Evaluation of Myocardial Perfusion in Man [antikvár]

Vigorito C, Rengo F (eds): Evaluation of Myocardial Perfusion in Man. Bibl Cardiol. Basel, Karger, 1989, No 44, pp 1-4 Role of Neuropeptides on Conductive and Resistive Coronary Vessels in Man Attilio Maseri Cardiovascular Research Unit, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK In normal conditions coronary blood flow is finely controlled to adapt promptly and adequately to the changes of myocardial metabolic requirements over a very wide range. This regulation takes place at the level of resistive vessels and is achieved by the interaction of local metabolic control, which swiftly adapts supply to demand, and by a myogenic control which is responsible for setting a high basal vasomotor tone and for maintaining vessel caliber constant when intravascular pressure varies. These two basic mechanisms, which operate also in denervated hearts, are modulated by neurohumoral stimuli. Neurohumoral modulation can produce both vasoconstriction and vasodilatation, reducing or increasing coronary flow relative to the value set by the metabolic control. These variations of flow must be associated with proportional changes of myocardial oxygen extraction (hence of coronary sinus oxygen saturation) when myocardial oxygen consumption remains constant. The mechanisms that control vasomotor tone in the coronary circulation are different in resistive and conduit vessels. In resistive vessels schematically we can identify three major components: (1) a myogenic component intrinsic to vascular smooth muscle which is responsible for maintaining a high resting tone; (2) a metabolic component which reduces the basal tone of resistive coronary vessels in proportion to the increase of myocardial Oj requirements, and (3) a neurohumoral component that can modulate myogenic and metabolic control by exerting dilator or constrictor actions. In conductive vessels, which are extramyocardial, tone is only controlled by myogenic and neurohumoral components.