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Biomedical subjects

G Matthews

Publications and source records attributed to G Matthews.

At least 37 records · Page 2Linked to original sources
PubMed2000

AIDS related systemic non-Hodgkin's lymphoma.

OBJECTIVE: To review the current literature on HIV associated non-Hodgkin's lymphoma. METHODS: A comprehensive Medline/Pubmed search of articles pertaining to HIV associated non-Hodgkin's lymphoma as well as personal experience from the treatment of over 200 patients at the Chelsea and Westminster Hospital, one of the largest centres for the management of HIV disease in Europe. CONCLUSION: High grade B cell non-Hogdkin's lymphoma is the second commonest tumour affecting people with HIV. The incidence of this tumour is not declining following the introduction of highly active antiretroviral therapy. Chemotherapy has been employed with modest success in this group of patients; however, the prognosis remains worse than for immunocompetent patients. Advances in molecular genetics and virology have led to a greater understanding of the biology of these tumours. However, these advances have yet to be translated into improvements in the clinical management of patients with AIDS associated non-Hodgkin's lymphoma.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2000

Attention, automaticity, and affective disorder.

This article reviews possible mechanisms for attentional bias in affective disorders and anxiety. Attentional bias is sometimes conceptualized as automatic in nature. However, there are methodological difficulties with studies purporting to demonstrate automaticity, and empirical and simulation evidence suggest that bias may be predominantly strategic. Bias in the voluntary control of attention may be driven by coping strategies, which in turn depend on appraisal of external demands, metacognitions of mental function, access of self-relevant knowledge in long-term memory, and self-focus of attention. The Self-Regulatory Executive Function (S-REF) model of emotion and attention specifies how these processes interact to influence attentional control. Clinical disorder is associated with loss of dynamic adaptability and a syndrome of perseverative rumination and worry that directs attention toward monitoring for threat and away from restructuring of maladaptive self-knowledge. Implications of the S-REF model for therapeutic interventions directed toward attentional control are discussed.

Adaptation, Psychological↗
PubMed2000

Associations between primary appraisals and life-events while controlling for depression.

OBJECTIVES: The main objective of this paper was to explore the associations between life-events and primary appraisals (threat, challenge and loss) controlling for depression. It was predicted that specific associations between life-events and primary appraisals would remain once depression had been partialled. A subgoal of this paper was to develop a content analytic coding frame for student life-events. DESIGN: This study was a retrospective survey in which participants provided accounts of recent stressful encounters, and completed indices of primary appraisals and depression. METHOD: The participants were 979 undergraduates who provided descriptions of life-events. A subsample of 391 provided additional information on primary appraisals and depression. The primary outcomes were the partial correlations between life-events and primary appraisals. RESULTS: There were significant associations between life-events and primary appraisals above and beyond variance explained by depression. Results also indicated that the definition of loss appraisals could be extended to include events that were related to anticipated future loss, especially if the event was also perceived as threatening. Also certain self-defined negative life-events were appraised as positive. Life-events were shown to vary systematically as a function of external constraints (e.g. stage of the academic year). CONCLUSIONS: A variety of events were associated with loss appraisals and this may have implications for risk factors in depression.

Adaptation, Psychological↗
PubMed2000

The effects of signal salience and caffeine on performance, workload, and stress in an abbreviated vigilance task.

In 2 experiments, a 12-min computerized vigilance task was demonstrated to reproduce the vigilance decrement, high workload (NASA-TLX), and stressful character (Dundee Stress State Questionnaire) of vigilance tasks lasting 30 min or more. In Experiment 1, the abbreviated task was also shown to duplicate the signal salience effect, a major finding associated with long-duration vigilance tasks. Moreover, Experiment 2 showed that performance on the abbreviated task can be enhanced by caffeine - a drug that benefits long-duration tasks. This enhancement effect was limited to performance, however, suggesting that caffeine influences factors that control signal detection but not those that control task-induced stress. The results parallel those obtained with long-duration tasks and support a resource-depletion model of the vigilance decrement. The abbreviated task might be useful in situations in which long-duration tasks are precluded (e.g., performance assessment batteries, neuropsychological testing, and brain imaging).

Adolescent↗
PubMed2000

A non-contact vital signs monitor.

The expansion and contraction of the lungs and heart result in movement of the chest wall that can be detected and monitored to determine respiration and heart rate. A prototype non-contact Vital Signs Monitor (VSM) has been developed which uses very low power, high frequency Doppler radar to detect these motions. Digital signal processing (DSP) techniques, imbedded in the VSM, are used to extract heart and respiration rate information from the resultant waveform. A 10-GHz prototype VSM was developed for the Air Force in the mid-1980s using analog technology. The objective was to assess a fallen soldier's clinical condition at distances up to 100 meters before committing resources to assist that individual. An updated and improved version of the original VSM was developed in 1997. This device was designed to operate at shorter distances, use a higher frequency carrier, and provide more specific heart and respiration rate information using digital signal processing techniques. The VSM radar system is a straightforward homodyne receiver. It operates using frequency modulated continuous wave (FM-CW) transmission, which allows for very low power levels. The safe human power density exposure level at its operating frequency of 35 GHz is 10 mW/cm2. A simple approximation using uniform distribution and an antenna aperture of 2 cm by 3 cm gives a power density at the antenna face of 0.017 mW/cm2, nearly a factor of 1000 below the safe level. When the VSM's antenna is trained on the chest wall of a subject, the VSM is capable of measuring and distinguishing minute movements resulting from the mechanical activity of the heart and lungs. As the subject's chest wall moves, the exact phase of the return signal changes. To avoid the possibility of phase-related dead spots, two signals differing in phase by 90 degrees are used to demodulate the signal to baseband (DC). The two resulting "time-varying DC" signals represent the sine and cosine of a phase angle corresponding to the changing position of the target, in this case the motion of the chest wall. The current VSM operates at a frequency of 35 GHz with a corresponding wavelength of only 8.6 mm. This provides a response sensitive enough to detect the small motions caused by cardiac function. The Vital Signs Monitor has several possible application areas. The fact that it is noncontacting would make it especially attractive for monitoring patients in burn units, NICUs, or trauma centers, where attaching electrodes is either inconvenient or not feasible. Results to date indicate a strong correlation between the cardiac component of the motion signal and an electrocardiogram (ECG). With careful signal processing and analysis, it may be possible to extract clinically useful information about cardiac condition, function, or performance from the surface-motion waveform. This could provide a safe, inexpensive, and painless addition to the diagnostic and monitoring tools currently available to cardiologists. Although there are technical obstacles to overcome in filtering gross motions of the subject, the VSM offers significant advances over conventional methods of measuring heart and respiration rate.

Fetal Monitoring↗
PubMed1999

Synaptic mechanisms of bipolar cell terminals.

Giant synaptic terminals of goldfish bipolar neurons allow direct studies of presynaptic mechanisms underlying neurotransmitter release and its modulation. Calcium influx via L-type calcium channels of the terminal triggers synaptic vesicle exocytosis, which can be monitored in isolated terminals by means of the associated changes in membrane capacitance. Information about the kinetics and calcium dependence of synaptic exocytosis has been obtained from capacitance measurements in these ribbon-type synaptic terminals.

Action Potentials↗
PubMed1999

Electrophysiology of synaptic vesicle cycling.

Patch-clamp capacitance measurements can monitor in real time the kinetics of exocytosis and endocytosis in living cells. We review the application of this technique to the giant presynaptic terminals of goldfish bipolar cells. These terminals secrete glutamate via the fusion of small, clear-core vesicles at specialized, active zones of release called synaptic ribbons. We compare the functional characteristics of transmitter release at ribbon-type and conventional synapses, both of which have a unique capacity for fast and focal vesicle fusion. Subsequent rapid retrieval and recycling of fused synaptic vesicle membrane allow presynaptic terminals to function independently of the cell soma and, thus, as autonomous computational units. Together with the mobilization of reserve vesicle pools, local cycling of synaptic vesicles may delay the onset of vesicle pool depletion and sustain neuronal output during high stimulation frequencies.

Animals↗
PubMed1998

BMP1-related metalloproteinases promote the development of ventral mesoderm in early Xenopus embryos.

Bone morphogenetic protein 1 (BMP1) is a metalloproteinase closely related to Drosophila Tolloid (Tld). Tld regulates dorsoventral patterning in early Drosophila embryos by enhancing the activity of Dpp, a member of the TGF-beta family most closely related to BMP2 and BMP4. In Xenopus BMP4 appears to play an essential role in dorsoventral patterning, promoting the development of ventral fates during gastrula stages. To determine if BMP1 has a role in regulating the activity of BMP4, we have isolated cDNAs for Xenopus BMP1 and a novel closely related gene that we have called xolloid (xld). Whereas xbmp1 is uniformly expressed at all stages tested, the initial uniform expression of xld becomes localized to two posterior ectodermal patches flanking the neural plate and later to the inner ectoderm of the developing tailbud. xld is also expressed in dorsal regions of the brain during tailbud stages and is especially abundant in the ventricular layer of the dorsal hindbrain caudal to the otic vesicle. Overexpression of either gene inhibits the development of dorsoanterior structures in whole embryos and ventralizes activin-induced dorsal mesoderm in animal caps. Since ventralization of activin-induced animal caps can be blocked by coinjecting a dominant-inhibitory receptor for BMP2 and BMP4, we suggest a role for BMP1 and Xld in regulating the ventralizing activity of these molecules.

Activins↗
PubMed1998

Rehabilitation in an individual with chronic arsenic poisoning: medical, psychological, and social implications.

Although arsenic poisoning was a common cause of homicide in the past, it is seldom suspected today; thus there may be serious delays in diagnosis and treatment of arsenic ingestion. Rehabilitation specialists have traditionally dealt with the debilitating consequences of the classic arsenic-induced sensorimotor peripheral neuropathy; however, a knowledge of the presentation of acute toxicity combined with the effects of chronic exposure is essential for proper treatment, particularly in the event of ongoing exposure. This case report demonstrates the wide spectrum of medical complications associated with arsenic poisoning and briefly reviews its pathophysiology and treatment from both the medical and psychosocial perspective.

Adult↗
PubMed1998

Ageing and word processing competence: compensation or compilation?

Composition and compilation were examined as two alternative hypotheses relating to 'cognitive competence' in older adults. Techniques of molar equivalence-molecular decomposition (ME-MD) and molecular equivalence-molar analysis (ME-MA) were used to investigate performance of experienced (over 100 hours) younger (18-30 years) and older (45-66 years) adults on a word processing task, requiring insertion and deletion of words from passages of text. There was some indication that typing skill may form the basis of a compensatory mechanism. However, differences between 'good' and 'poor' performers in the older sample supported the position that high levels of complex task skill in older adults are associated with the possession (possibly through maintenance) of high levels of basic cognitive capacities, and are not related to the integration of molecular task components.

Adolescent↗
PubMed1998

Driver stress and performance on a driving simulator.

Effects of stress on driving performance can depend on the nature of driver's stress reactions and on the traffic environment. In an experimental study, we assessed multiple dimensions of vulnerability to driver stress by a questionnaire that was validated in previous field studies and related those dimensions to performance on a driving simulator. Results were broadly consistent with prediction. A dimension of habitual dislike of driving was associated with reduced control skills, greater caution, and disturbance of moods. A measure of aggressive driving predicted more frequent and more error-prone overtaking, which are effects attributed to the use of confrontive coping strategies in interaction with other vehicles. An alertness measure predicted speed of reaction to pedestrian hazards. This research has practical applications for system design, automated monitoring of driver performance, selection and assessment of drivers, and training.

Adolescent↗
PubMed1997

Depletion and replenishment of vesicle pools at a ribbon-type synaptic terminal.

Synaptic depression was studied using capacitance measurements in synaptic terminals of retinal bipolar neurons. Single 250 msec depolarizations evoked saturating capacitance responses averaging approximately 150 fF, whereas trains of 250 msec depolarizations produced plateau capacitance increases of approximately 300 fF. Both types of stimuli were followed by pronounced synaptic depression, which recovered with a time constant of approximately 8 sec after single pulses but required >20 sec for full recovery after pulse trains. Inactivation of presynaptic calcium current could not account for depression, which is attributed instead to depletion of releasable and reserve vesicle pools that are recruited and replenished at different rates. Recovery from depression was normal in the absence of fast endocytosis, suggesting that replenishment was from a reserve pool of preformed vesicles rather than from preferential recycling of recently fused vesicles. Given the in vivo light response of the class of bipolar neuron studied here, it is likely that, under at least some illumination conditions, the cells produce a fast and phasic bout of exocytosis rather than tonic release.

Animals↗
PubMed1997

Implications of task-induced fatigue effects for in-vehicle countermeasures to driver fatigue.

Two driving simulator studies are reported which investigate the variation of fatigue effects with task demands and provide recommendations for system design to counteract driver fatigue. Two opposing explanations of the interactive effects of task demands and fatigue were examined. One explanation is that fatigue drains attentional resources, so that detrimental effects of fatigue on performance are accentuated when task demands increase. The alternative explanation is that fatigue disrupts matching of effort to task demands, such that the fatigued driver fails to regulate effort effectively when the task appears easy. In both studies, drivers performed both a fatiguing drive, in the first part of which they were required to perform a secondary detection task, and a control drive with no additional secondary task. In the last part of both drives, drivers were required to detect movement in pedestrian stimuli presented on both sides of the road. Vehicle control and steering movements were logged throughout both drives. The results are consistent with dynamic models of stress and sustained performance which suggest that fatigue may impair adaptation to conditions of underload, but are inconsistent with the attentional resource explanation. These task-specific fatigue effects have important implications for in-vehicle countermeasures to driver fatigue. Current approaches to the implementation of such devices fail to reflect the task-specific nature of fatigue effects. Fatigue-monitoring devices may only be valid in certain driving environments or contexts. Hence, it may be necessary to integrate performance-based feedback monitoring information with route and traffic density information from navigation systems.

Adaptation, Psychological↗