Pathophysiology of human cerebral ischemia: studies with positron tomography and /sup 15/oxygen
Patients with acute occlusion of a major cerebral artery sequentially call on a hemodynamic reserve quantifiable in terms of rCBF and rCBV and then an oxygen carriage reserve quantifiable in terms of rOER. If both are exhausted, ischemia supervenes and rCMRO/sub 2/ becomes linearly related to rCBF. Depending on the degree and duration of fall in rCMRO/sub 2/, variable degrees of infarction occur. Infarction occurs more rapidly in subcortical than cortical tissue. The phase of maximal rOER is short, and rapid evolution by either reflow or delayed cell death results in an invariable decline of rOER to subnormal levels in the face of a low rCMRO/sub 2/. This combination is characteristic of infarcted tissue. In some instances, partial infarction with a low perfusion reserve is observed with low rCMRO/sub 2/, high though submaximal rOER, and no increase in rCMRO/sub 2/ if rCBF is raised. This is a precarious situation predisposing to extension of infarction and suggests blood pressure should not be lowered acutely after a stroke unless the latter is caused by hypertensive encephalopathy. This pattern, however, is rare, short-lived, and usually followed by late reflow or further infarction as a further fall in rCPP occurs, transiently or permanently. Tests of rCPP and the two homeostatic mechanisms involved in maintaining rCMRO/sub 2/ using non-PET techniques suggest themselves and might form an objective basis for selection of patients for prophylactic revascularization or bypass operations. PET techniques are now becoming available for assessing the blood-brain barrier, tissue pH, and amino acid metabolism, all of which may have relevance to the further understanding of the evolution of infarcts.
- Research Organization:
- National Hospital for Nervous Diseases, London, England
- OSTI ID:
- 5028132
- Journal Information:
- Res. Publ. Assoc. Res. Nerv. Ment. Dis.; (United States), Journal Name: Res. Publ. Assoc. Res. Nerv. Ment. Dis.; (United States)
- Country of Publication:
- United States
- Language:
- English
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