Biomedical subjects

G R Shaw

Publications and source records attributed to G R Shaw.

26 records · Page 2Linked to original sources

PubMed1995

On the detection of QRS variations in the ECG.

Detection of subtle beat-to-beat variations in the morphology of the ECG is complicated by the effects of alignment errors and respiration. A method of directly estimating the alignment error (trigger jitter) from an ECG is derived by relating the variance to the squared slope of the averaged QRS complex. Results based on recordings obtained from 12 normal subjects and alignment performed by the cross-correlation method showed that the alignment errors were dependent upon the choice of the alignment channel, with the best distribution of the errors occurring when alignment was based on the vector magnitude of the three orthogonal leads. The estimated average alignment errors ranged from 0.33-0.42 ms, which were near the optimal value of 0.29 ms based on the sampling rate of 1000 samples/s. It was shown that the effects of respiration could be reduced by normalizing the amplitude of the QRS complexes. It was also estimated that a significant proportion of the variation (0.54-0.67) in the normalized ECG's could be attributed to alignment errors and noise.

Adult↗

PubMed1994

Prediction and monitoring of the carcinogenicity of polycyclic aromatic compounds (PACs).

Chemical carcinogenesis is a multistage process that includes initiation, promotion, and progression. Some carcinogenic PACs have been shown to activate proto-oncogenes and deactivate tumor-suppression genes in the carcinogenic process. The function of DNA repair processes appears to be changed in some cases by PACs. Many PACs are well known for their carcinogenic activity, but for this activity to be exerted, metabolic activation by microsomal enzymes must occur. The enzyme system responsible for PAC activation is the mixed-function oxidase system and, in particular, cytochrome P-450. In the case of PAHs, oxidation predominantly produces reactive diol-epoxides that can then be converted to carbonium ions as the reactive electrophiles that can then covalently bind to DNA. Regions of high activity exist in PAHs, namely, the "bay," "K," and "L" regions which are associated with pi electron distribution. The diol-epoxides can exist in either syn or anti forms, each of which has two enantiomers producing four stereoisomers in all. Energy considerations favor the formation of the anti form. Nitrogen-containing PACs can be metabolically activated in a manner similar to that for PAHs, or the nitrogen atom can be oxidized to form hydroxylamines. These reactive electrophiles can then form covalently bound DNA adducts. The monitoring of DNA adducts has been used in risk assessment for human exposure to PACs. This form of biomonitoring has advantages over the monitoring of external exposure or body levels of the chemicals in question. In the case of PACs, binding to DNA is an important step in the multistage carcinogenic process. The estimation of DNA adducts has been used in the monitoring of humans exposed to PAHs in a wide range of industrial situations. Recent research has shown a dose-response relationship between PAH adduct levels and human cancer, thus developing molecular epidemiology as a relevant science for the field of risk assessment. Techniques have been developed for the determination of DNA adducts and these include immunochemical, fluorescence spectroscopic, GC-MS, and 32P-postlabeling methods. The 32P-postlabeling assay is by far the most sensitive, with limits of detection being of the order of one adduct in 10(10) normal nucleotides. The use of HPLC for separation of adducted nucleotides in this postlabeling assay is becoming more common and gives better resolution of adducts than does the TLC technique used in the traditional assay. The detection of adducts on hemoglobin and other proteins has been used as a surrogate for DNA adduct estimation.(ABSTRACT TRUNCATED AT 400 WORDS)

Carcinogens, Environmental↗

PubMed1993

Systematic comparisons of interpolation techniques in topographic brain mapping.

The performance of one local interpolation technique, the nearest neighbors, and two global spline techniques, one planar and the other spherical, commonly used for topographic mapping of brain potential data has been quantitatively evaluated. The method of evaluation was one of cross-validation where the potential at each site in a 31-electrode full scalp recording montage is predicted by interpolation from the other sites. Errors between the measured potentials and those predicted by interpolation were quantified using 4 measures defined as inaccuracy, precision, bias and tolerance. The evaluation was applied to the background EEGs from 5 normal volunteers and from 4 patients with epilepsy, tumor or stroke. The results indicate that none of the interpolation techniques performed well and that for localized components in the EEG, the errors can increase almost without limit. Further, the global techniques performed significantly better than the local technique with 2 being the best order for the nearest-neighbor technique and 3 for the spline techniques. It is concluded that interpolation should not be used with electrode densities of the order of that provided by the international 10-20 system neither to increase the spatial resolution of the electroencephalogram nor in more sophisticated analysis techniques in quantitative EEG for estimates such as the radial-current density.

Brain↗

PubMed1993

Fatal intravascular synovial sarcoma in a 31-year-old woman.

A 31-year-old woman presented with acute right abdominal pain of 5 hours' duration. Imaging studies showed obstruction and dilatation of the inferior vena cava. The patient suffered a cardiopulmonary arrest; during emergency surgery 230 g of "clot-like" material was removed from the inferior vena cava, right heart, and pulmonary arteries. The patient died the following day. Pathologic examination of the resected material showed a biphasic synovial sarcoma. At autopsy only a minimal amount of residual tumor was present in the wall of the inferior vena cava. Tumor embolization from another site was excluded on the basis of radiologic studies and autopsy findings. This appears to be the second reported case of intravascular synovial sarcoma and the first reported case with a fatal outcome.

Adult↗

PubMed1991

Multisystem failure and hepatic microvesicular fatty metamorphosis associated with tolmetin ingestion.

Multisystem toxicity including both renal and hepatic failure has been reported with the use of nonsteroidal anti-inflammatory drugs. We report a fatal case of multisystem failure associated with tolmetin ingestion in a 15-year-old girl. Microvesicular fatty change was found in the liver at autopsy. To our knowledge, this is the first reported case of nonsteroidal anti-inflammatory drug-associated multisystem failure to have this histopathologic finding.

Adolescent↗

PubMed1987

Comparative kinetics for bioaccumulation of polychlorinated biphenyls by the polychaete (Capitella capitata) and fish (Mugil cephalus).

The bioaccumulation of Aroclors 1242, 1254, and 1260 from sediments by the polychaete (Capitella capitata) and from water by the mullet (Mugil cephalus) was measured in aquarium experiments and followed by clearance investigations. This allowed calculation of the bioaccumulation factor (KB), uptake rate constant (k1), clearance rate constant (k2), and derived half-life (t1/2). The k2 and t1/2 values were of comparable magnitude for each organisms, but k1 values, calculated for polychaetes on the basis of PCB concentrations in whole sediment, were considerably lower, as were the KB values similarly determined. Using the Freundlich equation, an expression was developed for KB assuming that uptake occurred from interstitial water. This expression required the use of empirically developed constants for sedimentary characteristics but gave values for k1 and KB comparable to the values obtained with the fish.

Animals↗

PubMedDate not supplied

Evidence for the presence of a widespread PCDD source in coastal sediments and soils from Queensland, Australia.

Recent studies have demonstrated the occurrence of elevated levels of higher chlorinated PCDDs in the coastal environment of Queensland, Australia. This study presents new data for OCDD contamination and full PCDD/F profile analysis in the environment of Queensland. Marine sediments, irrigation drain sediments and topsoil were collected from sites that were expected to be influenced by specific land-use types. High OCDD concentrations were associated mainly with sediments collected near the mouth of rivers which drain into large catchments in the tropical and subtropical regions. Further, analysis of sediments from irrigation drains could be clearly differentiated on the basis of OCDD contamination, with high concentrations in samples from sugarcane drains collected from coastal regions, and low concentrations in drain sediments from drier inland cotton growing areas. PCDD/F congener-specific analysis demonstrated almost identical congener profiles in all samples collected along the coastline. This indicates the source to be widespread. Profiles were dominated by higher chlorinated PCDDs, in particular OCDD whereas 2,3,7,8-substituted PCDFs were below the limit of quantification in the majority of samples. The full PCDD/F profile analysis of samples strongly resemble those reported for lake sediments from Mississippi and kaolinite samples from Germany. Strong similarities to these samples with respect to congener profiles and isomer patterns may indicate the presence of a similar source and/or formation process that is yet unidentified.

Agriculture↗

PubMedDate not supplied

Techniques to improve flow cytometric detection of light chain restriction.

OBJECTIVE: To compare 3-color flow cytometry (using a permeabilization step to detect cytoplasmic immunoglobulin in selected cases) with 2-color flow cytometry in the detection of light chain restriction (LCR). DESIGN: Analysis of clinical specimens submitted for lymphocyte immunophenotyping using both methods. SETTING: Marshfield Laboratories serving Saint Joseph's Hospital (525 beds) and the Marshfield Health Care Network. MAIN OUTCOME MEASURE(S): Sensitivity and specificity for detecting LCR in B-cell neoplasms. Final diagnosis based on review of clinical, laboratory and histologic data. RESULTS: Of 61 specimens, the 3-color method yielded better sensitivity, detecting LCR in 30 of 39 cases of B-cell neoplasms (77%) versus 16 of 39 (41%) for the 2-color method (P < 0.001). Both methods had comparable specificity (95-100%). The 3-color cytoplasmic technique identified another 4 cases yielding an overall sensitivity of 87% for a 2-tiered testing strategy. CONCLUSION: A 3-color surface technique, backed up by a permeabilization step in selected cases, provides a cost-effective and sensitive technique for detecting LCR.

Cost-Benefit Analysis↗