Regional myocardial perfusion and wall thickening during ischemia in conscious dogs

Abstract

We examined in conscious dogs the effects of reductions in myocardial blood flow (MBF) in three different layers across the wall on regional myocardial contractile function in the ischemic zone, measured as systolic wall thickening (%WT). In 16 dogs, %WT was measured with sonomicrometry and MBF was determined with microspheres (10- to 12-microns diam) during coronary stenosis of the left circumflex coronary artery. The stenoses were categorized into six groups by the effect on %WT (each group representing progressive 20% decrements in %WT from control), and individual and pooled regression analyses were performed on data from six of the dogs having multiple data points to evaluate the shape (linear or curvilinear) of the relationships between MBF and changes in %WT. Transmural contractile function was highly sensitive to acute reductions in MBF, especially reductions in the subendocardium. The shape of the normalized subendocardial MBF-%WT relation was mildly curvilinear by regression analysis (quadratic equation, gamma = -0.75x2 + 2.15x -0.39, r2 = 0.92). Likewise, mean transmural and midmyocardial MBF correlated well and closely with changes in %WT. Subepicardial MBF, however, correlated poorly with changes in %WT, there being no change in subepicardial MBF until %WT had been reduced more than 50%.

Comparative effects of pacing-induced and flow-limited ischemia on left ventricular function.

“…Alterations in myocardial blood flow and systolic function observed in this study during demand ischemia were quantitatively less severe than BCO of comparable duration (3 minutes), similar to results from previous studies. The changes in both systolic and diastolic function observed during postpacing ischemia, however, were qualitatively similar to changes in function obtained during the early phase of flow-limiting ischemia (30 In this study, various degrees of contractile impairment were consistently observed during pacinginduced ischemia. Additionally, we did not observe dissociation of systolic and diastolic function during postpacing ischemia in any of the dogs studied.…”

Influence of Acute Renal Failure on Coronary Vasoregulation in Dogs

“…A similar approach was used to assess differences between vascular responses to adenosine, acetylcholine, bradykinin, and l-arginine. End-diastolic wall thickness (EDT; onset of positive dP/dt) and end-systolic wall thickness (EST; approximately 20 ms before peak negative dP/dt) also were evaluated (26); because contractile function varies with the respiratory cycle, all measurements were determined at end expiration. Percentage of systolic myocardial wall thickening (SWT) was calculated using the equation SWT (%) ϭ EST Ϫ EDT/EDT ϫ 100.…”

Myocardial Hibernation

“…5 Characterization of the physiology of hibernation shows that perfusion and contractile function seem to be matched, 6 and that myocardial substrate utilization and energy metabolism tend to recover over hours despite active ischemia. 7 Reduced calcium responsiveness 8 and alterations in adrenergic receptor density 9 have been proposed as mechanisms for the decreased contractility.…”