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Biomedical subjects

M Edwards

Publications and source records attributed to M Edwards.

At least 73 records · Page 4Linked to original sources
PubMed2000

Successful contraception in a herd of Chinese goral (Nemorhaedus goral arnouxianus) with melengestrol acetate.

Thirteen Chinese goral (Nemorhaedus goral arnouxianus) (five males and eight females) were each given 0.8 mg of melengestrol acetate orally in pelleted food for 224 days. The previous breeding season, six of the eight females calved (two were immature). No calf was born during the treatment season. The season after treatment, six females calved (one was immature prior to treatment). Two females were moved to other institutions, and the status of these is unknown. On the basis of this information, melengestrol acetate in feed was successful in preventing conception and was reversible. This treatment did not prevent the siring of offspring the following year and did not prevent a female that was subadult prior to the treatment from calving.

Administration, Oral↗
PubMed2000

Vertical alignment axis for transtibial prostheses: a simplified alignment method.

BACKGROUND AND PURPOSE: To evaluate a simplified method of alignment for fitting a transtibial prosthesis known as the vertical alignment axis method. METHODS: We measured the relationship between the vertical projection of the prosthetic socket center (geometric center of the cross section of the transtibial prosthetic socket at the level of the patella tendon bar) and the alignment reference center (junction of the middle and posterior thirds of the longitudinal axis of the shoe) in 36 dynamically aligned transtibial prostheses. The prostheses were fabricated by students, and the fit (proper vs improper) was assessed by the faculty. RESULTS: The faculty members found 26 of the 36 prostheses to be properly fitted. The vertical projections of the socket centers of the properly-fitted prostheses were concentrated within a small area of the shoe tracing (a mean value of 1.3 mm medially and 6.4 mm anteriorly from the alignment reference center). Conversely, in the improperly-fitted prostheses, the vertical projections of the socket center were scattered well away from the alignment reference center; the mediolateral deviation was significantly greater for improperly-fitted prostheses than for those that were properly fitted (p < 0.001). CONCLUSIONS: These results demonstrate the usefulness of the vertical alignment axis procedure. This procedure may help clinicians to better understand the alignment of transtibial prostheses and gait deviations associated with improper prosthesis fit.

Adult↗
PubMed2000

Bile duct carcinoma: trends in treatment in the nineties.

Surgical resection provides the only known chance of cure for cholangiocarcinoma, and even then the 5-year survival is only 10 to 20%, and only one-third of patients are resectable for cure at the time of diagnosis. In recent years we have had considerable experience with endoscopic stenting to palliate common bile duct cancers. This has prompted us to evaluate our results for both endoscopic and surgical treatment of cholangiocarcinoma. From January 1990 through June 1999, we reviewed our endoscopic retrograde cholangiopancreatography registry and the hospital records for patients we treated for cholangiocarcinoma. Fifty patients were identified: 45 with cholangiocarcinoma and five with gallbladder cancer (who were excluded). The surgical group consisted of 16 patients: in 14 patients, resection for cure was possible whereas two had palliative procedures. There was one mortality (6%) and the median survival was 16 months. There have been no long-term surgical survivors, but 2 patients are alive at 24 months. We treated 29 patients with advanced disease with endoscopic stents (the endoscopic group) mainly for relief of obstructive jaundice. Six of 29 patients in the endoscopic group were critically ill and died in less than 4 weeks, whereas 23 patients who were in better condition survived for a mean of 10 months (range 2-84 months). We conclude that for common duct bile cancer surgical resection remains the treatment of choice but is applicable in only 30 to 35 per cent of cases. Endoscopic stenting effectively relieves jaundice and can provide long-term palliation comparable with surgical bypass; 12 of 29 patients in our endoscopic group survived 12 months or longer, and one is alive at 84 months after initial stenting.

Adult↗
PubMed1999

Cardiac operations in patients with low-grade small lymphocytic malignancies.

BACKGROUND: Low-grade small lymphocytic (B cell) malignancies (encompassing chronic lymphocytic leukemia and some types of non-Hodgkin lymphoma) are diseases of the elderly. Open cardiac procedures are known to have increased risk of postoperative infection and other morbidities in these immunodeficient patients. Outcome of open cardiac procedures in these patients was reviewed retrospectively. PATIENTS: Thirteen patients (aged 58-82 years, 11 men, 2 women) with these lymphocytopathologic diseases (8 with chronic lymphocytic leukemia and 5 with non-Hodgkin lymphoma) underwent cardiac operations between January 1977 and June 1998. Mean age was 72 +/- 2.1 years. Isolated coronary artery bypass grafting was performed in 11 and combined procedures and double valve replacement were performed in 1 each. Preoperatively, 9 patients were in a low-risk clinical stage. Mean preoperative duration of lymphocytopathologic disease was 6.1 +/- 1.6 years. Mean preoperative New York Heart Association functional class was 2.8. RESULTS: There was no operative death. Average stay in the intensive care unit was 41.4 +/- 8.6 hours. Postoperative leg and superficial sternal wound infections were encountered in 3 patients. Average postoperative hospital stay was 10.0 +/- 1.7 days. During the follow-up up to 72 months, 1 patient underwent a second cardiac operation. There was 1 late death 4 years later. Coronary stenting was done in 1 patient and a cardioverter-defibrillator was implanted in another patient for recurrent angina. Three patients underwent chemotherapy. Cardiac and lymphocytopathologic status remained stable in others. CONCLUSIONS: Acceptable outcome may be anticipated after cardiac operations in patients with low-grade chronic lymphocytic leukemia and non-Hodgkin lymphoma in early stages. However, the possibility of infection and progression of cardiac and lymphocytopathologic status in these patients should call for caution.

Age Factors↗
PubMed1999

Orientation and luminance polarity tuning of the transient-vergence system.

Previously, Edwards, Pope & Schoor, Vision Research, 38, 705-717, demonstrated that transient disparity vergence appears to be mediated by a system that employs a single low-pass sensitive spatial channel whose performance is not reduced by dichoptic mixed contrasts (no contrast paradox) or dichoptic mixed spatial frequencies. This broadband tuning to both contrast and spatial frequency may be indicative of a second-order or non-linear envelope extraction system. The current study tests for lack of tuning to orientation and luminance polarity which are typically taken as evidence of a second-order system. We found that when the transient vergence system was simultaneously presented with both convergent and divergent disparities, there was a small but distinct bias in favor of responding in the direction defined by matched orientations or luminance polarities over unmatched pairs. Although less frequent, responses to orthogonal carriers or opposite luminance polarities were possible. The vergence system could match a horizontal with a vertical carrier, or a light gaussian with a dark gaussian. The degree of orientation or luminance polarity tuning varied inversely with the disparity magnitude over the range of 2.5-5 degrees, and the orientation tuning peaked at a spatial frequency about 2 cpd. At all disparities tested, however, the tuning was very broad, and other candidate features for mediating transient-vergence need to be investigated.

Contrast Sensitivity↗
PubMed1999

Orientation tuning of the transient-stereopsis system.

Stereo-perception appears to be mediated by at least two systems: a transient system that processes stimuli presented briefly and a sustained one that processes stimuli presented for longer durations. In this paper we investigated the tuning of the transient-stereopsis system to stimulus orientation. Narrowband-gabor targets with a constant envelope size (Gaussian standard deviation of 1 degree) were presented for brief (140 ms) durations at large (from 4 to 8 degrees) disparities. The results were as follows: (1) while observers could extract depth from orthogonally-oriented gabors at above chance levels, their performance was worse than that with gabors of matched orientation; (2) varying the relative contrasts of the two orthogonally oriented gabors of the same spatial frequency resulted in a reduction in performance; (3) varying the relative spatial frequencies of the orthogonally-oriented gabors impaired performance, relative to that for matched frequencies; and (4) varying the relative contrasts of orthogonal gabors that were at different spatial frequencies could improve performance. These results indicate that transient stereo-performance in the orthogonal condition was not mediated by the channels that extracted depth in either the horizontal- or vertically-matched gabor conditions. This apparent lack of orientation tuning is indicative of a second-order pathway. That this performance was mediated by a binocular, as opposed to a monocular channel, is supported by the finding that performance decreased as the contrast of one of the gabors was reduced. The finding that performance with orthogonal gabors of unmatched spatial frequency (0.5 and 4 cpd) could be improved by varying their relative contrasts suggests that the binocular spatial-frequency tuning exhibited by this channel is broadband in nature. Finally, the observation that lowering the contrast of either the high or low spatial-frequency gabor improved performance suggests the presence of at least two broadband channels: one with its peak sensitivity at a low and the other at a high spatial-frequency.

Contrast Sensitivity↗
PubMed1999

Global-motion detection with transparent-motion signals.

A number of experiments were conducted to compare the ability of observers to extract unidirectional and bidirectional (transparent) global-motion signals. In the unidirectional condition, the noise signal consisted of purely randomly-moving dots while in the bidirectional condition, a number of the randomly moving dots were replaced by the same number of dots moving in a specific (secondary-signal) direction. The threshold measure was the minimum number of signal dots required to determine the global-motion direction. For the bidirectional condition, parameters varied were the angular separation between the global-motion and secondary-signal directions and the strength of the secondary signal. Thresholds for unidirectional and bidirectional conditions were the same when the angular difference between global-motion and secondary-signal directions were 90 degrees or greater, i.e. the ability of observers to extract a transparent signal was the same as their ability to extract a unidirectional one. Similarly, with motion-in-depth signals, thresholds for extracting a centripetal signal were not elevated by replacing a number of the randomly-moving noise dots with the same number centrifugally-moving dots. The results are interpreted as indicating that motion signals moving between 90 and 180 degrees to the global-motion direction provide uniform masking of the global-motion signal. For angular separations less than 90 degrees, a suprathreshold secondary signal resulted in threshold elevation. This result could be due, to stronger inhibition from motion units tuned to similar (< 90 degrees) directions, broad directional-tuning of the underlying motion units (changing the task from signal detection to a signal discrimination) or a combination of the two.

Depth Perception↗
PubMed1999

Extraction of depth from opposite-contrast stimuli: transient system can, sustained system can't.

The ability of observers to extract depth from opposite luminance-contrast-polarity stimuli was investigated. The stimuli consisted of two dichoptic-pairs of Gaussians, with one of the Gaussians in each pair having a positive contrast-polarity and the other a negative contrast-polarity. Stimulus durations ranging from 0.2 to 4 s were used. This range of durations was employed to reveal stereo mechanisms that were preferentially sensitive to transient or sustained stimuli. Stimuli were presented in a raised-cosine temporal envelope. Performance with stimuli of the same contrast-polarity was also tested. Observers could easily perceive depth with the same-polarity stimuli, at both long and short durations. Depth could be perceived with low-contrast opposite-polarity stimuli only at short durations. However, depth could be perceived with long-duration stimuli presented within a raised cosine temporal-envelope if a high contrast was used. Depth could also be perceived with low-contrast long-duration stimuli if they were presented within a rectangular temporal-envelope. These findings suggest there are separate sustained and transient mechanisms for stereopsis and that the transient-stereoscopic system can extract depth from opposite-contrast stereograms while the sustained system cannot. Further, it is likely that depth perception with opposite-contrast stereograms found in many previous studies was mediated by the transient-stereopsis system.

Contrast Sensitivity↗
PubMed1999

Depth aliasing by the transient-stereopsis system.

A fundamental problem in stereo-processing is determining which images in the two eyes correspond to the same object. This problem is particularly pronounced with periodic stimuli where it is theoretically possible to binocularly match a given feature in one eye with any of the identical features in the other eye. One way to minimise the likelihood of the occurrence of such aliasing is to restrict the upper-disparity limit that a particular binocular cell can process to one-half of the spatial period to which the cell is sensitive. While such a restriction would not be a major problem for the sustained stereo-system (which processes small disparities) it would be for the transient system (which is capable of processing disparities as large as 10 degrees). Large-field sinewave variations in luminance were used to compare the propensity of the sustained and transient systems to exhibit depth aliasing--that is to signal a depth sign that corresponds to a binocular match that is greater than the nearest-neighbour pairing. Results were that: depth aliasing was exhibited at short, but not at long durations; decreasing the disparity of the stimulus reduced the likelihood of depth-aliasing; and the critical disparity for this reduction in depth aliasing was dependent upon the spatial frequency of the stimulus, i.e. it was phase, not absolute disparity dependent. Based upon these results, we conclude that while the sustained system implements the half-cycle disparity-processing limit, the transient system does not.

Depth Perception↗
PubMed1999

Recurrence of maltreatment: an application of the National Child Abuse and Neglect Data System (NCANDS).

OBJECTIVE: The research describes and compares patterns of maltreatment recurrence across multiple states using large samples, confirms the patterns of recurrence found in the literature, and explores unreported patterns of recurrence. METHOD: A recurrence data set for calendar years 1994 and 1995 was constructed from the multi-state case level data from the National Child Abuse and Neglect Data System. These data were available for 10 states and included a range from 2,419 to 99,288 substantiated or indicated report-child pairs per state. A common set of data constructs lent consistency to data construction and analysis, while preserving differences in policy. Event History Analysis (survival) techniques were used. RESULTS: Single site studies were confirmed across the 10 states. These include the pattern where neglect is most likely to recur, followed by physical abuse and then sexual abuse. Similarly, younger children are more likely to recur. A finding of the analysis is that the likelihood of recurrence increases in a systematic and consistent fashion based upon the sequential ordering of recurrent maltreatment events. Also, the likelihood of recurrence is associated with the provision of postinvestigative services. CONCLUSION: Highly consistent patterns of recurrence were observed across states. Children experiencing multiple recurrences compared to no recurrence or one recurrence may represent a special at risk population requiring additional research. Adequate baselines and an understanding of recurrence is needed when considering recurrence as an outcome indicator or in developing risk assessment tools. Important recurrence patterns may be difficult to detect reliably with relatively small samples.

Adolescent↗
PubMed1999

Cardiac reoperations in octogenerians.

OBJECTIVE: In recent years, satisfactory outcome of primary cardiac operation in octogenerians and increased ageing of cardiac surgical population in western hospitals have led to increased expectations and referrals for reoperation. Outcome of reoperation in this aged subset was analysed. METHODS: Consecutive 18 octogenerians (mean age 81.2 years, 10 men, eight women) undergoing cardiac reoperations from November 1989 through August 1998 were retrospectively reviewed. RESULTS: They represented 6.2% of all octogenerian cardiac surgical patients and 2.7% of all reoperations during the same period. Mean preoperative NYHA class was 3.4 and Parsonnet score was 29.4. The interval to reoperation was 114.5+/-11.96 (4-188) months. Priority was urgent in 11 and elective in seven patients. The procedures included four AVRs, five MVRs (including two associated TVAs), six CABGs and one each of MVR with CABG, AVR with CABG and AVR, MVR and CABG. Average graft/patient was 2.3. Mean ICU stay was 4.6+/-1.5 (1-28) days. There was one hospital death (5.5%) on 18 pod after MVR in an 83-year-old woman. Mean postoperative stay was 20.2+/-5.13 (8-93) days. There were three late deaths (17.6%)--at 32 months after MVR, at 44 and 63 months after CABG. Long-term survivors were 90% among men and 50% among women who were followed up for 42.7+/-6.9 (9-93) months. Mean Karnofsky score in survivors at 1 year of follow-up was 78.5+/-2.9. Despite continued medication in all survivors, mean current NYHA is 1.9 and most have improved lifestyle. CONCLUSIONS: Satisfactory outcome may be expected after cardiac reoperations in highly selected octogenerians. However, increased procedural risks, complications, hospital stay and slower convalescence during early follow-up may be anticipated, and will indicate very careful screening. These results indicate a need to reconsider the treatment policy in primary operation with regard to choice of graft conduits and prosthetic valves in other elderly patients.

Age Factors↗
PubMed1999

Buffering capacities of soft drinks: the potential influence on dental erosion.

The pH of fruit juices and carbonated drinks are known to be low and have, therefore, been implicated in the increasing incidence of erosion. The ability of a drink to resist pH changes brought about by salivary buffering may play an important part in the erosion process. The aims of this study were to measure the initial pH of several widely available soft drinks and determine their buffering capacities. As part of a larger study, the following groups of drinks were tested: pure fruit juices, non-fruit-based carbonated drinks, fruit-based carbonated drinks, flavoured spring waters, and plain carbonated mineral waters as positive controls with still water as the negative control. The measurement of pH was carried out using a pH electrode connected to an Orion EA940 Ionanalyser. One hundred millilitres of each drink was then titrated with 1 M sodium hydroxide, added in 0.5 mL increments, until the pH reached 10. Each titration was repeated three times. The average initial pH was lowest for the non-fruit-based drinks (2.81+/-0.274) and highest for plain mineral water (7.4+/-0.1002). The buffering capacities can be ordered as follows: fruit juices>fruit-based carbonated drinks and flavoured mineral waters>non-fruit-based carbonated drinks>sparkling mineral waters>still mineral water. It is concluded that fruit juices and fruit-based carbonated beverages, with their increased buffering capacities, may induce a prolonged drop in oral pH.

Beverages↗
PubMed1999

Why? What? and How? IT provision for medical students in general practice.

OBJECTIVES: The aim of this paper is to discuss the increasing use of computers in undergraduate medical education and explore the why, what and how of providing IT facilities to undergraduate medical students when they are on placement in general practice. Adequate computing facilities are usually available within hospitals and medical schools, however, major changes are taking place in undergraduate education resulting in more teaching being undertaken in the community. Students will therefore need access to comparable facilities whilst in primary care settings in order for their training not to be compromised. SETTING: This paper describes one initiative addressing this need: the University Linked Practices (ULP) project in the Department of General Practice and Primary Care at St. Bartholomew's and the Royal London School of Medicine and Dentistry. DESIGN: We discuss the ways in which computers are currently being used in medical education and discuss some of the merits and drawbacks that are associated with this increasing drive to computerization.

Computer Literacy↗
PubMed1999

The effectiveness of different rat IgG subclasses as IgE-blocking antibodies in the rat basophil leukaemia cell model.

The degranulation of mast cells in an allergic response is initiated by the aggregation of high-affinity IgE receptors (Fc epsilon RI) by IgE and antigen. Recently it has been shown that such degranulation can be inhibited by cross-linking Fc epsilon RI and low-affinity IgG receptors (Fc gamma RII) which are also expressed by mast cells. The ability of various monoclonal antibodies to block the degranulation of rat basophil leukaemia (RBL) cells sensitized with IgE antidinitrophenyl (DNP) antibodies has been investigated. Sensitized cells were challenged with immune complexes formed using varying concentrations of antigen, and of both high- and low-valency antigen. It is reported here that rat IgG1 antibodies, which are associated in the rat with a Th1-type response, act as highly effective blocking antibodies over a wide concentration range. Rat IgG2a antibodies, which are associated with a Th2-type response, were able only to inhibit degranulation when immune complexes were formed with very low concentrations of high-valency antigen (DNP32-HSA). Under these conditions, some inhibitory activity was seen with high-affinity murine IgA anti-DNP but not with low-affinity rat IgG2b anti-DNP antibody-containing immune complexes. In addition to this inhibitory activity, IgG2a antibodies were shown to be capable of inducing degranulation of cells via unoccupied Fc epsilon RI. These results demonstrate that blocking activity may arise via both inhibitory receptors and by masking of antigen.

Animals↗