Biomedical subjects

R A Ruth

Publications and source records attributed to R A Ruth.

45 records · Page 3Linked to original sources

PubMedDate not supplied

Acoustic reflex response during curare-induced weakness.

The acoustic stapedial reflex (AR) was measured in five healthy subjects during intravenous administration of d-tubocurarine in four equal doses totaling 0.2 mg/kg. The behavior of the reflex in the face of progressive muscle weakness was assessed. Amplitude changes in the AR elicited by pulsed tones were compared to measurements of maximum respiratory pressures reflecting respiratory muscle strength. Total curare dose averaged 16.1 mg and produced symptoms progressing from mild diplopia with the initial dose to absence of hand-grip and head-lifting ability with the final dose. Peak-to-peak amplitude of the AR decreased progressively with each dose of curare. Effects were not strictly additive but showed the largest change with the last dose. Decreases in expiratory muscle strength closely paralleled changes in the AR, whereas changes in inspiratory muscle strength were less marked than the AR, especially with mild weakness. Therefore we concluded that the AR is a valid and sensitive index of neuromuscular transmission which has an advantage over most tests of muscle strength since subject effort and cooperation do not influence test results.

Adult↗

PubMedDate not supplied

Consideration of acoustic reflex magnitude (ARM) in cases of idiopathic facial paralysis.

Contralaterally elicited acoustic reflex growth functions were obtained from both ears of patients with unilateral idiopathic facial paralysis. Comparison was then made between the normal and impaired reflex arc by means of a simple calculation procedure. The resultant acoustic reflex magnitude (ARM) score was used to evaluate the symmetry of these responses, thereby providing an objective quantification of the functional status of the impaired reflex arc. These measures were found to be highly correlated with both the degree and rate of recovery of the facial motor impairment.

Acoustic Impedance Tests↗

PubMedDate not supplied

Stapedius muscle function tests in the diagnosis of neuromuscular disorders.

Muscle weakness and different patterns of fatigability are frequently seen in neuromuscular disorders. The value of a battery of stapedial muscle function tests in the diagnosis and management of these disorders has been evaluated. Each test of stapedial muscle function is described, and case examples of these tests in various neuromuscular disorders including myasthenia gravis and idiopathic facial nerve paralysis are reported.

Acoustic Impedance Tests↗

PubMedDate not supplied

A study of methods used to enhance wave I in the auditory brain stem response.

Auditory brain stem responses (ABR) were recorded in 15 audiometrically and neurologically normal adult subjects. The purpose of the study was to investigate various aspects of stimulus composition (intensity, click rate, and polarity) and response measurement parameters (band-pass filtering and electrode linkage) that might serve to enhance detectability of wave I in the ABR. Amplitude of wave I was significantly enhanced by an increase in intensity, a decrease in click rate, and use of a negative (rarefaction) polarity click. Amplitude of wave I was not significantly influenced by bandwidth of the response filter or by a horizontal (mastoid-to-mastoid) electrode linkage. Use of simultaneous response acquisition from an ipsilateral and contralateral reference electrode array did aid in the detection or visualization of wave I, particularly for lower stimulus intensity levels or faster click rates.

Acoustic Stimulation↗

PubMedDate not supplied

Use of otoacoustic emissions to screen for hearing loss in critically ill patients.

As part of a continuing quality improvement program, this project was undertaken to define the frequency of hearing loss in patients admitted to a surgical intensive care unit in order to identify patients at risk for impaired communication. The study evaluated 168 consecutive admissions over a ten week period to a ten bed adult surgical intensive care unit in a university hospital. Patients were screened as close to admission to the ICU as possible with otoscopy, tympanometry, and distortion product otoacoustic emissions. A total of 113 patients (226 ears, mean age 58.0+/-15.8 years) were screened within 1.5+/-1.4 days of ICU admission; 55 of the 168 admissions could not be screened (48 out of 55 due to short ICU stays). Of the 226 ears evaluated, 6.6 per cent had abnormal otoscopy and 43.2 per cent abnormal tympanograms. OAE failure occurred in 58.4 per cent of ears while OAE results were uninterpretable due to high ambient noise in 2.7 per cent of ears, and technical difficulty in 3.5 per cent of ears. Mean time for screening was 9.3 minutes. OAEs provide an efficient screening modality for hearing impairment in critically ill adults. The results suggest a significant prevalence of hearing impairment in the population studied. More definitive testing should be considered when clinically indicated in patients who fail OAE screening.

Acoustic Impedance Tests↗

PubMedDate not supplied

Acoustic reflex latency as a function of frequency and intensity of eliciting stimulus.

The purpose of the present study was to examine the functional between acoustic reflex (AR) latency and the intensity and frequency of the eliciting stimulus. AR latency was determined at various intensities for 500 Hz and 300 Hz pure tones, and for wide-band noise. The results of the study indicated that AR latency decreased as stimulus intensity increased for all stimuli; the exact nature of the relationship depended on the stimulus, however. Latency differences between the stimuli at a given sound pressure level tended to disappear at higher presentation levels. Of particular interest was the dependency of inter- and intrasubject variability on parameters of the eliciting stimulus. The data do no indicate that AR latency is mediated solely by the loudness of the eliciting stimulus.

Acoustic Stimulation↗

PubMedDate not supplied

Brain stem auditory evoked potential monitoring during profound hypothermia and circulatory arrest.

The effects of decreased temperature on brain stem auditory evoked potentials (BAEP) have been previously described in mild to moderate hypothermia. This report describes BAEP monitoring during profound hypothermia (11 degrees C) and circulatory arrest for repair of an aortic arch aneurysm. Recording of BAEP were interpretable during cooling to 14 degrees C, and demonstrated increasing interpeak (I-V) latency compatible with prolongation of brain stem conduction time. The changes rapidly returned to normal during rewarming from profound hypothermia, in a fashion similar to that seen after mild hypothermia, and therefore appear to be completely reversible.

Aorta, Thoracic↗

PubMedDate not supplied

A discussion of some temporal characteristics of electroacoustic impedance bridges.

The purpose of this study was to describe an acoustic method for measuring temporal characteristics of electroacoustic impedance bridges, and to present data on the temporal responses of three widely used electroacoustic instruments. The potential effects of these instrument parameters on measured characteristics of the acoustic reflex are discussed.

Acoustic Impedance Tests↗

PubMedDate not supplied

An artifact in acoustic reflex measurement: some further observations.

This study was designed to clarify characteristics of an artifact that has been reported to be a potential source of misleading information when determing acoustic reflex thresholds elicited by low-frequency tones. The study was conducted in two parts. Experiment 1 was concerned with an investigation of acoustic interactions in a sealed cavity between the probe tone from a commercial electroacoustic impedance bridge and interfering tones of various frequencies. Experiment 2 consisted of measurements of sound pressure levels in the sealed external ear canal of the probe ear when the contralateral ear was stimulated by air-conducted pure tones. The results indicated that acoustic reflex thresholds in 250-Hz tones probably cannot be determined for most persons unless special measures are taken to prevent the artifact. The artifact should not occur when the eliciting stimulus is 500 Hz, however.

Acoustic Stimulation↗