Pulmonary function testing: Difference between revisions

Revision as of 19:48, 15 June 2022

Revision as of 20:04, 15 June 2022

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===Spirometry===

{{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.

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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 |last=Evans |first=John A. |last2=Whitelaw |first2=William A. |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 |issn=0020-1324 |pmid=19796415}}</ref>

===Diffusing capacity===

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ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.

==Techniques 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 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, 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>

==Techniques==

=== 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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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>

==Clinical significance==

==Interpretation of tests==

{| class="wikitable" style = "float: right

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

|+Classification of COPD based on spirometry<ref>{{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>

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|last1=Mohanka|first1=Manish R.|last2=McCarthy|first2=Kevin|last3=Xu|first3=Meng|last4=Stoller|first4=James K.|title=A Survey of Practices of Pulmonary Function Interpretation in Laboratories in Northeast Ohio|journal=Chest|date=April 2012|volume=141|issue=4|pages=1040–1046|doi=10.1378/chest.11-1141|pmid=21940775}}</ref>

!Severity

!FEV1 % predicted

|-

|Mild (GOLD 1)

|≥80

|-

|Moderate (GOLD 2)

|50–79

|-

|Severe (GOLD 3)

|30–49

|-

|Very severe (GOLD 4)

|<30

|}

Changes in lung volumes and capacities from normal are generally consistent with the pattern of impairment. TLC, FRC, and RV increase with [[obstructive lung disease]]s and decrease with [[restrictive lung disease]]simpairment.

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>

== 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 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, 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==

==Interpretation of tests==

Changes in lung volumes and capacities are generally consistent with the pattern of impairment. TLC, FRC, and RV increase with [[obstructive lung disease]]s and decrease with [[restrictive lung disease]]s.

{{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|last1=Mohanka|first1=Manish R.|last2=McCarthy|first2=Kevin|last3=Xu|first3=Meng|last4=Stoller|first4=James K.|title=A Survey of Practices of Pulmonary Function Interpretation in Laboratories in Northeast Ohio|journal=Chest|date=April 2012|volume=141|issue=4|pages=1040–1046|doi=10.1378/chest.11-1141|pmid=21940775}}</ref>

==References==