Abstract
To study the effect of surface tension (ST) on lung mechanics during early development, in vivo pressure-volume and lung compliance/kg (CI) determinations were made in preterm lambs. GR I (n=31; 122-140 days gestation; 2.25-3.90 kg BW) were gas ventilated and GR II (n=14; 106-138 days gestation; 1.10-3.40 kg BW) were liquid ventilated with oxygenated fluorocarbon (RIMAR 101). After effective ventilation (PaO2>60 mmHg; PaCO2=30-45 mmHg) and acid-base status (pH=7.25-7.45) were achieved, pulmonary function was evaluated (30-60 mins postnatally). Regression analysis showed significantly different relationships between CL and age for GR I (r=0.95; p<.001) and GR II (r=0.99; p<.001). Whereas CL for GR II consistently exceeded that for GR I, this difference did not become significant until after 125 days gestational age (GA). These data indicate that minimizing interfacial ST has little effect on CL in animals <125 days GA, thereby suggesting that morphologic and tissue properties predominate surface properties in limiting lung distensibility at this early age. By defining the stage of development in which pulmonary function is most effectively improved by reduced ST, these findings suggest age-related criteria regarding the benefit of exogenous surfactant replacement therapy. (Supported by NIH Grant HL/HD 30525).
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