Study of distortion-product otoacoustic emissions during hypothermia in humans

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Summary

Aim

To evaluate the function of cochlear outer hair-cells under the influence of extra-corporeal circulation and moderate hypothermia during cardiac surgery.

Study Design

Prospective clinical study.

Methods

Distortion-product otoacoustic emissions (DPOAE) were registered before surgery, immediately after general anesthesia induction, during extra-corporeal circulation with moderate hypothermia and after the surgical procedure. Results: Comparison of response-amplitudes before and after surgery and before and after general anesthesia initiation did not demonstrate statistical difference. Comparison of amplitudes before and after extra-corporeal circulation with moderate hypothermia demonstrated a statistically significant decrease in responses amplitudes during hypothermia.

Conclusions

The amplitudes of DPOAE decreased during moderate hypothermia induced during extra-corporeal circulation.

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Most cited references 44

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Abstract: found
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Stimulated acoustic emissions from within the human auditory system.

Johann T Kemp (1978)

A new auditory phenomenon has been identified in the acoustic impulse response of the human ear. Using a signal averaging technique, a study has been made of the response of the closed external acoustic meatus to acoustic impulses near to the threshold of audibility. Particular attention has been paid to the waveform of the response at post excitation times in excess of 5 ms. No previous worker appears to have extended observations into this region. The response observed after about 5 ms is not a simple extension of the initial response attributable to the middle ear. The oscillatory response decay time constant was found to change from approximately 1 ms to over 12 ms at about this time. The slowly decaying response component was present in all normal ears tested, but was not present in ears with cochlear deafness. This component of the response appears to have its origin in some nonlinear mechanism probably located in the cochlea, responding mechanically to auditory stimulation, and dependent upon the normal functioning of the cochlea transduction process. A cochlear reflection hypothesis received some support from these results.

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Outer hair cell electromotility and otoacoustic emissions.

W E Brownell (1990)

Outer hair cell electromotility is a rapid, force generating, length change in response to electrical stimulation. DC electrical pulses either elongate or shorten the cell and sinusoidal electrical stimulation results in mechanical oscillations at acoustic frequencies. The mechanism underlying outer hair cell electromotility is thought to be the origin of spontaneous otoacoustic emissions. The ability of the cell to change its length requires that it be mechanically flexible. At the same time the structural integrity of the organ of Corti requires that the cell possess considerable compressive rigidity along its major axis. Evolution appears to have arrived at novel solutions to the mechanical requirements imposed on the outer hair cell. Segregation of cytoskeletal elements in specific intracellular domains facilitates the rapid movements. Compressive strength is provided by a unique hydraulic skeleton in which a positive hydrostatic pressure in the cytoplasm stabilizes a flexible elastic cortex with circumferential tensile strength. Cell turgor is required in order that the pressure gradients associated with the electromotile response can be communicated to the ends of the cell. A loss in turgor leads to loss of outer hair cell electromotility. Concentrations of salicylate equivalent to those that abolish spontaneous otoacoustic emissions in patients weaken the outer hair cell's hydraulic skeleton. There is a significant diminution in the electromotile response associated with the loss in cell turgor. Aspirin's effect on outer hair cell electromotility attests to the role of the outer hair cell in generating otoacoustic emissions and demonstrates how their physiology can influence the propagation of otoacoustic emissions.

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A fast motile response in guinea-pig outer hair cells: the cellular basis of the cochlear amplifier.

Lesley J. Ashmore (1987)

1. Outer hair cells from the cochlea of the guinea-pig were isolated and their motile properties studied in short-term culture by the whole-cell variant of the patch recording technique. 2. Cells elongated and shortened when subjected to voltage steps. Cells from both high- and low-frequency regions of the cochlea responded with an elongation when hyperpolarized and a shortening when depolarized. The longitudinal motion of the cell was measured by a differential photosensor capable of responding to motion frequencies 0-40 kHz. 3. Under voltage clamp the length change of the cell was graded with command voltage over a range +/- 2 microns (approximately 4% of the length) for cells from the apical turns of the cochlea. The mean sensitivity of the movement was 2.11 nm/pA injected current, or 19.8 nm/mV membrane polarization. 4. The kinetics of the cell length change during a voltage step were measured. Stimulated at their basal end, cells from the apical (low-frequency) cochlear turns responded with a latency of between 120 and 255 microseconds. The cells thereafter elongated exponentially by a process which could be characterized by three time constants, one with value 240 microseconds, and a second in the range 1.3-2.8 ms. A third time constant with a value 20-40 ms characterized a slower component which may represent osmotic changes. 5. Consistent with the linearity shown to voltage steps, sinusoidal stimulation of the cell generated movements which could be measured at frequencies above 1 kHz. The phase of the movement relative to the stimulus continued to grow with frequency, suggesting the presence of an absolute delay in the response of about 200 microseconds. 6. The electrically stimulated movements were insensitive to the ionic composition of the cell, manipulated by dialysis from the patch pipette. The responses occurred when the major cation was K+ or Na+ in the pipette. Loading the cell with ATP-free solutions or calcium buffers did not inhibit the response. 7. It is concluded that interaction between actin and myosin, although present in the cell, is unlikely to account for the cell motility. Instead, it is proposed that outer hair cell motility is associated with structures in the cell cortex. The implications for cochlear mechanics of such force generation in outer hair cells are discussed.

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Author and article information

Journal

Journal ID (nlm-ta): Braz J Otorhinolaryngol

Journal ID (iso-abbrev): Braz J Otorhinolaryngol

Title: Brazilian Journal of Otorhinolaryngology

Publisher: Elsevier

ISSN (Print): 1808-8694

ISSN (Electronic): 1808-8686

Publication date PMC-release: 19 October 2015

Publication date Collection: May-Jun 2008

Publication date (Electronic): 19 October 2015

Volume: 74

Issue: 3

Pages: 401-409

Affiliations

[1 ]MSc, Graduate Student - PhD.

[2 ]Professor at USP/SP, Associate Professor of otorhinolaryngology at UNIFESP/EPM. Department of Otorhinolaryngology and Head and Neck Surgery - Paulista Medical School - UNIFESP - São Paulo SP Brazil

Author notes

[* ]Send correspondence to: Andrei Borin - Rua Loefgreen 1587 apto. 152 São Paulo SP Brasil 04040-032.

Article

Publisher Item ID: S1808-8694(15)30575-9

DOI: 10.1016/S1808-8694(15)30575-9

PMC ID: 9442074

PubMed ID: 18661015

SO-VID: b35df133-1597-44fd-86f7-35df84bb2319

License:

This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Study of distortion-product otoacoustic emissions during hypothermia in humans

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Summary

Aim

Study Design

Methods

Conclusions

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Hearing Loss and Restoration

Most cited references 44

Stimulated acoustic emissions from within the human auditory system.

Outer hair cell electromotility and otoacoustic emissions.

A fast motile response in guinea-pig outer hair cells: the cellular basis of the cochlear amplifier.

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