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Biomedical subjects

J Piper

Publications and source records attributed to J Piper.

At least 19 recordsLinked to original sources
PubMed1992

Biliary complications in pediatric liver transplantation. A comparison of reduced-size and whole grafts.

One of the major changes in liver transplantation has been the application of reduced-size liver transplants(RLT). RLT has the great advantage of expanding the donor pool up to ten times the weight of the recipient, thereby decreasing pretransplant mortality in the pediatric age group. It has been suggested that RLT is a risk factor for biliary complications. To analyze the role of RLT and biliary complications, the results of 213 consecutive liver transplants in 164 pediatric patients over a 6-year period will were reviewed. These included 113 whole-liver transplants and 100 reduced-size liver transplants (49 reduced cadaveric liver transplants (RCLT), 38 split-liver transplants (SLT) and 13 living-related liver transplants (LRLT). The average weight and age were significantly higher in recipients receiving whole-size grafts (average weight 18.4 mg, average age 4.9 years) than in those receiving reduced size grafts (average age 2.3 years, average weight 11.1 kg). Biliary reconstruction consisted of Roux-en-Y, cholangiojejunostomy (n = 203) or choledochocholedochostomy (n = 10). There were 29 total biliary complications, (13.6%) with no significant difference in the complication rate between the whole (n = 13, 11.5%) or reduced livers (n = 16, 16%). Biliary leakage was the most common complication (n = 20), and it occurred at the biliary enteric anastomoses (n = 10), the roux limb (n = 7), or at the cut edge (n = 3). Of the leaks occurring at the biliary enteric anastomoses, 50% were caused by hepatic artery thrombosis. Biliary obstruction accounted for their remaining complications (n = 9) or 4.2%. Actuarial survival from 6 years to a minimum of two months of follow-up was 73% in the whole-size and 70% in reduced-size liver transplants. This series demonstrates that the incidence of biliary complications is similar in reduced-size and full-size grafts. No grafts were lost to biliary complications in the absence of hepatic artery thrombosis.

Biliary Tract Diseases↗
PubMed1992

Comparison of haemostatic activity in haemodialysis and peritoneal dialysis patients with a novel technique, haemostatometry.

Bleeding due to impaired primary haemostasis is common in uraemia. However, thrombo-embolic episodes are also a clinical problem in dialysis patients. Platelet reactivity to shear stress (haemostasis, H1 and H2), exposure to collagen fibre (thrombus growth) and coagulation of flowing blood (clotting time, CT1 and CT2) were measured in non-anticoagulated blood samples taken immediately before and 18-24 h after haemodialysis (n = 26) and from patients maintained on continuous ambulatory peritoneal dialysis (CAPD, n = 30). H1 (p < 0.001), H2 (p < 0.01), percent thrombus growth rate (p < 0.03), CT1 (p < 0.01 and CT2 (p < 0.05) were restored towards normal after haemodialysis. Results obtained in the CAPD patients demonstrated that the mean values for formation of the haemostatic plug lay between the pre- and posthaemodialysis values; however, CT1 (p < 0.01) and CT2 (p < 0.05) were prolonged in CAPD compared with values after haemodialysis. These data, which indicate platelet function from non-anticoagulated blood and coagulation under flow conditions, (1) confirm that there is impaired haemostasis in uraemia; (2) demonstrate an improvement in haemostasis after haemodialysis; (3) show that peritoneal dialysis results in a haemostatic profile which falls between the pre- and posthaemodialysis pattern, and (4) show that neither dialysis modality returns haemostasis to normal.

Adult↗
PubMed1992

Adaptive classifiers for dicentric chromosomes.

Classification of dicentric chromosomes in a practical automatic screening system comprises three stages. The first generates plausible centromere candidates from each chromosome in an automatically segmented metaphase, and uses contextual knowledge to generate distributions of "probably true" and "probably false" centromeres, thus adapting to the conditions within a particular metaphase. The second stage classifier uses these distributions to re-classify the candidates as centromeres or non-centromeres. From this classification, likely dicentrics are found by counting centromeres; a third classifier attempts to reject false positives among the likely dicentric chromosomes, by comparing the feature values of the proposed centromeres of a chromosome and rejecting chromosomes for which these values do not satisfy certain similarity criteria. The second stage classifier may be a simple box classifier, or may use a variety of parametric Bayesian methods. The performance of these alternatives has been tested both on reference data sets comprising about 600 metaphases, and on larger data sets when embedded in a practical fully automatic dicentric pre-screening system. When operating parameters were such that a similar number of true positives were found by both classifiers, the Bayesian classifier produced about half as many false positive errors as the box classifier, with the final false positive rate being in the region of one candidate dicentric chromosome in every four cells.

Chromosome Aberrations↗
PubMed1991

Some methods of combining class information in multivariate normal discrimination for the classification of human chromosomes.

We consider the use of discriminant analysis based on an assumption of multivariate Normality for allocating human chromosomes in an automated system. In this context, the assumptions which might be made about the covariance matrices for the different chromosome classes have important implications for the error rate of the system and the time required to allocate a chromosome. Linear discriminant functions based on the assumption of a common covariance matrix for all classes are fast but sometimes give bigger error rates than the assumption of a separate covariance matrix for each class. The latter assumption requires many more calculations to evaluate the associated quadratic discriminant functions. However, it is possible to assume that the covariance matrices for the different classes are, in various senses, similar to one another in order to derive other methods of combining class information on variability. These methods are here incorporated in the estimative maximum-likelihood approach to discrimination. The methods considered lead to machine classification times of human chromosomes intermediate between those for the assumptions of a common or unrelated covariance matrices. They also require the simultaneous estimation of fewer parameters than the use of a separate covariance matrix for each chromosome class. The methods are illustrated by three data sets of very different quality. Graphs of estimated error rate against classification time show that some of these ways of combining class information can be useful in the trade-off of error rate against time.

Chromosome Banding↗
PubMed1991

Radiation dosimetry by automatic image analysis of dicentric chromosomes.

A system for scoring dicentric chromosomes by image analysis comprised fully automatic location of mitotic cells, automatic retrieval, focus and digitization at high resolution, automatic rejection of nuclei and debris and detection and segmentation of chromosome clusters, automatic centromere location, and subsequent rapid interactive visual review of potential dicentric chromosomes to confirm positives and reject false positives. A calibration set of about 15,000 cells was used to establish the quadratic dose response for 60Co gamma-irradiation. The dose-response function parameters were established by a maximum likelihood technique, and confidence limits in the dose response and in the corresponding inverse curve, of estimated dose for observed dicentric frequency, were established by Monte Carlo techniques. The system was validated in a blind trial by analysing a test set comprising a total of about 8000 cells irradiated to 1 of 10 dose levels, and estimating the doses from the observed dicentric frequency. There was a close correspondence between the estimated and true doses. The overall sensitivity of the system in terms of the proportion of the total population of dicentrics present in the cells analysed that were detected by the system was measured to be about 40%. This implies that about 2.5 times more cells must be analysed by machine than by visual analysis. Taking this factor into account, the measured review time and false positive rates imply that analysis by the system of sufficient cells to provide the equivalent of a visual analysis of 500 cells would require about 1 h for operator review.

Cells, Cultured↗
PubMed1991

Liver transplantation in children from living related donors. Surgical techniques and results.

Pediatric liver transplantation with reduced size donor organs (RLT) has evolved into a standard clinical procedure increasing the choices of recipients for their treatment. Nevertheless organ availability remains a major problem. The authors therefore have proposed to study the use of hepatic segments from living related donors (LRT) in a group of 20 children less than 2 years of age or weighing less than 15 kg, in whom standard indications for transplantation existed. Volunteer related donors were selected after medical and psychiatric evaluations, and the suitability of the donor's liver was established by functional and radiologic criteria. A two-stage informed consent process assured appropriate "volunteerism." Nineteen infants received LRT as first grafts and one as a second graft. Seventeen of the recipients are alive 3 to 18 months after LRT. Fifteen of 20 patients are currently at home with the original graft and normal liver function (bilirubin less than 1.5 mg/dl) after a median hospital stay of 27 days (range, 14-93 days). Four patients underwent retransplantation, in all cases due to arterial thrombosis. The overall graft survival for 20 primary LRTs is 75%, with follow-up between 3 and 18 months. A number of technical problems occurred during our initial trial, the most aggravating being vascular thrombosis. Refined approaches to vascular reconstruction should reduce the incidence of thrombosis and improve the rate of survival in future cases. The donor group for the initial 20 LRT procedures comprised 12 mothers, 7 fathers, and 1 grandmother. In addition one father and one uncle, who was an identical twin of the recipient's father, who did not qualify for anatomic reasons, were used in repeat LRT. All donors survived and are now in normal health between 3 and 18 months after LRT, having returned to all activities enjoyed before donation. The median hospital stay was 6 days (range, 5-14). Complications were minimal, and all were limited to the first three procedures, in which a full left hepatectomy was performed. After alteration of the procedure into a left lateral segmentectomy, no complications were encountered. The left lateral segmentectomy presents minimal surgical trauma to the liver and should remain the primary approach for obtaining a liver graft from a living donor. For children, transplantation of a left lateral segment from a live donor provides a new way of providing a transplant of appropriate size and with good function. The success of this program has led to the acceptance of LRT for general clinical application in the authors' institution.

Adult↗
PubMed1990

Automatic detection of fragile X chromosomes using an X centromere probe.

In order to score for the fragile X syndrome, blood samples are prepared with absorption stain labeling by in situ hybridisation of the X chromosome centromeres. Metaphases are located, digitised at high resolution, and segmented fully automatically. A three stage adaptive classification scheme for labeled X chromosomes is then applied. This consists of a simple box classifier to identify plausible X and false positive X chromosomes, followed by a quadratic discriminant classifier that is re-trained for each sample. The modal number of X chromosomes is then determined for each sample and used to refine the classification. A simple fragile site detector is applied to the distal portion of the detected X chromosome long arms. From the results we estimate computer and operator time requirements for a screening system in which the operator reviews only the apparently fragile X chromosomes detected by the computer.

Biotin↗
PubMed1990

Relationships between happiness, behavioural status and dependency on others in elderly patients.

Feelings of dependency on others were measured, by different scales, in two different samples of elderly people: 33 acute in-patients and 25 attenders at a geriatric day hospital. Findings were similar in each location. Dependent attitudes increased with the duration of patients' previous in-patient experience, and correlated negatively with subjective well-being but not at all with behavioural status. These results are consistent with theories which attribute low morale to feelings of dependence and this, in turn, to the experience of residential care. They are inconsistent with the view that dependence on others is a positive feature of old age. In addition, patients' subjective well-being was completely unrelated to nurse ratings of their behavioural status, and subjective ratings by nurses correlated somewhat with patients' behavioural status but not at all with their subjective well-being.

Aged↗
PubMed1990

Status report on the US human growth hormone recipient follow-up study.

Three reported cases of Creutzfeldt-Jakob disease (CJD) in young adults who had received human growth hormone (hGH) raised concerns that pituitary-derived GH had been contaminated. Subsequently reported cases have confirmed this suspicion. The US Public Health Service is conducting an investigation to determine the extent of the problem of CJD in recipients of National Hormone Pituitary Program (NHPP) GH. In addition, other possible adverse effects of GH use including leukemia are being investigated. The design, conduct and current status of the study are the subject of this report. Interview data are now available on 5,240 of the 6,284 subjects treated by the NHPP for growth problems. Analysis is underway.

Creutzfeldt-Jakob Syndrome↗
PubMed1989

On fully automatic feature measurement for banded chromosome classification.

Procedures for fully automatic location of chromosome axis and centromere in metaphase chromosomes are described for a practical interactive chromosome analysis system that omits the usual stages of interactive axis and centromere correction. Accuracy of centromere finding and consequential determination of a chromosome's polarity, i.e., which end is which, is measured experimentally. The saving in interaction by not correcting centromeres is compared to the increase in errors at the classification stage and the consequent increase in interaction needed to correct these errors. Some previously unreported features for banded chromosome classification are described, and in particular a set of global shape features is introduced. The discrimination capability of the feature measurements is evaluated by use of simple statistics and by reference to the performance of classifiers trained with various feature subsets. Class discrimination capability of the global shape feature set is shown to be comparable to that of centromere position, a widely used local shape feature. The variability of feature measurements that might occur in data from different laboratories on account of differing tissue, preparation methods, and digitiser hardware is assessed using three data bases of G-banded human metaphase cells. It is shown that the differences can be considerable and that appropriate feature selection and classifier training substantially improve classification performance.

Chromosomes↗
PubMed1989

An automated system for karyotyping mouse chromosomes.

A system developed for interactive automated analysis of human chromosomes has been modified for use with mouse cells. The system is described, with emphasis on those features that facilitate retaining for different preparations or even different species. Some performance figures are presented.

Animals↗
PubMed1988

Commercially available technique for rapid laboratory detection of methicillin resistance among Staphylococcus aureus.

The MRS test is a commercially available test for detection of methicillin resistance among Staphylococcus aureus (MRSA), which was compared to standard techniques for efficacy and speed. Among 119 S. aureus strains tested (71 resistant to methicillin), it detected 90% of MRSA strains in 4 hr. The MRS test may have a role as a rapid screening test for MRSA in selected situations.

Humans↗
PubMed1988

Efficacies of rapid agglutination tests for identification of methicillin-resistant staphylococcal strains as Staphylococcus aureus.

Four commercially available rapid agglutination tests for the identification of Staphylococcus aureus were compared with the tube coagulase test for the identification of 300 methicillin-resistant isolates of staphylococci. Isolates tested included 207 methicillin-resistant S. aureus and 93 coagulase-negative staphylococci, collected from five medical centers. Strain variability was documented by phage typing and antimicrobial susceptibility patterns. Results of rapid identification tests ranged between 82 and 86% sensitivity, significantly poorer than the 98% sensitivity which the tube coagulase test provided.

Agglutination Tests↗
PubMed1988

Use of an alphoid satellite sequence to locate the X chromosome automatically, with particular reference to identification of the fragile X.

An alphoid DNA sequence primarily located on the X chromosome was labeled with biotin and hybridized in situ to preparations of metaphase chromosomes derived from fragile X-affected individuals; hybridization sites were detected immunologically. Labeled X chromosomes were located automatically in digitized images of metaphase cells by searching for the concurrence of a pronounced peak in the longitudinal density profile with the centromere in medium-sized chromosomes having a suitable centromeric index. Approximately 70% of the X chromosomes were detected by a simple classifier; this rate is similar to the automatic classification rate obtained with G-banded metaphases. The frequency of detection of the fragile X site obtained when scored directly from the microscope using this new preparation technique did not differ significantly from the frequency obtained in the same sample by means of a conventional technique. The frequency obtained by visual scoring of digitized images was slightly higher, but not significantly so.

Chromosome Mapping↗
PubMed1988

Investigations of patients allergic to the house dust mite Dermatophagoides pteronyssinus by crossed radioimmunoelectrophoresis using purified mite bodies and whole mite culture extracts.

Sera of 20 patients allergic to the house dust mite Dermatophagoides pteronyssinus were investigated by crossed radioimmunoelectrophoresis (CRIE) using extracts prepared from purified mite bodies (PMB) and whole mite culture (WMC). By CRIE, different allergen patterns and different numbers of allergens were detected in the two extracts. By summarizing the values of the CRIE patterns of the 20 patients' sera into allergograms, 6 out of 16 allergens in PMB and 5 out of 10 allergens in WMC extracts could be identified as major allergens. These diverging results, together with the published literature, emphasize the necessity to reevaluate the International Standard for D. pteronyssinus.

Allergens↗
PubMed1979

Efficient interaction for automated chromosome analysis using asynchronous parallel processes.

It is likely that any practical automated chromosome analysis system will be interactive. To prevent long pauses in the stream of operator interactions, it is necessary, if using standard computer hardware, to configure for asynchronous and parallel operation. A system is presented which uses several computer processors, which can support one or more operators, and which divides processing into interactive and noninteractive sections, smoothes the rate of presentation of interactions, and keeps both the operator and the computer fully employed.

Chromosomes, Human↗
PubMed1979

The energy audit: back to the basics.

Gathering information about the cost of energy and patterns of usage within the hospital is the first step in mounting a program for conserving resources. A survey of the plant or a full-scale audit by an energy team can help administrators plan an energy-saving program.

Conservation of Natural Resources↗