Husain, Aamir, et al. “FEV1/FEV6/As/an/Alternative/to/FEV1/FVC/in/the/Spirometric/Detection/of/Airway/Obstruction/in/Chronic/Smokers”. Annals of Punjab Medical College, vol. 10, no. 3, Aug. 2016, pp. 147-51, doi:10.29054/apmc/2016.281.