Effects of Middle Ear Oxygen and Carbon Dioxide Tensions on Eustachian Tube Ventilatory Function

The objective of this study was to determine the effect of middle ear (ME) gas composition on eustachian tube ventilatory function (ETVF). ETVF was evaluated by using forced-response and inflation-deflation tests in four alert cynomolgus monkeys during test sessions with different gas compositions. The ME was flushed with one of the four gas mixtures: 1. air; 2. 12% oxygen, 88% nitrogen; 3. 100% oxygen; and 4. 5% carbon dioxide, 21% oxygen, and 74% nitrogen before and during testing. The results documented lower opening, steady-state, and closing pressures, lower passive and active resistance, and greater dilatory efficiency following ME flushes with the hypercarbic and hypoxic gas mixtures when compared to the others. Also, for applied ME overpressure, the maximum pressure change during a swallow, the average pressure drop for all swallows, and the percentage of the applied pressure equalized were greater under hypoxic and hypercarbic conditions. These results show that ME gas composition affects ETVF and support feedback modulation of ME pressure regulation.     

Different reactions of human nasal and Eustachian tube mucosa after hyperbaric oxygen exposure: a pilot study

Impairment of Eustachian tube function has been observed after hyperbaric oxygen treatment as well as after diving on oxygen used as breathing gas. The aim of the present study was to evaluate the influence of hyperbaric oxygen exposure on Eustachian tube ventilatory function and airflow characteristics of the nose. Six police task force divers performing two consecutive dives within a regular training schedule on oxygen were examined. Middle ear impedance, and nasal airflow velocities before and after diving as well as on the morning after the dive day were measured. Middle ear impedance decreased overnight in comparison to pre-dive values (P = 0.027) as well as compared to the value after the first dive (P = 0.032). Rhinoflowmetry did not reveal any changes of nasal airflow velocities related to the dives. Furthermore, no association between middle ear impedance and nasal airflow velocities was found. An impairment of Eustachian tube ventilatory function was obtained after hyperbaric oxygen exposure during dives employing oxygen as breathing gas. This impairment, however, was not associated with altered airflow characteristics of divers’ noses. Thus, it seems unlikely that hyperbaric oxygen exerts an effect on the nasal mucosa similar to that on the Eustachian tube mucosa.     

Otologic aspects of diving

Ear diseases are the most common of all occupational diseases of diving. Otitis externa is the most frequent and troublesome infection in divers especially when the environment is humid. During compression, failure to equalize the pressure of the air-filled cavities surrounded by bone (middle ear, sinus) deprives the middle ear (or sinus) of aeration. Middle ear barotrauma is the most common barotrauma encountered in divers while external ear barotrauma (reversed ear) and inner ear barotrauma (with rupture of the round or oval window) are less common. Decompression sickness (Caisson disease) is primarily the result of inert gas bubbles; deafness and vertigo may result if the inner ear is involved. The most dramatic cause of disorientation under water is that due to vertigo. This vertigo is commonly a transient effect due to unequal caloric stimulation of the two labyrinths. The physical examination of the ear and nose necessary for assessment of diving fitness are discussed. A list of ENT contra-indications is presented which mandate temporary or permanent disqualification from diving.     

Partial oxygen tension of middle ear cavity in a normobaric environment

The present theory of eustachian tube function and middle ear ventilation posits that oxygen absorbed by the middle ear mucosa causes negative middle ear pressure which is relieved by periodic opening of the eustachian tube during swallowing and yawning. Measured by a PO2 sensor (Clark type) inserted into the middle ear cavity of normal adults through the eustachian tube, the partial oxygen pressure of the tympanic cavity was found 53.7 +/- 6.5 Torr (N:22). It was about one-third of ambient pressure (about 150 Torr), and showed no change when the eustachian tube was opened by swallowing. Our second study measured the effect of alterations in the systemic arterial blood oxygenation on middle ear gas exchange in 23 guinea pigs ventilated using 21% (room air), 50%, 70% and 100% oxygen at constant carbon dioxide blood gas tension. Partial oxygen tension (PO2) of middle ear cavity was measured by inserting a PO2 sensor into the tympanic bulla through a bore hole. The following results were obtained: (1) PO2 of the middle ear cavity was 39.3 +/- 2.2 Torr at room air, 42.2 +/- 0.84 Torr at 50%, 46.6 +/- 1.1 Torr at 70% and 54.5 +/- 3.7 Torr at 100% oxygen breathing. (2) There was a significant correlation between PO2 of the middle ear cavity and systemic arterial hyperoxygenation noted. Y = 30.79 + 0.056.X (r = 0.9440) (3) The rate of oxygen diffusion in the middle ear cavity was 2.665 x 10(-5) ml/min/cm2 and the rate of oxygen absorption in the middle ear space was 2.874 x 10(-5) ml/min/cm2. No significant difference between the rate of diffusion and that of absorption of oxygen in the middle ear cavity was noted. In our third study, electron microscopy shows that the submucosal capillaries of the human mastoid cells are structures which facilitate the intra- and extravascular transport of substances. It is known from these results that tympanic cavity pressure is kept equal to ambient pressure, or slightly higher to atmospheric pressure, by the respiratory function of the middle ear and mastoid cells so that outflow of air from the tympanic cavity to the pharyngeal orifice occurs during the ventilation of the eustachian tube at ambient pressure and inflow of air from the pharynx to the tympanic cavity is prevented in the absence of environmental pressure changes. The middle ear cavity has respiratory function, and in particular, such function of the mastoid cavity, which is larger in volume than the tympanic cavity, plays a significant role.(ABSTRACT TRUNCATED AT 400 WORDS)     

Middle ear pressure after changes in steady state

The combined effect of changes in middle ear (ME) gas composition and changes in systemic arterial blood oxygenation on total ME pressure was studied in three anesthetized juvenile Rhesus monkeys (Macaca mulatta). The gas composition of the ME was altered by ME inflation (politzerization) using either pure nitrogen, oxygen, or carbon dioxide while the animal was ventilated with either room air or 100% oxygen at constant carbon dioxide blood gas tension. Total ME pressure was measured indirectly by tympanometry (acoustic impedance) for a 5-hour duration. The changes in ME pressure were consistent and reproducible, exhibiting different pressure-time patterns unique for each gas. Carbon dioxide resulted in the most rapid decrease in ME pressure, followed by oxygen. The slowest decrease was observed in experiments with nitrogen. The systemic hyperoxygenation had little or no effect on the results. The findings were explained by the differences in relative permeabilities of these gases influencing ME gas diffusion, but the lack of systemic hyperoxygenation effect remained unexplained.     

Middle ear inflation with a gas mixture.

We studied the middle ear (ME) pressure in 13 atelectatic ears to evaluate the effect of politzerization or ME inflation by a catheter using both room air and a gas mixture. The gas contained 12% O2, 6% CO2 and 82% N2. Tympanometry was performed before and after the treatment. The elevated ME pressure induced by the treatments, whether with room air or the gas mixture, declined rapidly within the first 30 min. However, at 35 and 45 min after the treatment with room air, the mean decrease in pressure was significantly greater than with the gas mixture, which might be due to slow oxygen absorption through the ME mucosa.     

Carbon dioxide exchange via the mucosa in healthy middle ear.

BACKGROUND: Recent studies have shown that gas exchange via the middle ear mucosa, which is performed between the middle ear cleft and capillaries in the submucosal connective tissue, has an essential role in ventilation and pressure regulation in the middle ear cleft. We speculated that gas exchange via the mucosa is induced by the gas diffusion caused by the partial pressure gradient of gas between the middle ear cleft and submucosal capillaries. OBJECTIVE: To evaluate the capacity of the gas exchange via the mucosa in the healthy middle ear of humans by examining the effect of the respiratory mode on middle ear pressure. SUBJECTS AND METHODS: We selected 13 volunteers ranging in age from 25 to 44 years with healthy ear drums and type A tympanograms. Middle ear pressure was measured in 1 ear of each subject every 2 minutes using tympanometry while the respiratory mode was altered, with the subject in the supine position. RESULTS: The partial pressure of carbon dioxide in the venous blood (PvCO2) and middle ear pressure were decreased by hyperventilation and increased by hypoventilation. The partial pressure of oxygen in the venous blood showed little change. CONCLUSIONS: Carbon dioxide diffused into the blood from the middle ear cleft in accord with the partial pressure gradient when the PvCO2 was reduced by hyperventilation, resulting in a decrease of middle ear pressure, whereas CO2 diffused into the middle ear cleft when the PvCO2 was elevated by hypoventilation, resulting in an increase of middle ear pressure. These findings suggest that a bidirectional CO2 exchange via the middle ear mucosa functions in the normal human middle ear.     

A Model to Explain the Rapid Pressure Decrease After Air–Inflation of Diseased Middle Ears

Objectives: Air-inflation in humans and monkeys with significant negative middle ear pressure or with middle ear inflammation was shown to cause greater than ambient middle ear pressure initially, followed by a rapid rate of pressure decrease to approach the preinflation value. Study Design: A mathematical model of middle ear pressure regulation is presented and used to simulate air-inflation of the normal and diseased middle ear. Materials and Methods: The model represents the total volume of the middle ear as consisting of three subcompartments representing the airspace, effusion, and mucosa/blood. Gas exchange among those compartments was assumed to be diffusion limited, and the gas exchange between the mucosa/blood compartment and systemic blood was assumed to be perfusion limited. Disease was modeled as an increase in mucosal blood flow or, alternatively, as an increase in the volumes of the effusion and mucosa/blood compartments. Results: The predictions of the model agree better with the experimental data when the increased rate of pressure change after middle ear inflation in diseased ears is driven by an increased volume of the effusion compartment as opposed to an increased perfusion rate. The responsible mechanism is a rapid redistribution among subcompartments of the gas volume introduced into the air compartment. Conclusions: These results suggest that middle ear inflation with inert gas can be used to diagnose the presence and relative amount of middle ear effusion, and that current protocols for treating otitis media with effusion using inflation need to be modified to optimize their intended effect.     

Studies on gas tension in the normal middle ear. Gas chromatographic analysis and a new sampling technique

In studying mechanisms regulating the middle ear pressure it is essential to know the gas compositions of the middle ear. We have constructed a device which made it possible to sample middle ear gas without creating a negative pressure, thus eliminating the risk of admixture of atmospheric air. The samples were analysed by gas chromatography. In 26 normal subjects we found relatively stable values of carbon dioxide (median 52 mmHg, range 31-69 mmHg) and nitrogen (median 605 mmHg, range 563-627 mmHg). The values of oxygen were more fluctuating (median 54 mmHg, range 23-111 mmHg). In 10 of the subjects, arterial gases were determined simultaneously. No correlation could be shown between middle ear and arterial oxygen and carbon dioxide tensions. This investigation provides evidence contradicting the classical theory of a high negative middle ear pressure in Eustachian tube closure. We found strong indications that the Eustachian tube plays an active role in regulating the pressure in the normal middle ear, but variations in blood flow through the middle ear capillaries may also be an important regulating factor.     

Pressure chamber tympanometry in diving candidates

The currently recommended examination for diving fitness ascertains middle ear autoinflation ability only under surface pressure conditions. The purpose of our study was to document and quantify middle ear pressure equalization failure during simulated dives among diving candidates who had otherwise met the otologic criteria for diving fitness. Forty-two candidates for regular naval diving activity were included in the study. Tympanograms of both ears at 1 and 1.1 absolute atmospheres (ATA) were taken inside a pressure chamber with the subjects in two positions: seated and supine. At a pressure of 1 ATA, type A tympanograms were found in all 84 ears examined. At a pressure of 1.1 ATA, with subjects in the upright position, 19 (22.9%) of the ears had type C and 2 (2.4%) type B tympanograms, while with subjects recumbent during descent, 6 of the ears (7.2%) had type C and 7 (8.4%) type B. Our results suggest that successful autoinflation at surface ambient pressure does not necessarily reflect middle ear pressure equalization ability during descent in a dive.     

Middle ear pressure in patients with dizziness

The middle ear pressure was analyzed in 112 patients with dizziness. In 37 patients with Meniere's disease, the middle ear pressure on the low-pressure side was significantly lower, the middle ear pressure difference (between the high and low sides) was significantly larger, and the maximum compliance on the low-compliance side was significantly lower than in normal volunteers. The middle ear pressure difference was significantly larger during periods of dizziness or recurrent dizziness than at the time of remission. In patients with Meniere's disease, a middle ear pressure difference of more than 50 decapascals was significantly more common among those with abnormal blood gas levels than among those with normal blood gas levels. In 27 patients with cervical vertigo and 15 patients with vertebrobasilar insufficiency, the middle ear pressure difference was also significantly larger than in normal volunteers. These results suggest that the middle ear pressure difference might be closely related to dizziness in Meniere's disease and less closely related in cervical vertigo or vertebrobasilar insufficiency. The middle ear pressure difference might also be related to abnormal blood gas levels in patients with dizziness.     

Fluctuating hearing loss in presbyacusis

Thirty-six patients with bilateral symmetrical presbyacusis who reported a temporary improvement in the hearing of one ear following a Valsalva's manoeuvre were further investigated. Bone conduction and air conduction thresholds, middle ear pressure and middle ear compliance were measured before and after Valsalva's manoeuvre in the ears which had a subjective improvement in hearing following auto-inflation. Bone conduction thresholds remained unaltered in 66 per cent of ears while average air conduction thresholds varied by less than 5 decibels. Middle ear pressure was unchanged in over half the ears tested and in 81 per cent of the ears there was no change in middle ear compliance. There appears to be no simple explanation for the temporary subjective fluctuation in hearing reported by patients with presbyacusis.     

Tympanometry and laser Doppler interferometry measurements on otitis media with effusion model in human temporal bones.

HYPOTHESIS: The aim of this study is to investigate the effect of middle ear fluid and pressure on tympanic membrane mobility by using laser Doppler interferometry and to compare these results with tympanometry. BACKGROUND: Tympanometry has been commonly used for evaluation of otitis media with effusion, a middle ear disease with fluid in the cavity. However, this test lacks specific interpretations of middle ear disorders based on tympanometric data. Laser interferometry, as an advanced research tool to measure middle ear function, may provide knowledge of how tympanic membrane mobility is affected by middle ear fluid and pressure. METHODS: An otitis media with effusion model was created in seven human temporal bones for conducting experiments with tympanometry and laser interferometry. Middle ear pressure varied from -20 to +20 cm water, and the amount of fluid in the middle ear was gradually increased to fill the cavity. RESULTS: The displacement of the tympanic membrane measured by laser interferometry at selected frequencies decreased significantly corresponding to the middle ear air pressure changes. Tympanometry detected middle ear pressure by the change of tympanometric peak location, but the tympanogram shape was not affected by the middle ear pressure. The middle ear fluid was detected by tympanometry with as little as 0.3 mL, and laser interferometry was able to measure the displacement change of the tympanic membrane with 0.2 or 0.3 mL fluid at different frequencies. CONCLUSION: Laser interferometry can detect the effect of middle ear pressure and fluid on tympanic membrane movement as well as tympanometry does.     

Barotrauma in guinea pigs--stimulated tests of diving

For a systematic understanding of the effect of diving on hearing ability and middle and inner ear morphology, we have carried out simulated tests on 65 healthy guinea pigs, under water 60 meters deep, and then decompress rapidly. The tests proved that hearing ability changed most significantly 7 days after diving. After diving, all tympanogram curves, except those in 3 ears, changed to type B. Thirty-nine (37.85%) middle ears had been damaged, 4 (3.88%) had inner ears injured, as seen under light microscope. During decompression, three animals had nystagmus. Screen electronmicroscopy showed hair cell destruction and hair derangement. Transmission electronmicroscopy showed mitochondria damage. The results showed that damages in middle and inner ears were mainly mechanical, sometimes metabolic.     

Physiological gas exchange in the middle ear cavity

OBJECTIVES: Many reports pointed out that gas exchange in and out of the middle ear cavity occurs not only via the Eustachian tube but also across the middle ear mucosa. Our earlier study on children with otitis media with effusion (OME) for which a tympanic ventilation tube (TUBE) had been inserted revealed that the more severe the inflammatory change of the middle ear mucosa, the higher the degree of impairment of the transmucosal gas exchange function and the greater the decrease in the middle ear total pressure (METP). We hypothesized that the change in METP is caused by gas migration, and we conducted the present animal study to test this hypothesis and to determine the importance of METP measurement. MATERIALS AND METHODS: Using 30 rabbits, ten in a group in which the middle ear cavity gas was replaced with atmospheric air (Group 1, oxygen (O(2)) 20%, carbon dioxide (CO(2)) 0.03% and nitrogen (N(2)) 79.9%), ten in a group replaced with a high CO(2) pressure gas whose partial pressure of CO(2) only was increased to 5% (Group 2, O(2) 20%, CO(2) 5% and balanced with N(2)) and ten in a group replaced with a low O(2) pressure gas (Group 3, O(2) 5%, CO(2) 0.03% and balanced with N(2)), changes in the METP were measured. RESULTS: Group 1 showed a pressure change (increase, peak and then decrease in the METP) similar to that observed in a clinical cured group of OME with TUBE. In Group 2, no increase in the METP was observed and in Group 3 increase in the METP was observed but no decrease in the METP was observed. CONCLUSIONS: It was found that the increase in the METP is attributable to diffusion of CO(2). This study elucidated that the change in the METP is a physiological response. Since the METP correlates with the degree of histologic inflammatory change in the middle ear mucosa, which was revealed in our clinical study of OME, it was reconfirmed that measurement of the METP is an important test method for evaluation of the degree of improvement in the pneumatic cavity mucosa.     

Can Eustachian Tube Ventilatory Function Impairment After Oxygen Diving Be Influenced by Application of Free Radical Scavenger Vitamins C and E?

OBJECTIVES/HYPOTHESIS: To evaluate the influence of free radical scavenger vitamins C and E on eustachian tube ventilatory function changes related to oxygen dives. STUDY DESIGN: Prospective, randomized, double-blind, placebo-controlled study of middle ear impedance changes of oxygen divers being orally treated with free radical scavenger vitamins C and E. METHODS: Fifteen divers were allocated to two groups. Before diving on oxygen on consecutive days (days 1 and 2), divers in group 1 took a daily dose of 1 g ascorbic acid and 600 International Units d-alpha-tocopherol and divers in group 2 were given placebo. Before diving and 2 and 24 hours after diving on days 1 and 2, middle ear impedance was measured. RESULTS: Impedance decreased overnight after dive 1 (P =.04) but not after dive 2 (P =.31). No impedance differences were found between groups after the dive on day 1 (P =.83). Twenty-four hours after the dive on day 1 and after the dive on day 2, impedance values in both groups were different (P =.02 vs. P =.07), emphasizing slightly more negative pressures in the vitamin group. CONCLUSION: Vitamins C and E did not reduce eustachian tube ventilatory function impairment overnight after the dive on day 1, suggesting no evidence of free radical-mediated toxicity affecting the eustachian tube or middle ear mucosa. Repetitive oxygen dives may cause tissue adaptation suggesting other than antioxidant defense mechanisms.     

On the effect of hyperbaric oxygen (OHP) at the guinea pig's cochlea insulted by hypoxia (author's transl)

The effect of OHP (oxygen under high pressure) by examining 17 CO-intoxicated guinea pigs. The following effects have been observed: The microphonics recovered significantly faster after hypoxia caused by CO than under air. Hyperbaric oxygen has a protecting effect on the inner ear. If OHP is applicated before CO, the microphonics decrease less than under normal breathing. The postmortal microphonics increased to a level above the known postmortal slope, suggesting a diffusion of oxygen through the round window.     

Cyclical changes in nasal airway resistance and middle ear pressures

The relationship between unilateral changes in nasal airway resistance and the ipsilateral middle ear pressure were investigated in 8 otologically and rhinologically normal adults over the course of 7 1/2 h under laboratory conditions. Despite mean changes in unilateral nasal resistance of 0.75 Pa/cm3/s associated with the nasal cycle, no correlation existed with changes in ipsilateral Eustachian tube function, as judged by serial middle ear pressure recordings (r = 0.06, r2 = 0.00, p = 0.461). Middle ear pressure in healthy adults in a controlled environment remained very constant (mean = -6.71 +/- 0.52 daPa). 69% of middle ear pressures were equal to or above 0 daPa, which represents evidence in favour of a net positive production of middle ear gas.     

Otorhinolaryngologic disorders and diving accidents: an analysis of 306 divers

Diving is a very popular leasure activity with an increasing number of participants. As more than 80% of the diving related problems involve the head and neck region, every otorhinolaryngologist should be familiar with diving medical standards. We here present an analysis of more than 300 patients we have treated in the past four years. Between January 2002 and October 2005, 306 patients presented in our department with otorhinological disorders after diving, or after diving accidents. We collected the following data: name, sex, age, date of treatment, date of accident, diagnosis, special aspects of the diagnosis, number of dives, diving certification, whether and which surgery had been performed, history of acute diving accidents or follow up treatment, assessment of fitness to dive and special remarks. The study setting was a retrospective cohort study. The distribution of the disorders was as follows: 24 divers (8%) with external ear disorders, 140 divers (46%) with middle ear disorders, 56 divers (18%) with inner ear disorders, 53 divers (17%) with disorders of the nose and sinuses, 24 divers (8%) with decompression illness (DCI) and 9 divers (3%) who complained of various symptoms. Only 18% of the divers presented with acute disorders. The most common disorder (24%) was Eustachian tube dysfunction. Female divers were significantly more often affected. Chronic sinusitis was found to be associated with a significantly higher number of performed dives. Conservative treatment failed in 30% of the patients but sinus surgery relieved symptoms in all patients of this group. The middle ear is the main problem area for divers. Middle ear ventilation problems due to Eustachian tube dysfunction can be treated conservatively with excellent results whereas pathology of the tympanic membrane and ossicular chain often require surgery. More than four out of five patients visited our department to re-establish their fitness to dive. Although the treatment of acute diving-related disorders is an important field for the treatment of divers, the main need of divers seems to be assessment and recovery of their fitness to dive.     

Impedance measurement in divers during a scuba-diving training programme

An assessment of the strain on the tympanic membrane caused by diving was performed using impedance measurement of the middle ear in 21 untrained young men going through a scuba-diving training programme (scuba, self-contained under-water breathing apparatus). Tympanometry was carried out just before and after diving. The divers made 104 dives between them (median 5 each, range 2-7) at depths from 2 to 12 m (median 6 m). The results showed a significant increase in middle ear compliance on diving. The increase in compliance was significant at different depths, was transient, and fell to the initial level between the dives. We conclude that the strain exerted on the tympanic membrane and middle ear from barotrauma due to diving results in a reversible impairment of the recoiling capacity of the elastic fibrils of the tympanic membrane. This transient increase in compliance, we think, is the first measurable change in elasticity of the tympanic membrane. If barotrauma continue the changes could be irreversible.