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Biomedical subjects

G Mitchell

Publications and source records attributed to G Mitchell.

At least 55 records · Page 3Linked to original sources
PubMed1999

Ejection fraction by radionuclide ventriculography and contrast left ventriculogram. A tale of two techniques. SAVE Investigators. Survival and Ventricular Enlargement.

OBJECTIVES: We assessed the abilities of two methods to measure ejection fraction (EF)-radionuclide ventriculography (RVG) and contrast left ventriculography (Cath-EFa) to predict cardiovascular events. BACKGROUND: Both RVG and Cath-EFa are commonly used methods to measure left ventricular performance and assess prognosis. Their comparative abilities to predict clinical events have not been reported. METHODS: Both RVG EF and Cath-EFa were measured within 16 days of myocardial infarction (MI) in 688 patients. The results were divided into terciles. Prognosis by terciles was assessed for each technique. A multivariate analysis was performed to determine which EF measurement was a better predictor of prognosis. RESULTS: Average RVG-EF was 32%+/-7, while Cath-EFa was 42%+/-10. Both RVG and Cath-EFa were poorly correlated (R=0.42). Event rate declined across terciles with increasing EF for both techniques (events in lowest to highest tercile of Cath-EFa 40.7%, 25.9%, 11.6%, p < 0.001; and RVG-EF 39.9%, 26.1%, 15.6%, p < 0.001). There was concordance of terciles in 303 of 688 patients (44%). When patients in the highest RVG terciles were in the highest Cath-EFa tercile, the event rate was 7%. However, when patients in the highest RVG terciles were in the lowest Cath-EFa tercile, the event rate was 19%. Both Cath-EFa (p < 0.001) and RVG-EF (p < 0.001) were independent predictors of cardiovascular events. CONCLUSIONS: Ejection fraction measured by RVG or during catheterization is a valuable tool in the risk stratification of postinfarct patients. When disagreement is present between clinical impression and measurement by either method, the use of an alternative measurement is warranted and complementary.

Adult↗
PubMed1999

The plastid in Plasmodium falciparum asexual blood stages: a three-dimensional ultrastructural analysis.

The plastid in Plasmodium falciparum asexual stages is a tubular structure measuring about 0.5 micron x 0.15 micron in the merozoite, and 1.6 x 0.35 microns in trophozoites. Each parasite contains a single plastid until this organelle replicates in late schizonts. The plastid always adheres to the (single) mitochondrion, along its whole length in merozoites and early rings, but only at one end in later stages. Regions of the plastid are also closely related to the pigment vacuole, nuclear membrane and endoplasmic reticulum. In merozoites the plastid is anchored to a band of 2-3 subpellicular microtubules. Reconstructions show the plastid wall is characteristically three membranes thick, with regions of additional, complex membranes. These include inner and outer membrane complexes. The inner complex in the interior lumen is probably a rolled invagination of the plastid's inner membrane. The outer complex lies between the outer and middle wall membranes. The interior matrix contains ribosome-like granules and a network of fine branched filaments. Merozoites of P. berghei and P. knowlesi possess plastids similar in structure to those of P. falciparum. A model is proposed for the transfer of membrane lipid from the plastid to other organelles in the parasite.

Animals↗
PubMed1999

Employer-provided vision benefits: have they gone mainstream?

As managed care inches closer to becoming the standard mechanism for delivering health benefits to American workers, we looked to see if the status of vision/eye health benefits have changed in the 1990s. Has vision care become a "mainstream" benefit?

Delivery of Health Care↗
PubMed1999

Working with school nurses: improving children's vision and building relationships.

The 45,000-plus school nurses in the U.S. have an astonishing array of responsibilities, and serve as important gatekeepers to the health care of millions of children. By building relationships with local school nurses, doctors of optometry can play an important part in improving children's vision care, and build their practices as well. We take a look at the challenges school nurses face, and an AOA program designed to reach out to them and improve the quality of vision screenings.

Child↗
PubMed1999

Carrying hope.

Explore the source record for details and available documents.

Attitude of Health Personnel↗
PubMed1998

CXCR1 and CXCR2 are rapidly down-modulated by bacterial endotoxin through a unique agonist-independent, tyrosine kinase-dependent mechanism.

The expression of the seven-transmembrane domain chemokine receptors CXCR1 and CXCR2 modulates neutrophil responsiveness to the chemoattractant IL-8 and a number of closely related CXC chemokines. In the present study, we investigated the mechanism by which bacterial LPS induces the down-modulation of IL-8 responsiveness and CXCR1 and CXCR2 expression on human neutrophils. Treating neutrophils with LPS reduced IL-8R expression to 55 +/- 5% of the control within 30 min and to 23 +/- 2% within 1 h of stimulation. Furthermore, this down-modulation could not be attributed to increased concentrations of IL-8, TNF-alpha, or IL-1beta, since ELISA studies indicated that LPS-stimulated neutrophils did not release detectable amounts of these proteins before 2 h poststimulation. The tyrosine kinase (TK) inhibitors genistein and herbimycin A attenuated the LPS-mediated down-modulation of CXCR1 and CXCR2, indicating that the activation of a TK is required for LPS to mediate its effect. The effect of LPS on receptor expression paralleled the hyperphosphorylation of the protein TK p72syk. Although IL-8 induced a comparable down-modulation of CXCR1 and CXCR2, TK inhibitors did not attenuate this effect. These studies provide the first evidence of an agonist-independent, TK-dependent pathway of chemokine receptor regulation by endotoxin.

Antigens, CD↗
PubMed1998

Saguenay Lac Saint Jean cytochrome oxidase deficiency: sequence analysis of nuclear encoded COX subunits, chromosomal localization and a sequence anomaly in subunit VIc.

A biochemically distinct form of cytochrome oxidase (COX) deficiency found in the Saguenay region of Quebec is an autosomal recessive trait. The cDNA sequences of all 10 nuclear-encoded subunits from a patient's fibroblasts showed normal coding sequence. Sequences for subunit VIc in two atypical patients showed a heterozygous base substitution. Subunit VIc was localized to chromosome 18.

Animals↗
PubMed1998

Histological studies of the dorsal nasal, angularis oculi, and facial veins of sheep (Ovis aries).

Selective brain cooling (SBC) requires vasoactivity in the superficial veins of the face of the animal. This vasoactivity is possible because of an adequate amount of smooth muscle in the tunica media of each of these superficial vessels, enabling it to act as a "muscle sphincter". In this study, the angularis oculi, dorsal nasal, distal, and proximal parts of the facial veins in sheep were examined histologically to describe an anatomical basis for SBC. Measurements of the tunica media thickness, the lumen diameter, and the ratio of these measurements showed that the relative tunica media thicknesses in the angularis oculi vein and the dorsal nasal vein are statistically smaller (P < 0.001) than in the distal or the proximal parts of the facial vein. In the angularis oculi, dorsal nasal, and distal part of the facial vein, the tunicae mediae were composed of five to seven circularly arranged smooth muscle layers, suggesting their ability to vasoconstrict. The proximal part of the facial vein possesses both circularly and longitudinally arranged smooth muscle layers. The circular smooth muscle layers suggest a vasoconstrictory function, whereas the longitudinal smooth muscle layers suggest a vasoconstrictory function in this part of the facial vein. Both the dorsal nasal and the proximal part of the facial vein, but not the angularis oculi or the distal part of the facial vein, possess endothelial valves near their confluences with other veins. It was concluded from this study that the angularis oculi and the distal part of the facial vein vasoconstrict, whereas the proximal part of the facial vein vasodilates, enabling the necessary changes in blood flow in SBC.

Animals↗
PubMed1998

A model of bridging angiogenesis in the rat.

A model of angiogenesis has been developed in the rat. The epigastric vascular pedicle was exposed in the groin, a 7 mm segment of epigastric artery was excised leaving the vein intact and, after a variable period of time for angiogenesis to occur between the ends of the artery, a skin flap was elevated on the epigastric vascular pedicle so that it depended completely for its blood supply on bridging angiogenesis across the created gap. Skin flap survival and vessel counts were measured as indices of the angiogenic response. In this model we observed a spontaneous increase in vessel counts between the ends of the artery, and a corresponding increase in skin flap tissue survival until day 10 after which time vessel counts plateaued whilst tissue survival continued to increase until day 14. In the angiogenic pedicle, a time-dependent development of granulation tissue containing numerous macrophages and mast cells, and capillary sprouting were documented. When flap elevation was performed 7 days after arterial excision skin flap survival was 42%. Thus, in this model, 7 days is a suitable interval for the future evaluation of the effects of either pro- or anti-angiogenic agents.

Animals↗
PubMed1998

Excision and low-dose radiotherapy for refractory laryngeal granuloma.

Laryngeal granulomas are uncommon lesions of an inflammatory origin. They are conventionally managed by simple excision with the occasional use of adjuvant treatment depending on the aetiological factors. Unfortunately, recurrences can occur, requiring repeated excision. Some lesions are refractory to this approach and alternative management approaches include excision and immediate adjuvant radiotherapy. The use of radiotherapy in the management of benign disease can be limited by the risk of induction of late malignancy and informed consent of a patient must include an assessment of this risk. We describe a case of refractory laryngeal granuloma successfully treated by excision and immediate radiotherapy in a patient occupationally dependent upon his voice.

Combined Modality Therapy↗
PubMed1998

High dose behind inhomogeneities during medium-energy x-ray irradiation.

Medium-energy x-rays from orthovoltage treatment units are used for a variety of radiotherapy treatments ranging from cutaneous malignancies in the head and neck region to bone metastases. It was the aim of the present study to investigate the dose distribution due to secondary electrons close behind inhomogeneities in these radiation qualities. The dose was assessed in a solid water phantom using three plane-parallel ionization chambers (NE 2532/2, 'Markus' and 'Attix' chamber) and sheets of aluminium, copper, zinc, platinum, lead and bone equivalent material. The depth dose distribution directly behind the inhomogeneity was assessed using sheets of 15 microm thick polyethylene foil. A dose increase was found directly behind inhomogeneities of high atomic number with a rapid dose fall-off over the first 100 microm. The dose downstream of the inhomogeneity was found to increase with increasing beam quality from 120 kVp (HVL 2.8 mm Al) to 250 kVp (HVL 2 mm Cu). In the latter the dose was increased directly behind lead and platinum sheets by up to a factor of eight compared with a solid water depth of similar attenuation. The results of the study demonstrate the importance of using appropriate materials if shielding is in contact with the patient.

Bone Neoplasms↗
PubMed1998

Assessment of GP management of symptoms of dying patients in an Australian community hospice by chart audit.

BACKGROUND: With specialist palliative care services becoming widespread, and the place of the GP in palliative care being examined, audit of patient care delivered by GPs is required in order to ensure adequate standards of care. OBJECTIVE: We aimed to evaluate symptomatic care delivered to palliative care patients by GPs in an Australian community hospice with a developed quality assurance programme. METHODS: The study was set in a newly established community-based, GP-run hospice in a provincial city in Queensland, Australia. A chart audit was carried out of the first 20 patients admitted to a community-based hospice, in order to establish (i) whether attempts were made by the treating doctor to find the direct cause of symptoms before initiating management; and (ii) whether management accorded with developed consensus-based guidelines. RESULTS: Twenty patients were treated by 14 GPs; 135 new symptoms were identified in the records of these patients. Of the 125 symptoms for which guidelines could be identified in the literature, in 87 (70%) an attempt by the treating GP to find a direct cause could be demonstrated. Of the 114 symptoms with treatments defined in the guidelines, 107 (90%) treatments conformed to the guidelines. Constipation, nausea/vomiting, anorexia and back pain were the conditions for which there were the fewest attempts at establishing a direct cause before treatment. In most cases these conditions were treated in accordance with the guidelines. CONCLUSION: Quality assurance mechanisms present in an in-patient palliative care setting appear to be associated with high-quality care by GPs.

Aged↗
PubMed1998

Learning disability care staff's emotional reactions to aggressive challenging behaviours: development of a measurement tool.

OBJECTIVES: To describe the development of a rating scale measure of caregivers' emotional reactions to aggressive challenging behaviour, and to report preliminary psychometric data for the scale. DESIGN: Using previous research on staff working with people with learning disabilities, a range of likely emotional reactions to challenging behaviours were selected for possible inclusion in a rating scale measure. METHODS: A total of 83 care staff from 23 community residences for people with learning disabilities rated their recent emotional reactions to aggressive challenging behaviour using 18 emotion items. A further sample of 18 care staff participated in a test-retest study after the initial stages of scale development. RESULTS: A rating scale was developed on the basis of a factor analysis and further item analysis. The measure has two subscales: feelings of depression/anger (10 items), and feelings of fear/anxiety (5 items). The subscales have a high internal consistency, good test-retest reliability and are relatively unaffected by social desirability biases. CONCLUSIONS: The emotional reactions to aggressive challenging behaviour scale has excellent face and construct validity, and other preliminary psychometric data are promising. The scale has a number of potential research and clinical applications.

Activities of Daily Living↗
PubMed1997

An electrophysiological method for measuring the potassium permeability of the nerve perineurium.

An electrophysiological method is described for measuring the potassium permeability (PK) of the perineurium of the sciatic nerve of the frog. The method is based on the principle of grease-gap recording, in which an insulating compartment separates two surface recording electrodes. The sciatic nerves of frogs Rana temporaria and R. pipiens were isolated and mounted across a five compartment chamber, with Vaseline grease seals on the partitions between compartments. Compartments #1, #2 and #5 contained frog Ringer solution, #4 was filled with Vaseline and formed the grease gap, and #3 was the test compartment in which solutions could be changed. The nerve was stimulated via platinum electrodes in compartments #1 and #2, and DC potentials and compound action potentials (CAP) were recorded between Ag/AgCl electrodes connected through Ringer-agar bridges to compartments #3 and #5. In nerves with undamaged perineurium, changing from normal Ringer to high [K+] Ringer (100 mM, KCl replacing NaCl) for 2 min caused negligible change in DC potential or CAP, indicating that raised [K+] was not reaching the axon surface, and hence that the perineurium was exerting a diffusional restriction on K+ entry. In nerves damaged by stretching or drying, K+ pulses caused a depolarising change in DC potential (delta DC), and corresponding decline in CAP amplitude, consistent with a leaky perineurium allowing K+ entry and axonal depolarisation. Ringer made hypertonic by the addition of 2.5 M sucrose or 5 M NaCl caused increased perineurial permeability to K+. The method was calibrated by measuring the delta DC in response to raised [K+] in the range 5-100 mM [K+] in desheathed nerves; from this calibration curve relating delta DC to endoneurial [K+] it was possible to calculate the change in endoneurial [K+] occurring in intact preparations. The calculations showed that the undamaged perineurium had a PK of < 6.3 x 10(-7) cm.s-1, similar to the value calculated for in situ nerves using radioisotopic techniques, but less than the value reported for isolated perineurial cylinders. The method gives real-time information on the K+ permeability of the nerve perineurium and its modulation by experimental treatments.

Animals↗