Pulmonary function testing: Difference between revisions

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{{Pulmonary function}}

'''Pulmonary function testing''' ('''PFT''') is a complete evaluation of the [[respiratory system]] including patient history, physical examinations, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment.<ref>{{cite journal | vauthors = Burrows B | title = Pulmonary terms and symbols: A report of the ACCP-ATS joint committee on pulmonary nomenclature. | journal = Chest | date = May 1975 | volume = 67 | issue = 5 | pages = 583–593 | doi = 10.1378/chest.67.5.583 | pmid = 1126197 }}</ref> Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFTs are normally performed by a pulmonary function techniciantechnologist, respiratory therapist, respiratory physiologist, physiotherapist, [[pulmonology|pulmonologist]], or general practitioner.

==Indications==

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{{Main|Spirometry}}

[[File:DoingSpirometry.JPG|left|thumb|Spirometry]]

Spirometry includes tests of pulmonary mechanics – measurements of FVC, FEV₁, FEF values, forced inspiratory flow rates (FIFs), and MVV. Measuring pulmonary mechanics assesses the ability of the lungs to move huge volumes of air quickly through the airways to identify airway obstruction.{{cn|date=November 2023}}

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>{{cite web | title = Pulmonary Function Test in New York | date = June 2010 | vauthors = Gafanovich M | url = http://www.mynycdoctor.com/pulmonary-function-testing }}</ref>

==== Helium Dilutiondilution ====

{{Main|Helium dilution technique}}

The [[helium dilution technique]] for measuring lung volumes uses a closed, rebreathing circuit.<ref name="pmid5475674">{{cite journal | vauthors = Hathirat S, Mitchell M, Renzetti AD | title = Measurement of the total lung capacity by helium dilution in a constant volume system | journal = The American Review of Respiratory Disease | volume = 102 | issue = 5 | pages = 760–70 | date = November 1970 | pmid = 5475674 | doi = 10.1164/arrd.1970.102.5.760 | doi-broken-date = 112 AugustJuly 20232025 }}</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.{{cn|date=November 2023}}

==== Nitrogen Washoutwashout ====

{{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>{{cite journal | vauthors = Boren HG, Kory RC, Syner JC | title = The Veterans Administration-Army cooperative study of pulmonary function: II. The lung volume and its subdivisions in normal men. | journal = The American Journal of Medicine | date = July 1966 | volume = 41 | issue = 1 | pages = 96–114 | doi = 10.1016/0002-9343(66)90008-8 }}</ref>

===Plethysmography===

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===Maximal respiratory pressures===

{{main|Respiratory pressure meter}}

Measurement of maximal inspiratory and expiratory pressures is indicated whenever there is an unexplained decrease in vital capacity or respiratory muscle weakness is suspected clinically. Maximal inspiratory pressure (MIP) is the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece. Maximal expiratory pressure (MEP) is the maximal pressure measured during forced expiration (with cheeks bulging) through a blocked mouthpiece after a full inhalation. Repeated measurements of MIP and MEP are useful in following the course of patients with [[neuromuscular]] disorders.{{cn|date=November 2023}}

===Diffusing capacity===

{{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]].{{cn|date=November 2023}}

=== Bronchodilator responsiveness ===

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===Oxygen desaturation during exercise===

The six-minute walk test is a good index of physical function and therapeutic response in patients with [[chronica lung disease (disambiguation)|chronic [[lung disease]], such as [[COPD]] or [[idiopathic pulmonary fibrosis]].<ref name="pmid12890299">{{cite journal | vauthors = Enright PL | title = The six-minute walk test | journal = Respiratory Care | volume = 48 | issue = 8 | pages = 783–785 | date = August 2003 | pmid = 12890299 }}</ref><ref name="pmid19996335">{{cite journal | vauthors = Swigris JJ, Wamboldt FS, Behr J, du Bois RM, King TE, Raghu G, Brown KK | title = The 6 minute walk in idiopathic pulmonary fibrosis: longitudinal changes and minimum important difference | journal = Thorax | volume = 65 | issue = 2 | pages = 173–177 | date = February 2010 | pmid = 19996335 | pmc = 3144486 | doi = 10.1136/thx.2009.113498 }}</ref><ref name="pmid12091180">{{cite journal | author = ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories | title = ATS statement: guidelines for the six-minute walk test | journal = American Journal of Respiratory and Critical Care Medicine | volume = 166 | issue = 1 | pages = 111–117 | date = July 2002 | pmid = 12091180 | doi = 10.1164/ajrccm.166.1.at1102 }}</ref>

===Arterial blood gases===

[[Arterial blood gas]]es (ABGs) are a helpful measurement in pulmonary function testing in selected patients. The primary role of measuring ABGs in individuals that are healthy and stable is to confirm hypoventilation when it is suspected on the basis of medical history, such as respiratory muscle weakness or advanced [[COPD]].{{cn|date=November 2023}}

ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.{{cn|date=November 2023}}

== Risks ==

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==Technique==

=== Preparation ===

Subjects have 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.{{cn|date=November 2023}}

=== Quality control ===

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.

ReproducibilityRepeatability 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 | vauthors = Sim YS, Lee JH, Lee WY, Suh DI, Oh YM, Yoon JS, Lee JH, Cho JH, Kwon CS, Chang JH | display-authors = 6 | title = Spirometry and Bronchodilator Test | journal = Tuberculosis and Respiratory Diseases | volume = 80 | issue = 2 | pages = 105–112 | date = April 2017 | pmid = 28416951 | pmc = 5392482 | doi = 10.4046/trd.2017.80.2.105 }}</ref>

==Clinical significance==

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* <math>MIP_{LLN}</math> = maximum inspiratory pressure lower limit of normal in cmH20

* <math>MEP_{LLN}</math> = maximum expiratory pressure lower limit of normal in cmH20

* <math>age</math> = the patient's age in years<ref>{{cite journal |vauthors=Evans JA, Whitelaw WA |date=October 2009 |title=The assessment of maximal respiratory mouth pressures in adults |url=https://pubmed.ncbi.nlm.nih.gov/19796415/ |journal=Respiratory Care |volume=54 |issue=10 |pages=1348–1359 |pmid=19796415}}</ref>

== References ==