Understand the importance of forced vital capacity
December 13, 2019
5 min read
Measuring forced vital capacity (FVC) is part of a spirometry or pulmonary function test that is conducted to assess lung health, airflow, and help in disease diagnosis and effectiveness of medical treatment.
Forced vital capacity is the amount of air that can be forcibly exhaled from your lungs after inhaling as deeply as possible. It is an important measurement to know for health concerns, and is also useful if you want to improve your physical performance.
Read further to understand why forced vital capacity is an important measurement to be aware of, to understand how it is tested, and to see why breathing training is a tool to help you improve your forced vital capacity.
What is Forced Vital Capacity?
Forced vital capacity is a measurement of lung size (in liters) and represents the volume of air in the lungs that can be exhaled following a deep inhalation.
People who live with chronic lung diseases will often have their pulmonary function tested in order to diagnose, monitor, and treat different lung diseases.
A diagnostic test,Spirometry, is performed by deeply inhaling and forcefully exhaling into a spirometer (a device that records the various measurements of lung function).
One of the benefits of spirometry testing is that it can detect abnormalities in lung function even when no signs or symptoms of disease are evident.
Spirometry can also be used to assess the effectiveness of medical treatment. If a medication is given to open narrowed airways, it should be monitored by spirometry to ensure that normal airflow is restored.
If the FVC is within 80% of the reference value the results are considered normal.
Parameters of Vital Capacity to assess
The three key spirometry measurements (FVC, FEV1 and FEV1/FVC ratio) for a given individual are compared to reference values.
The reference value is based on healthy individuals with normal lung function and it tells the doctor the values that would be expected for someone of the same sex, age, and height.
Vital capacity (VC) refers to the maximal volume of air that can be expired following maximum inhalation. It is the total of tidal volume, inspiratory reserve volume, and expiratory reserve volume:
(VC = V + IRV + ERV)
Vital capacity may be measured as inspiratory vital capacity (IVC), slow vital capacity (SVC), or forced vital capacity (FVC). The FVC is similar to VC, but it is measured as the patient exhales with maximum speed and effort.
Forced Vital Capacity (FVC)
Forced vital capacity is the total amount of air that can be exhaled following a deep inhalation in an FVC test. Thenormal FVC range for an adult is between 3liters and 5liters.
Forced expiratory volume (FEV1)
Forced expiratory volume is the amount of air forcefully exhaled in one second following a deep inhalation (FEV1).
FEV1/ FVC ratio
This number represents the percent of the lung size (FVC) that can be exhaled in one second (FEV1).
The normal value for the FEV1/FVC ratio is 70%. Abnormalities of the FEV1 and FEV1/FVC are the result of a decrease in the airflow through the lungs, which may be caused by obstructive lung diseases.
Examples of obstructive diseases include emphysema and asthma. It is also possible to have situations where both restrictive and obstructive diseases are present.
Understanding Forced Vital Capacity and your lung function
First, it is important to point out that your body will automatically adjust to your need for oxygen.
For example, when you are physically active and need greater amounts of oxygen for your muscles, your respiratory breathing rate will speed up to provide oxygen to your body and muscles faster. That happens automatically in a process where sensors in your brain, blood vessels, muscles, and lungs detect your level of oxygen and carbon dioxide.
The amount that you exhale and breathe from your lungs, which is measured in the forced vital capacity tests, also indicates the residual volume, which is another important measurement of your lung function.
Residual volume is the volume of air that remains in the lungs after maximum forceful expiration. In other words, it is the volume of air that cannot be expelled from the lungs.
The residual volume helps the lung tissues from sticking together and prevents large fluctuation of O2 and CO2. However, too much of what is left in your lungs is unhealthy, and that is why you want to limit the residual volume.
Taking deeper breath decreases the residual volume, and at the same time, increases the capacity of your lungs, thus providing you with greater volumes of air inhaled and exhaled through each breath.
When you take deeper breaths you are actually training and exercising; you strengthen the whole respiratory system. That is the diaphragm, intercostals, and abdominals that contract and relax as your breath.
The different parameters of lung volume
As seen in the graph below, the volume of air that we inhale and exhale differs.
As depicted, thetotal lung capacity is about 5½ liters of air; however, most of this capacity is not used during normal breathing.
Tidal volume is defined as the volume of air moved into and out of the lungs during each ventilation cycle. At rest, an adult’s tidal volume is about a ½ liter (or only about 10% of total lung volume).
The inspiratory reserve volumeis the amount of air that can be taken into the lungs (above the tidal volume) upon forced inspiration.
The expiratory reserve volume is the amount of air that can be pushed out of the lungs (beyond the tidal volume) upon forced expiration.
Vital capacity is the total volume of air that can be moved into and out of the lungs.
Besides the factors that set a natural limit to our lungs, we are able to train and extend these different volumes and capacities. As much of the breathing process happens automatically, you train to optimize your lung function and breathing pattern.
The figure shows the lung volumes and capacities of normal adults.
Train your deep breathing and experience the difference in performance
Deep breathing can help people who suffer from chronic lung diseases to train and work with their breathing, and it can also improve general physical performance.
When your body needs more oxygen through intense and physical activity, you start to pant to get more air, which affects endurance. By learning to take deeper breaths, you are automatically training yourself to take in more oxygen per breath.
This happens because during the process your respiratory muscles are strengthened, therefore, becoming more empowered to take a deeper breath.
Your diaphragm, also known as belly breathing, is increasingly activated.
As a result, you utilize greater amounts of your lung’s capacity and increase your vital capacity. By increasing your vital capacity, oxygen is more sufficiently sent to your muscles. That means that you are able to train longer and with a lower sense of effort.
It makes you proactive and helps you to improve your breathing muscles, which increasingly will strengthen your ability to take deeper breaths during high-intensity activity.
Deeper breathing uses a bit more energy but also allows increased amounts of oxygen to enter the bloodstream with each breath. Oxygen in your bloodstreams increases your ability to perform longer and preserve more energy.