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Prevalence and correlates of a ‘knee’ pattern on the maximal expiratory flow‐volume loop in young adults

Visual inspection of the maximal flow‐volume curve is an important step in interpreting spirometry. Many young people have a convex inflection or ‘knee’ on the expiratory part of the loop. This is thought to be a normal variant, but this view is based on theoretical grounds, and the epidemiology of the knee pattern has never been reported.