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Lung function tests


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Lung function tests, also known as pulmonary function tests are advised by doctors for the following reasons:

  • To recognize breathing problem and chronic obstructive pulmonary disease
  • To evaluate asthma, lung allergies, bronchitis, respiratory infections, lung fibrosis, bronchiectasis, pulmonary tumour, and many other types of lung damage or infections etc.
  • To check for improvement of lung function after treatment 

We have explained the different types of lung function tests below:



Spirometry is an age old diagnostic test for evaluating lung conditions and the device that is used is known as spirometer. A mouthpiece is assembled to the device, where you need to inhale and exhale. Your breathing capacity and speed will be recorded in the spirometer. A chart will be obtained, known as spirogram which shows the following details:

Forced expiratory volume (FEV)- amount of air you can blow out in one, two or 3 seconds

Forced vital capacity (FVC)
- total amount of air you are capable of blowing out in one breath

Functional residual capacity (FRC)-
amount of air left out in lungs after normal expiration.

Vital capacity (VC)-
 total volume of air that can be exhaled after maximum inspiration.

Slow vital capacity (SVC)-
amount ofair that can be slowly exhaled after deep inhalation


Residual volume (RV)-
amount of air left out in lungs after complete expiration

Total lung capacity (TLC):  The total volume of lungs after maximum inhalation

Peak expiratory flow (PEF)-
maximum volume during forced expiration

Maximum voluntary ventilation (MVV)
- maximum amount of air inhaled and exhaled during one minute

Residual volume (RV)- Amount of air in the lungs after complete exhalation

Expiratory reserve volume (ERV)- difference between FRC and RV.

Lung Plethysmography

Through plethysmography, changes in volume of different areas of the body can be measured and so it can also be used as an effective lung function test. Plethysmography is used to calculate the air retention capacity of lungs.

This test is conducted inside a plethysmograph booth which is a small enclosed air tight chamber. You have to inhale and exhale through a mouthpiece as per the instruction of the technician while your nose will be clasped with clips. The pressure and volume in your lungs change as you breathe which will help the doctor to determine the total lung capacity and residual volume.


Gas diffusion tests

When oxygen is inhaled it finally reaches the tiny sacs inside the lungs known as alveoli. The oxygen then diffuses into the blood of the surrounding vessels. Diffusion test is done to evaluate how efficiently oxygen moves into and out of the lungs.
A mouthpiece will be placed around your mouth while your nose will be clasped with clips to prevent breathing through nostrils.

Carbon monoxide diffusion capacity will also be measured during the test. A safe amount of carbon monoxide will be present in the air that you inhale. You will be asked to perform various techniques of breathing by the technician which include breath holding and steady breathing.


Bronchial Provocation (Challenge) Testing

Challenge testing is done to detect and quantify airway hypersensitivity, especially for bronchial asthma. The patient is asked to inhale methacholine which is a bronchial constrictor or some allergen, with the help of a nebulizer in order to trigger asthma like symptoms. The reaction of the airways is then assessed with spirogram reading. Since the test provokes a reaction, it is also known as provocation test.

However, this test can incite an asthma attack or allergic response, so the individual is very carefully monitored.


Exercise stress test

Although, exercise stress test is meant for diagnosing heart conditions, it can also measure the performance of your lungs while you exercise on a treadmill or a bicycle. The function of the lung is measured by similar spirometry readings.

Written by: healthplus24.com, team
Date last updated: Feburary 07, 2014


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