Thresholds of cerebral ischemia

  • J. Astrup
  • L. Symon
  • N. M. Branston
  • N. A. Lassen


Function and metabolism of the brain are critically dependent on a sufficient oxygen supply. In man, cerebral blood flow (CBF) is about 50 ml/100 gm/min and the arteriovenous differences for oxygen (AVDO2) about 7 vol%, giving a cerebral oxygen consumption (CMRO2) of about 3.5 ml/100 gm/min. If CBF is moderately reduced as in the state of oligemia, the flow reduction will be balanced by a rise in AVDO2 so that a normal oxygen supply is maintained. A further reduction in CBF may still be balanced while AVDO2 approximates the arterial oxygen content, and at a normal metabolic rate, flow reductions down to about 20 ml/100 gm/min may be tolerated. This flow level is critical in the sense that below this level oxygen is insufficiently supplied, and since the AVDO2 is maximal, the CMR02 is given by the blood flow (ischemia) (Fig. l).Thus in the ischemic flow ranges a further reduction in flow enforces a proportional reduction in oxygen consumption. Experimentally this principle allows a determination of the critical low levels of local oxygen supply, given as local blood flow (CBF), leading to failure of fundamental brain tissue functions.


Cerebral Blood Flow Middle Cerebral Artery Occlusion Mean Arterial Blood Pressure Local Blood Flow Pump Failure 
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Copyright information

© Springer-Verlag New York Inc. 1977

Authors and Affiliations

  • J. Astrup
  • L. Symon
  • N. M. Branston
  • N. A. Lassen

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