Studies on pressure-volume relationships in excised equine lungs

Forty-eight lungs from fetal and neonatal horses were examined for pressure-volume relationships between pressures of 0 and 40 cmH2O. The inflation-deflation curves obtained were analysed by four different methods and the stability of the lung assessed in terms of hysteresis, stability indices and volume of air retained at maximal pressure (Vmax). Differences in the shape of the deflation curve between ventilated and non-ventilated lungs were similar to findings in other species. It is postulated that breathing alters lung-tissue elasticity during the neonatal period, as demonstrated by a significant increase in Vmax in specimens from foals breathing for more than 24 hr compared with those from stillborn foals or those aged less than 24 hr. Also, stability indices, such as those expressed by the % of air retained in the lungs on deflation from Vmax to 10 or 5 cmH2O pressure, are related to interfacial factors.