1. U.S. Census Bureau. P23-212, 65+ in the United States: 2010. Washington, DC: U.S. Government Printing Office; 2014. https://www.census.gov/content/dam/Census/library/publications/2014/demo/p23-212.pdf
2. National Center for Health Statistics. Health, United States, 2016: With Chartbook on Long-Term Trends in Health. Hyattsville, MD; 2017. https://www.cdc.gov/nchs/data/hus/hus16.pdf#020
3. López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. The halkmarks of aging. Cell. 2013 Jun 6;153(6):1194-1217. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3836174/
4. Johnson KN, Botros DB, Groban L, Bryan YF. Anatomic and physio pathologic changes affecting the airway of the elderly patient: Implications for geriatric-focused airway management. Clinical Interventions in Aging. 2015 Dec 4;10:1925-1934. DOI: 10.2147/CIA.S93796 eCollection 2015
5. D'Errico A, Scarani P, Colosimo E, Spina M, Grigioni WF, Mancini AM. Changes in the alveolar connective tissue of the ageing lung. An immunohistochemical study. Virchows Archiv A Pathological Anatomy and Histopathology. 1989;415(2):137-144