• The study of strips of cardiac muscle has provided much valuable information regarding those factors which determine the force generated during contraction. Interrelationships between force, velocity of shortening, di&stolic stretch, duration of systole, and contractility have been delineated. "5 These findings are not, however, directly and siiiaply applicable to the physiology of the intact heart because the force generated by the myocardium and the corresponding pressure are by no means synonymous. In order to relate the physiology of muscle strips to that of the intact ventricle, the quantitative relation between force in the wall of the ventricle and pressure in the cavity must be known.The importance of such considerations in cardiac physiology has long been recognized. Burton, 10 and Linzbaeh. 11 More recently, Levine and Wagman have discussed the possible influence of the size and shape of the heart on myocardial oxygen consumption, emphasizing the important distinction between the pressure developed by the ventricle and the tension exerted by the fibers. Supported by American Heart Association grant. Work was done during Dr. Hefner's tenure as an Established Investigator of the American Heart Association and Dr. Sheffield's tenure of a TJ. S. Public Health Service Research Fellowship (HF-9775).Received for publication March 30, 1962. lows: Gravitational effects are ignored since they are unimportant in this situation. Consider a static left ventricle of any shape and size containing blood under a given pressure, as in figure 1. Now visualize an imaginary plane through this ventricle as shown in the figure. This imaginary plane divides the ventricle into two parts and passes through a rim of myocardium and a cross-sectional area of the cavity. From elementary hydrostatics it is known that the pressure of the blood in the cavity creates a force in a direction perpendicular to the imaginary plane exactly equal to the product of the pressure (which is force per unit area) times that cross-sectional area of the cavity included in the imaginary plane. The shape of this cross-sectional area of the cavity in our imaginary plane is immaterial, and the size and shape of the rest of the ventricle are also completely without effect on this relation. Since we began by postulating a static ventricle, Newton's laws of motion require that the force mentioned above tending to separate the two parts of the ventricle on each side of the plane be exactly balanced by an equal and opposite force. This equal and opposite force must exist in the rim of myocardium included in the imaginary plane, shown by the stippled area in figure 1. Note that this force exists in the rim of myocardium determined by the imaginary plane, its direction is perpendicular to the plane, and its magnitude is determined only by the pressure and cross-sectional area of the cavity and is independent of the thickness of the wall, the shape or cross-sectional area of the rim, the size or shape of the remainder of the ventricle, the distribution of f...

The technique of intraoperative vessel dilation is sometimes used to facilitate microvascular anastomosis and prevent vasospasm. Although this technique is not new, its application has not gained widespread acceptance mainly due to concerns raised about potential damage to the vessels acutely and during the postoperative period, leading to decreased vessel patency. The goal of this study was to determine the acute and delayed histologic effects of hydrostatic dilation on rat femoral arteries and to compare the response of dilated arteries to vasodilating and vasoconstricting agents. The femoral arteries in 22 rats were used in 2 experimental groups; 9 in the acute group and 13 in the delayed group. Six animals served as controls. After the vessels were exposed, a microcatheter was inserted into a segment of the vessel that had been isolated between 2 vessel clamps. Saline was infused into the artery until a pressure of 300 mm Hg was attained and then maintained for 60 seconds. In the acute group, the animals were euthanized at the end of the dilation, while in the delayed group the animals were euthanized 24 hours later. Hydrostatic dilation of rat femoral arteries was found to increased vessel diameter acutely, with subsequent relief and prevention of vasospasm during the ensuing 24 hours. Histologically, there was no increased damage of the vessel walls in the dilated vessels compared with control vessels. Based on the data reported in this study, hydrostatic dilation of rat microvessels appears to be safe and may be used to technically facilitate microanastomoses and decrease vasospasm.