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Biomedical subjects

R B Ashman

Publications and source records attributed to R B Ashman.

At least 91 records · Page 5Linked to original sources
PubMed1989

Modern perspectives on vaginal candidiasis.

Vaginal thrush is not only a medical problem--it also causes significant psychological and emotional distress, particularly if the infections persist or recur. Women who suffer from frequent recurrences often express dissatisfaction with the treatment they receive, and such comments may be provoked by a lack of awareness on the part of the physician of the natural history of the infection, and of the difficulties inherent in its diagnosis and treatment.

Candidiasis, Vulvovaginal↗
PubMed1988

Elastic modulus of trabecular bone material.

An ultrasonic technique was used to measure both the elastic modulus (Young's modulus) of trabecular bone material and the elastic modulus of the cancellous structure. The average trabecular modulus, measured on specimens obtained from three human and one bovine distal femora, was 13.0 GPa (S.D. 1.47) and 10.9 GPa (S.D. 1.57), respectively. On human specimens the structural elastic modulus was found to be related to the structural (apparent) density raised to the 1.88 power. The elastic modulus from the bovine specimens showed a more linear relationship with the density of the cancellous structure (density raised to the 1.57 power).

Animals↗
PubMed1988

Murine candidiasis: strain dependence of host responses after immunization.

After recovery from acute infection with live Candida albicans, both CBA/H and BALB/c mice show increased resistance to colonization by the organism. However, the 'susceptible' CBA/H mice develop much stronger protective responses than do 'resistant' BALB/c mice. This is manifested particularly as a substantial amelioration of the severity of the lesions in the brain, and a very marked reduction in the number of fungal units therein. Analysis of granulocyte function in normal and immune mice of the two strains tended to exclude this as a basis for the different patterns of susceptibility and resistance.

Animals↗
PubMed1988

Mechanical comparison of anterior spinal instrumentation in a burst fracture model.

This study demonstrates that the broad 4.5 mm dynamic compression plate provides superior stiffness in axial and torsional loading compared to the two anterior rod constructs (Zielke-Slot and Kostuik-Harrington) and the thinner ASIF T-plate in this ex-vivo testing. The Armstrong National Research Council (NRC) plate, designed specifically for anterior spinal instrumentation, has essentially the same mechanical performance characteristics as the broad dynamic compression plate. When placed on the lateral aspect of the vertebral body, these latter two plates lie well away from the anterior vascular structures. Screws are placed slightly off set in the plate, two each in the vertebral bodies immediately above and below the fracture, the screws directed transversely across the vertebral body. The broad DCP plate is easily contoured and implanted, and will allow 1.8 mm of compression to be applied to a strut graft between vertebral bodies. Anterior surgery for the treatment of burst fractures with retropulsed bone provides a means for direct decompression of the spinal canal. With an appropriate implant, additional advantages include instrumentation over a shorter distance (one above and one below the fracture) and no need for further operative procedures to implant or remove posterior implants. Due to their superior stiffness in axial and torsional load, the broad dynamic compression plate and the Armstrong NRC plate appear to fulfill most nearly the ideal attributes of an anterior spinal implant for the treatment of burst fractures of the throacic and lumbar spine.

Aged↗
PubMed1988

Mechanical testing of spinal instrumentation.

Clinically, implant failure is often the result of fatigue from continuous cyclic loading. Because of the inadequacies of long-run cyclic testing, fatigue susceptibility of implants was investigated by means of strain measurements and stress analysis under physiologic loads. The implants were equipped with strain gauges during load-deformation testing, and the tensile stress (the component of stress-producing fatigue failure in metals) was calculated for that site on the implant. For metals most often implanted for spinal surgery, such as stainless steel and chrome-cobalt alloys, a stress exists, known as the endurance limit, below which failure will not occur, even if cycled indefinitely. By calculating the tensile stresses in an implant and relating them to the endurance limit, the implant's susceptibility to fatigue can be determined at the site of stress analysis without formal cyclic load testing.

Biomechanical Phenomena↗
PubMed1988

The posterior tether in scoliosis.

The hypothesis that a localized lordosis, or tethering of the posterior elements of the spine, is the primary cause of the vertebral rotation in idiopathic scoliosis was investigated in anatomic specimens of human and calf spinal columns. The specimens were axially loaded with and without a posterior tether created using Zielke instrumentation. Lateral deflection and axial rotation were monitored roentgenographically. The vertebrae of tethered spines showed increased rotation in the direction associated with idiopathic scoliosis. The spinous processes moved toward the concavity at the apex of the induced lateral curve. Conversely, untethered spines either exhibited little rotation or rotated in the opposite direction; the spinous processes moved toward the convexity of the curve. Rotations toward the convexity occur in rotational kyphosis. Thus the hypothesis that idiopathic scoliosis is a rotational lordosis is substantiated; the characteristic rotation can be explained with the aid of a geometric model.

Animals↗
PubMed1987

Mechanical consequences of rod contouring and residual scoliosis in sublaminar segmental instrumentation.

The mechanical performance of contoured Luque rods in a neuromuscular model of spine deformity was examined to define an upper limit of deformity above which rod stresses would exceed the endurance limit for 316L stainless steel and therefore predict fatigue failure. Bovine constructs varying from 0-120 degrees scoliosis were loaded axially, with strain recordings obtained at the apex of the curve. Relatively low loads produced enough tensile stress to contemplate implant fatigue in all except the nondeformed (0 degrees) construct. Construct stiffness was found to decrease rapidly in spines with greater than 38 degrees deformity. In addition, data on patients who had suffered rod fracture from four different centers were found to compare favorably with experimental observations. We conclude that the vulnerability of Luque rod constructs to implant failure, from a mechanical standpoint, is greater than is generally assumed. Cross-linking of rods was found to increase stiffness. Methods to decrease tensile stresses in the implants and increase stiffness include external immobilization, larger diameter rods, and procedures to enhance correction.

Adolescent↗
PubMed1987

Mouse candidiasis. II. Host responses are T-cell dependent and regulated by genes in the major histocompatibility complex.

Administration of a Thy-1.2-specific monoclonal antibody to BALB/c mice resulted in a significant decrease in the efficiency of clearance of Candida albicans from the spleen. The rate of clearance of organisms from the spleen of congenic mice was determined by genes in the major histocompatibility complex, as was the magnitude of the inflammatory response in the popliteal lymph node after footpad immunization. These results formally demonstrate the involvement of T cells in host responses to primary candida infection.

Animals↗
PubMed1987

A thin foot switch.

A common problem in determining a number of important gait parameters is a convenient means for indicating foot/floor contact. Various foot switches have been used in many forms, but still an ideal, commercially available switch has yet to materialize. This note describes one method for constructing very thin, (1 mm), durable, switches that have worked well in the Gait Analysis Lab at Texas Scottish Rite Hospital.

Biomechanical Phenomena↗
PubMed1987

Elastic properties of cancellous bone: measurement by an ultrasonic technique.

The high degree of porosity of cancellous bone makes elastic property measurement difficult by traditional mechanical testing methods. An ultrasonic technique is described with which mechanical properties of anisotropic, rigid, porous materials, such as cancellous bone, can be measured. The technique utilizes unique piezoelectric transducers operated in a continuous wave mode at a frequency of approximately 50 kHz. Both longitudinal and shear waves can be propagated and received with the transducers allowing both Young's moduli and shear moduli to be determined with the technique. A comparison between moduli measured with the ultrasonic technique and moduli measured with traditional mechanical testing shows the new method to be quite accurate in elastic property determination, (r2 = 0.935, Emech = 1.00E1dt + 23.3 MPa) (r2 = 0.656, Gmech = 1.08 Gult--3.3MPa).

Animals↗
PubMed1987

Murine candidiasis. Pathogenesis and host responses in genetically distinct inbred mice.

The pathogenesis of Candida albicans infection was compared in three inbred strains of mice--CBA/H; C57B1/6J and BALB/c. CBA/H mice developed the most severe lesions, and also showed the weakest inflammatory responses in the popliteal lymph node after challenge with live organisms in the footpad. Nevertheless, this strain cleared candida from the spleen more efficiently than either C57B1/6J or BALB/c mice. This apparently excludes a defect in phagocytosis as the basis for the increased susceptibility. The gene(s) determining susceptibility in CBA/H mice are located outside the major histocompatibility complex (MHC).

Animals↗
PubMed1987

The cytotoxic response to murine cytomegalovirus: requirements for the generation of MCMV-specific target cells.

The preparation of target cells susceptible to lysis by murine cytomegalovirus (MCMV)-immune T cells in vitro was investigated and found to be dependent upon target cell type, culture conditions, virus adsorption protocol and virus preparation. Optimally sensitive MCMV-infected targets were obtained by preculture of mouse embryo fibroblasts (MEF) in 3% vol/vol concanavalin-A-stimulated spleen cell supernatant (CSS)-supplemented medium, adsorption of salivary gland stock MCMV under 800 g centrifugation and at least 4 h further incubation at 37 degrees before addition of T cells. In contrast, salivary gland stock MCMV did not cause thioglycollate-induced peritoneal exudate cells to be susceptible to MCMV-specific T cell-mediated lysis, whereas tissue culture-passaged stock MCMV was successful. The preparation of MCMV-infected target cells is discussed in terms of the need for H-2 and viral antigen expression for T cell recognition.

Animals↗
PubMed1986

A colorimetric method for measuring the candidacidal activity of leucocytes.

The candidacidal activity of mouse neutrophils was determined by a colorimetric method, using a tetrazolium dye that detects living, but not dead, yeast cells. The assay is carried out in microtitre trays, read using a multiwell scanning spectrophotometer (ELISA reader), and can be analysed by computer.

Animals↗
PubMed1986

The pathogenesis of acute systemic candidiasis in a susceptible inbred mouse strain.

The histopathological features of the acute infection by Candida albicans in susceptible CBA/H mice, as well as its dissemination in various organs has been examined. The brain, in which the localization of blastospores is minimal, is the organ most severely affected. A significant deposition of blastospores occurs in lungs, liver, spleen and kidney, but of these organs, only in the kidneys is infection established. A transient myocarditis follows the minor blastospore deposition that occurs in the heart. Infection in the affected organs is characterized by abscess formation while in the brain the process is complicated by the development of hydrocephalus and a pachymeningitis that erodes the petrous temporal and involves the vestibular apparatus. There is also infection of the retinae with an accompanying endophthalmitis.

Acute Disease↗
PubMed1986

H-2 restriction and H-2 phenotypes of spleen cells from thymus-grafted radiation chimeras: evidence consistent with extrathymic suppression.

As an approach to analyzing the factors that contribute to determining H-2 restriction specificities of cytotoxic T cells, thymectomized semiallogeneic radiation chimeras were given transplants of fetal thymus from parental strain or F1 hybrid donors. A pronounced preference for lysis of infected targets of the same H-2 haplotype as the thymus was observed, the bias ranging from an undetectable preference through to absolute restriction to the thymic H-2. Virus-immune Tc cells could also be restricted to H-2 antigenic determinants of haplotypes expressed only by donated stem cell progeny lymphomyeloid cells. T cells from chimeras that had received thymuses of both parental strains were less effective than normal syngeneic F1 hybrid T cells in lysing allogeneic cells and both infected and uninfected parental targets. Variation in H-2 restriction bias from one chimera to another was not reflected in modulations to the class I H-2 phenotypes of the chimeric spleen cells.

Animals↗
PubMed1986

Self-tolerance and H-2 antigen expression in semi-allogeneic radiation chimeras are controlled by the extrathymic host environment.

Experiments with thymus-grafted radiation chimeras have implicated the H-2 type of the radio-resistant portion of the thymus as determining self for H-2 restricted T-cell responses. (P1 X P2)F1----P1 chimeras, shown to be fully reconstituted with donor haemopoietic cells, have displayed intolerance to P2 H-2 antigens and expressed aberrant levels of P2 H-2 on their spleen cells. We used semi-allogeneic radiation chimeras grafted with fetal thymuses from parental strain donors to compare the relative contributions of the thymus and the extrathymic periphery in determining self-tolerance and in modulating the H-2 phenotype of heterozygous chimeric spleen cells. As analysed by the rosetting titres of anti-H-2 antisera on chimeric spleen cells, by parental skin graft rejection, and by spleen cell anti-parent cytotoxicity after culture with parental stimulators, the decreased expression of non-host parental H-2 antigens was associated with anti-P2 T-cell reactivity, regardless of the H-2 type of the thymus. The donor thymus did not affect tolerance to parental H-2 or cause aberrant expression of H-2 antigens on spleen cells of syngeneic F1----F1 thymus-grafted chimeras.

Animals↗