Definition and Overview
Spirometry literally means the “measurement of one’s breath.” This function test, which is one of the most commonly recommended procedures for patients with pulmonary problems, measures the function of the lungs, in terms of the volume and flow of air that the individual can exhale and inhale. The resulting data from this procedure are called pneumotachographs, which can be used to diagnose and assess certain conditions such as cystic or pulmonary fibrosis, asthma, bronchitis, emphysema, and chronic obstructive pulmonary disease (COPD).
This testing procedure is performed with the use of a spirometer, which measures the air volume expired and inspired by the lungs, as well as the movement of this air into and from the lungs. Most types of spirometers can identify two kinds of ventilation patterns that might indicate an abnormality in the lungs: restrictive and obstructive.
There are different kinds of spirometers, which employ a variety of methods to measure airflow and volume, such as water gauge, ultrasonic, and pressure transducer. Typical spirometers can produce two kinds of graphs: the volume-time curve (with time in seconds in the x-axis, and volume in liters in the y-axis) and the flow-volume loop (a graphical representation of the total volume inhaled/exhaled on the x-axis and air flow rate on the y-axis).
Who Should Undergo the Procedure and Expected Results
Spirometry is recommended for those who:
- are having trouble with their breathing
- are suspected of having lung diseases such as bronchitis, asthma, or emphysema.
- experience shortness of breath or have been exposed to chemical fumes in the workplace.
- are about to undergo a complicated surgery (to ensure that lung function is at healthy levels to prevent any problem during the surgical procedure)
- are under certain medications (doctors can use spirometry to assess the effects of these medications to the patient’s lungs)
- have a chronic lung disorder
Children who cannot comprehend the instructions for the test do not qualify for this procedure. Typically, the procedure, which is performed without the use of sedation, is done on patients aged six and above.
A spirometry procedure typically produces an FVC (forced vital capacity), which informs the medical professional the largest amount of air that the patient can exhale (with force) after being told to inhale as deeply as possible. If the FVC shows lower than normal readings, the doctor can safely conclude that the patient has restricted breathing.
Another spirometry reading would be the FEV-1 (forced expiratory volume), which measures the amount of air that the patient can force from his or her lungs in a second. This information helps the medical professional determine and assess the extent of the patient’s breathing problem. If the FEV-1 shows a lower than normal reading, the patient might have a significant obstruction in his or her airways that prevent normal breathing.
How Does the Procedure Work?
The way spirometry is performed varies depending on the type of equipment being used. However, for FVC tests, the patient is usually asked to inhale as deeply as possible. This breath will then be exhaled as forcefully as possible into the mouthpiece of the spirometry machine, which is equipped with sensors that can measure the volume of air inhaled and exhaled. The patient will need to exhale into the sensor for around six seconds. The doctor will then ask the patient to inhale rapidly to identify the presence and assess the extent of obstruction of the upper airway.
There are also some spirometry machines that require the patient to quietly inhale and exhale into the sensor to measure the tidal volume. Some doctors use nose clips made of soft, flexible materials to prevent air from escaping through the patient’s nose. The machine can also be fitted with special mouthpieces to filter patient’s breath and prevent microorganisms from spreading.
Possible Complications and Risks
Generally, a spirometry procedure is very safe. Some patients report a brief shortness of breath or dizziness after the test has been performed, but these will go away after a moment or two.
Patients who have recently suffered from a heart attack or any heart-related condition are not ideal candidates for a spirometry because the test requires some effort on the patient’s part.
In very rare cases, spirometry is known to trigger breathing problems in patients.
Hegewald MJ, Crapo RO. Pulmonary function testing. In: Mason RJ, Broaddus VC, Martin TR, et al., eds. Murray and Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 24.
Reynolds HY. Respiratory structure and function: mechanisms and testing. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 85.