Biomedical subjects

S K Hirsh

Publications and source records attributed to S K Hirsh.

5 recordsLinked to original sources

PubMed1985

Threshold sensitivity and frequency specificity in auditory brainstem response audiometry.

Frequency-specific electric response audiometry can be performed on difficult to test young children if the child is sedated and proper choices are made of acoustic stimuli and recording parameters, although certain compromises are necessary. A very satisfactory sedative is secobarbital, administered intramuscularly in doses related to the weight of the child. As stimuli we recommend '2-1-2' tone bursts at 500, 1 000, 2 000, and 4 000 Hz: i.e., with a rise and fall of two periods and a plateau of one period of the modulated tone. A very robust and sensitive response that is not significantly modified by the sedation and is effective for all four frequencies is the P6-SN10 of the early brainstem sequence. To record this complex favorably requires a bandpass input filter of the Butterworth type with pass-band (at -3 dB) from 50 to 1 700 Hz and rejection rates of 24 dB/octave. With this combination, polarity of stimulus is unimportant and sweep time, rate of stimulation and number of responses averaged may be selected for convenience and simplicity. A routine that requires about an hour of testing time is described and the necessary correction factors are given for estimating a child's behavioral pure-tone thresholds. We believe that our threshold estimates are generally correct within 10 dB, and are sufficiently frequency-specific for proper selection of a hearing aid.

Acoustic Stimulation↗

PubMed1975

Audiometric comparison of the middle and late components of the adult auditory evoked potentials awake and asleep.

The middle and the late components of auditory evoked potentials were alternately recorded in sequential sets from 28 adults, both awake and asleep. Sleep was induced by secobarbital and was monitored for depth. 1000 c/sec tone pips in one laboratory or filtered clicks in the other were delivered at 10, 20 or 30 dB sensation level. Control collections without stimulation were included. For the middle responses a single simple scoring template and one set of voltage criteria could be used for all stages of waking and sleeping. For late responses different templates and voltage criteria were needed. Estimates of the threshold of detection of the evoked potentials were based on the percentage of clearly positive responses was often not attained at 30 dB SL, i.e., the threshold was indeterminate. In light sleep and awake the middle responses of most subjects gave thresholds more sensitive than the late by 10-15 dB and also fewer indeterminate trials. The results in our two laboratories agreed closely in spite of differences in equipment and details of procedure. The relatively low thresholds of the middle responses (median 17.5 dB SL awake and 15 dB SL in light sleep) suggest that the middle responses must be considered seriously for use in clinical electric response audiometry, even though one of the 28 subjects failed to yield any identifiable middle responses.

Adult↗

PubMedDate not supplied

Brain stem electric response audiometry (BSERA).

Brain stem electric responses, recorded with external electrodes on vertex and ear lobes, are excellent for audiometry of young children. The vertex-positive wave with latency of 6 to 9 msec resembles closely the action potential of the auditory nerve, with the same high-intensity short-latency component and low-intensity long-latency component. Thresholds are reliable with filtered clicks at 1 000 Hz and higher. Practical advantages and theoretical limitations are summarized.

Acoustic Stimulation↗

PubMedDate not supplied

The audiometric utility of brain stem responses to low-frequency sounds.

The human scalp-recorded vertex-positive brain stem response to a click or high-frequency tone pip is an excellent audiometric indicator. Its latency of 6-9 ms is practically independent of the polarity of the stimulus but is inversely related to intensity. With a 4,800- or 2,400-Hz tone pip (filtered click) its threshold of detectability is usually at or below 10 dB SL. With a 500-Hz tone pip, with rise and fall of 2-3 ms, the response at 30 dBSL is low in amplitude, rounded in wave form, and has a latency of about 10 ms. When the polarity of the stimulus is reversed, the latency shifts by 1 ms. At and above 40 dB, this late response is obsured by a larger and earlier response. High-pass (1,500 Hz) masking noise does not affect the low-level response but the earlier high-level response is reduced in amplitude and delayed by about 1 ms. The large early response seems to be initiated by stimulation of the basal turn of the cochlea by the low-frequency transient. The frequency-following response (FFR) to a 500-Hz tone burst with a 2-ms rise time has a threshold at about 40 dB SL. Its relatively short latency is appropriate to the basal turn. A later low-amplitude apically generated response can sometimes be detected, either at a lower stimulus level or in the presence of high-pass masking noise. The usual FFR often has complex wave forms and some individuals show only an onset response, even at 70 dB SL. It is almost impossible to edentify with certainty the first individual waves of FFR as they relate to the individual waves of the tone burst and as they change amplitude with intensity. The audiometric usefulness of the high-threshold responses to 500 Hz that are initiated in the basal turn is doubtful. The low-threshold responses initiated in the apical turn are so difficult to identify with certainty that they are not likely to be of clinical value unless high-pass masking noise can be used to clarify them.

Acoustic Stimulation↗

PubMedDate not supplied

A slow brain stem response for low-frequency audiometry.

Proper choices of stimuli and of brain stem electric responses allow us to estimate peripheral auditory thresholds at 500, 1 000, 2 000 and 4 000 Hz with an accuracy of about +/- 10 dB. With the help of sedation (secobarbital), such audiograms may be obtained from each ear of a child of any age in a single session. Tone pips (filtered clicks) or very brief tone bursts give a frequency selectivity that is clinically adequate. The rise time must be adjusted to the center frequency. A rise time of two periods with a plateau from zero to one period gives a good compromise between frequency specificity and a synchronous neural discharge. The best threshold indicator for tone pips of 2 000 Hz or higher (or unfiltered clicks) is P6 (Jewett V). At 60 dB nHL its latency is 6.0-7.0 ms (for children of 1 year or older), but near threshold it is 8.0-9.5 ms. An input pass-band of 140-3 000 Hz is appropriate. The best threshold indicator at 500 or 1 000 Hz is a nearly neglected slower wave with a scalp-negative crest at about 10 ms following a 60-dB click. Latency is 15 ms following a 500-Hz tone pip at 15 dB SL. We call this wave "slow negative (ten)" or SN10. To see it well a wider input pass-band such as 40-3 000 Hz is needed. SN10 is usually obscured by P6 or by frequency-following response at stimulus levels above 35 dB SL. The details are given of a clinical routine that allows the determination (+/- 10 dB) of 8 threshold endpoints within about 80 min. Several precautions and limitations are discussed, and also the origin of the SN10 wave.

Audiometry↗