Effect of increased intracranial pressure on the blink reflex in cats

Brainstem Monitoring in the Neurocritical Care Unit: A Rationale for Real-Time, Automated Neurophysiological Monitoring

Patients with severe traumatic brain injury or large intracranial space-occupying lesions (spontaneous cerebral hemorrhage, infarction, or tumor) commonly present to the neurocritical care unit with an altered mental status. Many experience progressive stupor and coma from mass effects and transtentorial brain herniation compromising the ascending arousal (reticular activating) system. Yet, little progress has been made in the practicality of bedside, noninvasive, real-time, automated, neurophysiological brainstem, or cerebral hemispheric monitoring. In this critical review, we discuss the ascending arousal system, brain herniation, and shortcomings of our current management including the neurological exam, intracranial pressure monitoring, and neuroimaging. We present a rationale for the development of nurse-friendly-continuous, automated, and alarmed-evoked potential monitoring, based upon the clinical and experimental literature, advances in the prognostication of cerebral anoxia, and intraoperative neurophysiological monitoring.

Blink Reflex May Help Discriminate Alzheimer Disease From Vascular Dementia

PURPOSE

Dementia has several different etiologies, and vascular dementia (VaD) is considered the second leading cause of dementia after Alzheimer disease (AD). Various studies used blink reflex in different spectrum of neurological diseases as a complementary diagnostic test. We performed blink test in AD, VaD, and mixed dementia to investigate different usefulness of blink reflex in differentiating these types of dementia.

METHODS

Blink reflex was performed for patients with AD (n = 18), VaD (n = 17), mixed dementia (n = 19), and normal subjects (n = 20). The absolute latency of R1, R2, and contralateral R2 (R2c) was determined and then compared with normal values. We used ROC curve to determine the screening cut-off value for R2 and R2c to discriminate dementia with vascular component and AD.

RESULTS

The mean age ± SD of patients was 71.61 ± 8.23, 66.71 ± 11.48, 75.26 ± 8.32, and 66.60 ± 3.91 years in 4 groups of AD, VaD, mixed dementia, and normal, respectively. R2 and R2c were recorded in fewer number of subjects with VaD or mixed dementia than AD and normal subjects. For mean R2 latency higher than 45 milliseconds, the sensitivity and specificity were 42% and 100%, respectively, and for latency higher than 45 milliseconds, the sensitivity and specificity were 72% and 89%, respectively.

CONCLUSIONS

R2 and R2c components of blink reflex could specifically discriminate between Alzheimer and dementia with vascular component. The interruption of descending corticoreticular pathways by small infarcts could explain it.

Electrically elicited blink reflex and early acoustic evoked potentials in circumscribed and diffuse brain stem lesions

In the present paper, the function of the brain stem in patients with brain stem lesions of various aetiology is investigated with electrophysiological methods. The clinical observations are supplemented by experimental investigations on cats, in which the blink reflex and the early acoustic evoked potentials were registered during the acute elevation of intracranial pressure. The findings in patients with circumscribed space-occupying lesions in the posterior fossa document that the registration of the BR and the BAEP have a functional diagnostic significance above and beyond the neurological and radiological investigation. In the case of the cerebellar space occupations, specific alterations could not be observed. On the contrary, the alterations of BR and BAEP indicate a general disturbance of brain stem function, possibly as a result of a general increase of intracranial pressure. In cerebellopontine angle tumours, both BR and BAEP showed specific alterations which were usually asymmetrical. The BR changes ipsilateral to the tumour are of major topodiagnostic significance, whereas the alterations of the contralateral potential are especially informative in the registration of BAEP. The alterations of BR and BAEP also allow an appraisal of the localization and extent of the lesion in primary space occupations in the brain stem: A pathological R1 indicates a pontine lesion, whereas pathological R2 responses are found in medullary and in oral pontine and mesencephalic lesions. In contrast to cerebellopontine angle tumours, the BAEP tends to show symmetrical alterations in primary brain stem lesions. The prolongations of interpeak latencies correspond to the brain stem segment concerned, and the same also applies to pathological amplitude reduction and deformations of individual potentials. In patients with localized brain stem damage, the reflex pathway of R2 is discussed on the basis of the BR findings. In contrast to the view held up to now that only structures situated caudal of the facial nucleus area are responsible for the genesis of the R2 response, it is assumed on the basis of our own observations that pontomesencephalic structures rostral to the facial nuclei are also important for the genesis of R2. Registration of BR and BAEP in patients with acute diffuse brain stem damage shows that both methods have a high diagnostic and prognostic value. Isolated damage and combined brain stem lesion can be demonstrated and the course can be followed up. Normalization of pathological findings reflects clinical recovery, and conversely a secondary deterioration indicates the presence of complications.(ABSTRACT TRUNCATED AT 400 WORDS)

Evoked potentials and brain stem reflexes

The recording of evoked potentials (EPs) has become one of the most useful functional diagnostic techniques in the neurosciences during recent years. In combination with the neurophysiological investigation of brain stem reflexes (BSRs) EPs provide good information concerning circumscribed and diffuse brain and brain stem lesions. In this article the role of EPs and BSRs will be pointed out with special regard to their use in neurosurgery concerning awake and comatose patients as well. Pathological findings caused by extracerebral factors or due to neurological (systemic) and otological diseases will be discussed from the aspect of differential diagnosis only. Evoked potentials described in this paper are short latency potentials which are related to more or less defined generators in the peripheral and central nervous system. EPs of long latency seem to play a role in cognitive, affective and integrative functions of the central nervous system and they will not be dealt with in this article. In recent years an increasing number of review articles and monographs dealing with several aspects of evoked potentials has appeared [16, 17, 18, 25, 69, 80, 84, 122, 123, 124, 127, 130].