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The spirometry test is performed using a device called a spirometer, which comes in several different varieties. Most spirometers display the following graphs:
A Volume-Time Curve:
showing volume (liters) along the Y-axis and time (seconds) along the X-axis.
A Flow-Volume Loop:
which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis.
The most commonly used guidelines for spirometric testing and interpretation are set by the American Thoracic Society (ATS) and the European Respiratory Society (ERS).
Procedure
The basic FVC test varies slightly depending on the equipment used. Generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as
hard as possible, for as long as possible. It is sometimes directly followed by a rapid inhalation (inspiration), in particular when assessing possible upper airway obstruction. Sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced exhalation. During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of micro-organisms, particularly for inspiratory maneuvers.
Limitations of test:
The maneuver is highly dependent on patient cooperation and effort, and is normally repeated at least three times to ensure reproducibility. Since results are dependent on patient cooperation, FEV1 and FVC can only be underestimated, never over-estimated. Due to the fact that patient cooperation is required, spirometry can only be used on children old enough to comprehend and follow the instructions given typically about 4-5 years old), and only on patients who are able to understand and follow instructions - thus, this test is not suitable for patients who are unconscious, heavily sedated, or have limitations that would interfere with vigorous respiratory efforts.
Other types of lung function tests are available for infants and unconscious persons.
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Hoboken Allergy & Asthma Specialists, LLC: - Spirometry
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