PubMed Health⌕ Search

Biomedical subjects

W Penny

Publications and source records attributed to W Penny.

12 recordsLinked to original sources
PubMed1999

Temporal and spatial complexity measures for electroencephalogram based brain-computer interfacing.

There has been much interest recently in the concept of using information from the motor cortex region of the brain, recorded using non-invasive scalp electrodes, to construct a crude interface with a computer. It is known that movements of the limbs, for example, are accompanied by desynchronisations and synchronisations within the scalp-recorded electroencephalogram (EEG). These event-related desynchronisations and synchronisations (ERD and ERS), however, appear to be present when volition to move a limb occurs, even when actual movement of the limb does not in fact take place. The determination and classification of the ERD/S offers many exciting possibilities for the control of peripheral devices via computer analysis. To date most effort has concentrated on the analysis of the changes in absolute frequency content of signals recorded from the motor cortex. The authors present results which tackle the issues of both the interpretation of changes in signals with time and across channels with simple methods which monitor the temporal and spatial 'complexity' of the data. Results are shown on synthetic and real data sets.

Computer User Training↗
PubMed1999

Myocardial bradykinin production during coronary balloon angioplasty in humans.

BACKGROUND: Recent studies have implicated the peptide bradykinin as a potential trigger of ischaemic preconditioning, the phenomenon whereby a brief episode of myocardial ischaemia induces an increased tolerance to subsequent more prolonged ischaemia. Brief myocardial ischaemia occurring during percutaneous transluminal coronary balloon angioplasty in humans is reported to be capable of inducing preconditioning. DESIGN: We studied the intracardiac production of bradykinin in eight patients (seven men, mean age 53.5 years) undergoing elective percutaneous transluminal coronary angioplasty for a single left anterior descending coronary artery stenosis. Paired blood samples were obtained from the coronary sinus and the proximal aorta at baseline, immediately before balloon deflation after a 2-min inflation, and at 1, 3 and 5 min post deflation. Bradykinin levels were measured by radioimmunoassay. RESULTS: There was no significant change either in aortic or coronary sinus bradykinin levels at any time point. CONCLUSIONS: Intracardiac production of bradykinin is unlikely to be a trigger for ischaemic preconditioning after brief myocardial ischaemia in humans.

Adult↗
PubMed1995

Magnesium deficiency in critically ill patients.

A study was performed to assess the value of estimation of intracellular magnesium in peripheral blood cells (red and mononuclear blood cells) in critically ill patients as an index of tissue magnesium content. A magnesium loading test was used to diagnose magnesium depletion in 16 critically ill patients. Patients were divided into magnesium depleted and non-depleted groups according to their response to the loading test. Pre-infusion plasma and intracellular (blood cell) magnesium levels were measured. There were no significant difference between the magnesium depleted (mean plasma magnesium 0.81 mmol.l-1, red blood cell magnesium 2.34 mmol.l-1, mononuclear blood cell magnesium 25.16 mmol.kg-1 dry weight) and non-depleted groups (mean plasma magnesium 0.90 mmol.l-1, red blood cell magnesium 2.18 mmol.l-1, mononuclear blood cell magnesium 18.1 mmol.kg-1 dry weight). We conclude that the diagnosis of magnesium depletion cannot be excluded in the face of normal plasma, red blood cell or mononuclear blood cell concentrations of magnesium.

Critical Illness↗
PubMed1992

Endothelium and atherosclerosis.

PURPOSE: To review the effect of damaged endothelium on the development of atherosclerotic disease. BACKGROUND: Atherosclerotic cardiovascular disease is a complex problem involving lipid deposition, blood pressure, rheologic forces, carbohydrate tolerance and thrombogenic factors. The loss of functional, if not structural, integrity of the vascular endothelium is closely related to the initiation of atherosclerosis. The endothelium contributes to local vascular regulation. Normal endothelial cells are thrombo-resistant; they prevent leukocyte adhesion and control vascular tone by converting angiotensin I into angiotensin II, inactivating bradykinin, norepinephrine, serotonin and ADP, and by secreting vasodilator substances, such as prostacyclin and endothelium-derived relaxing factor (EDRF), and contracting factors such as endothelin. Endothelin is a potent vasoconstrictor peptide that increases intracellular calcium, causing a rapid and transient increase in c-fos and c-myc messenger (m)RNA levels and DNA synthesis in rat vascular smooth muscle cells. In isolated vessel segments, altered endothelial vasoreactivity is usually demonstrated following mechanical trauma to the endothelium. METHODS AND RESULTS: We investigated the function of normal and damaged endothelium in pigs, following superficial balloon injury, which produces a significant alteration in endothelium-dependent coronary vasoreactivity. The anesthetized pigs were given an intracoronary (left anterior descending artery) infusion of acetylcholine. The balloon injury caused a local transient spasm while the distal uninjured vessel did not change. When acetylcholine was given before the balloon injury, the diameter of the left anterior descending artery did not change, even after preconstriction in vivo with prostaglandin (PG) F2 alpha, but acetylcholine given after the balloon angioplasty caused dose-dependent vasoconstriction. It is known that vasoconstriction in arteries can reduce blood flow and increase arterial wall-shear forces, which increase platelet deposition in injured arteries and may precipitate rupture of atherosclerotic plaques. CONCLUSION: The intact endothelium is one of the greatest sources of protection from arterial thrombosis, atherosclerosis and vasoconstriction.

Acetylcholine↗
PubMed1985

Cardiac postjunctional supersensitivity to beta-agonists after chronic chemical sympathectomy with 6-hydroxydopamine.

The sensitivity to sympathomimetic amines of isolated atria removed from sham-injected and 6-hydroxydopamine-treated (6-OHDA) guinea-pigs was examined in the presence of an extraneuronal uptake blocker and an alpha-adrenoceptor antagonist. Three weeks of pretreatment with 6-OHDA resulted in leftwards shifts of the dose-response curves for the positive chronotropic and inotropic responses of right and left atria to isoprenaline. The responses to the partial agonist salbutamol were also potentiated after 6-OHDA pretreatment, revealed as an increase in the maximum response relative to isoprenaline. The supersensitivity was post-synaptic in origin and independent of changes in disposition or metabolism, since it was observed with agonists immune to neuronal uptake and O-methylation, and in the presence of extraneuronal uptake inhibition by metanephrine. It was also specific for the beta-adrenoceptor, no supersensitivity to histamine being found. In the right atria, the supersensitivity was partially masked by an opposing depressant effect after 6-OHDA pretreatment which was observed with histamine. Dissociation constants (KA) for the left atrial inotropic responses to orciprenaline were determined by use of the antagonist Ro 03-7894. Atria from 6-OHDA-pretreated animals were supersensitive to orciprenaline, but the KA value did not differ from that after sham injection. It could therefore be concluded that the increase in sensitivity was not due to an increase in affinity for the beta-adrenoceptor.

Adrenergic beta-Agonists↗
PubMedDate not supplied

Neural networks in clinical medicine.

Neural networks are parallel, distributed, adaptive information-processing systems that develop their functionality in response to exposure to information. This paper is a tutorial for researchers intending to use neural nets for medical decision-making applications. It includes detailed discussion of the issues particularly relevant to medical data as well as wider issues relevant to any neural net application. The article is restricted to back-propagation learning in multilayer perceptrons, as this is the neural net model most widely used in medical applications.

Algorithms↗
PubMedDate not supplied

The influence of suction catheter tip design on tracheobronchial trauma and fluid aspiration efficiency.

The suctioning efficiency and trauma-producing characteristics of five commercially available tracheobronchial suction catheters (Pharmaseal Tri-Flo, NCC Gentle-Flo, Argyle Aero-Flo, Argyle Dual Side-Hole, and Pharmaseal Whistle-Tip) were experimentally evaluated in anesthetized healthy dogs. The tendency of catheters to invaginate or "grab" tracheobronchial mucosa was observed with a bronchofiberscope during suctioning. Mucosal grabbing was seldom seen even at high (greater than 300 torr) vacuum levels with the cateter tip in the trachea. All catheters were observed to invaginate mucosa in lobar and segmental bronchi, with the frequency of grabbing being a function of airway anatomy, airway size, catheter orientation, tip design, and vacuum level. Catheters with multiple side-holes appeared to invaginate mucosa less frequently than the single side-hole catheter. Repeated suctioning of anesthetized healthy dogs followed by tracheobronchial excision, gross observation, and histologic examination of mucosal tissue biopsies demonstrated significant differences in the frequency and severity of lesions caused by the tracheobronchial suction procedure. All catheters were observed to damage airway lining, the damage related to multiple side-hole catheters appearing to be associated entirely with the act of cateter insertion and not with the application of vacuum. Only the Whistle-Tip design produced measurable damage beyond that related to catheter insertion. The average tip-suctioning effectiveness for each catheter, determined in vitro by aspirating a thin, uniform layer of simulated mucus, was found to be significantly higher for the Tri-Flo and Whistle-Tip catheters than the others, the Aero-Flo being least effective. Preliminary attempts to demonstrate this difference in suctioning effectiveness by comparing the performance of the catheters which displayed the highest and lowest tip suction effectiveness in a standardized clinical suctioning procedure revealed no significant difference in the percentage of mucus removed by either catheter. Additional studies should clarify this apparent contradiction.

Animals↗