Pulmonary Function Test -Understanding Its Basics

In this blog we will briefly see what the pulmonary function test is, how it can help patients with asthma and other underlying lung conditions without going into very technical details and numbers.

 The pulmonary function test is a very unique test to assess the functionality of the lung.  If the chest x-ray of the person is the anatomy of the lung then the pulmonary function test is the physiology function of the lung.  It is like an electrocardiogram (ECG) of the lung to some extent, but not fully.

 The pulmonary function test is a test where one can assess the mechanics of the lung, the lung volumes, the diffusion capacity and airway resistance.  Whether the test is normal or abnormal needs to be looked into upon comparison with the person’s age, sex, race and height.  Weight generally does not have any relation in this calculation.  The numbers that come out in the test are compared with the reference numbers based on the protocol that is used.

 The pulmonary function test has components like spirometry, which is a common part of the test, generally done in a doctor’s office to quickly assess underlying obstructive or restrictive lung disease.  Obstruction lung disease is where there is obstruction of the lung either from asthma, chronic obstructive pulmonary disease (COPD), chronic bronchitis or a combination of the disease, etc.  The restrictive lung disease is where there is restriction of the lung, meaning it has become shorter or smaller in size.  Many times it may truly not be decreased but could be from body habitus and weight gain in most patients, but in conditions like pulmonary fibrosis, the lungs may shrink and may give restrictive lung disease.  The lung volumes are generally used for assessment.  Diffusion capacity is also one of the components to see how much of the diffusion of carbon monoxide occurs.

 Generally, in the spirometry component there is forced expiratory volume in first second (FEV1), forced vital capacity (FVC) and the ratio of FEV1/FVC are the common numbers that are used.  Generally, numbers ranging between 80 and 120 predicted for FEV1 and FVC is considered normal.  This gives an idea about if someone has underlying obstruction or restriction and based on the ratio of FEV1 upon FVC. If the FEV1 and FVC are decreased and the ratio of FEV1 and FVC is normal then it has restrictive changes. It will be obstructive changes if the ratio of the FEV1 and FVC is decreased.  In lung volumes, the TLC or total lung capacity is used and generally it is also between 80 and 120% of the predicted.  When numbers are falling out of this range, generally the pulmonary function test will be read as abnormal.

 The pulmonary function test helps to assess the severity of asthma or COPD or any other underlying condition like pulmonary function test, interstitial lung disease, etc.  A smoker should consider having a pulmonary function test if not done to assess and obtain a baseline of his or her lung capacity.  When a good bronchodilator response is seen on the pulmonary function test, it generally has a relation with underlying bronchial asthma.  A pleuritic assessment of lung disease can be performed either with complete pulmonary function test or with just a spirometry component of the pulmonary function test to monitor underlying lung disease.  The person with bronchial asthma or COPD, emphysema, and is on inhalers or nebulizer if they do not have a pulmonary function test performed then they may consider having the test to assess and obtain a baseline and periodically may be performed as clinically indicated to assess the progression or stability of the disease.

 The technique of the pulmonary function test is very important and a good cooperation with a respiratory therapist is key, otherwise the pulmonary function test may be a suboptimal test as it is an effort dependent test.

For patients with asthmatic bronchitis or bronchial asthma symptoms, who are on bronchial asthma treatment and been clinically  monitored, Pulmonary function test may help the monitoring of bronchial  asthma . In patient with chronic asthma as their asthma improves  its asthma  treatment  can be monitored  periodically with the pulmonary function test. Similarly patient with Emphysema on treatment can be monitored.

 To summarize this article, a pulmonary function test is a key lung test for patients with asthma, COPD and other lung disorders to help establish a baseline and assess the progression and/or stability of the disease if done periodically.  It is an effort dependent test so it needs to be done with correct technique otherwise may give rise to false results.  A good bronchodilator response seen on the pulmonary function test may be associated with patients with bronchial asthma.  Smokers may consider having a baseline pulmonary function test if not done.

4 thoughts on “Pulmonary Function Test -Understanding Its Basics

  1. Pingback: Pulmonary Function Test – Asthma Medications – Chronic Asthma … | Untreated Info

  2. Hey, I really liked this post. Spirometry has been hailed as the golden standard when it comes to testing the functionality of the lungs. However, I was surprised when I read that under the new diagnostic guidelines for COPD, spirometry should only be used to diagnose COPD in people who already show symptoms. Apparently, the results of recent research have shown that there is no benefit for people who have no respiratory symptoms.

    • Steve,
      In clinical practice patient when patient with copd seen in office or hospital setting are having respiratory symptoms, spirometry helps to evaluate its severity. As spiromtery is time consuming, patient’s effort dependent test and not a passive test like EKG, asymptomatic patients are droped off. Millions of active or ex- smokers who are symptomatic in this world with copd have not yet have spiromtery performed to access the severity of copd. They possibly needs to get tested first verses the asymptomatic where a difference can be made in copd managment.

  3. Well, I have to admit that I was unaware that spirometry was hailed as the golden standard for helping to diagnose new cases of COPD. I am little disappointed in myself for being so, since only last month was National COPD Awareness Month. Thank you for providing such an informative post, I know have a much better idea of the effectiveness of spirometry.

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