Thermography and thermometry in the assessment of diabetic neuropathic foot: a case for furthering the role of thermal techniques.

There are currently 3 established techniques employed routinely to determine the risk of foot ulceration in the patient with diabetes mellitus. These are the assessment of circulation, neuropathy, and foot pressure. These assessments are widely used clinically as well as in the research domain with an aim to prevent the onset of foot ulceration.

Noninvasive measurement techniques for monitoring of microvascular function in the diabetic foot.

There are, currently, 3 established clinical techniques routinely employed to determine the risk of ulceration in the diabetic foot. These are assessment of the circulation, the nervous control of sensation, and foot sensitivity to loading. Macrovascular measurements are used to assess sufficiency of the arterial supply to the foot.

In-shoe measurement of plantar blood flow in diabetic subjects: results of a preliminary clinical evaluation.

The findings of clinical pilot study (n = 9 subjects) using a new laser Doppler sensor for assessing blood flux in plantar skin tissue are described. Cutaneous blood perfusion was recorded under the first metatarsal head (right foot) in standing and walking. The sensor was located in a measurement shoe custom made for each test subject.

Progress towards automated diabetic ocular screening: a review of image analysis and intelligent systems for diabetic retinopathy.

Patients with diabetes require annual screening for effective timing of sight-saving treatment. However, the lack of screening and the shortage of ophthalmologists limit the ocular health care available. This is stimulating research into automated analysis of the reflectance images of the ocular fundus.

An in-shoe laser Doppler sensor for assessing plantar blood flow in the diabetic foot.

Increased pressure due, to sensory neuropathy, is important in the development of plantar ulceration in type II diabetes. However, additional factors are thought to pre-dispose the skin tissue to ulceration. Autonomic neuropathy and microangiopathy are the basis for the capillary steal theory and the haemodynamic hypothesis, developed to explain the aetiology of this type of ulcer, in terms of microvascular complications.

The application of engineering and technology in the management of diabetes.

Diabetes mellitus is a relatively common disorder in which many of the body's systems are affected, resulting in morbidity and mortality. Early diagnosis and good blood glucose control can delay or prevent the onset of these complications. This review illustrates how engineering and technology can help to achieve these goals.

Transducers for foot pressure measurement: survey of recent developments.

Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation, performance and limitations. Examples of capacitive, piezo-electric, optical, conductive and resistive types of transducer are presented.

Responses and calibration of amperometric glucose sensors implanted in the subcutaneous tissue of man.

Glucose sensors based on immobilized glucose oxidase and hydrogen peroxide detection at a platinum base electrode were constructed and studied before, during and after implantation into the subcutaneous tissue of 11 non-diabetic subjects. A 75-g oral glucose load was given to elevate the blood glucose concentration. Seven of 14 sensors responded to the oral glucose administration with an increase in current and the output of the remainder was unchanged by the glucose load.

In vitro testing of a simply constructed, highly stable glucose sensor suitable for implantation in diabetic patients.

We have constructed and tested in vitro a potentially implantable, needle-type amperometric enzyme electrode which is suitable for continuous monitoring of glucose concentrations in diabetic patients. The major requirements of stability during operation and ease of manufacture have been met with a sensor design which involves a simple dip-coating procedure for applying to a platinum base electrode an inner membrane of glucose oxidase immobilised in polyhydroxyethyl methacrylate (pHEMA), and an outer membrane composed of a pHEMA/polyurethane mixture. Sensors were operated at 700 mV for detection of hydrogen peroxide.

In vivo molecular sensing in diabetes mellitus: an implantable glucose sensor with direct electron transfer.

Miniature, amperometric glucose sensors were constructed for implantation in the subcutaneous tissue of normal and insulin-dependent diabetic subjects. To minimise dependence on fluctuating tissue oxygen tension, we employed the technology of mediated electron transfer, with 1,1'-dimethylferrocene acting as the redox shuttle between immobilized glucose oxidase and a platinum base electrode. In 6 normal subjects, the subcutaneous sensor responses mirrored the simultaneously-measured changes in blood glucose concentration after a 75 g oral glucose load and after intravenous injection of 0.

Potentially-implantable, amperometric glucose sensors with mediated electron transfer: improving the operating stability.

The major problems with existing amperometric enzyme electrodes for glucose sensing are oxygen sensitivity and output drift. The recently described miniature glucose sensors using immobilised ferrocene (dicyclopentadienyl iron) to mediate electron transfer from glucose oxidase to a base electrode are oxygen-independent but are often unstable. In this study, we test the hypothesis that the stability of ferrocene-based sensors can be markedly improved by better retention of the enzyme at the electrode.

Progress towards in vivo glucose sensing with a ferrocene-mediated amperometric enzyme electrode.

A range of miniature, amperometric enzyme electrodes have been constructed using the principle of mediated transfer of electrons. Ferrocene, or one of its derivatives, can be used in conjunction with immobilised glucose oxidase to produce sensors which are linear to at least 20 mmol/l glucose, have fast response times, are relatively oxygen insensitive and are suitable for implantation studies. In preliminary experiments in non-diabetic pigs, electrode responses followed blood responses, although mean tissue levels were about one fifth of those in blood.

Biosensors: clinical requirements and scientific promise.

Biosensors are currently very fashionable, even though they are not new! - an enzyme electrode being described almost 20 years ago by Updike and Hicks in 1967. The aim of this review is to put into perspective why biosensors are needed in clinical medicine and to describe some of the research that is being performed to develop such devices for, in particular, 'in vivo' applications.

Implantable glucose sensors: choosing the appropriate sensing strategy.

The special requirements for implantable glucose sensors which differ from laboratory analysers and in vitro probes include continuous operation without drift, compatibility with in vivo body conditions, electrical and toxicological safety and patient acceptability. We have studied the effect of oxygen tension, operating temperature and pH, and the stability of various potentially implantable amperometric glucose sensors so as to aid the choice of the technologies most suitable for in vivo application.

Subcutaneous implantation of a ferrocene-mediated glucose sensor in pigs.

Miniature, amperometric glucose sensors were constructed using entrapped 1,1'-dimethylferrocene to mediate electron transfer between immobilised glucose oxidase and a carbon base electrode. Electrodes were calibrated in buffered glucose solutions and then implanted in the subcutaneous tissue of anaesthetised, non-diabetic pigs. Subcutaneous tissue glucose concentrations, as measured by the sensor, were about 20% of blood glucose values, measured by a conventional glucose oxidase assay.

Potentially-implantable, ferrocene-mediated glucose sensor.

We describe the construction and in vitro testing of a new potentially-implantable amperometric glucose sensor which is based on mediated electron transfer between immobilized glucose oxidase and a graphite base electrode. Under potentiostatic control, entrapped 1,1'-dimethylferrocene acts as an alternative electron acceptor to oxygen and provides a sensing strategy which is relatively unaffected by possible fluctuations in in vivo oxygen tension. Simple 1 mm wide electrodes with a polyurethane membrane gave linear current responses to at least 20 mmol/l glucose with a mean response time of 68 s.

Evaluation of a new re-usable electrode for continuous monitoring of blood PO2 during open-heart surgery.

In 46 patients undergoing cardiac surgery blood PO2 was continuously monitored with an in-line oxygen electrode during cardiopulmonary bypass and readings were compared with intermittent measurements of samples on a blood gas analyser. In 35 patients in whom arterial PO2 was monitored, there were rapid changes in PO2 and the mean difference between the in-line electrode and the blood gas analyser was 6.63 kPa (p less than 0.

Continuous monitoring of blood PO2 in extracorporeal systems. An in vitro evaluation of a re-usable oxygen electrode.

The technique of intermittent sampling of blood during extracorporeal circulation and in vitro analysis to establish that the blood-gas status of the patient is within acceptable limits has drawbacks which may be overcome by continuous monitoring. An evaluation of an oxygen monitoring system and a comparison with a blood gas analyser have been performed. Blood of known PO2 was circulated at 15 degrees, 25 degrees and 37 degrees C in an extracorporeal system and the monitor readings and results from samples analysed on a blood gas analyser were compared with calculated partial pressures.

Metabolic indices of pulmonary damage. Changes in angiotensin converting enzyme and alpha 1 anti-trypsin activity after cardiopulmonary bypass.

The activity of angiotensin-converting enzyme was measured in patients undergoing cardiopulmonary bypass and in a control group requiring thoracotomy for pulmonary surgery. The activity of the enzyme was higher in patients with cardiac disease, fell during operations involving cardiopulmonary bypass, but did not change during thoracotomy for pulmonary surgery. Possible reasons for these differences are discussed.