[Medium-latency acoustically evoked brain potentials used for examination of the auditory pathway (author's transl)]. / Hörbahnuntersuchung mit akustisch evozierten Hirnpotentialen mittlerer Latenz.

Potentials of the 10-15 ms latency range evoked by acoustic clicks and Gauss-shaped tone bursts habe been investigated in normal hearing adults, 20 patients with cochlear damages, and 6 cases of temporal lobe processes. Methods and results are compared to those of brain stem audiometry. Mean and standard latency ranges are calculated for the different peaks (Fig. 1). Amplitudes should be used only for side difference evaluation in the same patient, because of their big interindividual variation. In cases of profound high frequency hearing loss (Fig. 2) medium-latency potentials yield true threshold values in the low frequency range, where brainstem potentials are failing. The medium latency potentials show a substantial decrease of amplitude for stimuli contralateral to the damaged side (Fig. 3). So this method can be a functional hearing test to detect or at least suspect temporal damages.

Chronic and acute transtentorial herniation with tumours of the posterior cranial fossa.

In patients with expanding lesions of the posterior fossa general hyper-reflexia (and bilateral latency shifts of auditory evoked brain stem potentials) have been noted as possible symptoms of chronic ascending transtentorial herniation. After ventricular tap, this chronic herniation may evolve into acute herniation with progressive reduction of consciousness which in our experience can only be survived by decompression of the compressed brain stem. The chronic transtentorial herniation is related morphologically to demyelination of the pyramidal tracts and the auditory pathways, whereas the acute transtentorial herniation is related to microcirculatory disturbances in the reticular formation of the mesencephalo-pontine junction.

[Damages of the auditory pathway at brain stem level investigated by acoustically evoked potentials (author's transl)]. / Untersuchung von Schädigungen der Hörbahn im Bereich des Hirnstammes durch Registrierung früher akustisch evozierter Potentiale

In 57 patients with operated expansive tumors in the postcranial fossa auditory evoked brain stem potentials were investigated. A group of 36 with neurological evidence for the brain stem compression showed significantly prolonged latencies (Fig. 1), whereas the evoked potentials were nearly normal in the preceding state of CSF circulatory disturbances (21 cases). For one patient with a neurinoma of the right trigeminal root the post-operative reduction of the pathological latency shift is demonstrated (Fig. 2). Latency evaluation of evoked brain stem potentials are used in our clinical routine for differential diagnosis of retrocochlear hearing damages.

Increase in cerebral perfusion pressure by arterial hypertension in brain swelling. A mathematical model of the volume-pressure relationship.

Brain swelling was produced in monkeys and cats by the inflation af an epidural balloon against the parietal lobe. Resulting changes in intracranial pressure (ICP) were correlated to variation in systemic arterial pressure (SAP). Intracranial perfusion pressure (ICPP) defined as the difference between SAP and ICP, was found to vary with the degree of arterial hyper-and hypotension. The relationship between SAP and ICP can be explained by an existing equilibrium between extramural pressure and vessel wall circumferential tension. A positive perfusion pressure can exist in brain swelling as long as vessel wall tension is preserved and the degree of expanding brain tissue volume is held below certain limits.