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Biomedical subjects

R K Simpson

Publications and source records attributed to R K Simpson.

At least 55 records · Page 3Linked to original sources
PubMed1992

Penetrating injuries restricted to the cauda equina: a retrospective review.

Thirty-three patients with penetrating injuries to the cauda equina were admitted to Ben Taub General Hospital (1980-1989). Thirty received gunshot injuries, and three had stab wounds. The average age was 30 years, and 30 patients were male. All patients had been admitted within 1 hour of injury and received spine films, myelography, or computed tomography. Deficits were "complete" if total loss of function existed and were "incomplete" if any function remained below the level of injury. Improvement at the end of followup was defined as any recovery of motor strength or regaining of a unilateral sensory level. Twenty-nine (88%) patients had incomplete neurological deficits. Of these, 15 (52%) had surgery, and of this patient group, 7 (47%) improved, 7 (47%) showed no change, and 1 (6%) worsened. Fourteen (48%) patients with incomplete deficits were treated conservatively; 10 (71%) improved, and 4 (29%) had no change. Four patients (12%) had complete deficits, 3 of whom had surgery, and all improved. One patient with a complete deficit was treated conservatively and did not improve. Ten (34%) patients had bowel or bladder dysfunction, and none improved regardless of the type of treatment. Complications (cerebrospinal fluid leak, pseudomeningocele, or wound infection) occurred in 5 (28%) operative patients and 1 (7%) conservatively treated patient. Early neurosurgical intervention for penetrating injuries of the cauda equina may be beneficial but carries an increased risk of complication.

Adult↗
PubMed1991

Segmental release of amino acid neurotransmitters from transcranial stimulation.

The present study used microdialysis techniques in an intact rabbit model to measure the release of amino acids within the lumbar spinal cord in response to transcranial electrical stimulation. Dialysis samples from the extracellular space were obtained over a stimulation period of 90 minutes and were examined using high pressure liquid chromatography. Neuronal excitation was verified by recording corticomotor evoked potentials (CMEPs) from the spinal cord. A significant increase in the release of glycine and taurine compared to sham animals was measured after 90 minutes of transcranial stimulation. Glutamate and aspartate release was not significantly elevated. GABA concentrations were consistently low. CMEP components repeatedly showed adequate activation of descending fiber pathways and segmental interneuron pools during dialysis sampling. Since glycine, and to a lesser extent taurine, have been shown to inhibit motor neuron activity and are closely associated with segmental interneuron pools, suprasegmental modulation of motor activity may be, in part, through these inhibitory amino acid neurotransmitters in the rabbit lumbar spinal cord.

Amino Acids↗
PubMed1991

Release of segmental amino acid neurotransmitters in response to peripheral afferent and motor cortex stimulation: a pilot study.

The role of amino acid (AA) neurotransmitters in the spinal cord has been primarily studied using in vitro preparations and histochemical methods. The technology necessary to estimate AA levels in an intact animal has only recently become available. Such an investigation could yield valuable information regarding the segmental neurochemical environment. We measured the release of AAs into the rabbit lumbar spinal cord in response to sciatic nerve and transcranial stimulation with stereotaxically placed microdialysis catheters. Samples were obtained periodically during 90 minutes of continuous stimulation of either the left or right sciatic nerve, or motor cortex. Quantification of gamma-amino butyric acid (GABA), aspartate, glutamate, glycine, and taurine was performed using high pressure liquid chromatography (HPLC). Adequate neural excitation was verified by recording somatosensory evoked potentials (SSEPs) or corticomotor evoked potentials (CMEPs). Sensory activation at intensities sufficient to activate small and large diameter peripheral fibers of the ipsilateral (to the microdialysis probe) sciatic nerve produced a significant change only in segmental glycine levels. Contralateral sciatic nerve stimulation failed to evoke a significant elevation of AAs. In addition, a significant increase in the release of glycine and taurine was measured after 90 minutes of transcranial stimulation. SSEP and CMEP components repeatedly showed adequate activation of primary afferent, descending motor fiber pathways, and segmental interneuron pools during dialysis sampling. Our data are consistent with the hypothesis that suprasegmental influence over peripheral afferent and motor activity may be, in part, through these amino acid neurotransmitters in the rabbit lumbar spinal cord.

Amino Acids↗
PubMed1991

Epidemiological characteristics of subarachnoid hemorrhage in an urban population.

Several risk factors for unfavorable outcome from subarachnoid hemorrhage (SAH) have been identified. The prevalence of such risk factors varies among ethnic groups and among men and women. The influence of ethnic background and gender as factors in the outcome after SAH has not been adequately studied and is the focus of the present investigation. Outcome in 145 consecutive patients was dichotomized as good and moderately disabled vs severely disabled, vegetative, and dead. A multiple logistic regression model was used to examine the factors of gender, ethnic group (white and non-white), age, admission neurological grade, pre-existing hypertension, and intravenous drug abuse. Our data reveal that hypertensive, white males, with a history of intravenous drug abuse, have a high risk of unfavorable outcome following SAH. These observations are important for the design and interpretation of future studies relating to SAH.

Adolescent↗
PubMed1991

Shielding of the spinal cord by cervical and facial structures in penetrating trauma.

Penetrating trauma to the cervical spine can result in major neurological deficits due to spinal cord damage. Discussed are four civilian cases of dramatic penetrating cervical injuries without spinal cord involvement. These injuries occurred in the anteroposterior direction, and the facial structures and/or vertebral bodies appeared to have provided some protection to the spinal cord. It is proposed that the cervical spinal cord may be less vulnerable to penetrating injuries in the anteroposterior plane due to incrementally collapsible compartments of facial soft tissue and bony sinus structures which can absorb kinetic energy and dissipate momentum.

Adult↗
PubMed1991

Recovery of amino acid neurotransmitters from the spinal cord during posterior epidural stimulation: a preliminary study.

Continuous posterior epidural spinal cord stimulation (SCS) has been an effective method for treating spasticity. The mechanisms of SCS include activation of inhibitory segmental neuronal systems and suprasegmental structures that produce inhibitory descending control. The neurochemical correlates of the mechanism of action have not been clearly defined. Microdialysis of the spinal cord extracellular space in an in vivo preparation during continuous epidural SCS was performed. The recovery of amino acid neurotransmitters, aspartate, glutamate, gamma-aminobutyric acid (GABA), glycine, and taurine from stimulated animals was compared to non-stimulated animals. Evoked potentials from the cortex and spinal cord of the stimulated animals were recorded to insure that there had been adequate epidural stimulation and normal segmental cord function. A significant increase in the concentration of glycine was seen after 90 minutes of continuous stimulation. The levels of the other amino acids were not significantly elevated. These results suggest that amelioration of spasticity with epidural SCS may involve enhanced glycine release, the major inhibitory neurotransmitter of the spinal cord.

Amino Acids↗
PubMed1991

The influence of long-term nifedipine or indomethacin therapy on neurologic recovery from experimental spinal cord injury.

Inhibition of prostaglandin pathways and calcium channel conduction has been shown to improve neurological outcome after spinal cord injury. Functional recovery from such intervention has been routinely evaluated by a simple motor examination or somatosensory evoked potentials (SSEPs) after short-term drug administration. We comprehensively evaluated the influence of continuously administered indomethacin and nifedipine on functional outcome after impact spinal cord injury. SSEP and cortico-motor evoked potential records and neurologic examinations were obtained over 6 weeks after injury. Terminal histopathologic changes within the spinal cord were also examined. Only indomethacin significantly improved neurological function and reduced the severity of histopathologic change. Evoked potential analysis was not found to be of prognostic value. Modulation of prostaglandin pathways may enhance neurological recovery after spinal cord injury.

Animals↗
PubMed1991

The influence of diabetes mellitus on outcome from subarachnoid hemorrhage.

Diabetes mellitus (DM) has been shown to be a risk factor for subarachnoid hemorrhage (SAH). However, the influence of this disease on outcome from SAH has not been adequately studied. We retrospectively reviewed 150 patients with SAH, including 22 with and 128 without DM. Our results indicate that pre-existing DM does not significantly influence outcome from SAH when examined in conjunction with other chronic diseases and epidemiological factors.

Adult↗
PubMed1991

Neurophysiologic monitoring of patients with head injuries.

Despite new technologic developments designed to analyze the brain's electrical activity, monitoring the electroencephalogram or evoked potentials has not yet provided important information with regard to acute management of patients with head injury. Measurement of cerebral blood flow as well as jugular oxygen saturation is of more practical importance. Particularly when monitored continuously, these measures can provide useful information about the use of hyperventilation and control of elevated systemic arterial pressure.

Brain↗
PubMed1990

Spinal cord ischemia-induced elevation of amino acids: extracellular measurement with microdialysis.

Excitatory amino acids have been implicated in the production of calcium mediated neuronal death following central nervous system ischemia. We have used microdialysis to investigate changes in the extracellular concentrations of amino acids in the spinal cord after aortic occlusion in the rabbit. Glutamate, aspartate, glutamine, asparagine, glycine, taurine, valine, and leucine were measured in the microdialysis perfusate by high pressure liquid chromatography. The concentrations of glutamate, glycine, and taurine were significantly higher during ischemia and reperfusion than controls. Delayed elevations in the concentrations of asparagine and valine were also detected. The elevation of glutamate is consistent with the hypothesis that excitotoxins may mediate neuronal damage in the ischemic spinal cord. Increased extracellular concentrations of asparagine and valine may reflect preferential use of amino acids for energy metabolism under ischemic conditions. The significance of increased concentrations of inhibitory amino acid neurotransmitters is unclear.

Amino Acids↗
PubMed1990

Intravenous cocaine abuse and subarachnoid haemorrhage: effect on outcome.

A retrospective study of subarachnoid hemorrhage associated with intravenous cocaine injection was undertaken in a large urban hospital. Patients who used intravenous cocaine had significantly poorer outcomes when compared with subarachnoid haemorrhage patients with no known exposure to the drug.

Adult↗
PubMed1989

Alterations in the corticomotor evoked potential following spinal cord ischemia.

A simple yet reliable model of spinal cord ischemia has been previously developed by inserting a Swan-Ganz catheter into the abdominal aorta of rabbits and inflating the balloon just inferior to the renal arteries. Recent investigations have shown that paraplegia is consistently reproduced if the balloon remains inflated for 20 min after loss of the N3 component of the somatosensory evoked potential. Because of its high reliability, this model has been frequently and successfully used to determine the efficacy of pharmacological agents thought to provide protection against spinal cord ischemia. Results from the present report demonstrate that a similar degree of reliability can be achieved in this model for testing motor activity. A simple method of evoking highly reproducible motor potentials, that can be percutaneously recorded from the spinal cord in response to cortical stimulation, was developed. Predictable and repeatable changes in the configuration of the corticomotor evoked potential were found during spinal cord ischemia and reperfusion. With this added dimension of functional assessment, future application of the current spinal cord ischemia model have been greatly expanded.

Action Potentials↗
PubMed1989

Neurogenic hyperthermia in subarachnoid hemorrhage.

We have described a patient with neurogenic hyperthermia caused by a diencephalic infarction. His hypothalamic dysfunction was a consequence of cerebral vasospasm from aneurysmal subarachnoid hemorrhage. Persistent elevation of body temperature did not respond to standard therapy, but successful treatment was achieved with cyproheptadine and indomethacin, presumably through antagonism of serotonin and prostaglandin activity.

Adult↗