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Biomedical subjects

R J Marshall

Publications and source records attributed to R J Marshall.

At least 19 recordsLinked to original sources
PubMed2005

Vehicle interior interactions and kinematics of rear facing child restraints in frontal crashes.

The performance of rear facing child restraints in frontal crashes can be determined by controlling a) the child's kinematics and b) interactions with vehicle structures. Twelve sled tests were performed to analyze the effect of the location and structural properties of vehicle interior components. The role of restraint kinematics was studied by developing computational models which underwent idealized motions. Stiff structures originally offset from the restraint, but which contact the restraint late in the test, cause increased injury values. Attachment methods which reduce child restraint rotation and more rigidly couple the restraint to the vehicle result in the best safety performance.

Accidents, Traffic↗
PubMed2003

Use of odds ratios on anaesthesia related studies.

In line with other medical journals, odds ratios are increasingly being reported in anaesthesia literature. The frequency of the use of odds ratio and how well it relates to the relative risk when it is interpreted as relative risk remains unknown. We investigated the use of odds ratio, and its relationship to relative risk and the incidence of outcome in this study. We identified 60 meta-analyses and 87 original articles that reported odds ratios. While relative risk could have been reported in 79% of the studies, only a small proportion (3%) of these studies have estimated and reported the relative risk in addition to the odds ratio. There is a significant bias if odds ratio is interpreted as relative risk, especially so when the incidence of outcome is high. While odds ratio is a valid measure of treatment effect in its own right, anaesthetists and investigators should be careful not to interpret odds ratio as equivalent to relative risk.

Anesthesia↗
PubMed2003

Interstitial nephritis associated with perianeurysmal retroperitoneal fibrosis.

Renal failure in retroperitoneal fibrosis is usually secondary to ureteric obstruction. We report a patient whose renal failure did not improve following relief of obstruction. Renal biopsy showed an interstitial nephritis, and function improved with steroid therapy. We suggest that renal biopsy should be considered in cases of renal failure associated with retroperitoneal fibrosis that do not respond to the relief of ureteric obstruction.

Aged↗
PubMed2002

Post-operative paraplegia following spinal cord infarction.

Thoracic epidural analgesia is a frequently utilised technique. Neurological complications are uncommon, but of grave consequence with significant morbidity. Spinal cord infarction following epidural anaesthesia is rare. We present a case where a hypertensive patient underwent an elective sigmoid colectomy under combined general/epidural anaesthesia for a suspected malignant abdominal mass. An epidural infusion was used for intra-operative and post-operative analgesia. During surgery, the blood pressure was labile and she was hypotensive. Postoperatively, the patient became confused, pyrexial and tachycardic and developed systemic inflammatory response syndrome requiring intensive care management. She developed a flaccid paralysis at L3 level with areflexia, analgesia and impaired sensation. A spinal cord infarct in the region of the conus extending into the thoracic cord was diagnosed. Complications of epidural anaesthesia are easily recognised when they develop immediately; their relationship to the anaesthesia and the post-operative period may be misjudged or underestimated when they appear after a delay, if neurological signs are masked by lack of patient cooperation and drowsiness or if the epidural anaesthesia is prolonged by long-acting drugs. New neurological deficits should be evaluated promptly to document the evolving neurological status and further testing or intervention should be arranged if appropriate. The association with epidural anaesthesia as a cause of paraplegia is reviewed. The aetiological factors that may have contributed to this tragic neurological complication are discussed.

Anesthesia, Epidural↗
PubMed2001

Displaying clinical data relationships using scaled rectangle diagrams.

A method is presented to draw rectangles to represent categorical data relationships. The idea is an adaptation of a scaled Venn diagram. Rectangles are drawn with area proportional to the frequency of categories and the rectangles are positioned to overlap each other so that the areas of overlap are in proportion to the joint frequencies of the characteristics. The diagrams are especially useful to illustrate symptom co-occurrence.

Arthritis, Rheumatoid↗
PubMed2001

The use of classification and regression trees in clinical epidemiology.

A critique is presented of the use of tree-based partitioning algorithms to formulate classification rules and identify subgroups from clinical and epidemiological data. It is argued that the methods have a number of limitations, despite their popularity and apparent closeness to clinical reasoning processes. The issue of redundancy in tree-derived decision rules is discussed. Simple rules may be unlikely to be "discovered" by tree growing. Subgroups identified by trees are often hard to interpret or believe and net effects are not assessed. These problems arise fundamentally because trees are hierarchical. Newer refinements of tree technology seem unlikely to be useful, wedded as they are to hierarchical structures.

Algorithms↗
PubMed2001

Determining and visualising at-risk groups in case-control data.

BACKGROUND: Case-control research is often exploratory; to determine factors that increase risk. Often, regression methods are used to determine combinations of risk factors that predispose to excess risk. Recently, tree-based methods have also been proposed. Both have limitations. An alternative approach is suggested, based on a search algorithm to identify at-risk subgroups. METHODS: Statistical methods to determine and visualise at-risk sub-groups in case-control studies are presented. The method of determining sub-groups--search partition analysis (SPAN)--searches among different Boolean combinations of risk factors. Sub-groups that have been identified are visualised by scaled rectangle diagrams. These show the size of sub-groups and the extent to which they overlap. RESULTS: Theory is presented for applying the method to case-control data. The methods are illustrated by analysis of three case-control studies: one on sudden infant death syndrome, a second on heart disease and a third on child pedestrian injuries. CONCLUSIONS: The methods provide a useful alternative to regression and tree-based analysis. They demarcate subgroups that, in the three examples, are easy to interpret and would not have been found by other methods. Scaled rectangle diagrams are a useful way to visualise the results.

Accidents, Traffic↗
PubMed2000

A case-crossover analysis of a case-control study of alcohol consumption and coronary events: the effects of exposure definition and the use of control data.

BACKGROUND: Case-crossover studies can be used to assess the effects of transient exposures in acute events by comparing cases' exposures at the time of the event against their usual exposure. Cases from a case-control study can also be analysed by this method if appropriate information is obtained. METHODS: We apply the case-crossover method to data collected in a case-control study of acute coronary events, to estimate the risk of alcohol consumption in the 24 h before a coronary event. Two questions, concerning the usual frequency of consuming alcohol and how much was consumed, were used in the analysis. The sensitivity of effect estimates to the two questions and to different ways of eliciting probabilities from them, are examined. The cases and controls were both analysed in the same way, assigning controls a 'pseudo-event' time at random. It is suggested that controls may provide a benchmark to establish whether bias exists in the case-series analysis. RESULTS: We find that the case-crossover analysis is sensitive to how exposure probabilities are assigned. Adopting a Poisson model for exposures leads to inflated risk estimates. The bias is removed if the control series is used to adjust estimates. There appears to be a small protective effect from alcohol consumption. CONCLUSION: Case-crossover designs have considerable potential, but reliable information on usual exposure limits their applicability. More research is required on how best to elicit exposure probabilities.

Alcohol Drinking↗
PubMed1999

Classification to ordinal categories using a search partition methodology with an application in diabetes screening.

A method is proposed for classification to ordinal categories by applying the search partition analysis (SPAN) approach. It is suggested that SPAN be repeatedly applied to binary outcomes formed by collapsing adjacent categories of the ordinal scale. By a simple device, whereby successive binary partitions are constrained to be nested, a partition for classification to the ordinal states is obtained. The approach is applied to ordinal categories of glucose tolerance to discriminate between diabetes, impaired glucose tolerance and normal states. The results are compared with analysis by ordinal logistic regression and by classification trees.

Age Factors↗
PubMed1999

An empirical investigation of exposure measurement bias and its components in case-control studies.

This study investigated bias due to misclassification of exposure in case control studies. Using a metaanalysis of data from a number of case control studies, in which a possibly misclassified exposure was validated against a more reliable one, estimates of misclassification indices and bias were obtained. The estimates were used to investigate whether misclassification indices, in particular, sensitivity and specificity and so-called quality indices, are typically nondifferential with respect to cases and controls. It is concluded that quality indices do not show any tendency to be either lower or higher in cases than controls. On the other hand, sensitivity tends to be higher in cases than controls and specificity lower. Estimates of misclassification bias may be either positive or negative and are consistent with random variation; there is little to suggest that bias is present in the studies analyzed.

Bias↗
PubMed1998

Neuromuscular blocking and cardiovascular effects of Org 9487, a new short-acting aminosteroidal blocking agent, in anaesthetized animals and in isolated muscle preparations.

This study was undertaken to investigate the neuromuscular blocking profile and cardiovascular effects of Org 9487, a new aminosteroidal, non-depolarizing, neuromuscular blocking agent structurally related to vecuronium, in anaesthetized animals and in isolated muscle preparations. In in vitro functional assays of neuromuscular blocking activity, Org 9487 was between eight and 15 times less potent than vecuronium. In cats and monkeys the potency of Org 9487 was approximately one-seventh and one-twentieth, respectively, that of vecuronium. In both species, Org 9487 induced rapidly developing (onset times between 1.5 min and 1.9 min) neuromuscular paralysis, which was shorter-lasting than that of vecuronium and similar in time course to suxamethonium. The vagal: neuromuscular blocking dose ratio for Org 9487 was 3 and ganglion block was seen only at approximately 20 times the neuromuscular blocking dose. There was no evidence in the rat that Org 9487, administered at doses up to 3 mg kg-1, inhibited noradrenaline re-uptake. In anaesthetized dogs, Org 9487 (3 x 90% blocking dose) induced only relatively small and transient haemodynamic effects. The administration of clinically relevant doses of neostigmine or pyridostigmine shortened the time-course profile of Org 9487, even when administered during profound neuromuscular block. In animals, Org 9487 is a low potency, nondepolarizing neuromuscular blocking agent with a time course profile similar to that of suxamethonium. Although Org 9487 is less selective than vecuronium for the neuromuscular junction, it is unlikely to produce prohibitive cardiovascular side effects in man.

Adrenergic alpha-Agonists↗