Abstract
Objective
The authors of the present study aimed to investigate the impact of hypoxemia on the auditory functions of OSAS patients and discussed their findings under the scope of the existing literature.
Materials and methods
160 patients who underwent a polysomnographic analysis for the diagnosis of possible sleep disordered breathing between January 2015 and December 2015 were enrolled in this study. Polysomnography tests were conducted at the sleep laboratory of the department of neurology at the same institute. Comprehensive otorhinolaryngological examinations of all participants were conducted by the same senior otorhinolaryngologist.
Three study groups and a control group were designated in the study. Each study group was designated according to the severity of the apnea hypopnea index (AHI) and blood oxygen saturation values of the participants. All participants underwent pure tone auditometry and otoacoustic emission testing (OAE). Statistical data analysis was performed using SPSS for Windows, version 17 (SPSS Inc., Chicago, IL, USA).
Results
Audiological assessment of the patients revealed that all patients in the control group and in mild OSAS group had normal hearing thresholds (lower than 26 dB). However, the patients who had moderate and severe OSAS had varying degrees of sensorineural hearing losses. As far as body mass indexes are concerned, statistically significant differences were observed among the groups ( p = 0.038).
Conclusion
There is convincing evidence that the risk of progressive dysfunction in vascular and neural structures of the body is inevitable for the patients who suffer from a chronic hypoxemic condition secondary to OSAS. The findings of the present study indicated auditory transduction and transmission mechanisms may also be affected in moderate and severe OSAS patients. Therefore, via taking necessary steps in preventing hypoxemia at the outset, OSAS patients may be protected from the long term detrimental effects of chronic hypoxemia on the auditory system.
1
Introduction
Hypoxemia is known to have a significant negative impact on the biochemical and hemodynamical regulatory mechanisms located in the central and peripheral nervous system. In response to chronic hypoxemia a number of pathologies including but not limited to dysfunctions in neural mediator turnover and a decrease in the adenosine levels in the central nervous system can be observed . Furthermore, repetitive oxidative stress secondary to chronic hypoxemia was found to be associated with endothelial dysfunction in microcirculation. This condition, in turn, was proposed to compromise the vascular supply of the peripheral nerves and leads to an inevitable loss in neural function .
From an otorhinolaryngological point of view, patients with obstructive sleep apnea syndrome (OSAS) usually suffer from such a serious hypoxemic state as a consequence of repetitive apneic episodes . Patients are known to exhibit decreased oxygen (0 2 ) concentrations in the bloodstream during their sleep. In addition, significant fluctuations in 0 2 levels may persist even during the day time in OSAS patients .
Chronic hypoxemia and the fluctuations in blood oxygen concentration observed in OSAS patients may be detrimental for the auditory transduction and transmission mechanisms. The sense of hearing is accomplished by the peripheral and central auditory mechanisms, which are both vulnerable to the effects of hypoxemia. Flawless generation and conduction of the neural signals from the cochlea to the auditory cortex necessitate the presence of an adequate and uninterrupted supply of oxygen to the components of this neural circuit . The authors of the present study aimed to investigate the impact of hypoxemia on the auditory functions of OSAS patients and discussed their findings under the scope of the existing literature.
2
Materials and methods
The study was conducted in a tertiary referral center in Turkey. Approval was granted from the local ethics committee (2015/72/06/04) and all patients were asked to fill in an informed consent form. Patients who underwent a polysomnographic analysis for the diagnosis of possible sleep disordered breathing between January 2015 and December 2015 were enrolled in this study. Polysomnography tests were conducted at the sleep laboratory of the department of neurology at the same institute. Comprehensive otorhinolaryngological examinations of all participants were conducted by the same senior otorhinolaryngologist. Patients who had an acute or chronic otorhinolaryngological disease which may have a negative impact on hearing mechanism (otitis media, eustachian tube problems, sino-nasal disorders and etc.) and other co-morbid chronic systemic conditions that are well known to be associated with hypoxemia and disturbances in the microvascular circulation, including diabetes mellitus (DM), hypertension (HT) and chronic obstructive pulmonary disease (COPD) were excluded from the study. Three study groups and a control group were designated in the study. Each study group was designated according to the severity of the apnea hypopnea index (AHI) and blood oxygen saturation values (SpO 2 ) of the participants. The blood oxygen saturation levels were measured by a pulse oximeter (Beijing Safe Heart Technology Ltd., China). The first, second and third groups were comprised of patients having mild (AHI: 5–15, SpO 2 > 85%), moderate (AHI: 15–30, SpO 2 = 65%–84%) and severe OSAS (AHI > 30, SpO 2 < 65%), respectively. Each group consisted of randomly selected 40 patients. The control group was comprised of individuals who had an AHI < 5.
All participants also underwent pure tone auditometry and otoacoustic emission testing (OAE). Pure tone audiometry (PTA) was conducted by the same audiometrist in accordance to the international standards using a two channel audiometer (Interacoustics A/S, Denmark). Hearing thresholds at 250 to 8 kHz for each ear were determined. Average PTA thresholds were calculated by using threshold levels at 500, 100, and 2000 Hz. Patients who had a hearing threshold greater than 25 dBHL were accepted to have auditory dysfunction. The degree of hearing loss was accepted as mild (26 to 40 dBHL), moderate (41 to 55 dBHL), moderately severe (56 to 70 dBHL), severe (71 to 90 dBHL), and profound (91 + dBHL). For OAE testing, Madsen AccuScreen TE device was used (Otometrics, Denmark). Normal outer hair cell function was determined by a ‘Pass/Clear Response’ result. Individuals with a ‘Refer/No Clear Response’ result were re-tested. Upon retesting, individuals with a persistent ‘Refer/No Clear Response’ result were accepted as having a sensorineural hearing loss.
Statistical data analysis was performed using SPSS for Windows, version 17 (SPSS Inc., Chicago, IL, USA). The chi-square (χ2) test was used to compare qualitative data. The Kruskal–Wallis test (KW) was used to compare the groups. Dunn’s multiple comparison test and the Tukey’s range test were used to compare the subgroups. Results were considered significant for p < 0.05.
2
Materials and methods
The study was conducted in a tertiary referral center in Turkey. Approval was granted from the local ethics committee (2015/72/06/04) and all patients were asked to fill in an informed consent form. Patients who underwent a polysomnographic analysis for the diagnosis of possible sleep disordered breathing between January 2015 and December 2015 were enrolled in this study. Polysomnography tests were conducted at the sleep laboratory of the department of neurology at the same institute. Comprehensive otorhinolaryngological examinations of all participants were conducted by the same senior otorhinolaryngologist. Patients who had an acute or chronic otorhinolaryngological disease which may have a negative impact on hearing mechanism (otitis media, eustachian tube problems, sino-nasal disorders and etc.) and other co-morbid chronic systemic conditions that are well known to be associated with hypoxemia and disturbances in the microvascular circulation, including diabetes mellitus (DM), hypertension (HT) and chronic obstructive pulmonary disease (COPD) were excluded from the study. Three study groups and a control group were designated in the study. Each study group was designated according to the severity of the apnea hypopnea index (AHI) and blood oxygen saturation values (SpO 2 ) of the participants. The blood oxygen saturation levels were measured by a pulse oximeter (Beijing Safe Heart Technology Ltd., China). The first, second and third groups were comprised of patients having mild (AHI: 5–15, SpO 2 > 85%), moderate (AHI: 15–30, SpO 2 = 65%–84%) and severe OSAS (AHI > 30, SpO 2 < 65%), respectively. Each group consisted of randomly selected 40 patients. The control group was comprised of individuals who had an AHI < 5.
All participants also underwent pure tone auditometry and otoacoustic emission testing (OAE). Pure tone audiometry (PTA) was conducted by the same audiometrist in accordance to the international standards using a two channel audiometer (Interacoustics A/S, Denmark). Hearing thresholds at 250 to 8 kHz for each ear were determined. Average PTA thresholds were calculated by using threshold levels at 500, 100, and 2000 Hz. Patients who had a hearing threshold greater than 25 dBHL were accepted to have auditory dysfunction. The degree of hearing loss was accepted as mild (26 to 40 dBHL), moderate (41 to 55 dBHL), moderately severe (56 to 70 dBHL), severe (71 to 90 dBHL), and profound (91 + dBHL). For OAE testing, Madsen AccuScreen TE device was used (Otometrics, Denmark). Normal outer hair cell function was determined by a ‘Pass/Clear Response’ result. Individuals with a ‘Refer/No Clear Response’ result were re-tested. Upon retesting, individuals with a persistent ‘Refer/No Clear Response’ result were accepted as having a sensorineural hearing loss.
Statistical data analysis was performed using SPSS for Windows, version 17 (SPSS Inc., Chicago, IL, USA). The chi-square (χ2) test was used to compare qualitative data. The Kruskal–Wallis test (KW) was used to compare the groups. Dunn’s multiple comparison test and the Tukey’s range test were used to compare the subgroups. Results were considered significant for p < 0.05.
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