Unexplained breathlessness
Testing can identify airflow, lung-volume, gas-transfer or exercise-related abnormalities.
Private respiratory testing in London
Lung Function Tests in London
Specialist respiratory assessment using objective tests to measure airflow, lung volumes, gas transfer, airway inflammation and exercise capacity.
- Comprehensive respiratory testing
- Consultant-led interpretation
- Personalised clinical recommendations
Understanding respiratory physiology
What are lung function tests?
Lung function tests are a group of investigations that measure how effectively the lungs move air, hold air, transfer oxygen and respond to exercise or inhaled medication.
Breathlessness, cough, wheeze and reduced exercise tolerance cannot always be explained by symptoms or chest imaging alone. Lung function testing provides objective information about how the lungs are working.
The tests required depend on the clinical question. Some patients need straightforward spirometry, while others benefit from detailed lung-volume, gas-transfer, airway-inflammation or exercise testing.
Results are interpreted alongside the medical history, examination, medication, smoking history, chest imaging and other investigations. A numerical result should not be interpreted in isolation.
A normal result on one test does not necessarily exclude respiratory disease. Different tests examine different aspects of lung function.
Reasons for assessment
Why might I need lung function testing?
Testing may be used to investigate symptoms, confirm or refine a diagnosis, monitor a known respiratory condition or assess fitness before treatment, surgery or air travel.
Persistent cough or wheeze
Spirometry, reversibility and FeNO may help investigate asthma and other causes of respiratory symptoms.
Monitoring respiratory disease
Serial measurements can monitor asthma, COPD, bronchiectasis, pulmonary fibrosis and other lung conditions.
Pre-operative or travel assessment
Lung function, CPET or hypoxic challenge testing may contribute to planning before surgery or air travel.
Measuring airflow
Spirometry and bronchodilator reversibility
Spirometry measures how much air can be exhaled and how quickly air can be breathed out following a full breath in.
Core respiratory investigation
What happens during spirometry?
You will usually sit upright and wear a nose clip. After taking a full breath in, you will seal your lips around a disposable mouthpiece and blow out as hard, fast and completely as possible.
The manoeuvre is repeated to ensure that the results are technically acceptable and reproducible.
FEV1
Forced expiratory volume in one second
The amount of air exhaled during the first second of a forced breath.
FVC
Forced vital capacity
The total amount of air exhaled during the complete forced breathing manoeuvre.
FEV1/FVC
Airflow ratio
Helps identify an obstructive ventilatory pattern.
Possible pattern
Obstructive
Air has difficulty leaving the lungs, as may occur in asthma or COPD.
Possible pattern
Restrictive
Reduced vital capacity may suggest smaller lung volumes, but full lung-volume testing is required to confirm restriction.
Possible result
Normal spirometry
Does not exclude all respiratory disease or intermittent asthma.
Measuring oxygen-transfer capacity
Gas transfer testing
Gas transfer testing assesses how effectively gas passes from the air sacs of the lungs into the bloodstream.
The test is often called the diffusing-capacity test, DLCO or TLCO. You breathe in a very small concentration of test gases, hold your breath briefly and then breathe out into the equipment.
The result provides information about the functioning surface area of the lungs, the pulmonary circulation and gas movement across the alveolar-capillary membrane.
TLCO or DLCO
Estimates overall transfer of carbon monoxide from the lungs into the blood.
KCO
Expresses transfer in relation to measured alveolar volume.
Clinical use
May help assess emphysema, fibrosis, pulmonary vascular disease and unexplained breathlessness.
Anaemia, smoking, oxygen use, incomplete inspiration and technical
factors may affect gas-transfer measurements.
Detailed physiological assessment
Lung volumes and airway inflammation
Additional tests can assess air remaining inside the lungs after exhalation and identify evidence of eosinophilic airway inflammation.
Static lung volumes
Lung-volume testing
Spirometry cannot measure all of the air remaining inside the lungs. Lung-volume testing provides measurements such as total lung capacity and residual volume.
- Total lung capacity
- The total amount of air in the lungs after the deepest possible breath in.
- Residual volume
- The air remaining in the lungs after breathing out as fully as possible.
- Functional residual capacity
- The volume remaining after a normal relaxed breath out.
Measurements may be obtained using body plethysmography or a gas dilution technique. They can confirm restriction and identify air trapping or hyperinflation.
FeNO testing
Fractional exhaled nitric oxide testing measures nitric oxide in a controlled exhaled breath. A raised result may support type 2 or eosinophilic airway inflammation.
Before a FeNO test
- Avoid smoking or vaping beforehand
- Avoid vigorous exercise shortly before testing
- Follow instructions about food and drinks
- Report recent infection or corticosteroid treatment
- Do not stop inhaled steroids unless instructed
Smoking, food, exercise, allergy exposure and corticosteroid treatment can influence the result. Instructions from the testing laboratory take priority.
Read the full FeNO guide
Monitoring variable airflow
Peak-flow monitoring
Peak expiratory flow measures the maximum speed at which air can be blown out after taking a full breath in.
A small handheld meter can be used at home, often in the morning and evening, over several days or weeks. The pattern of results is more informative than a single measurement.
01
Stand or sit upright
02
Take a full breath in
03
Blow out hard and fast
04
Record the best reading
Integrated exercise physiology
Cardiopulmonary exercise testing
Cardiopulmonary exercise testing, or CPET, assesses how the lungs, heart, circulation and muscles respond to progressively increasing exercise.
You will usually exercise on a stationary bicycle while wearing a mask or mouthpiece. Breathing, oxygen uptake, carbon-dioxide production, heart rhythm, blood pressure and oxygen saturation are monitored.
The workload increases gradually while the clinical team assesses symptoms and physiological responses.
Unexplained breathlessness
Helps distinguish respiratory, cardiovascular, muscular, deconditioning and breathing-pattern limitations.
Exercise capacity
Measures the integrated response to exercise rather than assessing the lungs at rest alone.
Pre-operative assessment
May contribute to risk assessment before selected major surgical procedures.
Clinical planning
Can guide further investigation, rehabilitation and exercise recommendations.
CPET can identify exercise-related abnormalities that may not be apparent during resting lung function or cardiac investigations.
Air-travel respiratory assessment
Fitness to fly and hypoxic challenge testing
A hypoxic challenge test can help assess whether a person with respiratory disease is likely to require supplemental oxygen during commercial air travel.
Simulating aircraft cabin conditions
What is a hypoxic challenge test?
Commercial aircraft cabins are pressurised, but the available oxygen pressure is lower than at sea level. During a hypoxic challenge test, the patient breathes a controlled low-oxygen gas mixture designed to simulate typical aircraft-cabin conditions.
Oxygen saturation, symptoms and sometimes arterial or capillary blood gases are monitored. If oxygen falls below the accepted clinical range, the test may be repeated with supplemental oxygen to identify an appropriate in-flight oxygen flow rate.
01
Baseline assessment
Resting oxygen levels and clinical history are reviewed.
02
Hypoxic gas mixture
The patient breathes controlled low-oxygen air while monitored.
03
Oxygen assessment
Saturation, symptoms and blood gases are assessed as required.
04
Travel recommendation
The result helps determine whether in-flight oxygen is needed.
Before your appointment
How should I prepare for lung function tests?
Preparation depends on the tests being performed. Follow the specific instructions provided by the clinic because medication restrictions are not identical for every patient or every investigation.
Check your inhaler instructions
Some bronchodilators may need to be withheld. Do not stop prescribed treatment unless instructed.
Avoid a heavy meal immediately beforehand
A very large meal may make deep breathing or exercise uncomfortable.
Wear comfortable clothing
Loose clothing is helpful. CPET normally requires suitable exercise clothing and footwear.
Allow enough time
Detailed testing may require several measurements and repeated breathing manoeuvres.
Before diagnostic spirometry or reversibility testing
How long might inhaled therapies need to be withheld?
These are commonly used washout periods when the aim is to assess baseline airflow or bronchodilator responsiveness. The instructions issued by the testing clinic always take priority.
| Inhaler category | Examples | Typical withholding period |
|---|---|---|
| Short-acting beta-2 agonist | Salbutamol, terbutaline | 4–6 hours |
| Short-acting muscarinic antagonist | Ipratropium | 12 hours |
| Long-acting beta-2 agonist | Formoterol, salmeterol | 24 hours |
| Ultra-long-acting beta-2 agonist | Indacaterol, vilanterol, olodaterol | 36 hours |
| Long-acting muscarinic antagonist | Tiotropium, umeclidinium, glycopyrronium, aclidinium | 36–48 hours |
| Combination inhaler | ICS/LABA, LABA/LAMA or triple inhalers | Follow the interval for the longest-acting bronchodilator component |
| Inhaled corticosteroid alone | Beclometasone, budesonide, fluticasone | Usually continued unless specifically instructed otherwise |
Do not withhold medication when doing so may be unsafe. If you become breathless or wheezy, use your inhaler according to your prescribed plan and tell the testing team what you took and when.
Clinical interpretation
Understanding your lung function results
Results are compared with reference values calculated from factors such as age, sex and height, using the reference equation selected by the laboratory.
Results are more than a percentage predicted
Interpretation considers the measured value, expected reference range, lower limit of normal, test quality and the pattern across several measurements.
Was the test reliable?
Spirometry and gas-transfer testing require acceptable, repeatable breathing manoeuvres.
What pattern is present?
Results may suggest obstruction, restriction, air trapping or reduced gas transfer.
Does it fit the history?
Findings are compared with symptoms, examination, imaging and other investigations.
Lung function testing in London
Do you need an objective assessment of your breathing?
Arrange a consultation for investigation of breathlessness, cough, wheeze, reduced exercise tolerance or monitoring of a known respiratory condition.
