Experimental pressure induced rupture of the tympanic membrane in man

Defining blast loading 'zones of relevance' for primary blast injury research: A consensus of injury criteria for idealised explosive scenarios

Blast injuries remain a serious threat to defence and civilian populations around the world. 'Primary' blast injuries (PBIs) are caused by direct blast wave interaction with the human body, particularly affecting air-containing organs. Work to define blast loading conditions for injury research has received relatively little attention, though with a continued experimental focus on PBIs and idealised explosion assumptions, meaningful test outcomes and subsequent clinical applications, rely on appropriate simulated conditions. This paper critically evaluates and combines existing PBI criteria (grouped into those affecting the auditory system, pulmonary injuries and brain trauma) as a function of idealised blast wave parameters. For clinical blast injury researchers, analysis of the multi-injury criteria indicates zones of appropriate loading conditions for human-scale test items and demonstrates the importance of simulating blast conditions that are both realistic and relevant to the injury type. For certain explosive scenarios, spatial interpretation of the 'zones of relevance' could support emergency response and hazard preparedness by informing triage, patient management and resource allocation, thus leading to improved health outcomes. This work will prove useful to clinical blast injury researchers, blast protection engineers and clinical practitioners involved in the triage, diagnosis, and treatment of PBIs.

Guidelines to inform the generation of clinically relevant and realistic blast loading conditions for primary blast injury research

'Primary' blast injuries (PBIs) are caused by direct blast wave interaction with the human body, particularly affecting air-containing organs. With continued experimental focus on PBI mechanisms, recently on blast traumatic brain injury, meaningful test outcomes rely on appropriate simulated conditions. Selected PBI predictive criteria (grouped into those affecting the auditory system, pulmonary injuries and brain trauma) are combined and plotted to provide rationale for generating clinically relevant loading conditions. Using blast engineering theory, explosion characteristics including blast wave parameters and fireball dimensions were calculated for a range of charge masses assuming hemispherical surface detonations and compared with PBI criteria. While many experimental loading conditions are achievable, this analysis demonstrated limits that should be observed to ensure loading is clinically relevant, realistic and practical. For PBI outcomes sensitive only to blast overpressure, blast scaled distance was demonstrated to be a useful parameter for guiding experimental design as it permits flexibility for different experimental set-ups. This analysis revealed that blast waves should correspond to blast scaled distances of 1.75<Z<6.0 to generate loading conditions found outside the fireball and of clinical relevance to a range of PBIs. Blast waves with positive phase durations (2-10 ms) are more practical to achieve through experimental approaches, while representing realistic threats such as improvised explosive devices (ie, 1-50 kg trinitrotoluene equivalent). These guidelines can be used by researchers to inform the design of appropriate blast loading conditions in PBI experimental investigations.

An insight to tympanic membrane perforation pressure through morphometry: A cadaver study

INTRODUCTION

A cadaveric experimental investigation aimed to show the rupture pressure of the tympanic membrane (TM) for otologists to evaluate its tensile strength.

METHODS

Twenty adult ears in 10 fresh frozen whole cadaveric heads (four males, six females) mean age 72.8 (SD 13.8) years (range 40-86) were studied. The tensile strength of the TM was evaluated with bursting pressure of the membrane. The dimensions of the membranes and perforations were measured with digital imaging software.

RESULTS

The mean bursting pressure of the TM was 97.71 (SD 36.20) kPa. The mean area, vertical and horizontal diameters of the TM were 57.46 (16.23) mm², 9.54 (1.27) mm, 7.99 (1.08) mm respectively. The mean area, length and width of the perforations were 0.55 (0.25) mm², 1.37 (0.50) mm, and 0.52 (0.22) mm, respectively. Comparisons of TM dimension, bursting pressure, and perforation size by laterality and gender showed no significant differences. The bursting pressure did not correlate (positively or negatively) with the TM or perforation sizes.

CONCLUSIONS

The TM can rupture during activities such as freediving or scuba diving, potentially leading to serious problems including brain injuries. Studying such events via cadaveric studies and data from case studies is of fundamental importance. The minimum experimental bursting pressures might better be taken into consideration rather than average values as the danger threshold for prevention of TM damage (and complications thereof) by barotrauma.

Mechanical damage of tympanic membrane in relation to impulse pressure waveform - A study in chinchillas

Mechanical damage to middle ear components in blast exposure directly causes hearing loss, and the rupture of the tympanic membrane (TM) is the most frequent injury of the ear. However, it is unclear how the severity of injury graded by different patterns of TM rupture is related to the overpressure waveforms induced by blast waves. In the present study, the relationship between the TM rupture threshold and the impulse or overpressure waveform has been investigated in chinchillas. Two groups of animals were exposed to blast overpressure simulated in our lab under two conditions: open field and shielded with a stainless steel cup covering the animal head. Auditory brainstem response (ABR) and wideband tympanometry were measured before and after exposure to check the hearing threshold and middle ear function. Results show that waveforms recorded in the shielded case were different from those in the open field and the TM rupture threshold in the shielded case was lower than that in the open field (3.4 ± 0.7 vs. 9.1 ± 1.7 psi or 181 ± 1.6 vs. 190 ± 1.9 dB SPL). The impulse pressure energy spectra analysis of waveforms demonstrates that the shielded waveforms include greater energy at high frequencies than that of the open field waves. Finally, a 3D finite element (FE) model of the chinchilla ear was used to compute the distributions of stress in the TM and the TM displacement with impulse pressure waves. The FE model-derived change of stress in response to pressure loading in the shielded case was substantially faster than that in the open case. This finding provides the biomechanical mechanisms for blast induced TM damage in relation to overpressure waveforms. The TM rupture threshold difference between the open and shielded cases suggests that an acoustic role of helmets may exist, intensifying ear injury during blast exposure.

Otologic outcomes after blast injury: the Boston Marathon experience

OBJECTIVE

Otologic trauma was the most common physical injury sustained after the April 15, 2013, Boston Marathon bombings. The goal of this study is to describe the resultant otologic morbidity and to report on early outcomes.

STUDY DESIGN

Multi-institutional prospective cohort study.

METHODS

Children and adults seen for otologic complaints related to the Boston Marathon bombings comprised the study population. Participants completed symptom assessments, quality-of-life questionnaires, and audiograms at initial and 6-month visits. Otologic evaluation and treatment, including tympanoplasty results, were reviewed.

RESULTS

More than 100 patients from eight medical campuses have been evaluated for blast-related otologic injuries; 94 have enrolled. Only 7% had any otologic symptoms before the blasts. Ninety percent of hospitalized patients sustained tympanic membrane perforation. Proximity to blast (RR = 2.7, p < 0.01) and significant nonotologic injury (RR = 2.7, p < 0.01) were positive predictors of perforation. Spontaneous healing occurred in 38% of patients, and tympanoplasty success was 86%. After oral steroid therapy in eight patients, improvement in hearing at 2 and 4 kHz was seen, although changes did not reach statistical significance. Hearing loss, tinnitus, hyperacusis, and difficulty hearing in noise remain persistent and, in some cases, progressive complaints for patients. Otologic-specific quality of life was impaired in this population.

CONCLUSION

Blast-related otologic injuries constitute a major source of ongoing morbidity after the Boston Marathon bombings. Continued follow-up and care of this patient population are warranted.

The initial response to the Boston marathon bombing: lessons learned to prepare for the next disaster

OBJECTIVE

We discuss the strengths of the medical response to the Boston Marathon bombings that led to the excellent outcomes. Potential shortcomings were recognized, and lessons learned will provide a foundation for further improvements applicable to all institutions.

BACKGROUND

Multiple casualty incidents from natural or man-made incidents remain a constant global threat. Adequate preparation and the appropriate alignment of resources with immediate needs remain the key to optimal outcomes.

METHODS

A collaborative effort among Boston's trauma centers (2 level I adult, 3 combined level I adult/pediatric, 1 freestanding level I pediatric) examined the details and outcomes of the initial response. Each center entered its respective data into a central database (REDCap), and the data were analyzed to determine various prehospital and early in-hospital clinical and logistical parameters that collectively define the citywide medical response to the terrorist attack.

RESULTS

A total of 281 people were injured, and 127 patients received care at the participating trauma centers on that day. There were 3 (1%) immediate fatalities at the scene and no in-hospital mortality. A majority of the patients admitted (66.6%) suffered lower extremity soft tissue and bony injuries, and 31 had evidence for exsanguinating hemorrhage, with field tourniquets in place in 26 patients. Of the 75 patients admitted, 54 underwent urgent surgical intervention and 12 (22%) underwent amputation of a lower extremity.

CONCLUSIONS

Adequate preparation, rapid logistical response, short transport times, immediate access to operating rooms, methodical multidisciplinary care delivery, and good fortune contributed to excellent outcomes.

Intratympanic hemorrhage and concussion in a football offensive lineman

BACKGROUND

A 26-year-old arena football lineman participating in a "bull in the ring" blocking and tackling drill was blindsided by an opposing teammate. He sustained a direct helmet-to-helmet blow to the right temporal area.

OBJECTIVES

This case describes a unique mechanism of ear barotrauma (intratympanic hemorrhage) and concussion caused by helmet-to-helmet contact in American football.

CASE REPORT

Initial sideline evaluation revealed mild headache, confusion, dizziness, photophobia, and tinnitus, all consistent with a concussion diagnosis. Physical examination revealed a large postauricular contusion over the right mastoid process and diffuse right intratympanic hemorrhage on examination. No hemotympanum or effusion of the middle ear was noted. Abnormalities were seen on vestibular testing and visual accommodation and convergence testing. Computed tomography and magnetic resonance imaging were performed with attention to the temporal bones and were normal. Neuropsychological testing was abnormal compared to baseline. Audiology testing was within normal limits. Diagnosis was intratympanic hemorrhage secondary to barotrauma caused by helmet-to-helmet contact, with mastoid contusion and season-ending concussion.

CONCLUSIONS

The tympanic membrane (TM) is a highly vascular membrane that is very sensitive to variations of atmospheric pressure. Overpressure can enter the external auditory canal, stretching and displacing the TM medially and causing injury to the tympanic membrane secondary to barotrauma. This concussed football player was never able to return to play due to his postconcussive symptoms. He had no residual hearing or ear problems.

Ear trauma in orlu, Nigeria: a five-year review

To review the presentation, types and aetiology of ear trauma and various factors affecting ear trauma in our patients over a 5 year period. All patients treated for ear trauma over a 5 year period were studied using their clinical records. Data extracted were analysed using SPSS version 11 software. The results were presented in simple descriptive and tabular forms. Forty-one patients, 18(43.90%) males and 23(56.10%) females were studied, ages 12-43 years, average 26.3 + 5 years. Blows/Slaps (65.85%) from assault was the commonest aetiology while bleeding from the ear (73.17%), hearing loss (70.73%) and tympanic membrane perforation (68.29%) were the most frequent presentations. Ear trauma is common and mostly affects the tympanic membrane. Sudden increase in canal pressure from blows/slaps was the major mechanism of injury. Management outcome was good except for few late presenters with compilations.

Amelioration of acute sequelae of blast induced mild traumatic brain injury by N-acetyl cysteine: a double-blind, placebo controlled study

Background

Mild traumatic brain injury (mTBI) secondary to blast exposure is the most common battlefield injury in Southwest Asia. There has been little prospective work in the combat setting to test the efficacy of new countermeasures. The goal of this study was to compare the efficacy of N-acetyl cysteine (NAC) versus placebo on the symptoms associated with blast exposure mTBI in a combat setting.

Methods

This study was a randomized double blind, placebo-controlled study that was conducted on active duty service members at a forward deployed field hospital in Iraq. All symptomatic U.S. service members who were exposed to significant ordnance blast and who met the criteria for mTBI were offered participation in the study and 81 individuals agreed to participate. Individuals underwent a baseline evaluation and then were randomly assigned to receive either N-acetyl cysteine (NAC) or placebo for seven days. Each subject was re-evaluated at 3 and 7 days. Outcome measures were the presence of the following sequelae of mTBI: dizziness, hearing loss, headache, memory loss, sleep disturbances, and neurocognitive dysfunction. The resolution of these symptoms seven days after the blast exposure was the main outcome measure in this study. Logistic regression on the outcome of ‘no day 7 symptoms’ indicated that NAC treatment was significantly better than placebo (OR = 3.6, p = 0.006). Secondary analysis revealed subjects receiving NAC within 24 hours of blast had an 86% chance of symptom resolution with no reported side effects versus 42% for those seen early who received placebo.

Conclusion

This study, conducted in an active theatre of war, demonstrates that NAC, a safe pharmaceutical countermeasure, has beneficial effects on the severity and resolution of sequelae of blast induced mTBI. This is the first demonstration of an effective short term countermeasure for mTBI. Further work on long term outcomes and the potential use of NAC in civilian mTBI is warranted.

Trial Registration

ClinicalTrials.gov NCT00822263

Removal of impacted cerumen in children using an aural irrigation system

OBJECTIVES

Impacted cerumen in the ear canal is a common problem that can cause discomfort or prevent assessment. Cerumen removal can have deleterious side effects if performed improperly. We created an aural irrigation system which is currently not available on the market to provide a continuous flow of water at a regulated pressure and temperature. The purposes of this study were to (1) evaluate the safety and efficacy of this aural irrigation system in children and (2) determine the success rate of cerumen disimpaction when used by an allied health professional.

METHODS

The following were evaluated in a nurse-run clinic: (1) referral patterns; (2) extent of canal occlusion; (3) cerumen consistency; (4) peak water pressure used; (5) patient discomfort; (6) efficacy of removal. Each ear was recorded as a separate event.

RESULTS

302 procedures were performed on 244 children (mean age 7.6 ± 4.1 years (range 0.5-18.3 years)). Patients were most commonly referred by an Otolaryngologist (63%), parent (17%), hearing aid provider (10%) or audiologist (9%). The most common reasons for referral were difficulty seeing the tympanic membrane (42%), fitting a hearing aid (20%) or performing an audiogram (11%). Prior to irrigation, 98% of canals were partially or fully occluded. After irrigation (mean peak pressure=488.21 ± 18.61 mm Hg (range 390-590 mm Hg), 92% of canals were completely free of cerumen (99% clear enough for evaluation or treatment). There was mild or no discomfort in 99% of patients and there were no incidences of trauma.

CONCLUSIONS

An aural irrigation system can be effective at clearing impacted cerumen from pediatric ear canals with minimal discomfort and no trauma and can be successfully employed in a completely nurse-run clinic.

Antioxidant treatment reduces blast-induced cochlear damage and hearing loss

Exposure to blast overpressure has become one of the hazards of both military and civilian life in many parts of the world due to war and terrorist activity. Auditory damage is one of the primary sequela of blast trauma, affecting immediate situational awareness and causing permanent hearing loss. Protecting against blast exposure is limited by the inability to anticipate the timing of these exposures, particularly those caused by terrorists. Therefore a therapeutic regimen is desirable that is able to ameliorate auditory damage when administered after a blast exposure has occurred. The purpose of this study was to determine if administration of a combination of antioxidants 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HPN-07) and N-acetylcysteine (NAC) beginning 1 h after blast exposure could reduce both temporary and permanent hearing loss. To this end, a blast simulator was developed and the operational conditions established for exposing rats to blast overpressures comparable to those encountered in an open-field blast of 14 pounds per square inch (psi). This blast model produced reproducible blast overpressures that resulted in physiological and physical damage to the auditory system that was proportional to the number and amplitude of the blasts. After exposure to 3 consecutive 14 psi blasts 100% of anesthetized rats had permanent hearing loss as determined at 21 days post exposure by auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) testing. Animals treated with HPN-07 and NAC after blast exposure showed a significant reduction in ABR threshold shifts and DPOAE level shifts at 2-16 kHz with significant reduction in inner hair cell (IHC) and outer hair cell (OHC) loss across the 5-36 kHz region of the cochlea compared with control animals. The time course of changes in the auditory system was documented at 3 h, 24 h, 7 day and 21 day after blast exposure. At 3 h after blast exposure the auditory brainstem response (ABR) threshold shifts were elevated by 60 dB in both treated and control groups. A partial recovery of to 35 dB was observed at 24 h in the controls, indicative of a temporary threshold shift (TTS) and there was essentially no further recovery by 21 days representing a permanent threshold shift (PTS) of about 30 dB. Antioxidant treatment increased the amount of both TTS and PTS recovery relative to controls by 10 and 20 dB respectively. Distortion product otoacoustic emission (DPOAE) reached a maximum level shift of 25-30 dB measured in both control and treated groups at 3 h after blast exposure. These levels did not change by day 21 in the control group but in the treatment group the level shifts began to decline at 24 h until by day 21 they were 10-20 dB below that of the controls. Loss of cochlear hair cells measured at 21 day after blast exposure was mostly in the outer hair cells (OHC) and broadly distributed across the basilar membrane, consistent with the distribution of loss of frequency responses as measured by ABR and DPOAE analysis and typical of blast-induced damage. OHC loss progressively increased after blast exposure reaching an average loss of 32% in the control group and 10% in the treated group at 21 days. These findings provide the first evidence that a combination of antioxidants, HPN-07 and NAC, can both enhance TTS recovery and prevent PTS by reducing damage to the mechanical and neural components of the auditory system when administered shortly after blast exposure.

Long-term tympanic membrane pathology dynamics and spontaneous healing in chronic suppurative otitis media

BACKGROUND

Children in the developing parts of the world have a high prevalence of chronic suppurative otitis media (CSOM). It is estimated that 65 to 330 million people worldwide have CSOM, yet very little is known about the natural course of the disease. The Inuit population of the Arctic regions is among those with the highest prevalences of CSOM. The aim of this study was to examine the long-term tympanic membrane changes since childhood among Inuit adolescents in Greenland and estimate the proportion of individuals affected by CSOM.

METHODS

Follow-up study (2009) on a population-based cohort of 591 children originally examined during 1993 to 1994 at 3 to 8 years of age. Follow-up was attempted among 348 individuals still living in the areas. Video otoscopy and tympanometry were used. Data on otologic disease, ear surgery, and antibiotic use for otitis media were collected from medical records.

RESULTS

Of 226 participants (65% of those contacted; median age, 22 years), 28 (12%) had present CSOM or had been surgically treated. Eleven were new cases of CSOM not seen between 1993 and 1994. Of those with CSOM in the initial study, 39% had healed spontaneously. The proportion of spontaneous healing was not influenced by the age at which CSOM was diagnosed in the initial study. Thirty-nine individuals (17%) had CSOM in either the initial study or at follow-up. Of these, 2 had never received antibiotic treatment for otitis media, and 15 had been treated less than 3 times. Eighty individuals (35%) at follow-up had CSOM, had undergone ear surgery, or had sequelae in the form of circular atrophy or myringosclerosis.

CONCLUSIONS

The proportion of spontaneous healing and the findings of new cases show that CSOM is a dynamic disease both on the individual as well as on the population level. Every third participant at follow-up had a perforation or sequelae from recurrent or long-lasting perforations, indicating a burden of disease from otitis media larger than what can be estimated in cross-sectional studies. There is a potential for increased treatment of otitis media in this population, which requires raised awareness of the disease in the population and the creation of guidelines customized to conditions in Greenland.

Giving context to post-deployment post-concussive-like symptoms: blast-related potential mild traumatic brain injury and comorbidities

In the military and Veterans Administration systems, individuals with potential MTBI are presenting with symptoms in excess of what would be expected based on initial injury characteristics and/or at unexpected time periods based on current research findings. This article investigates factors that might account for the discrepancy between current research expectations and some occurrences in clinical practice. The physics of blast waves, as well as animal and human research, relevant to explosions are reviewed. Additional factors that occur within the military blast exposure milieu are also explored because the context in which an injury occurs can potentially impact symptom severity and course of recovery. Differential diagnoses, iatrogenic illness, diagnosis threat, and symptom embellishment are also considered.

Forensic Lung Pathology

Sudden and unexpected natural deaths and nonnatural deaths may result from various pulmonary conditions. Additionally, several nonpulmonary conditions of forensic significance may be complicated by the development of respiratory lesions. Certain situations with pulmonary pathology are particularly likely to be critically scrutinized and may form the basis of allegations of medical negligence, other personal injury liability, or wrongful death.1

The neurological consequences of explosives

Neurological injuries produced by explosive blasts are the result of a cascade of events that begin with the initial explosion and evolve from the secondary, tertiary, and quaternary effects that the explosion engenders [Lavonis EJ. Blast Injuries. EMedicine.htm]. Only the results of the primary blast are predictable, and subsequent actions ripple outward in an increasingly random and chance sequence. This article reviews and explains how the ensuing chain of circumstances injures the nervous system, and what examining physicians should anticipate when they treat these patients.

TERRORISM AND BLAST EXPLOSIONS: LESSONS FOR THE AUSTRALIAN SURGICAL COMMUNITY

The prospect of a terrorist attack against Australian interests is currently being debated across our society. The explosive blast attack is most favoured by terrorists. Blast injuries create unique patterns of multisystem injury with contaminated wounds and extensive devitalized tissue. Australian civilian surgeons are increasingly likely to be involved in the management of these injuries, either in response to a terrorist incident in Australia or as part of delayed management of Australian nationals injured overseas. An appreciation of the unique complexities of blast injuries is equally important to both military and civilian surgeons. This paper covers the mechanisms and pathophysiology of blast injuries and discusses issues of surgical management as they would apply to an Australian civilian setting.

Impacted cerumen: composition, production, epidemiology and management

In the UK, some 2.3 million people suffer cerumen ('ear wax') problems serious enough to warrant management, with approximately 4 million ears syringed annually. Impacted cerumen is a major cause of primary care consultation, and a common comorbidity in ENT patients, the elderly, infirm and people with mental retardation. Despite this, the physiology, clinical significance and management implications of excessive and impacted cerumen remain poorly characterized. There are no well-designed, large, placebo-controlled, double-blind studies comparing treatments, and accordingly, the evidence surrounding the management of impacted cerumen is inconsistent, allowing few conclusions. The causes and management of impacted cerumen require further investigation. Physicians are supposed to follow the edicts and principles of evidence-based medicine and clinical governance. Currently, in patients with impacted cerumen, the lack of evidence makes this impossible.

Pressures of the porcine tympanic membrane

The mean rupture pressure of the porcine tympanic membrane (TM) was measured in 9 specimens. Pressure was delivered gradually into the external ear canal of an excised piece of temporal bone, via a syringe and polyurethane tubing attached to the canal. Tympanometry was used to ascertain the structural integrity of the TM before pressure delivery. Rupture pressure was defined to be that point at which a sudden drop occurred in the overpressure in the ear canal, as measured by a pressure gauge. From the results, we concluded that the mean rupture pressure for the porcine TM is 1.2 +/- 0.3 atm. This is of the same order of magnitude as and slightly less than pressures obtained for the human TM.

How can the hooded seal dive to a depth of 1000 m without rupturing its tympanic membrane? A morphological and functional study

Recent studies using a satellite-linked dive recorder have shown that the hooded seal (Cystophora cristata), a common Arctic pinniped, can dive to a depth of > 1000 m and stay submerged for close to 1 h. At these depths the water pressure reaches 100 atm, entailing obvious risk of serious damage to the hearing apparatus, mainly the tympanic membrane (TM) and middle ear (ME). We dissected and photodocumented the temporal bones of five newborn and three adult hooded seals in order to study the temporal bone structure and reveal its protective mechanisms for extreme pressure changes. Specimens were sectioned and stained for light microscopy. The thicknesses of the pars tensa and pars flaccida were found to average 60 and 180 microm, respectively. The ME cavity hosts a cavernous tissue of thin-walled vessels beneath the modified respiratory epithelium. The ME and external ear canal (EAC) volumes can be altered appreciably by filling/emptying the cavernous tissue with blood. The ossicles were fixed by contracting the tensor tympani and stapedius muscles simultaneously with complete occlusion of the EAC. According to Boyle's law, the volume of the gas-filled ME cavity at a depth of 1000 m is only 1% of its volume at the surface of the sea. Ascent from such a depth allows the gas in the ME cavity to expand, causing the TM to bulge laterally. This movement is counteracted by a reduction in the blood volume inside the cavernous sinuses, action in the tensor tympani and stapedius muscles and discharge of gas through the Eustachian tube. The presence of a firm, broad-based exostosis in the floor of the EAC lateral to the TM helps to obstruct the EAC.

Cartilage palisade tympanoplasty and diving

OBJECTIVE

To determine whether a patient with a serious defect of the tympanic membrane (TM) will be able to dive after surgery.

PATIENTS AND METHODS

The authors describe three patients who were divers with serious defects of the TM (more than 75% of TM). In all three cases, cartilage palisade tympanoplasty was used to reconstruct the TM.

RESULTS

Six months after surgery, the patients passed clinical examinations, audiograms (hearing restored to normal), tympanometry (increased stiffness of the TM), and pressure tolerance tests in hyperbaric chamber (30-m immersion was simulated for 4 minutes), and they began to dive again. Approximately 2 years after the surgery, all three patients are able to dive without any difficulties.

CONCLUSION

The authors conclude that patients can dive after cartilage palisade tympanoplasty.

Rupture pressures of membranes in the ear

The rupture pressures of the tympanic membrane, Reissner's membrane, the round window membrane, and the annular ligament have all been measured in cadaver ears from Norwegian cattle. For the tympanic membrane, a static overpressure was applied to the ear canal; for Reissner's membrane, to the endolymph; and for the round window membrane, to the perilymph. The rupture pressure of the annular ligament equals the rupture force to the footplate divided by the area of the oval window. The mean rupture pressures are 0.39 atm for the tympanic membrane, 0.047 atm for Reissner's membrane, greater than 2 atm for the round window membrane, and 29.4 atm for the annular ligament. This last pressure corresponds to 0.68 kilogram force applied to the footplate. The ruptures of the tympanic membrane appeared without exception as small tears in the pars flaccida. The rupture pressure of the tympanic membrane was also measured in a few ears from foxes.

Extended high-frequency audiometry in traumatic tympanic membrane perforations

Air- and bone-conduction audiometry in the frequency ranges 0.125-18 kHz and 0.25-16 kHz respectively were performed in 38 patients with unilateral traumatic tympanic membrane perforation. Sensorineural threshold elevation was found in 16 ears. In nine of these this was permanent and in four restricted to the frequency range > 8 kHz. Both sensorineural threshold elevation and tinnitus (n = 16) diminished with time. A temporary, mean 5 dB, bone-conduction threshold elevation > or = 8 kHz was seen in 26 ears before spontaneous tympanic membrane closure. Closure resulted in a 7-20 dB improvement of air-conduction thresholds in the 0.125-18 kHz range, somewhat less in the upper than in the lower frequencies. A 3 dB mean final conductive hearing loss > 8 kHz was found in these 26 ears approximately 5 months after injury, probably due to scars in the pars tensa at the site of the former perforations. Thirty-seven of 38 perforations had healed at final follow-up examination.

Can ear irrigation cause rupture of the normal tympanic membrane?: an experimental study in man

Rupture of the tympanic membrane (TM) during ear irrigation is a rare but unhappy event. In this study the maximum overpressures obtained in the deep part of the external auditory meatus (EAM) during ear irrigation were measured postmortem in 20 cadavers. The highest pressures were obtained in normal- or wide-dimension EAMs when a metal syringe was used. With this device, the median maximum overpressure was 240 mmHg (range 200-300 mmHg). Experiments with simulation of an obturating wax plug did not increase the maximum overpressure. Compared with the lowest overpressures which can rupture TMs the pressures measured in this study were insufficient to rupture normal TMs but sufficient to rupture atrophic TMs with the lowest tensile strength. This finding may have medicolegal implications.

Hearing loss in the 4-8 kHz range following tympanic membrane perforation from minor trauma

This study looked at the incidence of sensorineural hearing loss in the 4-8 kHz range in patients with unilateral tympanic membrane perforations from minor trauma who presented to the department in the past year. Eleven patients conformed to our inclusion criteria, one was lost to follow-up. Perforation was present in all patients in the pars tensa and no treatment was required in nine patients. The mean sensorineural hearing loss at 4,6 and 8 kHz was 28.2 dB on initial examination and 14.6 dB by Day 30. All 11 patients had normal hearing in the contra-lateral ear (mean 13.5 dB). In this group of patients with a tympanic membrane perforation from minor trauma the conductive hearing loss was accompanied by a significant (P = 0.001) but reversible high frequency sensorineural deafness.