Pulmonary Function in the Newborn Infant. V. Trapped Gas in the Normal Infant's Lung*

Trapped gas" has been defined by Bedell, Marshall, DuBois, and Comroe (1) as "that component of the thoracic gas volume which, having entered the thorax, is present in the lungs or pleural space but is unable to leave owing to intrapulmonary mechanical factors which prevent gaseous outflow." By measuring the ventilated portion of the thoracic gas volume (i.e., the func- tional residual capacity, FRC) with conventional dilutional methods (2) and comparing it to the to- tal (ventilated and nonventilated) thoracic gas volume (TGV) as determined by their compres- sion-decompression plethysmographic technique (3), these investigators demonstrated trapped gas in several adult patients with blebs, cysts, pneumo- thorax, intrapulmonary tumors, and especially, emphysema. They conclude that gas which is trapped in alveoli (as opposed to intrapleural or cystic sites) must exist in regions that are in inter- mittent communication with the airway.