Dal Negro RW, Paoletti M, Pistolesi M. Standard spirometry to assess emphysema in patients with chronic obstructive pulmonary disease: the Emphysema Severity Index (ESI). Multidiscip Respir Med. 2021 Dec 6;16(1):805. doi: 10.4081/mrm.2021.805. PMID: 35003734; PMCID: PMC8672489.