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Biomedical subjects

P Rolfe

Publications and source records attributed to P Rolfe.

At least 19 recordsLinked to original sources
PubMed1999

Blood perfusion of subcutaneous tumours in mice following the application of low-level direct electric current.

Electrotherapy with low-level direct electric current has been proved to be an effective local treatment of solid tumours. In the presented study an attempt was made to evaluate the effect of a single treatment with electrotherapy on blood perfusion of solid subcutaneous fibrosarcoma Sa-1 tumours in A/J mice. The tissue-staining method with Patent blue-violet dye, the rubidium extraction technique, and the noninvasive near-infrared spectroscopy method were used for this purpose. Results of all methods indicate that perfusion and subsequently oxygenation of tumours were reduced due to application of electrotherapy.

Animals↗
PubMed1999

Computer modelling of the adsorption of proteins on solid surfaces under the influence of double layer and van der Waals energy.

The study of protein interactions with surfaces is important in many branches of biomedical engineering. A computer model has been set up in order to aid the understanding and prediction of the likelihood of protein adsorption at a surface and of coagulation between two proteins. In this model, a protein is represented as a hard sphere, neglecting conformation changes which may occur during the adsorption process. The sphere is assumed to be in a medium whose properties are described by the ionic strength, the pH and the dielectric permittivity. It is considered to interact both with an infinite plane, representing the surface, and with another sphere, representing another protein. The model focuses on the total interaction energy between a protein and a surface and between two proteins. The energy is expressed according to the DLVO theory of colloidal stability, which assumes that the adsorption behaviour of proteins at a surface depends, first, on the van der Waals interactions energy and, second, on the electrostatic double layer interaction energy. The conditions under which adhesion is prevented correspond to the presence of local extremes of the energy function, whereas the conditions under which adhesion is likely to take place correspond to absence of local extremes.

Adsorption↗
PubMed1999

Qualitative modelling of the response of cytoskeletal actin filaments in endothelial cells subjected to shear stress.

An approach to modelling cytoskeletal function based on qualitative process theory and qualitative algebra is presented. A computer environment for qualitative modelling and simulation of physical systems, specifically oriented to the construction of biomedical knowledge bases, is used. The system that is being set up for the cytoskeleton is intended to serve as a tool for testing assumptions about cytoskeletal function, for the evaluation of experimental data and for planning experimental work. The aspects of cytoskeletal function that have been modelled so far are focal adhesion and the reorganisation of the vascular endothelial cell cytoskeleton in response to fluid-imposed shear stress. Starting from a natural language description, the subsequent levels of analysis leading to the formal structural description and the resulting implementation for these aspects within the development environment are presented.

Actins↗
PubMed1998

Toward a standardised information system for dentistry.

Information technology is growing rapidly in both its capability and capacity to support the delivery of health care. This paper describes the work of the Dental Interspec project, commissioned by the Department of Health. The aim of the project is to provide a framework for the development of information management and technology in dentistry. It is hoped that the work of this project can be built on to eventually produce integrated information systems which would have the potential to improve primary dental care delivery for both patients and dentists.

Computer Communication Networks↗
PubMed1998

Correlation of near infrared spectroscopy cerebral blood flow estimations and microsphere quantitations in newborn piglets.

We compared cerebral blood flow (CBF) estimated using transmission mode near infrared spectroscopy (NIRS) and a modification of the Fick principle with CBF quantitations by radioactive microspheres (MSs) in newborn piglets. Thirteen piglets were studied during steady state, ischemia, and during two reflow periods. NIRS and MS flows were not significantly different during any measurement period. NIRS flows were compared to total brain blood flows and to regional brain blood flows quantitated with MSs and correlated best with temporal cortical flows. Linear regression analysis of the NIRS flows plotted against MS-quantitated temporal cortical flows showed r = 0.71. Thus, CBFs obtained with NIRS were not significantly different from, showed the same directional changes, and correlated acceptably with flows quantitated by MSs.

Animals↗
PubMed1997

A survey of current in vivo radiotherapy dosimetry practice.

A questionnaire was sent out to 57 radiotherapy physics departments in the United Kingdom to determine the type of dosemeters used for in vivo measurements inside and outside X-ray treatment fields, and whether any correction is made for energy dependence when the dose to critical organs outside the main beam is estimated. 44 responses were received. 11 centres used a semi-conductor for central axis dosimetry compared with only two centres which used thermoluminescent dosimetry (TLD). 37 centres carried out dosimetry measurements outside the main beam; 25 centres used TLD and 12 centres used a semi-conductor detector. Of the 16 centres measuring the dose at both sites. 11 used a semi-conductor for the central axis measurement, but only four of those 11 changed to TLD for critical organ dosimetry despite the latter's lower variation in energy response. None of the centres stated that they made a correction for the variation in detector energy response when making measurements outside the main beam, indicating a need for a more detailed evaluation of the energy response of these detectors and the energy spectra outside the main beam.

Humans↗
PubMed1996

Feasibility of neonatal lung imaging using electrical impedance tomography.

The feasibility of detecting the lungs in preterm babies using electrical impedance tomography (EIT) was investigated. A single frequency instrument using 16 electrodes to apply current and detect peripheral voltages was constructed. The instrument applied AC current of 1.5 mA peak-peak at a carrier frequency of 20 kHz. Images were reconstructed using a sensitivity-regions backprojection method. A 9-day-old preterm baby was tested and data were collected at a speed of 10 frames/s. A dynamic image showing the lungs at full inspiration referenced to expiration is illustrated in this paper. Impedance measurements taken across the chest during the first 2 s did not show a clear pattern thus demonstrating irregular breathing. Region of interest analysis were carried out on the reconstructed images and tracked with time. Fourier transforms were then performed on these signals and a fundamental frequency at 1 Hz, corresponding to normal breathing rate of 60 breaths/min, was detected. Harmonics of the signal caused distortion especially on the left lung where the effects of cardiac events were more dominant.

Electric Impedance↗
PubMed1996

Development of a haemocompatible pO2 sensor with phospholipid-based copolymer membrane.

This paper describes research to improve the haemocompatibility of an intravascular pO2 sensor utilizing a novel copolymer membrane. This material is based on a methacrylate monomer having an electrically neutral head group, 2-methacryloyloxyethyl phosphorylcholine (MPC), copolymerized with n-butyl methacrylate (BMA). The MPC mimics the outer layer lipid structure of the red blood cell membrane, and thus poly (MPC-co-BMA) could be expected to show excellent compatibility with blood. In this paper the methods of preparation of a pO2 sensor covered with different types of membrane, including polyetherurethane (PU), polyvinyl chloride (PVC), poly (MPC-co-BMA) and a compound membrane [PVC+poly (MPC-co-BMA)] are described. The surface chemical structure of the different types of membrane were characterized with Fourier transform infrared spectroscopy. Scanning electron microscopy was used to examine the surface contamination after the sensors had been used in blood. The properties of the sensors were first assessed in phosphate-buffered solution, and the short-term and long-term performances were then demonstrated by use of buffer with mixed proteins, serum and whole human blood. The sensors coated with poly (MPC-co-BMA) and PVC+poly (MPC-co-BMA) membranes showed stable behaviour in static human blood, whereas the sensors with PU and PVC membrane were subject to a continuous signal deterioration during the test period.

Biocompatible Materials↗
PubMed1996

Data recovery from reduced electrode connection in electrical impedance tomography.

In electrical impedance tomography, a single channel failure causes distortion to the overall image. Mathematical modelling and curve-fitting techniques were used to recover corrupted data. A single channel was disconnected in two experiments on a saline-filled dish with one and two objects, respectively. Voltage gradient data were then synthesized from the overall shape of the curve and reconstructed. The technique demonstrated a considerable improvement in the image quality. We conclude that the technique can be adapted in applications where channel failure can occur regularly such as neonatal monitoring.

Biomedical Engineering↗
PubMed1996

Cerebral tissue oxygenation during hypoxia and hyperoxia using artificial placentation in lamb.

Aiming at a better understanding of the pathophysiologic basis of perinatal encephalopathy, we evaluated patterns of tissue oxygenation during hypoxia and hyperoxia. We utilized both laserspectroscopy and invasive tissue-Po2 microneed measurements synchronously in five newborn lambs (141-143 days of gestation). The model of artificial placentation provided defined changes of the blood gases, using a extracorporeal circuit with interposition of membrane lung. During hyperoxia, the Po2 at the blood outlet port of the lung was raised to > 300 mmHg for five minutes. During hypoxia, Po2 was diminished as oxygen at the gas phasis was replaced by nitrogen. After the induction of hyperoxia, a rise of tissue-Po2 was observed. The synchronously recorded data of the laserspectroscopy showed adequately rising HbO2 values in concordance (r = 0.97, p < 0.001). As a constant finding we did not observe Cyt-aa3 changes during induced hyperoxia with tissue-Po2 values of < 40 mmHg. Furthermore, no changes in blood volume occurred in this case. A different pattern of the laserspectroscopic parameters was found when the tissue-Po2 rose above a value of > 40 mmHg and Cyt-aa3 rose after a lag-time occurred. During induced hypoxia an immediate fall of tissue-Po2 corresponding with a fall of HbO2 in the spectroscopic tracing occurred (r = 0.87, p < 0.001). A fall of the Cyt-aa3 level was seen with a lag-time when the tissue-Po2 had reached values of below 10 mmHg. In addition, a rise of blood volume was recorded in all cases of induced hypoxia. In conclusion, the results indicated that cellular redoxe state remains stable over a large range of oxygen partial pressure changes.

Animals↗
PubMed1996

The selected ion flow tube (SIFT)--a novel technique for biological monitoring.

We describe the use of our selected ion flow tube (SIFT) technique for the rapid detection and quantification of trace gases in atmospheric air, with special reference to the analysis of human breath. It is based on the chemical ionization of the breath trace gases to the exclusion of the major breath gases, using 'soft' proton transfer from H3O+ ions. Breath samples can either be introduced into the SIFT from bags or by direct breathing into the apparatus, the advantage of the latter approach being that surface active gases such as ammonia and many organic vapours which adsorb onto bag surfaces can be more accurately quantified. We present examples of the analysis of laboratory air, the breath of a non-smoker and of a smoker taken from bag samples, and illustrate the rapid time response of the technique by showing the time profile of acetone on breath during direct breathing into the apparatus. The current partial pressure sensitivity of our SIFT method is within the range 30 ppb to in excess of 100 ppm, but with further development the device could be made more sensitive, 1 ppb being well within reach. A transportable SIFT device is under development which will have applications in environmental, medical and biological research, health and safety monitoring, and in clinical diagnosis.

Breath Tests↗
PubMed1995

Investigation of neonatal brain cytochrome redox by NIRS.

Near Infrared Spectroscopy (NIRS) has been used to detect changes in cerebral blood and tissue oxygenation. Redox state of enzyme cytochrome aa3 (Cyt aa3 is thought to give an indication of tissue oxygenation. This information would be of value in exploring the aetiology of cerebral ischaemic lesions in preterm infants. However we have found that the change in cerebral cytochrome redox in infants following desaturation was inconsistent and insignificant.

Brain↗
PubMed1995

Multivariate autoregressive modelling combined with transcephalic electrical impedance: method to relate neonatal systemic circulation and respiration to cerebral circulation.

We studied the pulsatile component of cerebral circulation with transcephalic electrical impedance (delta Z) in six preterm newborns, three of whom had severe cerebral bleeding, peri-intraventricular haemorrhage (PIVH). The transcephalic electrical impedance delta Z signal, ECG, arterial blood pressure, (aBP) and respirogram were recorded on analogue magnetic tape for 30 min. Artefact-free stationary segments (lasting for 2 min) of the four signals were digitised. A digital multivariate autoregressive (MAR) model was used to study frequency-specific variability in the signals and to quantify interrelations between the variabilities of delta Z, HR, aBP and respiratory signals. MAR modelling describes a system where all the signals simultaneously explain each other. The inherent variability of delta Z was lower and the influences of respiration and aBP on delta Z significantly greater in infants with severe PIVH than in controls. These changes were observed at high frequencies corresponding to respiration and heart rate. This may be interpreted as a marker of pressure passivism in the cerebral circulation following PIVH. We conclude that in preterm babies the application of MAR modelling, together with transcephalic impedance, may be a new, helpful and quantitative method for the study of simultaneous interrelations between variables of cerebral and systemic circulations and respiration.

Cerebral Hemorrhage↗
PubMed1995

Haemocompatibility of invasive sensors.

In recent years the importance and utilisation of invasive chemical sensors have increased, especially in respect to their function and behaviour in a biological environment. This review aims to highlight the development of various sensors and reflect on the problems which can occur when the sensors come into contact with blood. Thus their haemocompatibility is a key area of importance. A clear understanding of their interaction with plasma proteins at the point of interface is fundamental as this determines their ultimate capability to function safely and effectively. There is also an overview of various techniques that have been developed, together with a broad summary of inherent problems which may arise when aiming to improve the haemocompatibility of invasive sensors for in vivo applications.

Biocompatible Materials↗
PubMed1995

Fibre-optical sensor based on fluorescent indicator for monitoring physiological pH values.

A fibre-optical sensor has been developed based on the fluorescent indicator 8-hydroxyl-1,3,6-pyrene trisulphonic acid trisodium salt (HOPSA) for monitoring physiological pH values. Dowex-1 strongly basic anion exchange resin is used as the medium to immobilise the indicator on the end of an optical fibre. Polyurethane is coated on the sensor as the permeable membrane for H+. The properties of HOPSA in solution, as well as when immobilised on the sensor, are studied and found to have the potential for monitoring physiological pH values.

Biosensing Techniques↗
PubMed1995

In vivo assessment of catheter-tip PO2 sensor: sampling lumen fabrication.

Fabrication of the sampling lumen of an intra-arterial PO2 sensor is performed in standard catheters mechanically or by laser. Clinical evaluation is performed with respect to catheter insertion, complications, accuracy of oxygen sensor data and fibrin deposition on the catheter surface. The success rate for catheter insertion is 57% for 138 standard and 50% for 74 laser-cut catheters studied. The proportion of catheter failures (blocked or non-reading) is 14% in laser-cut compared with 30% in standard. These differences are not statistically significant at the 5% level. There is no clinically significant difference in sensor accuracy, with 37.5% of results within +/- 0.05 kPa and 80% within +/- 2.0 kPa of simultaneous blood gas values. Drift is within +/- 0.3 kPa h-1 for 78% of monitoring time. Significant errors of recalibration occur in 6% of calibrations. Scanning electron micrographs demonstrate a much smaller sampling lumen in the laser-cut group, but no reduction in fibrin deposition at the site of the sampling hole. The low success rate for catheter insertion is a problem because of cost implications. The accuracy of the system is usually sufficient for clinical purposes, provided the calibration is checked every 4 h.

Catheterization, Peripheral↗