Bhatt SP, Agusti A, Bafadhel M, Christenson SA, Bon J, Donaldson GC, Sin DD, Wedzicha JA, Martinez FJ. Phenotypes, Etiotypes, and Endotypes of Exacerbations of Chronic Obstructive Pulmonary Disease. Am J Respir Crit Care Med. 2023 Nov 15; 208(10):1026-1041.