Review Audiology Neurotology
Audiol Neurotol 2014;19:256–260 DOI: 10.1159/000363215
Received: March 25, 2014 Accepted after revision: April 25, 2014 Published online: July 29, 2014
Cardiovascular Risk Factors as Causes for Hearing Impairment Yahav Oron Katya Elgart Tal Marom Yehudah Roth Department of Otolaryngology, Head and Neck Surgery, Edith Wolfson Medical Center, Sackler School of Medicine, Tel Aviv University, Holon, Israel
Key Words Hearing loss · Aging · Stria vascularis · Diabetes · Hypertension · Hyperlipidemia · Smoking
Abstract The purpose of this paper is to provide a contemporary review of the correlation between cardiovascular risk factors (CVRFs) and hearing impairment (HI). We conducted a comprehensive review of the literature in order to assess the effects of the different CVRFs on HI. We focused on the pathological findings in the inner ear and their correlation with cochlear function in population-based studies. We found that CVRFs adversely affect hearing acuity. HI diagnosis should be accompanied by detecting and treating CVRFs, according to the presented outline, which may augment hearing rehabilitation and improve the general health and the well-being of the patient. © 2014 S. Karger AG, Basel
Introduction
The major cardiovascular risk factors (CVRFs) include an older age, male gender, hypertension, hyperlipidemia, lack of physical activity, smoking, diabetes mel© 2014 S. Karger AG, Basel 1420–3030/14/0194–0256$39.50/0 E-Mail [email protected] www.karger.com/aud
litus (DM) and positive family history of coronary heart disease [Oparil and Oberman, 1999]. These CVRFs were also investigated as risk factors for the development of hearing impairment (HI). The purpose of this paper is to review the current knowledge regarding the relationship between CVRFs and HI and to suggest possible prevention and treatment options. CVRFs are usually more common among older patients, as is presbycusis. Thus, it might be difficult to distinguish the effects of age and noise exposure on hearing acuity from the effects which CVRFs might have on hearing.
Blood Supply to the Inner Ear and Auditory Nerve
The internal auditory artery (IAA) is the source of blood supply to the cochlea and to the auditory nerve. The IAA is usually a branch of the anterior-inferior cerebellar artery and it is an end artery, without anastomosis to compensate for any obstruction of the blood vessel [Baloh, 2001; Kim and Hyung, 2009] (fig. 1). The IAA feeds the stria vascularis (SV) at the lateral wall of the cochlea. At the cochlear apex this blood supply becomes sparse [Friedland et al., 2009]. The SV has a major role in the production of the endocochlear potential, which is essential for normal hearing [Wangemann, 2006]. More mediYahav Oron, MD Department of Otolaryngology, Head and Neck Surgery Edith Wolfson Medical Center PO Box 5, 58100 Holon (Israel) E-Mail oron.yahav @ gmail.com
Color version available online
Fig. 1. The arterial supply to the inner ear. Reprinted with permission from Kim and Hyung [2009].
ally, the auditory nerve is supplied also by collaterals supplying the dura mater and by a network of vessels from the anterior-inferior cerebellar artery, namely the posterior-inferior cerebellar artery and the vertebral arteries [Kim et al., 1990].
CVRFs and Their Effect on Inner Ear and Auditory Nerve – Pathological Findings
CVRFs may affect the blood supply to the cochlea and to the auditory nerve through the production of atherosclerotic plaques in the blood vessels supplying the auditory system. This change in blood flow may cause impairment in the availability of glucose and oxygen to the cochlea [Brant et al., 1996]. In an animal model (rabbits), topical papaverine prevented mechanically induced vasospasm of the IAA [Morawski et al., 2003]. Among aged adults, degenerative changes were found in the cochlea, in the auditory nerve [Rosenhall and Rubin, 1975] and in the arteries of the internal auditory canal [Fisch et al., 1972]. These observations were thought to be the reason for presbycusis. DM is one of the CVRFs which has been extensively studied. The effect of DM upon the cochlea and the auditory nerve may occur through the accumulation of sorbitol, which can adversely affect the function of the nerve through atherosclerosis of the nerve’s vasa nervosum, through angioCardiovascular Risk Factors: Causes for Hearing Impairment
pathic changes in the SV and through atrophy of the spiral ganglion and degeneration of the myelin sheath [Kakarlapudi et al., 2003]. In mice in which diabetes was induced, cochlear blood vessel thickness was found to be increased, as well as changes in the SV, collapse of Reissner’s membrane and degeneration of the organ of Corti [Costa, 1967]. In an earlier study, additional changes in the auditory nerve and Scarpa’s ganglion were noted [Cojazzi, 1950]. Examination of temporal bones of patients with DM type 2 demonstrated angiopathy and degeneration of the SV and the outer hair cells [Fukushima et al., 2006].
Correlation between the Pathological Findings and the Cochlear Function
The correlation between atrophy of the SV and the function of the cochlea was demonstrated by Makishima [1978], who reported a positive correlation between narrowing of the IAA diameter and the severity of hearing loss. In this study, no narrowing of the IAA was found in the temporal bones of normal hearing subjects. They concluded by writing that ‘spiral ganglion atrophy…was caused by chronic reduction of blood supply due to arteriolar sclerosis’ [Makishima, 1978, p. 325].
Audiol Neurotol 2014;19:256–260 DOI: 10.1159/000363215
257
Population-Based Studies
Hypertension Gates et al. [1993] found worse hearing levels among participants with hypertension (in both men and women) and higher systolic blood pressure, higher blood glucose levels and low levels of high-density lipoprotein (only among women). A study by Brant et al. [1996] found a positive correlation between higher levels of systolic blood pressure and HI in frequencies above 500 Hz in a longitudinal study. Cardiovascular Disease Friedland et al. [2009] and Gates et al. [1993] found a positive correlation between cardiovascular diseases and low-frequency hearing loss. A possible etiology could be SV atrophy, through impaired blood flow to the cochlear apex. Smoking Agrawal et al. [2009] conducted a cross-sectional survey which found that both smoking and history of DM increased the odds of having HI. Smoking and DM, with concurrent exposure to noise, were found to have a synergistic detrimental effect on hearing. This effect on HI was across all frequencies, hinting that SV damage was a possible mechanism. Cigarette smoking (both active and passive) was also found to be a risk factor for HI [Cruickshanks et al., 1998]. The odds ratio of developing a HI was proportionally increased with the amount of pack-years of smoking. The possible mechanisms correlating HI and smoking might be an impaired blood flow through increased blood viscosity and an effect on the antioxidative pathways [Cruickshanks et al., 1998; Pouryaghoub et al., 2007]. Smoking also increased hearing thresholds in a dose-dependent manner according to Fransen et al. [2008]. Pouryaghoub et al. [2007] examined the effect of smoking on noise-induced hearing loss and found higher hearing thresholds among smokers. In a prospective study, smoking history and hypercholesterolemia were found to be significant risk factors for HI [Shargorodsky et al., 2010]. Hyperlipidemia As previously mentioned, Shargorodsky et al. [2010] reported that hypercholesterolemia should be considered as a risk factor for HI. According to Rosen and Olin [1965], lower cholesterol levels were associated with better hearing among hospitalized patients. Hypertriglyceridemia was found to be a risk factor for noise-induced 258
Audiol Neurotol 2014;19:256–260 DOI: 10.1159/000363215
hearing loss [Chang et al., 2007]. On the other hand, no such association was found by Gold et al. [1989]. Diabetes Mellitus The association between DM and HI may be affected by other cofactors such as age (presbycusis), hypertension, drug use, hyperlipidemia or hypercholesterolemia. In a recent meta-analysis [Horikawa et al., 2013], it has been shown that the prevalence of HI among DM patients was 2.1 times higher than in those without DM. Regarding age, the association between DM and HI was even higher among the younger age group (
Audiol Neurotol 2014;19:256–260 DOI: 10.1159/000363215
Received: March 25, 2014 Accepted after revision: April 25, 2014 Published online: July 29, 2014
Cardiovascular Risk Factors as Causes for Hearing Impairment Yahav Oron Katya Elgart Tal Marom Yehudah Roth Department of Otolaryngology, Head and Neck Surgery, Edith Wolfson Medical Center, Sackler School of Medicine, Tel Aviv University, Holon, Israel
Key Words Hearing loss · Aging · Stria vascularis · Diabetes · Hypertension · Hyperlipidemia · Smoking
Abstract The purpose of this paper is to provide a contemporary review of the correlation between cardiovascular risk factors (CVRFs) and hearing impairment (HI). We conducted a comprehensive review of the literature in order to assess the effects of the different CVRFs on HI. We focused on the pathological findings in the inner ear and their correlation with cochlear function in population-based studies. We found that CVRFs adversely affect hearing acuity. HI diagnosis should be accompanied by detecting and treating CVRFs, according to the presented outline, which may augment hearing rehabilitation and improve the general health and the well-being of the patient. © 2014 S. Karger AG, Basel
Introduction
The major cardiovascular risk factors (CVRFs) include an older age, male gender, hypertension, hyperlipidemia, lack of physical activity, smoking, diabetes mel© 2014 S. Karger AG, Basel 1420–3030/14/0194–0256$39.50/0 E-Mail [email protected] www.karger.com/aud
litus (DM) and positive family history of coronary heart disease [Oparil and Oberman, 1999]. These CVRFs were also investigated as risk factors for the development of hearing impairment (HI). The purpose of this paper is to review the current knowledge regarding the relationship between CVRFs and HI and to suggest possible prevention and treatment options. CVRFs are usually more common among older patients, as is presbycusis. Thus, it might be difficult to distinguish the effects of age and noise exposure on hearing acuity from the effects which CVRFs might have on hearing.
Blood Supply to the Inner Ear and Auditory Nerve
The internal auditory artery (IAA) is the source of blood supply to the cochlea and to the auditory nerve. The IAA is usually a branch of the anterior-inferior cerebellar artery and it is an end artery, without anastomosis to compensate for any obstruction of the blood vessel [Baloh, 2001; Kim and Hyung, 2009] (fig. 1). The IAA feeds the stria vascularis (SV) at the lateral wall of the cochlea. At the cochlear apex this blood supply becomes sparse [Friedland et al., 2009]. The SV has a major role in the production of the endocochlear potential, which is essential for normal hearing [Wangemann, 2006]. More mediYahav Oron, MD Department of Otolaryngology, Head and Neck Surgery Edith Wolfson Medical Center PO Box 5, 58100 Holon (Israel) E-Mail oron.yahav @ gmail.com
Color version available online
Fig. 1. The arterial supply to the inner ear. Reprinted with permission from Kim and Hyung [2009].
ally, the auditory nerve is supplied also by collaterals supplying the dura mater and by a network of vessels from the anterior-inferior cerebellar artery, namely the posterior-inferior cerebellar artery and the vertebral arteries [Kim et al., 1990].
CVRFs and Their Effect on Inner Ear and Auditory Nerve – Pathological Findings
CVRFs may affect the blood supply to the cochlea and to the auditory nerve through the production of atherosclerotic plaques in the blood vessels supplying the auditory system. This change in blood flow may cause impairment in the availability of glucose and oxygen to the cochlea [Brant et al., 1996]. In an animal model (rabbits), topical papaverine prevented mechanically induced vasospasm of the IAA [Morawski et al., 2003]. Among aged adults, degenerative changes were found in the cochlea, in the auditory nerve [Rosenhall and Rubin, 1975] and in the arteries of the internal auditory canal [Fisch et al., 1972]. These observations were thought to be the reason for presbycusis. DM is one of the CVRFs which has been extensively studied. The effect of DM upon the cochlea and the auditory nerve may occur through the accumulation of sorbitol, which can adversely affect the function of the nerve through atherosclerosis of the nerve’s vasa nervosum, through angioCardiovascular Risk Factors: Causes for Hearing Impairment
pathic changes in the SV and through atrophy of the spiral ganglion and degeneration of the myelin sheath [Kakarlapudi et al., 2003]. In mice in which diabetes was induced, cochlear blood vessel thickness was found to be increased, as well as changes in the SV, collapse of Reissner’s membrane and degeneration of the organ of Corti [Costa, 1967]. In an earlier study, additional changes in the auditory nerve and Scarpa’s ganglion were noted [Cojazzi, 1950]. Examination of temporal bones of patients with DM type 2 demonstrated angiopathy and degeneration of the SV and the outer hair cells [Fukushima et al., 2006].
Correlation between the Pathological Findings and the Cochlear Function
The correlation between atrophy of the SV and the function of the cochlea was demonstrated by Makishima [1978], who reported a positive correlation between narrowing of the IAA diameter and the severity of hearing loss. In this study, no narrowing of the IAA was found in the temporal bones of normal hearing subjects. They concluded by writing that ‘spiral ganglion atrophy…was caused by chronic reduction of blood supply due to arteriolar sclerosis’ [Makishima, 1978, p. 325].
Audiol Neurotol 2014;19:256–260 DOI: 10.1159/000363215
257
Population-Based Studies
Hypertension Gates et al. [1993] found worse hearing levels among participants with hypertension (in both men and women) and higher systolic blood pressure, higher blood glucose levels and low levels of high-density lipoprotein (only among women). A study by Brant et al. [1996] found a positive correlation between higher levels of systolic blood pressure and HI in frequencies above 500 Hz in a longitudinal study. Cardiovascular Disease Friedland et al. [2009] and Gates et al. [1993] found a positive correlation between cardiovascular diseases and low-frequency hearing loss. A possible etiology could be SV atrophy, through impaired blood flow to the cochlear apex. Smoking Agrawal et al. [2009] conducted a cross-sectional survey which found that both smoking and history of DM increased the odds of having HI. Smoking and DM, with concurrent exposure to noise, were found to have a synergistic detrimental effect on hearing. This effect on HI was across all frequencies, hinting that SV damage was a possible mechanism. Cigarette smoking (both active and passive) was also found to be a risk factor for HI [Cruickshanks et al., 1998]. The odds ratio of developing a HI was proportionally increased with the amount of pack-years of smoking. The possible mechanisms correlating HI and smoking might be an impaired blood flow through increased blood viscosity and an effect on the antioxidative pathways [Cruickshanks et al., 1998; Pouryaghoub et al., 2007]. Smoking also increased hearing thresholds in a dose-dependent manner according to Fransen et al. [2008]. Pouryaghoub et al. [2007] examined the effect of smoking on noise-induced hearing loss and found higher hearing thresholds among smokers. In a prospective study, smoking history and hypercholesterolemia were found to be significant risk factors for HI [Shargorodsky et al., 2010]. Hyperlipidemia As previously mentioned, Shargorodsky et al. [2010] reported that hypercholesterolemia should be considered as a risk factor for HI. According to Rosen and Olin [1965], lower cholesterol levels were associated with better hearing among hospitalized patients. Hypertriglyceridemia was found to be a risk factor for noise-induced 258
Audiol Neurotol 2014;19:256–260 DOI: 10.1159/000363215
hearing loss [Chang et al., 2007]. On the other hand, no such association was found by Gold et al. [1989]. Diabetes Mellitus The association between DM and HI may be affected by other cofactors such as age (presbycusis), hypertension, drug use, hyperlipidemia or hypercholesterolemia. In a recent meta-analysis [Horikawa et al., 2013], it has been shown that the prevalence of HI among DM patients was 2.1 times higher than in those without DM. Regarding age, the association between DM and HI was even higher among the younger age group (
