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Biomedical subjects

A M Peterson

Publications and source records attributed to A M Peterson.

At least 19 recordsLinked to original sources
PubMed2002

Venous angioma adjacent to the root entry zone of the trigeminal nerve: implications for management of trigeminal neuralgia.

Detection of a venous angioma at the root entry zone is important for surgical planning, so that the neurosurgeon will be aware that both veins and arteries may require microvascular decompression. In selected cases, alternative treatment may be indicated to avoid the potential surgical complication of a venous infarct. Trigeminal neuralgia typically occurs in the middle-aged to elderly population, usually the result of compression of the trigeminal nerve at its root entry zone by an ectatic, aging artery or, less commonly, a regional vein [1, 2, 3]. When associated with a venous angioma at the root entry zone, trigeminal neuralgia usually presents at a younger age [4, 5, 6]. We review the imaging examinations and clinical data of five patients with trigeminal neuralgia who had a venous angioma adjacent to the root entry zone of the trigeminal nerve, and discuss how the imaging findings affected their management.

Adult↗
PubMed2002

Cerebral responses to noxious thermal stimulation in chronic low back pain patients and normal controls.

Changes in regional cerebral blood flow (rCBF) have previously been demonstrated in a number of cortical and subcortical regions, including the cerebellum, midbrain, thalamus, lentiform nucleus, and the insula, prefrontal, anterior cingulate, and parietal cortices, in response to experimental noxious stimuli. Increased anterior cingulate responses in patients with chronic regional pain and depression to noxious stimulation distant from the site of clinical pain have been observed. We suggested that this may represent a generalized hyperattentional response to noxious stimuli and may apply to other types of chronic regional pain. Here these techniques are extended to a group of patients with nonspecific chronic low back pain. Thirty-two subjects, 16 chronic low back pain patients and 16 controls, were studied using positron emission tomography. Thermal stimuli, corresponding to the experience of hot, mild, and moderate pain, were delivered to the back of the subject's right hand using a thermal probe. Each subject had 12 measurements of rCBF, 4 for each stimulus. Correlation of rCBF with subjective pain experience revealed similar responses across groups in the cerebellum, midbrain (including the PAG), thalamus, insula, lentiform nucleus, and midcingulate (area 24') cortex. These regions represented the majority of activations for this study and those recorded by other imaging studies of pain. Although some small differences were observed between the groups these were not considered sufficient to suggest abnormal nociceptive processing in patients with nonspecific low back pain.

Adult↗
PubMed2001

Electronic prescribing in ambulatory practice: promises, pitfalls, and potential solutions.

OBJECTIVE: To examine advantages of and obstacles to electronic prescribing in the ambulatory care environment. DATA SOURCES: MEDLINE and International Pharmaceutical Abstract searches were conducted for the period from January 1980 to September 2000. Key words were electronic prescribing, computerized physician order entry, prior authorization, drug utilization review, and consumer satisfaction. In September 2000, a public search engine (www.google.com) was used to find additional technical information. In addition, pertinent articles were cross-referenced to identify other resources. DATA EXTRACTION: Articles, symposia proceedings, and organizational position statements published in the United States on electronic prescribing and automation in healthcare are cited. DATA SYNTHESIS: Electronic prescribing can eliminate the time gap between point of care and point of service, reduce medication errors, improve quality of care, and increase patient satisfaction. Considerable funding requirements, segmentation of healthcare markets, lack of technology standardization, providers' resistance to change, and regulatory indecisiveness create boundaries to the widespread use of automated prescribing. The potential solutions include establishing a standardizing warehouse or a router and gaining stakeholder support in implementation of the technology. CONCLUSIONS: Electronic prescribing can provide immense benefits to healthcare providers, patients, and managed care. Resolution of several obstacles that limit feasibility of this technology will determine its future.

Ambulatory Care Information Systems↗
PubMed2000

Cochlear implantation after labyrinthectomy.

OBJECTIVE: The goal was to report a method used for intraoperative ear selection for cochlear implantation using electrical brainstem response. Initial patient response and the longer-term results of cochlear implantation after labyrinthectomy were compared. STUDY DESIGN: This was a specific retrospective review of a single case of cochlear implantation after labyrinthectomy. SETTING: The study involved a tertiary referral center in both an ambulatory and a hospital setting. PATIENT: The study involved a report of a single patient who was evaluated for a possible cochlear implant and successfully underwent cochlear implantation. INTERVENTIONS: A case study of a profoundly deaf individual is presented, including the diagnostic measures used to determine the candidacy for cochlear implantation, the ear selected, and the rehabilitation. MAIN OUTCOME MEASURES: Both early (3 months) and later (14 months) postoperative results clearly demonstrate that a cochlear implant in a patient with a previous labyrinthectomy can be beneficial. RESULTS: The early and later results after cochlear implantation are compared in a single case study. CONCLUSION: This case study demonstrates that there is improvement in sound awareness, speech recognition, and communication after cochlear implantation in a previously labyrinthectomized ear.

Aged↗
PubMed1999

MR imaging response of brain metastases after gamma knife stereotactic radiosurgery.

PURPOSE: To characterize the magnetic resonance (MR) imaging response of brain metastases after gamma knife stereotactic radiosurgery and determine whether imaging features and tumor response rates correlate with local tumor control and survival. MATERIALS AND METHODS: Serial MR examinations were performed in 48 patients (25 men, 23 women; mean age, 58 years) with 78 lesions. Pretreatment and follow-up enhancing lesion volumes and imaging features were assessed. Rates of response to stereotactic radiosurgery were calculated. Prognostic imaging features affecting local control and survival were analyzed. RESULTS: Local tumor control was achieved in 66 (90%) of 73 metastases at 20 weeks after stereotactic radiosurgery; 61% maintained local control at 2 years. A homogeneous baseline enhancement pattern and initial good response rate (> 50% lesion volume reduction) predicted local control. Five metastases demonstrated a transient volume increase after treatment. The median survival time after stereotactic radiosurgery was 53 weeks and correlated with systemic disease burden and primary tumor type. CONCLUSION: Baseline homogeneous tumor enhancement and initial good response correlate with local control. Initial lesion growth does not preclude local control and may represent radiation-related change. Recognition of these serial MR imaging findings may guide image interpretation and influence treatment in patients with stereotactic radiosurgery-treated metastases.

Adult↗
PubMed1998

Therapeutic-interchange program for oral histamine H2-receptor antagonists.

A therapeutic-interchange (TI) program for oral histamine H2-receptor antagonists at a hospital is described. In 1992 the pharmacy and therapeutics committee at a large teaching hospital accepted cimetidine as the preferred oral H2 antagonist. However, the program to promote cimetidine met with little success. The manufacturer of nizatidine then offered the hospital that drug at a reduced cost relative to all other members of the drug class. The committee recommended including nizatidine on the formulary; implementing a TI program so that when an order for an oral H2 antagonist was written nizatidine would be dispensed; deleting cimetidine and ranitidine tablets from the formulary; and retaining cimetidine and ranitidine oral liquid and i.v. formulations. The program was approved by the medical executive committee and was implemented in August 1994. Extensive efforts to inform the pharmacy, medical, and nursing staffs about the program were undertaken, and the pharmacy established mechanisms for monitoring compliance. Two months into the program, 97% of eligible patients were receiving nizatidine. Actual cost savings in the first four months exceeded $40,000. In July 1997 the same program was applied to famotidine, which had replaced nizatidine as the most cost-effective H2 antagonist. A successful TI program for oral H2 antagonists was achieved by gaining physician support for the program, educating providers, monitoring compliance, and responding to changes in drug costs.

Cimetidine↗
PubMed1998

alpha2-adrenoceptors modulate NMDA-evoked responses of neurons in superficial and deeper dorsal horn of the medulla.

Extracellular single unit recordings were made from neurons in the superficial and deeper dorsal horn of the medulla (trigeminal nucleus caudalis) in 21 male rats anesthetized with urethan. NMDA produced an antagonist-reversible excitation of 46 nociceptive as well as nonnociceptive neurons. Microiontophoretic application of a preferential alpha2-adrenoceptor (alpha2AR) agonist, (2-[2, 6-dichloroaniline]-2-imidazoline) hydrochloride (clonidine), reduced the NMDA-evoked responses of 86% (6/7) of nociceptive-specific (NS) neurons, 82% (9/11) of wide dynamic range (WDR) neurons, and 67% (4/6) of low-threshold (LT) neurons in the superficial dorsal horn. In the deeper dorsal horn, clonidine inhibited the NMDA-evoked responses of 94% (16/17) of NS and WDR neurons and 60% (3/5) of LT neurons. Clonidine facilitated the NMDA-evoked responses in 14% (1/17) of NS, 9% (1/11) of WDR, and 33% (2/6) of LT neurons in the superficial dorsal horn. Idazoxan, an alpha2AR antagonist, reversed the inhibitory effect of clonidine in 90% (9/10) of neurons, whereas prazosin, an alpha1-adrenoceptor antagonist with affinity for alpha2BAR, and alpha2CAR, were ineffective. We suggest that activation of alpha2ARs produces a predominantly inhibitory modulation of the NMDA-evoked responses of nociceptive neurons in the medullary dorsal horn.

Adrenergic alpha-Agonists↗
PubMed1997

Forced choice and ordinal discrete rating assessment of image quality: a comparison.

This study compared a five-category ordinal scale and a two-alternative forced-choice subjective rating of image quality preferences in a multiabnormality environment. 140 pairs of laser-printed posteroanterior (PA) chest images were evaluated twice by three radiologists who were asked to select during a side-by-side review which image in each pair was the "better" one for the determination of the presence or absence of specific abnormalities. Each pair included one image (the digitized film at 100 microns pixel resolution and laser printed onto film) and a highly compressed (approximately 60:1) and decompressed version of the digitized film that was laser printed onto film. Ratings were performed once with a five-category ordinal scale and once with a two-alternative forced-choice scale. The selection process was significantly affected by the rating scale used. The "comparable" or "equivalent for diagnosis "category was used in 88.5% of the ratings with the ordinal scale. When using the two-alternative forced-choice approach, noncompressed images were selected 66.8% of the time as being the "better" images. This resulted in a significantly lower ability to detect small differences in perceived image quality between the noncompressed and compressed images when the ordinal rating scale is used. Observer behavior can be affected by the type of question asked and the rating scale used. Observers are highly sensitive to small differences in image presentation during a side-by-side review.

Fourier Analysis↗
PubMed1996

Mitochondrial cytochrome C oxidase subunit I of Manduca sexta and a comparison with other invertebrate genes.

A cDNA encoding mitochondrial cytochrome c oxidase subunit I (mt COI) from Manduca sexta (Lepidoptera: Sphingidae) was cloned and sequenced. AT (adenine-thymine) content is high and codon usage is biased and likely reflects the role of mt COI in electron transport. The encoded protein is 514 amino acids long, contains seven invariant His residues observed in COIs in all organisms and would be predicted to be composed of 12 transmembrane regions.

Amino Acid Sequence↗
PubMed1995

Long-term patient self-management of oral anticoagulation.

BACKGROUND: The management of oral anticoagulation is fraught with difficulties. This study assessed a new model of anticoagulation management regarding the ability, safety, and efficacy of patients to self-monitor and self-adjust the dose of their oral anticoagulants guided by a capillary whole-blood prothrombin time (PT) monitor. METHODS: This investigation is a retrospective cohort study of 20 patients compared with 20 matched control patients receiving oral anticoagulation at a tertiary medical institution. RESULTS: Study patients monitored their PTs 2153 times during a mean interval of 44.7 months compared with 1608 PTs in matched control patients during a mean interval of 42.5 months. Study patients made an average of 11.5 dosage changes per patient, contrasted with 22.7 changes per control patient (P < .001). The PTs in study patients were within the recommended therapeutic range in 88.6% (95% confidence interval, 87.2 to 89.9) of the determinations compared with 68.0% (95% confidence interval, 65.7 to 70.3; P < .001) of the determinations made by the matched control patients. In response to the 2153 PTs, study patients made 67 (3.1%) dosage decisions that were considered incorrect based on physician guidelines. None of these changes led to adverse outcomes. There was no significant difference in complication rates between the two groups. CONCLUSIONS: Results from what is the first long-term study of patient self-monitoring of PTs and self-adjustment of the warfarin sodium dosage for oral anticoagulation suggest that patients can successfully measure their own PTs, adjust their own warfarin dosage, and achieve a degree of therapeutic effectiveness at least as good, if not better than patients managed in an anti-coagulation clinic. Larger, prospective, randomized trials are needed to confirm the efficacy and safety of this new approach to therapy and to assess its cost-effectiveness.

Administration, Oral↗
PubMed1995

Purification, characterization and cDNA sequence of an alkaline chymotrypsin from the midgut of Manduca sexta.

The chymotrypsin in the midgut of Manduca sexta has been purified, characterized and the cDNA encoding the protein has been cloned. The enzyme exists as a monomer of approx. 24 kDa and shows maximal activity between pH 10.5 and 11.0. Kinetic studies reveal that the Michaelis constant (Km) for the synthetic substrate N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide varies only slightly between pH 7.5 and 11.5 and the Dixon plot shows a kinetically significant pKa at 9.2. The specificity of the purified enzyme was determined to be the peptide bond on the carboxyl side of tyrosine, phenylalanine, tryptophan, histidine, leucine, threonine and glycine. The protease is inhibited by TPCK, PMSF, chymostatin and DFP. A 1 kilobase chymotrypsin cDNA clone was isolated and sequenced. The cDNA sequence encodes a preproenzyme with a putative 17 amino acid signal sequence, a 41 amino acid activation peptide and a mature enzyme of 235 amino acids. The isolated clone encodes the highly conserved active site residues (His, Asp, Ser) and specificity pocket residues present in bovine chymotrypsinogen B. Northern analysis localizes the mRNA for the chymotrypsin to the anterior and middle third of the midgut.

Amino Acid Sequence↗
PubMed1995

Averaged electrode voltages used to identify nonfunctioning electrodes in cochlear implants: case study.

We present the case of an adult male whose internal cochlear implant unit failed. Several months elapsed following initial stimulation with the implant before the problem was identified and corrected. The sequence of the failure and its detection are detailed. Following reimplantation, the patient did not initially report improved sound quality. However, within a week of the initial stimulation of the second device, he reported being able to identify environmental sounds, and speech began to sound the way he remembered it before he lost his hearing. We suggest a method of detection that might improve the early identification of a nonfunctioning device or of nonfunctioning individual electrodes. Knowledge of specific nonfunctioning electrodes is important in device adjustment, especially for young children.

Audiometry, Pure-Tone↗
PubMed1995

Cochlear implantation in the senior citizen age group using the Nucleus 22-channel device.

Cochlear implantation has become a recognized beneficial method of assisting in the rehabilitation of the profoundly deaf individual. The only device that is currently approved by the Food and Drug Administration for implantation in children and adults in the United States is the Nucleus 22-channel device. Since 1988, the Nucleus is the only device that has been implanted at the Mayo Clinic, Rochester, Minnesota. Fifty-six patients ranging in age from 3 to 85 have received implants. Twenty-five (45%) were over 55 and 14 (25%) were 65 or older. All of the patients over 55 are currently using their implants. Several of the patients over 65 are continuing to be gainfully employed. The benefits, complications, and results are addressed.

Adolescent↗
PubMed1995

Vestibular effects associated with implantation of a multiple channel cochlear prosthesis.

This study revealed that some patients with cochlear implants have symptoms of vertigo and imbalance following implant surgery. Although most experience a resolution of these symptoms, some patients have more persistent disturbances of balance. A total of 52 patients were implanted with a Nucleus 22 channel cochlear implant device between September 1988 and February 1994. Preoperatively, all but five of the patients received a vestibular evaluation. Twenty-two of the 52 patients received both pre- and postoperative vestibular evaluation. The cochlear implant was worn and activated during the postoperative vestibular assessment. The vestibular assessment included electronystagmography, computerized dynamic posturography, and harmonic acceleration testing. Five of the 22 patients demonstrated bilateral vestibular weakness preoperatively; that is, no response to caloric stimulation or a total of less than 30 degrees per second for the four irrigations. These patients were not included in the caloric analysis portion of the study. The remaining 17 were divided into groups under 60 years of age (7 patients) and over 60 years of age (10 patients). Analysis of the pre-and postoperative caloric response of the implanted ear showed a significant drop in output for the group over 60 years of age. The difference for the group under 60 years of age was not significant. Forty percent of the patients in the over 60 age group and 43% of those in the under 60 age group developed a peripheral vestibular weakness postoperatively. However, younger individuals in general did not seem to have balance complaints and did not require vestibular rehabilitation as frequently as the older group. Potential cochlear implant candidates should be advised of the possibility of postoperative vestibular effects following cochlear implantation. Most of the symptoms are transient; however, there may be persistent symptoms of imbalance that may be benefited by vestibular rehabilitation.

Adolescent↗