Auditory evoked potentials during deviations from homeostasis: Theoretical and clinical implications

Abstract

Evoked responses of various modalities are being used for sensory and neurological clinical assessment. An additional application is their use in studying the functional activity of several sensory pathways and many brain regions during induced deviations from homeostasis in the intact animal. The auditory nerve-brain-stem evoked response (ABR) has been studied during hypoxia, hypercapnia, acidosis, hypoglycemia, systemic hypotension, intracranial hypertension and decreased cerebral perfusion pressure. In many such experiments the following were also recorded: EEG, cortical evoked potential (EP), somatosensory EP (including peripheral nerve, brain-stem and cortical components), visual and vestibular EP. Even though the EEG was already isoelectric, the ABR and many of the other EPs were not affected by relatively severe deviations in homeostasis, several of which have been shown to induce brain lesions and severe perturbations of energy metabolism. The ability of these brain pathways to produce electrical activity in such conditions may be due to the generation of such EP by oligosynaptic pathways and to compensatory mechanisms such as increased local cerebral blood flow. Clinically, these findings point out the usefulness of ABR recordings in the diagnosis of brain death and to the possibility that when ABR is continuously monitored in the intensive care patient, alterations in the ABR may indicate the need for immediate intervention.