HBOT increases oxygen pressure in the inner ear. Oxygen flows from areas of higher pressure to those of lower pressure. There is a marked decrease in oxygenation of the cochlea during and after acoustic stress and in acute hearing loss. During HBOT the oxygenation in the cochlea increases up to 460% and is still 60% above normal one hour after the session is completed.
The cells of the inner ear have no direct vascular supply and depend on oxygen supplied by diffusion. With an increase of oxygen pressure in the cochlea, it is possible to affect the sensory cells of hearing. An increase in oxygen pressure can help compensate for oxygen deficiency caused by trauma and encourages healing leading to functional recovery.
The hair cells in the inner ear react to damage caused by noise, viruses, ototoxic (toxic to the ear) substances or hypoxia (oxygen deficiency). The hair cells first swell and lose their function.
This effect is reversible in cases of minor damage. In cases of severe damage, or if the swelling persists for more than one year, the hair cells are completely destroyed and are replaced by non-functioning cells.
Most studies show that HBOT is most effective in reducing hearing loss and tinnitus in the first three months following hearing loss and/or acoustic trauma. An overview of clinical studies from Germany shows HBOT as effective for hearing loss in about 50% of the cases in reducing loss by 20 dB (decibels) or more. About 11% have full recovery of hearing.
In the case of tinnitus, evaluations of 7,766 patients in the same overview showed reduction of the intensity by 50% in approximately 70% of the cases that were treated within three months. About 30% of the patients had their condition completely resolved. In 30% of patients with tinnitus lasting more than three months before treatment was initiated, a 50% improvement in the intensity of the tinnitus was shown. No improvement was seen after 12 months of chronic tinnitus.
Another study followed 50 patients that were admitted for treatment within 48 hours of sudden hearing loss. This study did not rate the severity of tinnitus but the degree of hearing loss. Thirty patients had HBOT, and twenty were given vasodilators. Of the 30 patients that received HBOT, 25 (83.3%) experienced either a very good (50% or more) or a significant (25-50%) improvement.
Many people in Germany and Europe with chronic tinnitus and hearing loss are treated with HBOT. In Germany there are approximately 80 multi-person chambers and 80% of the treatments are for inner ear dysfunction. The German Society for ENT (ear, nose, and throat) Diseases includes HBOT as one, among other, accepted treatments for symptoms of hearing loss, tinnitus, vertigo, head injury and trauma. German health insurance covers the cost of treatment in most cases.
In the U.S., Medicare, as well as other health insurance providers, covers cases of sudden deafness or noise-induced hearing loss provided that treatment is started within three months of onset. However, no coverage for tinnitus, recent onset or not, is provided.
The Germans have treated both acute and chronic hearing loss, vertigo and tinnitus (ringing in the ear) and have reported good outcomes mostly for acute conditions, with less positive results for chronic conditions.
Also to be noted is that the compression and decompression phases of HBOT can have risks for barotrauma of the inner ear. This is especially of concern in those patients treated for an acute traumatic inner ear injury to the cochlea (the hearing organ) or the semicircular canals (the balance organs). This situation calls for the slow and carefully monitored compression and decompression phases.
Tinnitus is the most common symptom associated with inner ear damage. Much of the research on this subject comes from the Federal Republic of Germany. It is estimated that more than 1% of that population, about 800,000 cases, suffers from disabling tinnitus and hearing impairment. The yearly incidence of new cases is about 15,000.60
Chronic tinnitus is often part of a triad of hearing loss, vertigo and tinnitus because of the involvement of the cochlea and the vestibular apparatus. There are various causes of tinnitus including barotrauma, hypotension, ototoxic drugs, stress, vasculopathies of the inner ear, vasomotor disorders and viral infection of the inner ear.
There is just not a particularly good medical therapy for tinnitus and HBOT has given mixed results. A study from Germany has reported an improvement rate of 60-65% with HBOT. However, a minority of the cases worsened.61
Sudden deafness develops over a period of a few hours to a few days. The incidence has been estimated to range from 5-20% per 100,000 persons per year. The most common causes for sudden deafness are injury or acoustic trauma. Conventional treatment for sudden deafness involves infusions to improve microcirculation and vasodilators. Their effectiveness is unproved, and some researchers think these therapies are more harmful than helpful. Some of the pioneering work on sudden deafness has been done by Pilgramm in Germany.62
Causes of sudden deafness include thromboembolic disease, labile hyper/hypotension, microcirculatory disturbances, viral infections and auto immunological disorders, metabolic disorders such as hyperlipidemia and diabetes, exposure to ototoxic drugs, carbon monoxide poisoning, diving injuries such as barotrauma and decompression sickness, and miscellaneous other causes including stress.
The therapeutic usefulness of HBOT in sudden deafness has been confirmed by several researchers/clinicians, but most of the studies have lacked controls. And the spontaneous recovery rate, which is as high as 90%, makes both the selection of patients and the evaluation of results very difficult.
Acute acoustic trauma is an acute impairment of hearing caused by loud, sharp sounds like that of an explosion going off nearby. Trauma involves first the outside hearing hairs and then the inside ones, possibly the rupture of cell membranes and decreased cochlear blood flow, and decrease of hearing corresponding to decreased oxygen tension in the inner ear. Damaged sensory cells can maintain themselves in a transitional phase between regeneration and cell death, a sort of stunned state. In this transitional phase HBOT may help the cells suffering from hypoxia to survive.
There are many different protocols with different pressures and durations of exposure in the clinical literature. The following protocol is recommended in the Textbook, K.K. Jain, 2004:
Begin treatment within the first three days after the episode, use ten exposures on ten consecutive days using 2.5 ATA and 10% oxygen for one hour. Published clinical data on this subject have been reviewed by Lamm (1998) and reported by Jain.
Information on spontaneous remission rates differs greatly in the references—between 25-68% for spontaneous full remissions and 47-89% for spontaneous partial remissions. Statistically, 35% and 39% of patients experienced no success with non-steroidal drugs and placebo, respectively. These patients can still be helped with HBOT.
If the onset of symptoms is more than two weeks but no longer than 6 weeks, one half of the cases showed a marked hearing gain (more than 20 dB), one-third showed a moderate improvement (10-20 dB), and 13% showed no improvement. Four percent no longer experienced tinnitus, 81.3% showed an intensity decrease, and 1.2% had an increase in intensity. Thirteen and one-half percent remained unchanged. The results go down if therapy is done after 6 weeks but before 3 months but the condition is improved—about 30% improve. About 50% showed an improvement in tinnitus symptoms. If treatment is started after three months up to several years, no hearing improvement can be expected in the majority of patients. However, one-third of those patients reported a decrease in intensity of tinnitus.
60Jain, 2004, 373.