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Flow-Volume loop showing successful FVC maneuver. Positive values represent expiration, negative values represent inspiration. The trace moves clockwise for expiration followed by inspiration. (Note the FEV₁, FEV_1/2 and FEV₃ values are arbitrary in this graph and just shown for illustrative purposes, they must be recorded as part of the experiment).

Spirometry (meaning the measuring of breath) is the most common of the Pulmonary Function Tests (PFTs), measuring lung function, specifically the measurement of the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is an important tool used for generating pneumotachographs which are helpful in assessing conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and COPD.

[edit] Spirometry testing

Device for spirometry. The patient places his or her lips around the blue mouthpiece. The teeth go between the nubs and the shield, and the lips go over the shield. A noseclip guarantees that breath will flow only through the mouth.

Screen for spirometry readouts at right. The chamber can also be used for body plethysmography.

The spirometry test is performed using a device called a spirometer, which comes in several different varieties. Most spirometers display the following graphs, called spirograms:

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).

[edit] Procedure

The basic forced volume vital capacity (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 microorganisms, particularly for inspiratory maneuvers.

[edit] 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, FEV_1* and FVC can only be underestimated, never overestimated.(*FEV1 can be overestimated in people with some diseases - a softer blow can reduce the spasm or collapse of lung tissue to elevate the measure)

Due to the patient cooperation 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.

[edit] Related tests

Spirometry can also be part of a bronchial challenge test, used to determine bronchial hyperresponsiveness to either rigorous exercise, inhalation of cold/dry air, or with a pharmaceutical agent such as methacholine or histamine.

Sometimes, to assess the reversibility of a particular condition, a bronchodilator is administered before performing another round of tests for comparison. This is commonly referred to as a reversibility test, or a post bronchodilator test (Post BD), and is an important part in diagnosing asthma versus COPD.

**Explanation of common test values in spirometric tests**^[1]
Abbreviation	Name	Description
FVC	Forced Vital Capacity	This is the volume of air that can forcibly be blown out after full inspiration, measured in litres.
FEV₁	Forced Expiratory Volume in 1 Second	This is the maximum volume of air that can forcibly blow out in the first second during the FVC manoeuvre, measured in liters. Along with FVC it is considered one of the primary indicators of lung function.
FEV₁/FVC	FEV1%	This is the ratio of FEV₁ to FVC. In healthy adults this should be approximately 75–80%. In obstructive diseases (asthma, COPD, chronic bronchitis, emphysema) FEV₁ is diminished because of increased airway resistance to expiratory flow and the FVC may be increased (for instance by air trapping in emphysema). This generates a reduced value (<80%, often ~45%). In restrictive diseases (such as pulmonary fibrosis) the FEV₁ and FVC are both reduced proportionally and the value may be normal or even increased as a result of decreased lung compliance.
PEF	Peak Expiratory Flow	This is the maximal flow (or speed) achieved during the maximally forced expiration initiated at full inspiration, measured in litres per second.
FEF 25–75% or 25–50%	Forced Expiratory Flow 25–75% or 25–50%	This is the average flow (or speed) of air coming out of the lung during the middle portion of the expiration (also sometimes referred to as the MMEF, for maximal mid-expiratory flow). In small airway diseases such as asthma this value will be reduced, perhaps <65% of expected value. This may be the first sign of small airway disease detectable.
FIF 25–75% or 25–50%	Forced Inspiratory Flow 25–75% or 25–50%	This is similar to FEF 25–75% or 25–50% except the measurement is taken during inspiration.
FET	Forced Expiratory Time	This measures the length of the expiration in seconds.
SVC	Slow Vital capacity	Maximum volume of air that can be exhaled slowly after slow maximum inhalation.
TV	Tidal volume	During the normal, tidal breathing a specific volume of air is drawn into and then expired out of the lungs. This volume is tidal volume.
TLC	Total Lung Capacity	Maximum volume of air present in the lungs. Effectively the Vital Capacity plus residual volume.^{[dubious – discuss]}
DLCO	Diffusing Capacity	The carbon monoxide uptake from a single inspiration in a standard time (usually 10 sec). This will pick up diffusion impairments, for instance in pulmonary fibrosis. This must be corrected for anemia (because rapid CO diffusion is dependent on hemoglobin in RBC's a low hemoglobin concentration, anemia, will reduce DLCO) and pulmonary hemorrhage (excess RBC's in the interstitium or alveoli can absorb CO and artificially increase the DLCO capacity).^{[dubious – discuss]}
MVV	Maximum Voluntary Ventilation	A measure of the maximum amount of air that can be inhaled and exhaled in one minute, measured in liters/minute.

Note that functional residual capacity (FRC) cannot be measured via spirometry, but it can be measured with a plethysmograph or dilution tests (for example, helium dilution test).

Results are usually given in both raw data (litres, litres per second) and percent predicted - the test result as a percent of the "predicted values" for the patients of similar characteristics (height, age, sex, and sometimes race and weight). The interpretation of the results can vary depending on the physician and the source of the predicted values. Generally speaking, results nearest to 100% predicted are the most normal, and results over 80% are often considered normal. However, review by a doctor is necessary for accurate diagnosis of any individual situation.

[edit] Technologies used in spirometers

Volumetric Spirometers
- Water bell
- Bellows wedge
Flow measuring Spirometers
- Fleisch-pneumotach
- Lilly (screen) pneumotach
- Turbine (actually a rotating vane which spins because of the air flow generated by the subject. The revolutions of the vane are counted as they break a light beam)
- Pitot tube
- Hot-wire anemometer
- Ultrasound

[edit] See also

[edit] References

^ Miller, MR; Crapo R, Hankinson J et al. (July 2005). "General considerations for lung function testing". European Respiratory Journal 26 (1): 153–161. PMID 15994402. http://erj.ersjournals.com/cgi/content/full/26/1/153.

[edit] External links

[Miller-0] Miller, MR; Crapo R, Hankinson J et al. (July 2005). "General considerations for lung function testing". European Respiratory Journal 26 (1): 153–161. PMID 15994402. http://erj.ersjournals.com/cgi/content/full/26/1/153.

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