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Biomedical subjects

J McIntyre

Publications and source records attributed to J McIntyre.

At least 73 records · Page 4Linked to original sources
PubMed1995

Measurements of human force control during a constrained arm motion using a force-actuated joystick.

1. When interacting with the environment, human arm movements may be prevented in certain directions (i.e., when sliding the hand along a surface) resulting in what is called a "constrained motion." In the directions that the movement is restricted, the subject is instead free to control the forces against the constraint. 2. Control strategies for constrained motion may be characterized by two extreme models. Under the active compliance model, an essentially feedback-based approach, measurements of contact force may be used in real time to modify the motor command and precisely control the forces generated against the constraint. Under the passive compliance model the motion would be executed in a feedforward manner, using an internal model of the constraint geometry. The feedforward model relies on the compliant behavior of the passive mechanical system to maintain contact while avoiding excessive contact forces. 3. Subjects performed a task in which they were required to slide the hand along a rigid surface. This task was performed in a virtual force environment in which contact forces were simulated by a two-dimensional force-actuated joystick. Unknown to the subject, the orientation of the surface constraint was varied from trial to trial, and contact force changes induced by these perturbations were measured. 4. Subjects showed variations in contact force correlated with the direction of the orientation perturbation. "Upward" tilts resulted in higher contact forces, whereas "downward" tilts resulted in lower contact forces. This result is consistent with a feedforward-based control of a passively compliant system. 5. Subject responses did not, however, correspond exactly to the predictions of a static analysis of a passive, feedforward-controlled system. A dynamic analysis reveals a much closer resemblance between a passive, feedforward model and the observed data. Numerical simulations demonstrate that a passive, dynamic system model of the movement captures many more of the salient features observed in the measured human data. 6. We conclude that human subjects execute surface-following motions in a largely feedforward manner, using an a priori model of the surface geometry. The evidence does not suggest that active, real time use of force feedback is used to guide the movement or to control limb impedance. We do not exclude, however, the possibility that the internal model of the constraint is updated at somewhat longer latencies on the basis of proprioceptive information.

Arm↗
PubMed1995

Independence of bilateral symmetry detection from a gravitational reference frame.

Data were collected during three orbital flights aboard the Russian MIR space station from eight cosmonauts tested on a bilateral symmetry detection task. It is known that on earth subjects' performance is significantly superior for a vertical or horizontal than for an obliquely oriented axis of symmetry, giving a so-called oblique effect. The present results show that this oblique effect did not disappear in microgravity. They confirm that the detection of visual symmetry is not tied to a gravitational reference frame. An unexpected result of the experiments was that practice reduced the reaction time for detection of asymmetrical patterns below that for symmetrical patterns. This result suggests the presence of two separate detection processes. The detection of symmetry, being useful for the efficient encoding of visual information, is well developed in naive subjects. Extensive practice on a symmetry-detection task, however, increases the efficacy of the asymmetry-detection process.

Adult↗
PubMed1994

Secondary breast cancer in patients presenting with osteosarcoma: possible involvement of germline p53 mutations.

Second malignancies following treatment for osteosarcoma are unusual. Breast cancer occurring in patients with osteosarcoma has been reported following therapeutic chest irradiation. We now report three cases of breast cancer occurring in young women who were successfully treated for osteosarcoma. These women had not received therapeutic chest irradiation and in two of the three women there was no family history of breast cancer. Peripheral blood was available for study from one case. Of import, this case demonstrated a germline mutation in exon 7 of the tumor suppressor gene, p53. The mutation was detected by constant denaturing gradient gel electrophoresis and confirmed by DNA sequencing. In this particular patient, inactivation of the p53 gene may be involved in the development of both the first and second malignancy.

Adult↗
PubMed1994

Influence of smoking on immunological responses to hepatitis B vaccine.

When 115 health-care workers participated in a study that monitored their serological responses to hepatitis B vaccine at regular intervals, it was found that smoking significantly affected their antibody titre responses adversely. The study group was randomly allocated into two comparable groups that received hepatitis B vaccine either in a rapid schedule (vaccination at 0, 1, 2 and 12 months) or a standard schedule-most commonly used worldwide-(vaccination at 0, 1, and 6 months). A significantly higher proportion of smokers, in both schedules, failed to seroconvert and to achieve higher antibody levels at month 3 (p = 0.01) and at month 13 (p = 0.0003). At month 7 a similar pattern was noted in smokers following the standard vaccination schedule (p < or = 0.05), but not in those following the rapid schedule.

Adult↗
PubMed1994

Analysis of cells obtained by bronchial lavage of infants with respiratory syncytial virus infection.

To study the cellular infiltrate that occurs within the airways of infants with respiratory syncytial virus bronchiolitis, samples of airways secretions were obtained by bronchial lavage from the lower respiratory tract of infants ventilated for this condition and from the upper airway of non-intubated infants with this disorder using nasopharyngeal aspirates. Cytospin samples were prepared so that differential cell counts could be performed on the cells obtained and alkaline phosphatase-antialkaline phosphatase immunocytochemical analysis of lymphocyte subsets was carried out using a panel of monoclonal antibodies, which included anti-CD3, anti-CD4, anti-CD8, anti-CD19, and anti-TcR gamma delta. Results from the lower and upper airways were similar. Large numbers of inflammatory cells were obtained, of which neutrophils accounted for a median of 93% in the upper airway and 76% in the lower airway. The numbers of CD8 positive cells detected were small and consistently less than CD4 positive cells, median CD4:CD8 ratios being 22.5:1 and 15:1 for the lower and upper airways. CD19 positive cells were rarely observed and no gamma delta positive lymphocytes were detected. These results indicate that neutrophils probably play a major part in causing symptoms in these infants. They do not support the concept that excessive lymphocyte mediated cytotoxic activity is principally responsible for the pathology in respiratory syncytial virus bronchiolitis.

Acute Disease↗
PubMed1994

Minimal intervention dentistry.

The concepts of 'minimal intervention' or 'minimally invasive' restorative dentistry do not appear to be well understood or accepted. This paper attempts to clarify what is meant by these concepts, and to examine some of the difficulties preventing these concepts being fully implemented in general dental practice in Australia. Possible approaches to facilitating more widespread acceptance and adoption of these concepts are proposed.

Australia↗
PubMed1993

Re-irradiation of laryngeal carcinoma--techniques and results.

PURPOSE: Occasionally in the long-term survivors of early carcinoma of the larynx, following radiation therapy a second carcinoma may arise from the previously irradiated larynx. Traditionally, management of such lesions is by non-radiation means in the belief that a further full course of radiation therapy is not possible and may exceed the tolerance of the normal laryngeal structures. Unfortunately, surgical treatment of the second carcinoma is often either total or partial laryngectomy which may not be acceptable to the patients and therefore radiation therapy is used as an alternative. METHODS AND MATERIALS: This paper presents our experience in re-irradiation of laryngeal carcinomas arising from the previously irradiated larynx. As of October 1992 a total of 20 patients were available for evaluation. Most patients had Stage I and II laryngeal carcinoma and received high doses of re-irradiation ranging from 60 to 70 Gy either by conventional or accelerated hyperfractionation schemes. RESULTS: The 5-year actuarial local control and survival rates were 60 to 93%, respectively. The majority of the survivors had relatively normal and functional larynges. Those who failed locally had total laryngectomy without significant postoperative complications. CONCLUSION: With this information the radiation tolerance of laryngeal structures is found to be much higher than commonly believed and re-irradiation for early carcinoma of the larynx is possible and proved to be a useful alternative to surgery and laryngectomy is therefore reserved for failure. The techniques of re-irradiation will be discussed.

Adult↗
PubMed1993

Screening for TP53 mutations in osteosarcomas using constant denaturant gel electrophoresis (CDGE).

We have previously developed conditions to screen for TP53 point mutations inside the conserved domains II-V of the gene by using constant denaturant gel electrophoresis (CDGE). The present study reports conditions for screening more of the codons in the frequently mutated region exon 5-8 and for detecting mutations in sequences encoding functional domains in the N- and C-terminal part of the protein. The ability of the CDGE technique to detect mutations was studied using controls with known sequence deviations. The resolution power of the technique to separate different types of mutations was tested by using seven different single base pair mutants all residing in a stretch of four base pairs. All mutants were separated from the wild type. The established CDGE screening strategy was then used to look for mutations in DNA from 28 osteosarcomas. Six (21.5%) of the samples were shown to have a TP53 mutation, and the exact characterization was performed by direct sequencing. All of these were within the frequently reported mutated region exon 5-8.

Adolescent↗
PubMed1993

The effect of endotoxin-induced fever on thermoregulation in the newborn rabbit.

1. Metabolic responses of endotoxin-injected newborn rabbits were measured in a closed circuit calorimeter at a constant environmental temperature within their thermoneutral range. Oxygen consumption and colonic temperatures were then measured over a range of environmental temperatures from 21.0 to 40.0 degrees C and the responses of endotoxin-injected rabbits compared with non-injected litter mates. 2. To measure their preferred thermal environment, endotoxin-injected and non-injected litter mates were allowed to settle on a thermal gradient and their colonic temperatures measured. 3. In a constant environmental temperature of 37 degrees C, rises in oxygen consumption and colonic temperature following endotoxin injection were found to be biphasic. Oxygen consumption rose from 21 ml kg-1 min-1 to a maximum 35 ml kg-1 min-1 and colonic temperature rose from 39.0 to 39.8 degrees C. 4. The maximal rate of oxygen consumption was the same in both injected and non-injected animals, 53 ml kg-1 min-1, being provoked at the same environmental temperature of 24 degrees C. Minimal rates of oxygen consumption were also similar for the two groups but in the injected animals they were achieved at an environmental temperature of 39 degrees C, 2 degrees C higher than for non-injected animals. 5. We conclude that newborn rabbits challenged with a pyrogen have both behavioural and physiological responses. The thermogenic response is consistent with a change in sensitivity to feedback information rather than a simple shift in the central thermoregulatory set point. We find no evidence to support the view that in the febrile response a higher body temperature necessitates an increase in metabolic rate, the so-called Q10 effect.

Animals↗
PubMed1993

Age-related changes in endotoxin sensitivity and the febrile response of newborn rabbits.

Thermoregulatory responses to pyrogens in the immediate newborn period have been reported suppressed or undeveloped. In this study we investigated these responses in the newborn rabbit. Endotoxin (Escherichia coli LPS) was injected intraperitoneally in rabbits at different doses on day 0 (day of delivery), 1 or 3 of life, each animal being used only once. Oxygen consumption (VO2) and colonic temperature (Tc) were measured continuously for up to 5 h following endotoxin administration. On all days, a thermogenic response of a similar pattern was seen. At a low dose of endotoxin, there was a monophasic rise in VO2 that reached a peak at 2 h, followed by a plateau phase lasting a further 2-3 h. At an intermediate dose the response was biphasic with an initial smaller peak after 45-60 min and a second more sustained peak developing by about 2 h. At a higher dose the depression between the two peaks became deeper and longer with the second peak becoming more delayed and weaker. As animals got older, the doses needed to produce this sequence increased. On day 0 the increased VO2 caused by endotoxin was not accompanied by an increase in Tc. By day 3, Tc rose with the increase in VO2. We conclude that rabbits on the day of delivery respond to endotoxin with an increase in VO2 and by day 3 this is accompanied by an increase in Tc. The pattern of VO2, changes from monophasic to biphasic with increasing doses of endotoxin and the sensitivity to endotoxin decreases over the first 3 days of life.

Age Factors↗
PubMed1992

Maternal fever at parturition and its effects on the newborn rabbit.

The febrile response to administration of endotoxin has been reported to be suppressed in both pregnant animals at term and in their newborn. In a previous study we found that newborn rabbits under appropriate conditions to develop a febrile reaction to injected endotoxin. In this investigation we sought to discover whether pregnant rabbits at term had a febrile response to endotoxin, and if so, its effect on thermoregulation in their newborn. Endotoxin (E. Coli LPS) was injected into 19 pregnant rabbits at term. Six delivered spontaneously within an hour. At one hour, 13 were given oxytocin, and a further 8 delivered within five minutes. The colonic temperature (Tc) of the mothers before endotoxin administration and at delivery, and of their young, was measured. The results were compared with those of 10 pregnant rabbits not given endotoxin, and their young. Within 15 min of delivery newborn rabbits from each litter were placed on a thermal gradient to assess their thermoregulatory responses. Pregnant rabbits at term developed an impressive febrile response to injected endotoxin and their young were born with high colonic temperatures. Newborn rabbits from febrile mothers selected higher thermal environments and maintained a higher colonic temperature than the newborn of non-febrile mothers. We conclude that fever is sustained in the first hours of life in the newborn of mothers injected with endotoxin. The possible mechanisms are of considerable interest. None of the pregnant rabbits died after endotoxin administration, but the stillbirth rate was 50% compared with 10% in non-febrile does.

Animals↗
PubMed1991

'Birth to Ten'--pilot studies to test the feasibility of a birth cohort study investigating the effects of urbanisation in South Africa.

'Birth to Ten' is a birth cohort study currently being conducted in the Johannesburg-Soweto area. This paper describes the various pilot studies that were undertaken to investigate the feasibility of a cohort study in an urban area. These studies were designed to determine the monthly birth rate, the timing, frequency and duration of maternal antenatal visits, the timing and frequency of visits to well-baby clinics and the accuracy and reliability of routinely collected growth data. In addition, a birth data collection form was tested to ascertain the appropriateness of its use in clinics within the study area.

Birth Rate↗