Biomedical subjects

B C Towe

Publications and source records attributed to B C Towe.

15 recordsLinked to original sources

PubMed1997

Intravascular carbon dioxide monitoring using micro-flow colorimetry.

An intravascular carbon dioxide sensor is investigated which employs continuous perfusion of micro-quantities of reagent through silicone membrane tubing in contact with blood. Blood is sampled from a vessel by periodic withdrawal-reinfusion through a catheter and passes by the sensor membrane tubing integrated into the catheter system. Blood CO2 equilibrates across the silicone membrane causing a color change in the reagent micro-flow stream that is detected by an optical cell external to the vessel. In vivo trials on pigs demonstrate a stable sensor response, a fast response time, and high signal-to-noise ratios. The sensor also exhibits an immunity to temperature changes, reduced intravascular blood flow, photobleaching, and leaching. It has a 2 min response time, a +/-2 mmHg resolution, and minimal drift over a 12 h duration. Using a pig model, measured values compared with true values indicate a 0.998 correlation coefficient, a 1.3 mmHg precision, and a 1.7 mmHg bias.

Animals↗

PubMed1997

A microflow amperometric glucose biosensor.

We investigate a small glucose sensor that uses a flow-through enzyme bed and reaction endpoint approach that seems particularly suited to microdialysis-type subcutaneous or intravascular glucose sensors. The particular configuration has the advantage of relative insensitivity to blood oxygen changes and also to factors which affect enzyme activity compared to conventional polarographic type glucose sensors. We evaluate the placement of a microdialysis fiber into a near-surface blood vessel in the dog model as a means of blood glucose sampling and to determine the effects of protein deposition. We observe a progressive decline in intravascular membrane fiber transport that must be considered in sensor design.

Animals↗

PubMed1997

Investigation of a Lorentz force biomagnetometer.

This work evaluates an approach to the noninvasive measurement of small ionic current flows by a technique of Lorentz force magnetometry. An instrument was constructed that is basically a very sensitive force-balance that can measure Lorentz forces experienced by ionic currents flowing in small objects when exposed to strong oscillating magnetic fields. For objects that can fit on a microscope slide, the system is sensitive to ion current dipole moments as low as 180 pA-m. Images were made of ionic currents flowing in thin profiles by a process of scanning a localized magnetic field over the object, measuring generated Lorentz forces, and using a computer to reconstruct images. It can be shown that this method of Lorentz magnetometry has an immunity to ambient magnetic noise and has system characteristics that might suggest its possible use in biomagnetometry of small thin specimens.

Electromagnetic Fields↗

PubMed1996

In vivo and in vitro deactivation rates of PTFE-coupled glucose oxidase.

The deactivation of immobilized enzymes is a major lifetime limiting factor in several types of potentially implantable biosensors. The deactivation rate of covalently immobilized glucose oxidase was examined in vitro in mock physiologic environments and in the peritoneal cavity of mice. A first order deactivation model describes the observed exponential decay of the enzyme. Deactivation rate constants ranging from 0.198 to 1.3 per day were measured depending on experimental conditions. Enzymes immobilized on PTFE (Teflon) substrates in the peritoneal cavity of mice exhibited greater catalytic lifetimes than control samples kept in glucose solution in vitro.

Animals↗

PubMed1996

A vibrating probe thermal biochemical sensor.

Rapid vibration of small enzyme-thermopile biochemical sensors in solution has been observed to substantially improve their thermal noise rejection. Millimeter-order 20 Hz vibratory excursions of a thermal biosensor by a piezoelectric bender element were found to be effective in eliminating the need for temperature controlled dewars, flow streams, or special thermal environments ordinarily required to operate these sensors. Vibrated thermopiles have been made into biochemical sensors by attaching thin membrane hollow fibers to the thermopile sensing region and perfusing the lumen of the fiber with small quantities of an enzyme solution. This process can give the biosensor an extended lifetime by allowing easy replacement of the enzyme. Vibrated enzyme-thermopile biochemical sensors can be realized in a convenient and compact probe-type configuration that is directly immersible into a test solution.

Biosensing Techniques↗

PubMed1990

Thermoelectric enzyme sensor for measuring blood glucose.

A new calorimetric sensor has been developed which employs a thin-film thermopile in association with an immobilized enzyme. The thermopile detects the minute temperature rise that occurs when a specific chemical substrate is catalyzed by the enzyme. A prototype sensor is described which generates an equivalent proportional voltage response to glucose concentrations present in either buffer solution or blood. These sensors have remained useful for up to 18 days when operated intermittently for measuring glucose in buffer solutions, or for up to 4 days when operated continuously. When implanted inside cardiovascular shunts on anesthetized dogs, the sensors responded appropriately to changes in the blood glucose concentration.

Animals↗

PubMed1988