Discussion of presentation by A.G.B. Kovach
Autoregulatory mechanisms tend to maintain cerebral blood flow during hemorrhagic shock. Cerebral blood flow is not significantly altered until the perfusion pressure falls below 70 mm Hg during hemorrhage. The mechanism of cerebral autoregulation during hemorrhagic hypotension is unclear, although both metabolic and myogenic components appear to mediate cerebral autoregulation.1 Investigations by Dr. Kovach and others have observed that although total cerebral blood flow may only be moderately decreased in hemorrhage, areas of severe ischemia may be adjacent to more normally perfused tissue.2 Such studies define the need for measuring regional cerebral blood flows as well as total cerebral blood flow in hemorrhagic shock. Using hydrogen washout and thermodilution techniques, Kovach et al. 2,3 demonstrated a 60% reduction in hypothalamic flow after hemorrhage to 35 mm Hg. The authors concluded that autoregulation in the hypothalamus during hemorrhage differed from other regions of the brain. In contrast, Slater et al. 4 using radioactive microspheres reported similar patterns of blood flow alterations in cerebellum, gray matter, white matter, and the hypothalamus of conscious dogs subjected to hemorrhage.
KeywordsCerebral Blood Flow Hemorrhagic Shock Regional Cerebral Blood Flow Cerebral Autoregulation Cerebral Vasculature
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