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{{short description|Test to evaluate respiratory system}}
{{Infobox diagnostic
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| Image
| Alt
| Caption
| DiseasesDB
| image = A modern body plethysmograph using ultrasound
| ICD10 = ▼
| caption = Plethysmograph "body box"
| ICD9 = ▼
| MedlinePlus = 003853▼
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| MeshID = D012129▼
| eMedicine =
| LOINC =▼
| OPS301 = {{OPS301|1-71}} ▼
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{{Pulmonary function}}
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==Indications==
Pulmonary function testing is a diagnostic and management tool used for a variety of reasons, such as:
* [[Restrictive lung disease]]▼
===Pediatric neuromuscular disorders===▼
Neuromuscular disorders such as [[Duchenne muscular dystrophy]] are associated with gradual loss of muscle function over time. Involvement of respiratory muscles results in poor ability to cough and decreased ability to breathe well and leads to [[atelectasis|collapse of part or all of the lung]] leading to impaired gas exchange and an overall insufficiency in lung strength.<ref>Finder JD, Birnkrant D, Carl J, et al. Respiratory care of the patients with Duchenne muscular dystrophy: ATS consensus statement. Am J Respir Crit Care Med.2004;170 (4):456– 465</ref> Pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis.<ref name="pmid19420147">{{cite journal| author=Sharma GD| title=Pulmonary function testing in neuromuscular disorders. | journal=Pediatrics | year= 2009 | volume= 123 Suppl 4 | pages= S219–21 | pmid=19420147 | doi=10.1542/peds.2008-2952D | doi-access=free }}</ref>▼
* Monitor the effect of chronic diseases like [[asthma]], [[Chronic obstructive pulmonary disease|chronic obstructive lung disease]], or [[cystic fibrosis]].
* Detect early changes in lung function.
* Identify narrowing in the airways.
* Evaluate airway bronchodilator reactivity.
* Show if environmental factors have harmed your lungs
* Preoperative testing<ref>{{Cite web |title=Pulmonary Function Tests |url=https://www.thoracic.org/patients/patient-resources/resources/pulmonary-function-tests.pdf |access-date=June 15, 2022 |website=American Thoracic Society}}</ref>
Pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis.<ref name="pmid19420147">{{cite journal| author=Sharma GD| title=Pulmonary function testing in neuromuscular disorders. | journal=Pediatrics | year= 2009 | volume= 123 Suppl 4 | pages= S219–21 | pmid=19420147 | doi=10.1542/peds.2008-2952D | doi-access=free }}</ref>
▲
==Tests==
===Spirometry===
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The measurements taken by the spirometry device are used to generate a pneumotachograph that can help to assess lung conditions such as: asthma, pulmonary fibrosis, cystic fibrosis, and chronic obstructive pulmonary disease. [[Physician]]s may also use the test results to diagnose bronchial hyperresponsiveness to exercise, cold air, or pharmaceutical agents.<ref>Pulmonary Function Test in New York, Article. June 2010. Dr. Marina Gafanovich, MD - 1550 York Ave, New York NY 10028 - (212) 249-6218. [http://www.mynycdoctor.com/pulmonary-function-testing NYC Pulmonary Function Test.]</ref>
====
{{Main|Helium dilution technique}}▼
The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit.<ref>Hathirat S, Renzetti AD, Mitchell M: Measurement of the total lung capacity by helium dilution in a constant volume system, Am Rev Respir Dis 102:760, 1970.</ref> This technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed [[spirometer]], that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs.▼
==== Nitrogen Washout ====
{{Main|Nitrogen washout}}▼
The nitrogen washout technique uses a non-rebreathing open circuit. The technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs.<ref>Boren HG, Kory RC, Snyder JC: The veterans Administration-Army cooperative study of pulmonary function, II: the lung volume and its subdivisions in normal men, Am J Med 41:96, 1966.</ref>▼
===Plethysmography===▼
{{Main|Plethysmograph|Lung volumes}}▼
The plethysmography technique applies [[Boyle's law]] and uses measurements of volume and pressure changes to determine total lung volume, assuming temperature is constant.<ref>Dubois AB, et al: A rapid plethysmographic method for measuring thoracic gas volume: a comparison with a nitrogen washout method for measure FRC in normal patients, J Clin Invest 35:322, 1956.</ref>▼
There are four lung volumes and four lung capacities. A lung's capacity consists of two or more lung volumes. The lung volumes are [[tidal volume]] (V<sub>T</sub>), [[inspiratory reserve volume]] (IRV), [[expiratory reserve volume]] (ERV), and [[Lung volumes|residual volume]] (RV). The four lung capacities are [[total lung capacity]] (TLC), inspiratory capacity (IC), [[functional residual capacity]] (FRC) and [[vital capacity]] (VC).
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{{Main|Diffusing capacity}}
Measurement of the single-breath diffusing capacity for [[carbon monoxide]] (DLCO) is a fast and safe tool in the evaluation of both restrictive and [[obstructive lung disease]].
=== Bronchodilator responsiveness ===
When a patient has an obstructive defect, a bronchodilator test is given to evaluate if airway constriction is reversible with a short acting beta-agonist. This is defined as an increase of ≥12% and ≥200 mL in the FEV1 or FVC.<ref>{{Cite journal |last=Sim |first=Yun Su |last2=Lee |first2=Ji-Hyun |last3=Lee |first3=Won-Yeon |last4=Suh |first4=Dong In |last5=Oh |first5=Yeon-Mok |last6=Yoon |first6=Jong-seo |last7=Lee |first7=Jin Hwa |last8=Cho |first8=Jae Hwa |last9=Kwon |first9=Cheol Seok |last10=Chang |first10=Jung Hyun |date=2017 |title=Spirometry and Bronchodilator Test |url=http://e-trd.org/journal/view.php?doi=10.4046/trd.2017.80.2.105 |journal=Tuberculosis and Respiratory Diseases |language=en |volume=80 |issue=2 |pages=105 |doi=10.4046/trd.2017.80.2.105 |issn=1738-3536 |pmc=PMC5392482 |pmid=28416951}}</ref>
===Oxygen desaturation during exercise===
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==Techniques==
===
Subjects have an measurements of height and weight taken before spirometry to determine what their predicted values should be. Additionally, a history of smoking, recent illness, and medications is taken.
▲{{Main|Helium dilution technique}}
▲The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit.<ref>Hathirat S, Renzetti AD, Mitchell M: Measurement of the total lung capacity by helium dilution in a constant volume system, Am Rev Respir Dis 102:760, 1970.</ref> This technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed [[spirometer]], that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs.
===
In order for the forced vital capacity to be considered accurate it has to be conducted three times where the peak is sharp in the flow-volume curve and the exhalation time is longer than 6 seconds.
▲{{Main|Nitrogen washout}}
▲The nitrogen washout technique uses a non-rebreathing open circuit. The technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs.<ref>Boren HG, Kory RC, Snyder JC: The veterans Administration-Army cooperative study of pulmonary function, II: the lung volume and its subdivisions in normal men, Am J Med 41:96, 1966.</ref>
Reproducibility of the PFT is determined by comparing the values of forced vital capacity (FVC) and forced expiratory volume at 1 second (FEV1). The difference between the highest values of two FVCs need to be within 5% or 150 mL. When the FVC is less than 1.0 L, the difference between the highest two values must be within 100 mL. Lastly, the difference between the two highest values of FEV1 should also be within 150 mL. The highest FVC and FEV1 may be used from each different test. Until the results of three tests meet the criteria of reproducibility, the test can be repeated up to eight times. If it is still not possible to get accurate results, the best three tests are used.<ref>{{Cite journal |last=Sim |first=Yun Su |last2=Lee |first2=Ji-Hyun |last3=Lee |first3=Won-Yeon |last4=Suh |first4=Dong In |last5=Oh |first5=Yeon-Mok |last6=Yoon |first6=Jong-seo |last7=Lee |first7=Jin Hwa |last8=Cho |first8=Jae Hwa |last9=Kwon |first9=Cheol Seok |last10=Chang |first10=Jung Hyun |date=April 2017 |title=Spirometry and Bronchodilator Test |url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5392482/ |journal=Tuberculosis and Respiratory Diseases |volume=80 |issue=2 |pages=105–112 |doi=10.4046/trd.2017.80.2.105 |issn=1738-3536 |pmc=5392482 |pmid=28416951}}</ref>
▲===Plethysmography===
▲{{Main|Plethysmograph}}
▲The plethysmography technique applies [[Boyle's law]] and uses measurements of volume and pressure changes to determine lung volume, assuming temperature is constant.<ref>Dubois AB, et al: A rapid plethysmographic method for measuring thoracic gas volume: a comparison with a nitrogen washout method for measure FRC in normal patients, J Clin Invest 35:322, 1956.</ref>
==Interpretation of tests==
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== Risks ==
Pulmonary function testing is a safe procedure; however, there is cause for concern regarding untoward reactions and the value of the test data should be weighed against potential hazards. Some complications
== Contraindications ==
There are some indications against a pulmonary function test being done. These include a recent heart attack, stoke, head injury, an aneurysm, or confusion.<ref>{{Cite web |title=Lung Function Tests |url=https://www.lung.org/lung-health-diseases/lung-procedures-and-tests/lung-function-tests |access-date=2022-06-15 |website=www.lung.org |language=en}}</ref>
==Clinical significance==
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