Prognostic Value of the Six-Second Spirometry in Patients with Chronic Obstructive Pulmonary Disease: A Cohort Study - Prats, Eva; Tejero, Elena; Pardo, Paloma; Gavilan, Adelaida; Galera, Raul; Ramon Donado, Jose; Angel Racionero, Miguel; Casitas, Raquel; Zapatero, Antonio; Garcia-Rio, Francisco; (Plos One, 2015)