Evaluation and design of a small portable EMG amplifier with potential RMS output. (1/93)

The present study attempted to design and evaluate a small portable electromyogram (EMG) amplifier that can output enhanced EMG and its root mean square (RMS) value. The production and design were of a laboratory scale without any special or high cost circuit construction. The designed amplifier was actually innovated according to the actual working conditions based on physiological anthropology. The present amplifier was compared with commercially available products and proved to be of practical use. The device was installed with a sufficiently small body depicting 8-channel variable gain AC amplifier and variable time-window RMS-to-DC converter. The prototype was battery-driven and well-shielded to minimize external noise interference.  (+info)

Versatile, high-speed force transducer using a laser diode beam as an optical lever. (2/93)

A force transducer with variable sensitivity and speed is described. Its moving element is a cantilever beam that projects vertically into a muscle bath. A brace constrains bending of the beam to a short, proximal "hinge." Rotation of the beam about the hinge is amplified 30-fold by an optical lever consisting of a laser diode beam reflected from a mirror on the cantilever to a photodiode pair. This design places the electrical components at a distance from the damp environment of the muscle bath. Large changes in sensitivity and speed can be obtained by substituting different cantilevers. Smaller changes can be made by varying the length of the hinge. A transducer with a 6-mm cantilever optimized for the study of single, skinned skeletal muscle fibers is described in detail. This device had a resonant frequency of 22 kHz and sensitivity such that the total root-mean-square noise in the circuit was more than 500-fold smaller than the expected maximum force. Variations of this device with orders of magnitude different sensitivities are also described.  (+info)

The impact of hearing on communication. (3/93)

The study was designed to assess the impact of hearing impairment on communication between older hospital patients and medical staff and to see whether intervention to improve hearing influences perceived communication. Structured interviews were held with 200 mentally alert elderly hospital in-patients before and after the introduction of voice amplifiers and acetate cards depicting a hearing problem. Prior to intervention 22% of patients rated communication with their doctor as poor or unsatisfactory. Following intervention there was a significant improvement (Chi-square p=0.006), with only 6% of patients reporting communication with their doctor as poor or unsatisfactory. Most of the patients who felt communication was unsatisfactory could not hear what was being said. We conclude that simple measures can improve the number of older patients hearing what their doctor says and improve their perception of communication with the hospital doctor.  (+info)

Detection of ventricular fibrillation in implantable defibrillators with automatic gain control amplifiers: effects of programming sensitivity. (4/93)

AIMS: In newer implantable cardioverter-defibrillators with automatic gain control amplifiers the maximum possible sensitivity is programmed with the aim of securing optimal detection of ventricular fibrillation. This study was designed to prove that a reduction in maximum sensitivity is safe with respect to appropriate sensing of ventricular fibrillation, while avoiding sensing of extracardiac signals. METHODS AND RESULTS: Forty-two consecutive patients, undergoing defibrillator implantation/replacement with programmable maximum auto-gain sensing sensitivity (Ventak Mini III, Ventak AV , Guidant, St. Paul, MN, U.S.A.), were prospectively investigated. Thirty-four patients were implanted with a dual-coil lead system, providing integrated bipolar sensing (Endotak, Guidant, St. Paul, MN, U.S.A.), eight patients received a single-coil lead system with true bipolar sensing (Sprint, Medtronic, Minneapolis, MN, U.S.A.). During device implantation and pre-discharge testing, arrhythmia detection times of induced ventricular fibrillation were compared at programmed maximum (0.18 mV) and minimum (0.43 mV) sensitivity in a randomized manner. Seventy-six induced episodes of ventricular fibrillation were analysed. The mean arrhythmia detection times did not differ between the programmed sensing levels (maximum sensitivity: 1612 +/- 307 ms, vs minimal sensitivity: 1,602 +/- 330 ms; P = ns). The results were not affected by the type of implanted lead system (integrated bipolar versus true bipolar sensing). CONCLUSION: In the implantable defibrillator devices, reduction in maximum sensitivity did not impair the detection of induced episodes of ventricular fibrillation.  (+info)

Sensitive calibration and measurement procedures based on the amplification principle in motion perception. (5/93)

We compare two types of sampled motion stimuli: ordinary periodic displays with modulation amplitude m(o=e) that translate 90 degrees between successive frames and amplifier sandwich displays. In sandwich displays, even-numbered frames are of one type, odd-numbered frames are of the same or different type, and (1) both types have the same period, (2) translate in a consistent direction 90 degrees between frames, and (3) even frames have modulation amplitude m(e), odd frames have modulation amplitude m(o). In both first-order motion (van Santen, J.P.H. & Sperling, G. (1984). Temporal covariance model of human motion perception. Journal of the Optical Society of America A, 1, 451-73) and second-order motion (Werkhoven, P., Sperling, G., & Chubb, C. (1993). Motion perception between dissimilar gratings: a single channel theory. Vision Research, 33, 463-85) the motion strength of amplifier sandwich displays is proportional to the product m(o)m(e) for a wide range of m(e). By setting m(e) to a large value, an amplifier sandwich stimulus with a very small value of m(o) can still produce visible motion. The amplification factor is the ratio of two threshold modulation amplitudes: ordinary circumflexm(o=e) over amplified circumflexm(o), circumflexm(o=e)/circumflexm(o). We find amplification factors of up to about 8x. Light adaptation and contrast gain control in early visual processing distort the representations of visual stimuli so that inputs to subsequent perceptual processes contain undesired distortion products or 'impurities'. Motion amplification is used to measure and thence to reduce these unwanted components in a stimulus to a small fraction of their threshold. Such stimuli are certifiably pure in the sense that the residual impurity is less than a specified value. Six applications are considered: (1) removing (first-order) luminance contamination from moving (second-order) texture gratings; (2) removing luminance contamination from moving chromatic gratings to produce pure isoluminant gratings; (3) removing distortion products in luminance-modulated (first-order) gratings - by iterative application, all significant distortion products can be removed; (4) removing second-order texture contamination from third-order motion displays; (5) removing feature bias from third-order motion displays; (6) and the same general principles are applied to texture-slant discrimination in which x,y spatial coordinates replace the x,t motion coordinates. In all applicable domains, the amplification principle provides a powerful assay method for the precise measurement of very weak stimuli, and thereby a means of producing visual displays of certifiable purity.  (+info)

Improving the classroom listening skills of children with Down syndrome by using sound-field amplification. (6/93)

Many children with Down syndrome have fluctuating conductive hearing losses further reducing their speech, language and academic development. It is within the school environment where access to auditory information is crucial that many children with Down syndrome are especially disadvantaged. Conductive hearing impairment which is often fluctuating and undetected reduces the child's ability to extract the important information from the auditory signal. Unfortunately, the design and acoustics of the classroom leads to problems in extracting the speech signal through reduced speech intensity due to the increased distance of the student from the teacher in addition to masking from excessive background noise. One potential solution is the use of sound-field amplification which provides a uniform amplification to the teacher's voice through the use of a microphone and loudspeakers. This investigation examined the efficacy of sound-field amplification for 4 children with Down syndrome. Measures of speech perception were taken with and without the sound-field system and found that the children perceived significantly more speech in all conditions where the sound-field system was used (p < .0001). Importantly, listening performance with the sound-field system was not affected by reducing the signal-to-noise ratio through increasing the level of background noise. In summary, sound-field amplification provides improved access to the speech signal for children with Down syndrome and as a consequence leads to improved classroom success.  (+info)

Electrical engineering and nontechnical design variables of multiple inductive loop systems for auditoriums. (7/93)

This research analyzed both engineering and nontechnical issues involved in the use of Induction Loop Amplification (ILA) devices in auditoriums or large gathering places for hard-of-hearing individuals. A variety of parameters need to be taken into account to determine an optimal shape/configuration for the ILA device. In many cases, an optimal configuration is different from those proposed for classroom use (Ross, 1969; Hodgson, 1986; Clevenger, 1992). Experimental results were obtained for a double-loop configuration in such a setting (a university gymnasium/auditorium in this case). The results demonstrate that a double-loop configuration is a viable possibility for auditorium use. Several variables using this configuration were examined, and experimentation was done. Various implications, including consequent nontechnical issues specific to this application, are discussed as well. Technical and nontechnical aspects of the ILA configuration need to be examined together when designing an optimal system.  (+info)

The cochlear amplifier: augmentation of the traveling wave within the inner ear. (8/93)

PURPOSE OF REVIEW: There have been many recent advancements in our understanding of cochlear function within the past ten years. In particular, several mechanisms that underlie the sensitivity and sharpness of mammalian tuning have been discovered. This review focuses on these issues. RECENT FINDINGS: The cochlear amplifier is essentially a positive feedback loop within the cochlea that amplifies the traveling wave. Thus, vibrations within the organ of Corti are sensed and then force is generated in synchrony to increase the vibrations. Mechanisms that generate force within the cochlea include outer hair cell electromotility and stereociliary active bundle movements. These processes can be modulated by the intracellular ionic composition, the lipid constituents of the outer hair cell plasma membrane, and the structure of the outer hair cell cytoskeleton. SUMMARY: A thorough understanding of the cochlear amplifier has tremendous implications to improve human hearing. Sensorineural hearing loss is a common clinical problem and a common site of initial pathology is the outer hair cell. Loss of outer hair cells causes loss of the cochlear amplifier, resulting in progressive sensorineural hearing loss.  (+info)

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