title: Effect of ventilation on mechanical properties and pressure-flow relationships of immature airways.
abstract: Ventilation of immature airways has been shown to result in pressure-induced deformation and alteration of mechanical properties. These changes in mechanical properties may alter the effect of compressive pressures on pressure-flow relationships. To test this hypothesis, unventilated (Group I, n = 8) and ventilated (group II, n = 8; mean pressures of 8-12 cm H2O for 2 h duration) tracheal segments were excised from preterm lambs approximately 118 days gestation and mounted in a Krebs-filled chamber for determination of compliances and pressure-flow relationships. Compliance data were obtained for both the inflation loop (inflation compliance) and the collapsing loop (collapsing compliance) of the pressure-volume curve for each segment. Flow (V = 2-10 liter/min.) was introduced through the lumen of each segment at different chamber pressures (Pc = 5-30 mm Hg). Driving pressure (Pd) was recorded for each V and Pc. Airway resistance (R) was calculated as Pd/V. Group II had significantly greater (p less than 0.005) radii than Group I, suggesting ventilation-induced deformation. Group II had significantly lower (p less than 0.05) inflation compliance but significantly greater (p less than 0.05) collapsing compliance than group I. Two-factor analysis of variance demonstrated significantly greater (p less than 0.05) R in group II at each value of V and each Pc. These data may help to explain the flow limitation and gas-trapping observed in preterm infants who have been mechanically ventilated.
authors.affiliation: Department of Physiology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
authors.forename: R B
authors.initials: RB
authors.lastname: Penn
authors.forename: M R
authors.initials: MR
authors.lastname: Wolfson
authors.forename: T H
authors.initials: TH
authors.lastname: Shaffer
mesh_terms: D000818:Animals; D005314:Embryonic and Fetal Development; D005865:Gestational Age; D066298:In Vitro Techniques; D011312:Pressure; D012123:Pulmonary Ventilation; D012756:Sheep; D014132:Trachea / Q000196:embryology / Q000502:physiology*; D012122:Ventilators, Mechanical