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Biomedical subjects

R K Simpson

Publications and source records attributed to R K Simpson.

At least 37 records · Page 2Linked to original sources
PubMed1997

The effect of high hydrostatic pressure on Listeria monocytogenes in phosphate-buffered saline and model food systems.

Three strains of Listeria monocytogenes (NCTC 1194, a poultry isolate and the Scott A strain) were exposed to a range of pressures (300, 350, 375, 400 and 450 MPa) in 10 mmol 1(-1) phosphate-buffered saline (PBS) at pH 7.0 for up to 30 min at ambient temperature. Generally, increasing the magnitude and duration of compression resulted in increasing levels of inactivation, although the inactivation kinetics varied depending on the strain and pressure applied. The three strains also exhibited a wide variation in their resistance to high pressure. The resistance of the three strains to high pressure (375 MPa) was also assessed in a series of model food systems containing one of each of the three main food constituents: protein (1, 2, 5 and 8% w/v bovine serum albumin in PBS), carbohydrate (1, 2, 5 and 10% w/v glucose in PBS) and lipid (olive oil (30% v/v) in PBS emulsion). Overall, increasing the concentrations of bovine serum albumin (BSA) and glucose in the suspending medium resulted in decreasing levels of inactivation of all three strains; however, the minimum concentration of BSA and glucose required to increase survival to a level greater than that observed in PBS alone varied depending on the strain and on the duration of the treatment. The survival of all three strains was greater in the olive oil/PBS emulsion than in PBS alone at all treatment times.

Animals↗
PubMed1997

The effect of high hydrostatic pressure on the activity of intracellular enzymes of Listeria monocytogenes.

The effect of high hydrostatic pressure (100-550 MPa, 15 min, ambient temperature) on the activity of 13 metabolic enzymes produced by all three strains of Listeria monocytogenes (NCTC 11994, a poultry isolate and Scott A) was examined using gel electrophoresis. The enzymes assayed exhibited a wide variation in barotolerance. The pressure resistance of each particular enzyme was not dependent on the strain from which it was derived. This would seem to indicate that these enzymes were not a determining factor in relation to previously observed differences in the overall pressure resistance of the three strains.

Hydrostatic Pressure↗
PubMed1997

Locked-in syndrome resulting from cervical spine gunshot wound.

A patient sustained a cervical spine gunshot wound resulting in immediate quadriplegia and obstruction of both vertebral arteries. After an 8-hour delay, basilar artery thrombosis occurred and resulted in locked-in syndrome. Bilateral occlusion of the vertebral arteries after penetrating cervical trauma has not been reported previously. The incidence and treatment of traumatic basilar thrombosis and locked-in syndrome is reviewed. Rapid diagnosis of ascending thrombosis and prompt treatment with hyperdynamics and anticoagulation may improve outcome.

Adult↗
PubMed1996

Lactic acid and amino acid fluctuations measured using microdialysis reflect physiological derangements in head injury.

We examined the extracellular neurochemical milieu in 34 head injured patients using microdialysis while simultaneously monitoring intracranial pressure, cerebral perfusion pressure, and jugular venous oxygen saturation. Derangements of anaerobic metabolism reflected by increased lactate and lactate/pyruvate ratios, and release of amino acids were seen at the same time as physiological deterioration in the majority of instances. Clinical microdialysis may provide insights into the neurochemistry of head injury, and such information may lead to new methods of monitoring and treating head injured patients.

Adult↗
PubMed1996

Reduction in the mechanonociceptive response by intrathecal administration of glycine and related compounds.

We have previously reported that enhanced glycine release is produced by epidural spinal cord stimulation, a clinical method for treating neuropathic pain. Our current hypothesis is that glycine administered intrathecally reduces neuropathic pain as measured by the Randall-Selitto method. Neuropathic rats created by unilateral partial ligation of the sciatic nerve were treated with intrathecal infusion of glycine, strychnine, MK-801, or 5,7-DKA at 0.1 mumol, or artificial CSF for 2 hours at a rate of 10 microliters/min. Force required to produce the pain response was significantly increased after glycine administration and reduced using strychnine, a specific glycine receptor (Gly l) antagonist. Strychnine blocked the response to glycine when infused together. Administration of the non-specific NMDA receptor MK-801 antagonist and 5,7-DKA, a specific glycine-NMDA receptor (Gly 2) antagonist, however, failed to block the response to glycine. Our results provide evidence for the use of glycine and related compounds to treat neuropathic pain.

Animals↗
PubMed1996

"Slinky" coils for neuromagnetic stimulation.

Future advances in neuromagnetic stimulation depend significantly on the design of coils with improved focality. Although in the absence of internal current sources, no true focusing of magnetically induced currents is possible, improvements in the focality of current concentrations passing through an area of biologic tissue are achievable through variations of the shape, orientation and size of neuromagnetic stimulating coils. The "butterfly" and the "4-leaf" coils are two examples of planar designs which achieve improved focality through centralization of the maximum coil current and peripheral distribution of the return currents. We introduce the "slinky" coil design as a 3-dimensional generalization of the principle of peripheral distribution of return currents and demonstrate its advantages over planar designs.

Electric Stimulation↗
PubMed1996

The role of glycine in spinal shock.

Suppression of increased muscle tone by epidural spinal cord stimulation, an invasive method for treating spasticity, increases segmental concentrations of inhibitory amino acid neurotransmitters, particularly glycine. The role of glycine in spasticity and spinal shock was explored further in rabbits with ischemic spinal cord injuries that produced spastic paraparesis or flaccid paraplegia. H-reflexes were monitored following posterior tibial nerve stimulation and plantar surface recording. Spasticity was quantified by using H/M ratios. Spastic animals were intrathecally infused with 100 mmol/l solutions of glycine and related compounds. Glycine agonists suppressed tone whereas glycine antagonists increased tone. In addition, microdialysis sampling from the cord was done in injured, non-infused animals and aspartate, GABA, glutamate, glycine and taurine were measured. Flaccid animals had glycine levels two-three times higher than spastic or control animals. High concentrations of glycine within spinal cord segments is associated with spinal shock. Glycine and related compounds may be useful as treatment for excessive tone.

Amino Acids↗
PubMed1995

The influence of glycine and related compounds on spinal cord injury-induced spasticity.

Spasticity is a frequent and complex sequel to spinal cord injury. The neurochemical basis for the origin of spasticity is largely unknown. Glycine is among the most abundant neurotransmitters in the spinal cord. However, the role of glycine and related compounds in spasticity have received little attention. An ischemic spinal cord injury was created in rabbits, by an intraaortic balloon occlusion technique, which produced lower limb spasticity. A catheter was inserted into the cisterna magna and the spinal cord was bathed with 100 microM solutions of glycine, strychnine, D-serine, beta-alanine, MK-801, or artificial CSF for 4 hours at a rate of 10 microliters/min. H-reflexes were monitored before and during infusion by stimulating the posterior tibial nerve and recording from the plantar surface of the foot. Glycine, D-serine, and MK-801 depressed the H wave, strychnine produced a heightened H wave, and beta-alanine caused no significant changes. These results indicate that glycine and related compounds may influence spasticity.

Animals↗
PubMed1993

Glycine: an important potential component of spinal shock.

Amino acid neurotransmitters (AANTs) play a major role in maintenance of muscle tone. Abnormal AANT concentrations are associated with hyper- or hypotonic states. Flaccidity from spinal shock commonly occurs after spinal cord injury (SCI) and may be associated with changes in AANT concentrations. Ischemic SCIs created in the lumbar region of rabbits by intraaortic balloon occlusion produced spastic or flaccid injuries. Microdialysis sampling of AANTs from the injured segmental structures was done 3 days after SCI. Evoked potentials were used to monitor spinal cord stability. No significant changes in AANT levels occurred in the spastic or flaccid group after 4 hour sampling. However, flaccid animals had baseline glycine levels 2-3 times higher (p < 0.001) than spastic animals or controls. High concentrations of the inhibitory AANT glycine is associated with flaccidity following SCI, or spinal shock, but not spasticity. Glycinergic compounds directed toward suppression of excess muscle tone deserve further study.

Amino Acids↗
PubMed1993

Spinal epidural corticomotor evoked potentials as a predictor of outcome from ischaemic myelopathy.

Corticomotor evoked potentials have been suggested to accurately reflect neurological function, particularly with regard to the integrity of the spinal cord. However, the utility of these potentials to evaluate graded, chronic injury has received little attention. Using a rabbit model of ischaemic spinal cord injury we recorded corticomotor evoked potentials before, during, immediately after, and three days after producing an ischaemic spinal cord injury by inflating an intraaortic balloon. The animals sustained a stable mild, moderate, or severe neurological deficit. All ischaemic injured animals demonstrated near loss of the corticomotor evoked potential after the timed balloon occlusion period. Mildly injured animals did not demonstrate significant differences in corticomotor evoked potentials at reperfusion of three days post injury, when compared to controls. However, moderate and severely injured animals revealed significant reduction in late latency component amplitudes by > 50% and > 90%, respectively, when compared to controls. Changes in corticomotor evoked potential features are associated with altered neurological function after graded spinal cord injury.

Animals↗
PubMed1993

Spectral analysis of corticomotor evoked potentials in spinal cord injury. Part 1. Acute studies.

A model of graded spinal cord injury using ischaemia has been developed by using balloon occlusion of the abdominal aorta in rabbits. This model has been used to test pharmacological agents thought to provide protection against spinal cord injury based on changes in corticomotor evoked potentials (CMEPs). These highly reproducible signals are percutaneously recorded from the spinal cord in response to cortical stimulation and accurately reflect the degree of residual spinal cord function. The present study focused on the power spectra of CMEPs to clarify alterations in post-injury signals. This added dimension of previously unreported CMEP analysis will augment future applications of the current model.

Acute Disease↗
PubMed1993

Spectral analysis of corticomotor evoked potentials in spinal cord injury. Part 2. Chronic studies.

Corticomotor evoked potentials (CMEPs) have been suggested to accurately reflect neurological function, particularly with regard to the integrity of the spinal cord. However, the utility of these potentials to evaluate graded, chronic injury has received little attention. Frequency analysis has been suggested by the authors to be a method of simplifying interpretation of these complex signals. Ischaemic spinal cord injuries were produced in rabbits causing mild, moderate, or severe neurological deficits. CMEPs were recorded before, during, immediately following, and three days after injury. Alterations in the features of the power spectra reflected the degree of neurological injury. CMEP power spectra may predict neurological outcome and augment currently used electrodiagnostic tests.

Animals↗
PubMed1993

Segmental recovery of amino acid neurotransmitters during posterior epidural stimulation after spinal cord injury.

Epidural spinal cord stimulation (SCS) has been used as an effective method for managing pain and spasticity for over two decades. However, the mechanisms of these beneficial effects are largely unknown. Since neurotransmitters are likely to be involved, we examined the relationship between SCS and local segmental amino acid release into the spinal cord extracellular space. Microdialysis was performed during continuous epidural SCS in animals subjected to ischemic spinal cord injury. Recovery of amino acid neurotransmitters from stimulated, injured animals was compared to that from a control group. Evoked potentials from the cortex and spinal cord were recorded to insure adequate stimulation and stable cord function. A significant increase in the concentrations of glycine and taurine was seen before, during, and after 90 minutes of continuous stimulation and was independent of the degree of injury. Levels of the other putative amino acid neurotransmitters were not significantly elevated. These results suggest that amelioration of pain or spasticity by epidural SCS may result from maintenance of post-injury elevation in baseline glycine and taurine levels.

Amino Acids↗
PubMed1993

Systemic lidocaine therapy for poststroke pain.

Poststroke pain syndrome is commonly regarded as an intractable disease. We describe four patients who responded to an intravenous lidocaine infusion for relief of central pain after a stroke. The infusion was administered over a 48-hour period after an initial bolus of 50 to 100 mg intravenously over 40 to 120 seconds. Pain intensity and pain relief were measured by visual analog and numeric scales. All patients reported some relief within the first 12 hours of infusion. All patients were subsequently given a trial of mexiletine, an oral congener of lidocaine. Two have continued taking the drug and report excellent relief at 12 months' follow-up; the other two had side effects that precluded further use of the drug. We conclude that lidocaine can reduce poststroke pain, and we propose a treatment algorithm based on our experience with 40 additional patients treated for other neuropathic pain states.

Adult↗
PubMed1993

Video-assisted endoscopic thoracic ganglionectomy.

Sympathetic nerve disorders of the upper extremities can be treated by neurosurgeons using upper thoracic sympathectomy via a posterior approach. Descriptions have been published of alternative endoscopic procedures involving thermocoagulation, laser coagulation, or nonvideo-assisted ganglionectomy using equipment not widely available, with low morbidity and excellent results. The authors describe the use of an endoscopic approach to the thoracic sympathetic ganglia with systems designed for laparoscopic cholecystectomy. Thoracic ganglionectomy is reported in 22 patients with primary palmar hyperhidrosis and eight patients with reflex sympathetic dystrophy. The patients underwent double-lumen endotracheal intubation, after which 11- and 5.5-mm trocars were introduced into the chest cavity. Pneumothorax was produced with CO2 insufflation. Fiberoptic closed-circuit television was used to visualize the structures to be dissected. The parietal pleura over the heads of the first and second ribs was excised using 5-mm blunt and sharp insulated coagulating microscissors. The stellate and upper thoracic ganglia were clearly identified and dissected. The T-2 and T-3 ganglia were grasped with forceps and excised. A No. 16 French chest tube was introduced through a trocar, placed under water seal after the lungs were reinflated, and removed in the recovery room. The average hospital stay was 15.4 hours. There were no intraoperative complications. The average operating time was 30 minutes per side. Five patients had mild pleuritic pain which resolved within 2 weeks after surgery. Six (75%) of the eight patients with reflex sympathetic dystrophy had complete or partial relief of their symptoms (average follow-up period 5 months), and all patients had complete relief of hyperhidrosis (average follow-up period 8 months). Endoscopic ganglionectomy requires readily available and easily used instrumentation and provides a well-tolerated, cost-effective alternative to posterior thoracic sympathectomy for primary palmar hyperhidrosis and reflex sympathetic dystrophy.

Ganglionectomy↗
PubMed1993

The effect of long-term high-dose naloxone infusion in experimental blunt spinal cord injury.

The effect of long-term continuous subcutaneous infusion of naloxone on blunt spinal cord injury in the rat was assessed using four tests of neurological function, seven histological categories, and two electrophysiological measures. All four neurological function tests showed a trend toward improvement in naloxone-treated animals: the degree of improvement was statistically significant in two of the four categories. A significant reduction in myelin sheath edema was found in the naloxone-treated animals. Although there was a decrease in corticomotor-evoked potentials complexity following injury, there was no significant difference in naloxone-treated animals. Somatosensory-evoked potentials were significantly increased in amplitude and latency in naloxone-treated animals. This increase was most apparent at 60 min: no difference was found by 3 weeks postinjury. These results confirm earlier reports that naloxone can ameliorate the functional neurological deficits of spinal cord injury. Naloxone also produces alterations in the somatosensory-evoked responses in the early phase of treatment and significantly reduces myelin sheath edema.

Animals↗
PubMed1992

Use of tissue adhesive to secure spinal epidural stimulating electrodes: technical note.

Securing spinal cord stimulating electrodes (SCS) within the epidural space is often a challenging task. Complications of the technique include development of cerebrospinal fluid leaks and electrode migration. We report four patients who underwent a limited laminectomy for placement of epidural spinal cord stimulating electrodes to relieve pain and/or spasticity. Suturing electrodes to the dura was not possible, and a tissue adhesive was used. Two-year follow-up shows no migration of the electrodes. Tissue adhesive of "fibrin glue" is a viable alternative for securing epidural SCS electrodes.

Adult↗