Abnormal middle ear pressures during experimental influenza A virus infection--role of Eustachian tube function.

INTRODUCTION: Experimental infection of adults with influenza A virus, rhinovirus or RSV causes abnormal ME pressure in some, but not all subjects. The hypothesis tested in this study is that the response variability is caused by constitutional differences in the functioning of the Eustachian tube. METHODS: 18 adult subjects were experimentally infected with influenza A virus. On five occasions before virus exposure, middle ear pressure (by tympanometry) and Eustachian tube function (by sonotubometry) were recorded bilaterally. Tests were repeated on days 1 through 8 and 10 after infection. Individual ears were classified with respect to the number of pre-exposure, positive sonotubometric testings and the middle ear pressure response to infection was compared between ears with Eustachian tube openings at all pre-infection test sessions (GR-A) and those with at least one negative test (GR-B). RESULTS: Pre-exposure, 19, six, four, four, one and two ears had tubal openings on five, four, three, two, one and zero sessions, respectively. For that period, GR-A had significantly lesser average intra-ear and intra-group middle ear pressure variances compared to GR-B, but there were no between-group differences in the average middle ear pressure or in the number of observations of abnormal middle ear pressure. After virus exposure, middle ear pressure variances and the number of abnormal observations increased and the average pressure decreased in both groups, but the effects were more pronounced for GR-B ears. CONCLUSIONS: These results support the hypothesis that pre-existing good Eustachian tube function reduces the otological complications of viral upper respiratory tract infection.

Higher rates of pressure decrease in inflamed compared with noninflamed middle ears.

Recent clinical trials have renewed interest in middle ear inflation as a treatment for otitis media with effusion. However, air inflation in human beings with significant negative middle ear pressures was shown to be followed by a rapid pressure decrease to approach the preinflation values. In this experiment, the middle ears of anesthetized rhesus monkeys with unilateral inflammation were inflated at different times with air or N2, and pressures were recorded by tympanometry until they had stabilized or the animal had recovered from anesthesia. The results for air inflations reproduced those reported for human beings with negative pressures. Similarly, after N2 inflation a significantly greater rate of pressure decrease and significantly lesser terminal pressures were observed for inflamed ears when compared with the contralateral control ears. However, the rate of pressure decrease and the magnitude of the pressure drop were dampened by sequential N2 inflations. These observations have clinical implications with respect to the efficacy of inflation as a treatment for otitis media with effusion.

Trans-mucosal inert gas exchange constants for the monkey middle ear.

OBJECTIVE: The purpose of the study was to estimate the exchange constants for Argon and N2 across the middle ear mucosa of monkeys for use in mathematical models of middle ear pressure regulation. METHODS: In five anesthetized monkeys, the tympanic membrane was perforated and, with the animal breathing room air, a 13-ml probe attached to an Argon gas source and to a pressure transducer was introduced into the ear canal and sealed. The probe and middle ear volume was washed with Argon and then closed to the gas source. Gas samples were withdrawn from the probe at 15-min intervals for composition analysis using an online mass spectrometer. Probe partial pressures of Argon and N2 were regressed on time and the slopes of those functions were divided by the respective average partial pressure gradient for the interval to estimate the exchange constants. RESULTS: The average trans-mucosal exchange constants for Argon and N2 were 0.0007 +/- 0.0001 and 0.0003 +/- 0.0001/min, respectively. The average ratio of the two constants was 2.60 +/- 0.36 which is not different from the value of 2.3 predicted for perfusion limited gas exchange. CONCLUSION: These results confirm a very slow, perfusion limited trans-mucosal exchange of N2 and other inert gases across the middle ear mucosa. They infer that the required frequency of Eustachian tube openings to prevent the development of middle ear effusion is low and on the order of one/day.

Exchange rates of gases across the tympanic membrane in rhesus monkeys.

The exchange rates of CO2 and He across the tympanic membrane were estimated in 5 monkeys. For these experiments, the monkey was anesthetized and one arm of a polyethylene "T" tube was introduced into the external canal of the test ear and sealed to the ambient environment with wax. One arm of the T tube was attached to a pressure transducer and the other to an argon gas source via a valve. Silica tubing sealed within the probe provided periodic gas samples for composition analysis by an online mass spectrometer. Prior to each experiment, the probe was washed with Argon. In 5 experiments the probe was sealed within the external canal of animals with physiological middle ear gas compositions, and in 5 experiments the probe was sealed within the external canal of animals whose middle ears were partially washed with He. The gas in the probe was sampled and analyzed at 10-min intervals for up to 4 h. The results documented a significant increase in the percentage composition of CO2 but not He in the experiments conducted with physiological middle ear gas compositions, and increases in both He and CO2 in the experiments conducted after the middle ear was washed with He. Estimated, average exchange constants for He and CO2 were 0.0005 microl/min/mmHg and 0.0103 microl/min/mmHg, respectively. Using data from previous experiments, the relative trans-mucosal to trans-tympanic membrane gas exchange rates in monkeys are estimated to be in the order of 10:1 for inert gases and 180:1 for chemically active gases.

Effect of rimantadine treatment on clinical manifestations and otologic complications in adults experimentally infected with influenza A (H1N1) virus.

Susceptible adults (n = 105) were enrolled into a randomized double-blind study of rimantadine treatment of experimental influenza A infection. Subjects were cloistered for 8 days and challenged with a rimantadine-sensitive strain of influenza A H1N1 virus at the end of the first day. Forty-eight hours after challenge and for 8 days, 54 subjects received placebo and 51 received rimantadine (100 mg orally, twice a day). Symptoms, signs, and pathophysiologies were monitored. Nine subjects were not infected. Seventeen subjects (38%) in the rimantadine and 26 (53%) in the placebo group became ill. A beneficial effect of rimantadine was documented for virus shedding, symptom load, and sinus pain. Rimantadine had no effect on nasal patency, mucociliary clearance, nasal signs, or on symptoms and signs of otologic complications. These results do not support a preventive effect of rimantadine on the development of otologic manifestations of influenza A infection in adults.

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

Prechallenge antibodies: moderators of infection rate, signs, and symptoms in adults experimentally challenged with rhinovirus type 39.

This study determined the influence of serum neutralizing antibody titers on infection rate, symptom manifestations, and provoked signs and pathophysiologies in adults experimentally exposed to rhinovirus type 39 (RV-39). Antibody status was determined for 151 healthy volunteers who were then cloistered in a hotel for 6 days. At the end of the first cloister day, the volunteers were challenged with RV-39 in a median tissue culture infective dose of 100. On each of the 6 days, a nasal examination was performed, symptoms were scored, and objective tests of nasal mucociliary function, nasal airway patency, secretion production, and middle ear pressures were completed. Both subjects and investigators were blinded to the prechallenge serum homotypic antibody titers of the subjects. Four subjects presented with a wild virus and were excluded from the analysis. Of the 147 included subjects, prechallenge serum antibody titers to RV-39 were low (under 2) in 56 subjects, intermediate (2 to 8) in 51 subjects, and high (above 16) in 40 subjects. The high-titer group was significantly different from the low-titer group with respect to viral shedding, symptom load, subjective extent of illness, and secretion production, as well as in the frequency of subjects with abnormal nasal mucociliary clearance and positive middle ear pressures. The study results document that for experimental RV-39 exposure, high levels of homotypic serum neutralizing antibody titers are associated with protection from infection and a lessened degree of disease expression, but not with a reduction of otologic complications.

Efficacy of clarithromycin treatment of acute otitis media caused by infection with penicillin-susceptible, -intermediate, and -resistant Streptococcus pneumoniae in the chinchilla.

Because of the increasing frequencies of recovery of penicillin-resistant Streptococcus pneumoniae from the middle ears of children with acute otitis media, non-beta-lactam antibiotics are being explored as treatment alternatives to amoxicillin. In this study, the efficacy of a 10-day course of clarithromycin was evaluated with chinchillas. After the pharmacokinetic profiles for clarithromycin were established, 180 animals were assigned to one of three susceptibility groups (n = 60/group; penicillin-susceptible, -intermediate, and -resistant S. pneumoniae), and the right middle ear was infected with the appropriate strain of S. pneumoniae. Equal numbers of animals in each group were treated orally beginning on day 2 with a 10-day course of clarithromycin (15 mg/kg of body weight; given twice a day) or amoxicillin as a control (20 mg/kg twice a day). On days 4, 9, and 13, otomicroscopy and tympanometry were performed, and on day 13, the middle ears were cultured for bacteria. The results showed 100% eradication of the challenge organism in both treatment groups for the susceptible strains of S. pneumoniae. Cultures were negative in 87 and 74% (P > 0.05) of the animals challenged with the intermediate resistant strains and in 100 and 56% (P < 0.05) of the animals challenged with the resistant strains and treated with clarithromycin and amoxicillin, respectively. There were no differences between treatments in the diagnosis of effusion for any group. These results support the use of the chinchilla to evaluate drug efficacy in the treatment of acute otitis media and show clarithromycin to be effective in sterilizing the middle ears of animals challenged with penicillin-susceptible, -intermediate, and -resistant strains of S. pneumoniae.

Influenza A virus--induced acute otitis media.

To better understand the significance of viral upper respiratory tract infections in the pathogenesis of acute otitis media (OM), 27 adults underwent intranasal inoculation with influenza A virus. Monitoring consisted of antibody titer determination, tympanometry, and otoscopy. Microbiologic analysis consisted of cultures and polymerase chain reaction (PCR)-based detection for influenza A virus, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. All subjects became infected with the challenge virus. By day 4, 16 (59%) developed middle ear pressures of -100 mm H2O or below and 4 (25%) of them developed OM. One subject (4%) developed purulent OM requiring myringotomy for pain relief. Middle ear effusion cultures were negative. PCR analysis of that subject's middle ear effusion and nasal washes were positive for influenza A virus and S. pneumoniae. These findings support a causal role for viral upper respiratory tract infections in the pathogenesis of OM, possibly mediated by middle ear underpressures and viral and bacterial middle ear infection.

Gas exchange across the middle ear mucosa in monkeys. Estimation of exchange rate.

OBJECTIVE: To estimate the rate of exchange of selected gases across the middle ear (ME) mucosa and define the exchange limitations. DESIGN: At separate sessions, the ME was inflated via the eustachian tube with a bolus of pure nitrogen, carbon dioxide, oxygen, or nitrous oxide, and ME pressures were recorded by tympanometry at selected intervals for up to 4 hours. The slope of the function relating pressure change to pressure was calculated by least squares regression and used as an estimate of the rate constant for exchange of that gas (experiment 1). Because of the slow rate of nitrogen exchange, a second experiment was performed in which the tensor veli palatini muscle was unilaterally paralyzed. The ME was inflated with nitrogen, and the slope of the rate-pressure function for measurements at 24-hour intervals was used to estimate the rate constant. SUBJECTS: Ten juvenile cynomolgus monkeys, six for experiment 1 and four for experiment 2. RESULTS: The relative, average rate constants for carbon dioxide, nitrous oxide, oxygen, and nitrogen were 1, 10.7, 18.6, and greater than 700, respectively. Comparisons of these rates with those predicted by theory show that oxygen and carbon dioxide exchange is diffusion limited, and nitrous oxide and nitrogen is perfusion limited. CONCLUSIONS: The perfusion limitation for nitrogen suggests that its exchange rate is notably increased by inflammation from increased mucosal blood flow. Targeting inflammation for therapy of persistent ME effusions may decrease the rate of nitrogen exchange and reestablish normal ME pressure regulation.

In vivo observation with magnetic resonance imaging of middle ear effusion in response to experimental underpressures.

In this study, magnetic resonance imaging (MRI) was used to define, in vivo, the effect of acute middle ear (ME) underpressures on vascular permeability and the development of effusion. The MEs of four cynomolgus monkeys were unilaterally inflated with oxygen and carbon dioxide on different occasions and followed for a period of approximately 4 hours by tympanometry and MRI scanning. Carbon dioxide inflations caused the rapid development of ME underpressures of less than -600 mm H2O by 10 minutes. The MRI scans showed a progressive brightening of the ME and all associated air cells, indicative of the accumulation of effusion in three of the four experiments. An MRI contrast agent was administered to the vascular compartment during the course of the experiment and was rapidly transferred to the ME space, indicating vascular permeability to the agent. The contralateral, control side did not develop significant underpressures, effusion, or increased vascular permeability. Inflation with oxygen caused lesser underpressures and no accompanying changes in the MRI scans. These data support the hydrops ex vacuo theory and confirm the usefulness of MRI for in vivo documentation of the development of ME effusions and changes in vascular permeability of the mucosa in the experimental setting.

Otologic and systemic manifestations of experimental influenza A virus infection in the ferret.

In an effort to further validate an animal model and to better define the mechanisms relating viral upper respiratory tract infections and acute otitis media, we infected 10 ferrets intranasally with influenza A virus. Infection was monitored by cultures and antibody titers, illness was monitored by signs and temperatures, and otologic complications were monitored by otoscopy, tympanometry, and eustachian tube function testing. All animals became infected. Forced-response test results showed progressive increases in the passive function variables after inoculation. Inflation-deflation test results documented progressive impairment of active tubal function, which was accompanied by the development of middle ear underpressures. No otitis media was seen. The results suggest that influenza A virus infection results in progressive, subtotal occlusion of the eustachian tube lumen, which compromises the ventilatory function of the tube, thereby promoting the development of middle ear underpressures. These findings support the hypothesized pathophysiologic relationship between viral upper respiratory tract infections, eustachian tube dysfunction, middle ear underpressures, and acute otitis media. Given these pathophysiologic changes and previously documented physiologic similarities to the eustachian tube-middle ear system of human beings, we conclude that the ferret represents an appropriate animal model for studying the pathogenic processes related to viral upper respiratory tract infections, eustachian tube dysfunction, and otitis media and for testing of potential prophylactic and therapeutic regimens.

Reproducibility of the effects of intranasal ragweed challenges in allergic subjects.

BACKGROUND: Intranasal allergen challenges have been used to study the pathogenesis of disease expression, to evaluate the efficacy of therapies and to make diagnosis of allergic status. Few data, however, are available regarding the reproducibility of the responses to such provocative challenges. OBJECTIVE: The purpose of this study was to evaluate the reproducibility of selected responses of allergic subjects to intranasal pollen challenge. METHODS: Eighteen adults with ragweed allergy completed three dose-response challenge sessions at a minimum interval of 1 week. Sessions were single blinded and randomized to include two intranasal ragweed challenges (doses 10, 100, and 1000 PNU) and one placebo challenge conducted out of the ragweed season. Additionally, 12 of these subjects completed a third ragweed challenge session conducted during the ragweed season. Following administration of each dose, symptoms were scored, sneezes counted, and nasal patency measured by active posterior rhinomanometry. Total nasal secretion weight for each session was measured. RESULTS: For all measures, average dose response curves were identical for the two extra-seasonal ragweed challenges and these were significantly different from those of the placebo challenge session. Intra-individual responses to the two ragweed challenges were highly correlated between sneeze count and secretion weight, and were moderately correlated for objective and subjective measures of rhinorrhea and congestion. No significant increases in these responses were observed for the intra-seasonal ragweed challenge session. CONCLUSIONS: These results document a reproducible symptomatic and physiologic response to intranasal ragweed challenge.

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.

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.

Middle ear gas exchange in rhesus monkeys.

The mechanism of gas exchange between the middle ear and tissue is fundamental to understanding middle ear physiology and pathophysiology. In this study, the middle ears of six rhesus monkeys were inflated on separate occasions with nitrogen (N2), carbon dioxide (CO2), and oxygen (O2), and middle ear pressures were recorded at defined times postinflation for up to 4 hours. From these data, rate constants governing the exchange of these gases were estimated and compared to those predicted under both diffusion and perfusion limitations. The results show that the rate constants for middle ear to tissue exchange of O2 and CO2 are consistent with a diffusion-limited process. In contrast, middle ear pressure did not decrease over the study period following introduction of N2 into the middle ear. This is interpretable as a much slower rate of N2 exchange than that predicted by either perfusion or diffusion-limited models calibrated to the O2 and CO2 rate constants. These results have significant implications for middle ear gas exchange and suggest that for relatively short observation periods, the behavior of middle ear pressure is controlled by experimentally established O2 and CO2 gradients.

An experimental study of cefixime in the treatment of Streptococcus pneumoniae otitis media.

Previous studies using the chinchilla animal model demonstrated that the third generation cephalosporin cefixime (Suprax) with split dosing was as effective as ampicillin in sterilizing the middle ear cleft when infected with S. pneumoniae. In this investigator-blinded, randomized trial, a single daily dose of cefixime (8 mg/kg per day) performed as well as split dosing of cefixime (8 mg/kg every 8 h) and ampicillin (150 mg/kg every 8 h) in the time to sterilization of the middle ear cleft. No statistically significant differences were noted between groups in otoscopy or tympanometry. All antibiotic regimens performed better than saline control (P < 0.0001) with regard to time to sterilization of the middle ear cleft. The results of this study support the daily administration of cefixime as an effective agent for the treatment of otitis media due to its extended half-life and broad antibiotic spectrum.

Effect of experimental rhinovirus 39 infection on the nasal response to histamine and cold air challenges in allergic and nonallergic subjects.

To determine whether a viral upper respiratory tract infection can alter the responsiveness of the nasal mucosa, paired intranasal histamine and cold air challenge sessions were performed before and after (8 to 13 days) experimental rhinovirus infection in 18 nonallergic subjects and 20 subjects with seasonal allergic rhinitis. The nasal response to the challenges was measured as symptom scores for rhinorrhea and congestion, counts for sneezing, weight for expelled secretions, and inspiratory conductance for nasal patency. For both sessions, a greater response was observed in allergic subjects for sneezing, symptoms of rhinorrhea and congestion, secretion weights provoked by histamine challenge, and secretion weights provoked by cold air challenge when compared with the nonallergic subjects. A comparison of the responses to the paired challenge sessions showed greater responses for sneezing, secretion weight and rhinorrhea to histamine and for secretion weight to cold air challenges performed after rhinovirus infection. No differences were observed between allergic and nonallergic subjects with respect to the degree of enhanced responsiveness secondary to viral infection. These results document an increased responsiveness of the nose to these stimuli during the postsymptomatic period of a rhinovirus infection in both allergic and nonallergic subjects.

Nasal and otologic effects of experimental influenza A virus infection.

Past studies showed that experimental rhinovirus colds in adults resulted in eustachian tube dysfunction and abnormal middle ear pressures. In the present study, the symptoms and pathophysiologic findings accompanying experimental influenza viral infection were documented. A total of 33 healthy adult volunteers were intranasally challenged with an influenza A/Kawasaki/86 (H1N1) virus and cloistered over a 9-day postchallenge period to monitor for evidence of infection, signs and symptoms of illness, and the extent and frequency of pathophysiologic responses of the nose, eustachian tube, and middle ear. Results showed a protective effect of high (> or = 16) prechallenge specific hemagglutination-inhibition antibody titer on the rate of infection and the magnitude and extent of provoked symptoms and pathophysiologic findings. Infected subjects with low (< 16) prechallenge serum antibody titers (n = 21) developed significant respiratory illness. These subjects also had objectively measurable increases in nasal secretion production, and decreased nasal patency and mucociliary clearance rates. More than 80% of the infected subjects developed eustachian tube dysfunction, and approximately 80% had middle ear underpressures of less than -100 mm H2O on study days 4 and 5. Five of 21 infected subjects with low prechallenge antibody titers had otoscopic evidence of otitis media with effusion. These results support a causal role for viral upper respiratory tract infection in the pathogenesis of otitis media, possibly mediated by the early development of eustachian tube dysfunction and abnormal middle ear pressure.

Rhinovirus 39 infection in allergic and nonallergic subjects.

To determine if individuals with allergic rhinitis are hyperresponsive to upper respiratory tract viral infections, 20 allergic and 18 nonallergic, susceptible, adult volunteers were challenged and infected with rhinovirus type 39 before the pollen seasons. Before challenge and on each of 6 days of cloister, all volunteers were interviewed for symptoms and completed a test battery consisting of evaluations of secretion production by weighed tissues, nasal patency by active posterior rhinomanometry, nasal clearance by the dyed saccharin technique, pulmonary function by spirometry, eustachian tube function by sonotubometry, and middle ear status by tympanometry. The symptomatology and pathophysiology resulting from the rhinovirus infection were consistent with those reported in previous studies with this challenge system. Between-group comparisons revealed no differences in symptom presentation, nasal secretion production, or overall pathophysiologic response. However, for decreased mucociliary clearance rate, increased nasal congestion, eustachian tube dysfunction, and symptoms of sneezing, the allergic group demonstrated an earlier onset compared with that of the nonallergic group. The biologic significance of the differences in onset of dysfunction is tempered by the observation that the temporal pattern of responses in the allergic group was similar with that of nonallergic subjects in previous studies. The results of the present study do not support the hypothesis of a physiologic hyperresponsiveness to rhinovirus type 39 infection in allergic subjects during nonallergy seasons.