Saline extracts of minced normal canine lungs varying in sample weight from 0.25 to 3.0 gm. were prepared and the areas of hysteresis loops inscribed by the pneumatic surfactometer determined by planimeter. Using the variables of sample sizes and cycle times of 1.5, 3, 6, and 9 minutes a multiple linear regression analysis was performed to generate a three dimensional fitted polynomial surface. Maximum loop area differences between samples sizes were observed at a cycle time of 1.5 minutes and sample size of 2.0 gm. Sequential dilutions of a 2.0-gm. sample cycled at two minutes showed linear correlation with decreasing areas of the hysteresis loops. Superimposition of the dilution points on the computed polynomial surface showed good correlation for concentrations other than 50%. Quantitation of surface activity on the basis of hysteresis loop area is feasible as a rapid and convenient technic for study of whole lung samples.
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