Effects of composition 1 and trinitrotoluene explosive pressure on auditory tissue: an ovine cadaveric assessment

Introduction

Overview

Explosive events vary in duration, intensity, and circumstances. Their impact on both inanimate structures and living beings has been widely studied. The created pressure wave is the primary factor in determining the number or type of injuries caused by explosions not involving shrapnel. Recent events involving the purposeful detonation of explosives with the intent of causing human harm are often at a level that generates pressures that can cause varying types of bodily damage. This includes injuries to the ear.

There are a number of published studies that focus on the explosive pressures related to ear injuries (1-11). A common metric used to quantify this class of injury is the peak overpressure required to result in a 50% incidence of eardrum rupture (P₅₀). Richmond and co-workers (12) provided a comprehensive review of studies involving humans and animals, with dogs providing most of the data in the latter category. They found P₅₀ values for dogs of 78 kPa for fast-rising blasts in a shock tube, 205 kPa for complex wave patterns inside open shelters under nuclear blasts, and 296 kPa for smooth-rising overpressures. P₅₀ values of 100 kPa with threshold values ranging from 20 to 35 have been suggested for humans. However, because of practical factors, it can be difficult to control both the explosive environment and the known physical condition of the eardrum under which rupture occurs.

Blast-related ear injuries

Multiple factors affect the changes in local air pressure that result from explosions. Measuring their effects on living creatures is a major scientific and moral challenge. Accordingly, there is an important but relatively small amount of literature published on the effects of explosive pressures on animals, and even fewer on humans (9,10,12-14). A number of studies related to the damaging effects of explosive pressures on living tissue have focused on categorizing the types of injuries observed following an explosive event. Multiple studies have used the results from such events in the immediate aftermath of an explosion, even though there are significant challenges in re-creating the positions of the injured at the time of the blast (3,4,15,16).

Extensive documentation of ear injuries related to explosive blasts has been provided by Kerr and Byrne (3). Experimental evidence of ear injuries caused by blast effects has been most frequently linked using the measure of eardrum rupture of either human cadavers or post-blast analyses of the living (1). Wightman and Gladish (16) have also classified the types of injuries that can result from an explosion. Explosive pressures ranging between 8 and 104 kPa (1.2 and 15.1 psi) have been posited as bounds required to rupture the human tympanic membrane (3,4,15-17). The most commonly damaged portion of the ear from explosive events is the pars tensa, which is the taut and thick region of the tympanic membrane. Most of the studies completed to evaluate this range of rupture pressure frequently used an after-the-fact examination of individuals who had survived blast pressure. Physical exams were used to determine levels of damage and the most likely pressure associated with this level of injury (3,4,15,16). While very useful, these results were limited in the sense of being completed in an uncontrolled setting with a number of key parameters either unknown or poorly defined. The range of predictions for human eardrum rupture is relatively large and is likely associated with the fact that there are a large number of variables associated with these events, including but not limited to variability in ear tissue and the possibility of ear protection among individuals.

The primary structures of the ear, as they relate to the experiments completed in the present study, are the auditory canal and the tympanic membrane. Injuries to these components are often initiated by a shock to the receptor organs in the ear. In many cases, full recovery is expected in a relatively short period of time (2,3,8). Champion and co-workers (18) summarized levels of short-duration blast overpressure on unprotected ears. They predicted an auditory shift at 13.8 kPa, possible eardrum rupture at 34.5 kPa, and a 50% chance of eardrum rupture at 103.4 kPa. They also noted that the chances of damage to the cochlea or permanent hearing loss were linked to exposure to repeated blasts (16). Damage to the tympanic membrane is clearly associated with the distance from the explosion, but also, at least in theory, the head’s orientation relative to the explosive detonation’s position. It has also been noted that the tympanic membrane modulus of elasticity can generally decrease with age, potentially indicating a change in mechanical response to blast and higher chances of failure (19). This is because the percentage of collagen in older tissues tends to decrease, leading to limited deformation capacity before failure.

Although few studies examine blast effects on living beings, Cho and co-workers (14) studied living mice exposed to blasts generated in a chamber designed to deliver specific pressure waves of compressed air. This comprehensive work also incorporated hearing tests on the mice with damaged ears. However, because of the size and innate healing ability of rodents, translation of these data to human response was difficult. More recent studies have produced additional insight into blast effects on the ear. A study by Gan and co-workers (20) linked numerical simulations and experimental data of human cadavers under compressed air blast to determine the relationship between tympanic membrane rupture and blast wave direction. Jiang and co-workers (21) used laser Doppler vibrometers to measure the tympanic membrane response to blast pressure. A comprehensive model of tympanic membrane injury risk was recently developed by Iyoho and co-workers (22) using a large-scale experimental study of human cadavers (13).

To add to this limited body of literature, the primary goal of this work was to better quantify the pressures that induce eardrum rupture in ovine eardrum tissue under direct testing of composition 1 (C-1) and trinitrotoluene (TNT) detonations in open space conditions. A significant effort was dedicated to preparing and treating the eardrum samples both before and after the experiments. Sheep ears were selected because of evidence that there is a strong similarity in the anatomy and physiology of the sheep ear with that of humans (23,24). Specific attempts were made to limit the degradation of the eardrum tissue prior to testing. Three separate sets of explosives tests involving C-1 and TNT explosives, along with nineteen samples from thirteen different sheep ears, were completed. The determination of the range of pressures that caused full eardrum rupture, in addition to several other key observations, forms the foundation of this study.

Methods

Specimen selection and preparation

Extensive work has been accomplished in predicting peak pressures of explosives based on TNT equivalence and distance (25-27). The levels of these explosive pressures that are associated with damage to the tympanic membrane are somewhat of an open question in the literature. These values can vary widely regardless of species, but it may be possible to refine the bounds of eardrum rupture with more careful treatment of testing conditions. One of the first steps in performing a more controlled set of experiments to determine damage in cadaveric auditory tissue is to identify an appropriate class of test specimens. Although smaller animals, such as mice, have been used in blast experiments, there is a significant difference in size compared to the organs of humans. Seibel and co-workers (23,24) have noted that most medium-sized animals used in blast studies, including dogs, cats, and monkeys, also possess substantial anatomical and physiological differences when compared to humans.

One alternative species is sheep. Multiple anatomical and medical studies have been completed to confirm the strong similarity with the hearing systems of humans, and they appear to resolve, or at least reduce in intensity, many of the difficulties associated with other laboratory animals. Seibel and co-workers (24) used CT scans of sheep heads to quantify some of the major differences, with a special focus on the dimensions for external and middle ear anatomy. They concluded that sheep ear anatomy is related to that of humans by a factor of 2/3, which is a much closer ratio compared to other species when compared to humans. When combined with the fact that the anatomical layouts between sheep and humans are similar, they argued that sheep appear to provide a more accurate representation of ear response under blast conditions. It was further suggested that sheep are suitable models to use in other settings that include surgical training, implantation of hearing aids, and acoustic trauma studies (24). Lim (28) has also noted that the tympanic membranes of sheep and humans are morphologically similar. They contain the same types of cells and cell layers, indicating potential similarity of mechanical properties.

For the explosive tests reported here, cadaveric full decapitated heads were collected from unrelated studies immediately following necropsy. As no live-animal procedures were performed, based on institutional policies, no Institutional Animal Care and Use Committee (IACUC) approval was deemed necessary by Colorado State University for this study. All samples used were skeletally mature (greater than 3 years old; Columbia Rambouillet) and were prepared for the separate experiments as described below.

Types of explosives

There were two types of explosive charge that were used in the present study: (I) C-1 sheet explosive combined with detonation cord, both of which are based on pentaerythritol tetranitrate (PETN) with a relative effectiveness (RE) factor of 1.66; and (II) TNT, with an RE factor of 1. There are a number of factors that can influence the maximum pressure generated during an explosion, that include age, where the explosive was stored, how it was handled, and other environmental factors. Using tabulated values with direct physical measurement is problematic if the end goal is an improved estimate of pressures that cause eardrum rupture. To alleviate this limitation, direct measurements of the blast pressures were completed for all tests in this study to determine the exact pressure generated with each type of explosive charge. In all experiments, three ICP^® free-field blast pressure probes (29) were directed parallel to and in the direction of the blast at a location as near to the entrance of the ear canal or ear substructure as possible. These probes have a sensitivity of ±15%, and multiple probes were placed at varying radial locations to identify any anomalous pressure readings.

Explosive test setup and procedures

Three explosive tests (Tests I–III) were conducted sequentially on fresh cadaveric sheep specimens. Test I (“C-1 and det cord on intact ear chambers”) and Test II (“TNT on extracted ear chambers”) used isolated ear chambers or extracted ears mounted as described above. Tympanic membrane status was determined by direct visual inspection of the ear canal and ear chamber, including the use of a borescope inserted into the ear canal in Test II for purposes of comparison. Test III (“Imaging intact ear chambers after C-1/det cord exposure”) was performed on intact sheep heads exposed to similar charge configurations, with more detailed photographic imaging of the ear canals and tympanic membranes before and after blast. Differences in sample size between Tests I–III reflect the exploratory nature of this work and the practical constraints of open-air explosive testing.

Test I: C-1 and det cord on intact ear chambers

An initial sequence of blast tests was completed on sheep ears under relatively low levels of explosive detonation. This initial test used five intact sheep heads obtained immediately following euthanasia. The purpose of this initial testing was to determine rough estimates on the level of pressure that caused total eardrum perforation. The ears remained as part of the entire head, and the explosive charges consisted of 38.7 cm² (6 inch²) of C-1 PETN-based sheet explosive wrapped with 30.48 cm (12 inch) of wound Cordtex18 50-grain PETN per foot detonation cord. These specimens required no preparation prior to testing. All were mounted in an anatomical orientation and placed perpendicular to the blast direction. Only one ear was directly exposed to the blast pressure, with the ear on the opposite side of the head facing away from the direction of the blast. Specimens were attached to a vertical spike through the foramen magnum at the elevation to match that of the blast initiation height, and were supported so that the skull would not rotate or translate during the blast cycle. In this and all experiments, three ICP^® free-field blast pressure probes (29) were directed parallel to the direction of the blast at a location as near to the entrance of the ear canal or ear substructure as possible.

The stands that supported the pressure probes, specimens, and explosives were constructed from steel rebar and a metal plate and were reinforced with sandbags at the base prior to detonation. A wooden A-frame was used to directly position each charge and was generally destroyed during each shot. These had to be replaced for each successive test. At least four pressure probes were secured in place and positioned at varying locations near the specimen to compute the resulting pressures, with data processed using LabVIEW (30). All electronics were reinforced and stabilized to minimize any detrimental effects from the blast. All distances from the blast location to the entrance of the ear canal and/or the pressure sensor location were determined from repeated tape measure readings.

Test II: TNT on extracted ear chambers

A second set of tests used larger explosive loads of TNT. For these tests, different sheep specimens were used, where all soft tissues, including the ear pinna, were removed from the sheep skull. In addition, the mandible was dislocated to expose and provide access to the ear canal and the region of the skull that contained the inner ear. Following the clearing of the bone around the ear canal, a circular coring bit drill bit was used to completely remove the inner ear substructure from the sheep skull, where special care was taken to maintain the integrity of the inner ear chamber. The chambers were then wrapped in saline-soaked gauzes and frozen to −20 ℃. Prior to the experiment, the samples were allowed to slowly thaw to room temperature. The tympanic membrane was visually inspected both prior to and following storage to ensure that no damage occurred during the freeze-thaw cycle. There is at present no consensus related to the changes in properties of the tympanic membrane following repeated changes in temperature. However, data on the effects of freeze-thaw mechanisms for other biological soft tissues indicate that these effects are likely minimal up to two cycles (31). Images of each tympanic membrane were taken using a 3.9 mm (0.15 inch) ear borescope inserted into the ear canal for purposes of comparison.

A weighted tripod-style rebar stand was used to rigidly mount the isolated ear chambers that were now placed directly adjacent to and at the same radial distance and same perpendicular direction as the pressure probes. The ear specimens were fixed in place using clamps and zip-ties and placed above the corresponding pressure probe with the ear canal facing the explosion. The charges were 227 kg (approximately one-half pound) and 340 kg (approximately three-quarter pound) cylinders of TNT and generated a far stronger blast wave than those of the tests with C-1 and det cord. To maintain consistent levels of pressure, this meant that the specimens were generally placed at larger distances than for Test I. A total of six extracted ears were used in the TNT testing.

Test III: imaging intact ear chambers after C-1/det cord exposure

A third test was completed on intact sheep heads using similar charges of C-1/det cord that were used in Test I. For this test, special focus was given to more detailed imaging of the ears before and after blast exposure. A total of four intact frozen sheep heads were thawed over 72 hours. Sheep heads were placed in lateral recumbency, and a 5 mm video otoendoscope (Karl Storz Veterinary Endoscopy-America, Inc., Goleta, CA, USA) was inserted into each external canal at the level of the horizontal canal, approximately 2 mm from the tympanic membrane. Multiple digital images of the tympanic membranes of each sheep were obtained using the AIDA WD300 capture system (Karl Storz Veterinary Endoscopy-America, Inc.). Each sheep head was placed in lateral recumbency on the contralateral side, and the above procedure was repeated. The specimens were then subject to explosive charges designed to give similar pressures.

Post-explosion specimen treatment

Test I

Following completion of the testing, all sheep heads were frozen at −3 ℃ to await final dissection and processing. This required thawing of 24 hours, removal of all soft tissue away from the skull, dislocating the jawbone to remove it from the skull, and coring out the inner ear cavity. The cores of this substructure were then further trimmed, and slices made to completely expose the tympanic membrane. Detailed visual inspections were then completed for each of the specimens. This entire process was relatively difficult and resulted in changing the methodology for Test II.

Test II

Since the specimens in this test had already been prepared prior to testing, the post-explosion process was much simpler for this test. Each of the ear structures was given a visual inspection of the tympanic membrane immediately following the explosive shot using a 3.9 mm (0.15 inch) ear borescope. This allowed for a direct comparison between images before and after the explosion. The physical dimensions and geometry of the borescope, combined with the physiology of the shear ear, precluded the ability to image the entire membrane fully. Following this initial inspection, the ear cores were placed in a formalin solution for 4 days to fix and preserve the specimens until final processing. The specimens were then trimmed using a diamond-tipped abrasive blade to completely expose the tympanic membranes. A final determination of the damage was then confirmed.

Test III

Following blast exposure, all specimens were immediately transported back to the imaging lab, where the post-explosion images were completed in a manner identical to the imaging prior to blast exposure. These detailed images allowed for an immediate assessment of rupture. The image-blast exposure-image cycle was completed in under 2 hours.

Statistical analysis

Because the primary outcome was binary (tympanic membrane rupture: yes/no), we performed exploratory univariate logistic regression analyses with rupture status as the dependent variable and either peak overpressure (kPa) or radial distance (m) as the single predictor. The total sample included 15 independent ears (11 ruptured and 4 intact). Given this limited sample size and the occurrence of partial separation for peak pressure (no ruptures below 30 kPa and universal rupture above 40 kPa), we restricted inference to likelihood-ratio tests for association rather than to model-based estimates of effect size or prediction. Likelihood-ratio statistics were used to test the null hypothesis of no association between each predictor and rupture status.

Results

All test results, including the radial distances between the sheep head and the point of detonation, the recordings of peak pressure at all probe locations, the side of the sheep head that was facing the blast, and the end result of each specific test indicating if the eardrum was ruptured or remained intact for each of the trials, are shown in Table 1.

For quantitative analysis of blast effects, data from all three tests were combined only for the shared binary endpoint of tympanic membrane rupture (ruptured vs. intact) as a function of peak pressure and distance. Test-specific qualitative observations of soft tissue and middle ear injury obtained from the different imaging approaches were summarized within each test and were not pooled across tests.

Test I

Results from this test are noted in Table 1 as Trials 1–5. Representative time-pressure plots for this sequence of tests are shown in Figure 1. The two tests with a measured total pressure of 312 kPa were far above the range usually reported for eardrum rupture. These were primarily performed to guarantee damage for use in post-failure analysis of the specimens.

Figure 1 Blast pressure profiles for C-1 and det cord test. The amplitude of the pressure wave measured at three probe locations (75.9, 53.67, and 6.42 kPa) is shown for the initial test using shots of C-1 and det cord on the intact sheep heads. C-1, composition 1.

Test II: TNT on extracted ear chambers

The second set of tests had several advantages over the initial trials of Test I, primarily because the extracted ear chambers were far easier to maneuver than the intact sheep heads. Additionally, since an initial estimate of 34 kPa for eardrum rupture had been predicted, the charges could be varied within this region in an attempt to reduce the range for which rupture would occur. Specifically, an attempt was made to generate pressures that were either below 30 kPa or above 40 kPa to confirm initial bounds from Test I. The summary of all results for this test is shown as Trials 6–11 in Table 1, with the distances, peak pressures, and membrane status all shown. The lowest pressure at which damage was seen for these explosions was 42 kPa (6.1 psi).

Test III: C-1/det cord on intact ears: imaging results

These tests were specifically designed to generate eardrum ruptures that could provide high-quality images before and after blast exposure. Each of the eight eardrums is shown, with four sets of before/after imaging (Figure 2).

Figure 2 Images of ear canals of the third blast test for four pairs of sheep ears. (A) The left and right ears for the first specimen of Test III before (upper) and after (lower) exposure to a pressure of 75.8 kPa at the entrance of the left ear canal. The ears prior to testing are healthy tissue with no signs of rupture. The left ear (blast side) experienced full rupture of the tympanic membrane, with the right ear experiencing multiple ruptures. (B) The left and right ears for the second specimen of Test III before (upper) and after (lower) exposure to a pressure of 75.9 kPa at the entrance of the left ear canal. The ears prior to testing are healthy tissue with possible signs of scar tissue, but no signs of rupture. Both ears experienced full rupture of the tympanic membrane. (C) The left and right ears for the third specimen of Test III before (upper) and after (lower) exposure to a pressure of 75.9 kPa at the entrance of the left ear canal. The ears prior to testing are healthy tissue. The right ear had a severe blockage of the ear canal because of wax and fibrous tissue. The left tympanic membrane experienced a linear rupture while the right remained intact. (D) The left and right ears for the fourth specimen of Test III before (upper) and after (lower) exposure to a pressure of 75.9 kPa at the entrance of the left ear canal. The ears prior to testing are healthy tissue, with the air bubbles in the left ear appearing from the use of saline to flush the ear. Both ears experienced ruptures of the tympanic membrane.

Discussion

Although limited in quantity and range of pressures, the results from Test I proved useful to target the second set of tests. Specifically, identical pressures of 34.0 kPa were generated for two different eardrums, with one being ruptured and the other remaining intact. The three specimens subjected to pressures larger than 34.0 kPa all experienced rupture.

Despite the identical levels of explosive used for these tests, the generated pressures were not always identical, and identical pressures gave both ruptured and perforated tympanic membrane specimens. It is possible that there is a natural variability in the strength of the sheep ear under blast conditions, and only an increase in the number of specimens would allow this variation to be quantified. The peak pressure of 34 kPa provided a tentative threshold that served as a preliminary bound where the eardrum ceases to remain intact. The induced pressures for the second test with TNT were designed to be arrayed and refined around this value.

Exploratory logistic regression supported a statistically significant association between tympanic membrane rupture and both peak blast pressure and distance from the charge. The likelihood-ratio test P values were 0.0005 for peak pressure and 0.0161 for radial distance, respectively. However, because of the limited number of events and partial separation in the data, the corresponding odds ratio estimates and fitted probability curves were unstable and are not reported. Instead, we emphasize the empirically observed pressure bands (<30 kPa: no rupture; 30–40 kPa: mixed intact and ruptured membranes; >40 kPa: 100% rupture), which are directly supported by the observed data and provide a conservative basis for defining thresholds in this initial ovine cadaveric study.

Future work with larger sample sizes and controlled variation in blast parameters will be needed to develop a reliable dose-response (probability) curve for tympanic membrane rupture under open-air explosive conditions. The review of Lucke-Wold and co-workers (32) has discussed the importance of transitioning from outdated lung-based scaling parameters in studying blast traumatic brain injuries to far more relevant skull-based parameters. Although eardrum rupture represents a relatively severe level of damage, it is possible that lower levels of blast pressure can be associated with subclinical auditory damage similar to the neurological and psychiatric effects suggested by Hernandez and co-workers (33).

There are a number of factors that may have influenced the pressure and damage estimates presented here, in addition to prior caveats. These include the living conditions of the animals, their age relative to other specimens in their cohort, the medical history of the animal, and the time between being euthanized and the specimens being processed for testing. Although each of the sheep specimens used in this test was similar, they were not identical. Future testing should continue to study how these factors affect results, especially until a confirmed procedure for processing and analyzing deceased tissue is developed.

There are several additional factors that may have influenced the pressure and damage estimates presented here. These include the living conditions of the animals, their age relative to other specimens in their cohort, the medical history of the animal, and the time between being euthanized and the specimens being processed for testing. Although each of the sheep specimens used in this test was similar, they were not identical. Future testing should continue to study how these factors affect results, especially until a confirmed procedure for processing and analyzing deceased tissue is developed. It is also useful to recall the estimates for human eardrum rupture from Champion and co-workers (18): possible eardrum rupture at 34.5 kPa, and a 50% chance of eardrum rupture at 103.4 kPa.

This work should be considered an exploratory cadaveric assessment designed to establish an ovine blast-exposure model and to identify pressure ranges associated with tympanic membrane rupture under open-air explosive conditions. Three different explosive tests (Tests I–III) were conducted with differing sample sizes and imaging approaches, reflecting the sequential refinement of the experimental setup and the transition from isolated ear chambers and extracted ears (Tests I and II) to intact sheep heads with more detailed photographic imaging (Test III). Although the primary endpoint—binary tympanic membrane rupture—was determined using a consistent visual criterion across all tests, this heterogeneity and the limited overall sample size may constrain generalizability. Future work with larger, prospectively designed cohorts and standardized imaging protocols will be needed to confirm these results and to support more detailed quantitative modeling of blast-induced auditory injury.

One important issue that deserves further study is the dependence of the nature of eardrum rupture on the explosive type. In the present study, the intention of using different types of explosive shots was to determine the levels of peak pressure that caused rupture, rather than to characterize in detail the physical nature of the damage. Such an assessment would be of great value in designing protective systems, but it was outside the scope of the present work.

In summary, this study establishes a practical ovine cadaveric model for characterizing tympanic membrane rupture under open-air explosive loading and demonstrates that rupture can be linked to specific blast-pressure regimes across different charge types and test configurations. By combining high-fidelity pressure measurements with direct visualization of tympanic membrane integrity, we identify a conservative “no-rupture” range at low peak pressures, a mixed-response transition zone, and a regime of near-certain rupture at higher pressures. These findings provide experimental support for pressure-based risk bands that can be used to design and interpret future in vivo studies, to benchmark numerical blast models, and to inform the development of protective strategies and exposure guidelines. Although exploratory and limited in sample size, the work defines a reproducible test platform and quantitative framework that can be extended to living animal models and more complex auditory and neurological endpoints in subsequent investigations.

Conclusions

Based on the results of three sets of experiments described here, and realizing the limited number of specimens used in this study, the primary conclusions of this work track closely with these predictions but significantly lower the estimate at which eardrums consistently rupture. Specifically:

• Eardrum rupture for the sheep specimens in this study can be divided into three groups: (i) blast pressures under 30 kPa, for which the eardrums remained intact; (ii) blast pressures between 30 and 40 kPa, which resulted in both intact and ruptured tympanic membranes; and (iii) blast pressures over 40 kPa, at which 100% of the specimens (n=11) resulted in ruptured tympanic membranes.
• In three of four cases at about 76 kPa, the eardrum on the opposite side of the sheep head—which was not instrumented with pressure gages—was ruptured. The only exception was a single ear blocked by wax and fibrous tissue. Hence, in these three cases, there was no protection or benefit to having an auditory canal opening pointed in the direction opposite to that of the blast. One possible explanation for the rupture of the downwind/protected eardrum at these higher pressures is the negative phase of the pressure wave, for which the opposite ear is not protected. The magnitudes of this negative phase are in the range of direct positive peak pressures for the explosive shots that generated rupture from the directed blast. To the authors’ knowledge, the effects of negative blast pressure on auditory tissue have not been explored.
• Pressure predictions are based on blast pressures that result from C-1/det cord/TNT in open space. Comparative values developed under other circumstances (such as air pressure blasts within a confined chamber), and any differences between testing under these two different conditions, have not yet been determined.

In conclusion, this manuscript has systematically investigated the pressures causing eardrum rupture in ovine tissue, offering insights into human ear trauma under similar conditions. The study’s comprehensive approach, involving nineteen samples from thirteen different sheep ears and utilizing direct testing of C-1 and TNT detonations in open space conditions, has significantly contributed to understanding the biomechanical response of eardrums to blast pressures. Three distinct pressure groups were identified: under 30 kPa, between 30 and 40 kPa, and over 40 kPa, with the latter consistently resulting in ruptured tympanic membranes in all specimens (n=11). These findings align with, yet refine, the existing human eardrum rupture pressures, suggesting a lower threshold for consistent rupture. Notably, the study’s limitations, including the small sample size and variability in specimen conditions, underline the necessity for further research. Specifically, future studies should investigate the influence of factors such as living conditions, age, and medical history on eardrum rupture thresholds and expand upon the differential effects of blast pressures in varied testing environments, such as confined spaces vs. open areas. This work adds to the limited literature on eardrum rupture thresholds and sets the stage for more nuanced and precise future investigations in the field.

Acknowledgments

The assistance of Environmental Health Services at Colorado State University through the participation of Karl Swenson and Chris Giglio is gratefully acknowledged. The generous use of land overseen by the Colorado State University Foundation allowed many of these experiments to be completed.

Footnote

Data Sharing Statement: Available at https://atm.amegroups.com/article/view/10.21037/atm-25-93/dss

Peer Review File: Available at https://atm.amegroups.com/article/view/10.21037/atm-25-93/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://atm.amegroups.com/article/view/10.21037/atm-25-93/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Cadaveric specimens were obtained opportunistically from animals enrolled in unrelated studies following euthanasia. All tissues were collected post-mortem in accordance with institutional policies. As no live-animal procedures were performed and tissues were collected post-mortem, Institutional Animal Care and Use Committee (IACUC) oversight at Colorado State University was not required.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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