THE EFFECTS OF SURFACE TENSION ON LUNG FUNCTION DURING EARLY DEVELOPMENT

Abstract

Pressure-volume and lung compliance/kg determinations were made in a total of 45 preterm lambs during gas ventilation (GR I: n = 31; 122-140 days gestation; 3.3-3.9 kg birthweight and liquid fluorocarbon (RIMAR 101) ventilation (GR II: n = 14; 106-138 days gestation; 1.1-3.4 kg birthweight. After effective ventilation (PaO2 > 60mmHg; PaCO2 = 30-45mmHg) and acid-base status (pH = 7.25 - 7.45) were achieved, pulmonary function was evaluated. Regression analysis showed significantly different relationships between lung compliance and developmental age for GR I (r = 0.95) and GR II (r = 0.99). Compliance for GR II lambs was consistently greater than for GR I lambs, this difference did not become significant until after 125 days gestation. These results indicate that minimizing interfacial surface tension has little effect on lung compliance in animals at earlier gestational ages, therefore suggesting that morphologic and tissue properties predominate surface properties in limiting lung distensibility. By defining the stage of development in which pulmonary function is most effectively improved by reduced surface tension, these findings suggest age-related criteria regarding the benefit of exogenous surfactant replacement therapy. (Supported by NIH Grant HL/HD 30525).