Nine lungs containing atelectatic portions were obtained from subjects at autopsy. Several areas of each subject's lungs were extracted in saline solution and evaluated for surface activity by use of a modified Wilhelmy balance. Portions of both the atelectatic area and nonatelectatic area were included in the study. The lungs of thirteen patients who did not demonstrate any evidence of atelectasis at autopsy were studied by the same method as the controls.

The atelectatic lung sections demonstrated a decrease in surface activity as compared with the nonatelectatic lung sections of the same patients. The nonatelectatic portions were found to have normal marked surface activity similar in degree to that of the control lungs.

Experimental atelectasis in the dog, produced by mechanical means, showed abnormalities of surface forces similar to that seen in human atelectasis.

The interrelationships of the effects of surface forces in pulmonary dynamics are discussed, and some of the previous work in the field is briefly reviewed.

Adult human atelectasis is viewed as basically a mechanical phenomenon, with secondary deficiency of an “antiatelectasis” surfactant. This results in a vicious cycle of self-perpetuating alveolar collapse which may be difficult or impossible to reverse.