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Biomedical subjects

A Sances

Publications and source records attributed to A Sances.

119 records · Page 7Linked to original sources
PubMedDate not supplied

Physiological and histological effects of cerebellar stimulation.

Cerebellar implants have been placed in 62 patients with postoperative follow-up of 4 months to 3 years. Initially currents were applied through electrodes of alternate polarity on the superior surface of the cerebellar hemispheres and subsequently through negative electrodes on the superior surface to positive electrodes on the posterior surface. The amount of current required for clinical improvement was approximately the same as that required to significantly reduce the amplitude of the somatosensory evoked potential. The clinical and electrophysiological effects were proportional to the intensity of current and to the number of electrodes through which the currents were applied. Currents applied through the cerebellum were more effective than those confined near the cerebellar surface. Histological examination of the cerebellum from the chimpanzees and from 1 patient who died of causes unrelated to stimulation failed to demonstrate any evidence of neuronal damage related to application of current.

Animals↗
PubMedDate not supplied

Evaluation of electrode configurations in cerebellar implants.

Capacitively coupled currents of 100 Hz, 0.25 msec duration, were applied to multielectrode arrays implanted upon the superior and posterior surfaces of the chimpanzee cerebellum. The current required for 90% reduction in the amplitude of the evoked potential was inversely proportional to the number of electrodes upon the cerebellar surface. A study of various waveforms showed that z Hz, 0.25 msec pulse duration is near optimal for reduction of amplitude of the somatosensory evoked potential. The current densities per electrode were 5--11 mA/cm2 with a charge per pulse of 0.04--0.08 muC in humans with 15--20 electrodes on each superior surface and 10 electrodes on each posterior cerebellar surface.

Animals↗
PubMedDate not supplied

Innovations in neurologic implant systems.

Physiologic findings and clinical observations with several new implant systems are discussed. One system studied is designed with electrodes implanted over the anterior region of the spinal cord. Another system is designed with an anterior-posterior spinal cord electrode passing current across the spinal cord. Also given are observation and description of cortical and cerebellar implant systems. Current-density plots of the electrode arrays are included.

Arm↗
PubMedDate not supplied

A probe for measuring current density during magnetic stimulation.

Time-varying magnetic fields induce currents in conductive media, and when the induced current is large enough in excitable tissue, stimulation occurs. This phenomenon has been applied to the human brain and peripheral nerves for diagnostic evaluation of the neural system. One important aspect that is presently unknown is the current level necessary in tissue for stimulation induced by magnetic fields. This study presents a method of measuring the induced current density from pulsed magnetic fields in vitro and in vivo. The current-density probe was inserted into three concentrations of saline and into the brains of ten anesthetized cats. Two stimulation systems with coils 9 cm and 5 cm in diameter were used. The two systems provided sinusoidal and pulsatile coil currents. Measurements made in saline were compared with those calculated theoretically for a semi-infinite medium. The measured values were within 5% of the calculated values. Measurements made in the cat brain showed a 67% decrease compared with the theoretic model. This variance is attributed to the finite bounds of the skull. The results indicate that direct measurement of current density is possible. Subsequent measurements will aid in the design of improved magnetic stimulation systems.

Animals↗
PubMedDate not supplied

In vivo evaluation of nuclear magnetic resonance flowmetry: blood flow through the normal forearm.

A cylindrical crossed-coil nuclear magnetic resonance flowmeter has been developed to measure arterial blood flow through the human forearm. This paper describes the in vivo studies to evaluate the performance of the instrument. Flow rates were comparable to values reported in the literature. The NMR flowmeter is a noninvasive, contactless-type flowmeter and has the advantage of accurate measurement unimpaired by clothing, bandages, or casts. One measurement can be taken in less than 2 min.

Adolescent↗