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PubMed1991

Sensitivity limits in biomagnetic measurements.

It is important to understand the character and the contribution of thermal magnetic noise in designing the measurement site and the instrumentation for biomagnetic measurements. The ultimate limit of the sensitivity is the thermal noise due to the object under study. In the case of the human body, it has been estimated to be about 0.1/square root of Hz. Magnetically shielded rooms are necessary for ultrasensitive biomagnetic measurements of human subject, but they also generate external noise which in some cases may become detectable. This noise problem can be avoided if the innermost walls are constructed of magnetically soft ferromagnetic material. Close to the conducting walls the thermal noise is higher than at the centre. Thus, the shielded room should be relatively large in size. The gantry and other things inside the room may contain metal parts, which can cause excess noise. The intensity depends on the conductivity, geometry, location and movement of these parts. In comparison to bioelectric studies, this inductive noise coupling demands extra attention. In most biomagnetic measurements performed inside a magnetically shielded room, the limiting factor of the sensitivity is the thermal noise caused by electrically conducting thermal shielding used inside the cryogenic measurement dewar. Fortunately, it is possible to reduce the noise contribution arising from the superinsulation in the dewar by careful design. The properties and dynamics of the SQUIDs are well understood nowadays. Studies of the nonlinear character in the coupling between the SQUID and external detection coil have made it possible to reduce the noise contribution of the sensor itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioelectric Energy Sources↗
PubMed1991

Localization properties of multi-sensor biomagnetic systems.

The recent development of large multi-channel biomagnetic systems, with 20-30 adjacent magnetic sensors, is marking a significant progress in the detection and interpretation of biomagnetic signals, and definitely traces a new avenue towards a proper assessment of the technique in the clinical field. Several technological problems are being solved, mainly concerning the reliability of the SQUIDs and of the superconducting assembly, as well as the criogenic dewar. Also the choice of the geometry for the gradiometers to be coupled to the SQUIDs has a fundamental importance, not only from a technological point of view, but also in that it affects the localization properties of the system. The major attractions and drawbacks of both vertical and planar configurations will be briefly reviewed and few practical suggestions to overcome some of the difficulties will be proposed.

Action Potentials↗
PubMed1985

Evaluation of a myoelectric hand prosthesis for children with a below-elbow absence.

A clinical evaluation of a myoelectric hand prosthesis was carried out within a multicentre trial in three centres in the United Kingdom. The aim was to assess its effectiveness as an acceptable device for young children and to evaluate its technical efficiency. The trial ran for 2 3/4 years and included 87 children. The methodology used and the results obtained are presented with indications towards future developments.

Artificial Limbs↗
PubMed1976

Immunology of the acetylcholine receptor.

Myasthenia gravis is a spontaneously occurring autoimmune disease in which antibodies and lymphocytes are specifically reactive with nicotinic ACh receptors of skeletal muscle. Antibodies reactive with junctional receptors of human muscle are found in 90% of patients with myasthenia gravis and not at all in other diseases. Their capacity to cross the placenta suggests their involvement in the pathogenesis of neonatal myasthenia. The role of the thymus in myasthenia gravis remains a mystery, but it has a recently been established that the thymus contains nicotinic ACh receptors and that anti-receptor antibodies are present in myasthenic thymuses. Antibodies of myasthenic patients detect only partial cross reactivity between ACh receptors of different species. However, greater antibody binding is observed with receptors isolated from denervated rat muscle than with receptors from normal rat muscle. This suggests that extrajunctional and junctional ACh receptors might express different antigenic determinants. Although human antibodies bind minimally to ACh receptors of the electric organs of eels and marine rays, lymphocyte reactivity to electric eel receptors is found in high incidence in myasthenic patients. This suggests that electric organ and mammalian muscle ACh receptors may share more lymphocyte-defined than serologically-defined antigenic determinants. Both cellular and humoral immune responses to ACh receptors can be induced experimentally. Sufficient antigenic homology exists between receptors of different species that electric organ receptors are capable of inducing in mammals experimental autoimmune myasthenia gravis. Syngeneic muscle receptor also is immunogenic in rats. Induction of both myasthenia and antibodies to ACh receptor requires participation of thymus-derived lymphocytes. The majority of ACh receptors in myasthenic rat muscle exist complexed with antibody, but antibody is not bound directly to the receptor's ACh-binding site. Anti-receptor antibodies in vitro are capable of impairing the electrophysiological function of ACh receptors with minimal blocking of the ACh-binding site and in the absence of complement. Thus, myasthenia gravis and its experimental model provide unique biological tools for studying the structure, function and pathology of cell membrane receptors.

Acetylcholine↗
PubMed1975

Design of experimentation with a platinum-magnesium bioelectric battery.

The utilization of metal electrodes in the fabrication of a bioelectric battery has been the subject of intensive study for several years. Up to this date, subcutaneous cathodes of black platinum or of silver-silver chloride have been used in conjunction with anodes of aluminum or zinc. The subcutaneous black platinum is not reliable as a function of time due to the growth of overlying heterogeneous tissues. The utilization of a smooth platinum cathode in the right endoauricular position allows good reliability with time, but does not allow using a large surface area. Furthermore we have a reduction of the H-+ ions and not of the oxygen. A pure Domal magnesium anode was utilized with this cathode, which seemed to be a good compromise between to battery's voltage, its lifetime, and its lack of toxicity to body tissues.

Animals↗
PubMed1976

Animal experiments with biogalvanic and biofuel cells.

Animal experiments with biogalvanic cells have demonstrated that an average power of 80 muW can be derived continously for at least 2 years. There is a further scope to stabilize the power at 100 muW for considerable longer periods so that the chances of cardiac pacing with biogalvanic power have become bright. However, large scale efforts are necessary in in establishing the statistical reliability and the secured performance which are expensive and time consuming. Animal experiments with biofuel cells are still in preliminary stages. We derived a continous power of 40 muW (4MUW/cm2) at 575 mV over 150 days so far. This is the longest recorded period with such a high power density. The main problem in deriving higher power over longer period is to properly encapsulate the cell with materials which are hydrophilic and essentially biocompatible.

Animals↗
PubMed1978

Electrochemical behavior of amino acids and their influence on the anodic oxidation of glucose in neutral media.

Body fluids contain a large number of amino acids along with glucose. Therefore, the electrochemical behavior of amino acids should be considered in studying the anodic oxidation reaction of glucose for biological applications. Potential-sweep and steady-state measurements with different platinum electrodes under neutral conditions have shown that the oxidation of amino acids is basically possible. However, their presence, especially as a mixture, has a remarkable influence on the glucose oxidation and the anodic reaction is strongly inhibited. With respect to the degree of inhibition, they can be classified into two groups. The inhibiting effect is particularly drastic in the case of basic and unsaturated amino acids as well as the ones containing sulphur because of their strong absorption at the electrode surface. The glucose currents are inhibited by about 90% under steady-state. In addition to the direct electrochemical inhibition, the following bacterial decomposition of amino acids is probably also responsible for the drastic effect. However, about 10% of the glucose currents still remain measurable indicating that glucose is detectable at physiological concentrations even under extremly unfavorable conditions. This result is of basic importance in operating a biofuel cell or in measuring glucose concentrations.

Amino Acids↗
PubMed1979

Fitting below-elbow prostheses which convey a sense of touch.

A myoelectrically controlled electric hand has been modified so that the gripping force between thumb and index finger may be measured. The measurement is used to control a sensory feedback device applied to the surface of the skin within the socket of the prosthesis informing the wearer of the strength of grip exerted. Two people have been fitted with this prosthesis and they report that the sensory feedback gives them reassurance when using the arm. To date there has not been any noticeable adverse tissue reponse from the applied sensory stimulus.

Adult↗
PubMed1976

[Molecular mechanisms of the biological effects of UV radiation].

The biological processes taking place in the biosphere are for the largest part bound to the existence of ultraviolet-rays in form of sun rays. Here the furthering effect of the UV-rays on origination, maintenance and further development of life processes is contrasted by the harmful influences of the UV-rays. With the help of the hitherto known facts the primary and consecutive processes which underlie the biological effects of the UV-rays are discussed on molecular level. Furthermore, the possibilities of repairing these lesions caused by UV-rays as well as the biological consequences when repair damages are present are discussed. Finally on the basis of experimental examinations the author deals with the problems of the ultra-violet radiation of the blood.

Bioelectric Energy Sources↗
PubMed1976

Electronic system for the obtention of phase plane curves for action potentials.

This system is designed for the amplification of the bioelectrical signal, obtention of its derivative in respect to time, automatic brightness control for both beams of the oscilloscope, and stability. The system includes a central measuring section which is a modified Tektronix oscilloscope type 565. Automatic control of brightness as a function of sweeping speed allows photographic recordings.

Action Potentials↗
PubMed1976

Automatic microelectrode compensator (AMC).

A solid-state system designed for compensation of asymmetry potentials between microelectrodes, for bioelectric measurements, is described. Advantages over the manual compensator are the following: synchronic compensation of electrodes, application to automatized systems against aging effects in electordes, high speed, and elimination of general muisances of manual circuits. Besides, the system allows to measure digitally the polarization difference and resting membrane potential with precision of +/- 1 mV.

Bioelectric Energy Sources↗
PubMed1975

[The intracardial ECG during permanent pacemaker-implantation (author's transl)].

As our researches and prevailing procedures have proved a permanent pervenous pacer implantation necessitates an additional intra-cardial ECG in parallel with the practised approach under fluoroscopy and by measuring the threshold current. The patho-physiological prerequisites are explained in detail. By means of the characteristic shape of the ST-elevation and the determination of the amplitude in mV, deciding factors for an advantageous position of the electrode may be gained. In order to ensure safe function of the demand mechanism monitoring by an intra-cardial ECG to establish a sufficient signal amplitude in mV is indispensable. This is particularly applicable in case of leads with a small surface area resulting in a low threshold current value and a low amplitude of QRS-signals.

Adams-Stokes Syndrome↗