Method for Estimating Respiratory Surface Area of Mammalian Lungs from Their Physical Characteristics.

Abstract

The method described for estimating the surface area of the lungs depends on experimental determination of the work done by excised animal lungs as they deflate. By comparing the deflation pressure-volume curves obtained in gas-free lungs filled with saline, and the curves obtained when the lungs are filled with air, an estimate may be made of the work done, or free energy recovered, by the surface. This change in free energy equals the change in surface area multiplied by the surface tension coefficient of the lung air-liquid interface. Since no direct measurements of the latter have been made, a value of 50 dynes/cm (human blood serum) has been assumed. By this method the lung surface area is estimated to be for the particular lungs studied: rat, 246 cm2 (lung volume 5 cc); cat, 2480 cm2 (lung volume 100 cc); and dog, 5340 cm2 (lung volume 400 cc). A similar estimate for human lungs, assuming pressure volume curves similar to those obtained in the dog, gives 5 m.2 (lung volume 3500 cc). The significance of the difference between this estimate and previous much larger estimates obtained from anatomic measurements is discussed.