Total cerebral ischemia: application of a new model system to studies of cerebral microcirculation.

Reduction in cerebral blood flow (CBF) following global ischemia has been implicated as a pathogenetic mechanism in progressive brain damage seen after restoration of effective cardiac action and cerebral perfusion pressure. There are serious limitations to many of the techniques for measuring regional cerebral blood flow, particularly during low flow states. In 15 dogs anesthetized with thiopental, 12 minutes of total cerebral ischemia (TCI) was produced using a double balloon occlusion technique. Total and regional cerebral blood flows were sequentially measured before and after balloon release by left ventricular injection of 15 mu microspheres labelled with 5 different radionuclides. Total CBF was reduced 53 +/- 5% (mean +/- SEM) from pre-ischemic values between 1 and 3 hours after "resuscitation" despite normal perfusion pressure and arterial blood gases. CBF remained slightly reduced (24 +/- 7%) at 6 hours post-ischemia. Thirty minutes after balloon release, grey matter flow was reduced 38 +/- 8% from control values while adjacent white matter flow was increased 21 +/- 10%. However, by 1 hour after ischemia, grey and white matter flows were both reduced (60 +/- 3%, 41 +/- 5% respectively). Similar differences in brain stem and cerebellar flow were also observed. The majority (71-86%) of the reduction in total CBF seen at one hour post-TCI is due to increased cerebrovascular resistance, with 14-29% of the decrease related to arteriovenous shunting.