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Biomedical subjects

K Mitchell

Publications and source records attributed to K Mitchell.

At least 73 records · Page 4Linked to original sources
PubMed1995

Splenic preservation in the management of splenic epidermoid cysts in children.

Splenic epidermoid cysts are a rare entity. The traditional treatment was splenectomy, performed to prevent infection, hemorrhage, or rupture of the cyst. The authors reviewed their series of 19 children with congenital splenic cysts from 1914 to 1993 to assess the change in management of these lesions. The age of time of presentation ranged from newborn to 17 years (median, 12.0 years) The male:female ratio was 1.0:1.1. Five cysts were found incidentally at the time of autopsy. The cysts were 0.5 to 24 cm in diameter (median, 12.0 cm). Only cysts greater than 8 cm presented with clinical symptoms: 64% with an abdominal mass and/or 78% with abdominal pain. One patient presented with a left varicocele. There were no complications related to the cysts. A variety of radiographic studies were performed, but ultrasonography provided all required diagnostic information. All patients treated before 1971 (n = 9) underwent splenectomy, and five patients treated since 1983 had hemisplenectomy or cystectomy. Postoperative spleen scans (obtained in three of these patients) and platelet counts showed preservation of splenic function. Pathological examination showed epidermoid cysts in all cases. There were no postoperative complications. In conclusion, in this series of epidermoid splenic cysts in children, (1) the cysts presented with an abdominal mass and/or abdominal pain only if they were greater than 8 cm in size, and there were no complications owing to the cysts; (2) ultrasonography was the most cost-effective and least invasive method of evaluation; and (3) splenic preservation by hemisplenectomy or cystectomy, used to avoid the long-term risks of splenectomy, proved to be a safe, easy procedure, with maintenance of splenic function.

Adolescent↗
PubMed1994

In vivo dynamics of norepinephrine release-reuptake in multiple terminal field regions of rat brain.

Electrical stimulation of the ascending dorsal tegmental bundle of the locus ceruleus was used to elicit controlled release of norepinephrine. Real-time in vivo monitoring in the brains of urethane-anesthetized rats was observed with high speed chronocoulometry at rapidly responding carbon fiber electrodes. Using modeling similar to that developed for dopamine release, the electrochemical signals were characterized as the balance between norepinephrine release per electrical stimulation pulse and apparent Michaelis-Menten reuptake parameters. Stimulation produced simultaneous overflow release at all terminal fields examined. The release and reuptake characteristics varied considerably in different regions. If the parameters are normalized to endogenous concentration in the terminal fields, release but not reuptake correlates with innervation density in several regions. Stimulated release results in norepinephrine overflow and transport in most brain regions with half-lives of 1-3 s and overflow distances of 25-50 microns at most. A surprising exception occurs in the upper layers of cortex (cingulate and sensory) where half-lives may be in the 10s of seconds and spatial reach may be up to 100 microns. The uptake in the outer cortical layers appears to be minimal and comparable with only nonspecific reuptake.

Animals↗
PubMed1994

Assessing the validity of the updated Medical College Admission Test.

This report represents early information about the validity of the updated Medical College Admission Test (MCAT) battery introduced in 1991. Data are given on both the use of the new examination in the selection of medical students and its estimated predictive value for freshman students' performance. Admission officials from 114 institutions responded to a survey on medical school admission practices and on the use of MCAT data; also elicited were assessments of the examination in relation to its design and implementation objectives. Regression-based evaluations of the predictive validity of the MCAT, undergraduate grades, and of undergraduate selectivity data for first-year grades at 12 institutions are described. Survey responses suggest that MCAT data are viewed in relation to the varied information needs of admission decision making and are supplemented by other academic and nonacademic information in selection. The new battery generally is judged favorably by admission officials. Predictive validity results reflect the usefulness of MCAT scores, undergraduate grades, and selectivity data for identifying individuals apt to succeed in medical school. The authors conclude that preliminary information about the results of the new examination is encouraging. The members of the MCAT Validity Studies Advisory Group, who assisted the authors in framing and conducting the research presented in this report, continue their research and deliberations about the use, utility, and impact of the updated MCAT.

College Admission Test↗
PubMed1993

A phase I study of the left-shifting agent BW12C79 plus mitomycin C and the effect on the skeletal muscle metabolism using 31P magnetic resonance spectroscopy.

BW12C79 stabilizes the oxyhemoglobin molecule resulting in a reversible left-shift of the oxygen saturation curve. The activity of a number of bioreductive anticancer drugs, such as mitomycin C, may be enhanced under hypoxic conditions. Twenty-four patients with various malignancies received BW12C79 and mitomycin C. BW12C79 was administered i.v. with a loading dose (20-50 mg/kg) over 1 h followed by a maintenance infusion of 4 mg/kg/h for 5 h. Percentage modification of the oxyhemoglobin (degree of left-shift) was dose related with maximum modification of 56% and was maintained for the duration of maintenance infusion of BW12C79. Hemoglobin electrophoresis showed a fast moving band consistent with the BW12C79-oxyhemoglobin complex. Side effects at the top dose level comprised headache, nausea/vomiting, vein irritation, and myocardial ischemia. One other patient suffered from an acute encephalopathy of unknown etiology a few days following BW12C79. 31P magnetic resonance spectroscopy of exercising calf muscles showed increased breakdown of high energy phosphate stores and a greater reduction in pH. Recovery of the high energy phosphate stores after exercise was slow. These results were consistent with reduced oxygen supply due to either a left shift of the oxygen saturation curve and/or reduced muscle blood flow. BW12C79 did not interfere with the pharmacokinetics of mitomycin C. In conclusion, this phase I study demonstrates the feasibility of achieving a significant left shift in the oxygen saturation curve in cancer patients which is maintained for at least 5 h with acceptable toxicity. The maximum tolerated dose of BW12C79 was 50 mg/kg loading infusion followed by a maintenance infusion of 4 mg/kg/h. Magnetic resonance spectroscopy results were consistent with reduced supply of oxygen to exercising skeletal muscle. BW12C79 may be of potential benefit as an adjunct to bioreductive drugs in the treatment of solid tumors.

Adult↗
PubMed1993

An unexpected pathway for the metabolic degradation of 1,3-dialkyl-3-acyltriazenes.

In the presence of NADPH, rat liver microsomes catalyzed the degradation of a series of 1,3-dialkyl-3-acyltriazenes, and the extent of the reaction was correlated with compound lipophilicity. In the case of two methylcarbamoyltriazenes, 1-(2-chloroethyl)-3-benzyl-3- (methylcarbamoyl)triazene (CBzM) and 1-(2-chloroethyl)-3-methyl-3-(methylcarbamoyl)triazene (CMM), microsomal metabolites were isolated. Identification of the CBzM metabolites as 1-(2-chloroethyl)-3-benzyl-3-(hydroxymethylcarbamoyl)triazene and 1-(2-chloroethyl-3-benzyl-3-carbamoyltriazine, and the CMM metabolite as 1-(2-chloroethyl)-3-methyl-3-(hydroxymethylcarbamoyl)triazene indicated that the first metabolic step involves hydroxylation of the methylcarbamoyl substituent. Detailed studies of the metabolism of CBzM indicated that the Km for the reaction was 84 microM, and that metabolism was more efficient if microsomes were prepared from male than from female rats. During prolonged incubation, the metabolites of CBzM were also degraded. The degradation of CBzM and its metabolites was inhibited by SKF-525A and metyrapone, suggesting the involvement of a cytochrome P450 isozyme, and supporting the hypothesis that the process is oxidative rather than hydrolytic in both cases. Metabolic oxidation represents an alternative pathway to chemical or enzymatic hydrolysis for the in vivo decomposition of (methylcarbamoyl)triazenes. This mechanism may ultimately explain the antitumor efficacy and low acute toxicity of selected compounds.

Alkylating Agents↗
PubMed1993

Comparison of the effects of voltage-sensitive calcium channel antagonism on the electrically stimulated release of dopamine and norepinephrine in vivo.

IN vivo electrochemistry was used to monitor the effects of several voltage-sensitive calcium channel (VSCC) antagonists (e.g. divalent metal ions, diltiazem and omega-conotoxin GVIA (omega-CT) on the electrically evoked release of dopamine (DA) in the striatum and norepinephrine (NE) in the thalamus of the anesthetized rat. The results suggest that the N-type voltage-sensitive calcium channel is the primary VSCC involved in the electrically stimulated release of DA in the striatum, whereas stimulated release of NE in the thalamus was only partially dependent on N-type VSCC. In addition, DA release appears to be more sensitive to VSCC antagonism than does NE release with the in vivo application used in this study.

Animals↗
PubMed1993

Recovery from intravenous sedation with midazolam--the value of flumazenil.

A total of 40 patients receiving intravenous midazolam for surgical removal of impacted wisdom teeth were randomly assigned to recover either spontaneously or undergo reversal by the benzodiazepine antagonist flumazenil. Whilst initial postoperative recovery to a 'fully awake' state occurred more rapidly in the reversal group, objective psychomotor testing revealed significantly poorer performance postoperatively compared with spontaneously recovering patients; this emphasises the need to retain patients for at least 1 h prior to discharge home.

Adult↗
PubMed1993

A comparison between a Canadian regional trauma unit and an American level I trauma center.

Although there has been recent comparison of the Canadian and American health care systems, the issue of trauma has received little attention. Data were collected on all adult motor vehicle crash (MVC) victims admitted to the Sunnybrook Trauma Unit (CAN), Toronto, Canada, and the R Adams Cowley Shock Trauma Center (USA), Baltimore, Maryland from July 1986 through July 1990. Similar MVC victims at CAN and USA had equivalent mortality rates with similar discharge dispositions (p = NS), but patients at USA were twice as likely to be admitted to the ICU and had longer ICU stays (p < 0.01). The hospital-based cost for an average MVC patient at CAN was significantly less than for an average patient at USA and professional charges were at least five times greater at USA. This study provides some insight into the differences in trauma care between Canada and the United States.

Accidents, Traffic↗
PubMed1993

Real-time monitoring of electrically stimulated norepinephrine release in rat thalamus: I. Resolution of transmitter and metabolite signal components.

Electrical stimulation of an ascending path of the locus ceruleus-norepinephrine system was used to elicit release of norepinephrine at noradrenergic terminal fields of the rat thalamus. Overflow into the extracellular fluid space was measured by fast in vivo chronoamperometry. At pretreated carbon fibers, the electrochemical signal consists of a sharp peak of approximately 20-30 s duration followed by a slower, plateau-like decay to baseline. The peak, characterized by a variety of pharmacological manipulations and dialysis perfusion, is primarily due to norepinephrine. The plateau was shown to correspond to metabolite efflux of 3,4-dihydroxy-phenylacetic acid. By varying the degree of electrochemical pretreatment, the response time and sensitivity of the fibers can be tuned to follow the entire signal or to select the separate components for detailed evaluation. This approach can be used to provide new information on the spatial and temporal characteristics of stimulated neurotransmitter release.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

An immunocytochemical study of glycine receptor and GABA in laminae I-III of rat spinal dorsal horn.

In order to provide information about the function of glycine in the superficial three laminae of the rat dorsal horn and the possible coexistence of glycine and GABA at synapses in this region, we have carried out a combined study involving preembedding immunocytochemistry with a monoclonal antibody to the glycine receptor and postembedding immunocytochemistry with antiserum to fixed GABA. Glycine receptor-like immunoreactivity was present at axodendritic and axosomatic synapses in all three laminae, and at dendrodendritic synapses in lamina II. Although axons that formed axoaxonic synapses were often presynaptic at immunoreactive axodendritic synapses (and thus probably contained glycine), the axoaxonic synapses themselves did not show glycine receptor-like immunoreactivity. Many of the profiles that were presynaptic at glycine receptor-immunoreactive synapses showed GABA-like immunoreactivity. These results suggest that glycine acts as a postsynaptic inhibitory transmitter at various types of synapses in laminae I-III, and that it may coexist with GABA at many synapses in this region. However, it appears that while glycine and GABA may both be released at axoaxonic synapses, either glycine does not act as a transmitter at these synapses, or else it acts at an atypical receptor that was not recognized by the antibody used in this study.

Animals↗
PubMed1992

Body habitus as a predictor of injury pattern after blunt trauma.

The records of obese and nonobese victims of blunt trauma were compared to determine if obese individuals are predisposed to a specific injury pattern. Prospectively collected data on 6368 adults admitted to a level I trauma center over a 4-year period were analyzed. Twelve percent (743 patients) met Body Mass Index (weight/height2) criteria for obesity (greater than or equal to 30 kg/m2). The obese group was older (p less than 0.01) and had lower ISSs (p less than 0.05) and higher GCS scores (p less than 0.01). More obese patients were injured in vehicular crashes (62.7% vs. 54.1% [p less than 0.01]). The obese victims were more likely to have rib fractures, pulmonary contusions, pelvic fractures, and extremity fractures and less likely to have incurred head trauma and liver injuries (p less than 0.05). Obese people injured in vehicular crashes had a similar injury pattern with no difference in seating position, direction of impact, seat belt use, and ejection.

Accidents, Traffic↗
PubMed1991

Training medical practitioners in information transfer skills: the new challenge.

Traditionally, undergraduate medical education has concentrated on teaching students how to gather information or take medical histories from their patients. However, research increasingly indicates that there is a need for medical practitioners to improve their skills in information transfer in a way which will increase the probability that patients are active collaborators in their treatment. Consequently, Newcastle Medical School has sought to develop training packages for medical students in information transfer skills. This paper describes the resulting training programme with particular emphasis on the areas selected for training, the methods by which students are taught, the necessary interactional skills and the assessment procedures which are applied.

Clinical Competence↗
PubMed1990

Industrial rehabilitation comes of age.

Yes, industrial rehabilitation has come of age. The "trendiness" and "glitz" associated with such programs are now gone (or, at least, on the wane). These programs are now being subjected to the same scrutiny as other business ventures, no longer seen as the "cash cows" that single-handedly can end the financial woes of an organization. Along with this maturity has come an accreditation system with accepted standards of practice, care and methodological style; a data base reporting on the range and limits of program capability; and the realization by the insurance community that industrial rehabilitation can be effective and that these programs are reasonable assessment and intervention alternatives for selected patients. We have also noted that as these programs grow past their adolescence it will be important to pay close attention to basic questions of cost, value, and worth. While most programs have not been totally "institutionalized" into the health care provision system, their honeymoon phase has reached a positive conclusion. It's now time to look very closely at where we are today, remember where we have come from, and look to the future with a realistic and clear view.

Hospitals↗