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Health risks from exposure to noise from personal music playersVibrationVibration-induced hearing loss may be developed in patients after temporal bone surgeryor in subjects working with vibrating tools. In such cases, co-exposure to noise andvibration can increase hearing threshold shift compared to noise-only exposure.Recent studies concerning association of body vibration with sound trauma broughtcontradictory and inconclusive results (Palmer et al. 2002a, Silva et al. 2005).3.5.6.2. Ototoxic drugsSeveral drugs used in contemporary medicine can damage hearing. Ototoxic effectdepends on the dose, way of application and the type of medicine. Although these drugscan damage hearing at different levels of the auditory pathway, majority of them exertmainly cochlear ototoxic effect and they are competitive with noise in damaging haircells.The main groups of drugs that can cause hearing loss are:- antibiotics (aminoglycosides, macrolides)- antineoplastic drugs (cisplatinum, carboplatinum)- loop diuretics (furosemide, ethacrinic acid)- non-steroid anti-inflammatory drugs (acetyl salicylate acid)- antimalaric drugs.The most commonly used drugs that have been reported in the literature to result inhearing damage are aminoglycosides and anti-neoplasmatic drugs. Aminoglycosides areused parenterally in treating severe bacterial infections. After prolonged treatment withsuch aminoglycosides like gentymycin, kanamycin, amikacin, hearing loss at highfrequencies, tinnitus and vestibular disorders were noted. The changes in hearing areirreversible. Prior exposure to noise (and vibration) increases the risk of hearingimpairment due to aminoglycosides. The ototoxic effect depends on geneticallydetermined susceptibility; it increases with high concentration of ferrum ions in theblood, and low protein diet. Anti-oxidant substances (like Vitamins A, C and E) have beenshown to be protective.It has been shown that cancer chemotherapy with cis-platinum produces hearing loss inup to 31% of patients. As in noise-induced hearing loss and aminoglycoside-inducedhearing loss, these chemotherapeutics affect mainly hair cells of the basic turn in thecochlea and result in high-frequency (above 2 kHz) hearing impairment. Noise exposureat the time of chemotherapy significantly increases the risk of hearing damage.3.5.6.3. GeneticsThe advance of genetic research and associated tools triggered a series of explorations ofthe human genes possibly involved in NIHL, first evidences point to some candidategenes and seem to exclude other genes (Fortunato et al. 2004, Heinonen-Guzejev et al.2005, Yang et al. 2005, Yang et al. 2006, Van Laer et al. 2006, Yang et al. 2006,Sliwińska-Kowalska et al. 2006, Konings et al. 2007, Van Eyken et al. 2007). Themechanisms of acoustic trauma involve both metabolic stress and micromechanicaldamage to the outer hair cells, predominantly to their stereocilia. Thus, good candidategenes are those encoding oxidative stress enzymes, mitochondrial proteins, and proteinsinvolved in K + recycling pathway. The importance of oxidative stress genes has beenshown in knockout mice, including SOD1 -/- (Ohlemiller et al. 1999), GPX1 -/- (Ohlemiller etal. 2000), and PMCA2 -/- mice (Kozel et al. 2002), all of which were more sensitive tonoise than their wild-type littermates. However, these results have not been confirmed inhumans (Carlsson et al. 2005). A more recent study suggests a possible role ofpotassium recycling pathway genes in the susceptibility to NIHL in human workers (VanLaer et al. 2006).38
Health risks from exposure to noise from personal music playersSome of the differences in susceptibility to NIHL have been attributed to various othergenetically dependent factors, like eye colour (blue-eyed more susceptible), andpigmentation (African-Americans showed a somewhat better average in hearingthreshold levels than Caucasians), gender (women less susceptible than men), age, etc(Henderson et al. 1993, Pyykkö et al. 2007). Also short stature has been recentlyrecognized as a risk factor for developing sensorineural hearing impairment (Barrenäs etal. 2005).3.5.6.4. Other factorsThe gender of an individual has been often considered as a possible influencing factorwith men appearing somewhat more affected than women. The difference howeverseems minimal if present (Müller 1989).A predominance of left ear vulnerability as compared with right ear has been confirmed(Nageris et al. 2007) but the difference is small and shows mostly on average data.Cardio-vascular alteration was often studied as a possible factor influencing NIHL butdata are contradictory and the subject remains a matter of debate. Recent studies tendto confirm that alterations of blood pressure can be related with NIHL but it remainsunknown whether it might be a cause or a simultaneous effect (Souto Souza et al. 2001,Toppila et al. 2001, Narlawar et al. 2006, Ni et al. 2007). A more detailed presentation isprovided further in this report.Evidence that smoking increases the risk of NIHL were provided long ago, all recentstudies on this matter confirmed this assertion (Mizoue et al. 2003, Ferrite and Santana2005, Uchida et al. 2005, Burr et al. 2005, Wild et al. 2005, García Callejo et al. 2006,Pouryaghoub et al. 2007).Vitamin deficiencies were previously suspected to influence NIHL. Two recent studiesbrought evidence for the involvement of vitamin B12 (Quaranta et al. 2004, Gok et al.2004).The cochlear efferent innervation has long been known to be involved in NIHL. Recentstudies further showed that assessment of cochlear efferent functioning did not clearlyrelate with NIHL (Veuillet et al. 2001, Shupak et al. 2007, Wagner et al. 2005).The production of heat shock proteins constitute a physiological response to stress, firstevidence for their implication in NIHL was recently provided (Yang et al. 2004, Yuan etal. 2005).3.5.7. TherapiesMany therapies have been tried in the past with at best limited positive results. Recentprogress in cell biology has provided a wealth of new molecules with possible therapeuticpotential and several animal experiments have provided positive and promising results(as presented in another section of this report). Clinical trials over the last years havefollowed these progresses and brought preliminary results.Magnesium treatment, repeatedly found beneficial in the past, has been confirmed asefficient (Attias et al. 2004). Hyperbaric oxygenation was also confirmed as havingprotective effects (Winiarski et al. 2005) although some adverse effects have also beenreported depending on conditions of administration. Steroid administration a classicalclinical treatment for NIHL was again recently reported as beneficial (Nakaya et al. 2002,Winiarski et al. 2005).Many new drugs with anti-oxidant properties were found protective in animalexperiments, the published clinical trials however do not yet provide fully convincingevidence (Kaygusuz et al. 2001, Gok et al. 2004, Kramer et al. 2006). New drugs withanti-apoptotic properties were also shown beneficial in animal experiments, NIHL clinicaltherapy is limited at present to one positive report (Suckfuell et al. 2007).39
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