Once we reach maturity, we achieve a certain amount of lung tissue with the physical capability of holding a certain volume of air. Total lung capacity cannot be increased beyond what nature grants to a particular body. Only the elasticity of the lung tissue or chest wall can be increased. Jacobs compares lung capacity with the length of a stringed instrument’s bow. A small capacity requires breathing more often, like using an undersized bow on a violin requiring more up and down strokes.
To determine a person’s vital capacity, a test is given on a respirometer or spirometer. Other devices such as a Voldyne® and a measured air bag can also be used with less accuracy. These tests determine how much air [in liters] can be moved in or out of the lungs in a single breath.
After determining both the estimated vital capacity [from the formulas] and the actual vital capacity [from pulmonary function testing], the ratio is reported. It is determined by dividing the actual capacity by the estimated capacity. If, for example, a person has an actual capacity of five liters and an estimated capacity of four liters, this person would have a capacity of 125 percent of normal. Contrary to that, if a person had tested with a capacity of four liters with an estimated capacity of five liters, the ratio of 80 percent of normal – a shallow breather!
It is better to breathe use more air – it’s free!