Biomedical subjects

A P McLean

Publications and source records attributed to A P McLean.

At least 19 recordsLinked to original sources

PubMed2001

Sensitivity to relative reinforcer rate in concurrent schedules: independence from relative and absolute reinforcer duration.

Twelve pigeons responded on two keys under concurrent variable-interval (VI) schedules. Over several series of conditions, relative and absolute magnitudes of reinforcement were varied. Within each series, relative rate of reinforcement was varied and sensitivity of behavior ratios to reinforcer-rate ratios was assessed. When responding at both alternatives was maintained by equal-sized small reinforcers, sensitivity to variation in reinforcer-rate ratios was the same as when large reinforcers were used. This result was observed when the overall rate of reinforcement was constant over conditions, and also in another series of concurrent schedules in which one schedule was kept constant at VI ached 120 s. Similarly, reinforcer magnitude did not affect the rate at which response allocation approached asymptote within a condition. When reinforcer magnitudes differred between the two responses and reinforcer-rate ratios were varied, sensitivity of behavior allocation was unaffected although response bias favored the schedule that arranged the larger reinforcers. Analysis of absolute response rates ratio sensitivity to reinforcement occurrred on the two keys showed that this invariance of response despite changes in reinforcement interaction that were observed in absolute response rates on the constant VI 120-s schedule. Response rate on the constant VI 120-s schedule was inversely related to reinforcer rate on the varied key and the strength of this relation depended on the relative magnitude of reinforcers arranged on varied key. Independence of sensitivity to reinforcer-rate ratios from relative and absolute reinforcer magnitude is consistent with the relativity and independence assumtions of the matching law.

Animals↗

PubMed2001

Variable-ratio versus variable-interval schedules: response rate, resistance to change, and preference.

Two experiments asked whether resistance to change depended on variable-ratio as opposed to variable-interval contingencies of reinforcement and the different response rates they establish. In Experiment 1, pigeons were trained on multiple random-ratio random-interval schedules with equated reinforcer rates. Baseline response rates were disrupted by intercomponent food, extinction, and prefeeding. Resistance to change relative to baseline was greater in the interval component, and the difference was correlated with the extent to which baseline response rates were higher in the ratio component. In Experiment 2, pigeons were trained on multiple variable-ratio variable-interval schedules in one half of each session and on concurrent chains in the other half in which the terminal links corresponded to the multiple-schedule components. The schedules were varied over six conditions, including two with equated reinforcer rates. In concurrent chains, preference strongly overmatched the ratio of obtained reinforcer rates. In multiple schedules, relative resistance to response-independent food during intercomponent intervals, extinction, and intercomponent food plus extinction depended on the ratio of obtained reinforcer rates but was less sensitive than was preference. When reinforcer rates were similar, both preference and relative resistance were greater for the variable-interval schedule, and the differences were correlated with the extent to which baseline response rates were higher on the variable-ratio schedule, confirming the results of Experiment 1. These results demonstrate that resistance to change and preference depend in part on response rate as well as obtained reinforcer rate, and challenge the independence of resistance to change and preference with respect to response rate proposed by behavioral momentum theory.

Animals↗

PubMed1998

An outbreak of Serratia marcescens infections related to contaminated chlorhexidine.

An outbreak of Serratia marcescens infections occurred in a university tertiary-care hospital. Alcohol-free chlorhexidine solutions were contaminated with S marcescens. The majority of patient and chlorhexidine strains had similar pulsed field-gel electrophoresis banding patterns. Chlorhexidine was recalled, and the rate of S marcescens isolation returned to baseline. Chlorhexidine without alcohol should not be used as an antiseptic.

Anti-Infective Agents, Local↗

PubMed1997

Stomal ulcer after gastric bypass.

BACKGROUND: Stomal ulcer is a serious complication of gastrogastric fistula following Roux-en-Y gastric bypass for obesity. STUDY DESIGN: A 1-8 year continuous followup of 499 patients with gastric bypass in continuity (GB) and isolated gastric bypass (IGB) documented the incidence of fistula formation, development of stomal ulcer, stimulation of acid production within the gastric pouch, and response to treatment. RESULTS: In 123 GB patients, staple line disruption occurred in 36 (29%) and stomal ulcer occurred in 20 (16%). Gastrogastric fistula with stomal ulcer was significantly lower in 376 patients who underwent IGB, (ie, 11 patients [3%]). Significantly larger amounts of acid, a lower pH, and a greater time with a pH less than 2 were found in the gastric pouches of patients who developed stomal ulcer after Roux-en-Y gastric bypass. All patients had a perforated staple line. Successful closure of the staple line significantly decreased acid production and pH in the gastric pouch when tested before and after remedial operation with healing of stomal ulcers. CONCLUSIONS: Stomal ulcer after gastric bypass is the result of acid production in the bypassed stomach in the presence of a gastrogastric fistula. Separation of the gastric pouch from the main stomach decreases the incidence of fistula formation and stomal ulcer but does not eliminate it. Interposition of a well vascularized organ, the jejunum between the pouch and main stomach, is an attractive solution for patients who require remedial operations on the stomach and possibly for primary operations as well.

Follow-Up Studies↗

PubMed1996

Control of construction-associated nosocomial aspergillosis in an antiquated hematology unit.

OBJECTIVE: To determine the incidence of aspergillosis in patients with leukemia or bone marrow transplants during a construction-associated outbreak, and the effect of an environmental control program for Aspergillus. DESIGN: Clinical, microbiological, and pathological records were reviewed retrospectively once the outbreak was appreciated, and prospectively thereafter, to determine the presence or absence of aspergillosis and duration of neutropenia. SETTING: A university tertiary-care center with a single designated hematology-oncology unit. PATIENTS: From January 1988 to September 1993, there were 141 patients with leukemia or bone marrow transplants identified as being neutropenic during 231 admissions to this specialized unit. INTERVENTIONS: Installation of wall-mounted portable high-efficiency particulate air (HEPA)-filter air purifiers, application of copper-8-quinolinolate-formulated paint, replacement of perforated ceiling tiles with nonperforated type, sealing of all windows, replacement of horizontal, dust-accumulating blinds with vinyl, opaque, roller shades, and systematic and regular cleaning of surfaces. RESULTS: Thirty-six cases of nosocomial aspergillosis were diagnosed during this period. The incidence density (ID) in the preconstruction period was 3.18 per 1,000 days at risk. During construction activity-before the implementation of a control strategy-the ID increased dramatically to 9.88 per 1,000 days at risk. With infection control measures implemented and continued construction work, the ID decreased to 2.91 per 1,000 days at risk, comparable to the preconstruction baseline rate. CONCLUSIONS: An environmental control strategy incorporating widely available technology may have played an important role in controlling this outbreak of construction-associated invasive aspergillosis.

Air Pollution, Indoor↗

PubMed1995

Training general practitioners in surgical and obstetrical emergencies in Ethiopia.

A 6-month course for training general practitioners (GPs) in surgical emergencies was developed and piloted in Ethiopia. The course was designed after an assessment of the surgical manpower needs in Ethiopia. Seven GPs were selected by the Ministry of Health (MOH) from rural hospitals that had no surgical specialists but had operating facilities. The course consisted of 1 week of lectures followed by 11 weeks each in obstetrics/gynaecology and general surgery. The GPs trained in district hospitals under the supervision of surgical specialists. Emphasis was placed on practical experience in managing a limited number of previously identified surgical emergencies. Follow up 9 months after completion of the course showed that five of the seven GPs had completed significant numbers of life saving procedures. Complications occurred largely in advanced disease. Difficulties remain with the recognition of the GPs' training and their supervision. We conclude that GPs can be trained to provide life saving surgery in a short training programme at a modest cost, but mechanisms for ensuring ongoing support need to be established.

Emergency Medical Services↗

PubMed1994

Forgetting in rats following medial septum or mammillary body damage.

This study examined the effects of medial septal (MS) and mammillary body (MB) radio-frequency lesions in an automated delayed-matching-to-sample (DMTS) procedure using lever-position stimuli and rats. Memory performance pre- and postsurgery was assessed with a negative exponential decay function fitted to bias-free measures of recognition. Part 1 showed that MS, but not MB or sham-control surgery, impaired DMTS performance. This impairment in the MS group was best characterized as an increase in the rate of forgetting. Part 2 examined the interaction between MS and MB lesion effects and proactive interference arising from responses made on the previous DMTS trial. The results indicated that proactive interference effects were similar for all groups. These results provide further support for the critical role of the MS region in memory function but indicate that damage to this brain region does not disrupt memory function through a heightened sensitivity to proactive interference.

Animals↗

PubMed1993

List item memory in rats: effects of delay and delay task.

The Serial Position Effect (SPE) was studied in rats using 2 manipulations analogous to those that have been shown to decrease the recency effect but leave the primacy effect intact in human Ss. In Part 1, delays (5 s to 60 s) were imposed between exposure to a sequence of arms presented in a 12-arm radial maze and a subsequent test phase. In Part 2, the effect of free access to food in a short (10-s) delay was examined. The results from Parts 1 and 2 showed that the primacy and recency effects were differentially sensitive to the delay and events within it. In particular the recency effect was found to be more sensitive to disruption from these sources. The present demonstration of a reduction in recency with procedures analogous to those used with humans extends the evidence, suggesting that the SPE obtained in rats and humans is a similar phenomenon.

Animals↗

PubMed1992

Production of a serial position effect in rats using a 12-arm radial maze.

The effects of item position (the serial position effect: SPE) on the recognition of a list of arms presented in an 8-arm radial maze have not been shown to be robust across studies which differ in numbers of subjects, amount of training and task difficulty. The present study examined whether more robust SPEs could be obtained in rats with a 12-arm radial maze using a matching-to-sample serial probe recognition (SPR) procedure. In Part 1, 23 rats received extensive training on recognition of list of arms from a 5-arm list and, in Part 2, 20 rats received training with a 7-arm list. Both Parts 1 and 2 showed that a reliable and persistent SPE emerged due to superior recognition of items at the first and last serial positions compared with the middle positions. However, the SPE was more pronounced with the 7-arm than 5-arm list. It is argued that adequate task difficulty along with sufficient subject and trial numbers is necessary to produce a clear SPE. In Part 3, an alternative means of assessing accuracy derived from signal-detection theory is examined, and the procedural requirements for its use are identified. Although this measure did not alter the conclusions reached using percent correct, it is proposed that the bias-free measure, log d, is superior to traditional indices of memory performance which may obscure the presence of, or changes in, the SPE. The procedures used here provide a valuable means to produce clear, reliable and persistent SPEs. Such procedures are essential if researchers are to be confident about the effects of lesions or drugs upon list memory in their attempts to explore the neurological bases of memory and model human neurological disorders.

Animals↗

PubMed1992

Successive independence and behavioral contrast in a closed economy.

Two pigeons had access to multiple concurrent schedules of reinforcement for 24 hours per day in their home cages. The variable-interval schedules comprising the multiple concurrent schedules were varied across 16 conditions. In three sets of conditions, one schedule was varied while its concurrent alternative and the concurrent schedules in the other component were held constant. Behavioral contrast was observed; that is, as the rate of reinforcement arranged by the varied schedule decreased, response rates on the constant schedules typically increased. These conditions formed part of two larger sets of conditions in which the concurrent schedules in one multiple-schedule component remained constant while the concurrent schedules in the other component were varied. Successive independence was found, in that behavior allocation during the constant component did not vary as a function of the reinforcer ratios in the varied component. Successive independence between components in multiple concurrent schedules is a robust result that occurs in closed economies and under conditions that promote behavioral contrast.

Animals↗

PubMed1992

Another view to blood and body substance precaution: 1988-91.

Occupational transmission of human immunodeficiency virus (HIV) in hospitals can be prevented with the use of 'blood and body substance precaution'. At the Royal Victoria Hospital, an infection control objective is to get employees automatically to use blood and body substance precaution with all patients--without relying on isolation signs. The concept of blood and body substance precaution was introduced in 1988 and simultaneously used with disease-specific signs. It was observed that disease-specific signs were mostly used to identify HIV-positive patients; this was verified under documented surveillance from July 7 to August 8, 1990, when 60 patients (14 HIV-positive and 46 whose HIV etiology was unknown) were observed. All 14 known HIV-positive patients were isolated with signs, while only four of 46 unknown HIV-positive patients (8.6%) had signs. The views of individual employees were subsequently studied via a questionnaire and results from this survey showed there was preference for isolating HIV-positive patients and identifying them with a sign.

Attitude of Health Personnel↗

PubMed1991

Clostridium difficile disease in a department of surgery. The significance of prophylactic antibiotics.

A clustering of Clostridium difficile-associated disease in a department of surgery prompted a program of infection control and the evaluation of contributing factors. Fifty patients had diarrhea and positive assays for C difficile cytotoxin during the study period. Twenty-one of the 36 cases that developed among patients admitted to the surgical services occurred on two adjacent general surgery wards that shared attending surgeons and house staff. Perioperative prophylactic antibiotics predated C difficile-associated disease in 20 patients, 12 of whom had short courses (less than 24 hours). Symptoms were typically nonspecific and early diagnosis may be difficult. Incidence remained high, despite infection control measures, until the coincidental closure of two surgical wards. Clostridium difficile-associated disease is a nosocomial infection that can be associated with short courses of prophylactic antibiotics. Recommendations regarding the use of perioperative prophylaxis should recognize C difficile-associated disease as a significant potential complication.

Adult↗

PubMed1991

Genetic studies on a major merozoite surface antigen of the malaria parasite of rodents, Plasmodium chabaudi.

Diversity in a major merozoite surface antigen (MSA-1) of Plasmodium chabaudi has been examined using a panel of monoclonal antibodies (MoAbs). The antigen was found to be different in each of twelve cloned isolates, as shown by its reactivity with the MoAbs in immunofluorescence tests. In genetic crossing experiments, the diverse forms of this antigen were shown to be determined by allelic variation of a single gene. Recombination occurred between the MSA-1 gene, a second blood stage antigen and enzyme markers.

Animals↗

PubMed1988

Chromosome size variation in the malaria parasite of rodents, Plasmodium chabaudi.

Pulsed field gradient gel electrophoresis has been used to identify at least 10 large DNA fragments in the genome of the rodent malaria species Plasmodium chabaudi. The fragments range in size from approximately 650 to 5000 kb. All the fragments contain sequences homologous to a P. berghei telomere probe, suggesting that they represent intact chromosomes. Ribosomal RNA genes and P. chabaudi cDNA sequences have been mapped to specific fragments. The fragments vary in size in different cloned isolates of the parasite. In a cross between two cloned parasites differing in the sizes of chromosomes 4 and 5, independent segregation of each chromosome occurred during meiosis.

Animals↗

PubMed1986

Hepatic resection for metastatic disease.

Hepatic resection for metastatic disease is reviewed in 30 patients (mean age 58.9 years). The primary site was the colorectum in 25; the other primary tumours were leiomyosarcoma, plasmacytoma, and adenocarcinoma (all of gastric origin), ocular melanoma and an unknown primary. Operative procedures included 7 wedge resections, 5 segmentectomies and 21 lobectomies (11 right, 4 extended right and 6 left). Major complications in seven patients included intraoperative hemorrhage in three, two of whom died, bile-duct injury in two, small-bowel infarction in one and cerebrovascular accident in one. Operative death rate was 6.7% (2 of 30). Thirteen patients were alive and free of disease a mean of 24 months after hepatic resection while 5 more were alive with disease at a mean of 36.9 months. Life-table analysis projected a 5-year survival of 50.3% for those with colorectal primaries, with no apparent difference in survival between patients with single (55.0%) and multiple (54.0%) metastases. Improved survival was projected for patients with metachronous (66.6%) versus synchronous (45.0%) tumours, primary Dukes' class A or B (66.1%) versus Dukes' class C (46.0%) tumours and those having wedge resection or segmentectomy (66.6%) versus lobectomy or extended lobectomy (48.0%). Hepatic resection for metastatic disease can be done with acceptable morbidity and mortality and the expectation of substantially prolonged survival particularly in patients with metachronous lesions or Dukes's A or B colorectal primary lesions.

Actuarial Analysis↗

PubMed1986

The septic abdomen: open management with Marlex mesh with a zipper.

The "open" abdomen has gained popularity in the management of severe intraabdominal sepsis. Drawbacks include evisceration, need for ventilator support, and recurrent abdominal sepsis. We have applied a more aggressive and effective technique consisting of abdominal "closure" with a Marlex mesh sheet containing a zipper. Manual exploration and lavage is performed daily through the zipper in the surgical intensive care unit. Ten patients with severe abdominal sepsis were treated for the following: fecal peritonitis (three patients), radiation enteritis with fistula (one patient), diverticular abscess and dehiscence (one patient), diffuse postoperative abdominal sepsis (two patients), and necrotizing pancreatitis (three patients). Thirteen meshes were inserted, four at first operation and nine at the second to sixth operations. Eight patients survived (80%). Only three patients required respirators; two died. Two patients underwent drainage of three defined abscesses in the surgical intensive care unit. Three patients underwent five major operations through the zipper. Intestinal stomas were present adjacent to the mesh in six patients and were not a management problem. No fistulas resulted from this technique. The Marlex/zipper was removed when all septic signs abated and adhesions were allowed to form (average of 10 to 12 days). Daily aggressive manual lavage of the abdomen through a Marlex mesh/zipper is rapid, simple, and well tolerated. It has permitted effective management of severe septic peritonitis and easier wound care. This technique merits further controlled trials to ascertain its ultimate benefit in survival.

Abscess↗

PubMed1983

Prognosis in generalized peritonitis. Relation to cause and risk factors.

Generalized peritonitis was assessed in 176 patients, 67 (38%) of whom died. Cases were divided into causative groups: (1) appendicitis and perforated duodenal ulcer, (2) intraperitoneal origin other than appendix or duodenum, and (3) postoperative peritonitis. Mortalities were 10%, 50%, and 60%, respectively. Postoperative peritonitis was characterized by lack of influence of age on outcome, late operation, and more frequent organ failure. Delayed surgery carried a worse prognosis. Organ failure was a risk factor with 76% mortality, and was associated with late operation. Early surgery in organ failure improved survival. More sensitive indicators of early organ dysfunction might improve survival.

Adult↗

PubMed1983

An aggressive, nonshunting approach for control of bleeding esophageal varices.

Morbidity and mortality from variceal hemorrhage can be significantly reduced. A well-defined treatment protocol which obviates delay, procrastination and excessive blood loss is essential. Early aggressive endoscopic sclerotherapy is extremely safe and effective in controlling the acute hemorrhagic event. However, technical details remain to be standardized; rebleeding can be significant and sclerosing until roentgenologic obliteration is essential. Stapled esophageal transection and coronary vein ligation are a reasonable and effective surgical approach when necessary; however, the exact timing and place of this procedure in the therapeutic schema are not yet defined. It requires further phase one studies and not more randomized control trials! It can be difficult after recent sclerotherapy and would appear to require upper gastric devascularization or perhaps percutaneous embolization if gastric varices are venographically prominent. We have recently attempted to modify the procedure in such patients by stapling across the anterior and posterior gastric walls as an alternative or addition to complete esophageal transection. This is accomplished through a small gastrotomy adjacent to the gastroesophageal junction. Shunting procedures or more extensive surgical intervention does not appear necessary, desirable or warranted at this time; however, longer follow-up study is essential.

Aged↗