THE INFLUENCE OF TOTAL-BODY HYPERTHERMIA ON BRAIN HEMODYNAMICS AND BLOOD-BRAIN-BARRIER IN DOGS

This study was designed to examine the influence of total body hyperth ermia (TBHT) using an extracorporeal circuit with a heat exchanger on the cerebral blood flow (CBF), intracranial pressure (ICP), brain tiss ue pH, cerebral autoregulation and blood-brain barrier (BBB) permeabil ity in dogs. The rectal temperature of the dow was raised to 41.5 degr ees C, maintained at 41.5-42.0 degrees C for 2 hours (HT period) and t hen reduced to normothermia by cooling. Regional CBF was measured by t he hydrogen clearance method before heating, during the HT period and after cooling. ICP and brain tissue pH were monitored during the TBHT treatment. Autoregulation of the CBF during the HT period was assessed by measuring the regional CBF and the ICP in a state of induced hypo- or hypertension. The influence of TBHT on BBB permeability was examin ed using an immunohistochemical technique. The regional CBF increased from 38.1 +/- 6.5 (mean+/-SD) to 49.1 +/- 9.8 ml/100 g/min and the ICP from 10.3 +/- 4.2 to 16.8 +/- 3.4 mmHg when TBHT was raised. These re turned to normal values after cooling. The regional CBF and the ICP ch anged in parallel with drug-induced changes of mean arterial blood pre ssure during the HT period. These changes suggest that autoregulation of the CBF is paralysed during the HT period. Brain tissue pH decrease d rapidly when the rectal temperature exceeded 41.0 degrees C. The pH was 7.18 +/- 0.05 during the HT period and was relatively stable. The pH returned to a normal value after cooling. Immunopositive stain for albumin was not observed in heated brain tissue except for the normall y leaky pineal gland and the choroid plexus, indicating preservation o f BBB during TBHT. These results suggest that brain oedema may occur e asily due to paralysed cerebral autoregulation when the arterial blood pressure fluctuates excessively, so arterial blood presssure must be controlled strictly during TBHT.