Do ternary liquid mixtures exhibit negative main Fick diffusion coefficients?

Experimental data on Fick diffusion coefficients of ternary and higher mixtures depend on the reference frame; those which are in common use are associated with the average velocity either with respect to volume, mass or mole number. In this study, the dependence of diffusion coefficients on the reference frame is thoroughly analyzed for three ternary mixtures of different types. The first one, tetralin-isobutylbenzene-dodecane, can almost be considered as ideal, the second one, cyclohexane-toluene-methanol, exhibits liquid-liquid phase separation and the third one, water-ethanol-triethylene glycol, contains three associating species and is also strongly non-ideal. Experimental diffusion coefficient data sampled in the volume reference frame are transformed to the molar and mass reference frames. The required partial molar volumes are derived from present density measurements. Four additional mixtures are considered along a single or two composition paths. A highlight of this study is the existence of a strong similarity of the main diffusion coefficients in the volume and mass reference frames for all considered mixtures. When the excess volume is small, the coefficients in the molar reference frame are also similar. However, for the mixture with a large excess volume (containing water), the diffusion coefficients in the molar reference frame differ significantly, even indicating negative main diffusion coefficients. It is shown that negative main diffusion coefficients appear due to relatively large experimental uncertainties of cross diffusion coefficients, which are propagated and amplified by frame transformation.

Diffusion in Multicomponent Liquids: From Microscopic to Macroscopic Scales.

In spite of considerable research on the nature of aqueous alcohol mixtures that are characterized by microscopic inhomogeneity or incomplete mixing at the molecular level, transport properties have received little attention. We report the results of a study on diffusion in the ternary mixture of water with two alcohols, that is, water + methanol + ethanol, which is investigated on microscopic and macroscopic scales by means of molecular simulation and Taylor dispersion experiments. A novel protocol is developed for the comparison of mutual diffusion coefficients sampled by two fundamentally different approaches, which allows for their critical analysis. Because of complex intermolecular interactions, given by the presence of hydrogen bonding, the analysis of transport processes in this mixture is challenging for not only on the microscopic scale for simulation techniques but also on the macroscopic scale due to unfavorable optical properties. Binary limits of the Fick diffusion matrix are used for validation of the experimental ternary mixture results together with the verification of the validity of the phenomenological Onsager reciprocal relations. The Maxwell-Stefan diffusion coefficients and the thermodynamic factor are sampled by molecular simulation consistently on the basis of given force field models. The protocol for the comparison of the results from both approaches is also challenging because Fick diffusion coefficients of ternary mixtures depend on the frame of reference. Accordingly, the measured coefficients are transformed from the volume-averaged to the molar-averaged frame of reference, and it is demonstrated that both approaches provide not only similar qualitative behavior along two concentration paths but also strong quantitative agreement. This coordinated work using different approaches to study diffusion in multicomponent mixtures is expected to be a significant step forward for the accurate assessment of cross-diffusion.

Molecular dispersion energy parameters for alkali and halide ions in aqueous solution.

Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li(+), Na(+), K(+), Rb(+), Cs(+), F(-), Cl(-), Br(-), and I(-). The employed ion force fields consist of one Lennard-Jones (LJ) site and one concentric point charge with a magnitude of ±1 e. The SPC/E model is used for water. The LJ size parameter of the ion models is taken from Deublein et al. [J. Chem. Phys. 136, 084501 (2012)], while the LJ energy parameter is determined in the present study based on experimental self-diffusion coefficient data of the alkali cations and the halide anions in aqueous solutions as well as the position of the first maximum of the radial distribution function of water around the ions. On the basis of these force field parameters, the electric conductivity, the hydration dynamics of water molecules around the ions, and the enthalpy of hydration is predicted. Considering a wide range of salinity, this study is conducted at temperatures of 293.15 and 298.15 K and a pressure of 1 bar.

Communication: Fundamental equation of state correlation with hybrid data sets.

A strategy is proposed for empirical fundamental equation of state correlations for pure fluids on the basis of hybrid data sets, composed of experimental and molecular simulation data. Argon and hydrogen chloride are used as examples.

The neurobiology of cell death in glaucoma.

Glaucoma is an optic neuropathy in which the optic nerve axons are damaged, resulting in death of retinal ganglion cells (RGCs). The primary region of damage is thought to be the optic nerve head (ONH), with the lateral geniculate nucleus (LGN) and optic radiations to the visual cortex being secondarily affected. Neurotrophin deprivation resulting from optic nerve injury is thought to cause RGCs to die by apoptosis by inhibition of cell survival pathways. However, disruption of retrograde axonal transport is not the only mechanism associated with optic nerve damage and RGC death, and thus, an additional mechanism of injury is likely to be involved in glaucomatous optic neuropathy.

Prevalence of herpesviruses in cranial nerve ganglia.

A number of cranial nerve disorders are known to result from viral infection or reactivation, including Bell's palsy, Ramsay Hunt syndrome and herpetic laryngitis. The consequences of these diseases are well established although the patient population at risk is not. Prevalence studies in the general population are an initial step toward defining individuals at risk. The aim of this study was to determine the prevalence of herpesvirus DNA in cranial nerve ganglia in a random population sample. Qualitative molecular biologic analysis using polymerase chain reaction assay of the trigeminal, geniculate, vestibular, spiral and vagal ganglia was used in 18 randomly selected fresh cadaver heads. Herpes simplex virus (HSV) DNA was detected in 42% of all ganglia surveyed. Varicella zoster virus (VZV) DNA was detected in 44% of all ganglia. The difference in the prevalence rate between viruses was not significant (p = 0.63). At least 1 of the 2 viruses was found in 65% of all ganglia. Both HSV and VZV can commonly be recovered from cranial nerve ganglia. In order to confirm a viral etiology for various cranial nerve disorders, demonstration of a significant difference in prevalence of the viruses in specimens from afflicted individuals will be necessary.

Otic capsule fracture with preservation of hearing and delayed-onset facial paralysis.

The unusual occurrence of an otic capsule fracture with preservation of hearing is presented. In addition, the patient suffered facial paralysis beginning 6 days after the injury that rapidly recovered. Fifteen-month follow-up reveals stable hearing thresholds. The course of a fracture through the inner ear could be an important factor in determining the potential for hearing preservation.

Virtual endoscopic evaluation of labyrinthine fistulae resulting from cholesteatoma.

OBJECTIVES/HYPOTHESIS: Fistulae of the otic capsule occur in approximately 10% of cholesteatoma cases. Preoperative imaging of this complication is valuable in limiting intraoperative morbidity. Three-dimensional virtual endoscopic imaging provides a new method for analysis of conventional computed tomography (CT) imaging data. The purpose of the study was to examine the feasibility and efficacy of this technique in detecting labyrinthine fistulae caused by cholesteatoma. STUDY DESIGN: Retrospective case study. METHODS: Fifteen patients with surgically confirmed lateral semicircular canal fistula and preoperative CT scan were included. Scans meeting inclusion criteria were imported into a software program for production of virtual endoscopic images. Dehiscent and normal lateral semicircular canals were navigated while varying threshold values for surrounding bone. Changes in threshold values produce the effect of thickening or thinning the bone enveloping the semicircular canal. Threshold parameters that produced easy circumnavigation ("open") and intact inner surface of the lateral canal ("closed") were recorded. RESULTS: The fistula group demonstrated a significantly lower "closed" threshold level and, consequently, a greater range of navigation between "open" and "closed" thresholds. Intrasubject absolute differences in threshold values between normal and abnormal ears appeared to be the most accurate method for detecting a fistula. The suggested imaging parameters displayed an overall sensitivity for fistula detection of 67% with a specificity of 93%. CONCLUSIONS: The three-dimensional virtual endoscopic algorithm shows promise as a method for confirmation of otic capsule dehiscences. Sensitivity for detection is suboptimal but can be improved by alterations in image acquisition parameters.

External canal cholesteatoma.

OBJECTIVE: External canal cholesteatoma (ECC) may develop spontaneously or as a consequence of infection, trauma, or surgery. There is little information on the relative incidence of ECC according to cause. An analysis of cases was conducted to compare the clinical, surgical, and radiographic features of different types of ECC. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: All patients with cholesteatoma of the external auditory canal. INTERVENTION: Treatment was variable, ranging from local debridement and topical antibiotics to tympanomastoidectomy. MAIN OUTCOME MEASURE: Assignment of cause is based on the combination of clinical history, physical examination, and radiographic appearance. RESULTS: A total of 39 patients were reviewed, 5 of them with bilateral lesions. The cause was iatrogenic in 15, spontaneous in 13, trauma in 6, congenital in 2, postinflammatory in 2, and postobstructive in 1. Surgery was performed in 25 cases. Successful results were obtained in most patients. CONCLUSION: The cause of an ECC is determined on the basis of clinical features and radiographic appearance. The treatment plan is influenced by the cause of the ECC. Surgery is frequently necessary in congenital, posttraumatic, postobstructive, and iatrogenic ECC. Spontaneous lesions are usually controlled with office debridement.

Osteoma of the internal auditory canal.

OBJECTIVE: To review presenting symptoms and illustrate management options for this uncommon lesion. DESIGN: Case series and literature review. SETTING: Tertiary referral center. PATIENTS: Three cases of osteoma of the internal auditory canal are presented. Additional cases from the literature, diagnosed by radiographic appearance or gross description, are included for comparison. MAIN OUTCOME MEASURE: Response of clinical symptoms. RESULTS: Presenting symptoms are highly variable. Available reports do not adequately define the natural history of the lesion. CONCLUSION: The lack of a consistent presentation despite a similar radiographic appearance suggests that the osteoma is often an incidental finding.

Herpes simplex viral laryngitis.

The true incidence of herpetic infections of the larynx is unknown. This entity may be underreported because of the difficulty in establishing the diagnosis. This report describes an immune-competent patient in whom extubation failed because of mass lesions of the posterior glottis. A biopsy specimen of the lesions revealed herpes simplex virus. We review the clinical presentation and histopathologic findings in this patient.

Prevalence of herpes simplex virus in malignant laryngeal lesions.

OBJECTIVE: To determine the prevalence of herpes simplex virus (HSV) in malignant laryngeal lesions. STUDY DESIGN: Retrospective review. MATERIALS AND METHODS: Paraffin-embedded, histologically confirmed specimens containing benign laryngeal lesions, squamous cell carcinoma of the larynx, and squamous cell carcinoma of the oral cavity were identified from archived surgical specimens. Biopsies of normal-appearing oral cavity tissue were also obtained from fresh-frozen cadavers. These tissues were analyzed for the presence of HSV DNA using polymerase chain reaction techniques. Patient charts were reviewed for patient demographics, risk factors, stage, clinical course, treatment, and outcome. RESULTS: HSV was detected in nine laryngeal squamous cell carcinomas (75%) and in none of the benign laryngeal lesions (P = .0001). HSV was also found in three oral cavity squamous cell carcinomas (25%) and in none of the controls (P = .049). CONCLUSION: HSV is more prevalent in squamous cell carcinoma of the larynx and oral cavity than in their respective control groups, suggesting a role for carcinogenesis. HSV is more prevalent in squamous cell carcinoma of the larynx than of the oral cavity. Further studies to determine the role of HSV as a cocarcinogen and its interrelationship with other environmental factors in laryngeal cancer are warranted.

Meta-analysis of pediatric tympanoplasty.

OBJECTIVE: To determine which preoperative conditions or surgical techniques may influence the success of tympanoplasty in the pediatric population. DATA SOURCES: A MEDLINE search of the English-language literature from 1966 to May 1997 was conducted using the search terms pediatric or child and tympanoplasty or myringoplasty. STUDY SELECTION: Articles that provided age-specific data on tympanoplasty or myringoplasty were included. Of the original 651 studies retrieved, 30 were accepted for inclusion. The principal reason for exclusion was inability to separate adult and pediatric results in series that combined both patient populations. DATA EXTRACTION: Success was defined as an intact tympanic membrane for the purpose of this review. Data were tabulated by consensus of 2 reviewers. DATA SYNTHESIS: The effect of surgical technique, prior adenoidectomy, presence of active infection, size of perforation, status of the contralateral ear, age, and eustachian tube function on healing of the tympanic membrane after surgery was assessed. Only those studies providing data on a given parameter of interest could be included when comparing each variable. Weighted means were compared and subjected to sensitivity analysis. Simple linear regression analysis was used to assess the effect of age on outcome. CONCLUSIONS: Greater success in healing of the tympanic membrane following tympanoplasty in children is seen with advancing age. None of the other parameters studied was shown to be a significant predictor of success. Guidelines for reporting results of tympanoplasty are presented.

Delayed facial palsy after tympanomastoid surgery.

OBJECTIVES: The purpose of this report is to provide data on the incidence of delayed facial palsy (DFP) after tympanomastoid surgery, compare incidence among various otologic and neurotologic procedures, and discuss the possible etiology. STUDY DESIGN: The study design was a retrospective case review. SETTING: The study was conducted at a tertiary referral center. PATIENTS: The records of 486 patients with normal facial function before tympanomastoid surgery were reviewed. INTERVENTION: Patients underwent tympanomastoid surgery. OUTCOME MEASURES: Delayed facial palsy was defined as facial palsy occurring more than 72 hours after surgery. RESULTS: Seven of 486 (1.4%) patients had DFP after tympanomastoid surgery. In two patients, the DFP was caused by a postoperative wound infection. Facial palsy in the other five patients likely was caused by viral reactivation. CONCLUSIONS: Published data for otologic surgery suggest a rising incidence of DFP with increased manipulation of the sensory branches of the facial nerve. Viral reactivation is postulated to be an important contributing mechanism in the development of DFP. A number of viruses could potentially cause this phenomenon, but observations in this study implicate the varicella zoster virus. Patients with a history of viral reactivation may be at greater risk for development of this complication.

A temporal bone study of posterior semicircular canal resection for exposure of the internal auditory canal (PSCC resection).

Partial resection of the labyrinth is becoming accepted as a means of improving access to the internal auditory canal and central skull base neoplasms. In this investigation, an infralabyrinthine approach was performed on 20 temporal bones. The dissection was extended by transection of the endolymphatic duct, then excision of the posterior semicircular canal. The maximal lateral exposure of the internal auditory canal (IAC) was measured after each manoeuvre. Resection of the posterior semicircular canal increased lateral exposure in 7/20 specimens to an average 61% of the length of the IAC. Posterior canal resection improved superior exposure and increased the circumference of exposure in all specimens.

Short-term tympanostomy in conjunction with hyperbaric oxygen therapy.

OBJECTIVE: To determine the most effective method of short-term middle ear aeration in patients unable to tolerate hyperbaric oxygen (HBO) therapy. STUDY DESIGN: Prospective study comparing two methods of short-term tympanostomy in each patient. METHODS: Seventeen adult patients were referred for management of barotitis and inability to tolerate hyperbaric oxygen therapy (HBO). Each patient underwent CO2 laser tympanostomy on the right ear and tympanostomy with T-tube placement in the left ear. The tube was removed on completion of HBO. Patients were asked to rate pain and their satisfaction with each method of tympanostomy using a visual analog scale. Otorrhea, persistent perforation, recurrent barotitis, hearing loss, and otalgia occurring during the study period were documented. RESULTS: Laser tympanostomy was associated with a significantly lower incidence of otorrhea but was attended by recurrent barotitis in four of 16 patients. Laser tympanostomy was perceived as being less painful and was rated higher in overall satisfaction. CONCLUSIONS: Laser tympanostomy is an effective method for management of barotitis in patients unable to tolerate HBO. Otorrhea is significantly reduced, although a risk of recurrent barotitis exists if the laser perforation closes prior to completion of HBO. Both methods of short-term tympanostomy reduce complications when compared with a retrospective cohort.

Tympanic membrane perforations in the diabetic rat: a model of impaired wound healing.

Animal models of type I and type II diabetes mellitus have been studied intensively in an effort to define the pathophysiology of the diabetic condition. An often-observed clinical manifestation of diabetes is poor wound repair. Thus diabetic animals have emerged as useful models for the study of impaired wound healing. The healing of acute tympanic membrane (TM) perforations in diabetic animals has not been reported. This investigation compares time to closure of a standardized TM perforation in rats with streptozotocin-induced diabetes, Zucker diabetic fatty rats, and normal control rats. The Zucker diabetic fatty rats demonstrate a significantly prolonged time to closure compared with the other two groups. This animal model may be useful for future study of TM wound repair.

Complications of tympanostomy tubes inserted for facilitation of hyperbaric oxygen therapy.

OBJECTIVE: To document the incidence of complications occurring secondary to placement of tympanostomy tubes in patients undergoing hyperbaric oxygen therapy. DESIGN: Retrospective chart review. SETTING: Tertiary referral center. PATIENTS: Forty-five patients referred to the Department of Otolaryngology for inability to tolerate hyperbaric oxygen therapy between January 1, 1990, and December 31, 1995. INTERVENTIONS: All patients underwent bilateral myringotomy and tube placement. OUTCOME MEASURES: Charts were reviewed for complications of tube placement, including otorrhea, otalgia, hearing loss, persistent perforations, and tinnitus. RESULTS: Seventeen (38%) of 45 patients experienced complications, with most having more than 1. Most complications occurred after conclusion of hyperbaric oxygen therapy. Otorrhea was most common, occurring in 13 patients (29%). Persistent tympanic membrane perforations occurred in 7 patients (16%). CONCLUSIONS: The rate of complications is higher than reported for placement of tympanostomy tubes in other patient populations. Coexisting illness, such as diabetes mellitus, may contribute to the development of complications in patients undergoing hyperbaric oxygen therapy. Alternative methods of tympanostomy, with emphasis on shorter duration of intubation, should be considered in this patient population.