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Biomedical subjects

M W Johnson

Publications and source records attributed to M W Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1991

Retinal toxicity of human tissue plasminogen activator in vitrectomized rabbit eyes.

The retinal toxicity of human tissue plasminogen activator in normal rabbit eyes has recently been reported. We now report the retinal toxicity of tissue plasminogen activator in three groups of vitrectomized rabbit eyes. Group 1 underwent gas compression of the vitreous followed by tissue plasminogen activator injection in doses of 25, 50, and 100 micrograms (all doses were administered in 100 microL of fluid). Group 2 underwent lensectomy and vitrectomy followed by tissue plasminogen activator injection of 100 micrograms. Group 3 underwent lensectomy, vitrectomy, and complete fluid/gas exchange prior to injections of 12.5 and 25 micrograms of tissue plasminogen activator. Control eyes received 100 microL of balanced salt solution. In group 1, no retinal toxic reactions were observed after administration of 25 or 50 micrograms of tissue plasminogen activator, but all eyes receiving 100 micrograms demonstrated retinal damage on ophthalmoscopy, electroretinography, and light microscopy. In group 2, no retinal toxic reactions were seen after administration of 100 micrograms of tissue plasminogen activator. In group 3, two of 11 eyes receiving 25 micrograms of tissue plasminogen activator demonstrated toxic retinal changes by ophthalmoscopy, electroretinography, and light microscopy. These results suggest that gas compression of the vitreous does not significantly alter the toxic changes seen caused by tissue plasminogen activator. While lensectomy and vitrectomy appears to widen the therapeutic window for tissue plasminogen activator, the margin of safety is reduced with the addition of a large gas bubble.

Animals↗
PubMed1991

Electron beam effective source surface distances for a high energy linear accelerator.

The design of the Varian Clinac 1800 linear accelerator electron applicator system does not allow clearance for all head and neck patients to be treated at the standard calibration distance of 100 cm. Discrepancies have been found between dose calculations using the inverse square law for extended distances and their measured data. A 4 X 4 cm2 applicator at an energy of 9 MeV, for example, had dose differences of 13 and 23% at distances of 105 and 110 cm SSD. Because of these discrepancies, effective source surface distances (SSDeff) were determined for all the standard electron energies and applicators of a Clinac 1800. These effective source surface distances ranged from 41.6 cm to 92.6 cm for the 4 X 4 cm2 cone/6 MeV electron beam through the 25 X 25 cm2 cone/20 MeV electron beam. A summary of these distances and an analysis of the clinical use of both a best fit SSDeff and a common SSDeff for patient dosimetry calculations is presented.

Calibration↗
PubMed1991

Merger and medical staff: an approach to integration.

One of the most important aspects of a hospital merger is the impact on the medical staff. At University Hospital in British Columbia, which was established when two large general teaching hospitals merged, the comprehensive process to reorganize the medical staff structure was designed to account for this impact. Preliminary indications are that the process used was effective in creating a positive atmosphere and that the fundamental arrangements that resulted are conductive to future development. Although a formal evaluation of the overall integration of the medical staff at University Hospital is some time off, general evaluative criteria are proposed for future application.

British Columbia↗
PubMed1991

Tissue plasminogen activator treatment of experimental subretinal hemorrhage.

Previous investigators have suggested that subretinal blood damages the retina in part because of its solid fibrin meshwork. The role of fibrinolysis in facilitating the clearance of subretinal hemorrhage and preventing degeneration of the overlying retina was studied. Autologous whole blood (0.1 ml) was injected into the subretinal space of 20 rabbits. Twenty-four hours later, the animals were randomized to subretinal treatment with 2.5 micrograms of tissue plasminogen activator or a similar volume of physiologic saline. Mean subretinal hemorrhage thickness 3 days after treatment had decreased to 42% of pretreatment thickness in treated eyes and remained unchanged in control eyes (P less than 0.0005). By 7 days mean clot thickness was 9% in treated eyes and 60% in controls (P = 0.005). Light microscopy revealed severe progressive retinal degeneration in both groups. No histologic evidence of retinal toxicity was found in cat retina after subretinal injection of tissue plasminogen activator (50 micrograms/ml). Although treatment with tissue plasminogen activator accelerated the clearance of subretinal hemorrhage, it failed to prevent secondary retinal degeneration in this rabbit model.

Animals↗
PubMed1991

Transpalpebral extrusion of a silicone sponge exoplant.

We report an unusual case of scleral buckle extrusion in a 63-year-old woman. A 5 mm silicone sponge exoplant eroded through Tenon's capsule, conjunctiva, and full-thickness upper eyelid, traversing the tarsal plate.

Eyelids↗
PubMed1991

Colorectal cancer: current trends in initial clinical manifestations.

Colorectal carcinoma (CRC) is a common cause of cancer morbidity and mortality in the United States. There continues to be controversy regarding the effectiveness and feasibility of various screening programs for CRC. To determine how cases of CRC are currently detected, we reviewed a series of 246 consecutive patients with well-documented pathologic staging and clinical presentation. Patients with low stage CRC (0 or A) had smaller tumors, were less likely to be anemic at presentation, and were more likely to have tumors located in the left side of the colon than patients with tumors at stage B or higher. Thirty-two of the 246 tumors were detected in asymptomatic patients through screening. These tumors were more likely to be of a lower stage than those in patients with active gastrointestinal symptoms. In our experience active screening programs detect a relatively small number of CRCs. A majority (66%) of CRCs are still detected from symptoms referable to the gastrointestinal tract.

Aged↗
PubMed1990

Retinal toxicity of recombinant tissue plasminogen activator in the rabbit.

We studied the dose-dependent retinal toxicity of the available commercial preparation of human recombinant tissue plasminogen activator in the normal rabbit eye. Tissue plasminogen activator was injected into the midvitreous cavity of albino rabbits in doses (per 100 microL) of 25, 50, 75, and 100 micrograms. Control eyes received 100 microL of balanced salt solution or tissue plasminogen activator vehicle. No evidence of a retinal toxic reaction was seen in eyes receiving 25 micrograms of tissue plasminogen activator. One of four eyes injected with 50 micrograms showed loss of photoreceptor cells by light microscopy. Severe retinal damage was seen by ophthalmoscopy, electroretinography, and light microscopy in three of four eyes receiving 75 micrograms of tissue plasminogen activator and in all eyes treated with 100 micrograms of tissue plasminogen activator or equivalent vehicle. These results suggest that the commercial recombinant tissue plasminogen activator formulation has a narrow margin of safety in nonvitrectomized eyes and that a component of the vehicle is the toxic factor.

Animals↗
PubMed1990

Purtscher's-like retinopathy after childbirth.

Severe bilateral visual loss attributable to multiple retinal arteriolar occlusions occurred in four young women within 24 hours after childbirth. In two patients, labor was complicated by preeclampsia requiring cesarean section. One patient was suffering from pancreatitis. None had connective tissue disease or antecedent trauma. Ophthalmoscopy and fluorescein angiography revealed evidence of multiple superficial peripapillary and macular patches of ischemic retinal whitening simulating Purtscher's retinopathy. By 8 weeks, the white patches were resolving in all eyes and visual acuity had significantly improved in three of the four patients. The pathogenesis of this disorder is unknown but may involve arteriolar obstruction by complement-induced leukoemboli formed during parturition.

Adolescent↗
PubMed1990

Surgical management of the idiopathic uveal effusion syndrome.

Twenty-three eyes of 20 patients with idiopathic ciliochoroidal effusion underwent quadrantic partial-thickness sclerectomies without decompression of the vortex veins. The mean postoperative follow-up interval was 41 months (range, 6-86 months). Resolution of subretinal and/or supraciliochoroidal fluid occurred within 6 months in 19 eyes (83%) after one procedure and in 22 eyes (96%) after one or two procedures. The mean interval to reattachment for the 19 successfully treated eyes with nonrhegmatogenous retinal detachment (RD) was 2.4 months compared with an average preoperative detachment duration of 18.5 months (P = 0.0005). Recurrences were seen in 23% of eyes; all resolved spontaneously or with a single reoperation. Final visual acuity was improved by two or more lines in 13 eyes (56%), stable in 8 (35%), and worse in 2 (9%). The efficacy of this surgical technique supports the hypothesis that an abnormality of transscleral protein transport plays a primary pathophysiologic role in this disorder.

Adult↗
PubMed1990

The effect of scleral buckling on ocular rigidity.

In a study of enucleated human eyes, the authors investigated the effect of scleral buckling on the ocular pressure-volume relationship. Intraocular pressure was recorded continuously during intravitreal infusion of saline solution before and after the application of encircling silicone elements. Scleral buckling produced a marked reduction in ocular rigidity, with reversibility of the effect on removal of the buckling elements. Similar results were obtained during incremental intravitreal air injection. The authors propose that the greater extensibility of silicone compared with sclera and the induced alterations in ocular shape are the primary factors responsible for the observed change in ocular rigidity. The clinical implications of these findings for intravitreal gas injection are discussed.

Aged↗
PubMed1990

Evaluation of shoulder movement as a command control source.

The purpose of this study was to evaluate the use of scapular shoulder movement as a command control source. The focus of this study was on the evaluation of movement signals from quadriplegic subjects as well as on the processing of these signals for use as command inputs to a functional neuromuscular stimulation (FNS) hand-grasp system. The shoulder movement of three C5-level quadriplegic and nine normal subjects was studied using externally mounted two-degree-of-freedom transducers overlying the sternum and clavicles. The C5-level quadriplegic subjects tested had a considerably poorer range of motion than the normal subjects. The range of motion was greatest in elevation but was coupled with a significant component of retraction. The vertical command resolution of the quadriplegic subjects ranged from eight to 13 command levels, whereas the horizontal range contained four or fewer command levels. Normal subjects were able to produce 26 to 79 command levels along the vertical axis and 18 to 85 along the horizontal axis. Subjects were able to maintain a static command level to within several percent of their range in trials lasting from 10 to 30 s. The quadriplegic subjects performed poorly in tasks where they were required to move to a point along the horizontal or vertical central axis and then along the opposite axis. The normal subjects were readily able to perform these tasks. The interference with the command signal due to movement of the opposite extremity was significant, with a maximum error ranging between 25 and 86% along the vertical axis and between 38 and 105% along the horizontal axis. Rise time and normalized velocity (velocity divided by the size of the movement) were found to be suitable for distinguishing different types of shoulder movements independent of the size of the movement. Shoulder movement in quadriplegics is suitable as a command control source for a FNS hand-grasp system requiring one proportional command signal and at least one logical command signal with appropriate processing of the signals. The available transducers are cosmetically acceptable and are easy to don and doff. Use of shoulder movement as a command control source does not interfere with other activities of the user such as eating or talking. Shoulder movement also provides a command control source that is easy for the user to learn and provides some feedback to the user through shoulder proprioception.

Adult↗
PubMed1989

Malignant melanoma of the iris in xeroderma pigmentosum.

Xeroderma pigmentosum is an autosomal recessive, precancerous dermatosis caused by defective repair of ultraviolet-damaged DNA. Characterized clinically by progressive cutaneous pigmentary alterations and tumorigenesis, it serves as a model for ultraviolet carcinogenesis. We describe the clinical and histopathologic findings in a 31-year-old woman with xeroderma pigmentosum and a massive iris melanoma of the left eye. Histologic examination following enucleation revealed diffuse iris replacement by spindle and epithelioid cells with extension into the trabecular meshwork. Evidence of direct extraocular extension was absent, and a metastatic evaluation showed no abnormalities. To our knowledge, this is the first reported case of xeroderma pigmentosum complicated by melanoma of the iris. It provides further evidence suggesting a role for sunlight exposure in the pathogenesis of uveal melanoma.

Adult↗
PubMed1989

An isotopic study of biogeochemical relationships between carbonates and organic carbon in the Greenhorn Formation.

Carbon-isotopic compositions of total carbonate, inoceramid carbonate, micritic carbonate, secondary cements, total organic carbon, and geoporphyrins have been measured in 76 different beds within a 17-m interval of a core through the Greenhorn Formation, an interbedded limestone and calcareous shale unit of Cretaceous age (Cenomanian-Turonian) from the Western Interior Seaway of North America. Results are considered in terms of variations in the processes of primary production (which led to the biosynthesis of the molecular precursors of the geoporphyrins) and in secondary processes (those mediating the transformation of primary organic material into sedimentary total organic carbon). It is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the TOC isotopic record, and that, in these sediments, TOC is enriched in 13C relative to its primary precursor by 0.6 to 2.8%. This enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy. Variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate. This correlation is attributed to effects of environmental changes on the marine foodweb. These may have included increased atmospheric oxygen associated with the Cenomanian-Turonian oceanic anoxic event. The isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1.5% during the interval of deposition. It is suggested that this change is due to a variation in the makeup of the community of primary producers and/or to a decrease in the atmospheric abundance of CO2 during the oceanic anoxic event.

Animals↗
PubMed1989

An improved design of electrodes for measurement of streaming potentials on wet bone in vitro and in vivo.

Streaming potentials are generated by mechanical stress in wet bone and may constitute a control mechanism for bone remodeling. Measurement of streaming potentials in bone has attracted considerable effort in past years but quantitative studies have been hampered by relatively poor repeatability when using Ag.AgCl electrodes which contact bone via a wick moistened with electrolyte. Improvement now has been achieved with an electrode design that limits the specific area of contact of an agar/salt bridge by means of a silastic seal, thus permitting the same equipotential surface to be contacted for each set of measurements. This reduces variations caused by bone structure and impedance, and facilitates quantitative comparisons of the response of bone samples to selected variables. The new design also permits considerable qualitative improvement in recordings made from bone during locomotor function in experimental animals in vivo.

Acrylic Resins↗
PubMed1989

Serologic examination of aborted ovine and bovine fetal fluids for the diagnosis of border disease, bluetongue, bovine viral diarrhea, and leptospiral infections.

Fetal serum from most of 994 bovine and 553 ovine aborted fetuses was tested serologically for antibodies to border disease (BD), bovine viral diarrhea (BVD), and bluetongue (BT) viruses, and to Leptospira sp., and the results were compared with the results of isolation procedures, fluorescent antibody tests (FAT), and histologic examinations of the same fetuses. Antibodies to BT virus were not found in any of the 994 bovine and 553 ovine fetuses. Antibody titers to BVD virus were present in 39 of 966 bovine fetuses tested, and BVD virus was detected in 4 of the 39. Four of 74 fetuses in which the BVD virus was detected by FAT or isolation had titers to BVD virus. Microagglutination (MAT) titers to 1 or more of 5 serovars of leptospires were present in 52 of 773 bovine fetal sera tested. Leptospires were not detected by FAT in any bovine fetuses that had leptospiral antibody titers. Leptospires were detected by FAT in 15 aborted calves, and none of these had MAT titers. Antibody titers to BD virus were present in 80 of 486 fetal lamb sera tested, and the virus was detected by FAT or isolation in 3 of the 80 fetuses. Border disease virus was detected in 14 of 486 fetal lambs tested. Twelve of the 14 were tested serologically and 3 had titers to BD virus. Leptospiral antibody titers were present in 27 of 326 ovine fetal sera tested. Leptospires were not detected in any of the 326 ovine fetuses tested by FAT.

Abortion, Veterinary↗