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Biomedical subjects

J Webb

Publications and source records attributed to J Webb.

At least 19 recordsLinked to original sources
PubMed2006

Dependence of ammonia emissions from housing on the time cattle spent inside.

Buildings housing cattle contribute 19% (42 kt NH3-N yr(-1)) of total UK ammonia (NH3) emissions. In the UK there is not usually an abrupt switch from cattle being kept inside to when they are turned out to graze 24 h a day. Moreover, during the summer dairy cows return to the farm twice a day to be milked and may spend some time inside buildings. Hence, there is uncertainty over the treatment of the transitional and summer periods when inventorying NH3 emissions. The aim of this study was to measure, under controlled and replicated conditions, the relationship between the number of hours cattle spend in buildings and the NH3 emissions from those buildings. Our results indicate that NH3 emissions decrease as the proportion of the day cattle spend in the buildings decreases, although the trend is not linear. Daily emission rates from cattle housed for 2 h ranged from 1.6 to 6.2 g NH3-N lu(-1) whereas emissions from cattle housed for 24 h ranged from 8.1 to 24.1 g NH3-N lu(-1). To significantly reduce NH3 emissions in comparison to those from buildings where cattle are housed for 24 h, the occupancy would have to be reduced to no more than 6 h each day. Thus, the strategy of extending the grazing season by allowing cattle to graze for c. 4 to 12 h during the winter is unlikely to reduce NH3 emissions from buildings or overall.

Air Pollutants↗
PubMed2006

Decrease of soil fertility and release of mercury following deforestation in the Andean Amazon, Napo River Valley, Ecuador.

Soil erosion and degradation provoked by deforestation in the Amazon is a global concern, and recent studies propose a link between deforestation, soil erosion and the leaching of naturally occurring mercury (Hg). In the Ecuadorian Amazon, elevated deforestation rates and the proximity of volcanoes could play an important role in soil fertility and soil Hg levels. The goal of this study is to evaluate the impacts of deforestation on Andisol and Inceptisol fertility and Hg levels in the Napo River Valley, Ecuador. Results show a significant decrease in surface soil organic matter (-15% to -70% of C and N) and exchangeable cations (-25% to -60%) in deforested plots. Hg concentrations at the surface (0-5 cm), higher in Andisols (225 ng/g average) than in Inceptisols (95 ng/g average), show a decrease of up to 60% following deforestation. Soil erosion exposes the mineral horizon, a layer with a higher Hg burden, to the elements thus provoking and accelerating Hg leaching. These results suggest that deforestation and the associated Hg leaching could contribute to the fish Hg contamination measured in the Napo River watershed.

Agriculture↗
PubMed2005

Percutaneous valve repair and replacement techniques.

Valvular heart disease is a significant cause of morbidity and mortality. Rates increase with age and the prevalence will increase as the population ages. Several factors have led to an interest in expanding percutaneous valve repair and replacement techniques to more lesions in more patients. This review explores current percutaneous valve repair and replacement techniques in mitral stenosis, mitral regurgitation, aortic stenosis and aortic regurgitation in adults, outlines the future directions, and discusses some technique-related issues.

Endoscopy↗
PubMed2005

Managing ammonia emissions from livestock production in Europe.

Around 75% of European ammonia (NH(3)) emissions come from livestock production. Emissions occur at all stages of manure management: from buildings housing livestock; during manure storage; following manure application to land; and from urine deposited by livestock on pastures during grazing. Ammoniacal nitrogen (total ammoniacal-nitrogen, TAN) in livestock excreta is the main source of NH(3). At each stage of manure management TAN may be lost, mainly as NH(3), and the remainder passed to the next stage. Hence, measures to reduce NH(3) emissions at the various stages of manure management are interdependent, and the accumulative reduction achieved by combinations of measures is not simply additive. This TAN-flow concept enables rapid and easy estimation of the consequences of NH(3) abatement at one stage of manure management (upstream) on NH(3) emissions at later stages (downstream), and gives unbiased assessment of the most cost-effective measures. We conclude that rapid incorporation of manures into arable land is one of the most cost-effective measures to reduce NH(3) emissions, while covering manure stores and applying slurry by band spreader or injection are more cost-effective than measures to reduce emissions from buildings. These measures are likely to rank highly in most European countries.

Agriculture↗
PubMed2005

Monocytes are highly sensitive to clostridium difficile toxin A-induced apoptotic and nonapoptotic cell death.

In this study we investigated the in vitro responses of peripheral blood mononuclear preparations and purified monocytes to Clostridium difficile toxin A. In contrast to the responses of T and B cells, exposure to toxin A led to a rapid loss of monocytes in a time- and dose-dependent fashion (the majority of cells were lost within 24 h of exposure to >100 ng of toxin per ml). Transmission electron microscopy, flow cytometry, and fluorescence microscopy after propidium iodide and Hoechst staining showed that cell death in purified preparations of monocytes following exposure to 100 and 1,000 ng of toxin A per ml occurred by apoptosis. Further studies showed that 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazole-carbocyanine iodide aggregates were retained within toxin A-exposed monocyte mitochondria, but cytochrome c was released, suggesting that the apoptotic cascade was triggered in the absence of mitochondrial permeability transition. There was also an increase in caspase-3 activity in toxin A-stimulated monocytes. Following exposure to very high concentrations of toxin A (30 microg/ml), monocyte cell death was predominantly of the necrotic type, with rapid extracellular release of lactate dehydrogenase. These studies demonstrated that C. difficile toxin A has a cell-specific effect, in which monocytes exhibit greater susceptibility than lymphocytes and their death is induced in a concentration-dependent manner.

Apoptosis↗
PubMed2004

Fixed or mobile bearing unicompartmental knee replacement? A comparative cohort study.

Unicompartmental knee replacement (UKR) for anteromedial osteoarthritis is a well-established technique. Numerous clinical outcome studies demonstrate good medium and long-term results. The aim of this prospective study was to compare the complications and short-term clinical outcome of the St. Georg Sled, a fixed bearing UKR, with the Oxford mobile bearing UKR. Outcome at 2 years was assessed using the Bristol knee score and the Oxford knee score; in addition, complications occurring since formal scoring at 2-year follow-up were recorded. A total of 47 Oxford UKRs and 57 St. Georg Sled UKRs were performed in 91 patients, none of whom were lost to follow-up. At 2 years, both outcome measures were better for the St. Georg Sled Group. The pain component of the Bristol knee score was significantly better for this group (p-value = 0.013). Three patients in the Oxford group had bearing dislocations and a further four patients required revision (mean time to revision 3.0 years). In the St. Georg Sled group, three patients required revisions (mean time to revision 3.4 years). These results demonstrate that in the short-term, the Oxford mobile bearing prosthesis has a higher re-operation rate and that the St. Georg Sled achieves better pain relief. The functional scores of the two groups were similar.

Aged↗
PubMed2004

Identification of up-regulated genes by array analysis in scrapie-infected mouse brains.

The major neuropathological features of the transmissible spongiform encephalopathies (TSEs) are well documented, however, the underlying molecular events are poorly defined. We have applied cDNA expression arrays and quantitative RT-PCR to the study of gene expression in the brain, and more specifically in the hippocampus, of the well-characterized ME7/CV mouse model of scrapie. The number of genes showing consistent, scrapie-associated changes in expression was limited, and was primarily restricted to glial-associated genes. Increased expression of genes encoding glial fibrillary acidic protein, vimentin, complement component 1q (alpha and beta polypeptides), cathepsin D, clusterin and cystatin C was evident in the hippocampus from 170 days after inoculation (dpi), with expression increasing thereafter to terminal disease (225-235 dpi). Elevation of gene expression preceded clinical disease by approximately 30 days, and coincided with a 20-day period in the ME7/CV model during which 50% of the CA1 hippocampal neurones are lost. Increased expression of cystatin C, an inhibitor of lysosomal cysteine proteases, is a novel finding in the context of TSE neuropathology and was confirmed by Western analysis and immunocytochemistry.

Animals↗
PubMed2002

Ammonia emission, deposition and impact assessment at the field scale: a case study of sub-grid spatial variability.

A local ammonia (NH3) inventory for a 5x5 km area in central England was developed, to investigate the variability of emissions, deposition and impacts of NH3 at a field scale, as well as to assess the validity of the UK 5-km grid inventory. Input data were available for the study area for 1993 and 1996 on a field by field basis, allowing NH3 emissions to be calculated for each individual field, separately for livestock grazing, livestock housing and manure storage, landspreading of manures and fertiliser N application to crops and grassland. An existing atmospheric transport model was modified and applied to model air concentrations and deposition of NH3 at a fine spatial resolution (50 m grid). From the mapped deposition estimates and land cover information, critical loads and exceedances were derived. to study the implications of local variability for regional NH3 impacts assessments. The results show that the most extreme local variability in NH3 emissions, deposition and impacts is linked to housing and storage losses. However, landspreading of manures and intensive cattle grazing are other important area sources, which vary substantially in the landscape. Overall, the range of predicted emissions from agricultural land within the study area is 0-2000 kg N ha(-1) year(-1) in 1993 and 0-8000 kg N ha(-1) year(-1) in 1996, respectively, with the peak at a poultry farm located in the study area. On average, the estimated field level NH3 emissions over the study area closely match the emission for the equivalent 5-km grid square in the national inventory for 1996. Deposition and expected impacts are highly spatially variable, with the edges of woodland and small "islands" of semi-natural vegetation in intensive agricultural areas being most at risk from enhanced deposition. Conversely the centres of larger nature reserves receive less deposition than average. As a consequence of this local variability it is concluded that national assessments at the 5 km grid level underestimate the occurrence of critical loads exceedances due to NH3 in agricultural landscapes.

Agriculture↗
PubMed2002

Chorionicity determination in twin pregnancies: how accurate are we?

OBJECTIVES: To determine the accuracy of antenatal prediction of chorionicity in twin pregnancies in our institution. METHODS: Antenatal chorionicity was determined using the number of placental masses, the presence or absence of a twin peak sign and the fetal sex. The gestational age at assessment was documented. Postnatal diagnosis of chorionicity was determined by neonatal sex and placental pathology. RESULTS: Chorionicity was correctly determined in 95% of cases (n = 131); 91% of the monochorionic and 96% of the dichorionic pregnancies were correctly determined. If chorionicity was assessed prior to 14 weeks' gestation (n = 96) the correct diagnosis was made in all except one case. CONCLUSIONS: Ultrasound assessment of chorionicity has a high sensitivity and specificity. This is further improved if the assessment is performed prior to 14 weeks' gestation.

Adolescent↗
PubMed2002

Experience of explantation of Trilucent breast implants.

On 6 June 2000, the Medical Devices Agency (MDA) recommended that all Trilucent (soya-bean-oil filled) breast implants should be removed. This accelerated a trend that had already begun in our unit. This study follows our previous report on a 3 year series of women with Trilucent breast implants. The aim was to present our operative findings at explantation, and to correlate them with the preoperative signs and symptoms, the postoperative complications and the details of the hospital stay. In total, 44 patients (82 implants) underwent explantation, of whom 34 were cosmetic cases and 10 were reconstructive. Five patients had their implants removed before the MDA announcement. Implant rippling was the most common problem reported (25%), followed by pain (18%), implant deflation (9.1%) and capsular contracture (4.5%). Free oil was seen around the implant in 15 cases; four of these presented with clinical deflation, and three with rippling. The remaining eight patients were asymptomatic. We conclude that these implants tend to bleed, as evidenced by the presence of free oil around the implant in 34% of patients. The absence of free oil in 73% of the patients who presented with rippling suggests that the leaking oil is often metabolised and absorbed. The findings of this study are significant for women in whom free oil was found around the implant during explantation, and for those who still have Trilucent implants in place, for whatever reason, in spite of the MDA recommendation.

Adult↗
PubMed2002

239,240Pu and inorganic substances in aerosols from the vicinity of a waste isolation pilot plant: the importance of resuspension.

Aerosol samples were collected and analyzed to characterize the spatial and temporal variations in the concentrations of plutonium and selected inorganic substances in the atmosphere around the Waste Isolation Pilot Plant (WIPP). High-volume aerosol sampling was conducted at three sites: (1) On Site, (2) Near Field, and (3) Cactus Flats. 239,240Pu was determined by alpha spectrometry following chemical separations; mass loadings were determined gravimetrically. A separate set of low-volume aerosol samples was analyzed for major ions using ion chromatography and for trace elements by inductively-coupled plasma emission spectrometry and mass spectrometry. The average 239,240Pu activity concentrations in total suspended particle (TSP) samples (12 to 16 nBq m(-3)) were consistent with those previously reported, but they varied strongly with season, with the highest values generally in spring. Further, the 239,240Pu activity concentrations were comparable among the three sites, and therefore there was no evidence for elevated 239,240Pu activities due to WIPP operations. The fraction of the 239,240Pu activity concentrations in the PM10, samples (particles less than 10 microm diameter) relative to TSP was lower than the corresponding PM10/TSP ratios of either high-volume mass or several inorganics (sulfate, aluminum or lead), indicating that 239,240Pu tends to be on large particles. Aerosol mass loadings (microg m(-3)) and 239,240Pu activity concentrations were correlated for all sets of samples, but at On Site, the TSP samples showed higher mass to 239,240Pu ratios than the other sites. Thus activities or processes occurring at or near the WIPP site evidently produced aerosols that contributed to the mass loadings but contained less 239,244Pu than ambient aerosols. About 63% of the variability in 239,240Pu activity concentrations was explained by wind travel, sampling location, length of the sampling interval, and aerosol mass. 239,240Pu activity concentrations also were correlated with aluminum (an indicator of mineral dust), further implicating the resuspension of soils as an important determinant of 239,240Pu in aerosols. The 239,240Pu/Al ratios for the aerosols were higher than in soils, and this could be explained by the preferential binding of 239,240Pu to small soil particles that have large surface area to mass ratios and also have higher aluminum contents than larger particles.

Aerosols↗
PubMed2002

Voxel based morphometry of grey matter abnormalities in patients with medically intractable temporal lobe epilepsy: effects of side of seizure onset and epilepsy duration.

OBJECTIVES: To investigate the use of whole brain voxel based morphometry (VBM) and stereological analysis to study brain morphology in patients with medically intractable temporal lobe epilepsy; and to determine the relation between side, duration, and age of onset of temporal lobe epilepsy, history of childhood febrile convulsions, and grey matter structure. METHODS: Three dimensional magnetic resonance images were obtained from 58 patients with left sided seizure onset (LSSO) and 58 patients with right sided seizure onset (RSSO), defined using EEG and foramen ovale recordings in the course of presurgical evaluation for temporal lobectomy. Fifty eight normal controls formed a comparison group. VBM was used to characterise whole brain grey matter concentration, while the Cavalieri method of modern design stereology in conjunction with point counting was used to estimate hippocampal and amygdala volume. Age and sex were used as confounding covariates in analyses. RESULTS: LSSO and RSSO patients showed significant reductions in volume (using stereology) and grey matter concentration (using VBM) of the hippocampus, but not of the amygdala, in the presumed epileptogenic zone when compared with controls, but hippocampal (and amygdala) volume and grey matter concentration were not related to duration or age of onset of epilepsy. LSSO and RSSO patients with a history of childhood febrile convulsions had reduced hippocampal volumes in the presumed epileptogenic zone compared with patients without such a history. Left amygdala volume was also reduced in LSSO patients with a history of childhood convulsions. VBM results indicated bilateral thalamic, prefrontal, and cerebellar GMC reduction in patients, which correlated with duration and age of onset of epilepsy. CONCLUSIONS: Hippocampal sclerosis is not necessarily the consequence of recurrent temporal lobe seizures. A major cause of hippocampal sclerosis appears to be an early aberrant neurological insult, such as childhood febrile seizures. Secondary brain abnormalities exist in regions outside the presumed epileptogenic zone and may result from recurrent seizures.

Adolescent↗
PubMed2001

Estimating the potential for ammonia emissions from livestock excreta and manures.

This paper reports a desk study to quantify the total-nitrogen (N) and ammoniacal-N contents of livestock excreta, and to compare them with estimates of N losses to the environment from that excreta. Inventories of ammonia (NH3), nitrous oxide (N2O), dinitrogen (N2), and nitric oxide emissions (NO), together with estimates of nitrate (NO3-) leaching and crop N uptake were collated. A balance sheet was constructed to determine whether our estimates of N in livestock excreta were consistent with current estimates of N losses and crop N uptake from that N, or whether emissions of N compounds from livestock excreta may have been underestimated. Total N excretion by livestock in England and Wales (E&W) was estimated as 767-816 x 10(3) t of which 487-518 x 10(3) t was estimated to be total ammoniacal-N (TAN). Estimates of NH3 and N2O losses during housing and storage were derived from the difference between the total amount of TAN in excreta deposited in and around buildings, and the total amount of TAN in manure (i.e. the excreta deposited in and around buildings after collection and storage) prior to spreading and were ca. 64-88 x 10(3) t. The NH3-N emission from livestock buildings and manure storage in E&W quoted in the UK Emission Inventory (Pain et al., 1999. Inventory of Ammonia Emission from UK Agriculture, 1977. Report of MAFF contract WAO630, IGER, North Wyke) is ca. 80 x 10(3) t. Losses from NO3- leaching in the season after manure application and grazing were estimated as 73 and 32 x 10(3) t, respectively. Other gaseous losses of N were estimated as ca. 54 x 10(3) t. Crop uptake of manure N was estimated to be between 7 and 24 x 10(3) t. For manures, estimated N losses, immobilization and crop uptake total 326 x 10(3) t compared with estimates of 293-319 x 10(3) t TAN in excreta. Total N losses and crop uptake from TAN deposited at grazing were estimated to be 179-199 x 10(3) t compared with ca. 224 x 10(3) t TAN excreted. Thus all the TAN in manures appears to be accounted for, but ca. 25-45 x 10(3) t of TAN in urine deposited at grazing were not, and could be an underestimated source of gaseous emission or nitrate leaching.

Ammonia↗
PubMed2001

Hamstrings and the anterior cruciate ligament deficient knee.

This article outlines the background and preliminary results of the work I undertook during a year of full time research supported by the BASK Knee Research Fellowship. The work was done at the Oxford Orthopaedic Engineering Centre (OOEC). The chance to come out of full time clinical work should in my opinion always be taken. It allows you time to think in a little more depth about a particular area of interest and to work with people in full time research. I found that working alongside the Biomechanical Engineers and their PhD students was mutually beneficial. They learn more about the background to the clinical problems requiring their input, whilst the Orthopaedic trainees undertaking projects in the department learnt a more rigorous approach to our methodology.

Animals↗
PubMed2001

An audit of tunnel position in anterior cruciate ligament reconstruction.

We audited 114 primary anterior cruciate ligament (ACL) reconstructions. Notes were reviewed and tunnel positions assessed on lateral and AP radiographs. A literature review established optimal tunnel position. Sixteen surgeons performed 57 arthroscopic and 57 open reconstructions, using 24 hamstring and 90 bone-tendon-bone autografts. Eighty-five sets of radiographs were available for review. Sixty-five percent of femoral tunnels and 59% of the tibial tunnels were malpositioned in the sagittal plane. Guidelines for best practice are required for key procedures in each speciality. Tunnel position in ACL reconstruction can be easily measured and should be correct in at least 90% of cases.

Adolescent↗
PubMed2001

Rapid recovery after oxford unicompartmental arthroplasty through a short incision.

Forty Oxford medial unicompartmental arthroplasties (UCAs) were performed through a short incision medial to the patellar tendon, without dislocation of the patella, using updated instruments (Oxford Knee Phase III, Biomet Ltd., Bridgend, UK). The rate of recovery of these knees (measured by the time taken to achieve straight-leg raising, 70 degrees of flexion, and independent stair climbing) was compared with that of 20 Oxford UCAs performed through an open approach with dislocation of the patella. Both groups were compared with 40 AGC (Biomet) total knee arthroplasties performed for osteoarthritis during the same time period. The average rate of recovery after the short-incision UCA was twice as fast as after open UCA and 3 times as fast as after total knee arthroplasty. Accuracy of implantation, assessed from 11 variables seen on fluoroscopically centered postoperative radiographs, was the same after UCA by the short-incision approach as after the open approach, suggesting that the short-term advantage of increased speed of recovery was gained without affecting the long-term results. We now employ the short incision with the phase III instruments for all UCAs.

Aged↗