Chapter 6: Discussion and Conclusions

Choice of experimental animal. As mentioned in the review of the literature animals previously used in experimental investigations have been dogs, lambs, guinea-pigs, mice and rabbits. Dogs and lambs are less suitable as they are expensive and demand too much laboratory equipment and lodging facilities. It is difficult to study lung atelectases in guinea-pigs, as they normally have parts of their lungs disconnected from the respiration and thus atelectases (COHRS, JAFFE & MEESSEN 1958). The lungs of mice are small and do not have any advantages over rabbits. The lungs of adult rabbits are of a size similar to those of prematures and the anatomy is fairly similar. SHANKLIN & BERMAN (1964) formulated three demands which should be complied with in an experimental investigation of HMD: 1) It should manifest a syndrome similar to that of the human. 2) It should produce a lesion equivalent to the human lesion, after taking into account the differences between the tissues of the species. 3) It should be reproducible in sufficient quantity to study the variability "during set and changing conditions". The method employed by BERFENSTAM et colI. (1954 and 1958) using oxygen treatment of adult rabbits, seems to meet these demands and this method was therefore used in the present investigation. Pressure-volume measurements. So far no method has been presented allowing direct measurement of surface tension in the alveolar wall. PATTLE (1958) described an indirect method in which he studied the contraction of bubbles derived after sqeezing cut surface of lungs under water. CLEMENTS (1957) and AVERY & MEAD (1959) used another method, measuring the surface tension in a trough with filtered fluid in which a lung had been finely dispersed. With both methods values of the surface tension can be obtained but in both several artificial factors are included.