Eastwood, B., Jepsen, N., Coulter, K., Wong, C. and Zeng, I. (2016) “Challenges of undertaking a clinical trial using bubble-PEP in an acute exacerbation of chronic obstructive pulmonary disease: A feasibility study”, New Zealand Journal of Physiotherapy, 44(1), pp. 8–16. doi: 10.15619/NZJP/NZJP/44.1.02.