Pisi, G., and A. Chetta. “Airway Clearance Therapy in Cystic Fibrosis Patients”. Acta Biomedica Atenei Parmensis, vol. 80, no. 2, Aug. 2009, pp. 102-6, https://mattioli1885journals.com/index.php/actabiomedica/article/view/1204.