Editorial

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Abstract
Micropuncture data suggest that pial arterioles contribute only slightly less than parenchymal cerebral arterioles to total resting cerebrovascular resistance. Care must be taken in interpreting the micropuncture data, or the contribution of pial arterioles to cerebrovascular resistance may be erroneously underestimated. These considerations and the fact that pial arterioles have been shown to be highly reactive to a variety of physiological and abnormal stimuli suggest strongly that changes in pial arteriolar diameter should contribute importantly to control of flow to the underlying brain. In fact, parallels between changes in pial vascular diameter and regional blood flow have been observed. Moreover, since the responses of pial vessels to important vasoactive stimuli are qualitatively similar to those of the cerebral circulation as a whole when the latter are inferred from measurements of flow, the directly observable pial vessels may provide a model for the responses of the unseen parenchymal segments of the cerebrovascular bed. Such a model would be essential to our understanding of the control of cerebral blood flow, even if pial vessels themselves did not participate in the control of flow. Thus there are multiple reasons for continued study of the pial vessels, particularly with modern techniques developed for microcirculatory investigations.