Middle ear as a gas pocket

Identification of early inflammatory changes in the tympanic membrane with Raman spectroscopy

The tympanic membrane (TM) is a dynamic structure that separates the middle ear from the external auditory canal. It is also integral for the transmission of sound waves. In this study, we demonstrate the feasibility of using Raman spectroscopy to identify early chemical changes resulting from inflammation in the TM that can serve as an indicator of acute otitis media. Bacterial lipopolysaccharide (LPS) was injected trans-tympanicaly in a murine model. Presence of inflammatory response was assessed with binocular microscopy, confirmed with histopathology and immunofluorescence staining. Successful discrimination suggesting spectral differences among the control and LPS treated groups was achieved using principal component analysis. Raman imaging revealed major differences in collagen distribution and nucleic acid content. Image segmentation analysis on the trichrome stained tissue sections was performed to corroborate the Raman spectra. The spectral co-localization study suggests changes in the expression of collagen IV specific signals in LPS treated samples. The overall findings of the study support prospective application of RS in the diagnosis and therapeutic monitoring of otitis media.

[The modern approaches to the evaluation of the importance of chronic inflammation in the mucous membrane of the middle ear]

Despite the ever growing progress in antibiotic therapy and the advent of the new methods for this purpose, the number of patients suffering from chronic focal infection of the ENT organs has not decreased during the last decades which turns the problem of chronization of inflammation into a serious challenge for the physicians as exemplified by chronic inflammation in the mucous membrane of the middle ear. Pathological changes in the middle ear make up a large fraction of ENT diseases of importance not only for otorhinolaryngologists but also for the specialists in the related medical disciplines. The present article is an overview of etiological, pathogenetic, and pathomorphological aspects of chronization of the inflammation process that are known to occur in the mucous membrane of the middle ear. In the overwhelming majority of the cases, the main cause of the conversion of acute inflammation in the middle ear into the chronic condition is the inadequate (incorrect), inopportune or incomplete treatment of the acute inflammatory process in the middle ear.

Tubotympanic system functioning

The Eustachian (auditory) tube and tympanomastoid cavities form an anatomic and functional whole that cannot easily be divided, and is therefore known as the "tubotympanic system". The system has been the focus of several studies, with complex and sometimes contradictory results, making an overview of its functioning difficult to obtain. The objective of the present article is to review the current state of knowledge, as an indispensable preliminary to understanding tubotympanic system dysfunction, and notably the development of chronic otitis. The system as a whole is covered by mucosa, which provides continuity, although with certain particularities from one area to another, and plays a primordial role. Thus, under physiological conditions, gas diffusion across the tympanomastoid mucosa largely ensures the equilibrium of pressure between the middle ear and outside environment, the tube orifice being very little involved. Under large rapid change in atmospheric pressure, the aeration function of the Eustachian tube comes into play, governed by a reflex mechanism. The system also has other functions that are essential to good middle-ear functioning: protection against nasopharyngeal secretions and pathogens and against certain physiological noises; middle-ear cavity clearance by mucociliary transport of pathogens, partly related to submucosal gland secretion; and immune defense.

Surgical anatomy and pathology of the middle ear

Middle ear surgery is strongly influenced by anatomical and functional characteristics of the middle ear. The complex anatomy means a challenge for the otosurgeon who moves between preservation or improvement of highly important functions (hearing, balance, facial motion) and eradication of diseases. Of these, perforations of the tympanic membrane, chronic otitis media, tympanosclerosis and cholesteatoma are encountered most often in clinical practice. Modern techniques for reconstruction of the ossicular chain aim for best possible hearing improvement using delicate alloplastic titanium prostheses, but a number of prosthesis-unrelated factors work against this intent. Surgery is always individualized to the case and there is no one-fits-all strategy. Above all, both middle ear diseases and surgery can be associated with a number of complications; the most important ones being hearing deterioration or deafness, dizziness, facial palsy and life-threatening intracranial complications. To minimize risks, a solid knowledge of and respect for neurootologic structures is essential for an otosurgeon who must train him- or herself intensively on temporal bones before performing surgery on a patient.

Behaviour of middle ear cleft mucosa during inflammation: histo- morphometric study

CONCLUSION

This histo-morphometric study shows a significant reduction in the distance between the blood vessel's centre and the basal membrane of the middle ear cleft mucosa during inflammatory process. This could suggest that gaseous exchange is faster and more abundant in inflamed mucosa. The distance is significantly shorter in the postero-superior compartment of the middle ear cleft, possibly favouring a specific gas exchange function.

OBJECTIVES

The aim was to try to understand the morphologic changes that occur when the middle ear cleft mucosa suffers from chronic inflammation.

MATERIALS AND METHODS

Light microscopic computerized morphometry was used to measure the distance between the centre of the blood vessels and the basement membrane of the middle ear cleft mucosa.

RESULTS

In inflammation, the distance from blood vessel to mucosa is reduced in all five regions of the middle ear cleft. This distance is statistically the shortest in the postero-superior compartment of the middle ear cleft.

Continuous long-term measurements of the middle ear pressure in subjects without a history of ear disease

A new method was used for continuous measurement of the middle ear (ME) pressure during a 24-h period. In 10 subjects without a history of ear disease a small perforation was made through the tympanic membrane. A tight rubber stopper containing a small polyethylene tube was fitted into the external ear canal. Conventional tubal function tests were performed. The equipment was then carried by the subjects for 24 h of normal activity to monitor any slow or rapid dynamic pressure change in the ME. Body position was found to be the most important factor affecting ME pressure variation, during the 24-h continuous pressure measurements. A significant pressure rise occurred in the recumbent position in all but one subject. Few rapid pressure equilibrations were seen during the recordings, indicating few tubal openings. This implies that the pressure changes in the ME seen in this study were mainly the result of gas exchange over the mucosa. The investigation might be a base for reference when investigating different kinds of pathologic conditions in the ear.

Histomorphometric study of the normal middle ear mucosa. Preliminary results supporting the gas-exchange function in the postero-superior part of the middle ear cleft

This study concerns the distance between the centre of gravity of blood vessels and the basement membrane of the middle ear cleft mucosa. The measurements were performed perpendicular to the long axis of the cross-section of the vessels, and revealed a significant difference between two regions of the middle ear cleft. At the level of the postero-superior part (epitympanum, aditus ad antrum, mastoid antrum and highest part of the mastoid air cells system), the distance between the blood vessels and the basement membrane of the mucosa was statistically shorter than in the antero-inferior part of the middle ear cleft. This indicates a privileged function of gaseous exchange of the postero-superior part of the middle ear cleft and may divide the middle ear cleft into different functional parts.

Continuous 24-hour measurement of middle ear pressure

A new method was developed for continuous measurement of the middle ear pressure during a 24-h period. The equipment consisted of a piezo-electric pressure device and a digital memory. To allow continuous pressure recordings during normal every-day activities the equipment was made light and portable. The measurement accuracy of the equipment as well as the base-line and temperature stability were tested and found to meet to our requirements satisfactorily. In 4 volunteers with different middle ear conditions, a small perforation was made through the tympanic membrane. A rubber stopper containing a small polyethylene tube was fitted into the external ear canal. Tubal function tests were made to establish the equipment's ability to monitor fast pressure changes. The tests were well in accordance with other methods of direct pressure measurements. The equipment was carried by the volunteers for 24 h to monitor any slow or rapid dynamic pressure changes in the middle ear. Four continuous 24-h measurements are presented. The method was found to be suitable for valid measurements of dynamic pressure changes in the middle ear during normal every-day activities. It may become a useful instrument in the search for a better understanding of the development of chronic middle ear disease.

Role of Allergy in Eustachian Tube Blockage and Otitis Media with Effusion: A Review

Recent studies continue to support a role for allergy in the pathogenesis of otitis media with effusion. Although a variety of mechanisms have been proposed to relate these two disease conditions causally, none has been completely validated by experimental or clinical studies. This review suggests that the observed relationship between allergy and otitis media with effusion is caused by mediators of inflammation and cytokines and colony-stimulating factors released by mucosal mast cells and other inflammatory and epithelial cells in the nose and nasopharynx. These mediators produce blockage of the eustachian tube through a number of mechanisms, which may include local injury or vascular- or neural-mediated changes in the eustachian tube opening pressure and in middle ear perfusion. It is likely that the nasal allergic response in patients predisposes to eustachian tube blockage and, if prolonged, causes changes in gas absorption in the middle ear space. This gas exchange primarily involves nitrogen absorption, which may take several days to develop. This persistent underpressure will then lead to middle ear effusion. Irrespective of the theoretical mechanism, the relationship between allergy and otitis media with effusion will remain controversial until well-controlled clinical studies are conducted documenting that in select populations antiallergy therapy is efficacious in preventing or limiting the duration of otitis media with effusion.

Gas diffusion in the middle ear

The ex vacuo theory, claiming that in cases of middle ear underaeration air enters the middle ear through the Eustachian tube in diminished amounts while oxygen continues to leave it into the blood by diffusion as in normal condition, does not provide a complete explanation for the aeration problems encountered in middle ear pathology. This study shows that when atelectatic ears are politzerized (hyperinflated) with different gases, these gases disappear with a speed that correspond to the diffusion coefficient of the different gases. This finding together with the fact that the composition of middle ear gases is very similar to that found in the venous circulation suggests that it is a diffusional process of several gases from the middle ear into the blood and in the opposite direction that mainly determines the middle ear pressure.