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{{short description|Test to evaluate respiratory system}}
{{Infobox diagnostic
| Name
| Image
| Alt
| Caption
| DiseasesDB
| image = Body plethysmograph box.jpg
| caption = Plethysmograph "body box"
|
| ICD9 =
| ICDO =
| MedlinePlus = 003853
|
| MeshID = D012129
| LOINC =
| HCPCSlevel2 =
| OPS301 = {{OPS301|1-71}}
| Reference_range =
}}
{{Pulmonary function}}
'''Pulmonary function
==Indications==
Pulmonary function testing is a diagnostic and management tool used for a variety of reasons, such as:
* Diagnose lung disease.
* 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 the 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>
===Neuromuscular disorders===
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 | vauthors = Sharma GD | title = Pulmonary function testing in neuromuscular disorders | journal = Pediatrics | volume = 123 | issue = Suppl 4 | pages = S219–S221 | date = May 2009 | pmid = 19420147 | doi = 10.1542/peds.2008-2952D | doi-access = free }}</ref>
[[Duchenne muscular dystrophy]] is 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 name="pmid15302625">{{cite journal | vauthors = Finder JD, Birnkrant D, Carl J, Farber HJ, Gozal D, Iannaccone ST, Kovesi T, Kravitz RM, Panitch H, Schramm C, Schroth M, Sharma G, Sievers L, Silvestri JM, Sterni L | display-authors = 6 | title = Respiratory care of the patient with Duchenne muscular dystrophy: ATS consensus statement | journal = American Journal of Respiratory and Critical Care Medicine | volume = 170 | issue = 4 | pages = 456–465 | date = August 2004 | pmid = 15302625 | doi = 10.1164/rccm.200307-885ST }}</ref>
==Tests==
===Spirometry===
{{Main|Spirometry}}
[[File:DoingSpirometry.JPG|left|thumb|Spirometry]]
Spirometry includes tests of pulmonary mechanics – measurements of FVC, FEV<sub>1</sub>, 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
====
{{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 = 12 July 2025 }}</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 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>{{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>
===
{{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 name="pmid13295396">{{cite journal | vauthors = DuBois AB, Botelho SY, Bedell GN, Marshall R, Comroe JH | title = A rapid plethysmographic method for measuring thoracic gas volume: a comparison with a nitrogen washout method for measuring functional residual capacity in normal subjects | journal = The Journal of Clinical Investigation | volume = 35 | issue = 3 | pages = 322–6 | date = March 1956 | pmid = 13295396 | pmc = 438814 | doi = 10.1172/JCI103281 | url = }}</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).
===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 ===
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 | 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>
===Oxygen desaturation during exercise===
The
===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}}
==
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 include dizziness, shortness of breath, coughing, pneumothorax, and inducing an asthma attack.<ref>{{Cite web |date=2019-11-19 |title=Pulmonary Function Tests |url=https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/pulmonary-function-tests |access-date=2022-06-15 |website=www.hopkinsmedicine.org |language=en}}</ref><ref>{{Cite web |title=Pulmonary function tests: MedlinePlus Medical Encyclopedia |url=https://medlineplus.gov/ency/article/003853.htm |access-date=2022-06-15 |website=medlineplus.gov |language=en}}</ref>
== Contraindications ==
There are some indications against a pulmonary function test being done. These include a recent heart attack, stroke, 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>
==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}}
===
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.
Repeatability 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==
Changes in lung volumes and capacities from normal are generally consistent with the pattern of lung impairment.
Spirometry is required for a diagnosis of COPD.<ref name=":0">{{Cite web |title=2022 GOLD Reports |url=https://goldcopd.org/2022-gold-reports-2/ |access-date=2022-06-15 |website=Global Initiative for Chronic Obstructive Lung Disease - GOLD |language=en-US}}</ref>
==Interpretation of tests==
{| class="wikitable" style = "float: right
|+Classification of COPD based on spirometry<ref name=":1">{{Cite book |last=Global Initiative for Chronic Obstructive Lung Disease |url=https://goldcopd.org/2022-gold-reports-2/ |title=Pocket Guide to COPD Diagnosis, Management, and Prevention |page=11}}</ref>
!Severity
!FEV1 % predicted
|-
|Mild (GOLD 1)
|≥80
|-
|Moderate (GOLD 2)
|50–79
|-
|Severe (GOLD 3)
|30–49
|-
|Very severe (GOLD 4)
|<30
|}
{{See also|Spirometer#History - Interpreting Spirometry}}
Professional societies such as the [[American Thoracic Society
=== COPD ===
The [[Global Initiative for Chronic Obstructive Lung Disease]] provides guidelines for the diagnosis, severity, and management of [[Chronic obstructive pulmonary disease|COPD]].<ref>{{Cite web |title=About Us |url=https://goldcopd.org/about-us/ |access-date=2022-06-16 |website=Global Initiative for Chronic Obstructive Lung Disease - GOLD |language=en-US}}</ref> To determine obstruction in a patient's lungs, the post-bronchodilator FEV1/FVC needs to be <0.7.<ref name=":0" /> Then, the FEV1 percentage of predicted result is used to determine the degree of obstruction where the lower the percent the worse the obstruction.<ref name=":1" />
=== Maximum respiratory pressures ===
Several calculations are needed for what a normal maximum inspiratory (MIP) and expiratory pressure (MEP) is. For males this found by:
<math>MIP=120-(0.41 \times age)</math>
and
<math>MEP=174-(0.83 \times age)</math>
To find the lower limit of what is acceptable in males the equations are:
<math>MIP_{LLN}=62-(0.15 \times age)</math>
and
<math>MEP_{LLN}=117-(0.83 \times age)</math>
For females, the equations are slightly different. For the normal values this is used:
<math>MIP=108-(0.61 \times age)</math>
and
<math>MEP=131-(0.86 \times age)</math>
For find the lower limit of what it should be without impairment this form of the equations is used:
<math>MIP_{LLN}=62-(0.50 \times age)</math>
and
<math>MEP_{LLN}=95-(0.57 \times age)</math>
where
* <math>MIP</math> = maximum inspiratory pressure in cmH20
* <math>MEP</math>= maximum expiratory pressure in cmH20
* <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 |journal=Respiratory Care |volume=54 |issue=10 |pages=1348–1359 |pmid=19796415}}</ref>
== References ==
{{reflist}}
{{Respiratory system procedures}}
[[Category:Pulmonary function testing| ]]
[[Category:Respiratory therapy]]
[[Category:Medical tests]]
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