Oberwaldner, B.; Evans, J.C.; Zach, M.S. (1986). "Forced expirations against a variable resistance: a new chest physiotherapy method in cystic fibrosis". Pediatric Pulmonology. 2 (6): 358–67. doi:10.1002/ppul.1950020608. PMID3543830. S2CID25137971.
Oberwaldner, B.; Evans, J.C.; Zach, M.S. (1986). "Forced expirations against a variable resistance: a new chest physiotherapy method in cystic fibrosis". Pediatric Pulmonology. 2 (6): 358–67. doi:10.1002/ppul.1950020608. PMID3543830. S2CID25137971.
Oberwaldner, B.; Evans, J.C.; Zach, M.S. (1986). "Forced expirations against a variable resistance: a new chest physiotherapy method in cystic fibrosis". Pediatric Pulmonology. 2 (6): 358–67. doi:10.1002/ppul.1950020608. PMID3543830. S2CID25137971.