC) showed that aerosol lung deposition decreased with the increasing nasal cannula gas flow, which, however, was not observed in patients with distressed breathing. In our previous in vitro study, we investigated the effects of the ratio of nasal cannula gas flow to subject's peak inspiratory flow (GF: IF) on the aerosol lung deposition, and we found that aerosol deposition in lung increased as the GF: IF decreased with an optimal GF: IF between 0.1 to 0.5 producing a stable "lung" deposition in both quiet and distress breathing. Thus we aimed to further validate such an optimal GF: IF in patients with reversible airflow limitations by the delivery of bronchodilators. Methods and analysis COPD and asthma patients with positive response to four actuations of albuterol via metered dose inhaler (MDI) and valved holding chamber (VHC) will be enrolled and consented in the study. After a washout period (1-3 days), patients will be randomly assigned to three groups with different nasal cannula gas flow: 50L/min, GF: IF = 1.0, and GF: IF = 0.5. In each treatment arm, patients will firstly receive saline, then followed by an escalating doubling dosages (0.5, 1, 2, and 4mg) of albuterol in a total volume of 2mL, delivered by mesh nebulizer (VMN, Aerogen, Ireland) via heated nasal cannula at 37℃. An interval of 30 min will be maintained between two doses of albuterol, and pulmonary spirometry will be measured at baseline and after each dose. Titration will be terminated when an additional FEV1 improvement was \< 5%.