T. A. Hussain, N. Y. Mohammed, N. Y. Mohammed, N. Y. Mohammed, and R. G. W. Al-Kadi, “The effect of age on pulmonary performance using (FEV1/FVC) % as indicator”, JFacMedBagdad, vol. 52, no. 4, pp. 459–561, Jan. 2011, doi: 10.32007/jfacmedbagdad.524957.