Spirometry is a test that determines the effectiveness of the various mechanical forces involved in lung and chest wall movement. It measures the maximum amount of air that can be exhaled rapidly and forcibly after a maximal deep inspiration. The results are a measure of airway function and the patency of the airway. The forced expiratory maneuver is also useful to quantify the extent and severity of airway obstruction.

Lung capacities, volumes, and flow rates are clinically measured by a mechanical device called a spirometer. The mechanical signal is converted to an electrical signal, which records the amounts of gas breathed in and out and produces a spirogram. Spirometers can be grouped into two major categories: (1) the mechanical or volume-displacement types (water-filled, dry-rolling seal, wedge, or bellows) and (2) the electronic or flow-sensing types (pneumotachometer or hot-wire anemometer). The values obtained provide quantitative information about the degree of obstruction (obstructive ventilatory impairment) to expiratory airflow or the degree of restriction (restrictive ventilatory impairment) of inspired air.

The helium dilution test measures static lung volumes and is performed with the use of a spirometer, along with helium and oxygen. This procedure only measures the air in the lung that undergoes gas exchange. The test may be performed with or without use of a bronchodilator and is not recommended for patients with chronic obstructive pulmonary disease (COPD) because of unequal distribution of helium in damaged lungs.

Nitrogen washout technique is used to measure anatomic dead space in the lungs. The patient inhales 100% oxygen and then exhales via a one-way valve that measures nitrogen content and volume. The test may be performed with or without use of a bronchodilator.

Body plethysmography, also known as lung plethysmography, is considered the gold standard for measuring lung function. The test is performed with the patient seated in a transparent box while taking breaths in and out using a mouthpiece.