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Biomedical subjects

J C Fothergill

Publications and source records attributed to J C Fothergill.

8 recordsLinked to original sources
PubMed2000

Electrochemical lesions in the rat liver support its potential for treatment of liver tumors.

BACKGROUND: An effective therapy is needed for patients with surgically unresectable liver tumors who have very limited life expectancy. One possible treatment is electrochemical tumor necrosis. This study investigated the natural history of electrochemical lesions in the normal rat liver. MATERIALS AND METHODS: A direct current generator, connected to platinum electrodes, was used to create controlled areas of liver necrosis. Animals were sacrificed 2 days, 2 weeks, 2 months, and 6 months after treatment and the macroscopic and histological appearance of the necrotic lesions was followed. RESULTS: No animal died as a result of electrolysis; postoperatively, all gained weight normally. Liver enzymes were significantly (P < 0.001) elevated after treatment, but returned to normal after a week. Two days after electrolysis, histology confirmed an ellipsoidal area of coagulative necrosis at the site of the electrode tip and commonly a segment of peripheral necrosis. After 2 weeks there was histological evidence of healing. By 6 months, very little necrotic tissue remained within a small fibrous scar. CONCLUSIONS: Electrolysis is a safe method for creating defined areas of liver necrosis that heal well with no associated mortality. This study supports the potential of electrolysis for treating patients with unresectable liver tumors.

Animals↗
PubMed1996

The design of an optical fiber pressure transducer for use in the upper airways.

The development of an optical fiber transducer for use in biomedical applications has been presented. The design was targeted for use in the upper airways of patients with sleep disorders stemming from partial or total occlusion of the airway. The transducer's preliminary specification was suited for that of upper airway manometry: a resolution of 10 Pa over the range +/- 5 kPa, a single transducer being less than 0.94 mm in diameter. Amplitude modulated optical fiber sensors are susceptible to loss due to bending of the fiber core and cladding. The design of the transducer uses a series of three optical fibers, one emitting and two receiving, the combination of the two receiving optical fibers is used to reduce effects of light loss: a bend radius of 50 mm is typical for the insertion into the naso-pharynx. The transducer transduction element is a silicone gel coated with reflective titanium dioxide, the meniscus deforms under pressure and modulates the intensity of light reflected back into the receiving optical fibers. The main disadvantage of optical fiber pressure transducers is their susceptibility to temperature drift. Temperature in the airway rarely changes more than 17 degrees C. The frequency of breathing and the high thermal mass of the catheter means that temperature drift in this application is not significant, and will cause an insignificant error of 12 Pa. The transducer is inexpensive to produce, and may be deemed disposable: approximately $20 in material costs (using current manufacturing techniques this can be halved). The system has the added advantage of being electrically, magnetically, and chemically passive. The potential for miniaturization is limited only by the mechanical strength of the optical fibers as mechanical problems associated with fragile elastic membranes do not apply.

Airway Obstruction↗
PubMed1993

Automated measurement of QT interval dispersion from hard-copy ECGs.

Increased "dispersion" of the QT interval of the electrocardiogram has been proposed as a marker for increased risk of cardiac arrhythmias, but definitive identification of its independent predictive value requires accurate and reproducible measurement in large numbers of cases. A personal computer-based technique for (1) converting hard-copy electrocardiograms to digital records and (2) automatically measuring QT interval dispersion from the digitized records has been developed and validated. Hand measurements of the RR interval from the original tracing and cursor or automated measurements from digitized waveforms correlated to within 1%. QT intervals measured by cursor on digitized waveforms were a mean of 14 ms (95% confidence interval, 10-19 ms) longer than manual measurements on original tracings. Automatic QT interval measurements were a mean of 5 ms longer than cursor measurements (95% confidence interval, 3-7 ms). Automated measurements were observer independent and repeatable (coefficient of variation for repeat measurements, 0.137% RR and 0.370% QT). Estimates of QT dispersion (expressed as coefficient of interlead QT variation) were made for 14 patients with documented recurrent ventricular and 15 control subjects. The median coefficient of interlead QT variation was 8.8% (range, 4.4-12.4%) for arrhythmia patients and 3.6% (range, 2.7-6.3%) for the control group (P < .001). The automatic measurements were more conservative and less likely to give spuriously large values for QT dispersion than manual measurements. Automated QT dispersion measurements should facilitate future studies on predicting the risk of ventricular arrhythmias.

Analog-Digital Conversion↗
PubMed1990

Portable directional ultrasonic Doppler blood velocimeter for ambulatory use.

The design of a portable directional Doppler velocimeter and of purpose-built probes intended for monitoring blood flow in femorodistal bypass grafts in ambulatory patients are described. The design is based on a continuous-wave Doppler technique with quadrature demodulation. The Doppler unit was interfaced to a 'personal-stereo' recorder to store the Doppler signals. The advantages and the limitations of recording flow in ambulatory patients are discussed. Examples of blood flow data collected from femorodistal bypass grafts are given.

Arteries↗
PubMed1990

Selective noninvasive electrode to study myoelectric signals.

The paper describes the design and construction of a selective surface electrode for use in a clinical environment. The main criterion of the design was to enable the recognition of individual motor unit action potential trains (MUAPTs) at moderate force levels. The main features of the electrode are, first, a small concentric bipolar arrangement to avoid electrode/muscle fibre alignment problems and to allow measurements within a small, well defined probed volume; secondly, the non-requirement for conducting paste or gel; and thirdly, the casing acting as an earth plate. All of these simplify its use. The results of tests undertaken with the electrode showed that it was able to pick up individual MUAPTs at up to 20 per cent of maximum voluntary contraction from the first dorsal interosseous muscle. Tests were carried out on the small hand muscles to further demonstrate the usefulness of the electrode. A computer program was written to calculate the shift in frequency of the power spectrum of the recorded myoelectric signal with muscle fatigue and hence indirectly to demonstrate the ability of the electrode to detect the reduction in muscle fibre conduction velocity.

Action Potentials↗
PubMed1988

Optical and electrochemical detection of DNA.

There is a growing demand for the production of a DNA biosensor with applications in medicine, the food industry, agriculture, veterinary science and environmental science. In this paper we describe methods for the optical and electrochemical detection of DNA using the enzyme horseradish peroxidase (EC 1.11.1.7) and glucose oxidase (EC 1.1.3.4). We have used bis-methylacridinium nitrate and luminol for the optical detection of DNA using a purpose built, inexpensive luminometer. Using this system detection limits of 10(-11) g of plasmid DNA have been observed. Electrochemical detection of DNA was carried out by the use of a fluoride ion selective electrode and stripping voltammetry. DNA was detected down to 10(-9)-10(-10) g of DNA by the enzymatic release of halogen ions from organohalogen compounds.

Animals↗
PubMed1977

Catabolism of L-lysine by Pseudomonas aeruginosa.

Pseudomonas aeruginosa PACI grows poorly on L-lysine as sole source of carbon but mutant derivatives which grow rapidly were readily isolated. Studies with one such mutant, P. aeruginosa PAC586, supported the existence of a route for L-lysine catabolism which differes from those reported previously in other species of Pseudomonas. The postulated route, the cadaverine or decarboxylase pathway, is initiated by the decarboxylation of L-lysine and involves the following steps: L-lysine leads to cadverine leads to I-piperideine leads 5-aminovalerate leads to glutarate semialdehyde leads glutarate. Evidence for this pathway is based on the characterization of the pathway reactions and the induction of the corresponding enzymes by growth on L-lysine. The first three enzymes were also induced by growth on cadaverine and to a lesser extent by 5-aminovalerate. No evidence was obtained for the presence of pathways involving L-lysine 2-monooxygenase or L-pipecolate dehydrogenase, but another potential route for L-lysine catabolism initiated by L-lysine 6-aminotransferase was detected. Studies with mutants unable to grow on L-lysine supported the existence of more than one catabolic pathway for L-lysine in this organism and indicated that all routes converge on a pathway for glutarate catabolism which generates acetyl-CoA. Pipecolate catabolism also appeared to converge on the glutarate pathway in P. AERUGINOSA. The results suggested that the growth rate of the parental strain is limited by the rate of transport and/or decarboxylation of L-lysine. The cadaverine pathway was present, but not so highly induced, in the parental strain P. aeruginosa PACI. Pseudomonas fluorescens contained enzymes of both the cadaverine (decarboxylase) and oxygenase pathways, strains of P. putida (biotypes A and B) contained enzymes of the oxygenase pathway but not the decarboxylase pathway and P. multivorans appeared deficient in both. All these species possessed L-lysine aminotransferase activity.

Cadaverine↗