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Biomedical subjects

R H Pudenz

Publications and source records attributed to R H Pudenz.

At least 19 recordsLinked to original sources
PubMed1991

Hydrocephalus: overdrainage by ventricular shunts. A review and recommendations.

Selected literature review of the clinical course of patients with ventricular shunts for hydrocephalus shows that the effects of cerebrospinal fluid overdrainage are subdural hematoma, craniosynostosis, slit ventricle syndrome, and low intracranial pressure syndrome. These occur sequentially at different age groups, but approximate averages of incidence and time of occurrence after first shunt reveal an overall incidence of 10%-12% for at least one of these appearing at 6.5 years after shunting. The basic etiology, diagnosis, and variety of treatment modalities available are reviewed, including the need for shunt closing intracranial pressure control. Included is a hydrocephalus program designed to minimize the need for long-term extracranial shunts and to maximize therapeutic intracranial procedures for hydrocephalus.

Cerebral Ventricles↗
PubMed1979

Intracellular calcium deposition in brain following electrical stimulation.

The effects of electrical stimulation of the cat cerebral cortex have been evaluated by light and electron microscopy following a wide variety of stimulation parameters (QD/ph of 10 - 300 muC/cm2/ph). Platinum or rhodium disc electrode arrays were bilaterally implanted subdurally on the parietal cortex and subjected to 36-hour stimulations (9 hrs./day for 4 days). Prominent among the degenerative changes shown by electron microscopy were dense crystalline inclusions that were identified as calcium hydroxyapatite (CHA) crystals by electron diffraction and energy dispersive X-ray analysis. The appearance of intracellular calcification generally paralleled the onset of other degenerative changes in stimulated tissue, including gliosis, mitochondrial swelling, lipid inclusions, degenerating cells, neuronal loss, and phagocytic activity. A preferential deposition of calcium was noted in mitochondria of several cell types and in postsynaptic dendrites. The mechanism of the apparently electroresponsive calcium deposition is obscure; however, a plausible explanation is that increased cyclic AMP levels, known to occur with electrical stimulation of nervous tissue, result in enhanced calcium plasmalemmal permeability.

Animals↗
PubMed1979

Evaluation of electrode array material for neural prostheses.

Matrix support materials for brain surface electrodes used in neuroprosthetic applications were evaluated after chronic subdural implantation over the parietal cortex of the cat. Four types of array fabricated with Silastic, Dacron mesh, or platinum wire annuli were implanted for periods ranging from 5 weeks to 1 year. We evaluated the arrays by access resistance measurements and gross and histological observations of the tissue beneath both nonstimulated and stimulated electrodes. A porous type matrix constructed of Dacron mesh proved to be the superior design because of its minimal compression of the cortical surface, facility of handling during implantation and autopsy, and satisfactory electrical characteristics provided by a good electrode-brain interface. (Neurosurgery, 5: 681--686, 1979).

Animals↗
PubMed1978

Microsurgical cannulation of the thoracic duct in cats. Technical note.

The authors describe a new technique for the microsurgical cannulation of the thoracic duct. A small silastic tube is utilized which can be joined to a subcutaneously implanted one-way flow, CSF, Ommaya-type reservoir. Extended drainage is avoided. No deletion or alteration of major venous channels occurs. Lymph collection is accomplished by tapping the subcutaneous reservoir with a small-bore needle.

Animals↗
PubMed1977

Neuropathological effects of intracerebral platinum salt injections.

Multiple intracerebral injections of a mixture of platinum salts were made in 9 adult cats and the brains studied by light and electron microscopy at 5-12 days post injection. At the center of the lesions normal cortical architecture was completely replaced by edematous areas containing lipid-laden macrophages and cellular debris. The lesion periphery was characterized by perivascular edema and degenerative changes including cytoplasmic lipid inclusions and vacuolations with selective vulnerability of neurons. Membranous cytoplasmic bodies (MCB), zebra bodies and multiple nucleoli were observed in several cell types. This ultrastructural pattern, mimicked to some extent, that observed following electrical stimulation of brain following chronically implanted platinum and rhodium electrodes. The induction of zebra bodies and MCB, both of which are morphologic features of human neurolipidoses associated with congenital enzyme deficiencies, suggests an inhibitory effect of platinum on brain enzymes. Functional electrical stimulation of brain and other organs is currently being employed in a wide variety of clinical applications (14, 15). A mandatory consideration is that of the long-term effects of the stimuli as well as the electrodes themselves on the tissues involved. The histological effects and mechanisms of tissue damage following chronic application of electrical stimuli to brain have been the subject of several investigations in this laboratory (1, 14-18). Factors contributing to neural damage induced by electrical stimulation include noxious products resulting from electrode dissolution. In vitro studies employing electrochemical (3,9) and scanning electron microscopy (6) techniques have established that erosion of noble metal electrodes occurs, even when passing relatively small stimulation currents. Such electrode dissolution is of particular importance in long term applications of neural prostheses. The present study was initiated to assess the contribution of platinum electrode erosion products to neurla damage following electrical stimulation of brain, specifically to distinguish morphological changes resulting directly from electrode solubilization as opposed to electrical factors. Accordingly, intracerebral injections of graded volumes of platinum salts were made in an attempt to stimulate the presence of platinum electrode dissolution products.

Animals↗
PubMed1977

Effects of electrical stimulation of brain.

The use of implantable neural prostheses activated by radiofrequency transmission requires that the materials in the device and the stimulation techniques are not injurious to neural tissue, particularly the neurons. In this report, we discuss our experiences in the search for safe stimulation techniques. Acute and chronic experiments have been performed to evaluate electrode design and materials and to observe the effects of various stimulus protocols on the blood-brain barrier and brain. Neural tissue underlying the stimulated and control electrodes has been examined with both light and electron microscopy. Observations up to the present time indicate that the charge per phase is the most relevant stimulus parameter although the importance of charge density and current density cannot be underestimated.

Animals↗
PubMed1976

Microvascular bipolar coagulator. Technical note.

A bipolar coagulator fabricated from jeweler's forceps of various sizes is described. The unit has proved very useful in microvascular neurosurgical procedures that require high magnification.

Electrocoagulation↗
PubMed1975

Electrical stimulation of the nervous system.

Twenty-seven patients with chronic pain had dorsal column stimulators implanted for pain control over a period of three years. Technical factors of electrode placement and type of unit were not found to correlate with the degree of pain relief. The preoperative psychological attitude of the patient correlated highly with the degree of pain relief and was the single most important factor in patient selection and evaluation. Theoretical concepts of pain psychophysiology in relation to the gate theory and areas for more extensive investigation of pain are discussed.

Attitude↗
PubMed1975

Electrical stimulation of the brain. II. Effects on the blood-brain barrier.

Acute and chronic studies of the effects of electrical stimulation on the blood-brain barrier (BBB) of the cat cerebral cortex are reported. The findings emphasize the importance of avoiding direct-coupled, monophasic waveforms in stimulating nervous tissue. Biphasic waveforms with balanced charges in each half-wave of the stimulating pulse can be used for up to 36 hours of continuous stimulation if the charge per phase (Q/ph) does not exceed 0.45 microcoulombs. Charge density (QD) is also an important parameter. When stimulating in the bipolar mode, BBB breakdown will occur first beneath the smaller electrode of the pair. Following electrical injury, the BBB will be partially restored within one week, and, with rare exceptions, be completely intact after one month.

Animals↗
PubMed1975

Electrical stimulation of the brain. I. Electrodes and electrode arrays.

Investigators engaged in studying the effects of electrical stimulation on the blood-brain barrier (BBB) and brain usually find it necessary to fabricate the electrodes and electrode arrays required in their acute and chronic experiments. Techniques for fabricating spring-mounted, concentric and salt-bridge electrodes and electrode arrays are described in this report.

Blood-Brain Barrier↗
PubMed1975

Electrical stimulation of the brain. III. The neural damage model.

A major concern in the use of neural prostheses is whether electrical stimualtion can cause irreversible damage to neurons. The Neural Damage Model was devised to study the problem and to provide guidlines. The cerebral cortex of cats was stimulated continuously for 36 hours with balanced, biphasic waveforms. The charge per phase, charge density and current density were varied in 16 separate tests. Of these stimulus parameters the charge per phase was more closely correlatable with neuronal damage than charge density and current density. Furthermore, the findings in this study suggest that current flow is more important than electrochemical reactions in causing neural damage. Correlation between blood-brain barrier (BBB) breakdown and neuronal damage was valid only in the group of animals sacrificed immediately following stimulation. The BBB is restored within one month following electrical injury. Convulsive seizures occurred in all but one of the animals during electrical stimulation. A technique for localizing the electrode sites at autopsy and in the microscopic sections is described.

Animals↗
PubMed1975

Electrical stimulation of the brain. IV. Ultrastructural studies.

The ultrastructural response of tissues of the cat's central nervous system to chronic electrical stimulation with various parameters has been evaluated at four and a half days post stimulation. Cellular alterations included widespread cytoplasmic vacuolations, architectural derangement and disruption of plasmalemma and other membranes. Lipid inclusions and dense crystalline bodies were prominent in astrocyte-like phagocytic cells in the more severe lesions. Despite endothelial damage in brain parenchymal capillaries, significant extravasation of horseradish peroxidase was not observed. The ultrastructural damage observed following electrical stimulation varied from mild to severe. Although none of the parameters tested was found to be "safe" for clinical applications, it should be emphasized that the stimulations delivered in the present study were essentially continuous.

Animals↗