Screen-printed transcutaneous oxygen sensor employing polymer electrolytes.

A disposable, transcutaneous oxygen sensor has been designed and implemented using screen-printing technology for all fabrication stages. The sensor incorporates an integral heating element to promote transcutaneous diffusion of blood gases so that a reliable estimation of arterial blood gas concentration can be obtained. The oxygen sensing part of the device consists of a screen-printed Clark cell implemented as electrodes, electrolyte and membrane. A three-electrode configuration is employed with gold working and counter electrodes and a silver/silver chloride reference electrode. Several different polymer electrolyte and membrane materials were evaluated in the construction of the device, and their performances were compared. A fully automated gas testing rig was constructed to enable oxygen levels to be varied under computer control. Cyclic voltammetry and static analysis of the sensors were carried out at different oxygen concentration levels and in various test environments. Linear relationships were established with an averaged sensitivity level of 0.02 microA(mmHg)(-1) and high regression coefficients of 0.99. The prototype covered with a polytetrafluoroethylene membrane gave the experimental result of I (microA) = -0.025PO2 (mmHg) - 0.085. Several factors influenced the performance of the sensors. The investigations have greatly contributed towards an understanding of the suitability of the materials in achieving a viable, low-cost sensor.

Recording compliance of dental splint use in obstructive sleep apnoea patients by force and temperature modelling.

Fibre-optic sensors are used to monitor the force and temperature of dental splints worn by patients suffering from sleep apnoea. Owing to the small size of the sensors, they can be easily embedded within the splint in a way that does not affect the effectiveness of the splint, and, at the same time, are able to indicate whether the splint has been properly worn by the patient. The overall dimensions of the sensor are approximately 0.375 mm thickness, 1 cm length and 3 mm width. The force and temperature sensors are calibrated and found to have sensitivities of better than 0.5 N and 0.1 degrees C, respectively. Trials performed on patients show that the measurement of pressure and temperature is an effective way of monitoring the proper usage of the dental splint by the patients.

Continuous cardiac output monitoring system.

A continuous cardiac output monitoring system has been developed in the laboratory to allow the real-time measurement of the cardiac output. This form of continuous cardiac output measurement allows the doctor to view the beat-to-beat cardiac output and can be employed to measure artery constrictions as well. The sensor comprises a laser Doppler velocimeter and an impedance measurement unit. The laser Doppler velocimeter is capable of measuring bi-directional blood flow within the vessel while the impedance measurement unit determines the cross-sectional area of the vessel. In laboratory tests, it was demonstrated on a heart-lung machine that the product of the two parameters measured is proportional to the actual flow volume of up to 6 lmin(-1) with a mean percentage error of 12.4% and a mean square error of 0.09 (using the lmin(-1) scale) were obtained. This is significantly more accurate than the measurement made using the thermodilution cathether.

Investigation into the effects of haematocrit and temperature on the resistivity of mammalian blood using a four-electrode probe.

Haematocrit and temperature effects on resistivity are investigated using the electrical impedance method. Measurements are made extensively for pig's blood. The experimental set-up basically involves four ring electrodes being placed around a wooden probe that is subsequently immersed into a syringe containing pig's blood. The syringe is then submerged in water maintained at a constant temperature while measurements are taken. The resistivity of blood is found to increase linearly by approximately 2.9% as the haematocrit level increases from 18% to 49% at a fixed temperature of 37 degrees C. Furthermore, the resistivity is found to decrease linearly by approximately 22% with temperature increasing from 33 degrees C to 42 degrees C for all practical levels of haematocrit.