Eastwood B, Jepsen N, Coulter K, Wong C, Zeng I. Challenges of undertaking a clinical trial using bubble-PEP in an acute exacerbation of chronic obstructive pulmonary disease: A feasibility study. NZJP [Internet]. 2016 Mar. 1 [cited 2024 Sep. 20];44(1):8–16. Available from: https://nzjp.otago.ac.nz/nzjp/article/view/122