J. M. Ospina Díaz, F. G. Manrique Abril, L. Fernández Cely, M. Roa Cubaque, and A. Valero Ortiz, “Pulse oximetry in six minutes walking test as a predictor of functional respiratory alteration in workers at artisanal coal mining”, Univ. Salud, vol. 16, no. 2, pp. 167–176, Oct. 2014.