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Biomedical subjects

J M Yates

Publications and source records attributed to J M Yates.

At least 19 recordsLinked to original sources
PubMed2000

Ectopic neural activity from myelinated afferent fibres in the lingual nerve of the ferret following three types of injury.

Sensory disturbances following nerve injury may result from abnormal neural activity initiated at the injury site. We have studied the activity generated in the lingual nerve after three types of injury which may have variable potentials for the initiation of sensory disturbances. We have also compared the results with those found after damage to the inferior alveolar nerve, another branch of the trigeminal nerve, to determine whether differences in nerve fibre type or location affect the level of abnormal activity. In anaesthetised adult male ferrets the left lingual nerve was either ligated and cut distally, chronically constricted, or sectioned and allowed to regenerate. Following recovery periods of 3 days-6 months, single unit electrophysiological recordings were made from central to the injury site. After all three types of injury, some of the damaged axons at the injury site developed spontaneous activity (up to 36% of units) and mechanical sensitivity (up to 35% of units). There were significantly fewer spontaneously active units after ligation than after the other two types of injury but the level of mechanical sensitivity was not significantly different between the three types of injury. There was a significant increase in the spontaneous activity between 3 weeks and later recovery periods following both ligation and section injuries, and this late increase was not seen in our previous studies on the inferior alveolar nerve. Differences in the time-course of ectopic activity in adjacent branches of the trigeminal nerve suggest that the fibre types or anatomical relationships affect the outcome of injury.

Afferent Pathways↗
PubMed1998

Sympathectomy does not affect the early ectopic discharge from myelinated fibres in ferret inferior alveolar nerve neuromas.

Ectopic neural activity from damaged axons is thought to contribute to the development of sensory disorders following nerve injury. Here we have studied the role of sympathetic fibres in the generation or potentiation of this abnormal activity by determining the effect of predegenerating these fibres. Twelve adult ferrets were used in the study and six of them underwent sympathectomy by removal of the left superior cervical ganglion. Electrophysiological recordings were made from myelinated axons in fine filaments dissected from the inferior alveolar nerve, 3 days after it had been ligated further distally, and the level of spontaneous activity and mechanical sensitivity was determined. There was no significant difference between the level or characteristics of spontaneous activity, or the level of mechanical sensitivity, in the two groups of animals. We conclude that, in this animal model, the absence of sympathetic nerve fibres does not affect the development or characteristics of ectopic neural activity in the early period following nerve injury.

Animals↗
PubMed1996

Geographical variations in rates of ophthalmic surgery.

AIMS/BACKGROUND: Geographical variations in health care are common. There is, however, no simple explanation for why they arise. Variations in rates of ophthalmic surgery in the population aged 65 and over were investigated, with the aim of determining their cause. METHODS: Routine data sources were used to obtain the 1991-2 age and sex standardised rates for English health districts with an ophthalmic unit. Weighted least squares regression was used to study the relation between these rates and various factors describing the population and the provision of care. RESULTS: Surgery rates varied more than threefold. High rates of surgery were associated with high throughput and bed numbers (both p < 0.001), high proportions of day case surgery (p < 0.001), long waiting lists (p < 0.001), and a high number of theatre sessions (p = 0.002). Conversely, a high percentage of emergency admissions was associated with lower rates of surgery (p = 0.004). These six variables accounted for 58% of the variation. CONCLUSION: Geographical variations were found to exist, less than two thirds being explained by differences in the provision of care. The remaining variation may partly be attributed to private practice and the lack of consensus for many ophthalmic procedures (the 'surgical signature'), including a lowering of the threshold for surgery. These findings have implications for the planning of ophthalmic services.

Aged↗
PubMed1995

Evidence that hypoxia markers detect oxygen gradients in liver: pimonidazole and retrograde perfusion of rat liver.

Nitroimidazole markers of tumour hypoxia bind to normoxic liver and the question has been raised whether this is due to low oxygen concentration or microregional activity of specialised nitroreductases. To answer this question, the binding patterns of the 2-nitroimidazole, pimonidazole, were compared following perfusion of surgically isolated rat livers in anterograde and retrograde directions. Perfusion at low flow rates in anterograde or retrograde directions can be used intentionally to alter oxygen gradients without altering enzyme distributions. Perfusion by means of the portal vein (anterograde direction) produced pimonidazole binding in the pericentral region of liver similar to that observed for pimonidazole binding in vivo. A complete reversal of this binding pattern occurred when the isolated liver was perfused by way of the central vein (retrograde direction). In this case, pimonidazole binding occurred in the periportal region. The extent and intensity of binding in the periportal region during perfusion in the retrograde direction was similar to that in the pericentral region during perfusion in the anterograde direction. It is concluded that low oxygen concentration rather than the non-homogeneous distribution of nitroreductase activity is the primary determinant of 2-nitroimidazole binding in liver.

Animals↗
PubMed1995

Method for cohort and nested case-control studies: the prevalence, timing and effectiveness of obstetric ultrasound, Victoria 1991-1992.

The study was designed to assess the effectiveness of obstetric ultrasound in the diagnosis of congenital malformations and to establish its prevalence of use and timing. Statewide data were collected in 138 of the 141 obstetric hospitals in Victoria over a 12-month period during 1991-1992. Within the final cohort of 55,226 mothers providing responses, a nested case-control study group was formed. This group comprised 719 cases (infants born with one or more malformations potentially diagnosable at 16-20 weeks) and 703 controls (non-malformed infants). The cases for the group were extracted from the Victorian Congenital Malformations Register; controls were randomly selected from the Victorian Perinatal Data Collection Unit's database. Of the 1422 in the study group, 1328 medical records were validated in 100 hospitals. The design, method, procedure, sample and outcome are described for the cohort and nested case-control studies. At the conclusion of the study it was established that major variations between the cohort and missing data were confined to mothers less likely to have had a spontaneous vaginal delivery or to those with poor perinatal outcome. There was no significant selective loss of cases or controls in the nested case-control study group.

Case-Control Studies↗
PubMed1995

The prevalence and timing of obstetric ultrasound in Victoria 1991-1992: a population-based study.

A statewide study to ascertain the number of ultrasound scans received by women in pregnancy, to identify the proportion having a scan at 16 to 20 weeks' gestation, and to establish where the scan at 16 to 20 weeks was performed was carried out between January, 1991 and June, 1992 in Victoria. Additional data were collected by midwives and entered on the perinatal morbidity statistics form routinely completed for all births. Of 52,319 women providing responses, 3.1% did not have a scan. Of the remaining 96.9% who had a scan, 73.5% were scanned at 16 to 20 weeks' gestation. Predictors of not having a scan were maternal birthplace and higher parity: previous perinatal death(s), and attendance at nonteaching hospitals predicted the opposite. Predictors of being scanned were location of hospital (country), maternal birthplace, higher parity and maternal age (< 20 years). Substantial differences in frequency and timing were found between hospitals attended. Factors associated with the pattern of scanning are not readily explicable in terms of risk of malformations or women's choices.

Adult↗
PubMed1995

[Closure of large psychiatric hospitals in England].

Contrary to the procedure followed in German-speaking countries, British national health policy since the fifties has been to promote and actively effect the closure and winding up of large psychiatric hospital centres in favour of alternative structures. The present article presents a preliminary balance sheet on 39 hospitals that have been closed since 1961 to the present day in the course of this shift-in-emphasis policy.

Community Mental Health Services↗
PubMed1994

Characterization of phosphodiester adducts produced by the reaction of cyanoethylene oxide with nucleotides.

Cyanoethylene oxide (CEO), a putative toxic and carcinogenic metabolite of acrylonitrile, is a direct-acting mutagen. The focus of this study was to elucidate potential adducts responsible for the mutagenic effect of CEO by characterizing products from the reaction of CEO with nucleotides. The reaction of CEO with the 5'-monophosphates of deoxyguanosine, deoxyadenosine, deoxycytidine or deoxythymidine resulted in the formation of at least one adduct for each nucleotide. Using two-dimensional NMR spectroscopy and fast atom bombardment mass spectrometry, CEO-nucleotide adducts (approximately 25% modification) were characterized as 2-cyano-2-hydroxyethyl phosphodiesters. The isolate from the reaction of deoxyguanosine-5'-monophosphate (dGMP) with CEO contained a second adduct, identified as N7-(2-cyano-2-hydroxyethyl)-dGMP. Single and double strand breaks, which were observed in supercoiled pBR322 plasmid DNA exposed to CEO (> 50 mM), may arise following formation of cyanohydroxyethyl phosphotriester adducts. The characterization of these phosphodiester adducts in vitro may provide insight into the intermediates responsible for the genotoxic effect of CEO in vivo.

Chromatography, High Pressure Liquid↗
PubMed1993

Characterization of an adduct and its degradation product produced by the reaction of cyanoethylene oxide with deoxythymidine and DNA.

Cyanoethylene oxide (CEO), the putative toxic and carcinogenic metabolite of acrylonitrile, is a direct-acting mutagen. CEO reacted with deoxythymidine (dT) to form a single adduct (approximately 3% dT modified). Using two-dimensional NMR spectroscopy and fast atom bombardment mass spectrometry, this adduct was identified as N3-(2-cyano-2-hydroxyethyl)deoxythymidine. Subsequently, degradation of the adduct yielded N3-(2,2-dihydroxyethyl)deoxythymidine, a hydrated form of N3-(oxoethyl)deoxythymidine. N3-(2-cyano-2-hydroxyethyl)deoxythymidine was also detected in the reaction of [2,3-14C]CEO with calf thymus DNA. Small UV peaks, not present in the control, were detected from the reaction of CEO with dA, dG and dC. However, neither their retention times nor spectral characteristics corresponded with the standards used in this study. Characterization of this cyano-hydroxyethyl adduct and its degradation product following in vitro exposure of nucleosides to CEO may provide insight as to the types of adducts that could be assessed as biomarkers in vivo, and the modifications responsible for the mutational effects of CEO.

Animals↗
PubMed1991

Clearing the cataract backlog in a (not so) developing country.

There is a significant backlog of patients waiting for cataract operations in the United Kingdom. In England in the first quarter of 1989, there were 74,000 patients in total on ophthalmology waiting lists, of which approximately 75% were cataract cases. Although there is currently a significant shortfall of around 225 consultant ophthalmologists, as defined by the College of Ophthalmologists' standard, the backlog is also due to the imbalance in, and inefficient use of, resources. There are a number of possible ways of clearing the backlog, including local initiatives, contracting for clinical services and the expansion of day-case surgery, which has been shown to be a cost-effective alternative to in-patient surgery. However, not only are reorganisations in the provision of surgical services required, managerial initiatives also need to be taken.

Ambulatory Surgical Procedures↗
PubMed1981

Midnight magic?

Explore the source record for details and available documents.

Bed Occupancy↗
PubMed1975

The influence of age and the level of arterial blood pressure on the changes in forearm blood flow resulting from sudden alterations in local vascular transmural pressure.

Forearm blood flow was measured by venous occlusion plethysmography in normotensive subjects of various ages and in patients with treated or untreated hypertension. Brief exposure of one forearm to pressures below atmospheric was used to study the transient local changes in arterial inflow which occurred with changes in transmural pressure induced in this way. The increase in initial arterial inflow with such an exposure to suction in a group of young normotensive women was only slightly reduced in two groups of older women. However, a group of subjects with untreated hypertension showed a significantly smaller initial inflow during the suction. There was some indication that adequate treatment of high blood pressure might reverse this effect.

Adult↗