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Biomedical subjects

D G Clayton

Publications and source records attributed to D G Clayton.

At least 19 recordsLinked to original sources
PubMed1995

Quantification of thrombelastographic changes after blood component transfusion in patients with liver disease in the intensive care unit.

Thrombelastography (TEG) can be used to monitor hemostasis and guide transfusion therapy during orthotopic liver transplantation. However, data are limited regarding the type and quantity of blood components necessary for TEG-guided blood component transfusion in coagulopathic critically ill patients with liver disease. We evaluated changes in four thrombelastogram variables (reaction time, thrombin constant time, alpha angle, and maximum amplitude) in whole blood samples after 74 separate blood component transfusions in 60 critically ill patients with a coagulopathy and liver disease. Only platelets significantly improved TEG variables in patients who received a single type of blood component. Each unit of platelets decreased the reaction and thrombin constant time by 0.43 (P < 0.05) and 0.82 (P < 0.005) min, respectively, increased the alpha angle by 1.5 degrees (P < 0.005), and the maximum amplitude by 1.4 mm (P < 0.005). In patients who received multiple blood components, cryoprecipitate decreased the thrombin constant time by 0.56 min/U (P < 0.05), and each unit of platelets decreased the thrombin constant time by 0.39 min (P < 0.005), and increased the alpha angle and maximum amplitude by 0.63 degrees (P < 0.05) and 0.99 mm (P < 0.005), respectively. We conclude that platelet transfusions, alone or in combination with other blood components, are most effective for improving abnormal TEG variables in coagulopathic critically ill patients with liver disease.

Blood Coagulation Disorders↗
PubMed1994

Interaction between genetic and environmental risk factors for Alzheimer's disease: a reanalysis of case-control studies.

To study the interaction among genetic and environmental risk factors, a reanalysis of case-control studies of Alzheimer's disease (AD) was conducted based on the original data of all studies carried out to January 1, 1990. Seven studies were included in the present analysis, comprising a total of 814 AD patients and 894 control subjects. When comparing those with a positive and negative family history of dementia, similar odds ratio were found for late maternal age [1.7; 95% confidence interval (0.6-4.8) vs. 2.0 (1.1-3.5)], head trauma [1.7 (0.7-4.2) vs. 1.9 (1.1-3.2)], and history of depression [2.0 (0.2-19.8) vs. 2.1 (0.8-1.7)]. This suggests a model in which these risk factors increase the risk for AD independent of family history of dementia. Among those with a positive family history of dementia, the odds ratios for family history of Down's syndrome [4.2 (0.9-20.0)] and of Parkinson's disease [3.3 (0.4-28.2)] tended to be higher than among those with a negative family history of dementia [2.6 (0.8-8.5) and 2.4 (0.8-7.0), respectively]. However, for both disorders the difference in odds ratio was not statistically significant. For history of cigarette smoking, there was no association to AD for those with no first degree relatives with dementia and an inverse relation with AD for those with a positive family history. Although in all analyses, family history of dementia remained significantly associated with AD in the absence of other factors, the odds ratio associated with family history of dementia tended to be lower for those with a positive smoking history, particularly for those with two or more affected relatives. These findings suggest that smoking may interact specifically with a genetically determined process.

Aged↗
PubMed1991

A comparison of the performance of 20 pulse oximeters under conditions of poor perfusion.

The performance of 20 pulse oximeters with finger probes was evaluated by comparison of their readings with directly measured arterial blood oxygen saturations. The samples were taken from patients who had undergone cardiac surgery under hypothermic cardiopulmonary bypass and had poor peripheral perfusion. The mean difference (bias, accuracy), standard deviation (precision) and drop-out rate for each pulse oximeter was determined. An overall ranking of performance of each pulse oximeter was calculated using five criteria (accuracy, precision, number of readings within 3% of standard, percentage of readings given within 3% of standard, expected overread limit in 95% of cases). Two pulse oximeters achieved a combination of accuracy and precision such that 95% of measurements would be expected to be within 4% of the co-oximeter value; these two also had the lowest drop-out rate.

Carboxyhemoglobin↗
PubMed1991

Pulse oximeter probes. A comparison between finger, nose, ear and forehead probes under conditions of poor perfusion.

The performances of 10 pulse oximeters using finger probes were compared with the same pulse oximeters using alternative probes (eight finger probes, two nose probes and a forehead probe) in poorly perfused patients. All readings were then compared with directly measured arterial blood oxygen saturations. The mean difference (bias, 'accuracy'), standard deviation (precision) and 'drop out' rate for each pulse oximeter combination was determined. An overall ranking of performance of each pulse oximeter was calculated using five criteria (accuracy, precision, number of readings within 3% of standard, percentage of readings given within 3% of standard, expected overread limit in 95% of cases). Nose and forehead probes performed poorly. Some ear probes performed well compared to some finger probes, but the overall performance of probes in other sites compared to finger probes was worse, (p = 0.05). Two of eight ear probes and no nose or forehead probes would be expected to be within 4% of the reference value in 95% of readings. The use of finger probes rather than probes in other sites is recommended in the patient with poor peripheral perfusion.

Adult↗
PubMed1991

A Monte Carlo method for Bayesian inference in frailty models.

Many analyses in epidemiological and prognostic studies and in studies of event history data require methods that allow for unobserved covariates or "frailties." Clayton and Cuzick (1985, Journal of the Royal Statistical Society, Series A 148, 82-117) proposed a generalization of the proportional hazards model that implemented such random effects, but the proof of the asymptotic properties of the method remains elusive, and practical experience suggests that the likelihoods may be markedly nonquadratic. This paper sets out a Bayesian representation of the model in the spirit of Kalbfleisch (1978, Journal of the Royal Statistical Society, Series B 40, 214-221) and discusses inference using Monte Carlo methods.

Algorithms↗
PubMed1990

Exercise in leisure time: coronary attack and death rates.

Nine thousand three hundred and seventy six male civil servants, aged 45-64 at entry, with no clinical history of coronary heart disease, were followed for a mean period of 9 years and 4 months during which 474 experienced a coronary attack. The 9% of men who reported that they often participated in vigorous sports or did considerable amounts of cycling or rated the pace of their regular walking as fast (over 4 mph, 6.4 km/h) experienced less than half the non-fatal and fatal coronary heart disease of the other men. In addition, entrants aged 55-64 who reported the next lower degree of this vigorous aerobic exercise had rates less than two thirds of the remainder; entrants of 45-54 did not show such an effect. When these forms of exercise were not vigorous they were no protection against the disease, nor were other forms of exercise or high totals of physical activity per se. A history of vigorous sports in the past was not protective. Indications in these men are of protection by specific exercise: vigorous, aerobic, with a threshold of intensity for benefit and "dose response" above this threshold, exercise that has to be habitual, and continuing, which suggests that protection is against the acute phases of the disease. Those men who took vigorous aerobic exercise were demonstrably a favourably "selected" group; they suffered less of the disease, however, whether at low risk or high by the several risk factors that were studied. Men with exercise-related reduction in coronary heart disease also had lower death rates from the total of other causes, and so lower total death rates than the rest of the men.

Coronary Disease↗
PubMed1989

Transplants from living donors in the United Kingdom and Ireland: a centre survey.

A survey was carried out to determine for the first time the extent of transplantation from living donors in the United Kingdom and Republic of Ireland and the views of transplant surgeons regarding future developments. Questionnaires were sent to 32 transplant centres representing 18 health regions and covered their extent of experience of transplantation, sources of donors, ages of donors and recipients, outcome of transplantation, and views on expansion of living donor transplantation services. Replies received from 27 transplant centres representing 17 health regions gave data on more than 1200 transplants from living donors. Transplants from living donors accounted for 0-25% of the total experience of health regions. Two centres had abandoned living donor transplantation. Sixty per cent of transplant surgeons favoured expansion of the living donor programme to meet a shortage of kidneys from cadavers, and the remainder thought that existing programmes were optimal. Living donor transplantation promises to be an important factor in the future planning of health care resources.

Adult↗
PubMed1989

Cardiovascular response during cerebral angiography under general and local anaesthesia.

Nineteen patients with subarachnoid haemorrhage who had cerebral angiography with the new contrast medium iohexol, were randomly allocated to receive either local anaesthesia plus sedation, or general anaesthesia. Arterial blood pressure, PaO2, PaCO2 and patient acceptability were examined. Significant fluctuations in arterial blood pressure occurred in the patients who received general anaesthesia. Local anaesthesia was associated with a stable blood blood pressure, adequate spontaneous ventilation and good patient acceptability. The quality of films obtained was examined and found to be of good or very good diagnostic quality in all cases in both groups of patients. Greater use of local anaesthesia with sedation for angiography is recommended.

Adolescent↗
PubMed1988

Asian mothers' risk factors for perinatal death--the same or different? A 10 year review of Leicestershire perinatal deaths.

A case-control study of all perinatal deaths in Leicestershire was established in 1976. By 1985 some 1342 singleton perinatal deaths had occurred. Perinatal mortality among patients of Asian origin was consistently higher than that among European women. Many of the sociomedical risk factors for perinatal death known at booking were common to both population groups. In this population of Asian women, however, low social class was not associated with perinatal risk and illegitimacy hardly ever occurred. In contrast, previous infertility among the Asian women was associated with risk of perinatal death, while no such association was found with European women. In 19% of perinatal deaths care was either inadequately provided or taken up. The case-control design in these circumstances provides a practicable way to evaluate causal factors and at the same time to provide information of value to educators and health service planners.

Adolescent↗
PubMed1988

Inaccuracies in manometric central venous pressure measurement.

Manometric measurement of CVP was compared to electronic measurement in ten patients. Manometric measurement was found to give readings of up to 5 cmH2O greater than electronic, with a mean difference of 2.4 cmH2O. This was shown to be due to two factors. Firstly, a meniscus effect caused an error of 1.07 cmH2O in the manometers used. Secondly, an error attributed to the way mean values of CVP are commonly read from manometers caused a further over estimate of 1.33 cmH2O. In intensive care units, where it is important to recognise and treat small changes in CVP, the use of electronic transducers to measure CVP is recommended.

Central Venous Pressure↗
PubMed1987

Diagnostic plots for departures from proportional hazards in cohort study data.

The assumption of proportional hazards is routinely made in the analysis of cohort studies, whether a simple SMR calculation or a full survival analysis is used. In this paper, we introduce simple plots for checking the validity of the assumption. The plots are of two kinds. The first, which has been used previously for survival data, makes use of the fact that the individual integrated hazards are distributed as unit exponential varieties under proportional hazards, and involves plotting their estimates against expected exponential order statistics. The second displays the evolution of relative risk as a function of time, and in this case, a choice of time scale must be made for the plots. A score test for proportional hazards is also derived, and the methods are illustrated by data on cancer mortality among the employees of a South Wales nickel refinery.

Age Factors↗
PubMed1986

Tumour basement membrane laminin in adenocarcinoma of rectum: an immunohistochemical study of biological and clinical significance.

Well-defined basement membrane laminin was seen in 98/158 (62%) rectal adenocarcinomas stained by an immunoperoxidase method. Only 27 (28%) patients with laminin-positive tumours developed distant metastases, compared with 39 (65%) patients with laminin-negative carcinomas. The corrected 5-year survival rates for patients with laminin-positive and laminin-negative tumours were 65% and 23%, respectively. Twenty-five out of 30 (83%) well-differentiated adenocarcinomas and only 3/15 (17%) poorly differentiated tumours contained basement membrane laminin, with moderately differentiated carcinomas showing intermediate laminin status (70/110, 64%, laminin positive). Forty-three of 60 (72%) of laminin-negative tumours had metastasized to regional lymph nodes. These data suggest that laminin may be a marker for differentiation. However, laminin status yields information about tumour behaviour which is not confined to stage and grade, and multivariate analysis shows that it is a better indicator of prognosis than tumour grade as assessed by conventional histology. Although laminin status alone is a less useful predictor of prognosis than Dukes' stage, a patient with a laminin-positive adenocarcinoma of rectum is 2.7 times as likely to survive 5 years than a patient with a laminin-negative tumour. Assessment of laminin status, together with Dukes' stage is, therefore, commended as a more precise and objective indicator of prognosis than histological degree of differentiation in colorectal carcinoma.

Adenocarcinoma↗
PubMed1985

Paradoxical air embolism during neurosurgery.

Four cases of air embolism which occurred during neurosurgical procedures in the sitting position are described, in whom the signs could be due to air in the coronary or cerebral arteries. It is suggested that, during venous air embolism in the sitting position, a significant number of patients are haemodynamically at risk from paradoxical air embolism, and that the serious consequences of venous air embolism in neurosurgery may be due to this.

Aged↗
PubMed1985

Contamination of internal jugular cannulae.

137 internal jugular vein cannulae from 113 patients undergoing open heart surgery were cultured using standard broth culture and a semiquantitative culture technique. 60 of the cannulae were placed using an aseptic technique and 77 using a standard non sterile technique. Significant contamination was found in 18.3% of the cannulae in the aseptic group and 15.6% in the standard group. The contaminating organism was Staphylococcus epidermidis in 87.1% of cases. No advantage in using an aseptic technique of cannula insertion was demonstrated. It was concluded that the major source of contamination was elsewhere.

Antisepsis↗
PubMed1984

Occurrence of cancer in Asians and non-Asians.

Cancer registration data for a defined geographical area, covering a seven year period, were modified to include the variable "Asian ethnic origin." The data were then used to test the hypothesis that a difference would be found between Asians and non-Asians in the pattern of cancer by site. Whereas the incidence of cancer of all sites appeared to be significantly lower in Asians (p less than 0.05), after taking account of this, and adjusting for the very different age distributions of the two populations, a highly significant difference (p less than 0.0005) was found between the two groups in the distribution of cancer between sites. Although, given the size and young age structure of the Asian population, absolute numbers of cases were small, a significant excess of Asian cases (compared with the expected) occurred for cancer of the tongue, oral cavity, pharynx, and oesophagus. For most sites there were fewer Asian cases than would be expected, particularly so for the stomach, testis, and skin. The results indicate the need for formal epidemiological study to test specific aetiological hypotheses which may account for these apparent differences.

Asia↗
PubMed1983

Quality of obstetric care provided for Asian immigrants in Leicestershire.

Between 1976 and 1981 some 939 perinatal deaths occurred to women living in Leicestershire, of which 128 (14%) were to Asian women. The qualifications of the general practitioners, the gestation at which women start antenatal care, and perinatal death were used as structural, process, and outcome measures for evaluating the services provided to Asian immigrants within this population. Perinatal deaths were divided into four groups: congenital malformation, macerated stillbirth, asphyxia in labour, and immaturity. Asian mothers had one and a half times the risk of perinatal mortality when social class, parity, height, legitimacy, and the general practitioner's qualifications were taken into account. Asian and non-Asian mothers with general practitioners who were not on the obstetric list had more than twice the risk of a perinatal death when a similar adjustment was made. Recommendations include priority allocation of community midwives to practitioners not on the obstetric list, the establishment of postgraduate courses for such doctors, and the continued evaluation of the effect of such proposals on perinatal mortality.

Asia↗