Summer - United States Special Operations Command

get shot and 21% more likely to have their entire tankcrew killed by the enemy. 4Hearing damage has been a battlefield riskever since the introduction of explosives and artillery,and the U.S. military recognized it in Iraq andAfghanistan and issued earplugs early on. But thesheer number of injuries and their nature, particularlythe high incidence of tinnitus, came as a surprise tomilitary specialists and outside experts. According toVA figures, despite all that has been learned over theyears, U.S. troops are suffering hearing damage atabout the same rate as World War II veterans. 13,21Given today’s unpredictable weaponry (i.e. roadsidebombs), even the best hearing protection is only partlyeffective, and only if it’s properly used.It makes more sense to prevent hearing damagethan to provide a lifetime of disability, but evenhearing protection has its limits and it is important tonote that some hearing impairments are unavoidabledespite use of hearing protection and other measures.Some exposures are so extreme that they will exceedthe protective capability of hearing protective devices.As previously noted, damage can occur at 85 decibels.The best protection cuts that by only 20-25dB. 13 Thatis not enough to protect the ears against an explosionor a firefight, which can range upwards of 180+ dB.Furthermore, much of the fighting consists of ambushes,bombings, and firefights, which come suddenlyand unexpectedly, giving Soldiers little time touse their issued hearing protection. In addition, someInfantrymen resist or refuse to wear their hearing protectionfor fear of dulling their senses and missing criticalcommands or sounds that can make the differencebetween life and death.HBO 2 THERAPY EFFICACY IN TINNITUSMedical treatments for tinnitus are well documentedand there is probably no other disease forwhich such a variety of treatments have been proposed.Yet, still today, many different treatment regimens arebeing propagated. Vasodilators, vitamins, steroids, anticoagulants,heparin, histamine, tranquillizers, diuretics,prostacyclin, hypervolemic hemodilution,carbogen, and stellate ganglion block. 3,25 Whether appliedseparately or together, all have demonstrated limitedeffectiveness at best. Experimentally, rheologicalagents and plasma expanders neither cause an improvementin inner ear blood supply nor result in ahigher oxygen supply in the inner ear. 26 In addition,two forms of tinnitus rehabilitation are currently beingprescribed, tinnitus masking and psychological treatment;both offer symptomatic treatment, with the goalof treatment being only to lessen the awareness of tinnitusand its impact on quality of life.Since the end of the 1960s, hyperbaric oxygen(HBO 2 ) therapy has been used experimentally for certainacute and chronic illnesses of the inner ear. 25 Therole of HBO 2 in the treatment of tinnitus was investigatedin the past: Pilgramm et al. in 1985, firstly, andSchumann et al. in 1990, secondly, reported aboutHBO 2 usefulness in tinnitus treatment, reporting animprovement of 62.2% in 557 patients’ tinnitus afterreceiving 10 applications of HBO 2 therapy. 25,27 Whileskepticism remains high in the Untied States, physiciansin Germany and Japan continue to recognize itsclinical applications in diseases of the inner ear andhave demonstrated improved outcomes in the treatmentof acute acoustic trauma, NIHL, and tinnitususing HBO 2 therapy. 7,26 The rationale for this therapyis based on the oxygen transportation mechanism inhuman organisms.The basis for hyperbaric oxygenation is thebreathing of pure oxygen at a pressure which is increasedcompared to atmospheric pressure (1.0ATA). 9,26,28-30 The effectiveness of high pressure oxygentherapy is based on raising the partial pressure ofoxygen in the blood and thus the pressure differenceto tissue. The concentration of oxygen in the atmosphereis 21%. At 1.0 ATA, the oxygen in blood is almostentirely carried by hemoglobin. Becausehemoglobin is approximately 97% saturated under normalconditions, greatly increasing the oxygen-carryingcapacity of blood by increasing hemoglobinsaturation is not possible.During hyperbaric oxygen therapy the patientsits inside a pressurized chamber. Air pressure insidethe chamber is increased up to 2.5 times normal atmosphericpressure at sea level (2.5 ATA). The patientthen breathes pure oxygen from a mask. Inhalation ofhyperbaric oxygen can enhance the amount of oxygencarried in blood by increasing the quantity of oxygendissolved in plasma. When breathing 100% oxygen ata surrounding pressure of 2.5 ATA, the quantity of dissolvedoxygen in 100ml of plasma increases from0.3ml, to 6.8ml, which is approximately 20 timeshigher than normal. 9,26The driving force for oxygen diffusion fromthe capillaries to tissue can be estimated by the differencebetween the partial pressure of oxygen on the arterialside and the venous side of the capillaries. Thedifference in the partial pressure of oxygen from thearterial side to the venous side of the capillary systemis approximately 37 times greater when breathing100% oxygen at 3.0 ATA than air at 1.0 ATA. 29The increased tissue oxygenation achievedduring HBO 2 therapy can support poorly perfused andhypoxic areas. Under this increased pressure, theamount of dissolved oxygen is sufficient, even withouthemoglobin, to supply body tissues with oxygenby diffusion. With an increase of the pressure of oxygenin the inner ear, it is possible to influence the auditorysensory cells (inner and outer hair cells) and theperipheral auditory nerve fibers. 30 These cells have nodirect vascular supply and depend entirely on oxygen36Journal of Special Operations Medicine Volume 9, Edition 3 / Summer 09