ACCURATE METHOD TO STUDY STATIC VOLUME-PRESSURE RELATIONSHIPS IN SMALL FETAL AND NEONATAL ANIMALS

We designed an accurate method to study respiratory static volume-pres sure relationships in small fetal and neonatal animals on the basis of Archimedes' principle. Our method eliminates the error caused by the compressibility of air (Boyle's law) and is sensitive to a volume chan ge of as little as 1 mu l. Fetal and neonatal rats during the period o f rapid lung development from clay 19.5 of gestation (term = day 22) t o day 3.5 postnatum were studied. The absolute lung volume at a transr espiratory pressure of 30-40 cmH(2)O increased 28-fold from 0.036 +/- 0.006 (SE) to 0.994 +/- 0.042 mi, the volume per gram of lung increase d 14-fold from 0.39 +/- 0.07 to 5.59 +/- 0.66 ml/g, compliance increas ed 12-fold from 2.3 +/- 0.4 to 27.3 +/- 2.7 mu l/cmH(2)O, and specific compliance increased B-fold from 24.9 +/- 4.5 to 152.3 +/- 22.8 mu l. cmH(2)O(-1).g lung(-1). This technique, which allowed us to compare ch anges during late gestation and the early neonatal period in small rod ents, can be used to monitor and evaluate pulmonary functional changes after in utero pharmacological therapies in experimentally induced ab normalities such as pulmonary hypoplasia, surfactant deficiency, and c ongenital diaphragmatic hernia.