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همودایلوشن
A reduction in arterial oxygen content, and therefore cerebral oxygen delivery, can be achieved either by a reduction in Pao2 (hypoxemic hypoxia) or by a reduction in hemoglobin concentration (anemia, hemodilution).
Both hemodilution and hypoxemic hypoxia lead to cerebral vasodilation and an increase in CBF.
Of the two variables, however, hypox- emic hypoxia is a far more potent variable in CBF aug- mentation than hemodilution.
Cerebral oxygen delivery is better maintained during hypoxia when arterial content is equivalently reduced by hypoxia or hemodilution (see Fig. 11.7C).
However, this may result not only from a reduction in viscosity but also as a compensa- tory response to reduced oxygen delivery.15 Although arte- rial oxygen content can be reduced by both hypoxia and by hemodilution, the increase in CBF that accompanies hypoxia is of a greater magnitude than that by hemodilu- tion induced reduction in oxygen delivery.11 The effect of a reduction in viscosity on CBF is more important with focal cerebral ischemia, a condition in which vasodilation in response to impaired oxygen delivery is probably already maximal.
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