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Pulmonary Function Tests (PFTs)

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What are Pulmonary Function Tests/ PFTs?

It is a test carried out to tell us about the functioning status of our lungs. It helps us to understand how properly our lungs are working and in what condition they are in. It also helps in accessing the ongoing treatment/ shows whether the condition of lungs is improving or not.

Pulmonary Function Tests detects the amount of oxygen moving in and out of the lungs, how much air the lungs can hold, how much air is left behind in the lung after breathing out normally and forcefully, and the rate at which air flows.

Pulmonary Function Tests

Why and when is Pulmonary Function Tests done?

According to certain symptoms/ signs/ Diagnostic tests indicating Lung disease

• Cough

• Wheezing

• Difficulty in breathing

• Breathlessness

• Allergies

• Infections

• Crackling sound

• Chest pain

• Abnormal chest X-ray

Assessment of on-going treatment in patients with Lung Disease

• Asthma


• Interstitial Fibrosis

• Occupational hazards

• Tuberculosis

• Pulmonary vascular Disease

• Chronic bronchitis

• Lung Cancer

Part of Preoperative evaluation routine

• Lung resection

• Lung transplant

• Cardiothoracic surgery

• Abdominal surgery

In people who are at High risk of developing Lung disease

• Occupational exposure/ hazards

• Exposure to radiation

• Medication / Cancer treatments/ Immunosuppressant

In disease that can be associated with Lung Complications

• Connective tissue disorders

• Neuromuscular disease

• Rheumatoid arthritis

Assessment in post Transplant cases

• Infection

• Acute rejection

• Obliterative bronchiolitis

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When not to do PFTs?

• Cardiac issues

• Pneumothorax

• Cardiac arrest

• Unstable angina

• Recent thoraco-abdominal surgery

• Recent ophthalmic surgery

• Active tuberculosis

• Aneurysm in chest, brain or abdomen.

How to prepare for Lung function test (Pulmonary Function Tests)?

• If you are on drugs that help in opening up your air way (asthma/ COPD) you should ask your doctor and stop them before taking the Pulmonary Function Tests.

• Pain medications have shown to alter the result of the test, hence discuss with doctor regarding pain-killers you might be taking.

• Avoid large meals before the test, as it prevents your lung from expanding to its full capacity.

• Avoid coffee, tea and chocolates before the rest Pulmonary Function Tests.

• Wear loose and comfortable clothes.

• Avoid wearing jewelries.

• Avoid smoking.

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Few terms used to describe the Pulmonary Function Tests/Lung function test

• Vital capacity (VC) it is described as the total volume of air that is breathe out/ exhaled after taking in air/ inhaling as much as one can.

• Tidal volume (VT) it is described as the amount of air breathe in/inhaled or breathe out/exhaled during normal breathing.

• Minute volume (MV) it is described as the total amount of air breathe out/exhaled per minute(60secs).

• Functional residual capacity (FRC) it is described as the amount of air left in lungs after breathing out/exhaling normally.

• Residual volume it is described as the amount of air left in the lungs after breathing out /exhaling maximum as one can.

• Total lung capacity it is described as the total volume of the lungs when it is filled with air as much as it is possible.

• Forced vital capacity (FVC) it is described as the amount of air breathe out/ exhaled forcefully after quickly breathing in /inhaling air as much as one can.

• Forced expiratory volume (FEV) it is described as the amount of air breathe out/ exhaled during the first, second, and third seconds of the FVC test.

• Forced expiratory flow (FEF) it is described as the average rate of air flow during the middle half of the FVC test.

• Peak expiratory flow rate (PEFR) it is described as the fastest rate at which one can force air out of the lungs.

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What are the different types of test performed?

• Spirometry – Its one of the common PFTS performed. Spirometer devices are used to assess the pulmonary functioning in form of how long the lung can hold , take in and move out the air. (less air in – restrictive type; less air out- obstructive type of lung disease).It is also helpful in assessment of the the on going treatment and in grading the seriousness the disease. It measures lung functioning against time. Measures forced expiratory volume in one second, the forced vital capacity and ration of the two.

• Lung volume determination/ Body plethysmography- It measures amount of air in the lungs when you inhale deeply and amount of air left behind in your lung after your breathe out with maximum effort. A person sits inside an airtight box , breathes in or breathes out to a particular volume and then a shutter drops and closes the breathing tube. The person can to breathe through the closed shutter. When there is increase in chest volume there is reduction in the box volume hence pressure increases in the box. Static lung volumes are measured by measuring pressure changes in the constant volume box or measuring the volume in the constant pressure box.

• Diffusion capacity of carbon monoxide- It measures the ability of lungs to transfer gases (oxygen and carbon monoxide) from inhaled air to the blood cells present in lung vessels.

• Assessment of Respiratory muscle strength- inhaling and exhaling mouth pieces are used to measure maximum inspiratory and expiratory, respectfully, pressure in the the blocked mouth piece. This test is useful in cases of motor neuron disease where respiratory muscles are weakened and cause respiratory failure.

• Pulse Oximetry- It measures the amount of oxygen present in the blood where the device is clipped to the finger and it measures the oxygen level, totally non-invasive and easy.

• Methacholine Challenge testing- Methacholine is given to the patient and if the patient reacts to it (drug causes mild tightening/constriction of the airways when inhaled) , the test is stated positive.

• Six-minute walk test- Individual is asked to walk for 6 minutes, to and fro, on hard or flat surface . it helps in measuring the aerobic capacity and endurance, determines how fatigue/ being exhausted influences breathing of the individual.

• Cardiopulmonary stress testing– it basically measures the strength of the lungs and heart. Treadmill or a stationary bicycle is used, you are asked to exercise on it and doctor looks out at the heart rate and oxygen uptake. While carrying out the exercise you are made to breathe out into a tube that measures your lung functioning as they work harder.

• Arterial blood gases- It is carried out by para-medical stuff/ nurse who will use a needle to take out blood from blood vessels and test it for levels of oxygen and carbon dioxide in the blood.

• Exhaled nitric oxide is measured in the exhaled breath. It helps in diagnosing asthma since inflamed airways have higher concentration of nitric oxide levels.

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What are complications associated with PFTs?

• Shortness of breath

• Coughing

• Asthmatic attack

• Dizziness


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