Using Bayesian networks in the construction of a bi-level multi-classifier. A case study using intensive care unit patients data

Combining the predictions of a set of classifiers has shown to be an effective way to create composite classifiers that are more accurate than any of the component classifiers. There are many methods for combining the predictions given by component classifiers. We introduce a new method that combine a number of component classifiers using a Bayesian network as a classifier system given the component classifiers predictions. Component classifiers are standard machine learning classification algorithms, and the Bayesian network structure is learned using a genetic algorithm that searches for the structure that maximises the classification accuracy given the predictions of the component classifiers. Experimental results have been obtained on a datafile of cases containing information about ICU patients at Canary Islands University Hospital. The accuracy obtained using the presented new approach statistically improve those obtained using standard machine learning methods.     

A voltage-dependent K+ current contributes to membrane potential of acutely isolated canine articular chondrocytes

The electrophysiological properties of acutely isolated canine articular chondrocytes have been characterized using patch-clamp methods. The 'steady-state' current–voltage relationship ( I–V ) of single chondrocytes over the range of potentials from −100 to +40 mV was highly non-linear, showing strong outward rectification positive to the zero-current potential. Currents activated at membrane potentials negative to −50 mV were time independent, and the I–V from −100 to −60 mV was linear, corresponding to an apparent input resistance of 9.3 ± 1.4 GΩ ( n = 23). The outwardly rectifying current was sensitive to the K⁺ channel blocking ion tetraethylammonium (TEA), which had a 50% blocking concentration of 0.66 m m (at +50 mV). The 'TEA-sensitive' component of the outwardly rectifying current had time- and membrane potential-dependent properties, activated near −45 mV and was half-activated at −25 mV. The reversal potential of the 'TEA-sensitive' current with external K⁺ concentration of 5 m m and internal concentration of 145 m m , was −84 mV, indicating that the current was primarily carried by K⁺ ions. The resting membrane potential of isolated chondrocytes (−38.1 ± 1.4 mV; n = 19) was depolarized by 14.8 ± 0.9 mV by 25 m m TEA, which completely blocked the K⁺ current of these cells. These data suggest that this voltage-sensitive K⁺ channel has an important role in regulating the membrane potential of canine articular chondrocytes.     

Diversity of enteric viruses detected in patients with gastroenteritis in a tertiary referral paediatric hospital

The genetic diversity of enteric viruses co-circulating in a cohort of patients with viral gastroenteritis in a large tertiary paediatric hospital in London, UK, was determined. Multiple strains of noroviruses (NV), sapoviruses (SV) and astroviruses (HAsV) were detected in these patients, indicating the likelihood of multiple introductions from different sources, possible sub-clinical infections and simultaneous infection with different viruses in immunocompromised and other patients. Routine screening of immunocompromised patients and infection control procedures are important to prevent nosocomial infection.     

Routine mortality monitoring for detecting mass murder in UK general practice: test of effectiveness using modelling.

BACKGROUND: The Shipman Inquiry recommended mortality rate monitoring if it could be 'shown to be workable' in detecting a future mass murderer in general practice. AIM: To examine the effectiveness of cumulative sum (CUSUM) charts, cross-sectional Shewhart charts, and exponentially-weighted, moving-average control charts in mortality monitoring at practice level. DESIGN OF STUDY: Analysis of Scottish routine general practice data combined with estimation of control chart effectiveness in detecting a 'murderer' in a simulated dataset. METHOD: Practice stability was calculated from routine data to determine feasible lengths of monitoring. A simulated dataset of 405,000 'patients' was created, registered with 75 'practices' whose underlying mortality rates varied with the same distribution as case-mix-adjusted mortality in all Scottish practices. The sensitivity of each chart to detect five and 10 excess deaths was examined in repeated simulations. The sensitivity of control charts to excess deaths in simulated data, and the number of alarm signals when control charts were applied to routine data were estimated. RESULTS: Practice instability limited the length of monitoring and modelling was consequently restricted to a 3-year period. Monitoring mortality over 3 years, CUSUM charts were most sensitive but only reliably achieved >50% successful detection for 10 excess deaths per year and generated multiple false alarms (>15%). CONCLUSION: At best, mortality monitoring can act as a backstop to detect a particularly prolific serial killer when other means of detection have failed. Policy should focus on changes likely to improve detection of individual murders, such as reform of death certification and the coroner system.     

Mapping of gene loci in the Q13–Q15 region of chromosome 12

The gene loci CDK4, GLI, CHOP and MDM2 have been mapped to the q13–q15 region of chromosome 12. Using fluorescencein situ hybridization onto simultaneously DAPI-banded metaphase chromosomes and interphase nuclei, we have more precisely mapped and ordered these loci, together with a number of Genethon microsatellite markers. GLI and CHOP localize to 12q13.3–14.1, CDK4 to 12q14 and MDM2 to 12q14.3–q15, and the gene order is cen-GLI/CHOP-CDK4-MDM2. The Genethon microsatellites D12S80 and D12S83 flank MDM2.     

Reticulospinal actions on primary afferent depolarization of cutaneous and muscle afferents in the isolated frog neuraxis

The effects of the brainstem reticular formation on the intraspinal excitability of low threshold cutaneous and muscle afferents were studied in the frog neuraxis isolated together with the right hindlimb nerves. Stimulation of low threshold fibers (less than two times threshold) in cutaneous nerves produced short latency, negative field potentials in the ipsilateral dorsal neuropil (200–400 m depth) that reversed to positivity at deeper regions (500–700 m). Stimulation of low threshold fibers (less than two times threshold) in muscle nerves produced, instead, negative responses that acquired their maximum amplitude in the ventral neuropil (700–900 m depth). These electrophysiological findings suggest, in agreement with observations in the cat, that low threshold cutaneous and muscle afferents end at different sites in the spinal cord. Intraspinal microstimulation applied within the dorsal neuropil produced antidromic responses in low threshold cutaneous afferents that were increased in size following stimulation of the dorsal or ventral roots, as well as of the brainstem reticular formation. This increase in excitability is interpreted as being due to primary afferent depolarization (PAD) of the intraspinal terminals of cutaneous fibers. Antidromic responses recorded in muscle nerves following intraspinal stimulation within the ventral neuropil were also increased following conditioning stimulation of adjacent dorsal or ventral roots. However, stimulation of the bulbar reticular formation produced practically no changes in the antidromic responses, but was able to inhibit the PAD of low threshold muscle afferents elicited by stimulation of the dorsal or ventral roots. It is suggested that the PAD of low threshold cutaneous and muscle afferents is mediated by independent sets of interneurons. Reticulospinal fibers would have excitatory connections with the interneurons mediating the PAD of cutaneous fibers and inhibitory connections with the interneurons mediating the PAD of muscle afferents. Although our results provide no direct information on whether the reticulospinal depression of the PAD elicited in low threshold muscle afferents is due to inhibition along the pathways producing PAD of muscle spindle or of tendon organ afferents, it seems likely — by analogy with what has been seen in the cat spinal cord — that these inhibitory actions are mostly restricted to the pathways producing PAD in the terminal arborizations of muscle spindle afferents. These results emphasize the specificity of the descending control of the synaptic efficacy of low threshold cutaneous and muscle afferents which could be of importance for motor performance.     

Catheter-related bacteremia from femoral and central internal jugular venous access

The objective of this prospective observational study was to determine the influence of femoral and central internal jugular venous catheters on the incidence of catheter-related bacteremia (CRB). We included patients admitted to a 12-bed polyvalent medico-surgical intensive care unit over 4 years who received one or more femoral or central internal jugular venous catheters. We diagnosed 16 cases of CRB in 208 femoral catheters and 22 in 515 central internal jugular venous catheters. We found a higher incidence of CRB with femoral (9.52 per 1,000 catheter days) than with central internal jugular venous access (4.83 per 1,000 catheter days; risk ratio = 1.93; 95% confidence interval: 1.03-3.73; P = 0.04). Central internal jugular venous access could be considered a safer route of venous access than femoral access in minimizing the risk of central venous catheter-related bacteremia.     

The mammalian testis-specific thioredoxin system

Redox control of cell physiology is one of the most important regulatory mechanisms in all living organisms. The thioredoxin system, composed of thioredoxin and thioredoxin reductase, has emerged as a key player in cellular redox-mediated reactions. For many years, only one thioredoxin system had been described in higher organisms, ubiquitously expressed in the cytoplasm of eukaryotic cells. However, during the last decade, we and others have identified and characterized novel thioredoxin systems with unique properties, such as organelle-specific localization in mitochondria or endoplasmic reticulum, tissue-specific distribution mostly in the testis, and features novel for thioredoxins, such as microtubule-binding properties. In this review, we will focus on the mammalian testis-specific thioredoxin system that comprises three thioredoxins exclusively expressed in spermatids (named Sptrx-1, Sptrx-2, and Sptrx-3) and an additional thioredoxin highly expressed in testis, but also present in lung and other ciliated tissues (Txl-2). The implications of these findings in the context of male fertility and testicular cancer, as well as evolutionary aspects, will be discussed.     

The effects of competition and motor reprogramming on visuomotor selection in unilateral neglect

Patients with unilateral neglect following right hemisphere damage may have difficulty in moving towards contralesional targets. To test the hypothesis that this impairment arises from competing motor programs triggered by irrelevant ipsilesional stimuli, we examined 16 right hemisphere patients, eight with left visual neglect and eight without, in addition to eight healthy control subjects. In experiment 1 subjects performed sequences of movements using their right hand to targets on the contralesional or ipsilesional side of the responding limb. The locations of successive targets in each sequence were either predictable or unpredictable. In separate blocks of trials, targets appeared either alone or with a simultaneous distractor located at the immediately preceding target location. Neglect patients were significantly slower to execute movements to contralesional targets, but only for unpredictable movements and in the presence of a concurrent ipsilesional distractor. In contrast, healthy controls and right hemisphere patients without neglect showed no directional asymmetries of movement execution. In experiment 2 subjects were required to interrupt a predictable, reciprocating sequence of leftward and rightward movements in order to move to an occasional, unpredictable target that occurred either in the direction opposite to that expected, or in the same direction but twice the extent. Neglect patients were significantly slower in reprogramming the direction and extent of movements towards contralesional versus ipsilesional targets, and they also made significantly more errors when executing such movements. Right hemisphere patients without neglect showed a similar bias in reprogramming direction (but not extent) for contralesional targets, whereas healthy controls showed no directional asymmetry in either condition. On the basis of these findings we propose that neglect involves a competitive bias in favour of motor programs for actions directed towards ipsilesional versus contralesional events. We suggest that programming errors and increased latencies for contralesional movements arise because the damaged right hemisphere can no longer effectively inhibit the release of inappropriate motor programs towards ipsilesional events. Received: 1 October 1996 / Accepted: 21 October 1997