Biomedical subjects

M R Stephenson

Publications and source records attributed to M R Stephenson.

5 recordsLinked to original sources

PubMed1990

Voyager flight crew hearing threshold levels resulting from 5- and 9-day continuous in-flight noise exposure.

The flight crew of the Voyager aircraft were continuously exposed to a broadband noise for nearly 5 days during a trial flight, and for over 9 days during their nonstop flight around the world. Evaluation of the threshold shifts resulting from these exposures represents a unique opportunity to study the effect of human exposure to intense continuous noise for long durations. Postflight audiometry demonstrated that the 9-day flight did not result in larger hearing threshold shifts than those following the 5-day flight. Neither crewmember incurred a permanent threshold shift from these exposures.

Adult↗

PubMed1984

Post-noise-exposure auditory sensitivity and temporal integration recovery functions.

Normal-hearing young adults (N:12) were exposed to a band-limited noise (1.4-2 kc/s) at 100 db SPL for 15 min. Pre- and post-exposure threshold measurements were made at 2 and 4 kc/s at durations of 500 and of 20 msec, at time intervals of TTS2, TTS15 and every 30-min interval thereafter for 4 hrs. Greater TTS occurred at both frequencies with the 500-msec than with the 20-msec duration. Threshold recovery patterns over time were similar for both durations but thresholds for the 20-msec duration recovered sooner. There was a delayed recovery function at 4 kc/s for the relative differences (20 vs 500 msec). Implications of the findings were discussed.

Acoustic Stimulation↗

PubMed1980

Identification of the minimum noise level capable of producing an asymptotic temporary threshold shift.

The present study was designed to identify the minimum noise level capable of producing an asymptotic temporary threshold shift (ATTS). It was estimated that at some level below 85 dBA, probably 70-80 dBA, there existed an exposure level at which no ATTS would occur. It is assumed that if a long-duration noise does not produce temporary changes in hearing levels, then it would not produce permanent changes either. This level would then define an exposure condition below which personnel could be exposed for indefinite periods of time without adverse auditory effects. Subjects were exposed to continuous pink noise for 24 h at levels of 65, 70, 75, 80, and 85 dBA. TTS growth and recovery was measured at specific intervals throughout each condition. Results demonstrate that at the most sensitive frequency (4000 Hz), at ATTS threshold level would be predicted in the region of 75-80 dBA.

Adult↗

PubMed1977

Asymptotic behavior of temporary threshold shift and recovery from 24- and 48-hour noise exposures.

Temporary hearing loss (TTS) from long-duration noise exposure reaches an asymptote between 8 and 16 h and does not increase further during continued exposure for durations of at least 48 h. Potential auditory hazards of long-duration exposures are examined in terms of growth and recovery patterns of TTS. TTS growth and recovery patterns were compared during 24- and 48-h exposures of humans to continuous pink noise at a level of 85 dB A-weighted. Results indicate similar patterns of acquisition and relatively equal amounts of TTS for the two exposure durations. However, recovery of preexposure hearing at 4000 Hz following termination of the 48-h noise exposure differed somewhat from that which followed the 24-h exposure. The implications of these findings for long missions in noisy environments are discussed.

Adult↗

PubMed1976

Long-duration exposure to intermittent noises.

The effects were examined of various patterns of interruption--of continuous noise by periods of quiet--on the growth and recovery of temporary threshold shift of hearing over an exposure period of 24 h. Monaural thresholds of hearing were measured prior to, during, and following exposure to a pink noise at a level of 85 dBA and to four conditions in which the pink noise was interrupted with various on-off ratios. The interrupted exposure patterns and levels were adjusted to make their average levels equivalent to 85 dBA. Among the results: 1) the growth of TTS clear.ly reached an asymptote for all interrupted exposure conditions, even when the TTS was as small as 5 dB, 2) the interrupted exposures produced lower asymptotic levels than the continuous exposure with the same amount of energy, and 3) the TTS recovery patterns were essentially the same at 1 h and beyond, for all conditions. These data support the concept that, following a long exposure, one should be provided at least as much time for recovery as the duration of the exposure.

Aerospace Medicine↗