A correlation of the effects of normoxia, hyperoxia and anoxia on PO2 of endolymph and cochlear potentials

Chronic Obstructive Pulmonary Disease is a Risk Factor for Sensorineural Hearing Loss: A US Population Study

OBJECTIVES

The goal of this study is to determine if chronic obstructive pulmonary disease (COPD) is associated with sensorineural hearing loss (SNHL) in a national database.

STUDY DESIGN

Cross-sectional study.

SETTING

National sample of the United States population.

PATIENTS

Adults with audiometric and spirometry data from the National Health and Nutrition Examination Study (NHANES) database.

INTERVENTIONS

None.

METHODS

A total of 2,464 adults with spirometry and audiometry data from the NHANES database (2009-2012) were studied. Outcome measures included hearing, measured by high-frequency pure tone average (HFPTA; 3, 4, 6, 8 kHz) and low-frequency pure tone average (LFPTA; .5, 1, 2 kHz) frequencies. SNHL was defined as a HFPTA or LFPTA threshold more than 25 decibels (dB) in the better ear. Multivariable regression analyses explored the association between hearing loss and COPD.

RESULTS

The prevalence of COPD was 19.8% in individuals with SNHL in the better ear and 4.7% in individuals with normal hearing (p < 0.001). Presence of COPD was associated with elevated hearing thresholds (worse hearing) at each individual frequency. The presence of COPD was independently associated with a 3.29 dB (95% CI: 1.48, 5.09) increase in HFPTA (p < 0.001), and 2.32 dB (1.13, 3.50) increase in LFPTA (p < 0.001) after controlling for medical, social, and environmental covariates. The presence of COPD was independently associated with a 1.85-fold (1.12, 3.06) increased odds of isolated low-frequency SNHL (p = 0.017).

CONCLUSIONS

COPD was independently associated with sensorineural hearing loss after controlling for multiple confounding factors. These results contribute to the evidence that COPD and pulmonary dysfunction can be comorbid with hearing decline.

Cellular localization of facilitated glucose transporter 1 (GLUT-1) in the cochlear stria vascularis: its possible contribution to the transcellular glucose pathway

Immunoreactivity for the facilitated glucose transporter 1 (GLUT-1) has been found in the cochlear stria vascularis, but whether the strial marginal cells are immunopositive for GLUT-1 remains uncertain. To determine the cellular localization of GLUT-1 and to clarify the glucose pathway in the stria vascularis of rats and guinea pigs, immunohistochemistry was performed on sections, dissociated cells, and whole-tissue preparations. Immunoreactivity for GLUT-1 in sections was observed in the basal side of the strial tissue and in capillaries in both rats and guinea pigs. However, the distribution of the positive signals within the guinea pig strial tissue was more diffuse than that in rats. Immunostaining of dissociated guinea pig strial cells revealed GLUT-1 in the basal cells and capillary endothelial cells, but not in the marginal cells. These results indicated that GLUT-1 was not expressed in the marginal cells, and that another isoform of GLUT was probably expressed in these cells. Three-dimensional observation of whole-tissue preparations demonstrated that cytoplasmic prolongations from basal cells extended upward to the apical surface of the stria vascularis from rats and guinea pigs, and that the marginal cells were surrounded by these protrusions. We speculate that these upward extensions of basal cells have been interpreted as basal infoldings of marginal cells in previous reports from other groups. The three-dimensional relationship between marginal cells and basal cells might contribute to the transcellular glucose pathway from perilymph to intrastrial space.

Study of auditory function in patients with chronic obstructive pulmonary diseases

This study was designed to measure auditory function in patients with chronic obstructive pulmonary diseases (COPDs) who generally suffer from chronic hypoxemia. Control and COPD subject groups received a battery of tests to assess overall hearing sensitivity and peripheral (end-organ and eighth-nerve) and brain-stem auditory function, as well as blood-gas analysis. Results showed a statistically significant difference for all audiological measures between the control group and a COPD subgroup--the presumptive hypoxic subjects (partial oxygen tensions, PO2, <75 mm Hg). Correlation analyses of results from all subjects (regardless of PO2) also revealed significant covariance with PO2 for overall, RMS, amplitude of click-evoked otoacoustic emissions (RA), hearing threshold level, and auditory brain-stem response (ABR, I-V inter-peak latency). Chi2 or Fisher's exact tests were statistically significant for frequencies of cases classified according to a criterion PO2 of 70 mm Hg (putative critical O2 for completely normal auditory function) and either hearing thresholds falling below or RA values above 1.5 standard deviations of the control-group means, respectively. However, chi2 was not significant for a comparable criterion of ABR I-V IPL. In general, clinically significant hearing loss was uncommon in COPD patients, and the observed effects represented relatively small changes in the auditory measures examined. Still, overall, changes were in the direction of poorer function, and these results suggest physiologically significant impact of chronic hypoxemia and the need for further study to evaluate thoroughly this medical condition as a potential risk factor for audio-vestibular dysfunction.

Pathological findings in the temporal bone of newborn infants with neonatal asphyxia

Hypoxia in adults frequently causes damage to the brain, but not the inner ear. However, hypoxia in neonates with inadequate blood-inner ear barrier function causes damage to the inner ear, leading to hearing loss and equilibration disorder. Clinically, asphyxiated neonates sometimes have the complication of sensorineural hearing impairment at high frequencies. Many reports suggest that this problem is caused by hypoxic encephalopathy. However, it is not clear whether inner ear disorders are present. In this report we examined the inner ear pathology of four asphyxiated neonates using serial sections of temporal bone. The subjects (n=4) were 1-13-day-old neonates with pregnancy periods of 24-36 weeks. Their fetal growth curves were within the normal range. There was one case each of twin pregnancy, placental abruption, placenta previa and meconium aspiration syndrome. For the case of severe neonatal asphyxia, damage to the inner ear included the degeneration and disappearance of outer hair cells of the organ of Corti and edematous changes in the stria vascularis. Degeneration of spiral ganglion and vestibular ganglion cells was observed in two of the other cases.

Alterations in oxygenation of cochlear endolymph during loud sound exposure

The oxygen tension (pO2) of endolymph of the guinea pig cochlea was measured during exposure to loud sound (12 kHz or high-pass noise; 110 dB SPL up to 1 h duration). A small, but significant, steady decline in mean pO2 was observed after both pure tone and high-pass noise exposure. The extent of the change in pO2 varied from 0-50% in individual animals, compared with unexposed control animals. All exposed animals had an extensive loss of compound action potential (CAP) thresholds at frequencies of 8-30 kHz. However, there was no relationship between the extent of the change in pO2 of endolymph and CAP threshold loss.

Cochlear blood flow: measurement techniques

The measurement of inner ear blood flow and other microvascular variables is subject to unique technical problems which are compounded by methodological limitations. As a result, the interpretation of experimental results is often difficult. This report discusses the most important methods currently available for cochlear blood circulation measurements and the technical problems associated with their use. The use of a combination of measurements to resolve problems of interpretation is stressed. An extensive review of the pertinent literature is provided in relation to each method.

Dynamic aspects of guinea pig inner hair cell receptor potentials with transient asphyxia

DC and AC receptor potentials of cochlear inner hair cells in response to tone bursts of various frequencies and intensities were continuously measured during and following periods of transient asphyxia. The effects of asphyxia were most pronounced for low sound pressure level (SPL) acoustic stimuli near the characteristic frequency (CF) of the inner hair cell, leading to vulnerability of the 'tip' of the cell's frequency tuning curve (FTC). The resulting changes in the shape of the FTC are, first, a reduction in tip criterion sensitivity of 10-20 dB without significant loss in sharpness of tuning. Later, when the full effect of 30-45 s asphyxia occurs, tip sensitivity loss between 30 and 65 dB is accompanied by greatly broadened tuning and a shift downward in frequency of the CF by greater than 1/4 octave. The CF shift is due to a progressive loss of high frequency sensitivity. The linear segment of the input-output (intensity) function, plotted as log DC receptor potential versus SPL (at the original CF), becomes longer during the early phase asphyxia, and the slope of the segment declines by 50%. At high SPLs, for all frequencies, the time course of the receptor potential change was similar in shape to that exhibited by the endocochlear potential (EP). In particular, for high sound levels, the recovery of response matches the EP while for low level tip frequency sounds recovery is protracted. No difference between the decline of the AC and DC receptor potentials at CF was observed. Inner hair cell resting membrane potential (Em) hyperpolarized during asphyxia by 2-6 mV, correlating with the change in EP according to a ratio of 1/10 (Em/EP).

The Davis theory: a review, and implications of recent electrophysiological evidence

The Davis theory of mechano-electrical transduction asserts that the endocochlear potential and the hair cell resting potential summate to provide a driving force for current flow through the hair cell. However, while a variety of agents which depress the endocochlear potential simultaneously depress auditory nerve sensitivity and reduce the cochlear microphonic, recent reports suggest that the hair cells may be depolarised without such effects ensuing. The relevant literature is reviewed.

Auditory brainstem responses in perinatal asphyxia

Averaged auditory brainstem responses (ABR) elicited by unfiltered clicks were recorded from 14 asphyxiated neonates with clinical evidence of CNS suppression at 3-17 days of age, and from a group of healthy neonates matched in gestation period and weight. Statistically significant differences were found between the two groups in several ABR parameters and characteristics. In general, longer ABR component latencies and interwave intervals were the rule in the asphyxiated group. Short-term follow-up of the asphyxiated infants suggested that the ABR is sensitive to recovery trends from hypoxic encephalopathy. The results of a 6-month follow-up are also summarized. The results are discussed with regard to the histopathological and experimental information available from current literature.

Endocochlear potential and scala media oxygen tension during partial anoxia

The endocochlear potential and the scala media oxygen tension were measured from the basal coil of the guinea pig cochlea during levels of partial respiratory anoxia. This was accomplished by simultaneously positioning two electrodes (for endocochlear potential and PO2) into the endolymph by a transbasilar membrane approach, in order to minimize blood capillary damage. The intracochlear pO2 was stable until the respiratory oxygen concentration was reduced to 16 per cent on the average. Thereafter, a further reduction of oxygen in the respiratory mix reduced both the endolymph pO2 and the endocochlear potential. The coupling between the endocochlear potential and endolymph pO2 is proportional over a 70 to 80 per cent reduction in endolymph pO2, and at this point the endocochlear potential is reduced by 50 per cent. For partial levels of respiratory oxygen that are not too low (e.g., > 12 per cent oxygen) it is possible to maintain partial levels of intracochlear pO2 for at least six minutes. During this time period the endocochlear potential is also held at a stable but reduced level.