Smoking decreases vital capacity, which is the maximum amount of air people can expel from their lungs after maximum inhalation, according to New Health Guide. Vital capacity is equivalent to the sum of tidal volume, inspiratory reserve volume and expiratory reserve volume.
New Health Guide states that the vital capacity of adults is between 3 to 5 liters. It varies from person to person, depending on factors like age, sex, weight, height and ethnicity. Smoking leads to chronic respiratory disease, which is one of the causes of low vital capacity. Doctors use vital capacity to assess the capacity of the lungs to hold air. It is measured by having a person breathe out and then inhale as much as he can; doctors then measure the amount of air inhaled. Studies have shown that smoking decreases this capacity, even for people who have not smoked for a long time. A study found that people who started smoking during their adolescent years had the lowest vital capacity, and adolescent girls had somewhat lower capacity than boys.
Every cigarette affects a person’s breathing function and damages the lungs, according to BeTobaccoFree.gov. Smoking causes chronic bronchitis, which leads to swelling of the lining of the bronchial tubes. When this occurs, less air flows to and from the lungs.