Vestibular Symptoms, Balance and Vestibular Function in Patients with Vestibular Schwannoma

Bakgrunn: Vestibularisschwannom (VS) er en godartet svulst på den 8.hjernenerve som ofte fører til hørselstap, øresus, ustøhet og vertigo. Behandling avhenger av svulstens størrelse og om svulsten vokser, og inkluderer enten observasjon (wait-andscan), stråling eller operasjon. Man vet lite om det naturlige forløpet av sykdommen når det gjelder vestibulære symptomer og funksjon. Mål: Å undersøke hvordan vestibulære symptomer og funksjon påvirkes av et ubehandlet VS, både på kort og lang sikt. Materialer og metode: Pasienter med nylig diagnostisert, ubehandlet VS ble inkludert i periodene 2001-2010 og fra juni 2017 til juni 2019; henholdsvis en gruppe pasienter som ble fulgt opp regelmessig i inntil ti år og en tverrsnitts studie. Resultater: Ingen svimmelhet ble rapportert av 35% av pasientene. Moderat til alvorlig svimmelhet ble rapportert hos 31% og var assosiert med kanal parese og postural ustøhet. I gruppen uten vekst av tumor i oppfølgningsperioden (N=114) fant vi ikke signifikant økning av svimmelhet, postural ustøhet eller kanal parese. Vi fant videre at ustøhet ved posturografi predikerte vekst av tumor innen 3 år (OR=5,6 og 95% CI 2,6-11,8). 6-canal video hode impuls test (vHIT) og kalorisk prøve var de mest sensitive testene med sensitivitet på henholdsvis 51% og 47%. vHIT av posteriore kanal var ofte abnormal på den friske siden (17%). Kombinasjonen av kalorisk prøve og cervicale vestibulære myogene potensialer (cVEMP) økte sensitiviteten til 65% samtidig som bare noen få hadde abnormal test på non-tumor siden (6%). Konklusjoner: Majoriteten av ubehandlede pasienter med VS opplevde enten ingen svimmelhet eller kun milde symptomer. Funnene våre indikerer en god prognose når det gjelder vestibulære symptomer og vestibulær funksjon hos pasienter som behandles konservativt i form av wait-and-scan. Ustøhet målt på posturografi, predikerte vekst av svulsten innen 3 år hos pasienter med ubehandlet VS. En konsekvens av dette kan være at ustødige pasienter trenger mer aktiv oppfølgning. Kombinasjonen av kalorisk prøve og cVEMP var den mest nyttige, noe som skyldtes en relativ høy sensitivitet og en lav andel av abnormale resultat på den friske siden.Background: Vestibular schwannoma (VS) is a benign tumor on the 8th cranial nerve that often leads to hearing loss, tinnitus, unsteadiness and vertigo. Treatment is based on tumor size or whether there is growth of tumor, and includes either observation (wait-and-scan), radiosurgery or microsurgery. Little is known about the natural course of the disease when it comes to vestibular symptoms and function. Aim: To study how vestibular symptoms and function are affected by untreated VS, in a short- and long-term perspective. Material and methods: Patients with newly diagnosed untreated VS were included in the periods 2001-2010 and from June 2017 to June 2019. A cohort followed up regularly for up to ten years and a cross-sectional study, respectively. Results: No dizziness was reported by 35% of the patients. Moderate to severe dizziness was reported by 31% and was associated with canal paresis and postural instability. In the subgroup with no growth of tumor during follow-up (N=114) we found no significant increase in dizziness, postural unsteadiness or canal paresis. Furthermore, unsteadiness on posturography predicted tumor growth within 3 years (OR= 5.6, 95 % CI 2.6, 11.8). The 6-canal video head impulse test (vHIT) and the caloric test were the most sensitive tests with sensitivities of 51% and 47 %, respectively. Posterior canal vHIT often showed abnormal results on the non-tumor side (17%). The combination of caloric test and cervical vestibular evoked myogenic potentials (cVEMP) increased the sensitivity to 65%, while only a few had abnormal tests on the non-tumor side (6%). Conclusions: The majority of untreated VS patients experienced either no dizziness or only mild symptoms. Our findings suggest a favorable long-term prognosis for vestibular symptoms and functions in patients managed through a wait-and-scan approach without tumor-growth. The presence of unsteadiness, as measured by posturography, predicted tumor growth in untreated VS patients within three years. An implication of this could be that unsteady patients need more active management. The combination of caloric test and cVEMP was most useful, due to the relatively high sensitivity and low prevalence of abnormal tests on the non-tumor side.Doktorgradsavhandlin

Flowability of Dry and Water Wet Barite Powder

Barite is added to drilling fluids as weight material to increase its density. Over time, when the drilling fluids are left static in the annulus, gravitational forces will make the barite settle out. This settled barite is today the main reason for casing cut and removal process, which accounts for up to 50% of time related to P&A operations. Knowledge of settled barite on top of cement behind casing is also essential for perf, wash & cement procedures. The most compact barite sediment can be characterized as a non-elastic dense wet particle sediment where the packing of the particles and the particle size of the grains varies. To fully understand the packing mechanism of the consolidated barite sediments characterization of barite powder (both dry and wet) is important. In this study we have done comparable measurements with a Jenike shear test, which measures direct shear strength under different loading conditions, and compared these to rheological measurements using an Anton Paar powder module under the same loading conditions. Experiments were performed on both dry and wet (by 2.5 wt% and 5 wt% water) barite and with 1, 3, 6 and 9 kPa loading. The results from the Jenike test and the powder module were found to be complimentary. At a low water content, the sample showed an increase in flowability, while with a high-water content a decrease the flowability was observed compared to that of dry barite.acceptedVersio

Long-term effects of conservative management of vestibular schwannoma on dizziness, balance, and caloric function

Objectives: To study the development of dizziness, caloric function, and postural sway during long-term observation of untreated vestibular schwannoma patients. Study Design: Retrospective review of a prospectively maintained longitudinal cohort. Setting: Tertiary referral hospital. Subjects and Methods: Patients with vestibular schwannoma undergoing wait-and-scan management were included—specifically, those who did not require treatment during a minimum radiologic follow-up of 1 year. Baseline data and follow-up included magnetic resonance imaging, posturography, bithermal caloric tests, and a dizziness questionnaire. Main outcomes were prevalence of moderate to severe dizziness, canal paresis, and postural instability at baseline and follow-up, as compared with McNemar’s test. Results: Out of 433 consecutive patients with vestibular schwannoma, 114 did not require treatment during follow-up and were included. Median radiologic follow-up was 10.2 years (interquartile range, 4.5 years). Age ranged from 31 to 78 years (mean, 59 years; SD, 10 years; 62% women). Median tumor volume at baseline was 139 mm3 (interquartile range, 314 mm3). This did not change during follow-up (P = .446). Moderate to severe dizziness was present in 27% at baseline and 19% at follow-up (P = .077). Postural unsteadiness was present in 17% at baseline and 21% at follow-up (P = .424). Canal paresis was present in 51% at baseline and 56% at follow-up (P = .664). Conclusions: There was no significant change in the prevalence of dizziness, postural sway, or canal paresis during conservative management of vestibular schwannoma, while tumor volume remained unchanged. This indicates a favorable prognosis in these patients with regard to vestibular symptoms.acceptedVersio

Vestibular Tests Related to Tumor Volume in 137 Patients With Small to Medium-Sized Vestibular Schwannoma

Objective: The video head impulse test (vHIT) and cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP) are new methods for measuring peripheral vestibular function. The objectives of this study were to compare these tests and the traditionally used caloric test in patients with small and medium-sized untreated vestibular schwannoma (VS) and to measure the correlation between the tests' results and tumor volume. Study Design: National cross-sectional study. Setting: Tertiary university clinic. Methods: Prevalence of abnormal cVEMP, oVEMP, caloric test, and 6-canal vHIT results on the tumor side and the nontumor side were compared and related to tumor volume with regression analyses in 137 consecutive VS patients assigned to a wait-and-scan protocol in the period 2017 to 2019. Results: The sensitivity of 6-canal vHIT, caloric test, cVEMP, and oVEMP to detect vestibulopathy in VS patients was 51%, 47%, 39%, and 25%, respectively. Normal tests were found in 21% of the patients. The results of vHIT and caloric test were related to tumor volume, but this was not found for cVEMP and oVEMP. Conclusion: The caloric test and 6-canal vHIT showed the highest sensitivity in detecting vestibulopathy in untreated VS patients. vHIT, and particularly the posterior canal, was limited with a high prevalence of abnormal results on the nontumor side. A combination of cVEMP and caloric test was favorable in terms of a relatively high sensitivity and low prevalence of abnormal results on the nontumor side. Larger tumors had a higher rate of pathology on caloric testing and vHIT.publishedVersio

Digital Cement Integrity: A Methodology for 3D Visualization of Cracks and Microannuli in Well Cement

Leakages of greenhouse gases, such as methane and carbon dioxide from wells, may have considerable environmental consequences. Although much emphasis is currently put on understanding well barrier failures, and thus, preventing well leakages, especially for an important barrier material as cement, there are still several knowledge gaps and unknowns. However, a step-change in well integrity understanding may be obtained by applying advanced characterization techniques and scientific approaches to studying well barrier materials and their failure mechanisms. This paper describes the development of an experimental methodology that uses X-ray computed tomography to obtain 3D visualizations of cracks and microannuli in annular cement sheaths. Several results are included that demonstrate the value of using such digital methods to study well cement, and it is shown that such experimental studies provide an improved understanding of cement sheath integrity. For example, it is seen that radial cracks do not form in symmetrical patterns and that microannuli do not have uniform geometries. Such experimental findings can potentially be used as benchmark to validate and improve cement integrity simulation tools.publishedVersio

Hydrogen dissociation under equilibrium and non-equilibrium conditions A study using molecular dynamics

The aim of this thesis project was to model reactions using classical molecular dynamics simulations under both equilibrium and non-equilibrium conditions and to study the effect of the reaction on the transport properties of the system. The dissociation of hydrogen was chosen as a model system based on its importance for the hydrogen society, and the availability of interaction potentials to model the reaction. According to procedures described by Stillinger andWeber, a three-particle interaction potential was added to the pair potential. With this it was possible to properly describe the dissociative reaction. Equilibrium studies was performed at different temperatures and densities. From this, a detailed analysis of the interaction potential, the pair correlation functions and the contributions from the two- and three particle interactions on the overall pressure was performed. This made it possible to determine a temperature and density range where the degree of dissociation was significant. The Small System method was extended to calculate partial molar enthalpies from fluctuations of particles and energies in a subsystem embedded in the simulation box. It was proven that this method worked well for both reacting and nonreacting mixtures. This method was applied to the hydrogen dissociation reaction. From this the reaction enthalpy was determined as a function of temperature, pressure and composition of the reacting mixture for three different densities. The reaction enthalpy was found to be approximately constant (460–440 kJ/mol) for a gas (0.0052 g/cm3), 410–480 kJ/mol for a compressed gas (0.0191 g/cm3) and 500–320 kJ/mol for a liquid (0.0695 g/cm3) for temperatures in the range 4000- 21000 K. With knowledge of the reaction enthalpy, the thermodynamic equilibrium constant, and thus the deviation from ideality was found. Non-equilibrium simulations was used to study the coupled transport of heat and mass both transport of hydrogen through a palladium membrane and for the dissociative reaction in a bulk phase. For the first case, transport coefficients had to be estimated. For the latter case, the coefficients were determined for the first time directly from the fluxes in the system using non-equilibrium molecular dynamics simulations. The transport properties for both systems were then determined from the coefficients. For transport across a membrane, it was illustrated how a temperature gradient could be used to enhance and control the flux of hydrogen through the membran

Leakages Through Radial Cracks in Cement Sheaths: Effect of Geometry, Viscosity, and Aperture

Annular cement sheath is considered to be one of the most important barrier elements in the well, both during production and after well abandonment. It is however well-known that mechanical damage to the cement sheath might result in leakage pathways, such as microannuli and radial cracks, and thus loss of zonal isolation. In this paper, we have studied the effect of geometry, aperture, and viscosity on the resulting pressure-driven flow through real radial cracks in cement sheaths using computational fluid dynamics (CFD) simulations. Real radial cracks were created by downscaled laboratory pressure cycling experiments and the resulting geometries were mapped by X-ray computed tomography (CT). This gave a unique 3D volume of the degraded cement sheaths which provides detailed information about the morphology, such as the irregular apertures and roughness, as well as locations of the radial cracks. In this study, we have used five experimentally created geometries, varying from barely connected to fully connected and almost uniform cracks. Additionally, theoretical uniform models with homogeneous aperture and a smooth surface were created for comparison. The simulations were performed by importing the experimentally created leak paths into a CFD simulation software, making it possible to determine the actual flowrate as a function of pressure drop. Methane gas, water, and oil were used as model fluids. The simulation results show that fluid flow through real cracks in cement sheath is complex with torturous paths, especially around bottlenecks and narrow sections. Additionally, the results show that flow of both methane gas- and water are not linear and hence does not follow Darcy's law. This illustrates that simple models are not able to fully describe fluid flow through such complex geometries

Digital Cement Integrity: A Methodology for 3D Visualization of Cracks and Microannuli in Well Cement

Leakages of greenhouse gases, such as methane and carbon dioxide from wells, may have considerable environmental consequences. Although much emphasis is currently put on understanding well barrier failures, and thus, preventing well leakages, especially for an important barrier material as cement, there are still several knowledge gaps and unknowns. However, a step-change in well integrity understanding may be obtained by applying advanced characterization techniques and scientific approaches to studying well barrier materials and their failure mechanisms. This paper describes the development of an experimental methodology that uses X-ray computed tomography to obtain 3D visualizations of cracks and microannuli in annular cement sheaths. Several results are included that demonstrate the value of using such digital methods to study well cement, and it is shown that such experimental studies provide an improved understanding of cement sheath integrity. For example, it is seen that radial cracks do not form in symmetrical patterns and that microannuli do not have uniform geometries. Such experimental findings can potentially be used as benchmark to validate and improve cement integrity simulation tools