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Biomedical subjects

C F Walker

Publications and source records attributed to C F Walker.

10 recordsLinked to original sources
PubMed1990

A prototype retractor system designed to minimize ischemic brain retractor injury: initial observations.

The authors have developed and patented a neurosurgical retractor system incorporating an infrared emitter and detector that allows detection of cerebral pulsations. Gentle contact with the surface of cat brains shows cerebral pulsations that correlate with arterial pulse as well as mechanical ventilation. The amplitude of cerebral pulsations decreases with higher retraction pressure and disappears at approximately 20 mmHg. The pressure on the surface of the brain decreased 50% in 5 minutes even though the position of the retractor was maintained constant. The authors postulate that monitoring cerebral pulsation may prove useful in clinical neurosurgery with respect to avoiding excessive retraction, which causes brain damage.

Animals↗
PubMed1984

Kappa opiate receptor agonists: effects on behavior and on brain function and structure in rhesus monkeys.

In the present study several drugs that are predominantly agonists of kappa receptors were tested in rhesus monkeys prepared with deep and surface brain electrodes. The administration of two benzomorphan derivatives and of ethylketocyclazocine induced acute behavioral effects resembling catatonia concomitant with generalized spike and slow-wave electroencephalographic activity at widespread brain sites, that lasted for about 1 hr. After administration of one to three doses of these agonists (the benzomorphan derivatives to five monkeys and the ethylketocyclazocine to two monkeys), chronic recording changes developed, characterized by continuous high-amplitude spiking activity focal at the anterior septal region and periaqueductal gray of the mesencephalon. They increased in intensity with the passage of time, the monkeys having been followed as long as 5 months without further drug administration. Light microscopy and electron microscopy showed no structural abnormalities in the monkey brains at the sites of altered recordings, although occasional dendritic atrophy was noted at all cortical and subcortical brain sites examined. Chronic recording changes did not develop in a monkey that received U-50,488H on eight occasions. And none of the electrode-implanted monkeys that served as controls (having received no kappa agonists) developed recording changes. The sites affected by the active kappa agonists were those at which abnormal activity has been correlated with psychotic behavior. The ability of the kappa agonists to induce a lasting physiologic change without corresponding structural change at those focal sites implicated in schizophrenia may prove a useful probe in further investigations into the cause of schizophrenia and its ultimate treatment.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1983

Finite element analysis of current pathways with implanted electrodes.

A technique for numerical solution to complex electric field distribution problems has been devised. The specific application for which it was developed is the analysis of current density and isopotential line spacing from implanted neurostimulation electrodes. Three configurations of cerebellar stimulation electrodes in clinical use were studied for current spread to regions distant from the cerebellum using a planar model of the human head, neck, and upper torso in mid-saggital section. It was found that an array of cathodes on the superior cerebellar surface and an array of anodes on the inferior cerebellar surface causes significant current spread to the brainstem, a prediction confirmed by clinical observation in patients with previously implanted electrodes of this configuration. Results modelling other electrode configurations are also presented, along with a study of the effects of possible inaccuracies in available impedance data for neural tissue.

Brain Diseases↗
PubMed1982

Cerebellar vermal atrophy in psychiatric patients.

Our findings indicate that a notable number of patients who have functional psychosis (50%) or seizures (38%) show cerebellar vermal atrophy on visual inspection of CAT head scans, in contrast to 0.5% to 3.7% of patients with other disorders. In addition to the visual reading of 1700 scans in the present study, we used two methods to demonstrate cerebellar vermal atrophy objectively: (i) low-density measurements of the posterior fossa in relationship to total brain area, and (ii) sagittal reconstruction of the vermis. We postulate that cerebellar vermal atrophy reduces the cerebellum's inhibitory influences on activity of the rostral forebrain structures where unit overactivity has been correlated with emotional dyscontrol and clinical seizures. We further postulate that cerebellar vermal atrophy reduces facilitory activity of the brain's pleasure system (septal region).

Adult↗
PubMed1981

Cerebellar pacemaker patients: an update.

Of the initial group of 38 patients in whom we have used cerebellar stimulation for treatment of intractable behavioral pathology, 25 continue to have beneficial effects. However, there have been significant technical problems due to failure of the equipment. While impairing treatment, these complications have provided inadvertent controls. The procedure must still be considered developmental at this time, despite promising therapeutic efficacy.

Cerebellum↗
PubMed1977

Parameters of stimulation and perception in an artificial sensory feedback system.

The relationships between stimulus parameters and perceptions in a prosthetic feedback system were measured using psychophysical methods. Electrical stimulation of the median nerve produced a monotonic relation between frequency of stimulation and the perceived magnitude of the stimulus. There were two qualitatively different perceptions of the stimulation; one for low frequencies and one for high. These two qualities fit different psychophysical continuua, kind of stimulation, and amount of stimulation.

Adult↗
PubMedDate not supplied

The detrimental effects of electric current on normal human sperm.

This in vitro study was conducted to determine the direct effects of electric current and associated increase in temperature on human sperm. Washed sperm samples from normal volunteers were subjected to an electric current (0 to 100 mA) in a small, customized Plexiglas chamber for up to 10 minutes. Resistive heating was monitored by a miniature temperature probe. An aliquot (7 microliters) obtained from the exposed sample (at 0, 3, 7, and 10 minute intervals) was evaluated for sperm motion parameters, viability, gross morphology, and electron microscopic analyses. As the current increased, there was a time-dependent decrease in the percentages of motility, viability, and curvilinear velocity. Light and electron microscopic evaluations of the sperm showed no demonstrable damage to the head, mid piece, or tail regions on electric stimulation. A gradual time-dependent increase in the temperature of the medium was observed with electric current. Separate evaluations in the absence of an electric current showed a significant increase in percent motility and curvilinear velocity until 40 degrees C. These results suggest that an electric current, independent of temperature (up to 40 degrees C), is detrimental to sperm motion and viability. Further studies are indicated to evaluate whether electric current during electroejaculation may be in part responsible for poor sperm recovery in men with spinal cord injury.

Electricity↗