Speaker's Highlight

• Don Sin University of British Columbia, St. Paul Hospital (Canada)
  Kenneth R. Chapman Toronto General Hospital Research Institute (Canada)
• Parameswaran Nair McMaster University (Canada)
  Carolyn Calfee UCSF (U.S.A.)
• Gregory P. Downey University of Colorado School of Medicine (U.S.A.)
  David A. Schwartz University of Colorado School of Medicine (U.S.A.)
• Neil Schluger Tuberculosis Control Branch, California Department of Public Health (U.S.A.)
  Nick Kim Critical Care & Sleep Medicine, University of California San Diego (U.S.A.)
• Nicola Hananiah Baylor College of Medicine (U.S.A.)
  Jae-Joon Yim Seoul National University College of Medicine (Republic of Korea)
• Koichiro Asano Tokai University School of Medicine (Japan)
  Diahn-Warng Perng Taipei Veterans General Hospital (Taiwan)
• Konstantinos Kostikas University of Ioannina (Greece)
  Karin Klooster University Medical Center Groningen (Kingdom of the Netherlands)

• The Clinical Significance of Air Trapping on Pulmonary Function Tests

  Air trapping is a common but often under-recognised finding in respiratory assessment. It occurs when gas enters the lungs during inspiration but cannot be fully expelled during expiration, leaving an increased volume of air behind. Pulmonary function tests can reveal this pattern before a patient develops obvious resting breathlessness or a marked reduction in FEV1.

  For Australian clinicians, the finding matters across general practice, hospital respiratory clinics and occupational health. A patient may describe being “a bit wheezy” after a bushfire-smoke exposure, while another may report reduced exercise tolerance on a steep walk in Hobart or during hot weather in western Sydney. The test result needs to be interpreted alongside symptoms, exposure history, imaging and the quality of the manoeuvres.

  Finding	What it may indicate	Useful next step
  Raised residual volume	Incomplete emptying after expiration	Check technique, bronchodilator response and clinical context
  Raised RV/TLC ratio	Gas trapping relative to total lung capacity	Consider small-airway disease or obstructive pathology
  Increased FRC	Hyperinflation or resting gas trapping	Correlate with dyspnoea and exercise limitation
  Normal spirometry with high RV	Early or peripheral airway dysfunction	Consider full lung volumes and expiratory CT when indicated
  Reduced DLCO with hyperinflation	Possible emphysema or pulmonary vascular involvement	Integrate imaging, smoking history and cardiovascular assessment

  What Air Trapping Means Physiologically

  Residual volume is the amount of air remaining after a maximal forced expiration. When airway narrowing, loss of elastic recoil or premature closure prevents complete emptying, residual volume rises. Functional residual capacity may also increase, placing the patient at a higher operating lung volume before the next breath begins.

  The RV/TLC ratio is often more informative than residual volume alone because it shows how much of the total lung capacity remains trapped. A high ratio can signal obstructive physiology even when the FEV1/FVC ratio is within the reference range. This is particularly relevant in early small-airway disease, where conventional spirometry may appear reassuring.

  Body plethysmography is generally the preferred method for measuring thoracic gas volume and detecting hyperinflation. Gas dilution techniques can underestimate trapped gas because poorly ventilated lung regions may not communicate fully with the test gas. Results should always be checked against predicted values, z-scores, reference equations and test acceptability.

  Conditions Associated With Gas Trapping

  Chronic obstructive pulmonary disease is a major cause, especially when emphysema or airway-predominant disease produces expiratory flow limitation. Asthma can also cause air trapping, including between attacks when baseline spirometry is close to normal. Bronchiolitis, bronchiectasis and occupational inhalation injury are additional possibilities.

  Air trapping is not a diagnosis by itself. A high residual volume may reflect suboptimal expiration, obesity-related changes, neuromuscular weakness or a technical problem. The report should state whether the patient achieved a satisfactory end-expiratory plateau and whether the measured lung volumes are internally consistent.

  In Australia, exposure history may include tobacco, vaping, wood smoke, mining dust, agricultural chemicals and repeated bushfire smoke. A patient from the Hunter Valley, Pilbara or regional Queensland may have a different occupational risk profile from someone working in an inner-Melbourne office. These details can materially change the significance of an abnormal lung-volume pattern.

  Why It Matters Clinically

  Air trapping increases the work of breathing and can create dynamic hyperinflation during exertion. The patient may be unable to inhale deeply because the next breath begins before the previous breath has fully left the lungs. This can produce exertional breathlessness, early fatigue and reduced walking distance, even when resting oxygen saturation is normal.

  In COPD, hyperinflation is associated with symptom burden and exercise limitation. Bronchodilators may reduce airway resistance and improve emptying, although the change in FEV1 may be modest. For selected patients, a reduction in hyperinflation can be clinically meaningful even when the headline spirometry numbers change very little. Discussion of anticholinergic therapy is therefore best based on symptoms, exacerbation history, reversibility and the broader clinical picture.

  A normal FEV1/FVC ratio should not automatically dismiss the result. If the patient has persistent exertional symptoms, recurrent “chest infections” or unexplained wheeze, full lung volumes and, where appropriate, expiratory high-resolution CT may reveal mosaic attenuation or regional gas trapping. Imaging should be ordered when it will answer a specific clinical question rather than simply confirm an isolated test abnormality.

  Interpreting Results In Practice

  Interpretation begins with the quality report. Poor seal, coughing, premature termination or inadequate expiratory time can falsely elevate residual volume or obscure obstruction. The clinician should review the flow-volume loop and determine whether the measured values fit together physiologically.

  Useful clinical questions include:

  • Is the patient symptomatic during exertion, at night or after a respiratory infection?
  • Is there a meaningful bronchodilator response?
  • Are RV, TLC and FRC all increased, or is only one value abnormal?
  • Could obesity, weakness or poor test technique explain the pattern?
  • Are smoking, vaping, occupational dust or bushfire exposures relevant?
  • Would expiratory CT, exercise oximetry or cardiopulmonary exercise testing add value?

  Australian services vary in access to plethysmography and specialist review. A GP in a regional town may initially rely on quality spirometry and referral pathways, while a metropolitan respiratory laboratory can provide full lung volumes and diffusion capacity in one visit. Clear reporting helps ensure that patients moving between a local hospital, a private laboratory and a tertiary service receive a consistent interpretation.

  Applying Findings To Patient Care

  Management should target the underlying condition rather than the number alone. Asthma requires assessment of variable symptoms, eosinophilic or allergic features and inhaler technique. COPD care may include smoking cessation, vaccination, pulmonary rehabilitation, inhaled therapy and an action plan for exacerbations. Bronchiectasis calls for attention to sputum burden, airway clearance and recurrent infection.

  In remote and regional Australia, travel distance can affect follow-up, so a practical plan may combine local spirometry with periodic specialist review. Patients exposed to summer smoke in New South Wales or Victoria may benefit from advice about indoor air quality and medication access during poor air days. Aboriginal and Torres Strait Islander patients should receive culturally safe care, with attention to community context, continuity and barriers to testing.

  The key point is that air trapping is a physiological clue, not a standalone label. When a technically sound test shows elevated residual volume or hyperinflation, the finding can uncover early airway disease, explain disproportionate breathlessness and guide further assessment. Its true clinical significance emerges when lung volumes are read alongside symptoms, exposures, imaging and the patient’s everyday function.

  Richard Russell Nuffield Department of Clinical Medicine, University of Oxford (United Kingdom)
• Mona Bafadhel King’s College London (United Kingdom)
  David Jackson Guy’s and St Thomas’ Hospital, King’s College London (United Kingdom)
• James Chalmers University of Dundee (United Kingdom)
  David Price University of Aberdeen (United Kingdom)