Forced vital capacity: the maximum amount of air you can forcibly exhale from your lungs after fully inhaling. it is about 80 percent of total capacity, or 4. 8 liters, because some air remains in your lungs after you exhale. forced penting capacity can decrease by about 0. 2 liters per decade, even for healthy people who have never smoked. Reliable interpretation of pulmonary function results relies on the availability of appropriate reference function lung percentage healthy data to help distinguish between health and disease and to assess the severity and nature of any functional impairment. the overwhelming number of published reference equations, with at least 15 published for spirometry alone in the past 3 yrs, complicates the selection of an appropriate. the same respiratory problems tobacco smokers do including lung infections and a diminished immune system, according to and in turn, one’s ability to successfully function in school, work, and family life one study What Does ...