Regional differences in gas trapping (airway closure) between apex and base of excised rat lungs

Excised rat lungs were ventilated with air under three conditions: (a) while suspended by the trachea and surrounded by air, (b) while inverted and surrounded by saline, and (c) while upright and surrounded by saline. The distribution of transpulmonary pressures over which gas trapping occurred in the lung for each of the three conditions was found by a method previously described by Frazer et al. (1979). A distribution having a small standard deviation (SD) indicates more uniform gas trapping in the lung while a larger SD indicates less uniform gas trapping. Results showed that the SD was 0.63 for the inverted lung in saline, 1.10 for the lung in air, and 1.57 for the upright lung in saline. We conclude that gas trapping in lungs inverted in saline occurs more uniformly than gas trapping in lungs in air or upright in saline. The results obtained in saline in the upright and inverted position also imply that as the lung is deflated surrounded by air, gas trapping initially occurs in the base of the lung before it occurs in the apex. Since gas trapping and airway closure are related, there could also be intrinsic dissimilarities in airway closure between the apex and base of excised rat lungs suspended by the trachea in air.