S. Farag, T., and M. EL-Syed. “Utility of Vest High Frequency Chest Wall Oscillation Device Versus Flutter Device in Acute Exacerbation of Chronic Obstructive Pulmonary Disease”. International Journal of Research in Medical Sciences, vol. 6, no. 1, Dec. 2017, pp. 1-9, doi:10.18203/2320-6012.ijrms20175703.