Pressure--volume relationships of tracheae in fetal newborn and adult rabbits.

The physical properties of the trachea in fetal, newborn, and adult rabbits change with age. Tracheal dimensions and pressure--volume relationships were determined in excised tracheae at a wide developmental age range (from early gestational age to infancy and adulthood). At intraluminal pressures of 0 to 10 cm H2O, the tracheal specific compliance was 0.089 (cm H2O)(-1) for a 21 day old fetus. By adulthood, the tracheal specific compliance decreased five fold to 0.017 (cm H2O)(-1); a dramatic proportion of this reduction occurred during fetal life itself, followed by a steady, progressive decline to adult age. The volume of the tracheal segment, at intraluminal pressure of 20 cm H2O, increased by 29% (adult), 41.5% (31 day fetus) and 113% (21 day fetus). Developmental alterations in the specific airway compliance suggest significant changes in anatomical dead space would occur as a function of maturation and airway transmural pressure.