Evaluation of pulmonary function is important in many clinical situations, both when the patient has a history or symptoms suggestive of lung disease, and when risk factors for lung disease are present, such as cigarette smoking . An overview of pulmonary function testing will be presented here, summarizing the types of pulmonary function tests and their indications. Specific aspects of pulmonary function testing are discussed elsewhere. (See "Office spirometry" and "Reference values for pulmonary function testing" and "Diffusing capacity for carbon monoxide".)
PULMONARY FUNCTION TESTS
The major types of pulmonary function tests include spirometry, measurement of lung volumes, and quantitation of diffusing capacity. Measurements of maximal respiratory pressures and flow-volume loops, which record forced inspiratory and expiratory flow rates, are also useful in specific clinical circumstances (table 1).
Spirometry — Spirometry, which includes measurement of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), is the most readily available and most useful pulmonary function test. It takes 10 to 15 minutes, uses a $2000 instrument, and carries no risk. (See "Office spirometry" and "Flow-volume loops".)
The slow vital capacity (SVC) can also be measured with spirometers which collect data for at least 30 seconds. The SVC may be a useful measurement when the forced vital capacity (FVC) is reduced and airways obstruction is present. Slow exhalation results in a lesser degree of airway narrowing, and the patient may produce a larger, even normal vital capacity. In contrast, the vital capacity with restrictive disease is reduced during both slow and fast maneuvers. Thus, if the slow or forced vital capacity is within the normal range, it is generally unnecessary to measure static lung volumes (residual volume and total lung capacity) .
Flow-volume loop — Flow-volume loops, which include forced inspiratory and expiratory maneuvers, should be performed whenever stridor is heard over the neck during forced breathing or for evaluation of unexplained dyspnea. Airway obstruction located in the pharynx, larynx, or trachea (upper airways) is usually impossible to detect from standard FVC maneuvers. Reproducible forced inspiratory vital capacity (FIVC) maneuvers may detect variable upper airway obstruction , as can be seen with vocal cord paralysis or dysfunction, which causes a characteristic limitation of flow (plateau) during forced inhalation but little if any obstruction during exhalation (figure 1). (See "Flow-volume loops".)