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Biomedical subjects

M O'Brien

Publications and source records attributed to M O'Brien.

At least 217 records · Page 12Linked to original sources
PubMed1991

The effect of the three columns of the spine on the instantaneous axis of rotation in flexion and extension.

Instrumentation designed for stabilization and correction of spinal deformities must limit the amount of motion in flexion and extension. In flexion or extension, the vertebral bodies move about a specific point called the instantaneous axis of rotation. The ability of the implant to limit this motion is a function of its relation to the axis of rotation of the spine. The goal of this study was threefold: 1) to define the instantaneous axis of rotation of the spine in flexion and extension; 2) to study the effect of the loss of the three columns of the spine on the location of the instantaneous axis of rotation; and 3) to determine how the above parameters relate to the choice of anterior or posterior instrumentation. Ten human cadaver spines were subjected to compressive loads in flexion and extension. The columns of the spine were then destroyed in sequence at L3. The instantaneous axis of rotation for each vertebral body was found by the method of Reuleaux, and the effect of the compromise of the columns on the location of the instantaneous axis of rotation was noted. Understanding the exact location of the instantaneous axis of rotation after a specific injury would allow the clinician to objectively choose the best surgical approach and the appropriate instrumentation.

Humans↗
PubMed1990

Anatomical and functional recovery following spinal cord transection in the chick embryo.

Following complete transection of the thoracic spinal cord at various times during embryonic development, chick embryos and posthatched animals exhibited various degrees of anatomical and functional recovery depending upon the age of injury. Transection on embryonic day 2 (E2), when neurogenesis is still occurring and before descending or ascending fiber tracts have formed, produced no noticeable behavioral or anatomical deficits. Embryos hatched on their own and were behaviorally indistinguishable from control hatchlings. Similar results were found following transection on E5, an age when neurogenesis is complete and when ascending and descending fiber tracts have begun to project through the thoracic region. Within 48 h following injury on E5, large numbers of nerve fibers were observed growing across the site of transection. By E8, injections of horse-radish peroxidase (HRP) administered caudal to the lesion, retrogradely labelled rostral spinal and brainstem neurons. Embryos transected on E5 were able to hatch and could stand and locomote posthatching in a manner that was indistinguishable from controls. Following spinal cord transections on E10, anatomical recovery of the spinal cord at the site of injury was not quite as complete as after E5 transection. Nonetheless, anatomical continuity was restored at the site of injury, axons projected across this region, and rostral spinal and brainstem neurons could be retrogradely labelled following HRP injections administered caudal to the lesion. At least part of this anatomical recovery may be mediated by the regeneration or regrowth of lesioned axons. Although none of the embryos transected on E10 that survived to hatching were able to hatch on their own, because several sham-operated embryos were also unable to hatch, we do not attribute this deficit to the spinal transection. When E10-transected embryos were aided in escaping from the shell, they were able to support their own weight, could stand, and locomote, and were generally comparable, behaviorally, to control hatchlings. Repair of the spinal cord following transection on E15 was considerably less complete compared to embryos transected on E2, E5, or E10. However, in some cases, a degree of anatomical continuity was eventually restored and a few spinal neurons rostral to the lesion could be retrogradely labelled with HRP. By contrast, labelled brainstem neurons were never observed following E15 transection. E15 transected embryos were never able to hatch on their own, and when aided in escaping from the shell, the hatchlings were never able to stand, support their own weight or locomote.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Reward dominance and passive avoidance learning in adolescent psychopaths.

This study tests predictions that adolescent psychopaths are hyperresponsive to rewards (Quay, 1988) and deficient in passive avoidance learning (Newman & Kosson, 1986). Forty male adolescent juvenile offenders were divided into psychopaths and nonpsychopaths using cluster analysis. Subjects were administered a passive avoidance learning task which required learning when to respond to cards associated with either reward or punishment. Results showed a greater responsivity to reward in psychopaths, with no group differences in passive avoidance errors. Results lend support to the view that psychopaths tend to focus on the prospect of reward under conditions of mixed incentives and, when sufficiently motivated, are capable of improved performance. Together with findings of recent psychophysiological studies, these results suggest that adolescent psychopaths may have latent abilities which could have treatment implications.

Adolescent↗
PubMed1990

Reduced lateralization in verbal dichotic listening in adolescent psychopaths.

One possible explanation for previous findings of abnormal linguistic processing in psychopaths is that they are less lateralized for verbal processes. This study tests the hypothesis that adolescent psychopaths show evidence of reduced lateralization on a verbal dichotic listening task. Four self-report and behavioral measures of psychopathy were used to define psychopathy using cluster analytic techniques in 40 juvenile offenders aged 13 to 18 years. Psychopaths were found to have reduced ear asymmetries relative to nonpsychopaths, a result indicating reduced lateralization for verbal material. The effect does not appear to be mediated by group differences in age, ethnic background, IQ, overall performance, left-handedness, selective attention to one ear, or interhemispheric transfer deficits. This result suggests that the previous finding by Hare and McPherson is robust, provides some preliminary validity for the assessment of psychopathy before age 18, and indicates initial support for the utility of cluster analytic techniques in the assessment of psychopathy.

Adolescent↗
PubMed1990

Enzymatic profiles of 11 barophilic bacteria under in situ conditions: evidence for pressure modulation of phenotype.

Barophilic bacteria are microorganisms that grow preferentially (facultative barophiles) or exclusively (obligate barophiles) under elevated hydrostatic pressure. Barophilic bacteria have been isolated from a variety of deep-sea environments. Attempts to characterize these organisms have been hampered by a lack of appropriate methodologies. A colorimetric method for the detection of 19 constitutively expressed enzymes under in situ conditions of pressure and temperature has been devised, using a simple modification of the commercially available API ZYME enzyme assay kit. By using this method, enzyme profiles of 11 barophilic isolates, including an obligate barophile, were determined. Nine of the 10 facultatively barophilic isolates examined exhibited a change of phenotype in at least one enzyme reaction when tested at 1 atm (1 atm = 101.29 kPa), compared with results obtained under in situ pressure. The assay is simple and rapid and allows for direct determination of enzyme activity under conditions of high pressure and low temperature.

Atmospheric Pressure↗
PubMed1989

Phase II study of combination 4'-epidoxorubicin and mitomycin C in recurrent epithelial ovarian cancer.

Thirty-three evaluable patients who had epithelial ovarian cancer that had not responded to treatment were entered into a phase II study of combination epirubicin and mitomycin C. Epirubicin (65 mg/m2) and mitomycin C (4 mg/m2) were administered separately, each as an i.v. bolus every 4 weeks. Ten patients (30%) had a complete or partial responses. The median duration of response was 20 weeks (range, 9-53). The regimen was well tolerated. Myelotoxicity occurred in four patients requiring hospitalization for septicaemia. Eleven patients had a blood transfusion. Alopecia was common, and nausea and vomiting, though frequent, usually mild. Cardiological toxicity was observed in one patient only. She developed congestive cardiac failure after an acute myocardial infarction. This regimen is active in advanced ovarian cancer that has not responded to prior treatment and warrants further study combination with other active drugs as a first-line regimen for ovarian cancer.

Adult↗
PubMed1989

The contribution of the three columns of the spine to spinal stability: a biomechanical model.

UNLABELLED: The load carrying capacity (LCC) of the human spine was evaluated in 10 human cadaver spines. The specimens consisted of segments from T11 to S1 with markers placed on the specimens at each vertebral level in both Ap and lateral planes. The specimens were loaded to 1250 N and spinal deflections were recorded and photographed at 125 N intervals during the loading cycle. In 5 specimens, axial and flexion loads were applied to the intact spine. The anterior and middle columns were destroyed in sequence at L2 and the loading process repeated. In the remaining 5 specimens, axial and extension loads were applied with the spine intact and after the posterior and middle columns were destroyed in sequence at L2. Load deflection curves were generated for each test and comparisons were made between intact spines and spines with single and double column destruction. RESULTS: When the axis of loading was anterior to the posterior longitudinal ligament (PLL), destruction of the anterior and middle columns reduced the LCC by 46% and 68% respectively and destruction of the posterior and middle columns reduced the LCC by 30% and 63% respectively. There was minimal change in the LCC when the axis of loading was posterior to the PLL and the anterior and middle columns were destroyed. Two column destruction of the spine reduced its load carrying capacity for flexion loads by 70%. In thoracolumbar spinal fractures where flexion loads are predominant and anticipated, the authors conclude that surgical stabilisation is indicated with double column failure.

Humans↗
PubMed1989

The contribution of the three columns of the spine to rotational stability. A biomechanical model.

A function of the spine as a structural column is its ability to resist torsion. The goal of this study was to evaluate the contribution of the columns of the spine to torsional rigidity. Ten human cadaver spines were harvested and frozen. The specimens, consisting of segments from T11 to S1, were subjected to torsional loads of up to 20 N-m. Rotation was recorded throughout the loading cycle. The columns of the spine were destroyed at the L2-3 interspace in a predetermined fashion and loading was repeated. The data were plotted as torsion versus rotation in degrees. The curves of each loading cycle were compared and the ratios of the intact and compromised specimens were calculated. The contribution of each column of the spine to torsional rigidity was determined. In an intact lumbar spine, the anulus was the most effective structure in resisting torsion. Experience gained in this study supports the following conclusion: Flexion-distraction injuries of the thoracolumbar and lumbar spine involving soft tissue destruction of the anterior column and anulus result in rotational instability.

Aged↗
PubMed1989

Glomus tumours: an immunohistochemical profile of 11 cases.

We studied 11 glomus tumours immunohistochemically, with a panel of connective tissue and epithelial markers. Most tumours contained small nerve fibres located in connective tissue septae between groups of glomus cells, thus accounting for the frequent occurrence of pain associated with glomus tumours. All tumours stained positively for muscle-specific actin and vimentin. Immunostaining for high and low molecular weight cytokeratins, desmin, myoglobin, S-100 protein, neurofilaments and Factor VIII related antigen was negative. Our findings confirm and amplify the proposed smooth muscle histogenesis of glomus tumours. This immunohistochemical profile may be of diagnostic value in the differential diagnosis of atypical glomus tumours.

Adolescent↗
PubMed1989

Social interactions and play patterns of parents and toddlers with feminine, masculine, and neutral toys.

Children as young as 18 months display sex-stereotyped toy choices. The present study was designed to determine whether parents encourage involvement with sex-stereotyped toys or avoidance of cross-sex-stereotyped toys and to determine whether masculine and feminine toys lead to different patterns of parent-child interaction, regardless of gender. 40 parent-toddler dyads were videotaped while playing with 6 different sets of sex-stereotyped toys. Equal numbers of boys and girls were observed with mothers and fathers. The children showed greater involvement when playing with same-sex-typed toys than with cross-sex toys even when statistically controlling for parents' behaviors. Parents' verbal behaviors, involvement, and proximity to the child differed across toy groups, regardless of the parent's or child's gender. Parents' initial nonverbal responses to the toys, however, were more positive when the toys were stereotyped for the child's and parent's gender than when they were not.

Female↗
PubMed1989

Intraperitoneal Vancoled does not cause chemical peritonitis.

A prior report has suggested that loading doses of intraperitoneal Vancoled (vancomycin, Lederle) cause chemical peritonitis in patients with catheter infections. The present open-label study was conducted to determine the effects of a 30 mg/kg intraperitoneal loading dose of Vancoled given to five patients with a culture-positive, erythematous, draining exit-site infection. Prior to dosing, all dialysate was drained and sent for baseline cell count and culture. The loading dose was added to the dialysate and infused in the usual fashion. A sample of dialysate was drained at two hours and sent for cell count and culture. The entire exchange was drained at four hours and also sent for cell count and culture. Serum vancomycin concentrations wer measured at four hours. Baseline dialysate contained less than 9 white blood cells per microliter in all patients. Two and four hour samples contained less than 4 and less than 11 white blood cells per microliter, respectively. All fluid was sterile. WB C differential counts were unremarkable. No adverse effects occurred. The mean serum vancomycin concentration was 26.5 micrograms/ml. Intraperitoneal Vancoled did not cause chemical peritonitis and was well-tolerated by patients with exit-site infections.

Adult↗
PubMed1988

Enzymatic characterization of three aeromonas species using API Peptidase, API "Osidase," and API Esterase test kits.

An enzymatic characterization of 16 strains of Aeromonas species including A. hydrophila (7), A. sobria (5), and A. caviae (4) was carried out using API Peptidase (strips numbered 1, 2, 3, 4, 5, and 6); API Esterase and API "Osidase" test strips. A total of 89 substrates was used in the assay and included 59 arylamides (aminopeptides), 10 esters, and 20 carbohydrates. All three species were remarkably uniform in their reactivities. Nineteen (32%) of the arylamide substrates used were hydrolyzed by all three species. Very strong arylamidase activity was displayed by all three species for L-lysine, L-hydroxyproline, L-arginine, L-alanine, L-proline, and L-leucyl-L-alanine. Esterase activity was strongest against caproate (C6), caprylate (C8), nonanoate (C9), and caprate (C10) substrates. Only a limited number of carbohydrate substrates were hydrolyzed; strong N-acetyl-beta-D-glucosaminidase activity was given by all strains. Both A. hydrophila and A. caviae gave strong beta-D-glucosidase reactivities, while A. sobria appeared to be negative for this enzyme. The results of our preliminary study show that some of the enzymes examined may be useful in the identification and differentiation of these species. The API enzyme assays yielded rapid (4 hr) results. The assays were easy to perform, relatively inexpensive and reproducible. The importance of replicate testing and the inclusion of uninoculated (buffer only) controls as part of the assay is emphasized.

Aeromonas↗
PubMed1988

Osteoporotic correlates of alcoholism in young males.

A group of 22 white males (ages, 28 to 40 years) with histories of chronic alcohol abuse ranging from 1 to 21 years were evaluated for trabecular bone mineral density in the left femoral neck area. A group of age and weight-matched white males with no history of alcoholism served as controls. All participants completed medical history questionnaires regarding fracture history, dietary habits, medications, and physical activity. Singh femoral trabecular indices also were measured for the alcoholic participants. Analysis of bone mineral data as measured by dual photon absorptiometry revealed no statistically significant reduction in the bone mineral densities of the alcoholic group when compared to the controls. No differences were seen in the areas of the femoral neck, Ward's triangle, and greater trochanter. Duration of alcoholism also was not correlated with the degree of osteopenia. Singh index measurements of right and left femoral heads were compared and revealed no significant differences within individual patients. Left femoral Singh index values averaged 5.5 (range, 4 to 6) for the alcoholic group and were not indicative of decreased bone mineral density. It is concluded from this study that chronic alcoholism associated with heavy smoking most likely has a debilitating effect on the trabecular bone density of white males, yet clinical and radiographic evidence is not widely manifested in men under the age of 40 years.

Adult↗