From the Guidelines
Vital capacity of the lungs is measured using a spirometer, with the patient taking a deep breath in and then exhaling fully into the device, and the total volume of air exhaled represents the vital capacity, typically between 3-5 liters in healthy adults, as stated in the most recent study 1. To measure vital capacity, the patient should be seated comfortably, with a nose clip to ensure all air passes through the mouth. The following steps should be taken:
- Check the spirometer calibration
- Explain the test to the patient
- Prepare the patient by asking about smoking, recent illness, medication use, etc.
- Measure the patient's weight and height without shoes
- Instruct and demonstrate the test to the patient, including correct posture and inhalation and exhalation techniques
- Perform the manoeuvre, having the patient assume the correct posture, attach a nose clip, and place the mouthpiece in the mouth
- Repeat the manoeuvre as necessary, coaching the patient vigorously, and check test repeatability. The test should be performed while the patient is seated comfortably, with a nose clip to ensure all air passes through the mouth. For accurate results, patients should avoid smoking, heavy meals, and vigorous exercise before testing. Vital capacity measurement is important for diagnosing respiratory conditions like COPD, asthma, and restrictive lung diseases, as it helps determine the functional capacity of the lungs and the severity of any impairment, as discussed in 1 and 1. It is also important to note that the use of pre- and post-bronchodilator spirometry can help in the diagnosis of COPD, as stated in 1 and the measurement of forced vital capacity (FVC) and forced expiratory volume (FEV) are crucial in assessing lung function, as mentioned in 1 and 1.
From the Research
Measurement of Vital Capacity
Vital capacity can be measured using spirometry, a pulmonary function test that quantifies respiratory volumes and flows.
- Forced vital capacity (FVC) is a parameter measured by spirometry, which is the volume of air that can be forcibly exhaled from the lungs after a maximal inhalation 2, 3, 4, 5.
- Spirometry is a simple, non-invasive test that is easy to perform and can be used to screen, diagnose, and monitor respiratory diseases 2.
- The measurement of vital capacity is an important aspect of pulmonary function testing, as it can help identify abnormalities in lung function, such as obstruction or restriction 3, 6.
Methods of Measurement
There are different methods of measuring vital capacity, including:
- Forced expiratory volume in one second (FEV1) and its ratio to FVC (FEV1/FVC) can be used to detect airflow limitation and classify the severity of chronic obstructive pulmonary disease (COPD) 3.
- Peak expiratory flow (PEF) and the ratio of % predicted PEF to % predicted vital capacity (%PEF/%VC) can be used to screen for pulmonary fibrosis 6.
- Portable spirometers can be used to measure vital capacity and other pulmonary function parameters, and have been shown to be reliable and usable compared to laboratory spirometers 4, 5.
Devices Used for Measurement
Different devices can be used to measure vital capacity, including:
- Laboratory spirometers, such as the Jaeger MasterScreen PFT, which are considered the gold standard for pulmonary function testing 4, 5.
- Portable spirometers, such as the Yue Cloud spirometer and the Medcaptain VC-30 Pro, which offer advantages in terms of affordability, user-friendliness, and portability 4, 5.