Mechanical Properties and Function of Pericardium E - 23 - 638

This paper considers the effects of the pericardium on a mechanical model of the heart. The model, based on the theory of large elastic deformation, makes use of experimental data for the pericardium reported herein. INTRODUCTION The pericardium is the tough fibrous sac enclosing the lean of most vertebrates, including man. It serves to .told the heart in a fixed position and to isolate and xotect it from other thoracic structures. The periAirdial sac contains fluid (pericardial fluid similar to )lood serum) which serves to lubricate the outer .urfaces of the heart. Anatomically, the pericardium consists of a thin nembrane covering the heart (the visceral pericariium), surrounded by a thick fibrous sac (the parietal cricardi um). The sac is generally attached to the great 'essels, the sternum, the vertebral column and the .iaphragm (Holt, 1970). Histologically, the parietal pericardium consists of lterlaced collagen and elastin fibers, relative cornosition being a function of age in man (Holt, 1970). The pericardium is not essential to life and its =oval does not result in any obvious disability, tough there may be long term effects such as cardiac ypertropy (Fowler, 1970). Its constrictive function, owever, can have fatal consequences in pathological tuations, such as cardiac tamponade (impairment of iastolic filling of the heart caused by an unchecked .se in intrapericardial pressure) and constrictive periirditis (inflammation of the pericardium, resulting in Astriction of the heart). From this discussion, it appears that the mechanical sponse of the pericardium can have important effects n cardiac function. Its restriction of free myocardial i ;pansion can effect myocardial wall stresses. Elevated ress may be responsible for ischemia of the ventriliar wall (Mirshy, 1973). This may be important in .ses of pericarditis associated with myocardial farction. Attempts to model the heart (Demiray, 1976; lirsky, 1973; Voukydis, 1972a, b, c; Janz et al., 1972; ould et al., 1972; Ghista et al., 1969; Mirsky, 1969; hista et al., 1968; Wong et al., 1968) have not eluded the pericardium. These models may be critized in many ways. Nevertheless, much current search in biomechanics has as its goal a model of • Received 10 October 1978. cardiac function in health and disease. Such a model must include the effects of the pericardium. Very little is known about the mechanical response of the pericardium. Only three papers (Rabkin et al., 1974, 1975; Hildebrandt et al., 1969) could be found from 1940. These papers are based on a small number of experiments, six in the case of Rabkin et al. (1974, 1975) and an unspecified number in the case of Hildebrandt et al. (1969). In this paper, the one-dimensional elastic response of dog pericardium was determined in 20 experiments. The results were analyzed statistically and used to model the effect of the pericardium on the heart.