. Effect of passive myocardium on the compliance of porcine coronary arteries. Am J Physiol Heart Circ Physiol 285: H653-H660, 2003; 10.1152/ajpheart.00090.2003.-The objective of this study was to determine the effect of passive myocardium on the coronary arteries under distension and compression. To simulate distension and compression, we placed a diastolicarrested heart in a Lucite box, where both the intravascular pressure and external (box) pressure were varied independently and expressed as a pressure difference (⌬P ϭ intravascular pressure Ϫ box pressure). The ⌬P-cross-sectional area relationship of the first several generations of porcine coronary arteries and the ⌬P-volume relationship of the coronary arterial tree (vessels Ͼ0.5 mm in diameter) were determined using a video densitometric technique in the range of ϩ150 to Ϫ150 mmHg. The vasodilated left anterior descending (LAD) coronary artery of six KCl-arrested hearts were perfused with iodine and 3% Cab-O-Sil. The intravascular pressure was varied in a triangular pattern, whereas the absolute cross-sectional area of each vessel and the total arterial volume were calculated using video densitometry under different box pressures (0, 50, 100, and 150 mmHg). In the range of positive ⌬P, we found that the compliance of the proximal LAD artery in situ (4.85 Ϯ 3.8 ϫ 10 Ϫ3 mm 2 /mmHg) is smaller than that of the same artery in vitro (16.5 Ϯ 6 ϫ 10 Ϫ3 mm 2 /mmHg; P ϭ 0.009). Hence, the myocardium restricts the compliance of the epicardial artery under distension. In the negative ⌬P range, the LAD artery does not collapse, whereas the same vessel readily collapses when tested in vitro. Hence, we conclude that myocardial tethering prevents collapse of large blood vessel under compression. digital subtraction angiography; video densitometry; mechanical properties; mechanics; tethering THE MECHANICAL PROPERTIES of coronary vessels play an essential role in understanding the physiological functions of the vessels, and as a result, have direct clinical implications in the diagnosis and treatment of patients with coronary artery disease and atherosclerosis (22,27). Anatomically, the coronary arteries originate from the aortic ostia, just above the aortic valve, and continue along the surface of the heart as they penetrate into the myocardium where they deliver blood throughout the thickness of the heart (16). The posterior aspect of the proximal coronary artery is partially embedded into the myocardium, whereas the anterior portion is surrounded by the serous visceral pericardium. As the coronary artery descends along the ventricle, it becomes fully embedded into the myocardium.A number of previous studies (1, 2, 9, 10, 13, 15, 21) have examined the mechanical properties of coronary arteries under in vitro conditions; i.e., after dissection of the vessels from the myocardium. For example, Patel and Janicki (21) determined the in vitro pressure-diameter relationship for isolated segments of the dog's left circumflex. The pressure-diameter relationship of excised coro...
The pressure-induced remodeling of coronary veins is important in coronary venous retroperfusion. Our hypothesis is that the response of the large coronary veins to pressure overload will depend on the degree of myocardial support. Eleven normal Yorkshire swine from either sex, weighing 31-39 kg, were studied. Five pigs underwent ligation of the left anterior descending (LAD) vein, and six served as sham-operated controls. The ligation of the coronary vein caused an increase in pressure intermediate to arterial and venous values. After 2 wk of ligation, the animals were euthanized and the coronary vessels were perfusion-fixed with glutaraldehyde. The LAD vein was sectioned, and detailed morphometric measurements were made along its length from the point of ligation near the base down to the apex of the heart. The structural remodeling of the vein was circumferentially nonuniform because the vein is partially embedded in the myocardium; it was also axially nonuniform because it is tethered to the myocardium to different degrees along its axial length. The wall area was significantly larger in the experimental group, whereas luminal area in the proximal LAD vein was significantly smaller in the same group compared with sham-operated controls. The wall thickness-to-radius ratio was also significantly larger in the experimental group in proportion to the increase in pressure. The major conclusion of this study is that the response of the vein depends on the local wall stress, which is, in part, determined by the surrounding tissue. Furthermore, the geometric remodeling of the coronary vein restores the circumferential stress to the homeostatic value.
Biliary duct obstruction is an important clinical condition that stems from cholelithiasis, the neoplasm in the wall or, most commonly, gallbladder stones. The objective of this study is to understand the structural and mechanical remodeling of the common bile duct (CBD) postobstruction. Porcine CBD was ligated near the duodenum that increased the duct's pressure from 6.4 to 18.3 cmH(2)O in the first 12 h and to 30.7 cmH(2)O after 32 days. The remodeling process was studied after 3 h, 12 h, 2 days, 8 days, and 32 days (n = 5 in each group) after obstruction. One additional animal in each group was sham operated. At each scheduled time, the time course of change of morphometry (diameter, length, wall thickness, etc.) and mechanical properties (stress, strain, etc.) was documented. It was found that the diameter increased by about threefold and the wall thickness of the CBD doubled in the 32-day group compared with the sham group (P < 0.001). The stress and strain increased initially with increase in pressure but recovered to near the control values by day 32 due to the structural and mechanical adaptations. Hence, the net effect of the structural and mechanical remodeling is to restore the stress and strain to their homeostatic values. Furthermore, the strain recovers more rapidly and more completely than stress. Finally, the remodeling data were expressed mathematically in terms of indicial response functions (IRF), i.e., change of a particular feature of a CBD in response to a unit step change of the pressure. The IRF approach provides a quantitative description of the remodeling process in the CBD.
Cross-sectional area measurement using videodensitometry coronary arteriography is a function of the out-of-plane angle of the vessel segment with respect to the face of the image intensifier. Therefore, absolute cross-sectional area measurement using videodensitometry requires correction for the out-of-plane angle. In this study, a simple technique to measure the out-of-plane angle of a vessel segment using images from two different projections is presented. The technique was tested using vessel phantoms imaged at different out-of-plane angles. A vessel segment with an out-of-plane angle of less than 20 degrees introduces less than 5% error in the cross-sectional area measurements. However, an out-of-plane angle of 60 degrees can introduce more than 90% error. The results of the measurements show that correction for the out-of-plane angle reduces the error in cross-sectional area measurement to less that 5%. The correction for the out-of-plane angle makes it possible to measure the absolute cross-sectional area using videodensitometery, which can be used to assess a diseased vessel segment with any complex geometry.
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