Vital capacity is defined as the amount of air that can be forcibly exhaled after a deep inspiration. The lung volume increases in a taller person due to increased thorax size and increased lung size.
Lung volumes and lung capacity are different definitions of the respiratory cycle. Each stage is measured by the amount or volume of air based on the action that is occurring, such as inhaling or exhaling. While lung volumes are directly measured, lung capacities are interpreted from lung volumes. Vital capacity is determined by adding the tidal volume or regular breathing inspiration with the inspiratory reserve volume, known as forcibly inhaled air following normal inspiration, and the expiratory reserve volume, or the forcibly exhaled air. These volumes are affected by age of person. Infants have much smaller lungs as opposed to fully grown, healthy adults. Also, the size of the lungs affects the amount of volume during each stage of the cycle. When someone is taller, the lungs are generally larger, which in a healthy adult increases the surface area and increases all volumes during the respiratory cycle. The average vital capacity of a healthy adult male is 4,800 milliliters, which is 80 percent of total lung capacity.