Comparisons of human populations for histologic features of atherosclerosis. A summary of questions and methods for geographic studies.

Aortas and coronary arteries from six populations were studied histologically. Two kinds of fibrous plaques could be defined morphometrically, a fibroplastic and an atheronecrotic kind. These two kinds of abnormality were quantitated, the percentage of the specimen affected by atheronecrosis being one quantity, and the average fibroplastic thickness of nonnecrotic intima being the other. These two quantities were found to be correlated with each other, showing that aortas or coronary arteries severely affected by one of these processes tended to be seriously affected also by the other process. This correlation persisted after age adjustment. The two processes, however, failed to parallel each other across population boundaries. Moreover, some of the subjects with coronary heart disease had excessive fibroplasia with minimal atheronecrosis, while others had excessive atheronecrosis with minimal fibroplasia, as if an excess of only one or the other can be fatal. A novel theory is proposed to explain these and other results. It is proposed that the arterial intima undergoes fibroplastic thickening under the time-dependent action of one set of hypothetical causes and that another set of hypothetical causes promotes the emergence of atheronecrosis in the most thickened and aged places. These two sets of causes appear to be independent of each other in their distribution among human populations.