Johnston, C. L., R. James, and J. H. Mackney. “The Current Use of Positive Expiratory Pressure (PEP) Therapy by Public Hospital Physiotherapists in New South Wales”. New Zealand Journal of Physiotherapy, vol. 41, no. 3, Nov. 2013, pp. 88–93, https://nzjp.org.nz/nzjp/article/view/64.