Search PubMed⌕ Search

Biomedical subjects

B Clark

Publications and source records attributed to B Clark.

At least 55 records · Page 3Linked to original sources
PubMed1995

[Brain metastasis. Palliative treatment with radiosurgery].

This is a retrospective review of 52 patients with metastatic brain disease who underwent stereotactic radiosurgery at McGill University in Montreal. The radiosurgical treatment was performed with the dynamic rotation technique in which there is continuous and simultaneous movement of treatment couch and machine gantry of a 10 MV linac. All patients were treated with a single isocenter and a median dose of 1800 cGy was delivered. In 88% of the cases radiosurgery was given after failure from whole brain conventional irradiation. All 52 cases were assessed with brain CT post radiosurgery. The median follow up time was 6 months (range 1-37 months) and the response rate (partial or complete) was 64%. Only 4 patients (7%) developed late complications related to the treatment. These findings are similar to the literature. Stereotactic radiosurgery is a well tolerated, effective and minimally invasive treatment technique which has a high response rate in selected patients with small, well delineated metastatic brain lesion. Its definitive value as a single therapy or combined with whole brain conventional radiotherapy is being studied in prospective and randomized trials.

Adult↗
PubMed1994

The effect of comprehensive outpatient pulmonary rehabilitation on dyspnea.

To evaluate the effect of outpatient pulmonary rehabilitation (OPR) on dyspnea, we measured this symptom using a visual analogue scale during graded treadmill exercise testing and with baseline and transitional dyspnea indices (TDI). The latter measure overall dyspnea in three spheres: functional impairment, magnitude of task, and magnitude of effort. Twenty patients with COPD referred for OPR were randomly assigned to either a treatment group (T, n = 10), with dyspnea evaluated at baseline then shortly following a 6-week OPR program, or a control group (C, n = 10), with dyspnea evaluated at baseline then following a 6-week waiting period. No significant change in maximal exercise performance from baseline to repeated testing was observed in either group. Dyspnea at maximum treadmill workload (Dmax), which did not significantly change in C, decreased from 74.4 +/- 18.9 percent at baseline to 50.5 +/- 23.2 percent post-OPR in T (p = 0.006). The Dmax related to minute ventilation (Dmax/VEmax) and oxygen consumption (Dmax/VO2max) also significantly decreased following OPR. The reduction in exertional dyspnea was apparent by the second minute of exercise. Additionally, TDI focal scores were significantly higher in T than C (2.3 +/- 1.06 vs 0.2 +/- 1.75 units, p = 0.006), indicating decreased overall dyspnea following OPR. These results point to significant improvements in both exertional and clinically assessed dyspnea following OPR.

Aged↗
PubMed1993

A technique for fractionated stereotactic radiotherapy in the treatment of intracranial tumors.

PURPOSE: The excellent treatment results obtained with traditional radiosurgery have stimulated attempts to broaden the range of intracranial disorders treated with radiosurgical techniques. For major users of radiosurgery this resulted in a gradual shift from treating vascular diseases in a single session to treating small, well delineated primary tumors on a fractionated basis. In this paper we present the technique currently used in Montreal for the fractionated stereotactic radiotherapy of selected intracranial lesions. METHODS AND MATERIALS: The regimen of six fractions given every other day has been in use for "fractionated stereotactic radiotherapy" in our center for the past 5 years. Our current irradiation technique, however, evolved from our initial method of using the stereotactic frame for target localization and first treatment, and a "halo-ring" with tattoo skin marks for the subsequent treatments. Recently, we developed a more precise irradiation technique, based on an in-house-built stereotactic frame which is left attached to the patient's skull for the duration of the fractionated regimen. Patients are treated with the stereotactic dynamic rotation technique on a 10 MV linear accelerator (linac). RESULTS: In preparation for the first treatment, the stereotactic frame is attached to the patient's skull and the coordinates of the target center are determined. The dose distribution is then calculated, the target coordinates are marked onto a Lucite target localization box, and the patient is placed into the treatment position on the linac with the help of laser positioning devices. The Lucite target localization box is then removed, the target information is tattooed on the patient's skin, and the patient is given the first treatment. The tattoo marks in conjunction with the target information on the Lucite target localization box are used for patient set-up on the linac for the subsequent 5 treatments. The location of the target center is marked with radio-opaque markers on the target localization box and verified with a computerized tomography scanner prior to the second treatment. The same verification is done prior to other treatments when the target center indicated by the target localization box disagrees with that indicated by the tattoo marks. The new position of the target center is then determined and used for treatment positioning. CONCLUSION: The in-house-built frame is inexpensive and easily left attached to the patient's skull for the 12 day duration of the fractionated regimen. Positioning with the Lucite target localization box verified with tattoo marks ensures a high level of precision for individual fractionated treatments.

Brain Neoplasms↗
PubMed1993

Accelerated fractionation in inoperable non-small cell lung cancer. A phase I/II study.

BACKGROUND: A prospective, single-treatment-arm, Phase I/II trial was performed to determine the tumor response to an accelerated regimen and assess the feasibility and toxic effects of this approach in patients with inoperable non-small cell lung cancer (NSCLC). METHODS: Thirty-seven previously untreated patients with inoperable NSCLC who had no evidence of metastatic disease entered the study. All patients were able to walk and had disease that was measurable or assessable. Patients with palpable supraclavicular disease and weight loss were also eligible. Radiation therapy consisted of an altered fractionation regimen with a concomitant boost technique. The original lung volume received a dose of 40 Gy in 20 daily fractions to the computerized axial tomography (CT)-defined primary tumor and mediastinal nodes. The boost dose (10 Gy) was administered concomitantly with the last five fractions of the original volume treatments, with an interfraction interval of 6-8 hours. The maximal allowed dose to the cord was 46 Gy. RESULTS: At a median follow-up of 36 months, complete response was achieved in 29% (9 of 31) of the patients and a partial response in 42% (13 of 31). The overall survival rate at 36 months was 10% (median survival time, 8 months). Survival rates were 25%, 8%, and 0% for the complete responders, partial responders, and nonresponders, respectively. Local failure alone was observed in 35.5% of all patients, local and distant failure in 42%, and distant failure only in 13%. Treatments were well tolerated, and all patients were able to complete the planned regimen. Grade 1 and 2 esophagitis occurred in 65% and 26% of the patients, respectively. The clinical condition of two patients (6%) was compatible with radiation pneumonitis. Moist desquamation of the skin occurred in two patients, but most had either mild (55%) or moderate (19%) skin erythema. Late complications have been limited to radiologically detected lung fibrosis. CONCLUSIONS: The accelerated fractionation schedule used in this trial was well tolerated with shortening of overall treatment time. Local tumor control and overall survival are similar to those resulting from conventional fractionation without an increase in normal tissue effects. These results are encouraging, and additional studies testing higher tumor doses are warranted.

Aged↗
PubMed1993

Schistosoma mansoni: analysis of an unusual infection phenotype in the intermediate host snail Biomphalaria glabrata.

Snails from a B. glabrata stock, selected for nonsusceptibility to the NMRI strain of S. mansoni, exhibited unusual schistosome infections, with multiple sporocysts prominent in the head-foot (foot-sporocysts). When F1 progeny from numerous crosses between well-defined susceptible (S) and resistant (R) parental snails were exposed, 60% of the infected snails also exhibited this unusual phenotype. F1 progeny from S x S snail crosses developed normal infections. Foot-sporocysts usually developed much later than secondary sporocysts of normal infections and before 12 weeks postexposure the tissue reaction surrounding foot-sporocysts was less intense than reactions to sporocysts in other tissues of the body. Cercariae were seen emerging directly from foot-sporocysts. Infection of S x R hybrid progeny by three other strains of S. mansoni also resulted in the production of foot-sporocysts. Development of the foot-sporocyst infection phenotype in progeny from many snail crosses suggests that this phenotype is more common than previously recognized. Over 50% of the F1 progeny from S x R parental crosses developed patent infections, a fact relevant to the possible biological control of schistosomiasis by the introduction of refractory snails into endemic areas.

Animals↗
PubMed1993

General pharmacology, pharmacokinetics, and toxicology of nedocromil sodium.

The pharmacokinetic properties of nedocromil sodium give this agent a high safety margin in the treatment of asthma. Only 5% to 10% of an inhaled dose is absorbed, primarily from the respiratory tract, but also from the secondary oral route. Nedocromil sodium has very rapid plasma clearance and is confined to the extravascular space. The drug is not metabolized in either humans or animals, which renders animal testing relevant to the safety of this compound in humans. Tests conducted in several models did not uncover any adverse effects, even at high infused or inhaled doses. Also, nedocromil did not appear to interact with a variety of other drugs that are likely to be used concomitantly. These data support the long-term use of nedocromil sodium at doses required for therapeutic efficacy.

Animals↗
PubMed1993

A comparative study of the numbers of bacteria present in enteral feeds prepared and administered in hospital and the home.

Levels and types of bacterial contamination were compared in enteral feeds prepared and administered in hospital or in the home. Samples of feed administered to children suffering from cystic fibrosis were collected for microbiological analysis immediately after preparation, immediately prior to use (unless administered after preparation) and at the end of feeding. No bacteria were detected in 51 (70%) of the 73 feeds sampled on the hospital ward, and in most of the remaining feeds viable counts were less than 10(1) colony-forming units (cfu) ml-1. However, only four (18%) of the feeds sampled in the home were free from bacterial growth and the remaining 18 feeds contained from 10(1) to more than 10(6) cfu ml-1. Bacteria isolated from feeds sampled both in hospital and the home, included Staphylococcus spp., Bacillus spp., viridans and faecal streptococci, Klebsiella spp. and Enterobacter spp. Enterobacter cloacae was isolated from 11 of the 73 hospital feeds and four of the 22 home feeds. Staphylococcus aureus was isolated from five of the home feeds but from none of the hospital feeds. The higher incidence and numbers of bacteria found in home enteral feeds indicate that further, more detailed studies need to be carried out to find the sources and routes of this contamination and devise methods to minimize the problem.

Bacteria↗
PubMed1993

Role of endothelin and prostaglandins in radiocontrast-induced renal artery constriction.

Infusion of radiocontrast agents in vivo results in renal artery constriction and subsequent renal hypoperfusion. To examine the role of endothelin and of prostaglandins in radiocontrast-mediated renal vasoconstriction, rats were treated with an endothelin receptor antagonist, CP170687, and with indomethacin. The dose of CP170687 utilized was sufficient to reverse endothelin1-mediated constriction of isolated aortic rings and of renal blood flow in intact rats. In normal rats there was a transient drop in renal blood flow to 80% of baseline following sodium iothalamate injection, an effect which was not prevented by CP170687. In rats first given indomethacin, the drop in renal blood flow was more pronounced (to 63% of baseline) and was sustained. In this instance, CP170687 fully reversed the sustained decrease of renal perfusion. CP170687 also diminished the rise in systemic blood pressure seen following iothalamate injection. In the absence of indomethacin, iothalamate increased urinary prostaglandin E2 to a maximum of sevenfold above baseline values. In summary, injection of radiocontrast results in an immediate decrease in renal blood flow that is counteracted by an increase in renal prostaglandin formation. When prostaglandin synthesis is inhibited, prolonged endothelin-mediated renal vasoconstriction is observed that is reversed by an endothelin receptor antagonist.

Animals↗
PubMed1993

Futurism and the health care supervisor.

In countless ways, the United States is looked at as a model by much of the world. In the new corporate environment, decision making must be fast and accurate, dictating in turn that accurate information must flow faster. Information systems can absorb the side effects of change and interactive process developed to assess, define, and agree to a new set of work relationships. The strategic use of information and information systems is a mindset to which all members of the organization need to acculturate themselves. It should be set in each of the work teams, the organization, and its managers as a way of thinking, not merely a job or a task at hand. Experimenting with alternative designs and various management techniques in the 1990s may lead to a prosperity in the next century. Futurism may help us get there.

Decision Making, Organizational↗
PubMed1992

Prevalence of hepatitis C virus antibodies in Sydney blood donors.

OBJECTIVE: To determine the prevalence of hepatitis C virus (HCV) antibodies in the Sydney blood donor population. DESIGN: All blood donations collected from Red Cross blood donors in Sydney from February 1990 until April 1991 were tested for HCV antibodies. For those samples found reactive in an anti-HCV screening test, a confirmatory test was carried out for the presence of HCV antibodies and the alanine aminotransferase level was measured. RESULTS: The prevalence of repeated reactivity to the screening test was 0.45% among blood donations overall, and 1.02% in donors giving blood for the first time in the study period. The confirmatory test result was positive for 30.8% of donations found to be repeatedly reactive in the screening test. There was little change over the study period in the HCV antibody prevalence of donors giving blood for the first time, but there was a clear decrease in the prevalence among all donations. Prevalence in males was nearly twice the prevalence in females--a difference which was consistent across age groups. The highest prevalence in both sexes was in the age group 30-34 years. Among samples for which the screening test results was positive, there was a strong correlation between the reactivity recorded for the screening test and both the proportion found positive by the confirmatory test and the proportion with an elevated alanine aminotransferase level. CONCLUSION: The small proportion of blood donations found to be repeatedly reactive by anti-HCV screening and the relatively good correlation with the confirmatory test and liver function assay indicate that a policy of discarding these donations will decrease the risk of transfusion-transmitted HCV infection without materially affecting the supply of blood.

Adult↗
PubMed1992

Gangliogliomas in childhood.

Ganglioglioma is a tumour of the central nervous system composed of an admixture of dysplastic nerve cells resembling pleomorphic ganglion cells, and glial elements, which may be astrocytic and/or oligodendroglial in appearance. A series of 12 patients aged between 9 months and 15 years 9 months, all of whom had suffered epilepsy refractory to medical treatment for up to 8 years, is presented. Computed tomographic and magnetic resonance scans were of prime use in localisation of the tumours. Calcification was noted preoperatively in 4 of 12 cases. The majority of patients obtained at least partial relief from symptoms after complete or partial resection. Histologically, 11 of the tumours included grade 1 astrocytic elements and the remaining one exhibited grade 2 areas. The diagnosis of ganglioglioma should be suspected in a child with refractory, long-standing epilepsy. Prognosis of these tumours is determined by the astrocytic component; if this is of low grade, surgical excision may result in marked symptomatic improvement or cure.

Adolescent↗
PubMed1992

Restoration of learning ability in fornix-transected monkeys after fetal basal forebrain but not fetal hippocampal tissue transplantation.

Monkeys with bilateral transection of the fornix were severely but selectively impaired on learning and retention of visuospatial conditional discriminations, visual conditional discriminations and non-conditional spatial-response tasks. Bilateral transplantation of cholinergic-rich fetal basal forebrain tissue into the hippocampus abolished significant learning impairments on all those tasks impaired by fornix lesions when tested three to nine months after transplantation whereas bilateral transplants of non-cholinergic fetal hippocampal tissue into hippocampus showed no such beneficial effect. Acetylcholinesterase staining was severely depleted throughout the dentate gyrus and hippocampus in fornix-transected monkeys compared with animals with control corpus callosum ablations. Staining was largely restored to normal in the host hippocampus and dentate gyrus in monkeys with cholinergic transplants, whereas acetylcholinesterase staining was abnormal in those with non-cholinergic grafts. These experiments suggest that where a "higher order" cognitive function, in this case the acquisition of specific types of information into long-term memory, is disturbed by a neuropharmacologically simple lesion, cognitive function can be restored by transplantation of neurons containing appropriate neurotransmitters.

Analysis of Variance↗
PubMed1992

Striatal monoamine neurotransmitters and metabolites in dominantly inherited olivopontocerebellar atrophy.

We measured the levels of the monoamine neurotransmitters and metabolites in striatum of 14 patients with end-stage dominantly inherited olivopontocerebellar atrophy (OPCA). On average, dopamine levels were reduced in putamen (-53%), caudate (-35%), and nucleus accumbens (-31%). However, individual patient values showed a wide variation, indicating that mild to moderate striatal dopamine loss is a common but not constant feature of OPCA. Seven patients had marked putamen dopamine loss (-62% to -81%) but without evidence of correspondingly severe substantia nigra cell damage; this suggests the possibility of a "dying-back" phenomenon in which nerve terminal loss precedes cell body degeneration. Severe substantia nigra cell loss with almost total (-95% to -99%) putamen and caudate dopamine depletion was present in two patients; however, none of the 14 patients had had a clinical diagnosis of parkinsonism or was receiving antiparkinsonian medication. Mean striatal serotonin levels were normal, whereas concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid were elevated by 47% to 63%; this suggests increased activity of raphe dorsalis serotonin neurons innervating the striatum, which might aggravate the functional consequences of the dopamine deficit.

Biogenic Amines↗
PubMed1992

Transmitter-operated channels in rabbit retinal astrocytes studied in situ by whole-cell patch clamping.

Glutamate and GABA open ion channels in the membranes of astrocytes found on the vitreal surface of the rabbit retinal visual streak. The glutamate-operated channels are opened by kainate, quisqualate, and AMPA, but not by NMDA, aspartate, or the metabotropic agonist 1-aminocyclopentane-1 S,3R-dicarboxylic acid. The effects of glutamate and its analogs can be blocked by 20 microM 6-cyano-7-nitroquinoxaline-2,3-dione. The conductance increase evoked by 10 microM glutamate, a concentration of this transmitter near to that found in the vitreous humor that bathes these cells, was equivalent to 22% of the cell's resting conductance. The conductance increase evoked by 1 microM GABA, a concentration near that found in the vitreous, was equivalent to 131% of the cell's resting conductance. The effects of GABA can be blocked by bicuculline. These data show that GABA, and non-NMDA-type glutamate receptors play an important part in determining the resting potential of visual streak astrocytes in situ and that these channels may be of general importance for the functions of astrocytes in vivo.

Animals↗