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Biomedical subjects

K R Peters

Publications and source records attributed to K R Peters.

At least 19 recordsLinked to original sources
PubMed2006

Characterizing neuropsychiatric symptoms in subjects referred to dementia clinics.

OBJECTIVE: To characterize the neuropsychiatric symptoms (NPS) of subjects classified as not cognitively impaired (NCI), cognitively impaired-not demented (CIND), and dementia. METHODS: A Canadian Cohort Study of Cognitive Impairment and Related Dementias (ACCORD) is a longitudinal investigation of individuals referred to eight Canadian dementia centers for evaluation of cognitive impairment and neurobehavioral symptoms. Of the inception cohort of 804 subjects for whom the informant-based Neuropsychiatric Inventory (NPI) was completed at study entry, 35 were classified as NCI, 193 as CIND, and 576 as dementia. The three diagnostic groups were compared on each of the 12 NPI items. Within each diagnostic group, comparisons were also made between symptomatic (NPS+; total score > 1) and asymptomatic (NPS-; total score = 0) subjects on measures of general cognitive status and functional disability. A subset of the NCI and CIND individuals were also compared on a comprehensive neuropsychological test battery. RESULTS: There was at least one NPI item reported in 60% of subjects with NCI, 74% with CIND, and 89% with dementia. The item scores for delusions, hallucinations, agitation, apathy, disinhibition, aberrant motor behavior, and problems with appetite were greater in dementia subjects than in NCI or CIND. There were no significant differences between subjects with NCI and CIND on any NPI item. For each diagnostic group, NPS+ subjects were more impaired on functional but not neuropsychological measures. CONCLUSIONS: Across all levels of cognition, neuropsychiatric symptoms (NPS) are an important feature in individuals referred to dementia clinics. The current data suggest that NPS may precede cognitive deficits in individuals classified as not cognitively impaired and cognitively impaired-not demented.

Aged↗
PubMed1998

Grebe syndrome: clinical and radiographic findings in affected individuals and heterozygous carriers.

Grebe syndrome is a recessively inherited acromesomelic dysplasia. We studied, clinically and radiographically, 10 affected individuals, originating from Bahia, Brazil. The phenotype is characterized by a normal axial skeleton and severely shortened and deformed limbs, with a proximo-distal gradient of severity. The humeri and femora were relatively normal, the radii/ulnae and tibiae/fibulae were short and deformed, carpal and tarsal bones were fused, and several metacarpal and metatarsal bones were absent. The proximal and middle phalanges of the fingers and toes were invariably absent, while the distal phalanges were present. Postaxial polydactyly was found in several affected individuals. Several joints of the carpus, tarsus, hand, and foot were absent. Heterozygotes presented with a variety of skeletal manifestations including polydactyly, brachydactyly, hallux valgus, and metatarsus adductus. Grebe syndrome is caused by a missense mutation in the gene encoding cartilage-derived morphogenetic protein-1.

Abnormalities, Multiple↗
PubMed1997

Evaluation of an on-line patient exposure meter in neuroradiology.

PURPOSE: To assess the clinical performance and usefulness of an on-line patient exposure meter installed on a neuroradiologic biplane imaging system. MATERIALS AND METHODS: A commercial on-line patient exposure meter was installed on each plane of a biplane neuroradiologic imaging system. The meter computed skin exposures on the basis of selected technique factors (tube potential and current) and information about patient location relative to the x-ray tube. Simulations were performed to measure the system accuracy with an angiographic anthropomorphic head phantom with the skin exposures measured with an ionization chamber. Skin doses were computed for 114 consecutive patients who underwent diagnostic and interventional neuroradiologic procedures. RESULTS: Agreement between measured and computed skin exposures in fluoroscopy, plain radiography, and digital imaging was generally within 5% of the true skin dose. For all fluoroscopic and radiographic procedures, total median skin doses were 1.20 and 0.64 Gy for the frontal and lateral planes, respectively. In both planes, patient skin doses resulted primarily from digital subtraction angiographic acquisitions. In 29 (25%) patients, the skin dose exceeded 2.00 Gy, but no radiation-induced deterministic effects were observed. CONCLUSION: An on-line patient exposure meter can provide accurate radiation skin dose data in patients undergoing diagnostic and therapeutic neuroradiologic procedures.

Angiography↗
PubMed1994

Radiation-induced temporary epilation after a neuroradiologically guided embolization procedure.

A 34-year-old woman underwent embolization of a left paraorbital arteriovenous malformation guided with a bi-plane x-ray system in two sessions separated by 3 days. Imaging included 110 minutes of fluoroscopy and 46 digital subtraction angiography acquisitions. Entrance skin dose rates were determined with measurements performed on a skull phantom. The maximum possible skin dose was estimated to be 6.6 Gy, which is consistent with the temporary epilation in the right occipital region of the skull reported by the patient approximately 5 weeks later.

Adult↗
PubMed1994

Childhood abuse of parents of alcohol and other drug misusing adolescents.

Parental history of childhood physical/sexual abuse was examined among 68 parents of hospitalized middle-class adolescent alcohol/drug misusers and 68 parents of comparable nonhospitalized adolescents. Childhood physical and/or sexual abuse was reported by 54% of control and 48% of patient mothers and 46% of patient and 47% of control fathers, nonsignificant group and gender differences. Abused as compared to nonabused parents reported significantly greater alcohol dependency, more lifetime medical and childhood hyperactivity symptoms, lower levels of socialization, and greater levels of verbal ability, neuroticism, and addiction proneness.

Adolescent↗
PubMed1993

Plasma laudanosine levels in patients given atracurium during liver transplantation.

Atracurium, a nondepolarizing muscle relaxant, does not depend on the liver for clearance, but its principal metabolite, laudanosine, is eliminated primarily by the liver and is potentially neurotoxic. We measured atracurium and laudanosine levels in 15 adult patients during the three stages of liver transplantation to assess the effect of major impairment of liver function. Atracurium was given in a bolus dose of 0.5 mg/kg followed by continuous infusion at a rate adjusted to maintain 95-99% of total neuromuscular block, as judged by train of four response to facial nerve stimulation. Atracurium levels remained constant at 1.4-1.8 micrograms/mL during the 180-min preanhepatic and 75-min anhepatic stages but decreased to a mean of 1.0 microgram/mL by the end of the 180-min postanhepatic stage. In contrast, laudanosine levels increased during each stage, being 0.40 +/- 0.18, 0.50 +/- 0.22, and 0.43 +/- 0.16 micrograms/mL after the preanhepatic, anhepatic, and postanhepatic stages, respectively. The highest individual value recorded was 1.02 microgram/mL. We conclude that, despite increases in laudanosine levels during each stage of liver transplantation in patients receiving atracurium, those levels are only about one-tenth of the maximum values previously reported in humans.

Adult↗
PubMed1993

Embolization of a dural arteriovenous fistula of the ventral cervical spinal canal in a nine-year-old boy.

A 9-year-old patient presented with an acute left hemiparesis secondary to an intradural hemorrhage of the cervical spinal cord. Angiography revealed a dural arteriovenous (AV) fistula with multiple venous aneurysms fed by a radicular branch of the right vertebral artery. This AV fistula did not contribute blood flow to the cervical segment of the spinal cord, which was tested by an intra-arterial injection of methohexital. Interruption of the fistula was possible by transluminal embolization with polyvinyl alcohol and silk. At a 6-month follow-up, the patient was neurologically intact, and angiography demonstrated no AV fistula. This case illustrates an unusual presentation of a dural AV fistula. Dural AV fistulas are rare in the cervical region and extremely unusual in patients less than 20 years of age. The lesion proved to be amenable to transluminal embolization alone, without the need for surgery, with a dramatic resolution of the neurological deficit.

Acute Disease↗
PubMed1992

Freeze-substitution of chemically stabilized samples for biological field emission scanning electron microscopy.

The high resolution imaging capabilities of modern field emission scanning electron microscopes require adequately improved tissue preparation procedures to prevent the collapse of macromolecular structures and the extraction of molecules. A routine cryo-stabilization technique is described which utilizes chemical crosslinking and cryo-dehydration for mechanical and chemical stabilization of protein and lipid structures and increase of electrical conductivity of the sample. Thiocarbohydrazide (TCH) serves as a general mordant for osmium tetroxide crosslinking. However, extensive washing after all impregnation steps is necessary to dissolve unspecific osmium black precipitations at the sample surface. Collagen I aggregates showed increased stability against collapse after TCH osmification alone, whereas pulmonary surfactant liposomes require additional freeze-substitution in methanol and Freon 113 for stabilization during critical point drying. Environmental scanning electron microscopy (at water vapor pressures of 5-10 torr within the specimen chamber) was used to control, in the wet phase, the stabilization procedure at the level of chemical crosslinkage. It could be confirmed that tannic acid, often used to stabilize lipids, leads to artificial rearrangement of bilayered liposomes into compact presumable multilayered bodies, whereas the TCH osmification preserved liposome structures and their aggregates. The increase of electrical conductivity of sliced tissue was demonstrated on kidney. Support technologies for the cryo-stabilization procedures are described in detail, as well as simple routines for first stabilization trials with new samples. On pulmonary tissue, the excellent preservation of alveolar shape and fine structures of intermediate forms of surfactant are described.

Animals↗
PubMed1992

Lecture practices in United States anesthesiology residencies.

We obtained data on lecture practices from 100 of the 110 university-affiliated anesthesiology residency programs certified in the United States in 1988. Of these residency programs, 36% had a majority of their lectures before the operating room schedule began, 57% had no lectures at all in this early time slot, and 78% had morning lectures at least once a week in conjunction with a delayed operating room start. Seventy-one percent of programs had one or more afternoon lectures each week. An attendance of more than 80% was reported in 66% of the programs for morning lectures and in 50% of the programs for afternoon lectures, which is a significant difference. Aggregate pass rates on the American Board of Anesthesiology written examinations in 1987 and 1988 correlated significantly with morning-lecture attendance, but not with afternoon-lecture attendance, number of lecture days per week, or mandatory lecture attendance. These findings suggest the need for further study and definition of the role of lectures in resident education in anesthesiology.

Anesthesiology↗
PubMed1991

Persistent nidus blood flow in cerebral arteriovenous malformation after stereotactic radiosurgery: MR imaging assessment.

Stereotactic radiosurgery has become a major force in the treatment of arteriovenous malformations (AVMs) of the brain. After treatment, obliteration of flow through the malformation occurs in 75%-85% of cases within 2 years, assuming the entire AVM nidus can be encompassed by the radiation field. Because the follow-up period is relatively long, a noninvasive means to assess residual transnidus blood flow is desirable. The authors report favorable findings after a comparative analysis of 85 posttreatment magnetic resonance images and 27 follow-up cerebral arteriograms in 34 patients treated with stereotactic radiosurgery. The authors found that transnidus flow can be determined from apparent signal intensity differences between tandem two-dimensional gradient-recalled echo images obtained first without and then with gradient moment nulling (flow compensation), with empirically derived pulse parameters. This method provides a means to monitor the reduction in AVM matrix size and to assess the extent of persistent arteriovenous shunting (ie, blood flow) across the nidus.

Brain↗
PubMed1989

Alcohol use by heroin addicts: evidence for an inverse relationship. A study of methadone maintenance and drug-free treatment samples.

This study examines the relationship between the patterns of use of alcohol and heroin by narcotics addicts, and evaluates the hypothesis--frequently reported during methadone maintenance--that this form of treatment can be causally implicated in an increased consumption of alcohol. Data were obtained on lifetime patterns of alcohol and heroin use of 375 Anglo and Chicano male addicts sampled from two treatment sources: the nonmethadone (drug-free) California Civil Addict Program (CAP) and several Southern California Methadone Maintenance (MM) programs. Repeated-measures MANOVAs revealed that alcohol and heroin consumption were inversely related throughout the addicts' careers. This pattern was evident in the addiction, treatment, and postdischarge stages of Anglo and Chicano addict careers, in both the CAP and MM samples. Consequently, the authors reject the hypothesis that increased alcohol consumption is caused solely by addicts' participation in methadone maintenance treatment. Rather, the findings suggest that addicts' alcohol use during methadone treatment reflects a lifetime pattern of increased alcohol use following any decline in heroin intake.

Adult↗
PubMed1988

Outpatient pediatric neurosurgery.

In a 16-month period, 31 children underwent outpatient operations for a variety of neurosurgical problems. None of the patients experienced any anesthetic complications. One patient was admitted for management of a surgical complication and was discharged uneventfully 4 days later. A saving of at least 49.5% in hospital charges was produced when surgery was performed in the outpatient surgical facility, and a 19.8% reduction in costs was achieved when the main hospital operating suite was used on an outpatient basis. Neurosurgical procedures can be safely and inexpensively performed on an outpatient basis, even in children.

Ambulatory Care↗
PubMed1988

Attachment of plasma membranes of cultured cells to silicon chips for high magnification imaging in scanning electron microscopy.

In the membrane preparation method described in this paper, a polylysine-coated silicon chip is adsorbed to the exposed apical surface of a cell monolayer. Upon removal, the adsorbed chip separates the plasmalemma from the residual bodies of the cultured cells. This sandwich-membrane separation approach simplifies access to the cytoplasmic aspects of both the apical and the basal plasmalemma which remains on the culture substrate and is covered to a varied extent by cytoplasmic infrastructures. To stabilize the attached membranes, small crosslinking agents are used in a controlled osmium impregnation. Large crosslinkers are avoided since they induce thickening of fine structures. Optimal conditions for attachment of plasmalemma of cultured adrenal endothelial cells to the cationic chip are defined. Effective cleaning procedures of the chips and useful molecular weights of polylysine are determined by quantitating colloidal gold adherence to the surface of the chips. The specimens are examined by high resolution scanning electron microscopy.

Adrenal Cortex↗
PubMed1986

The endothelial pocket. A new structure in fenestrated endothelia.

A new endothelial cell structure, named the endothelial pocket, has been found by combined transmission and scanning electron microscopic studies of renal peritubular capillaries. Transmission EM observations made on these and other fenestrated capillaries demonstrated that each pocket consists of an attenuated fold of fenestrated endothelium that projects approximately 200 nm into the lumen above the rest of the endothelial surface. Beneath this luminal fold, there is a space and then another layer of fenestrated endothelium which abuts the basal lamina. The linear density of endothelial pockets was measured in the capillaries of the kidney cortex, intestinal mucosa and exocrine pancreas in mice and determined to be 0.067, 0.017 and 0.007 pockets X micron-1 respectively. Cationic ferritin decoration of the anionic sites on the luminal surface of the endothelium in these capillary beds revealed that both unlabelled and labelled diaphragms are clustered. In such specimens, the majority of the luminal diaphragms on endothelial pockets did not have cationic ferritin binding sites detectable by either scanning or transmission EM. On this account as well as on account of their general morphology, endothelial pockets appear to be multifold versions of the simple transendothelial channel.

Animals↗