Spirometry · What Is It, Indications, Technique, Results, and More

Spirometry is a basic pulmonary function test (PFT) that measures the amount of air that moves in and out of the lungs in one forced breath. When performed correctly, the results of spirometry can help assess lung function and detect respiratory disorders like asthma or chronic obstructive pulmonary disease (COPD). Other pulmonary function tests include plethysmography, which measures how much air is inside the lungs after a full exhalation; and the lung’s diffusing capacity for carbon monoxide (DLCO), which is a measure of how well gases are transferred between the lungs and the blood.

Spirometry is performed to detect the presence or absence of lung disease in individuals with a history of tobacco use, exposure to lung irritants, or respiratory symptoms, such as shortness of breath, persistent coughing, increased sputum, or wheezing. Specifically, it can be used to diagnose asthma and other obstructive lung disorders like COPD.  In conditions like COPD, spirometry can also help determine the severity of airway obstruction and monitor the progression of the disease and the efficacy of treatment. Finally, spirometry is sometimes performed as part of a preoperative evaluation to assess lung function and determine the individual’s ability to tolerate anesthesia and surgery.

A spirometry test is generally performed by trained healthcare professionals in primary care settings or specialist clinics and typically lasts between 15 and 30 minutes. Before a spirometry appointment, individuals may be advised to cease smoking and avoid exercising vigorously at least 1 hour before the test. They may also be recommended to wear loose, comfortable clothing that doesn’t restrict the chest area and withhold bronchodilator (e.g., albuterol, salbutamol) use the day before the test. On the day of the appointment, the operator will measure the height and weight of the individual. If they used an inhaled bronchodilator on the day of the test, individuals may also record the dose and time it was taken.

A spirometry test is performed with the individual sitting upright with their feet flat on the floor. The individual will be given a disposable mouthpiece attached to a device called a spirometer. Then, they will be instructed to take a deep breath in, then forcibly exhale into the spirometer until all of the air is emptied from their lungs. Next, the individual will be asked to breathe in again as forcefully and fully as possible. In cases where bronchodilator response is being assessed, spirometry will be repeated a few minutes after administering a short-acting bronchodilator like salbutamol (i.e., Ventolin).

Doing a spirometry properly requires considerable effort and may require several attempts to obtain acceptable results. The test is complete when the spirometry has yielded three curves that meet acceptability and repeatability criteria. Although spirometry is a safe, non-invasive test, individuals can sometimes feel lightheaded or dizzy during or after the test due to the intense breathing effort.

Spirometry test results are interpreted by assessing the shape of the flow–volume curve and comparing the individual’s results with reference values obtained from populations matched for the same age, sex, height, and ethnicity.

The main spirometric indices are the FVC, or forced vital capacity, which is the maximum amount of air a person can forcibly exhale from their lungs after a maximum inhalation; and the FEV1, which is the volume of air exhaled during the first second of this forced exhalation. Other values, such as forced expiratory flow between 25% and 75% of FVC (FEF25–75%) and forced expiratory volume in 6 seconds (FEV6), are not commonly used as they have limited clinical value.

There are two main types of abnormal ventilatory patterns: obstructive and restrictive. In obstructive lung diseases, like asthma or COPD, there is a significant reduction in FEV1 due to the narrowing of the airways, which hinders how fast air can leave the lungs during expiration. Conversely, FVC is usually normal or only slightly decreased, which results in a disproportionate decrease in FEV1 relative to FVC. A FEV1/FVC ratio of less than 0.7 is considered the hallmark of obstructive lung disease and the degree of FEV1 reduction can be used to determine the severity of the airway obstruction.

In restrictive lung diseases, like pulmonary fibrosis or interstitial lung diseases, there is a decrease in the amount of air the lungs can hold, which results in a decreased forced vital capacity, or FVC. Because there is less air in the lungs, the volume of air exhaled during the first second of exhalation, or FEV1, is reduced as well. As a result, the FEV1/FVC ratio, which is normally between 0.7 and 0.8, usually stays the same because both volumes decrease proportionally.

Both obstructive and restrictive lung diseases can change the spirometry flow-volume curve, which is used to show how airflow relates to lung volume. In obstructive lung diseases, the flow-volume curve is typically concave, whereas in restrictive lung diseases, it has a normal shape but is smaller than usual.

Bronchodilator response is used to determine if a person’s airflow obstruction improves with the use of bronchodilators. To determine if airflow obstruction is reversible or not reversible,  spirometry is performed before the administration of a short-acting bronchodilator, like salbutamol (e.g., Ventolin), and then post-bronchodilator spirometry is performed 10 to 15 minutes afterward.

A positive bronchodilator response is generally defined as an increase of ≥12% and ≥200 mL in either FEV1 or FVC compared with baseline values. A positive bronchodilator response is often seen in individuals with asthma, whereas a persistent or fixed airway obstruction is characteristic of COPD.

Spirometry is a pulmonary function test (PFT) that measures how much air moves in and out of the lungs during a forced breath and how quickly it does so. This test can be performed to assess lung function and diagnose lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and restrictive lung disorders. It involves taking a deep breath in, and then forcibly exhaling into a spirometer until all of the air is emptied from the lungs. Lung function is assessed by comparing the individual’s results with normal reference values and with previous results, if available. The main spirometry values include forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), and FEV1/FVC ratio.