Pressure-induced deformation in immature airways

The effect of positive pressure ventilation on the highly compliant fetal airways was evaluated utilizing fetal rabbit tracheal segments. The degree of mechanical and dimensional deformation was quantified to the pressure applied intermittently (IPP) or continuously (CPAP) for 60 min. Excised tracheal segments were obtained at 21, 27, and 31 days fetal rabbit gestation (term = 31 days) and from 18 +/- 6-month-old adults. Internal diameter, resting length, and volume of the tracheal segments were measured, and their pressure-volume relationships were determined by plethysmography. Tracheal specific compliance at deflation pressure of 0 to 10 cm H2O was calculated from these data. In all fetal groups, the application of positive pressure resulted in a decrease of both tracheal distensibility and the slope of the pressure-volume curves; in addition, a highly significant decrease in tracheal specific compliance was documented. At 21 days gestation, the tracheal specific compliance decreased from 0.089 to 0.034 cm H20-1 (P less than 0.001) after CPAP and to 0.025 cm H2O (P less than 0.001) after IPP. For the same group, the resting tracheal volume increased by a dramatic 89% (P less than 0.001) after CPAP and by 124% (P less than 0.001) after IPP. The magnitude of these alterations decreased as gestational age advanced; the changes were not significant by adulthood. These data indicate that significant pressure-induced deformation (barotrauma) is sustained by susceptible immature airways.