Forced vital Capacity (FVC) is a measure of the amount of air someone can forcibly expel out of the lungs after taking a breath to fill the lungs as much as possible. A value in liters of air is typically used to express FVC. This measure is an important indicator of lung health. In people like conditions with chronic obstructive pulmonary disorder (COPD) and asthma, forced vital capacity is usually lower than expected for people of a similar gender, height, fitness level, and weight.
During lung function testing, known as spirometry, FVC is one of the things that will be measured. The patient is asked to take a deep breath to fill the lungs as much as possible. This breath does not need to be fast or forceful. Once the lungs are full, the patient blows out as hard and as fast as possible into a device capable of measuring the amount of air that the patient expels.
Forced vital capacity is plotted on a graph that typically shows a spike and a long downward tail. The spike represents the initial burst of air released from the lungs. As the patient's lungs deflate, less air is emitted, and the amount of air released over time falls as a result. This creates the distinctive tail seen on a FVC graph.
This test is usually repeated several times to develop an average. Patients may have trouble adjusting to the equipment and this can result in a skewed initial value. As patients get accustomed to the equipment and the process, the values will be more accurate. Averaging allows the clinician to even out the score across several measures to come up with a meaningful value.
Athletes usually have a higher forced vital capacity because their lungs are more developed, especially if they have been playing sports and working out for a long time. People like swimmers, runners, and bikers can have significantly better lung health than other individuals. Larger people also tend to have higher values because their lungs are bigger. Charts are available to compare a patient's results to people with a similar profile to determine whether they fall within normal values. If the values of a forced vital capacity test are unusually low, it is an indicator that something is wrong with the patient's lungs. Additional testing may be needed to learn more about what is happening inside the patient's body and why.