Effects of hypoxia on coronary microcirculation during postnatal development

Abstract

Coronary microcirculation, functioning as an exchange system for solutes (e.g., oxygen, carbon dioxide, substrates, metabolites) between blood and tissues in the myocardium, is anatomically based on the microvasculature including arterioles, capillaries, and venules. Arterioles (30–300 μm in diameter), surrounded by one or two layers of smooth muscle cells, regulate their vascular tone by constriction or dilatation. Capillaries (10 μm or smaller in diameter), not accompanied by smooth muscle cells but by occasional pericytes, serve as the main functional elements in the solute exchange by diffusion. Small venules (10–50 μm in diameter) are accompanied by pericytes and larger venules (up to 200 μm in diameter) by one or two layers of thin smooth muscle cells. Resistance vessels of coronary vasculature (i.e., small arteries and arterioles) play important roles in coronary fl ow regulation and turgor effect (e.g., myocardial stiffness). Myocardial blood fl ow is known to be determined by myocardial oxygen demand (heart rate, contractility, ventricular work), oxygen-carrying capacity of arterial blood (hemoglobin, arterial blood saturation of hemoglobin), perfusion pressure, extravascular compressive force, and coronary vascular resistance (smooth muscle tone). Also, myocardial blood fl ow is infl uenced by structural alteration of coronary vasculature, for example, vascular growth during postnatal development and vascular hypertrophy during ventricuReceived: 17 September 2010 © The Japanese Association for Thoracic Surgery 2011