Middle Ear Gas Composition and Middle Ear Aeration

Abstract

Partial pressures of the gases in the middle ears of 14 guinea pigs were measured continuously on-line with a specially designed mass spectrometer. The average values were carbon dioxide 67.55 mm Hg, oxygen 48.91 mm Hg, and nitrogen 596.54 mm Hg. These values confirm earlier measurements and show that the gas composition of the middle ear differs basically from that of air and resembles that of venous blood. These findings are indicative of bilateral diffusion between the middle ear cavity and the blood. We propose that under physiologic as well as under pathologic (ie, atelectatic) conditions, the gas content of the middle ear is also controlled by diffusion. This mechanism fits well with the fluctuating character of atelectatic ears. Thus, a negative middle ear pressure could be secondary to excessive loss of gases through increased and excessive diffusion, although additional mechanisms are probably also involved. A likely contributing factor is poor pneumatization of the mastoid, with consequent absence of a physiologic pressure regulation mechanism by its pneumatic system.

Changes in Availability of Oxygen Accentuate Differences in Capsular Polysaccharide Expression by Phenotypic Variants and Clinical Isolates of Streptococcus pneumoniae

“…In particular, the availability of oxygen is decreased in the common manifestations of pneumococcal disease such as pneumonia, empyema, and otitis media where the exudative inflammatory response occludes air spaces and limits gas exchange. Oxygen levels in the uninflamed middle ear space, for example, resemble that of venous blood, are less than a third that of the airway, and may be further reduced by the presence of effusion (8,9,26). If an effect similar to that described in this study occurs in vivo, the reduced-availability of oxygen would select for an upregulation in CPS expression.…”

“…The results of this study suggest that (i) the oxygen availability on the airway surface suppresses CPS production and, therefore, may facilitate adherence of pneumococci during the commensal state, and that (ii) the less-aerobic microenvironment encountered, for example, in the dense consolidation of the alveolar spaces during pneumonia or the inflammatory exudate in the middle ear space during otitis media may enhance virulence by triggering increased expression of CPS (8,9,26). Phenotypic differences in clinical isolates, furthermore, support the concept that different host environments select for distinct subpopulations of pneumococci in natural infection.…”

The mastoid as a functional rate-limiter of middle ear pressure change

“…P e N2 ≥ P v N2 ≥ P a N2 [25,26]. From this it follows that P a N2 − P v N2 ≥ P a N2 − P e N2 and a constant of proportionality (F e N2 ) can be chosen such that (P a N2 − P v N2 ) = F e N2 (P a N2 − P e N2 ).…”

Otitis media with effusion: expectant management

“…A composição normal dos gases no ouvido médio está em equilíbrio com a circulação venosa local em relação ao O 2 e CO 2 , enquanto N 2 tem uma diferença de 50mm Hg 52 . A fisiologia básica respiratória no procedimento de autoinsuflação, conforme é proposta atualmente, contraria a afirmação de que ele é um tratamento efetivo para crianças com OMCS.…”