Any problems with our respiratory system can be very unsettling. The simplest of ailments, like a common cold can make us feel so unwell. Imagine walking a short distance and feeling out of breath, sounds uncomfortable, doesn’t it? You might wonder, I have never had breathing difficulty before, what is going on? You decide to see a doctor. He evaluates you, and chances are, he will advise you to get a Pulmonary function test done.
What is Pulmonary function test?
PFT is an extensive evaluation used to assess the respiratory system.
These tests measure
- Lung volume
- Lung capacity
- Flow rate
- Efficiency of gas exchange
The patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis are also taken into account.
Pulmonary function tests are performed by two methods:
- A spirometer is a device, which has a mouthpiece attached to a small electronic machine.
- Patient is evaluated inside an air-tight box that resembles a telephone booth.
Parameters measured on a pulmonary function test:
- Tidal volume (VT) - The volume of air inhaled or exhaled during normal breathing.
- Minute volume (MV) - The total volume of air exhaled per minute.
- Vital capacity (VC) - The total volume of air that can be exhaled after deep inhalation.
- Total lung capacity - The total lung volume, when filled with maximum air.
- Forced vital capacity (FVC) - The amount of air exhaled forcefully after maximum inhalation.
- Forced expiratory volume (FEV) - The volume of air expired in the first, second, and third seconds of the test.
- Residual volume - The amount of air left in the lungs after exhaling forcefully.
- Peak expiratory flow rate (PEFR) - The fastest rate that you can force the air out of the lungs.
- Functional residual capacity (FRC) - The volume of air left in lungs after exhaling normally.
- Forced expiratory flow (FEF) - The rate of flow during the middle half of the FVC test.
- DLCO - Diffusion capacity of carbon monoxide.
Spirometry used in the pulmonary function test, uses an instrument called Spirometer.
It measures the volume of air breathed in and out. It also measures how rapidly air flows in and out through the mouth piece of the Spirometer. The measurements are recorded on a Spirograph. PFT also determines the efficiency of gas exchange in the alveoli.
Some Pulmonary Function Test, such as thoracic gas volume and other lung volume measurements, can be measured by plethysmography.
Why are Pulmonary Function Tests used?
- Respiratory infections
- Breathing difficulty due recent surgery or injury
- Chronic lung conditions like asthma, emphysema, chronic bronchitis or bronchiectasis,
- Asbestosis, caused due to chronic asbestos inhalation.
- Airway restriction from tumors, chest wall scarring.
- Routine assessment in patient prior to surgery.
When is pulmonary function test contraindicated?
- Hemoptysis (coughing up blood with sputum)
- Pneumothorax (air in the chest cavity)
- Recurrent and unpredictable chest pain.
- Eye surgery performed within 2 weeks of the PFT - intraocular pressure might increase owing to forced breathing required for pulmonary function test and, can be detrimental.
- Recent abdominal or thoracic surgery.
- Patients who experience fainting spells.
- Patients with active tuberculosis are not assessed with Pulmonary function tests.
Preparing for the pulmonary function test:
If you are already on a bronchodilator treatment, your doctor might advice you to stop that prior to the Pulmonary Function test, to assess the basal function of the lungs.
Alternatively, your doctor might ask you to continue the treatment, to assess how effective the treatment is.
Avoid having a big meal before the pulmonary function test.
Avoid smoking 4-6 hours before the Pulmonary Function Test.
What can you expect during the Pulmonary function test?
Since Pulmonary Function Tests require some forced breathing, you might experience some shortness of breath or light-headedness.
You will be asked to breathe through your mouth, into a mouthpiece. A nose clip is applied on your nose to ensure there is no nose breathing. Some people might find this uncomfortable.
Claustrophobic people might have a problem while performing the Plethysmography, as you are expected to stand inside an airtight box.
The findings of the Pulmonary function test, are usually correlated with clinical history and other investigations like chest X-ray.