Cardiac Function and Circulatory Control

Extract

[...] A second control of the magnitude of coronary blood flow under increased workload or demand conditions is nitric oxide, which is produced by coronary vascular endothelial cells and has a direct local vasodilating effect on coronary arteries and the more distal bed. Nitric oxide is a byproduct in a number of reactions that lead to an increase in the activity of nitric oxide synthase, an enzyme that produces nitric oxide from the amino acid L-arginine. In addition to adenosine and nitric oxide, other longer-acting coronary vasodilators such bradykinin, prostaglandins, and CO2 may have a direct effect in maintaining coronary artery blood flow. [...]

[...] These curves plot end-diastolic pressure versus either cardiac output or mean arterial pressure to provide an overall characterization of LV pump function in practical terms and to demonstrate the dependence of pump function on afterload resistance and contractility. DETERMINATION OF MYOCARDIAL OXYGEN CONSUMPTION AND ENERGY METABOLISM The heart relies almost exclusively on oxidation of fatty acids and glucose as an immediate source of energy. The heart normally extracts free fatty acids preferentially from the coronary perfusion for oxidative energy production. [...]

[...] The major element in this increase in cardiac function in normal young individuals is an augmentation in sympathetic drive to the heart and a withdrawal of vagal tone. The heart rate is increased, contractility is increased (resulting in increased ventricular ejection and an increase in the ventricular ejection fraction), ejection and filling rates are increased, aortic impedance is decreased, and systolic blood pressure is increased. In a young individual, withdrawal of vagal tone and greater sympathetic drive during maximal exercise increase the heart rate from 60 to 70 beats per minute at rest to 170 to 200 beats per minute. [...]

[...] Arenito CARDIAC FUNCTION AND CIRCULATORY CONTROL The heart is a muscular pump connected to the systemic and pulmonary vascular systems. Working together, the job of the heart and vasculature is to maintain adequate circulation of blood to the organs at rest and during periods of exercise. To understand perturbations that cause symptoms and disease, it is first necessary to understand the normal anatomy and physiology of the heart, its interaction with the vascular system, and its regulation by the autonomic nervous system. [...]

[...] The physiologic roles of these structural proteins in maintaining normal contractile function has become clear recently by the use of murine models in which these genes are under-expressed and by the identification of specific inherited human cardiomyopathies that are due to point mutations of the genes encoding each of these proteins. EXCITATION-CONTRACTION COUPLING The sequence of events that lead to myocardial contraction is triggered by electrical depolarization of the cell; electrical depolarization increases the probability of sarcolemmal calcium channel opening, which in turn results in calcium influx into the cell. [...]