Search PubMed⌕ Search

Biomedical subjects

M D Smith

Publications and source records attributed to M D Smith.

At least 343 records · Page 19Linked to original sources
PubMed1993

A biomechanical analysis of atlantoaxial stabilization methods using a bovine model. C1/C2 fixation analysis.

The reliability and initial postoperative stability of six widely used C1-C2 surgical constructs were evaluated by nondestructive biomechanical testing of ten fresh bovine upper cervical spine segments. The six fixation techniques were the simple midline sublaminar C1 wiring (SMW), the modified Gallie wiring (MGW), the Brook wedge arthrodesis (BWA), the bilateral lateral mass screw (LMS), and the Clark arthrodesis without (CWO) and with (CW) the adjunctive use of polymethylmethacrylate (PMMA) cement. Instability was produced by resection of the base of the dens. Intact, destabilized, and instrumented constructs were tested in unconstrained flexion, extension, torsion, anterior, and posterior shear forces. The LMS and CW techniques proved the most effective in achieving C1-C2 stability. Sublaminar C2 wiring methods tended to have greater torsional and shear stiffness. Less rigid fixation techniques frequently loosened. All non-PMMA-enhanced wired constructs failed to restore the ability to adequately resist the posterior translation of C1 on C2. Stabilization of an unstable atlantoaxial articulation is best accomplished by a lateral mass screw or sublaminar C1-C2 PMMA-enhanced technique. Other techniques provided less consistent and reliable surgical fixation. Because of the inadequacy of wired constructs to resist posterior shear in patients with this instability pattern, the usual treatment may need to be modified to include more prolonged or protective external immobilization or more rigid fixation techniques. Although less rigid, the SMW and the MGW techniques are safer because they require less-frequent passage of sublaminar wires, avoid potential problems with PMMA, and obviate the hazards of further lateral dissection and insertion of the transarticular screws.

Animals↗
PubMed1992

Cloning and characterization of genes for the PvuI restriction and modification system.

The genes encoding the endonuclease and the methylase of the PvuI restriction and modification system were cloned in E.coli and characterized. The genes were adjacent in tandem orientation spanning a distance of 2200 bases. The PvuI endonuclease was a single polypeptide with a calculated molecular weight of 27,950 daltons. The endonuclease was easily detectable when the gene was expressed from its endogenous promotor and present on a low copy plasmid, but expression was considerably enhanced when the endonuclease gene was placed under the control of a strong promoter on a high copy plasmid. The methylase did not completely protect plasmid DNA from R.PvuI digestion until the methylase gene was placed under lac promotor control in a multicopy plasmid. In the absence of the M.PvuI methylase, expression of the R.PvuI endonuclease from the lac promotor on a multicopy plasmid was not lethal to wild type E.coli, but was lethal in a temperature-sensitive ligase mutant at the non-permissive temperature. Moreover, induction of the R.PvuI endonuclease under lambda pL promotor control resulted in complete digestion of the E.coli chromosome by R.PvuI.

Base Sequence↗
PubMed1992

Quantitative evaluation of the growth of established cell lines on the surface of collagen, collagen composite and reconstituted basement membrane.

As a step in the development of a system for assessing growth of human urothelium and transitional cell carcinoma, the growth of two established cell lines on collagen-based membranes has been evaluated. HT1080 (metastatic human fibrosarcoma) and WI38 VA13 (virus-transformed human fibroblasts) were grown on substrates of collagen, collagen/hyaluronic acid or chondroitin sulphate and reconstituted basement membrane (Matrigel). Cell growth was quantified using a new fluorimetric assay utilizing carboxyfluorescein diacetate. There were differences in morphology between cells grown on collagen and those grown on polystyrene. There were, however, no differences in growth of the WI38 VA13 cells on collagen compared with polystyrene, but growth of the HT1080 cells was increased on membranes of collagen/2.5% hyaluronic acid and collagen/5% chondroitin sulphate, and decreased on Matrigel. Adequate growth on collagen substrates is dependent on cell line. The fluorimetric assay used was suitable for quantifying cell growth on such substrates.

Basement Membrane↗
PubMed1992

Temporal variability of color Doppler jet areas in patients with mitral and aortic regurgitation.

The temporal variability of color flow jets during regurgitation has not been systematically examined. We therefore analyzed color Doppler images in 52 patients (29 with mitral regurgitation and 23 with aortic regurgitation) for frame-to-frame variability in the size of the regurgitant color jet. Planimetered jet areas varied markedly throughout the flow period, with the difference between the largest and smallest mitral regurgitant jets ranging from 1.1 to 11.9 cm2 in individual patients. Maximal and minimal aortic regurgitant jets varied from 1.5 to 6.6 cm2 between frames. The point during the cardiac cycle at which the largest regurgitant jet area was recorded also varied markedly for mitral and aortic lesions. Mitral regurgitant jets peaked at 51% of systole, with a range from 9% to 100%. The point during diastole at which the maximal aortic regurgitant jet was recorded varied from 2% to 84%, with a mean of 31.2% of the diastolic period. The persistence of the flow disturbance was examined as the percent of systole or diastole during which the maximal jet area remained at least 50% or 75% of its maximal size. Mitral regurgitant jets remained at least one-half maximal size for a mean of 60.7% (range, 20% to 90%) of systole, but remained at 75% of maximal size for a mean of only 39% of systole. Aortic regurgitant jets persisted at over one-half maximal size for a mean of 63.2% (range, 30% to 90%) of diastole, but sustained 75% of maximal size for a mean of only 44% of diastole.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve↗
PubMed1992

An evaluation of the Hamo LS-76 washing, drying and disinfecting machine for anaesthetic equipment.

This report evaluates a machine designed to wash, disinfect and dry anaesthetic equipment. Following adjustments to the program these objectives could be reliably achieved within a reasonable time. Multifunction machines should be considered for future use in Sterile Service Departments, although a careful assessment of the workload capacity should be made before purchase.

Anesthesiology↗
PubMed1992

Value and limitations of transesophageal echocardiography in determination of left ventricular volumes and ejection fraction.

Several formulas exist for estimating left ventricular volumes and ejection fraction using conventional two-dimensional echocardiography from transthoracic views. Transesophageal imaging provides superior resolution of endocardial borders but employs slightly different scan planes. The estimation of left ventricular volumes by transesophageal echocardiography has not been validated in human patients. Therefore, the purpose of this study was to compare left ventricular volumes and ejection fraction derived from transesophageal short-axis and four-chamber images with similar variables obtained from ventriculography. End-diastolic and end-systolic volumes and ejection fraction were calculated using modified Simpson's rule, area-length and diameter-length models in 36 patients undergoing left ventriculography. Measurements of left ventricular length were obtained from the transesophageal four-chamber view and areas and diameters were taken from short-axis scans at the mitral valve, papillary muscle and apex levels. Data from transesophageal echocardiographic calculations were compared with end-diastolic volume (mean 172 +/- 90 ml), end-systolic volume (mean 91 +/- 74 ml) and ejection fraction (mean 52 +/- 15%) from cineventriculography using linear regression analysis. The area-length method (r = 0.88) resulted in a slightly better correlation with left ventricular end-diastolic volume than did Simpson's rule (r = 0.85) or area-length (r = 0.84) formulas. For end-systolic volume, the three models yielded similar correlations: Simpson's rule (r = 0.94), area-length (r = 0.93) and diameter-length (r = 0.95). Each of the methods resulted in significant underestimation of diastolic and systolic volumes compared with values assessed with angiography (p less than 0.003). Ejection fraction was best predicted by using the Simpson's rule formula (r = 0.85) in comparison with area-length (r = 0.80) or diameter-length (r = 0.73) formulas. Measurements of left ventricular length by transesophageal echocardiography were smaller for systole (mean 5.7 +/- 1.6 cm) and diastole (mean 7.7 +/- 1.2 cm) than values by ventriculography (mean 9.2 +/- 1.4 and 8.1 +/- 1.6 cm, respectively; p less than 0.0001), suggesting that underestimation of the ventricular length is a major factor contributing to the smaller volumes obtained by transesophageal echocardiography. In conclusion, currently existing formulas can be applied to transesophageal images for predicting left ventricular volumes and ejection fraction. However, volumes obtained by these models are significantly smaller than those obtained with angiography, possibly because of foreshortening in the transesophageal four-chamber view.

Adult↗
PubMed1992

Stress Doppler echocardiography in the evaluation of ischemic heart disease.

Doppler echocardiography enables convenient, noninvasive evaluation of global, systolic performance at rest and during exercise. Early studies suggested that Doppler parameters of systolic function were sensitive to exercise-induced myocardial ischemia and could identify patients with severe coronary artery disease. Subsequent investigation, however, has identified several factors in addition to myocardial ischemia that can significantly influence exercise Doppler study results. Thus, in order to obtain reliable information, the many factors that can influence Doppler measurements of aortic flow velocity and acceleration must be accounted for. Further work in this area is likely to produce results that encourage greater application of this technique in experimental and clinical research. At present, the role of stress Doppler echocardiography in the evaluation of ischemic heart disease remains uncertain.

Coronary Disease↗
PubMed1992

Effect of adding cognitively demanding tasks on soccer skill performance.

The effect of adding cognitively demanding elements to the performance of a real-world motor task in which functional interference among the elements in performance existed was investigated across level of expertise. The primary task involved running as quickly as possible through a 15.25-m slalom course. Two secondary tasks were used, dribbling of a soccer ball and identification of geometric shapes projected on a screen located at the end of the slalom course. 4 novice, 5 intermediate, and 5 expert female soccer players served as subjects and performed three trials each of three experimental conditions: running through the slalom course, running through the slalom course while dribbling a soccer ball, and running through the slalom course while dribbling a soccer ball and identifying geometric shapes. Analysis of variance using a 3 (experimental condition) x 3 (level of expertise) design gave significant main effects and a significant interaction. The latter indicated that, although the addition of cognitively demanding elements caused a decrement in performance, the amount of decrement decreased as level of expertise increased. It was concluded that structural interference between elements of performance decreased the positive effect of automation of one element on dual task performance.

Adolescent↗
PubMed1992

Immunohistochemical analysis of synovial membranes from inflammatory and non-inflammatory arthritides: scarcity of CD5 positive B cells and IL2 receptor bearing T cells.

Rheumatoid Arthritis (RA) synovial membranes were examined by single and dual immunohistological techniques with a number of monoclonal antibodies against lymphocyte and macrophage related antigens. CD4 positive T lymphocytes frequently expressed MHC Class II antigens and were found in sublining collections in close association with activated macrophages as well as B lymphocytes. CD8 positive T cells surrounded these collections as well as being scattered throughout the membrane and also frequently expressed MHC Class II antigens. IL2 receptor (IL2r) expression on T cells and CD5 expression on B cells were rarely seen in these synovial membranes. Similar immunohistological architecture was found in synovial membranes from patients with psoriatic arthritis (PA) and Reiter's Syndrome (RS). Normal synovium contained few T cells, with few cells expressing MHC Class II antigens. Synovium from osteoarthritis (OA) patients also demonstrated similar immunohistological changes to those found in inflammatory arthritides, suggesting that there are only quantitative rather than qualitative differences between the synovial membrane immunohistological architecture from patients with inflammatory and noninflammatory arthritides.

Adult↗
PubMed1992

A sex-specific analysis of correlates of homicide victimization in United States cities.

A considerable amount of research has been devoted to determining structural correlates of homicide across places in the United States. However, recent research has found that general correlates may not hold when homicide rates are disaggregated into analysis of specific groups. Adopting a public health approach, we explore the possibility that male and female rates of homicide victimization may show differential patterns of association with selected social-structural risk factors across a sample of U.S. central cities. The results show that both male and female homicide victimization is related to a general set of factors derived from the theoretical framework of social disorganization. At the same time, it is found that these factors are better predictors of male than female homicides. Suggestions are made for research to discern additional factors, perhaps distinct from those of men, related to the rather considerable variation in the prevalence of female homicide across communities in the United States.

Adolescent↗
PubMed1992

Proximal femoral bone density and its correlation to fracture load and hip-screw penetration load.

The bone mineral density of 22 random, fresh proximal human femora was estimated by roentgenography using the Singh index (SI) and measured using a regional bone mineral density computed tomographic protocol. Uniaxial compression was used to produce an impacted subcapital fracture. The femoral heads then were isolated and mounted on a sliding screw plate compression device and loaded to failure in a push-out or hip-screw penetration mode. Wide intraobserver variation, poor reproducibility, and poor prediction of the experimental fracture properties of the proximal femur were noted for SI values. Regional bone mineral density provided a reliable estimate of both the gross fracture loads and hip-screw penetration loads. In addition, there was a high correlation between trabecular density and the experimental fracture properties of the proximal femur. Therefore, The validity of the SI as an indicator of the mechanical properties of the proximal femur should be reconsidered.

Biomechanical Phenomena↗
PubMed1992

Novel quantitative methods for the determination of biomaterial cytotoxicity.

Two novel methods for the determination of biomaterial cytotoxicity using cell culture are presented. The methods combine a standardized protocol for producing extracts from medical devices with either the established MTT assay or a new fluorimetric assay. The suitability of both methods for evaluating the toxicity of candidate materials was demonstrated by resolution of the differences in the toxic effects of serial dilutions of a PVC extract on BHK21 and HT1080 cells. The tests yield highly reproducible, quantitative results and can be applied to materials in the usual physical forms applicable to artificial organs.

Animals↗