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Journal of Experimental Biology 76,149-165 (1978)
Published by Company of Biologists 1978

Static Pressure-Volume Curves for the Lung of the Frog (Rana Pipiens)

G. M. HUGHES ¹ and G. A. VERGARA ²

¹ Research Unit for Comparative Animal Respiration, University of Bristol, Woodland Road, Bristol BS8 1UG
² Research Unit for Comparative Animal Respiration, University of Bristol, Woodland Road, Bristol BS8 1UG; Department of Pharmacology, The Medical School, University of Bristol, Bristol BS8 1TD

1. Static pressure/volume curves have been determined for isolated frog lungs inflated with either air or saline. In both cases a hysteresis was present: the pressure required to produce unit change of volume being greater during inflation than deflation.

2. The pressure necessary for a given volume change was less for the saline-filled than the air-filled lungs. The difference between these curves is due to the surface tension at the air/lung interface.

3. Pressure/volume curves for air-filled lungs in situ were similar to curves for isolated lungs. However, a greater pressure was required for the same volume change during both inflation and deflation.

4. Compliance was calculated from different parts of air pressure/volume curves and gave values greater than those obtained using similar calculations for higher vertebrates.

5. These observations support other evidence for the presence of a surfactant in the lung lining of frogs in spite of the relatively large diameter of their ‘alveoli.’ The precise role of such a lining is uncertain and it is concluded that similar forces may be involved during the inflation and deflation of lungs of frogs and higher vertebrates in spite of differences in gross morphology.