gastrapping

Gas trapping is a radiologic and physiologic phenomenon in which air remains in the lungs during expiration due to uneven airway narrowing or obstruction, often reflecting small airways disease or loss of elastic recoil. It leads to inefficient emptying of the lungs and can contribute to regional hyperinflation.

Causes and mechanism include conditions that restrict airflow in the small airways, such as asthma, chronic obstructive pulmonary disease, bronchiolitis, and mucus plugging. Inflammation, edema, or structural changes can cause airway closure on exhalation, trapping air distally. Over time, gas trapping can increase residual volume and contribute to persistent hyperinflation, with symptoms like dyspnea and wheeze.

Imaging and detection rely on expiratory studies. On expiratory radiographs or CT scans, regions with gas trapping fail to deflate normally and may appear as persistent lucency or relatively less increase in density compared with well-deflated lung. Expiratory CT is particularly useful for characterizing small airways disease and can help localize affected lung regions.

Clinical significance involves recognizing gas trapping as a hallmark of small airways disease and as a discriminator between different patterns of lung disease. It often correlates with functional measurements such as increased residual volume and a reduced FEV1/FVC ratio on spirometry. Gas trapping can inform treatment decisions and prognosis, especially in diseases like asthma and COPD.

Management targets the underlying cause and may include bronchodilators and anti-inflammatory therapies, cessation of smoking, infection control when present, and supportive care. Strategies are tailored to the condition driving the air trapping and to the patient’s overall clinical status.