Roger P. Gaumond

The effects of metals on a transcutaneous energy transmission system

The effects of metal objects on the mutual inductance, self-inductance, and effective series resistance (ESR) of the coaxial coils of a transcutaneous energy transmission system (TETS) were investigated theoretically and experimentally. The theory considers a thin conducting sheet of infinite size aligned parallel to a current-carrying coil. Results of the theory indicate that coil parameters vary with the distance from the sheet to the coil. Changes in mutual and self inductance are independent of the conductivity and thickness of the sheet, with a larger percentage change for mutual inductance than for self inductance. Changes in ESR are proportional to the surface resistivity of the sheet. Experimental measurements using several aluminium sheets and a titanium alloy can in the presence of the TETs coils used for the Penn State artificial heart showed excellent agreement with the theory for inductance parameters and agreed within a factor of 2 for ESR measurements when skin effect was considered.<<ETX>>

Permanent circulatory support systems at the Pennsylvania State University

Two systems which provide long-term circulatory support are described: the left ventricular assist system and the total artificial heart. These systems are based on the design of a pusher plate actuated blood pump, driven by a small brushless DC electric motor and rollerscrew driver. An implantable motor controller maintains suitable physiologic flow rates for both systems and controls left-right balance in the total artificial heart. Other parts of the system include an intrathoracic compliance chamber, transcutaneous energy and data transmission system, and internal and external batteries.<<ETX>>

Models for the generation of the binaural difference response

Two simple models are examined in order to explain the observation that a portion of the binaural-evoked response is less than the sum of monaural-evoked responses in human and animal subjects. The sum of monaural responses minus the binaural response is called the binaural difference (BD). Each model acts on binaural input signals and applies a single memoryless nonlinearity. One model (IE) applies a rectifying nonlinearity to the difference of input signals, while the other (EE) applies a compressive nonlinearity to the sum of input signals. These models are suggested by properties of inhibitory-excitatory (IE) and excitatory-excitatory (EE) neurons of the auditory brainstem. Parameters can be found that enable each model to produce a ratio of BD to summed monaural response which is invariant with input stimulus level. The IE model, but not the EE model, has a BD whose level is linearly related to input stimulus level.

Ratio of variance to mean of action potential counts for an auditory nerve fiber model with second-order refractory behavior

Sequences of interval times were generated with the first- and second-order interval probability dependence proposed by Gaumond et al. [J. Neurophysiol. 48, 856-873 (1982)] to characterize cochlear nerve fiber spontaneous action potential (AP) sequences. The ratio F(T) of the variance to the mean of the count of APs in bins of T s was computed for the simulated sequences, and compared to the corresponding measure for cochlear nerve fiber data presented by Lowen and Teich [J. Acoust. Soc. Am. 92, 803-806 (1992)]. The simulations were generally consistent with the data in the range 15 < T < 100 ms.

Automated analysis of feeding behavior in small animals

Discusses the implementation of an automated apparatus for recording and quantifying food choice behavior by small animals. A computer controls the apparatus by positioning a video camera over each one of twelve petri dishes. When the camera is in position, an image of the underlying dish is captured and the digitized image is returned to the computer for further processing. Within the computer a digital image processing procedure analyzes and quantifies the observed behavior.

Nerve fiber stimulation threshold for multiphase stimuli

The authors determined the strength-duration curves for stimulus pulse waveforms of one, two, or three rectangular phases of alternating polarity. Stimuli represented the induced transmembrane current density for a voltage-clamped unmyelinated axon. For any pulse length, the one-phase pulse always required the least current density to cause an action potential, while the two-phase pulse always required the most. For short pulse lengths (</spl tausub m/, time constant for sodium gate activation at resting potential), the three-phase pulse curve approached that of the one-phase pulse; for long pulse lengths (>/spl tausub mem/, time constant of the resting membrane), the three-phase pulse curve approached that of the two-phase pulse.<<ETX>>

Roundoff Errors in Signal Averaging Systems

In biomedical signal averaging applications where a small repetitive signal is to be extracted form a very noisy waveform (noise variance ¿2n), the A/D converter range is set at ±A¿n where A typically has a value of 3 or 4. In this case, A/D roundoff noise using a (b + 1)-bit A/D converter degrades the SNR of the resulting signal estimate by an amount slightly greater than 10 log (1 + A2¿2b/12). Application of this result to the design of a system for digital acquisition and averaging of the acoustic brainstem response indicates that an increase of A/D resolution beyond the first few bits yields little improvement in the SNR of the measurement.

Spacing analysis of a focal magnetic stimulating coil

A promising coil geometry for focal stimulation of neurons through magnetic induction is the quad-square coil. This configuration utilizes four 90/spl deg/ corners at the center to produce large values of dE/sub x//dx (considered the activating function in neural stimulation). The values of dE/sub x//dx produced by the center of the coil are limited by the coil dimensions and coil spacing. A closed form solution of the limiting function in terms of coil dimension, spacing, and stimulating depth is presented and the relationship between dE/sub x//dx and spacing is graphically shown.

Field potentials in rat brain stem during binaural acoustic stimulation

Electric field potentials were measured in rat brain stem while presenting monaural or binaural acoustic click stimuli. The binaural difference (BD) potential, defined as the sum of field potentials due to menaural stimuli minus that due to a binaural stimulus, was recorded at 1‐mm intervals along a track passing through the inferior colliculus and the superior olivary nuclei. Scalp surface potentials were recorded simultaneously. Prominent BD potentials were observed at all intracranial locations. Scalp surface BD was contemporaneous with an intracranial BD waveform that reversed sign at a level midway between the inferior colliculus and the olivary nuclei. The onset of BD potentials at or below this level occurs 1 ms after the appearance of prominent monaural and binaural response waveforms. This latency difference suggests the existence of an additional synapse in the pathway leading to the structure responsible for BD generation compared to pathways leading to other structures in the superior olivary ...

Binaural difference in rat

The binaural difference (BD) is the sum of monaural acoustic brainstem responses (ABRs) minus the binaural ABR. Its construction implies operation of a nonlinear element with binaural input. The BD in five rats was studied using insert earphones that provided 60 dB of interaural isolation measured in the occluded external meatus. Scalp to chin BD consisted of a double‐peaked complex with a following trough occurring during peaks IV and V of the sum of monaural ABRs. BD magnitude was defined as the maximum peak‐to‐trough waveform amplitude. As stimulus intensity increased, BD magnitude increased linearly with the magnitude of ABR peak I. A bilaterally symmetric stimulus generally yielded smaller BD magnitude than did stimuli with small bilateral asymmetry (8‐dB interaural intensity difference, 64‐μs interaural time difference). With larger asymmetry, BD magnitude decreased. The linear increase of BD magnitude with ABR peak I magnitude is consistent with operation of an element that applies a rectification ...