Design of a system for contact-free measurement of the conductivity of biological tissue.

The electrical impedance of tissue can give important informations about the viability of the tissue. A non-invasive and contact-free measuring system using an inductive sensor is presented. Using a single pick-up coil the system is not sensitive enough for measuring the small changes in conductivity of biological tissue. Employing a gradiometer instead of a single pick-up coil can improve the resolution of the system. The developed data acquisition system is realized using four parts: A lock-in-amplifier, providing a sinusoidal signal and measuring the signal of the sensor, a power amplifier, driving the excitation coil of the sensor, the inductive sensor and a preamplifier for buffering a reference signal and amplifying the output signal of the sensor. In this paper the focus is on the hardware that was set up. Results of measurements on inhomogeneous phantoms are shown.

Oxidative stress in hemodialyzed patients during exhausting exercise.

BACKGROUND: This study was designed to study the effect of an exhausting exercise test on plasma lipid peroxidation marker (malondialdehyde, MDA) and on vitamin E levels in hemodialyzed patients (HD) compared to healthy control subjects (HC). METHODS: Eight sedentary chronically HD, (39.0+/-10.8 years) and eight sedentary HC (38.4+/-12.4 years) were studied. Before exercise, the activity of scavenger enzymes [plasma and erythrocyte glutathione peroxidase (GPX), and erythrocyte superoxide dismutase (SOD)] was determined. All subjects performed a symptom-limited exercise test; respiratory gas exchanges were collected on-line and blood was sampled five min before exercise, at exhaustion and after 30 min of recovery. RESULTS: At rest, the activity of plasma and erythrocyte GPX and erythrocyte SOD was significantly lower in HD than in HC. Exercise provoked an increase of plasma MDA concentration after recovery in HD patients, whereas our HC group show a decrease in MDA plasma level immediately after exercise, returning to the rest values during recovery. Exercise induced no change of vitamin E concentration in HD whereas in HC it increased during recovery. CONCLUSIONS: Our results indicate that: 1) at rest: although hemodialyzed patients showed lower scavenger enzymes activity than HC subjects, there was no difference in MDA plasma level between groups; 2) there is some evidence that physical exercise contribute to oxidative stress during recovery in HD patients, and 3) exercise induced an increase in plasma vitamin E concentration in healthy subjects.

Relief of the occluded ear sensation to improve earmold comfort.

Earmold comfort is an important factor in the overall satisfaction a hearing-impaired person has with a hearing aid system. Recent research into the subjective effects of earmold venting indicates that, for the naive hearing-aid user, the solid mold produces a "closed" and "blocked" sensation that is relieved to a degree, depending on the vent diameter. To improve earmold comfort, all earmolds should be vented. However, there are certain types of hearing loss where conventional venting techniques would be undesirable, in particular, cases of severe to profound hearing loss where venting would not only adversely affect the desired frequency response characteristics of the hearing aid but would also lead to serious acoustic feedback problems. For this reason a simple system has been developed with sintered filters in the vent line, thus allowing all earmolds to be vented to relieve the occluded ear sensation although retaining the acoustic characteristics of the closed earmold.