Pulmonary function testing: Difference between revisions

Revision as of 03:59, 16 June 2022

Revision as of 17:02, 16 June 2022

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{{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.

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 | title = The assessment of maximal respiratory mouth pressures in adults | journal = Respiratory Care | volume = 54 | issue = 10 | pages = 1348–1359 | date = October 2009 | pmid = 19796415 | url = https://pubmed.ncbi.nlm.nih.gov/19796415/ }}</ref>

===Diffusing capacity===

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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>

==TechniquesTechnique==

=== Preparation ===

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.

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==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 where the post-bronchodilator FEV1/FVC is <0.7 indicating airflow limitation.<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

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|<30

|}

{{See also|Spirometer#History - Interpreting Spirometry}}

Changes in lung volumes and capacities from normal are generally consistent with the pattern of lung impairment.

Professional societies such as the [[American Thoracic Society]] and the [[European Respiratory Society]] have published guidelines regarding the conduct and interpretation of pulmonary function testing to ensure standardization and uniformity in performance of tests. The interpretation of tests depends on comparing the patients values to published normals from previous studies. Deviation from guidelines can result in false-positive or false negative test results, even though only a small minority of pulmonary function laboratories followed published guidelines for spirometry, lung volumes and diffusing capacity in 2012.<ref>{{cite journal | vauthors = Mohanka MR, McCarthy K, Xu M, Stoller JK | title = A survey of practices of pulmonary function interpretation in laboratories in Northeast Ohio | journal = Chest | volume = 141 | issue = 4 | pages = 1040–1046 | date = April 2012 | pmid = 21940775 | doi = 10.1378/chest.11-1141 }}</ref>

=== COPD ===

Spirometry is required for a diagnosis of COPD where the post-bronchodilator FEV1/FVC is <0.7 indicating airflow limitation.<ref>{{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>

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 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 title2009 |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 | date = October 2009 | pmid = 19796415 | url = https://pubmed.ncbi.nlm.nih.gov/19796415/ }}</ref>

==Interpretation of tests==

{{See also|Spirometer#History - Interpreting Spirometry}}

Professional societies such as the [[American Thoracic Society]] and the [[European Respiratory Society]] have published guidelines regarding the conduct and interpretation of pulmonary function testing to ensure standardization and uniformity in performance of tests. The interpretation of tests depends on comparing the patients values to published normals from previous studies. Deviation from guidelines can result in false-positive or false negative test results, even though only a small minority of pulmonary function laboratories followed published guidelines for spirometry, lung volumes and diffusing capacity in 2012.<ref>{{cite journal | vauthors = Mohanka MR, McCarthy K, Xu M, Stoller JK | title = A survey of practices of pulmonary function interpretation in laboratories in Northeast Ohio | journal = Chest | volume = 141 | issue = 4 | pages = 1040–1046 | date = April 2012 | pmid = 21940775 | doi = 10.1378/chest.11-1141 }}</ref>

== References ==