Gastric xenon trapping mimicking COPD: recognition using an effervescent agent.

Trapping of xenon 133 in the stomach due to gas swallowing can mimic xenon 133 retention in the left lower lobe due to obstructive lung disease on pulmonary ventilation/perfusion studies. In such cases, ingestion of sodium citrate-bicarbonate-simethicone crystals, which form CO2 gas on contact with water, can distend the xenon-containing stomach and allow clear delineation of its gastric location. This approach is useful in selected cases and may help avoid false-positive diagnoses of obstructive airways disease.