Pharmacology of the human isolated coronary artery : effects of 5-HT, platelets and peptides

Ischemia of the heat1 is characterized by a deprivation of oxygen combined with inadequate removal of metabolites. Myocardial ischemia may be due to an increased oxygen requirement, or to a decreased supply of oxygen to the myocardium. The myocardial consumption of oxygen is determined by myocardial wall tension, contractility, and heart rate. Processes in the myocardium, not directly related to contractile function, require only 20% of the total oxygen consumption, while the amount needed for electrical depolarization is only approximately 1% of total oxygen consumption. The myocardial oxygen demand is increased by physical exercise or by mental stress. In healthy individuals, an increased oxygen demand is likely to be compensated via an increase of coronary blood flow. An increased oxygen demand may result in cardiac ischemia only in patients with existing coronary artery impairment. Myocardial oxygen supply is dependent mainly on coronaty blood supply. The coronary at1ery diameter declines passively when the lumen is narrowed by intimal hyperplasia or atherosclerosis, or by the formation of a secondaty thrombus in a susceptible coronary at1ery segment. In addition to that, the mechanisms regulating coronaty at1ery diameter may be altered in such a way that contraction of the coronaty artery smooth muscle contributes actively to the already present luminal naHowing. In a small group of patients, vasoconstriction may be solely responsible for myocardial ischemia. The coronary at1elY mechanisms underlying disturbed coronary m1elY flow regulation are outlined in chapter 2. For now it must be emphasized that the present chapter on clinical aspects of ischemic heart disease is bound to be incomplete when considering the voluminous detailed text books on this topic. However, this chapter should be read as a prologue, setting the stage for hypotheses and experimental investigations, which are only a modest reflection of clinical reality described here.

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