Total Lung Capacity Tab:
From the instant of the "first breath," the lungs have a certain total volume called the total lung capacity. This is the entire volume of air in the lungs after one inhales as much as one can. Total lung capacity equals the sum of the residual volume and the vital capacity.
Residual Volume Tab:
After the "first breath," the lungs are never completely emptied. Thus, there is a certain portion of air that is always present in the lungs. After one exhales as much air as possible, the portion remaining in the lungs is called the residual volume. In actuality, this is not "dead air," because air circulation continually refreshes the air of the residual portion. During quiet breathing, it amounts to about two-fifths of the total air volume exchanged.
Vital Capacity Tab:
The vital capacity of the lung is the total amount of air that can be exchanged during total filling and emptying of the lung. For example, if one inhales as much air as one can and then exhales as much as possible, the volume exhaled would be the vital capacity.