Abstract
In the isolated, perfused dog's tongue, alterations of pulse pressure, at constant mean pressure, can produce parallel or oppositely directed changes in blood flow or can leave the flow unaffected. Parallel changes occur when the vascular bed is passively distensible; opposite changes occur when active contraction of smooth muscle overcomes the effects of passive distensibility, and no change is found when the two effects balance. The first is seen at mean pressures below 80 mm Hg or peak pressures above 155 to 165 mm Hg. The other reactions are produced in the mean pressure range in which autoregulatory reactions occur, viz. opposite changes when the pulse pressure is low and no change under conditions close to in situ mean and pulse pressure. Even when pulse pressure has no observable influence on flow, therefore, it modifies vascular tone. The active response of vascular smooth muscle to pulse pressure persists in part after the removal of the stimulus, opposing stress-relaxation of resistance vessels. Tissue weight changes reflect alterations in capacitance vessel volume which may vary in direction from the volume changes occurring in resistance vessels.
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