Abstract
We determined whether cerebral blood flow autoregulation is altered during hypoxic hypoxia in 10 anesthetized, ventilated dogs. Cerebral blood flow (CBF) was measured globally and regionally (rCBF) via the cerebral venous outflow and radiolabelled microsphere techniques. Mean arterial blood pressure was lowered from control (120 mmHg) in decrements of 10 mmHg. Each level of pressure was maintained for 5 min. Cisterna magna pressure and cerebral venous outflow pressure were maintained at 0 mmHg. PaCO2 and pH were maintained constant throughout the experiment. The lower limit of autoregulation during normoxia (PaO2=88 torr) was approximately 58 mmHg. At that point, CBF began to decrease from control levels of 25 ml/min down to 10 ml/min at 30 mmHg. Cerebral vascular resistance (CVR) decreased as cerebral perfusion pressure (CPP) decreased, but continued to decrease beyond the lower limit of autoregulation. With further reduction in CPP (to 30 mmHg), CVR sharply increased. With hypoxia (PaO2=25 torr), CBF increased to 70 ml/min, but the lower limit of autoregulation was only slightly altered (63 mmHg). Microsphere measurements of rCBF confirmed these results. We conclude that cerebral autoregulation is intact during severe hypoxia. These data demonstrate that the classically defined lower limit of autoregulation is not the point of maximal cerebral vasodilation. Supported by NS-20020.
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Traystman, R., Wilson, D., Koehler, R. et al. 220 HYPOTENSIVE AUTOREGULATION OF CEREBRAL BLOOD FLOW DURING HYPOXIA. Pediatr Res 19, 147 (1985). https://doi.org/10.1203/00006450-198504000-00250
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DOI: https://doi.org/10.1203/00006450-198504000-00250