Biomedical subjects

R S Karlovich

Publications and source records attributed to R S Karlovich.

At least 19 recordsLinked to original sources

PubMed1992

Research project shows importance of pre-employment hearing testing.

Forty employees received pure-tone baseline hearing tests at the time they began employment as LSM operators for the U.S. Postal Services; the workplace eight-hour average sound level (TWA) was 85 dBA. Nineteen operators from the original group had their hearing retested three years later. None of the retested subjects showed large or systematic changes in hearing sensitivity over the three-year period. For the audiometric frequencies most susceptible to noise exposure (3000, 4000, 6000 Hz), only 5 percent of the operators showed a bilateral change in threshold greater than 5 dB at any frequency, and none of them showed more than a 10 dB threshold change in both ears. None of the operators displayed a Standard Threshold Shift as described by OSHA. The data further suggested that many workers began their LSM work assignment with a pre-existing hearing loss and, based upon audiometric and history information, the impairment probably resulted from prior occupational and/or nonoccupational noise exposure. The importance of hearing-conservation programs for employees is emphasized.

Adult↗

PubMed1983

Psychoacoustic tuning curves and averaged electroencephalic responses in a patient with low-frequency sensory-neural hearing loss.

A 10-year-old girl whose bilateral, low-frequency, sensory-neural hearing loss had been noted three years earlier showed a drop in speech discrimination in her left ear with no corresponding decrease in pure-tone sensitivity. Psychoacoustic tuning curves and middle-component averaged electroencephalic responses to tone-pips suggested that damage to the left ear had become greater than indicated by the pure-tone audiogram, accounting for the drop in speech discrimination. This case suggests caution in inferring the magnitude of damage to the peripheral auditory system from tonal thresholds.

Audiometry, Evoked Response↗

PubMed1978

Acoustic-reflex dynamics for pulsed signals.

Contralateral acoustic-reflex measurements were taken for 10 normal-hearing subjects using a pulsed broadband noise as the reflex-activating signal. Acoustic impedance was measured at selected times during the on (response maximum) and off (response minimum) portions of the pulsed activator over a 2-min interval as a function of activator period and duty cycle. Major findings were that response maxima increased as a function of time for longer duty cycles and that response minima increased as a function of time for all duty cycles. It is hypothesized that these findings are attributable to the recovery characteristics of the stapedius muscle. An explanation of portions of the results from previous temporary threshold shift experiments on the basis of acoustic-reflex dynamics is proposed.

Acoustic Impedance Tests↗

PubMed1977

The acoustic reflex and temporary threshold shift: temporal characteristics.

One ear of each of seven normal-hearing subjects was exposed to a continuous 1000-Hz tone at 110 dB SPL for three minutes. During exposure, a broad-band noise at 100 dB SPL was presented to the contralateral ear. The noise was either continuous or pulsed. Four pulsed conditions employed repetition periods of 360, 180, 90, or 9 msec with a 50% duty cycle. A control condition in which no noise was presented was also included. Temporary threshold shift was measured at selected postexposure times at the frequency one-half octave above the exposure frequency. TTS2 was greatest for the control condition and least for the 360- and 180-msec conditions. Results are discussed in relation to the dynamics of the acoustic reflex, particularly reflex relaxation, reflex adaptation, and reflex temporal summation.

Acoustic Stimulation↗

PubMed1975

Acoustic-reflex response to sustain signals.

Acoustic-reflex activity was observed for 10 normal-hearing young adults using three sustained activating signals: 500-Hz tone, 4000-Hz tone, and broad-band noise. Reflex activity was observed over a period of three to five minutes at activator levels of 5, 10, and 15 dB above individual acoustic-reflex thresholds. General findings were that (1) acoustic-reflex adaptation was present to some degree for all three activating signals, (2) the amount of reflex adaptation varied with the spectrum of activating signals (reflex adaptation was greatest for the 4000-Hz activator, less for the noise activator, and least for the 500-Hz activating signal), (3) the rate of reflex adaptation differed with activator spectrum (reflex-adaptation rate was relatively rapid for the 4000-Hz activator, slower for noise, and much slower for the 500-Hz activating signal), and (4) reflex adaptation did not appear to vary systematically with activating-signal level except for the 500-Hz activator, in which case reflex adaptation appeared to begin earlier in time and to be of greater magnitude as the activating-signal level was increased.

Acoustic Stimulation↗

PubMed1974