Figure 2 – Schematic diagram of the decline in lung function with age in nonsmokers, smokers and those who quit. Black: never-smoker or not susceptible to smoke; red: regular smoker and susceptible to smoke; green: quitter at age 45 years; blue: quitter at age 65 years. FEV1: forced expiratory volume in 1 s. The horizontal pink line indicates the level at which symptoms are likely to be disabling and the broken black line the level at which death is likely. Note that stopping smoking slows the rate of decline of lung function.
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