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Biomedical subjects

D L Johnson

Publications and source records attributed to D L Johnson.

At least 253 records · Page 14Linked to original sources
PubMed1987

Intracranial metastases from malignant spinal-cord astrocytoma. Case report.

A patient with postoperative intracranial seeding from a malignant spinal-cord astrocytoma is presented. This case is compared with 17 previously cited cases of intracranial dissemination from spinal-cord astrocytoma. Factors associated with tumor dissemination include histological malignancy, proximity of the tumor to cerebrospinal fluid (CSF) pathways, and surgical manipulation. Hydrocephalus with infiltration of the basal cisterns also appears to be a consistent feature in these patients. Cytological studies of the CSF in this and previous cases were noted to be misleading, whereas intravenous contrast-enhanced cranial computerized tomography was invaluable for diagnosis of tumor dissemination in each case. Prophylactic irradiation of the entire neuraxis may limit intracranial metastases from malignant astrocytomas of the spinal cord.

Brain↗
PubMed1987

Free radical scavengers improve functional recovery of stunned myocardium in a model of surgical coronary revascularization.

This study examined whether treatment with the oxygen free radical scavengers, superoxide dismutase and catalase, could improve functional recovery in hearts subjected to regional ischemia and global cardioplegic arrest. Regional left ventricular (LV) function was assessed in open chest pigs with sonomicrometry and micromanometry to calculate an index of regional work from the LV pressure-segment length relationship. After measuring baseline preischemic function, the left anterior descending artery was occluded, creating a region-at-risk in 20% of the LV mass. Cardiopulmonary bypass was begun 15 minutes after initiation of regional ischemia and was followed immediately by cardioplegic arrest for 45 minutes, after which time the coronary artery occluder was removed to simulate coronary revascularization. Starting just before removal of the aortic cross-clamp and continuing for the first 30 minutes of reflow, animals received an aortic root infusion of either superoxide dismutase (3600 U/kg) and catalase (20,000 U/kg) or a control saline solution infusion. In each group, seven animals were successfully weaned from cardiopulmonary bypass without inotropic support. After 2 hour of reperfusion, the recovery of baseline function in the region-at-risk was 44% +/- 7% in the treated animals and 4% +/- 13% in the untreated animals (p less than 0.05). In this experimental model, oxygen free radical scavengers were effective in preserving functional recovery in regionally ischemic myocardium reperfused under conditions simulating surgical revascularization in the setting of acute myocardial ischemia.

Animals↗
PubMed1986

Observer error in blood pressure measurement.

This paper describes an experiment undertaken to determine observer error in measuring blood pressure by the auscultatory method. A microcomputer was used to display a simulated mercury manometer and play back tape-recorded Korotkoff sounds synchronized with the fall of the mercury column. Each observer's readings were entered into the computer, which displayed a histogram of all readings taken up to that point and thus showed the variation among observers. The procedure, which could easily be adapted for use in teaching, was used to test 311 observers drawn from physicians, nurses, medical students, nursing students and others at nine health care institutions in Ottawa. The results showed a strong bias for even-digit readings and standard deviations of roughly 5 to 6 mm Hg. The standard deviation for the systolic readings was somewhat smaller for the physicians as a group than for the nurses (3.5 v. 5.9 mm Hg). However, the standard deviations for the diastolic readings were roughly equal for these two groups (approximately 5.5 mm Hg).

Auscultation↗
PubMed1986

Preparation and characterization of a viral DNA molecule containing a site-specific 2-aminofluorene adduct: a new probe for mutagenesis by carcinogens.

The synthetic oligonucleotide heptamer 5'-ATCCGTC-3' was reacted in vitro with N-acetoxy-N-(trifluoroacetyl)-2-aminofluorene and the resulting product isolated by reverse-phase high-performance liquid chromatography (HPLC). This purified oligonucleotide, which was shown by chemical and enzymatic analysis to be a heptamer containing a single N-(deoxyguanin-8-yl)-2-aminofluorene adduct, was then used to situate the putatively mutagenic aminofluorene lesion within the genome of M13 mp9 by ligating it into a complementary single-stranded region located at a specific site in the negative strand of the duplex M13 mp9 DNA molecule. The presence of the adduct at the anticipated location was confirmed by taking advantage of the facts that AF adducts inhibit many restriction enzymes when located in or near their restriction sites and that the AF moiety should be contained within the HincII recognition sequence on M13 mp9 DNA. Upon attempted cleavage of the M13 DNA containing the site-specific AF adduct with HincII, we find that the large majority of the DNA remained circular, demonstrating the incorporation of the AF adduct in high yield into the DNA molecule at this location. This system should prove useful in vivo for the study of mutagenesis by chemical carcinogens and in vitro to study the interaction of purified DNA metabolizing proteins with a template containing a site-specific lesion.

Base Sequence↗
PubMed1986

Measurement of adenosine triphosphate and 2,3-diphosphoglycerate in stored blood with 31P nuclear magnetic resonance spectroscopy.

Conditions for blood storage are chosen to assure adequate levels of adenosine triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG). Because of the invasive nature of the techniques, biochemical assays are not routinely used to measure levels of these compounds in stored blood. However, 31P NMR spectroscopy measures phosphorylated intermediates in intact cells and could be used without disruption of the storage pack. We compared levels of ATP and 2,3-DPG measured by 31P spectroscopy and standard enzyme-linked biochemical assays in whole blood (WB) and packed red blood cells (PRBCs) at weekly intervals during a 35-day storage period. NMR demonstrated a marked decrease in 2,3-DPG and an increase in inorganic phosphate after the first week of storage. No significant differences in ATP concentrations were seen in WB during the storage period, but a significant decrease in ATP in PRBCs was documented. There was good agreement in levels of ATP and 2,3-DPG measured by NMR and biochemical techniques. 31P NMR spectroscopy is a noninvasive technique for measuring ATP and 2,3-DPG which has a potential use in quality assurance of stored blood.

2,3-Diphosphoglycerate↗
PubMed1986

Tissue distribution properties of technetium-99m-diamide-dimercaptide complexes and potential use as renal radiopharmaceuticals.

A series of new ligands and the corresponding technetium-99m chelates based on diamide dimercaptide donor groups were synthesized as derivatives of technetium-99m 1,2-bis(2-thioacetamido)ethane, a complex shown to be excreted by renal tubular secretion. Chelation with 99mTc resulted in single radiochemical products or the expected numbers of stereoisomers. They were purified by high-performance liquid chromatography (HPLC) and evaluated in mice as potential renal tubular function agents. The in vivo properties were sensitive to the presence of functional groups, the positional isomerism of the carboxylate group functionality, and the chelate ring stereochemistry of the ligand. The presence of methyl groups slowed renal transit and decreased renal specificity. Cyclohexyl rings fused to the ethylene bridge of the center chelate ring decreased renal excretion while aromatic rings essentially abolished renal excretion. Slow hepatobiliary clearance was observed as an alternate mode of excretion. Polar groups, such as hydroxyl, carboxylate, and carboxamide, increased renal excretion rates and specificity in a stereochemically dependent manner. 99mTc chelates of 1,3-bis(2-thioacetamido)-2-hydroxypropane, 3,4-bis(2-thioacetamido)butanoate and 1,8-dimercapto-2,7-dioxo-3,6-diazanonanoate were identified as promising new renal radiopharmaceuticals.

Amides↗
PubMed1986

Contours of the edentulous palate.

Diagnostic casts were made of the palates of 123 patients who had complete dentures. Categorization of all cross-arch palatal forms yielded a distribution in which 93% showed some variation of a U-shaped palatal form, be it angular or mildly curved. Along the midline, 12% had steep anterior inclines, curved midpalatal regions, and curved posterior palates; 69% had moderate anterior inclinations, curved midpalates, and curved posterior palates; 12% had palates that were moderately inclined anteriorly, flat in the midpalatal section, and flat posteriorly. The remaining palates were predominantly flat in two of the three regions measured.

Cephalometry↗
PubMed1986

Relationship of scores on PPVT-R and WISC-R with special education children and youth.

Comparisons of the Peabody Picture Vocabulary Test-Revised and the Wechsler Intelligence Scale for Children-Revised were made with 104 children diagnosed as learning disabled and mentally retarded. Significant but modest correlations were found between all but one of the WISC-R scaled scores (i.e., Coding) and PPVT-R standard scores, and between WISC-R IQs and PPVT-R standard scores. Significant differences were found among mean Verbal, Performance, and Full Scale IQs and mean PPVT-R standard scores. The PPVT-R standard scores underestimated WISC-R Verbal IQs by 7 points, WISC-R Performance IQs by 17 points, and WISC-R Full Scale IQs by 11 points.

Adolescent↗
PubMed1986

Perimesencephalic cistern obliteration: a CT sign of life-threatening shunt failure.

Death from cerebrospinal fluid shunt malfunction is a rare but tragic event. The authors describe seven children who when admitted were lethargic but arousable because of shunt failure. Sudden deterioration prompted unscheduled emergency shunt revision in each case. Two children subsequently died. Although neither the history nor the physical findings predicted this life-threatening shunt malfunction, obliteration of the perimesencephalic cistern was apparent on all preoperative computerized tomography (CT) scans. For reference, the scans of 43 other hydrocephalic children were drawn randomly from the hospital files and analyzed. It is concluded that CT evidence of obliteration of the perimesencephalic cistern is a useful warning of life-threatening shunt failure.

Adolescent↗
PubMed1986

Synthesis and biological evaluation of technetium-99m MAG3 as a hippuran replacement.

A new technetium-chelating agent based on a triamide monomercaptide tetradentate set of donor groups, mercaptoacetylglycylglycylglycine (MAG3), was synthesized and evaluated. Chelation with 99mTc resulted in a single radiochemical product as expected. Studies in mice of [99mTc]MAG3 indicated excretion rates faster than omicron-iodohippurate (OIH) both in normal and in probenecid treated animals. Specificity for renal excretion was essentially complete. Clearance studies in rats resulted in 2.84 ml/min/100 g for [99mTc]MAG3, 2.17 for OIH, and 1.29 for [125I]iothalamate. Extraction efficiencies were 85% for [99mTc]MAG3, 69% for OIH and 39% for [125I]iothalamate. Probenicid depressed the clearance both of [99mTc]MAG3 and OIH at 25 and 50 mg/kg/hr, but to a greater extent with [99mTc]MAG3. The greater effect is offset, however, by the larger fraction secreted by the renal tubular cells. The animal results suggest that [99mTc]MAG3 may be a useful alternative to [131I]OIH.

Animals↗
PubMed1985

An evaluation system for teaching clinical removable prosthodontics.

The continuous assessment and updating of clinical evaluations are integral aspects of dental education. The purpose of this article was to describe the development, implementation, and assessment of an evaluation system for clinical removable prosthodontics. A system based on a three-point scale (RST) was adopted and implemented with the intent of maximizing evaluation effectiveness while minimizing stress on students and faculty members. To date, the RST system has improved both the quality of clinical evaluation and the level of clinical learning. The RST clinical evaluation system appears to be defusing students' ardent quests for grades while promoting the teaching potential within the evaluation process. The system also stimulates student self-evaluation, improves the consistency of faculty grading, facilitates student counseling, and permits an in-depth analysis of the evaluation system at regular intervals.

Clinical Competence↗
PubMed1985

Trilateral retinoblastoma: ocular and pineal retinoblastomas.

Trilateral retinoblastomas, the syndrome of bilateral retinoblastoma associated with ectopic retinoblastoma in the pineal gland, is rare but well recognized. In contrast to bilateral retinoblastomas alone, the ocular retinoblastomas in trilateral retinoblastoma develop before the age of 6 months, and a family history positive for retinoblastoma is usually obtained. The retinal tumors are often quiescent at the time that the pineal tumor is discovered, and show no evidence of metastatic spread after enucleation of the globes. Pathologically, the pineal tumor is indistinguishable from the ocular retinoblastoma. The pathophysiology of this syndrome is not well understood, but a germinal mutation is thought to target photoreceptor tissue for further postzygotic mutation. Eventual expression depends on the inherited host resistance to the carcinogenic manifestation of these genes. The low host resistance of trilateral retinoblastoma is evident by the early age of presentation, the multicentric occurrence of the tumor, and the high early mortality rate despite aggressive management.

Brain Neoplasms↗