ABSTRACT
The control of blood flow is a process involving neural and metabolic mechanisms. It is widely accepted that neural processes accomplish short term control of blood precapillary flow resistance such that blood pressure and flow are regulated. While metabolic processes dominate in the long term [Guyton, 1963] they ultimately determine the regulated blood flow levels in the various tissues in accordance with metabolic demands. This is achieved locally by the precapillary sphincters that adjust the duration and number of capillaries open and which, in turn, determine the value of the peripheral resistance, Rs. Another theory suggests that it is the mechanical effect of pressure and flow that stimulates vascular smooth muscle to react. However experiments have shown that tissue blood flow and systemic circulation is directly related to its metabolic demand [Berne and Levy, 1977]. Experimental observations of low frequency flow oscillations can be found in studies of a single vascular bed as well as the entire systemic circulation. This differs from mechanical stimulation where researchers have employed a drug response. For example,
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Kenner and Ono [1972] have observed what they termed flow autooscillations in the carotid and femoral arteries of the dog, following intravenous administration of acetylcholine. Similar oscillations in flow have been observed following the infusion of adenosine into the coronary circulation [Wong and Klassen, 1991]. These researchers attributed this response to opposing vasodilator and vasoconstrictor processes.
