By Dr. Dineshani Hettiarachchi Sirisena
World Lung Day falls on 25 September 2019. This year, the theme is “healthy lungs for all” and calls for universal health coverage where all people receive the health services they need. An important part of health services in relation to achieving healthy lungs is proper diagnosis, early detection, and the better monitoring of respiratory diseases, in which lung function tests play an important role.
This week, we spoke to Dr. Lakmali Amarasiri, who is a senior lecturer in physiology at the Faculty of Medicine of the University of Colombo and has a special interest in lung function testing, to learn more about the importance of these tests, their availability in our country, and important information for patients who have been asked to undergo such tests.
How common are respiratory diseases?
Respiratory diseases are a leading cause of death and disability in the world. The World Health Organisation (WHO) reports that millions suffer from chronic obstructive pulmonary disease (COPD) and asthma, and over four million people die prematurely from chronic respiratory disease. Millions also die due to pneumonia, tuberculosis, and lung cancer.
Respiratory diseases are emerging in Sri Lanka as well. It is estimated that we have nearly one million asthmatics in Sri Lanka, with the prevalence in children ranging from 17% to 27%. The overall prevalence of COPD is 10.5% and the risk for obstructive sleep apnoea is 14.5%. In 2016 in Sri Lanka, diseases of the respiratory system were the third leading cause of hospitalisation and accounted for around 17% of deaths.
Lung function tests (LFTs)
Lung function tests are tests that assess breathing. To breathe normally, we need a properly functioning respiratory system which comprises not only the lungs, but also the airways (from the nose down to the bronchioles), rib cage, and muscles attached, and a complex set of mechanisms that also involves the brain areas and nerves that control our breathing. LFTs assess the respiratory system by measuring how well air flows through airways, the capacity of lungs, and how well oxygen is transferred to blood through the lungs. Malfunction of any of these structures due to injury or infection can lead to respiratory disease and cause abnormalities in lung function.
The role of LFTs in management of a respiratory disease
LFTs help in diagnosis, early detection, and monitoring the progression of such diseases. For example, in a person who wheezes, with the use spirometry, it is possible to differentiate between asthma and COPD as well as grade the severity of the disease, which is important to determine the extent of treatment. Spirometry also assesses fitness for surgery.
Sometimes, asthmatic patients have normal lung function, unless they encounter a trigger such as dust, strong smells or smoke, and exercise. To diagnose asthma in such patients, bronchoprovocation tests are performed. Spirometry is performed before and after provocation with a chemical substance or an exercise challenge on a treadmill or bicycle.
Impulse oscillometry and body plethysmography can detect very early airway narrowing by measuring airway resistance. These tests are also useful to assess airway obstruction in children and feeble patients as they do not require much effort. Airway resistance measurement is also useful to detect upper airway obstruction in snorers and in patients with obstructive sleep apnoea.
In patients who complain of difficulty in breathing or fatigue on exertion, the six-minute walk test, incremental shuttle test, and cardiopulmonary exercise test help to differentiate whether the cause is related to the heart, respiratory system, or oxygen utilisation in the tissues. This is coupled with oxygen assessment if the patient’s oxygen saturation levels drop during testing to determine how much oxygen needs to be supplemented.
Lung volume assessment is important in patients with low lung capacity, e.g. muscle disorders or skeletal deformities and before surgery in people with overinflated lungs.
The DLCO test assesses the ability of the lung membrane to transfer oxygen and its uptake by haemoglobin in the red blood cells. This test is useful in monitoring patients with diseases of the lung tissue, e.g. lung fibrosis and in patients who take toxic medication that may affect the lungs (such as chemotherapy).
Fitness to fly tests are useful to assess whether patients with respiratory disease will require oxygen supplements during air travel.
Serial LFTs are very useful to monitor progression of disease, whereas changes in X-rays and CT scans may take time to manifest.
Usefulness of LFTs in exercise-induced difficulty in breathing
Sometimes, people experience difficulty in breathing or wheezing during or after exercising. The common practice is to prescribe an inhaler to be taken before exercise. However, difficulty in breathing related to exercise could also be due to problems in the heart, lactic acid build up, or problems in oxygenation at tissue level. Cardio pulmonary exercise testing, which involves simultaneous measurement of breathing, heart rate, and ECG, helps in differentiating the underlying problem in such cases. The best test to detect exercise-induced airway narrowing is the eucapnic voluntary hyperventilation test where the patient is made to breathe deeply and rapidly for some time, and spirometry measured before and after.
LFT in healthy individuals
LFTs can be utilised to assess healthy people as well. For example, cardiopulmonary exercise testing assesses endurance in athletes. High and low oxygen assessments are performed to assess fitness in pilots, mountaineers, and divers.
What to expect during a LFT
Most tests involve breathing through a bacterial filter according to instructions given by the technician. In body plethysmography, the patient is seated inside a glass chamber.
During exercise assessment tests, the patient may be asked to run or walk on a treadmill or cycle in between breathing tests.
There can be certain challenges during LFTs as they can be confusing. However, all the patient needs to do is listen carefully and follow instructions. It is very important that there is a skilled technician performing these tests. If the test is not performed properly, the test result would be wrong and misleading.
Is there any special preparation required?
Usually, there is no special preparation required. However, it is important that the patient wears comfortable, loose clothes that do not restrict full chest and abdominal expansion and does not eat a large meal within two hours of testing. There is no need to fast. The patient should not smoke within one hour of testing and consume alcohol within four hours of testing. The patient should be well with no history of illness at least within the past two weeks.
If the physician has requested for a bronchodilator reversibility test to assess whether airway narrowing improves with bronchodilators, the bronchodilator medication must not be taken up to a certain time before the test. Usually, the unit will provide instructions for the patient before he/she goes for the test and it is very important to carefully adhere to the preparation instructions before going for the test.
Safety of LFTs
Most tests involve exhaling into a tube and involve normal breathing. Spirometry and exercise testing, which involves forceful breathing, should not be performed in some conditions (e.g. if the patient is ill, in pain, is coughing up blood, has had a heart attack, surgery, pulmonary embolism, or aneurysm within the past month, has a neck injury, etc.). These contraindications should always be excluded before testing. Exercise testing and bronchoprovocation is always performed under the supervision of a physician and skilled technicians in a specialised unit with facilities for immediate resuscitation, as there is a very small risk of triggering an asthma attack or cardiac arrest. But the risk of these side effects is very small.
Are these tests available in Sri Lanka?
Yes, spirometry is available in many hospitals in both state and private sectors. Some of the other tests are available in several state specialised units, including the Central Chest Clinic of the National Hospital of Sri Lanka and a few private hospitals.
Take-home messages
- Respiratory diseases are increasing in Sri Lanka.
- Management of a respiratory disease is better when it is detected early and properly monitored.
- Lung function tests are important in early detection, diagnosis, and most importantly, in assessing the functional capacity of a patient.
- Lung function tests are now available in specialised units of the state and private sectors.
- It is important to get your lung function test done at a centre that prepares you, ensures proper test performance, and takes adequate safety precautions.
- Lung function tests should be performed when you are not ill.
- Lung function tests must always be performed through a bacterial filter to prevent cross infection between patients.
About the writer
The writer, Dr. Dineshani Hettiarachchi Sirisena, is a family physician with a special interest in rare genetic diseases and regenerative medicine currently working as a lecturer at the Department of Anatomy, Faculty of Medicine, University of Colombo, Sri Lanka.
