Age-related differences in the distortion of the sheep lung in response tolocalised pleural stress

1. In order for diastolic filling to occur, the heart must displace the lun g. Given the changes in lung structure and compliance that follow birth, we sought to determine whether the neonatal lung resists neighbouring structu res encroaching into its space more than the adult lung and whether the lun g surface making up the cardiac fossa resists, distortion more than the lat eral surface does. 2. Pleural distortions, induced by applied pressures (P-appl) of 20-120 g c m(-2) at airway pressures (P-aw) of 2.5-15 cmH(2)O, were recorded in isolat ed lungs of adult, neonatal (4-week-old) and newborn (1-week-old) sheep. 3. The depth of pleural distortion increased (P < 0.05, ANOVA) with increas ing P-appl in all lungs. Adult lungs were significantly more distortable th an newborn and neonatal lungs (P < 0.05). As P-aw increased, the distortabi lity of the adult lung decreased progressively (P < 0.05) while the distort ability of the newborn and neonatal lung remained constant at P-aw of 2.5 a nd 5 cmH(2)O. 4. Adult lungs also differed from newborn and neonatal lungs in that the ca rdiac fossal surface was significantly less distortable than the lateral su rface. 5. As newborn and neonatal lungs are less easily distorted than adult lungs , the potential for the lungs to limit cardiac filling is greater in the ne wborn and neonate than in the adult.