Effect of passive myocardium on the compliance of porcine coronary arteries

Abstract

. 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...

Flow restoration post revascularization predicted by stenosis indexes: sensitivity to hemodynamic variability

“…At ␤ ϭ 1, the parameters remain unchanged compared with their measured or predicted values (see APPENDIX A). High and low stiffness values (␤ ϭ 0.4 and ␤ ϭ 1.6, respectively; Table 1) reflect three standard deviations from the average of measured pressure-diameter curves (11). The scale factor ␤ was used due to lack of data regarding the changes in the material constitutive laws of both vessel wall and myocardium [see In situ Vessel Compliance in the supplement available with the online version of this article (the Online Supplement)] in disease states that affect coronary stiffness (e.g., diabetes, hypertension, atherosclerosis).…”

“…The choice of the vascular stiffness factor ␤ (Eq. 3) and its high and low values (␤ ϭ 0.4 and ␤ ϭ 1.6, respectively) are based on data (11), where the limits reflect 3 SDs from the measured pressure-diameter curves. A higher than unity ␤ value represents a lower than reference vessel stiffness, and vice versa.…”

“…For example, for a fixed value of stenosis geometry (%AS), Q s /Q n is expected to decrease under high aortic blood pressures. Since vascular compliance is nonlinear (5,11), high inlet pressure increases the microvascular lumen diameters and, therefore, decreases the resistance to a higher extent than that of the stenosed vessel (Fig. 1B).…”

“…Based on a similar qualitative two-resistor analysis, it was previously argued (39,41) that FFR exactly represents Q s /Q n only if the downstream microvessels are rigid. When the vessels are compliant (5,11), however, vascular distensibility, which is not measured in the clinic (14), causes FFR to underestimate Q s /Q n .…”

“…B: changes in blood perfusion pressure affecting Qs/Qn. Pressure diameter curve of the coronary microvasculature (sketched for simplicity as identical for both the stenosed artery and for its downstream microcirculation) is sigmoid in shape (1,11). Due to the difference in inlet pressure between the stenosed vessel and the microcirculation, an increase in inlet pressure inflates the stenosed artery diameter to a lower extent than the microvasculature diameter, thus increasing the relative resistance of Rs as compared with Rmicro,s (A).…”