Investigation of electrical impedance variations of dog brain tissue during experimental metabolic disturbances

Experiments were carried out on dogs using bielectrode probes having as adequate impedancemeter. The probe is introduced via a cranial opening into the grey matter. This gives the following: a low frequency reading which is related to the extra cellular fluid component; a high frequency reading which is related to the total overall liquids; and a proportionality ratio of these liquids in the explored volume. The impedance variations are functions of the nature and intessity of vascular disturbance. Variation of the low frequency impedance (5 kHz) is the most significant. The experimental prodedure consists of: 1) Abrupt and permanent circulatory arrest; 2) Circulatory reduction by haemorrhage followed by recovery (if necessary by means of blood transfusion); 3) Anoxia by CO inhalation, recovery affected by means of O2 inhalation; and 4) Hypoglycemic coma induced by intravenous injection of insulin. The changes in the biochemical state of the cerebral tissue give very large variations of the low frequency impedance. It is these variations which are to constitute the object of this communication.