Feature

Tinnitus, a Military Epidemic:
Is Hyperbaric Oxygen Therapy the Answer?
ABSTRACT
Tinnitus is the phantom perception of sound in the absence of overt acoustic stimulation. Its impact on the military population is alarming. Annually, tinnitus is the most prevalent disability among new cases added to theVeterans Affairs numbers. Also, it is currently the most common disability from the War on Terror. Conventional med-ical treatments for tinnitus are well documented, but prove to be unsatisfying. Hyperbaric oxygen (HBO2) therapy may improve tinnitus, but the significance of the level of improvement is not clear. There is a case for large ran-domized trials of high methodological rigor in order to define the true extent of the benefit with the administration ofHBO2 therapy for tinnitus.
THE PHYSIOLOGY OF HEARING
Hearing is a series of events in which sound termittently. Tinnitus can be caused by or accompany waves in the air produce electrical signals and cause many conditions, including presbycusis, Meniere’s dis- nerve impulses to be sent to the brain where they are in- ease, otosclerosis, head injury, cerebellar-pontine angle terpreted as sound. The auditory system consists of the tumors, otitis media, meningitis, dental disorders, and external, middle, and inner ears, as well as the central certain medications. However, most tinnitus is due to auditory pathways in the brain. Sound waves enter the noise induced sensorineural hearing loss with result- external ear via the pinna and reach the middle ear ing dysfunction within the auditory system.2, 5, 6 where they strike the eardrum and cause it to vibrate.
The presence of tinnitus often is an early indi- The vibrations set the middle-ear bones (malleus, cator of cochlear hair cell dysfunction or loss, as in the incus, stapes) in motion. Movement of the stapes case of excessive noise exposure.3 The pathogenesis is causes pressure waves in the fluid contained within the assumed to consist of micromechanical traumatic and cochlea, which contains the organ of Corti, the sensory biochemical-metabolic damage to the outer hair cells.3 organ for hearing. The primary sensory receptors for Studies have shown how hair cells of the inner ear hearing, the inner hair cells, are found within the organ react to damage caused by noise.7,8 In acoustic trauma, of Corti as are the outer hair cells, which primarily fa- defined as an acute impairment of hearing caused by cilitate the sensory response of the inner hair cells.1 sharp sounds, like that of a gun going off, the partial The fluid in the cochlea moves the top portion of the pressure of oxygen decreases significantly in the fluid hair cells, called the hair bundle, which initiates the spaces of the inner ear.7 Morphological damage re- changes that lead to the production of the nerve im- sults, leading to intra and extracellular ion imbalances pulses. The nerve fibers connected to the hair cells, pri- marily the inner hair cells, are excited and transfer the swelling and structural damage of the dendrites, alter- auditory information to the brain where they are inter- ations of mitochondria and the cell-structure, separa- tion of hair-cells from tectorial membrane, oedema ofthe endothelium, and oedematous closure of functional THE ETIOLOGY OF TINNITUS
endarteries with blocking of the microcirculation.7 If Tinnitus, the perception of sound in the ab- the swelling persists for a prolonged period, the hair sence of an external source, is a chronic and debilitat- cells degenerate and are replaced by non-functioning ing condition often described as ringing, hissing, endothelial cells.7,9 PET scanning and functional MRI buzzing, chirping, high-pitched squealing, or roaring studies indicate that the loss of cochlear input to neu- in the ears or in proximity to the head.2-4 According to rons in the central auditory pathways (such as occurs the National Research Council, tinnitus is considered a with cochlear hair cell damage due to noise trauma) symptom rather than an illness.2 The perceived noise can result in abnormal neural activity in the auditory can be within one or both ears, within or around the cortex.3 Such activity has been linked to tinnitus. It is head, or perceived as an outside distant noise. It can be important to note, that sounds of moderate intensity as pulsatile or nonpulsatile and be continuous or occur in- encountered in everyday life usually do not affect the oxygen tension within the cochlea.7 As tinnitus is usu- posed to 157-163dB and a gunner with a machine gun, ally accompanied by hearing loss, similar mechanisms 145dB.2,5,10,12 Those suffering from an improvised ex- plosive device (IED) are exposed to impulse noise inexcess of 180dB.13 THE CHARACTERISTICS OF NOISE
Duration is defined as the length of time you Noise, defined medically as an intense sound are exposed to a noise. The louder the sound and more capable of producing damage to the inner ear, leads to prolonged the exposure, the shorter amount of time it one of the most common conditions evaluated by oto- takes to cause hearing damage. For unprotected ears, laryngologist: noise induced hearing loss (NIHL).
the allowed exposure time decreases by one half for Noise can be further categorized as impulse noise, the each 5dB increase in the average noise level.5,14 For product of explosive devices, or impact noise, caused instance, exposure is limited to eight hours per day at by a collision of two hard surfaces. However de- 90dB, four hours per day at 95dB, and two hours per scribed, both are produced by a sudden intense sound day at 100dB. The highest permissible noise exposure wave capable of causing inner ear damage. Excessive for the unprotected ear is 115dB for 15 minutes per noise exposure is the most common cause of hearing day.5,14 Sounds of less than 75dB, even after long ex- loss.2,5,6 When an individual is exposed to sounds that posure, are unlikely to cause hearing loss.
are too loud or loud sounds over a long period of time, Hearing loss that results from exposure to sensitive structures of the inner ear can be damaged, sound with energy spread across a wide range of fre- resulting in NIHL. In humans, outer hair cells are usu- quencies, such as impulses common to military set- ally the first type of sensory cell to be damaged.2 As tings, is often characterized by a gradual increase in the hearing loss progresses and becomes more per- threshold as frequencies increase. The hearing loss manent, the degeneration involves both outer and typically reaches a maximum between 3000 and 6000 inner hair cells. As the number of hair cells decreases, hertz (Hz), followed by a return toward normal hearing so does an individual’s hearing. With severe perma- at still higher frequencies. This pattern of hearing loss nent hearing losses, both sensory and supporting cells is often referred to as the “noise-notch” audiogram and of the organ of Corti are missing. In these cases, the is a clinical hallmark often used to distinguish noise-re- degenerative layer of the organ of Corti is replaced by lated hearing loss from that associated with other eti- an undifferentiated layer of squamous epithelium and ologies, such as ototoxic medications or aging.2 the sensory nerve fibers are destroyed.9 The type andamount of the resulting hearing loss are typically de- CHRONIC NOISED-INDUCED HEARING LOSS AND
termined by the following acoustic parameters: the in- ACOUSTIC TRAUMA
tensity of the noise, the duration of exposure to the Chronic NIHL is a disease process that occurs gradually over many years of exposure to less intense Intensity of sound is measured in units called noise levels. It is generally caused by long term expo- decibels (dB), a measurement of the amount of energy sure to high intensity continuous noise with superim- or air pressure moving from the source to our ear.10,11,20 posed episodic impact or impulse noise. The hearing The faintest sound humans with normal hearing can loss associated with chronic NIHL is variable between detect has a value between zero and ten decibels, and individuals, but the principal characteristics remain rel- the loudest sound the human ear can tolerate without pain is about 120 decibels.10 Decibels are measured • It is always sensorineural affecting the hair cells in logarithmically, being 20 times the log of the ratio of a particular sound pressure to a reference sound pres- • It is nearly always bilateral and symmetric.
sure. This means that as decibel intensity increases • It will only rarely produce a profound loss.
by units of 20, each increase is 10 times the lower fig- • It will not progress once noise exposure is stopped.
ure. Thus, 20 decibels is 10 times the intensity of 0 • The higher frequencies (3000-6000Hz) are more af- decibels, and 40 decibels is 100 times as intense as 20 fected than the lower frequencies, with the greatest decibels.20 The Navy considers any sound above 84dB as noise hazardous and having the potential to • Continuous noise is more damaging than intermit- cause hearing damage if it is loud enough or lasts long enough.4,5,10,12 The higher the intensity of the sound, • Tinnitus is often associated with NIHL.
the greater its potential to cause hearing damage. Sin-gle exposures to impulse noises above 140 decibels One exception to these features would be the have the potential to cause permanent damage.4 Ac- individual who had significant noise exposure second- cording to the U.S. Army Center for Health and Pre- ary to rifle shooting. In this case, an asymmetrical loss, ventative Medicine, a gunner on a 105 millimeter with the ear nearest the gun barrel demonstrating towed howitzer experiences an impulse noise of slightly worse hearing, would be expected.14 183dB.2,4 A servicemember who shoots a rifle is ex- Journal of Special Operations Medicine Volume 9, Edition 3 / Summer 09 The development of chronic NIHL progresses gunfire and explosive detonations suggest that im- through two phases. A brief hearing loss, more com- pulse/impact noise is likely to precipitate tinnitus as- monly referred to as a temporary threshold shift (TTS), sociated with acoustic trauma, excessive noise characterizes the first stage. It occurs after noise ex- exposure, and NIHL.2,4,6,10,12 According to research posure and completely resolves after a period of rest.
published in the December 2005 issue of American Often reported as auditory fatigue, most studies indi- Journal of Audiology (AJA), Soldiers sent to battle cate that it is associated with no sensory cell damage or zones are over 50 times more likely to suffer NIHL loss minimal, reversible cell changes.14,18 Eventually, after and/or tinnitus than Soldiers who do not deploy.21 Ac- repeated exposure to noises intense enough to produce cording to a report released in 2007 by the House Ap- TTS, a permanent threshold shift (PTS) will occur.
propriations Subcommittee on Military Quality of Life, This is an irreversible increase in hearing thresholds as a result of ongoing combat operations, one in three and defines the second stage of chronic NIHL. At this post-deploying Soldiers report acute acoustic trauma point, there has been irreversible hair cell damage.5,14,18 and one in four report hearing loss and/or hearing com- In contrast to chronic NIHL, acoustic trauma refers to a sudden permanent hearing loss caused by a From World War II and well through the Viet- single exposure to an intense sound. It occurs when nam War, hearing damage has been a leading disabil- excessive sound energy strikes the inner ear. Exposure ity. According to the Department of Veterans Affairs, to noise from firearm use during military service is hearing damage is the number one disability in the War probably the most frequent etiology of acute acoustic on Terror, with some experts predicting the true toll trauma worldwide; therefore, it may be regarded as a could take decades to become clear.13 According to the professional disease in military populations.19 The American Tinnitus Association (ATA), more will be sound pressure levels capable of causing acoustic spent on veterans’ disability compensation for tinnitus trauma vary between individuals but average around and other hearing conditions over the coming years 130-140dB.14 The hearing loss is sudden, sometimes than for any other medical injuries from the Iraq and painful, and is often followed by a new onset of tinni- Afghan wars.4 Between 2000 and 2005, the number of tus. For the vast majority of patients, tinnitus presents veterans with tinnitus disabilities more than doubled as the most annoying symptom, with the risk for per- and the amount paid to veterans with tinnitus disabili- manent tinnitus being considered more critical for the ties went up more than two-and-a-half times.4,22 patient than any degree of hearing loss resulting from Presently, tinnitus is the most prevalent disability acoustic trauma.19 Although the audiogram may show among new cases added to Veterans Affairs numbers; the typical 3000-6000Hz sensorineural notch seen with nearly 70,000 of the more than 1.3 million troops who chronic NIHL, down-sloping or flat audiograms that have served in Afghanistan and Iraq are collecting dis- affect a broad range of frequencies are more com- ability for tinnitus.13,23 In fact, recent studies demon- mon.2,14,20 Direct mechanical injury to the sensory cells strated that 49-50% of all Soldiers exposed to explosive of the cochlea is thought to be the mechanism of injury blasts in Iraq and Afghanistan had tinnitus and 60% had tinnitus, often related to hearing loss.4,13,22,24 The Noise exposure and NIHL are the most com- number of servicemembers on disability because of mon cause of tinnitus.2,5,6 The relationship between hearing damage is expected to grow 18% a year, with noise exposure, NIHL and tinnitus has been addressed payments totaling $1.1 billion annually by 2011.4,13 in a number of articles. A review of these studies was The economic consequences to the military for presented by Axelsson & Barrenas, 1991, and it was hearing impairment, to include tinnitus, include lost found that noise exposure and NIHL were by far the time and decreased productivity, loss of qualified most common cause of tinnitus; if “acoustic trauma” workers through medical disqualification, military dis- was included, at least one-in-three cases were caused ability settlements, retraining, and expenses related to by noise.6 Tinnitus may occur following a single ex- medical treatment such as hearing aids and audiomet- posure to high-intensity impulse/impact noise (a short ric testing.10 While the economic consequences are sig- burst of acoustic energy which can either be a single nificant, the military implications in a combat zone can burst or multiple bursts of energy), long-term exposure to repetitive impulses, long-term exposure to continu- A study published in the Army RD&A Bulletin ous noise, or exposure to a combination of impulses in 1990, concluded that those with hearing impairments were 36% more likely to hear the wrong command, and30% were less likely to correctly identify their target. 4 THE “IMPACT” OF NOISE ON THE MILITARY
Additionally, it was noted that Soldiers with hearing A staggering number of Soldiers and Marines impairments only hit the enemy target 41% of the time, caught in roadside bombings and firefights in Iraq and while Soldiers without hearing impairments hit the Afghanistan are coming home with ringing in their enemy target 94% of the time. Those with hearing im- ears. High rates of tinnitus among patients exposed to pairments were 8% more likely to take the wrong tar- get shot and 21% more likely to have their entire tank role of HBO2 in the treatment of tinnitus was investi- gated in the past: Pilgramm et al. in 1985, firstly, and Hearing damage has been a battlefield risk Schumann et al. in 1990, secondly, reported about ever since the introduction of explosives and artillery, HBO2 usefulness in tinnitus treatment, reporting an and the U.S. military recognized it in Iraq and improvement of 62.2% in 557 patients’ tinnitus after Afghanistan and issued earplugs early on. But the receiving 10 applications of HBO2 therapy.25,27 While sheer number of injuries and their nature, particularly skepticism remains high in the Untied States, physi- the high incidence of tinnitus, came as a surprise to cians in Germany and Japan continue to recognize its military specialists and outside experts. According to clinical applications in diseases of the inner ear and VA figures, despite all that has been learned over the have demonstrated improved outcomes in the treat- years, U.S. troops are suffering hearing damage at ment of acute acoustic trauma, NIHL, and tinnitus about the same rate as World War II veterans.13,21 using HBO2 therapy.7,26 The rationale for this therapy Given today’s unpredictable weaponry (i.e. roadside is based on the oxygen transportation mechanism in bombs), even the best hearing protection is only partly effective, and only if it’s properly used. The basis for hyperbaric oxygenation is the It makes more sense to prevent hearing dam- breathing of pure oxygen at a pressure which is in- age than to provide a lifetime of disability, but even creased compared to atmospheric pressure (1.0 hearing protection has its limits and it is important to ATA).9,26,28-30 The effectiveness of high pressure oxy- note that some hearing impairments are unavoidable gen therapy is based on raising the partial pressure of despite use of hearing protection and other measures.
oxygen in the blood and thus the pressure difference Some exposures are so extreme that they will exceed to tissue. The concentration of oxygen in the atmos- the protective capability of hearing protective devices.
phere is 21%. At 1.0 ATA, the oxygen in blood is al- As previously noted, damage can occur at 85 decibels.
most entirely carried by hemoglobin. Because The best protection cuts that by only 20-25dB.13 That hemoglobin is approximately 97% saturated under nor- is not enough to protect the ears against an explosion mal conditions, greatly increasing the oxygen-carry- or a firefight, which can range upwards of 180+ dB.
ing capacity of blood by increasing hemoglobin Furthermore, much of the fighting consists of am- bushes, bombings, and firefights, which come sud- During hyperbaric oxygen therapy the patient denly and unexpectedly, giving Soldiers little time to sits inside a pressurized chamber. Air pressure inside use their issued hearing protection. In addition, some the chamber is increased up to 2.5 times normal at- Infantrymen resist or refuse to wear their hearing pro- mospheric pressure at sea level (2.5 ATA). The patient tection for fear of dulling their senses and missing crit- then breathes pure oxygen from a mask. Inhalation of ical commands or sounds that can make the difference hyperbaric oxygen can enhance the amount of oxygen carried in blood by increasing the quantity of oxygendissolved in plasma. When breathing 100% oxygen at a surrounding pressure of 2.5 ATA, the quantity of dis- 2 THERAPY EFFICACY IN TINNITUS
Medical treatments for tinnitus are well docu- solved oxygen in 100ml of plasma increases from mented and there is probably no other disease for 0.3ml, to 6.8ml, which is approximately 20 times which such a variety of treatments have been proposed.
Yet, still today, many different treatment regimens are The driving force for oxygen diffusion from being propagated. Vasodilators, vitamins, steroids, an- the capillaries to tissue can be estimated by the differ- ticoagulants, heparin, histamine, tranquillizers, diuret- ence between the partial pressure of oxygen on the ar- terial side and the venous side of the capillaries. The carbogen, and stellate ganglion block.3,25 Whether ap- difference in the partial pressure of oxygen from the plied separately or together, all have demonstrated lim- arterial side to the venous side of the capillary system ited effectiveness at best. Experimentally, rheological is approximately 37 times greater when breathing agents and plasma expanders neither cause an im- 100% oxygen at 3.0 ATA than air at 1.0 ATA.29 provement in inner ear blood supply nor result in a The increased tissue oxygenation achieved higher oxygen supply in the inner ear.26 In addition, during HBO2 therapy can support poorly perfused and two forms of tinnitus rehabilitation are currently being hypoxic areas. Under this increased pressure, the prescribed, tinnitus masking and psychological treat- amount of dissolved oxygen is sufficient, even with- ment; both offer symptomatic treatment, with the goal out hemoglobin, to supply body tissues with oxygen of treatment being only to lessen the awareness of tin- by diffusion. With an increase of the pressure of oxy- nitus and its impact on quality of life.
gen in the inner ear, it is possible to influence the au- Since the end of the 1960s, hyperbaric oxygen ditory sensory cells (inner and outer hair cells) and the peripheral auditory nerve fibers.30 These cells have no 2) therapy has been used experimentally for cer- tain acute and chronic illnesses of the inner ear.25 The direct vascular supply and depend entirely on oxygen Journal of Special Operations Medicine Volume 9, Edition 3 / Summer 09 supplied by diffusion. During exposure to HBO2 ther- author of this paper was unable to identify any addi- apy, the oxygenation in the cochlea increases by 460- tional studies that met all the criteria, but was able to 600% and is still 60% above normal one hour after find a number of prospective and retrospective studies termination of the therapy.9,26,30 An increase in oxygen evaluating the benefits of HBO2 therapy for the treat- pressure can compensate for oxygen deficiency caused by trauma and gives rise to biological mechanismswhich can facilitate cellular and vascular repair.9,30 Ad- PROSPECTIVE STUDIES
ditionally, HBO2 therapy has been shown to improve Two of the randomized controlled trials, iden- hemorheology by causing a reduction in hematocrit, a tified by Bennett et al., reported on improvements in reduction of platelet aggregation, and an increase in the tinnitus for patients with an early/acute presenta- flexibility of erythrocytes.31 Hyperoxia has also been tion.15,16,26 The Hoffmann et al. 1995a trial contributed shown to reduce edema by reducing vascular perme- 20 subjects with idiopathic sudden sensorineural hear- ability and causing a rapid and significant vasocon- ing loss (ISSHL) with or without tinnitus; all subjects had no improvement after 14 days of pharmacological HBO2 is considered a relatively benign inter- treatment with hydroxyethyl starch, pentoxifylline, and vention with few adverse effects. Visual disturbance, cortisone. The Schwab et al. 1998 trial contributed 33 usually reduction in visual acuity secondary to confor- subjects with sudden hearing loss and tinnitus seen mational changes in the lens, and barotrauma, affecting within two weeks of onset of tinnitus and without any the middle ear, are the most frequently reported com- prior therapy. In each study the HBO2 group’s therapy plications.15,16,29 The majority of patients recover spon- consisted of 100% oxygen at 1.5 ATA for 45 minutes taneously over a period of days to weeks from their daily, five days each week for two to four weeks (10 to visual disturbances and most episodes of barotrauma 20 sessions). The control groups underwent no treat- do not require the therapy be abandoned. Barotrauma ment. While the two trials reported a greater mean im- of the middle ear can be treated by placement of pres- provement in tinnitus (using a visual analogue scale sure equalization tubes or milder cases with deconges- between 0 and 10) in the HBO2 arm compared to the tants and/or instruction regarding pressure equalization control arm, statistical pooling was not possible due to techniques. Less commonly, estimated only to occur in the authors neglecting to report the standard deviation one in 5,000 to 11,000 treatments, HBO2 may be asso- around the means. As a consequence, clinical signifi- ciated with acute central nervous system oxygen toxi- city.15,16,29 Exposure to 100% oxygen at 3.0 ATA for The third article considered suitable, by Hoff- three hours induces grand mal seizures in most people; mann et al. 1995b, was the only randomized human at less than 3.0 ATA, seizures are rare.29 Oxygen-in- controlled trial reporting on improvements in tinnitus duced seizures are typically benign and produce no for patients with a chronic presentation.15,16 This study long-term sequelae. Additional complications include contributed 44 subjects with ISSHL and tinnitus for barotraumas affecting the dental cavities and sinuses, longer than six months. HBO2 therapy consisted of pulmonary barotraumas, drug reactions, and injuries or 100% oxygen at 1.5 ATA for 45 minutes daily, five death related to chamber fires. Decompression sick- days each week for three weeks. The control group ness can also occur, though rare in patients breathing breathed air at 1.5 ATA on the same schedule as the HBO2 group. While the HBO2 therapy group did demonstrate some improvement in tinnitus, the im- CURRENT LITERATURE
provement did not reach statistical significance: The evidence for HBO2 therapy for acute and p=0.12.15,16 chronic tinnitus based on randomized controlled trials In each of these studies the HBO2 therapy con- is poor. In July 2004, Bennett et al. underwent an ex- sisted of breathing 100% oxygen at 1.5 ATA for 45 tensive search of what they considered to be “suitable” minutes. In studies reporting significant improve- randomized human trials assessing the outcome of tin- ments, HBO therapy consisted of breathing 100% oxy- nitus with HBO2 therapy. The inclusion criteria con- gen at 2.0 to 2.5 ATA for 90 minutes.
sisted of a randomized controlled study, a review with In 2007, a comparative trial by Porubsky et al.
new data, was not a comparative trial in which all sub- evaluating the influence of time interval from the onset jects/groups received HBO2 therapy, subjects were ran- of tinnitus until the first HBO2 therapy was published.31 domly allocated, and report was not a case study.15,16 In addition to time interval, the study compared the in- The initial search identified six randomized human tri- fluence of other factors: treatment protocols, gender, als meeting the criteria. However, after appraisal of the noise characteristic, and pretreatment expectations.
full report, three articles were excluded because they This author will only comment on treatment protocols did not contain new data. A follow-on search was con- and time interval from tinnitus onset to treatment.
ducted by Bennett et al. in 2006; no additional studies In this study, 360 patients suffering from tin- were identified.16 Using the same inclusion criteria, the nitus were randomized into two HBO2 treatment pro- tocols: group A: 2.2 ATA for 60 minutes and group B: from the onset of their tinnitus, reported improvement.
2.5 ATA for 60 minutes. Both series were administered Of the 39, how many were treated within three months once a day for 15 consecutive days; 156 patients un- from the onset of their tinnitus, and if added to those derwent protocol A and 156 protocol B. Forty-eight who demonstrated improvement if treated within two patients were treated inconsistently, leaving out single weeks from the onset of their tinnitus, would a signif- days of treatment. No patient had less than twelve icant difference between time intervals be seen? HBO2 sessions. One month after the end of HBO2 In a study published in 2003 by Narozny et al., treatment, the therapeutic effect was evaluated ac- 61 patients with tinnitus (29 acute, 32 chronic) under- cording to the patient’s subjective assessment of tinni- went HBO2 therapy with simultaneous pharmacother- tus. A non-treatment control group was not indentified.
apy (group A).25 HBO2 therapy was administered once In 92 patients HBO2 therapy was started within the daily at a pressure of 2.5 ATA for 90 minutes (three pe- first two weeks after the onset of tinnitus; in 93 there riods of 20 minutes with two five-minute air breaks was a delay between two weeks and six months; in 41 and 20 minutes needed for compression and decom- cases the delay was 6-12 months; and in 126 patients pression). The patients breathed 100% oxygen more than one year elapsed between the onset of tin- throughout the treatment with exception of the two nitus and HBO2 treatment. Eight patients did not an- five-minute air breaks. Patients with acute tinnitus un- derwent 15 + 6 HBO2 expositions, patients with A complete remission of tinnitus was reported chronic tinnitus 18 + 6 expositions. Before, immedi- by 12 (3.3%) subjects, 122 (33.9%) felt a decrease in ately, and six months after the end of treatment, the intensity, 157 (56.3%) patients did not notice any level of tinnitus was assessed by means of a visual ana- changes and 25 (6.9%) patients complained that their log scale (VAS), Vernon’s tinnitus severity scores tinnitus became louder after HBO2.31 Out of the 12 pa- (VTSS), and questionnaire by Tyler and Baker. The tients who had a complete remission of tinnitus, 10 obtained results were compared with 122 patients (83.3%) had HBO2 within the first two weeks after the (group B) with tinnitus (70 acute and 52 chronic) onset of tinnitus and two (16.6%) later than two weeks treated only pharmacologically. Tinnitus improvement but within the first six months. Out of the 122 patients after therapy was stated by comparison of tinnitus level who felt that their tinnitus had lessened, 37 (30.3%) before and after therapy (in percentage).
had HBO2 therapy within the first two weeks after the Satisfactory improvement of tinnitus loudness onset and 39 (31.9%) were treated within the first six (more than 50% in comparison to primary state), using months. Only nine (7.4%) who started HBO2 six to the VAS, was demonstrated in 58.6% of patients with twelve months after the onset of tinnitus had improve- acute tinnitus in group A. Of the 58.6% who demon- ment and thirty-four (27.9%) felt a lessening of tinni- strated satisfactory improvement, 41.4% showed ex- tus after more than twelve months delay until HBO2.31 cellent improvement (75% to 100%) and 17.2% The authors determined there was no statisti- showed some improvement (50% to 75%). No im- cally significant difference between treatment groups provement (less than 50%) was seen in 41.4% of the A and B (p > .05). Furthermore, they concluded there acute tinnitus patients in group A. Comparative analy- is no statistically significant difference between the sis of group B subjects with acute tinnitus reflected time intervals until the start of HBO2 therapy.31 41.4% with satisfactory improvement, 30.0% with ex- This study compared a treatment protocol of cellent improvement, and 11.4% with some improve- 2.2 ATA for 60 minutes to a treatment protocol of 2.5 ment. No improvement was noted in 58.6% of the ATA for 60 minutes. This study could have been en- acute tinnitus patients in group B. Satisfactory tinni- hanced if it would have compared two groups in which tus improvement in patients with chronic tinnitus there was a bigger difference between treatment pro- (group A) was 81.3%, 6.3% with excellent improve- tocols (i.e. one group breathing 100% oxygen at less ment, and 75.0% with some improvement. No im- than 2.0 ATA) and/or included a non-HBO2 therapy provement was noted in 18.7%. Comparative analysis control group. Additionally, the study grouped patients of group B subjects with chronic tinnitus revealed into a treatment group receiving therapy within the first 65.4% with satisfactory improvement, 25.0% with ex- two weeks after onset of tinnitus and one in which the cellent improvement, and 40.4% with some improve- patient received therapy later than two weeks but ment. No improvement was noted in 34.6% of the within the first six months. Again the authors reported chronic tinnitus patients in group B.25 Similar results no statistical significant difference between the time were obtained by VTSS and questionnaire. After six intervals until the start of HBO2 therapy. Most studies months, there was an inconsiderable regression of the group subjects into those suffering from tinnitus for positive effect of therapy, especially in patients with three months or less and those suffering from tinnitus chronic tinnitus, in group A as well as in group B.
for greater than three months, but less than six months.
The authors (Narozny et al.) concluded HBO2 Of the 122 patients treated, 39 (31.9%) who were therapy may contribute to the treatment of tinnitus, par- treated within the first six months, but after two weeks ticularly its chronic severe form. Their results were Journal of Special Operations Medicine Volume 9, Edition 3 / Summer 09 similar to those of other authors, indicating that HBO2 In another study published in 1997 by Kau et therapy can reduce tinnitus even if it has been present al.,26 355 patients with tinnitus, who had not responded to treatment with medications, were given HBO2 ther- The authors reported the wrong data for the apy. Of the 355 patients, 192 suffered from tinnitus for acute tinnitus group B patients in their results section less than three months and 163 suffered from tinnitus and unfortunately based their conclusions using the in- for more than three months. HBO2 therapy consisted correct data. Using the correct data (shown in Table 2 of a pressure increase phase of 20 minutes, at the end of there study) HBO2 therapy is shown to be more ben- of which a diving depth of 2.5 ATA was reached. This eficial in the acute tinnitus stage (group A compared to pressure was held for 70 minutes which was then fol- group B) than it is in the chronic stage (group A com- lowed by an ascent phase lasting 20 minutes. Pure pared to group B). While there is a 17.2% difference in oxygen was inhaled by mask during the entire treat- satisfactory improvement in acute tinnitus patients com- ment period. The number of treatments was not re- paring group A to group B, there is only a 15.9% dif- ported and a non-HBO2 therapy control group was not ference in satisfactory improvement in chronic tinnitus identified. Subjective evaluation of tinnitus was ex- pressed by means of a visual analog scale.
In a prospective controlled study conducted by For the patients in whom the first episode of Biesinger et al.(1998), 211 cases of acute tinnitus (tin- tinnitus was within three months before HBO2 therapy, nitus for less than three months) were assessed after re- excellent improvement was seen in 6.7%, noticeable ceiving one of three treatment protocols.32 Of the 211 improvement in 44.3%, unchanged in 44.3%, and a cases of acute tinnitus, 69 patients were treated with temporary increase in the severity of tinnitus in haemodilution and cortisone alone and had no HBO2 4.7%.26,30 Patients who had tinnitus for more than three therapy. Of the 142 patients that had HBO2 therapy, 72 months before HBO2 therapy showed a less favorable of these were after unsuccessful haemodilution. response. In none of the patients did the tinnitus fully Of the 69 cases in which the patients received resolve. Noticeable improvement was reported by haemodilution only, 36.2% healed completely, 38.8% 34.4% of the patients, no change in tinnitus was ap- cases did not notice a change, and 25% of the patients preciated by 62% of the patients and an intermittent in- reported a decompensation. Of the 142 cases receiving crease was reported by 3.6% of the patients.26,30 HBO2 therapy, 64.1% healed completely, 17.9% expe- The authors feel the results justify the position rienced no change, and 18% reported a decompensa- that patients, who have been treated unsuccessfully by tion. Out of the 72 cases receiving HBO2 therapy after “conventional” means, may still have a chance of im- failure of haemodilution, 51.4% healed completely, provement in their symptoms when they can be given whereas 37.5% reported improvement, 11.1% experi- HBO2 therapy within three months of the onset of their enced no change in their tinnitus, and 0% of the cases worsened.7,32 The results demonstrated a better outcome In 1997, an article by Bohmer was published for patients with acute tinnitus if they received HBO2 reporting on two prospective studies conducted at the therapy, especially the high rate of decompensated tin- Institute for Hyperbaric Medicine, Orthopaedic Uni- nitus in patients receiving solely haemodilution.
versity Clinic, Frankfurt, Germany.28 In the first study, In a study published in 1997 by Delb et al.,33 a 47 patients received HBO2 therapy within three months total of 193 patients, having undergone and failed pri- of tinnitus first occurring. In each case they received mary intravenous hemorheologic therapy, were treated pharmacotherapy often combined with cortisone prior with HBO2 therapy. Tinnitus was evaluated before, to undergoing HBO2 therapy. In 64% of the cases an after ten sessions, and after 15 sessions using a tinnitus improvement was attained. During the follow-up ex- questionnaire. Measurable improvements of the tinni- aminations 27% of the patients confirmed a further de- tus occurred in 22% of the patients, moderate improve- crease of the ringing in their ears during the two ment in 17% of cases, excellent improvement in 10.4% of cases and complete resolution in two patients.33 In the second study, 381 patients underwent Though clinical significance was not reported, the im- HBO2 therapy for the treatment of their tinnitus. On provement rate decreased in those cases where the time average 15 single treatments for 90 minutes with a from onset of tinnitus exceeded 40 days. In addition, pressure of 2.2 to 2.5 ATA were carried out. Daily, at while the improvement rate slightly increased in pa- the same time each day, the patients were asked to sub- tients receiving 15 sessions compared to those receiving jectively annotate their sound volume. Complete res- 10 sessions, the clinical significance, once again, was olution of tinnitus was seen in 3.9% of the patients.
not reported. The authors concluded that HBO2 ther- Noticeable improvement was seen in 34.1%, slight im- apy seems to be a moderately effective additional treat- provement in 31.8%, no improvement in 28.1%, and ment in the therapy of tinnitus after primary worsening of tinnitus in 2.1% of the patients.28 With hemorheologic therapy, provided the time from onset of HBO2 therapy, the improvement of tinnitus sound from “becoming less” to “being completely healed” was ap- preciated in the first six months of tinnitus first occur- for tinnitus than on any other disability, with payments ring. The major advances starting with “unbearably expecting to reach $1.1 billion annually by 2011.4,13 loud” to “bearable” were made during the first two to A considerable number of therapies have been proposed since tinnitus first appeared in medical liter- The author recommends that HBO2 therapy ature. However, the results of established, conserva- should be liberally applied when infusion therapy tive medical treatment regimes for tinnitus are shows no success. Even after four to six months suc- unsatisfying. It has been shown that common pharma- cessful results were obtained with tinnitus patients.28 cological treatment does not yield better results thanplacebo therapy.30,31,36 The knowledge of hyperbaric RETROSPECTIVE STUDIES
oxygen therapy for the hyperoxygenation of tissue has In 1998, Lamm et al., and in 2003, Lamm re- led to further development of medical indications over ported on a retrospective meta-analysis of 50 clinical the past 50 years. Indications for ENT therapy include studies carried out on a total of 4,109 patients who re- decompression trauma of the inner ear, idiopathic sud- ceived HBO2 therapy following unsuccessful conven- den hearing loss, acute acoustic trauma, acute noise- tional treatment with drugs for patients suffering from induced hearing loss, osteoradionecrosis and tinnitus.30,34 Providing the onset of the disorder was osteomyelitis, otogenic infection of the skull base, and longer than two weeks but not longer than six weeks, otitis externa maligna.30 HBO2 treatment increases the 4% of the patients suffering from tinnitus reported inner ear pO2; decreases hematocrit, plasma viscosity, complete resolution, 81.3% observed a decrease in tin- and platelet aggregation, and improves microcircula- nitus intensity, 13.5% reported no change and 1.2% re- tion.29,30,37 In spite of its clear-cut rationale, an effec- ported a temporary increase in tinnitus.30,34 These tiveness of HBO2 therapy has not been objectively results were confirmed in some of the prospective stud- documented for tinnitus and its use in the United States ies described above as well as additional studies by has not been widely applied (this is not approved by Nakiashima et al. (1998), Shiraishi et al. (1998) and the Undersea and Hyperbaric Medicine Society). Due Murakawa et al. (2000).26,33 The authors concluded to the low number of recognized, controlled, double- that HBO2 therapy is recommended and warranted in blind clinical trials demonstrating the effectiveness of those patients treated within three months of the onset HBO2 therapy for tinnitus, this therapy lacks official recognition and skepticism remains high. In a retrospective evaluation of 7766 patients methodological quality in many of the reported trials, in 13 publications showed reduction of the molestation variability and poor reporting of entry criteria, the in- and intensity of tinnitus by 50% in approximately 70% consistent nature and timing of outcomes, and poor re- of the cases (30%-88%) if treated within the first three porting of both outcomes and methodology make months.7,9,35 Chronic tinnitus with duration of more comparisons and meta-analysis impossible. In addi- than three months or bilateral manifestation showed tion, treatment protocols and patient inclusion criteria improvement rates of 50% in around 30% of the cases are not standard, and poorly reported in some trials. No after ineffective conservative treatment. Follow-ups standard severity scale is employed across these trials, and the time to entry varies from within hours to years.
An additional retrospective study published by Many of the patients were negatively selected, they had Hoffmann et al.28 250 patients who had been treated already been treated by various methods and only those unsuccessfully with infusion therapy received HBO2 who had not responded to these therapies were treated therapy. These subjects were compared to patients who with HBO2 therapy. Moreover, many of the studies did not receive HBO2 therapy. The subjects were neglected to identify a control group and many did not under observation for 21 months. In this study, 60% of patients undergoing HBO2 therapy ascertained a steady tinnitus improvement. Other HBO2 therapy centers CONCLUSION
have also shown good results; Almeling et al. (1996), Many of the reports indicate the effectiveness Dauman et al. (1985), Meazza et al. (1996), and Taka- of HBO2 therapy for tinnitus, but a majority of them are retrospective and many suggest using HBO2 ther- apy as an adjuvant to standard medical treatment.
DISCUSSION
Nonetheless, the results justify the position that patients Tinnitus is the phantom perception of sound in with tinnitus, who have been treated conventionally, the absence of overt acoustic stimulation.36 Its impact may still have a chance of improvement of their con- on the military population is alarming. Annually, tin- dition when they can be given HBO2 therapy within nitus is the most prevalent disability among new cases three to six months. These studies have shown that hy- added to Veterans’ Affairs rolls and is currently the perbaric oxygenation treatment can suppress acute and number one disability in the War on Terror. There is even longer existing tinnitus. It appears that during the more being spent on veterans’ disability compensation first six months, HBO2 therapy has a positive and Journal of Special Operations Medicine Volume 9, Edition 3 / Summer 09 promising effect on tinnitus. However, the most sig- 4. Lite, J. (2007). Iraq & Afghanistan war vets suffer from hear- nificant improvement in tinnitus is notable when HBO ing loss, tinnitus. The New York Daily News, November 11.
therapy is administered within the first three months at 5. American Hearing Research Foundation (2008). Noise-induced hearing loss. Retrieved March 16, 2009, from American Hear-ing Research Foundation Website: http://www.americanhear FUTURE RESEARCH
ing.org/disorders/hearing/noise_induced.html Because of its subjective nature, assessing the 6. Axelsson, A; Prasher, D. (2000). Tinnitus induced by occu- level of distress remains the primary impediment in the pational and leisure noise. Noise & Health:A Quarterly appraisal of tinnitus studies. In patient studies, differ- Inter-disciplinary International Journal; 2(8): 47-54.
ences in the level of tinnitus, duration, medical history, 7. Reimer Hyperbaric of Canada (1998). Hyperbaric oxygen in and involvement of etiological factors in the initiation the treatment of sudden deafness, acute tinnitus and acute and mental habituation may obscure any correlation acoustic trauma. Retrieved March, 5 2009, from Reimer Hy- with a treatment outcome.38 There is a case for large perbaric of Canada Website: http://www.reimerhbo.com/tin randomized trials of high methodological rigor in order to define the true extent of the benefit (if any) from ad- 8. Oeken, Jens. (1998). Distortion product otoacoustic emissions in acute acoustic trauma. Noise & Health: A Quarterly Inter- from tinnitus. A critical multicenter analysis with iden- disciplinary International Journal; 2(1): 56-66.
tical documentation of a large number of patients 9. Keate, B. (2008). Hyperbaric oxygen therapy for tinnitus. should establish the therapeutic value of HBO Retrieved March 16, 2009, from Arches Tinnitus Formulas apy for well defined groups of patients. In addition, Website: http://www.tinnitusformula.com/infocenter/arti further studies to evaluate the actual effect of HBO therapy should concentrate on the development of dou- 10. Naval Safety Center (2008). Acquisition safety – noise control aboard ships. Retrieved December 2, 2008, from Navy Safety Though the authors of several studies report Center Website: http://www.safetycenter.navy.mil/acquisition/ various degrees of improvement in up to 50% to 70% 11. National Institute of Health (2008). Noise-induced hearing loss tinnitus is rare. In no study was it reported to be greater Retrieved March 16, 2009, fromNational Institute on Deafness and Other Communication Disorders Website: lished to be beneficial in the treatment of tinnitus, cost http://www.nidcd.nih.gov/health/hearing/noise.aspx analysis for treating tinnitus versus paying out VA ben- 12. Whittle, R. (2006). Hearing loss on rise among troops: Army efits should be conducted. Will curing approximately plans to reduce military audiologist, add civilians. The Dallas 4% of cases significantly reduce VA compensation for tinnitus and/or will a significant reduction in a patient’s 13. MSNBC (2008). Hearing loss is silent epidemic in U.S. Troops: tinnitus affect VA compensation? A final evidence Soldiers coming home with permanent hearing damage and based recommendation will be possible after conclu- ringing in ears. Retrieved December 2, 2008, from MSNBC sion of several randomized, controlled, double-blind Website: http://www.msnbc.msn.com/id/23523729/.
studies. Currently, there are six major prospective tri- 14. Rosen, E.J.; Vrabec, J.T.; Quinn, F.B. (2001). Noise-induced hearing loss. Grand Rounds Presentation, UTMB, Dept. of Oto-laryngology; January 2001.
ACKNOWLEDGEMENTS
15. Bennett, MH; Kertesz, T; Yeung, P. (2005). Hyperbaric oxygen The opinions or assertions contained herein are the therapy for idiopathic sudden sensorineural hearing loss and tin- private views of the author and are not to be constructed as nitus: A systematic review of randomized controlled trials. The official or reflecting the views of the Department of the Journal of Laryngology and Otology; 119(10): 791-798.
Navy, Department of Defense, nor the U.S. Government.
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Journal of Special Operations Medicine Volume 9, Edition 3 / Summer 09 ADDITIONAL REFERENCES
Hoffmann, G; Bohmer, D; Desloovere, C. (1995). Hyperbaric Schwab, B; Flunkert, C; Heermann, R; Lenarz, T. (1998). HBO oxygenation as a treatment of chronic forms of inner ear hearing in the therapy of cochlear dysfunctions – First results of a ran- loss and tinnitus. In: Li W-R Cramer F. eds. Proceedings of the domized study. In: Gennser M. ed EUBS Diving and Hyperbaric Eleventh International Congress on Hyperbaric Medicine. Best Medicine: Controlled manuscripts of XXIV Annual Scientific Meeting of the European Underwater and Baromedical Society.
Stockholm: EUBS; 40-42.
Hoffmann, G; Bohmer, D; Desloovere, C. (1995). Hyperbaricoxygenation as a treatment for sudden deafness and acute tinni- Pilgramm, M; Lamm, H; Schumann, K. (1985). Hyperbaric oxy- tus. In: Li W-R. Cramer F. eds. Proceedings of the Eleventh In- gen therapy in sudden deafness. Laryngologie, Rhinologie, ternational Congress on Hyperbaric Medicine. Best Publishing; Schumann, K; Lamm, K. Hetlich, (1990). Zur Wirksamheit derhyperbaren Saurestofftherapie bei alten Horstorungen. Berichtuber 557 Fale aus dem Jahre 1989, HNO; 38: 408-411.
LCDR Thomas Baldwin is the Senior Medical Officer at Special Boat Team Twenty-Two,Stennis Space Center, Mississippi. He is a graduate of the University of Texas Health Sci-ence Center at San Antonio Medical School and also holds a Master’s Degree in PhysicalTherapy from the U.S. Army-Baylor University program at Fort Sam Houston.

Source: http://doktor.baromedical.hu/media/wysiwyg/PDF/2009333Baldwin.pdf