Predicted lung volumes and capacities are based on anthropometric factors (height, weight, sex, age) that vary among different individuals. In some cases, these predicted values may not be accurate because of a variety of medical conditions that affect breathing.
Typical physiologic changes in lung volumes occur during health and disease, with normal increases in respiratory reserves and residual volume (RV), and a normal total lung capacity (TLC) percentage. Obstructive diseases result in hyperinflation of the RV, and increased TLC, with an FVC that can be as high as 150% in emphysema and severe fibrosis.
Other pulmonary disorders are less common but can have significant effects on breathing. For example, many general anesthetics and surgical procedures can negatively impact pulmonary mechanics.
Lung volume is divided into three subdivisions: tidal volume, inspiratory reserve volume (IVR), and expiratory reserve volume (ERV). The tidal volume is the amount of air that is moved into the lungs during each ventilation cycle.
During a healthy person's life, tidal volume is usually around a half-liter. However, it can be higher than this because gas gets trapped in the lungs - called lung hyperinflation.
The total amount of air that can be forcefully exhaled after inhaling with maximum speed and effort is measured as forced vital capacity (FVC). A normal FVC ranges between 3 to 5 liters. During an FVC test, you must inhale with maximum effort and then exhale as deeply as possible. A normal FVC can be a strong indicator of your health and help you breathe easier.
