THE INFLUENCE OF MECHANICAL FACTORS ON THE STRUCTURE OF THE PERIPHERAL ARTERIES AND THE LOCALIZATION OF ATHEROSCLEROSIS BY

In a study of the peripheral arteries a period of development lasting until the end of the second decade of life is described. During this time there is evidence of medial hypertrophy and a continued formation of the longitudinal muscular cushions described in the foetus. Bands of longitudinal muscle also appear in the media of certain vessels. It is considered that the findings confirm the functional significance of foetal cushions and further suggest their relationship to the stresses of pulsation. In the later decades the tendency of atherosclerotic plaques to develop at the site of cushions is believed to reflect the importance of mechanical factors in the localization of this disease. The finding of cushion-like thickenings com-posed of longitudinal muscle and elastic tissue in the walls of the popliteal and lower end of the brachial artery of the foetus was reported in a previous communication (Robertson, 1960). These occurred mainly at the mouths of branches and were found to be similar to intimal thicken-ings previously described in the coronary arteries of the foetus (Dock, 1946; Minkowski, 1947). It was believed that they represented the physio-logical reaction of the vessel wall to a pulsatile longitudinal stress, and their presence in only certain of the muscular arteries was attributed to the unrestricted movements of these vessels during pulsation. Mechanical stresses have been considered by many to be important in the genesis of athero-sclerosis, and those due to pulsation have been most often incriminated (Duguid, 1926; Moschcowitz, 1942). For this reason, it was thought that it would be of interest to study the subsequent development of foetal cushions in the peripheral arteries of the adult and to determine their relationship to atherosclerosis. During the course of this work it was observed that many of the changes which occur focally in the arteries of the foetus are continued in a more exaggerated form into early adult life. It is believed that this reflects a continuous process of arterial develop-ment which is the physiological response of the vessel to certain well-defined haemodynamic stresses