Pulmonary Function Tests

Many people are referred by their GP or hospital consultant for lung function, also called pulmonary function tests, for a wide variety of reasons they are commonly referred to as PFTs.

These reasons could include:

- Investigations into cause of shortness of breath, cough, wheeze, frequent chest infections or other symptoms related to the lungs.
- Assessment of how patients are responding to their respiratory inhalers or tablets.
- Therefore it is common practice to have an initial assessment followed by another test in two or three months
- Monitoring of the progression of conditions such as COPD, asthma, lung fibrosis, to assess if the patient is fit for an upcoming surgery and other reasons that your doctor will explain to you.

It is important to follow any instructions you may have received with your appointment letter regarding preparation for the test, particularly concerning the use of your inhalers or other medications before you are tested. If you do not follow these instructions, it may not be possible to complete your tests, and this may mean a second visit at a later date.

Click the other information boxes above for a brief outline of the common PFTs, which will give some basic information on the tests performed and what each test measures.

Spirometry

Spirometry is normally the first lung function test performed in the laboratory, it measures how much and how quickly you can move air in and out of your lungs and is therefore useful in assessing airway function. The patient seals their lips around small plastic cylinder which is connected to a spirometer and is instructed to perform a couple of normal breaths before taking a full breath in and blowing out as hard and as fast as possible for as long as possible followed by a sharp breath back in again. The test is repeated at least three times and a maximum of eight times.

From this test the following lung function values are obtained:

Forced Vital Capacity (FVC) - the amount of air you can forcibly breathe out after a full breath in.
Force Expiratory Volume in 1 Second (FEV1) - the amount of air you can forcibly breathe out in one second.
Peak Expiratory Flow (PEF) - measures the highest flow rate reached during a forced breath out.
FEV1/FVC Ratio - the percentage of the FVC exhaled in one second.

All lung function results are expressed as a percentage of the predicted values. Predicted values are calculated from population studies to give expected values for a person of similar height, age, sex and race.

A low FEV1 with a reduced FEV1/FVC ratio may indicate an obstructive lung disorder.

The Spirometry test is increasingly being provided at primary care level, for example at GP surgeries, as spirometry is an essential tool for assessing and monitoring asthma and COPD, the most common lung diseases. It would be worth checking if your GP provides this test as it may save you a long wait for the test and a trip to the hospital.

The remaining tests can only be carried out in a hospital based Pulmonary Laboratory.

Transfer Factor/Diffusion Capacity (DLCO)

The DLCO measures how effectively oxygen crosses from the lung to the bloodstream and is therefore useful in investigations into disorders related to the function of the lung tissues. Certain lung diseases affect gas exchange in your lungs. For example, gas transfer will be reduced emphysema and pulmonary fibrosis.

At the end of a full breath out, a valve is opened and the patient is instructed to perform a full inspiration of a special gas mixture. It does contain carbon monoxide but in such small amounts that it is not harmful. Carbon Monoxide is used as it has very similar properties to oxygen. The patient holds the breath for a maximum of 10 seconds and then breathes out again fully. The gas analyzers compare the concentrations of exhaled gas to the known inhaled gas and calculate the level of diffusion that has occurred.

This test will be performed a minimum of two times, up to a maximum of 5 times, and you will be given a minimum of 4 minutes rest between each test.

Lung volumes

Even after the patient empties their lungs completely, there is still a volume of air left in the lungs to keep them inflated. This volume is called the Residual Volume (RV). Calculating the RV allows us to measure the Total Lung Capacity (TLC). It is important to measure the RV and TLC in certain patients.

In obstructive lung diseases such as COPD, the RV can be much higher than normal. This is known as air trapping. In restrictive lung diseases the TLC is lower than normal. The RV and TLC cannot be measured directly by spirometry but is measured indirectly in a Pulmonary function lab by three different methods.

Body plethysmography -
the patient is seated inside a large airtight Perspex (transparent) booth and performs normal breaths. At the end of a normal breath, a shutter is closed in the mouthpiece and the patient is instructed to perform panting maneuvers against the closed shutter. The pressures changes that occur within the box are used to calculate the RV indirectly. If you feel claustrophobic in the booth, you can open the door from the inside and exit at any time.

Nitrogen Washout Method -
the patient breathes normally until a stable breathing pattern is observed. At the end of a normal breath, a valve is opened and the patient begins breathing 100% oxygen. The oxygen replaces the nitrogen in the lungs until the nitrogen concentration reaches 1.5%. The volume of oxygen used and the time the test takes is used to calculate the RV and then the TLC.

Helium Dilution Method -
Method -At the end of a normal breath, a valve is opened and the patient begins breathing 9-14% Helium until the concentration of helium in the lungs is in equilibrium with the helium in the spirometer. The concentration of helium at equilibrium and the change in helium concentration are used to calculate the RV and TLC.


Provocation Tests

Exercise Provocation Test
Exercise Provocation test is used in the diagnosis of exercise- induced asthma. To begin with the patient performs a Spirometry test. The patient then exercises on a treadmill at 80% of their predicted maximum heart rate for 6-8 minutes at a speed of 3-5 mph and incline 10-12%. The patient performs Spirometry at 1, 3, 5, 10, 15, 30 minutes after stopping exercise. A drop in the patient’s FEV 1 of greater than 12% is considered a positive test. Once the test is finished a bronchodilator is given to the patient to help their FEV 1 return to the pre-test values.

Airway Challenge Testing
Airway Challenge Testing assesses the sensitivity of the airways. The test may be done using a substance called Mannitol, Histamine or Methacholine depending on the instruction of your respiratory consultant. Either one of these substances are administered to the patient and may induce bronchospasm (a feeling of chest tightness) in sensitive airways. To begin the test, the patient performs a Spirometry test. Then the first (lowest) dose is administered to the patient using a nebulizer or dry powder device and spirometry is repeated immediately. The above steps are repeated with a series of higher concentrations. Depending on the test used, a drop in the FEV 1 of 15-20% is considered significant. The lower the concentration at which the drop occurs, the greater the sensitivity of the airways. A short-acting bronchodilator is administered at the end of the test to bring the FEV 1 back to the baseline value.

Exercise Testing

Cardiopulmonary Exercise Test (CPET)
Patients experiencing unexplained shortness of breath on exertion may be referred for a cardiopulmonary exercise test. CPETs are normally performed on a stationary bike or treadmill. The patient is connected to a mouthpiece and flow sensor to record ventilation during exercise while a 12-lead ECG, blood pressure cuff and oxygen saturation monitor cardiovascular responses. The test aims to exercise the patient to their maximum within 8-12 minutes. By monitoring the responses of the patient’s heart, lungs and muscles to exercise, we can determine whether there is a cardiovascular or respiratory limitation or both to exercise or if the patient is simply deconditioned (unfit).

Six-minute walk test
The six-minute walk test is commonly used in a pulmonary rehabilitation programme. The aim of the test is for the patient to walk for as far as possible in six minutes between two cones positioned about 30 meters apart. The distance traveled is recorded along with the patient’s perceived exertion using the Borg Scale. The patient’s oxygen saturation is continuously recorded using a small wrist watch type device on the patient’s wrist and finger. The test may also be performed while the patient breaths supplemental oxygen to assess the patient’s oxygen requirement.

Incremental shuttle walk test (ISWT)
The ISWT is a field test that simulates a cardiopulmonary exercise test. The patient walks between two cones to a set of bleeps played on a tape. The pace is initially slow but speeds up every minute as the bleeps get closer together. The test ends when the patient is unable to reach the cones before the bleeps. The number of shuttles walk is recorded and this can be used to prescribe the intensity of exercise. The test must be performed at least twice as there is a learning effect.

Allergy Testing

Skin Allergy Testing
A skin allergy test tests the sensitivity of a patient to common allergens such as grass pollen,house dust mite and animal . These allergens may be contributing to the patient’s symptoms. During the test, a drop of each allergen solution is placed on the skin on the underside of the forearm or on the back in very young patients. A single use sterile lancet is used to pierce the skin underneath the solution (the sensation is just like a tiny scratch and does not hurt). After 15-20 minutes the skin is checked for any reactions. The allergen may cause a reddening of the skin and produce a blister-like bubble on the skin surface called a weal. A positive reaction is taken as a weal diameter of greater than 3mm.

Sleep Studies

Patients with sleep breathing disorders such as obstructive sleep apnoea may be referred to the pulmonary function laboratory for sleep studies.

Overnight Oximetry:
The patient is sent home with a wrist watch type device which measures the oxygen saturation continuously during the night. The patient returns the device the following day for analysis.

Limited Sleep Study:
The patient attends a hospital (local lab policy applies) appointment to be instructed how to attach the sleep measuring equipment. They are usually sent home and asked to wear the equipment overnight then return the next morning with the equipment for analysis.

Polysomnography:

(PSG) is a comprehensive test that measures many physiological parameters during sleep such as brain electrical activity, eye and chest muscle movements, airflow at the nose and mouth, chest and abdominal movements, periodic leg movements, heart rate and oxygen saturation. This advanced sleep study is only carried in a few specialized sleep centres and requires overnight stay in the hospital.

CPAP Treatment:

Patients that are diagnosed with obstructive sleep apnoea may be treated with a continuous positive airway pressure (CPAP) machine. Respiratory physiologists liaise with respiratory nurse specialists to help in the selection and fitting of CPAP masks and also measure the response to therapy using PSG with CPAP.

Asthma

Asthma is a long lasting lung disease in which the muscle surrounding the airways in the lungs tightens, causing them to narrow, become swollen and fill up with an increased level of mucus. It is caused by an over-sensitive reaction to certain substances like house dust, pollen animal hair and tobacco smoke. Environmental conditions like hot or cold air can also have an effect, as can exercise or stress. As a result of these changes, the movement of air in and out of the lungs is reduced. asthmatic patients may experience breathlessness, wheeze, cough and chest tightness. Asthma can occur at any stage in life, but is most common in childhood. It is also more common within families; you have a higher chance of having asthma if a relative is an asthmatic. In Ireland, nearly half a million have the disease. In most cases, asthma can be successfully treated and the symptoms completely reversed.

Treatment normally involves inhalers, but sometimes, oral medication is also involved. These treatments reduce the airway swelling and tightening, decrease the level of mucus and open up the airways. Avoidance of the triggers that bring on asthma will also help.

For further information on Asthma and for instructions on the correct use of your inhalers, please follow the below links.

Asthma Society of Ireland www.asthma.ie

Inhaler Technique Videos - https://www.asthma.ie/get-help/resources/inhaler-technique-videos

Chronic Obstructive Pulmonary Disease

Chronic Obstructive Pulmonary Disease (COPD) is a term used to include two lung disease, Chronic Bronchitis and Emphysema, or a combination of both. It is a long lasting disease that normally gets worse over time. Chronic Bronchitis is a disease in which the medium sized airways in the lungs become swollen, and fill up with an excess of mucus. This causes the diameter to narrow, reducing the movement of air in the lungs. Emphysema affects the air sacs in the lungs where oxygen and carbon dioxide are exchanged. The walls of these air sacs are weakened and damaged, and become less elastic, causing them to collapse inward. This also causes the smaller airways supplying them to collapse. Eventually the walls are destroyed. As a result of this, air becomes trapped in the air sacs, and the lungs over-expand with air. This affects the exchange of air in the lungs. COPD patients experience breathlessness, wheezing, chest tightness and a cough (which produces mucus).

The most common cause of COPD is cigarette smoke, although inhaling other toxic gases can cause it. Treatment involves smoking cessation, inhaled medication and oxygen therapy in some cases. Unlike Asthma, inhaled medication is not as effective at reversing the airway narrowing in COPD.

For further information on COPD, management to the disease and smoking cessation, please follow the links below:

COPD Ireland- www.copd.ie

Smoking Cessation http://copd.ie/living-with-copd/smoking-cessation/

Idiopathic Pulmonary Fibrosis (IPF)

Pulmonary Fibrosis is a disease that affects the areas of the lungs in which air is exchanged. These areas become scarred and inflamed to some extent, which affects the movement of oxygen into the blood and the removal of carbon dioxide (waste product). Pulmonary Fibrosis patients can experience a dry cough (does not produce mucus) and breathlessness. Another result of this scarring is that the lungs become stiff and more rigid, and cannot expand fully. This reduces the capacity of the lungs and adds to the breathlessness. It is a long lasting disease that gradually gets worse over time. The cause of Pulmonary Fibrosis is unknown, but it is thought to arise from an excessive immune response i.e. a situation where the body attacks its own cells.

There is no standard treatment for people with Pulmonary Fibrosis and it may differ from patient to patient. It generally involves attempts to reduce the swelling, but has had limited success. In some cases, the disease becomes inactive itself. Many studies and trials are now underway which are trying to develop a new approach to the treatment of the disease. Pulmonary Fibrosis patients can be monitored with Pulmonary Function Tests.

For further information on pulmonary fibrosis, please follow the link below:

Irish Lung Fibrosis Association- www.ilfa.ie

Sarcoidosis

Sarcoidosis is a disease that can affect any part of the body, but commonly affects the lungs, eyes and skin. Its cause is unknown, but is thought to occur when the body’s immune system attacks the body’s own cells. The immune system is the body’s defence mechanism, consisting of cells that attack foreign particles and germs. In some cases, these cells organise themselves into groups or clusters, in certain areas of the body to fight infection. In Sarcoidosis of the lungs, these clusters build up in the areas where air is exchanged and impair the transfer of oxygen and carbon dioxide (waste product).

They also cause these areas to become swollen. Sarcoidosis patients experience breathlessness, loss of energy, tiredness and a dry cough (does not produce mucus). Some cases of Sarcoidosis are resolved without treatment, but some need steroid therapy to reduce the swelling in the lungs. Other cases get worse over time and the lungs become scarred and more rigid, which prevents them from expanding properly. In Ireland, 1or 2 in 1500 people are affected.

For further information and support, you can visit the Irish Lung Foundation on the below link:

Irish Lung Foundation- www.irishlungfoundation.ie/sarcoidosis.html

Pulmonary Hypertension

Pulmonary Hypertension is high blood pressure in the pulmonary artery. This is the blood vessel that carries blood with a low amount of oxygen and a high amount of carbon dioxide (waste product) content to the lungs, so oxygen can be added and carbon dioxide released. Narrowing of the artery and its branches causes the high blood pressure. This reduces the movement of blood and impairs the exchange of air. Also, the chamber in the heart that pumps blood to the lungs has to work much harder than normal, and becomes large and swollen, resulting in heart failure.

People with Pulmonary Hypertension experience breathlessness, dizziness, swelling of the legs or ankles and tiredness after work or activity. It is a long-term condition. Pulmonary Hypertension has many causes including heart disease, blood clots and lung disease and can be more common within families. Some causes are unknown. Treatment generally involves medication to reduce blood clots, reduce swelling of the limbs and widen the blood vessels. Oxygen therapy may also be used.

For further information and support, you can visit the Pulmonary Hypertension Association Ireland website on the below link:

Pulmonary Hypertension Association Ireland https://www.pulmonaryhypertension.ie/pha-ireland

Heart Disease

Many diseases of the heart can also affect the function of the lungs. Any heart disease that causes a reduction in the amount of blood supplying the lungs will have an effect on the exchange of air that takes place there. Also, Heart Failure will cause a condition called Pulmonary Oedema, which is a build-up of fluid within the lungs. This impairs the exchange of air and also prevents the lungs from expanding properly, consequently reducing the capacity of the lungs. Other heart conditions can cause a build-up of fluid between the lungs and the rib cage. This will also reduce the capacity of the lungs.

For further information and support, you can visit the below links:

Irish Heart Disease Awareness- www.ihda.ie

Irish Heart Home- www.irishheart.ie

Sleep Disorders

The most common sleep disorder is Obstructive Sleep Apnoea syndrome (OSAS). Patients with OSAS experience reductions in blood oxygen levels when asleep due to repeated pauses and/or reductions in breathing. OSAS is implicated in a number of instances including hypertension and an increased risk of being involved in a road traffic accident. Other sleep disorders include insomnia and narcolepsy.

For further information and support, you can visit the Irish Sleep Disorders Foundation on the link below:

Irish Sleep Disorders Foundation https://www.sdsf.ie/

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Last Updated: Monday, 7th September 2020

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