Lung mechanics in growing guinea pigs

Lung mechanics were studied in four groups of guinea pigs: neonatal (1), prepubertal (II), postpubertal (III) and adult (IV). The animals were anesthetized and tracheotomized, and an esophageal catheter was inserted. Functional residual capacity (FRC) was measured by body plethysmography. After curarization, the lungs were inflated to a transpulmonary pressure of 30 cm H2O. The resulting change in volume was added to FRC to obtain the total lung capacity (TLC). Lung compliance (CL) normalized for dry lung weight (CL/LW) was calculated. An exponential function was fitted to the experimental P-V curve and the shape constant k was considered as an index of lung distensibility. During growth TCL (ml) increased with BW (g): TLC = 0.3 BW0.69 (r = 0.96). Two significantly different equations (P less than 0.001) were found between TLC (ml) and LW (g): between I and II, TLC = 32.4 LW1.24 (r = 0.88) and between III and IV, TLC = 22.9 LW0.53 (r = 0.73). An increase in lung distensibility as reflected by a significant increase in both CL/LW and the shape constant k was observed. In neonates and in prepubertal animals CL/LW was equal to 1.53 +/- 0.64 and to 2.38 +/- 0.51 ml/cm H2O/g (mean +/- 1 SD), respectively (P less than 0.01) and k to 0.146 +/- 0.026 and 0.219 +/- 0.035 cm H2O-1 (P less than 0.001). From prepuberty to adulthood no further significant changes were observed. These results showed that even in a species with an advanced maturation at birth, lung mechanics changed with growth.