Biomedical subjects

R Tabari

Publications and source records attributed to R Tabari.

6 recordsLinked to original sources

PubMed1997

Effects of systemic hyperoxia on eustachian tube ventilatory function.

Middle ear negative pressure and effusions, decreased middle ear compliance, and abnormal tympanometry results have been described after diving on oxygen. Middle ear gas hyperoxia has been shown to down-regulate the eustachian tube ventilatory function (ETVF). The purpose of the present study was to investigate to what extent systemic hyperoxia in the face of air-equivalent middle ear gas composition might interfere with the ETVF. ETVF was investigated in four young adult female cynomolgus monkeys by the forced-response and inflation-deflation tests using air while the animals breathed either room air or 100% normobaric oxygen. Higher opening, closing, and steady-state pressures were observed under systemic hyperoxia. The percentage of the applied pressure equalized, and the maximal pressure change on a single swallow in the deflation test were both lower under hyperoxic conditions. The results show that systemic hyperoxia might impair ETVF. This observation adds to our understanding of the pathophysiology of middle ear dysfunction observed after diving on oxygen.

Animals↗

PubMed1997

Magnetic resonance imaging of the development of otitis media with effusion caused by functional obstruction of the eustachian tube.

In this study, magnetic resonance imaging (MRI) was used to define in vivo the effect of experimental functional obstruction of the eustachian tube (ET) on vascular permeability and the development of middle ear (ME) effusion. After collection of baseline data for ME pressure and MRI, the right tensor veli palatini muscle of 10 cynomolgus monkeys was injected with botulinum toxin A to induce ET obstruction. The left tensor veli palatini muscle was injected with saline in 4 monkeys. Right and left ME pressures and compliances were measured twice daily over a follow-up period of 36 days, and MRI scanning sessions including administration of a contrast agent, gadopentetate dimeglumine, were repeated on days 3, 6, 11, 15, 21, 29, and 36 in 6 animals and on days 15, 21, 29, and 36 in 4 animals. Two right ears did not develop underpressures, 5 developed persistent underpressures, and 3 developed underpressures that resolved. No changes in MRI parameters were noted for the ears that did not develop underpressures, but a progressive brightening of the ME on T2-weighted images, indicative of the development of inflammation and effusion, was noted for the others. Also, an increasing rate of transfer of the contrast agent between the vascular and ME compartments, indicative of increasing vascular permeability, was observed to track the temporal changes in ME pressure. These results support a causal relationship between ET dysfunction, ME underpressures, increased vascular permeability, and otitis media with effusion

Acoustic Impedance Tests↗

PubMed1996

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-de-flation 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.

Animals↗

PubMed1995

Effects of dopamine, dobutamine and phentolamine on middle ear pressure and blood flow in cynomolgus monkeys.

To test the hypothesis that changes in mucosal perfusion could influence gas exchange and thus, middle ear pressure, the effects of systemically administered drugs showing alpha adrenergic effects on mucosal perfusion and middle ear pressure were evaluated in 4 cynomolgus monkeys. Two drugs with well characterized sympathomimetic effects, dopamine and dobutamine, were studied, and dopamine was combined with an antagonist, phentolamine. For each experiment, the monkeys were anesthetized with pentobarbital and followed for a 90 min baseline period. Then, the drug was administered for 60 min with follow-up extending through that period and for an additional 60 min. Data consisted of repeated measurements of rectal temperature, heart rate, blood pressure, left middle ear pressure and right mucosal blood velocity, volume and flow. The results documented an increase in middle ear pressure after intravenous infusion of either dopamine or dobutamine and an attenuation of the response by concurrent administration of phentolamine. Laser Doppler measurements documented a variable, non-directional change in blood volume, velocity and flow. The changes in the middle ear pressure observed following systemic administration of autonomic drugs are consistent with the rapid establishment of a transmucosal pressure gradient secondary to changes in the supply and/or metabolism of gases.

Animals↗

PubMed1995

Effects of intranasal challenge with histamine, bradykinin and prostaglandin on middle ear pressure and blood flow in cynomolgus monkeys.

Previous studies documented a significant increase in middle ear pressure following intranasal challenges with ascaris antigen or histamine in sensitized cynomolgus monkeys. To confirm that effects and investigate the mechanism, 4 monkeys were intranasally challenged at separate sessions with histamine (10 mg), bradykinin (1, 10 mg) and prostaglandin D2 (PgD2, 0.5, 1.0 mg) and followed for 90 min. Before and after challenge, middle ear pressure, mucosal blood flow, heart rate, blood pressure, body temperature and the partial pressures of O2 and CO2 in the venous blood were measured. The results showed that while bradykinin challenge had no effect on these measures, PgD2 provoked increased middle ear pressure, and histamine resulted in a biphasic pattern of increasing pressures followed by decreasing pressures. The pattern of change in middle ear pressure after histamine challenge was explicable by a mechanism involving transmucosal gas exchange, while that for PgD2 was related to increased mucosal inflammation. These results document the development of positive middle ear pressures during provoked nasal inflammation and may have relevance to similar observations in the clinical setting.

Administration, Intranasal↗

PubMedDate not supplied

PCR-based detection of bacterial DNA after antimicrobial treatment is indicative of persistent, viable bacteria in the chinchilla model of otitis media.

PURPOSE: Bacterial deoxyribonucleic acid (DNA) has been previously detected by polymerase chain reactions (PCR) in a significant percentage of culturally-sterile pediatric middle-ear effusions. The current study was designed to determine whether this represents the existence of viable bacteria or the persistence of residual DNA in the middle-ear cleft. MATERIALS AND METHODS: The middle-ear cavities of two sets of chinchillas were inoculated with either: 1) 100 colony-forming units (CFU) of live Haemophilus influenzae, 2.2 x 10(6) CFU of pasteurized Moraxella catarrhalis, and 1000 ng of DNA (>10(8) genomic equivalents) from Streptococcus pneumoniae; or 2) 100 CFU of live S pneumoniae, 2.2 x 10(6) CFU of pasteurized M catarrhalis and 1000 ng of purified DNA from H influenzae. Animals were treated with ampicillin for 5 days beginning on day 3. A single-point longitudinal study design was used for sampling to eliminate the possibility of contamination. RESULTS: No DNA was detectable from the heat-killed bacteria or the purified DNA after day 3. However, DNA from the live bacteria persisted through day 21, even though all specimens were culture-negative following the initiation of antimicrobial therapy. CONCLUSION: These findings indicate that purified DNA and DNA from intact but nonviable bacteria do not persist in the middle-ear cleft in the presence of an effusion, even following high copy inoculation. In contrast, antibiotic-treated bacteria persist in some viable state for weeks as evidenced by the differential ability of the PCR-based assay systems to detect the live bacteria, but not detect the heat-killed organisms.

Ampicillin↗