Innovative vestibular testing

Dizziness and vertigo are common complaints in the general population, affecting yearly 15-20% of adults and 5-25% of children of school age and having considerable impact on everyday life. As the assessment of peripheral vestibular deficits is challenging, it is crucial to dispose of techniques to provide clinicians support for the correct diagnosis. The aim of this dissertation is therefore to apply in the clinical context cutting-edge diagnostic tools for the easy, quick and reliable assessment of peripheral vestibular impairments and the related functionality. Traditional techniques for the evaluation of semicircular canals, such as the caloric test, the rotational test or the search-coil Head Impulse Test, present several disadvantages, being unpleasant, expensive, time-consuming, not always available at the bedside or appropriate for any group of patients. Additionally, testing the vestibular system at low frequencies, such as in the caloric test, does not cover the physiologically relevant range. The video Head Impulse Test (vHIT) represents an alternative to indirectly evaluate semicircular canals’ function, stimulating the vestibulo-ocular reflex (VOR) with high-frequency head rotations and measuring the resulting eye and head movements. The first study reported in this dissertation extends the potentiality of the vHIT, assessing its feasibility in a group of healthy children and validating its use as a simple and well-tolerated bedside test for the vestibular screening of the pediatric population. The quantitative outcomes of the vHIT, however, do not always reflect functionality, i.e., how efficient is the VOR in stabilizing the visual scene during head perturbations. This represents the starting point for the development of tests whose aim is to assess the subjective perception of this ability. Among the most recently introduced techniques, the Head Impulse Testing Device (HITD) quantifies, without recording eye movements, patient’s reading abilities while performing high-frequency passive head rotations during equally challenging visual stimuli. The second section introduces and validates a new diagnostic tool, the Head Impulse Testing Device-Functional Testing (HITD-FT), which combines the HITD with eye movements recording. The HITD-FT is tested on healthy participants, whose vestibular functionality is transiently impaired by opioid administration. The work assesses the combined effect of VOR and re-fixation saccades on gaze stabilization during high-frequency passive head rotations. Moreover, it describes the role of covert re-fixation saccades on image stabilization and in enhancing overall dynamic vision. The HIDT-FT is furthermore exploited within the context of this dissertation to monitor the overall dynamic visual performance of vestibular patients during rehabilitation. The same experimental set-up, with healthy subjects undergoing opioid administration, is lately also exploited to explore the causes underlying post-operative nausea and vomiting, whose mechanism is still not completely understood. Preliminary studies suggest that opioids, acting on semicircular canals, generate a mismatch between the altered canals’ inputs and other non-consistently altered sensory inputs, triggering nausea and vomiting. The here reported study investigates whether the mismatch between semicircular canals’ inputs and other vestibular sensory inputs, or the mismatch between vestibular and visual inputs, are clinically relevant. A better understanding of this mechanism, i.e. that intra-vestibular mismatches have a particular importance, can help reducing the unpleasant side effects and improve pain management with opioids.Schwindelsyndrome sind häufig. Sie betreffen jährlich 15-20% der Erwachsenen und 5- 25% der Schulkinder und haben erhebliche Auswirkungen auf den Alltag. Die Beurteilung peripherer vestibulärer Defizite ist eine Herausforderung. Daher ist es entscheidend, Meth- oden zur Verfügung zu haben um Mediziner bei der Diagnosestellung zu unterstützen. Ziel dieser Doktorarbeit ist es, innovative Diagnose-Tools zur einfachen, schnellen und zuverlässigen Beurteilung der Funktion des vestibulären Systems in die Klinik zu übertragen. Traditionelle Methoden zur Evaluation der Bogengänge wie Kalorik, Drehstuhltest oder der Search-Coil-Kopfimpulstest haben mehrere Nachteile: sie sind unangenehm, teuer, zeitaufwändig, nicht am Krankenbett verfügbar oder eignen sich nicht für jede Patientengruppe. Die Untersuchung des vestibulären Systems im Niederfrequenzbereich wie bei der Kalorik deckt zudem nicht den physiologisch relevanten Bereich ab. Der videobasierte Kopfimpuls-Test (vHIT) ist dafür eine Alternative. Durch Stimulation des vestibulo- okulären Reflexes (VOR) mit Hochfrequenz-Kopfdrehungen und Messung von Auge- und Kopfbewegung wird dabei indirekt die Funktion der Bogengänge untersucht. Die erste Studie dieser Doktorarbeit erweitert die Anwendung des vHITs; seine Durchführbarkeit wird bei gesunden Kindern geprüft. Er stellt sich als einfacher und gut verträglicher „Bed- side Test“ für das vestibuläre Screening bei Kindern heraus. Die quantitativen vHIT Ergebnisse alleine spiegeln nicht immer wider, wie gut das Se- hen während Kopfbewegung stabil gehalten wird. Dies war Ausgangspunkt für die Entwicklung von Tests zur subjektiven Wahrnehmung dieser Funktion. Eine neue Methode auf diesem Gebiet, der Head Impulse Testing Device (HITD), untersucht - ohne Mes- sung der Augenbewegungen - die Lesefähigkeit anspruchsvoller visueller Stimuli während passiven Hochfrequenz-Kopfimpulsen. Im zweiten Teil der Doktorarbeit wird ein innovatives Diagnose-Tool – Head Impulse Testing Device – Functional Testing (HIDT-FT)– eingeführt und validiert. Der Test kombiniert HIDT mit Augenbewegungsmessung. Der HITD-FT wird an gesunden Probanden geprüft, deren vestibuläre Funktion mit Opi- oiden vorübergehend beeinträchtig ist. Die Studie untersucht den kombinierten Effekt von VOR und Re-Fixationsakkaden auf die Blickstabilisierung während passiver Hochfrequenz- Kopfimpulsen. Außerdem wird die Rolle sogenannter verdeckter (covert) Re-Fixationsakkaden bei der Bildstabilisierung und beim dynamischen Sehen geprüft. Der HITD-FT wird im Rahmen der Doktorarbeit zudem erfolgreich zur Dokumentation des dynamischen Sehens bei der Rehabilitation vestibulärer Patienten eingesetzt. Zum Schluss wird ein ähnlicher Versuchsaufbau mit Gabe von Opioiden bei Gesunden benutzt, um der Ursache von postoperativer Übelkeit und Erbrechen näher zu kommen, deren Mechanismus bisher nicht gut verstanden ist. Vorarbeiten legen nahe, dass Opiate eine Wirkung auf die Bogengänge haben und dass so eine Inkongruenz zwischen geänderten Bogengangs-Eingängen und nicht konsistenten geänderten anderen sensorische In- puts entsteht, die zu Übelkeit und Erbrechen führt. Die hier vorgelegte Arbeit untersucht, ob die Inkongruenz zwischen Bogengangsinformation und anderen vestibulären Sensoren oder die zwischen vestibulärem und visuellem Eingang klinisch relevant ist. Das Verständnis, dass intra-vestibuläre Inkongruenzen vor allem von Bedeutung sind, kann helfen diese unangenehmen Nebenwirkungen zu reduzieren und die Schmerzbehandlung mit Opiate zu verbessern

Contentious Politics in the Arab Middle East: Jordanian Salafism and the Social Appropriation of Tradition

In which ways do intellectuals affect social and political mobilization? How do they impact the trajectory of contention – the kind of mobilization and its developments - through their ideological work? Prominent intellectuals seem to play a relevant role in contentious politics, yet this role is still undertheorized. In this project, I analyze this question in the context of contemporary Arab Salafism, a particularly literal interpretation of Sunni Islam. I seek to unpack the processes by which prominent Islamist intellectuals impact and shape two Salafi currents originating and operating across Jordan during the 1990s and beyond. The first current is labeled \u27Quietist\u27 Salafism, as its members engage mostly in preaching, proselytizing and provision of social services; they refrain from direct political activities or overt confrontation with state authorities. The second current is known as \u27Jihadi\u27 Salfism, and espouses instead a confrontational and at times violent stance vis à vis state power. I posit that Islamist intellectuals in both instances impact mobilization in similar ways through three main mechanisms: diffusion, whereby they facilitate the spreading and transmission of ideas and concepts formulated elsewhere; elaboration, whereby they build upon the existing body of knowledge on a given subject, providing novel insights, interpretations or at times formulating new ideas altogether; and systematization, whereby they (re)organize the otherwise relatively fragmented or incoherent worldview of their followers and acolytes. Together, these mechanisms compound into a process that I call ‘the social appropriation of tradition\u27, by which group members, harking back to elements belonging to a shared and exemplar tradition, rearticulate the central aims of the group to include sustained social and political mobilization. In this way we may properly locate the intellectual efforts of prominent thinkers within a theoretical framework, parsing out and assessing their contribution to episodes of political contention

Tuning the bulk properties of bidisperse granular mixtures by small amount of fines

We study the bulk properties of isotropic bidisperse granular mixtures using discrete element simulations. The focus is on the influence of the size (radius) ratio of the two constituents and volume fraction on the mixture properties. We show that the effective bulk modulus of a dense granular (base) assembly can be enhanced by up to 20% by substituting as little as 5% of its volume with smaller sized particles. Particles of similar sizes barely affect the macroscopic properties of the mixture. On the other extreme, when a huge number of fine particles are included, most of them lie in the voids of the base material, acting as rattlers, leading to an overall weakening effect. In between the limits, an optimum size ratio that maximizes the bulk modulus of the mixture is found. For loose systems, the bulk modulus decreases monotonically with addition of fines regardless of the size ratio. Finally, we relate the mixture properties to the 'typical' pore size in a disordered structure as induced by the combined effect of operating volume fraction (consolidation) and size ratio

Rehydration of food powders: interplay between physical properties and process conditions

Dehydrated food powders with poor dissolution or dispersion can dramatically compromise food processing, with consequences for the final product quality and consumer experience. In this study, the reconstitution performance of maltodextrin powders with different moisture content and molecular weight, has been determined by varying the processing conditions, including agitation speed, liquid temperature, powder addition rate and mode of addition to the liquid surface. In particular, the inter-relationship between the glass transition temperature (Tg) of the powder, its moisture content and the liquid temperature (TL) is highlighted. When TL ≥ Tg, the individual maltodextrin granules tend to swell, restricting further dispersion and rehydration. It has been shown that higher liquid temperatures reduce the dispersion of food powders containing high molecular weight carbohydrates. Increasing the rate of powder addition to the liquid surface under low agitation conditions has been shown to result in faster reconstitution of low-molecular weight maltodextrin, whilst, on the other hand, the corresponding reconstitution rates of high-molecular weight maltodextrins are reduced. On the basis of this work and a previous study [X.Y. Ong, S.E. Taylor and M. Ramaioli, Pouring of Grains onto Liquid Surfaces: Dispersion or Lump Formation? Langmuir (2019) 11150-11156] an improved, yet simple, approach to improve powder dispersion in a liquid is also demonstrated, by optimizing the distribution of the powder on the liquid surface. This approach avoids powder grains accumulating as heterogeneous lumps on the liquid surface and has been applied herein to a wide range of food powders

Recent advances in the simulation of particle-laden flows

A substantial number of algorithms exists for the simulation of moving particles suspended in fluids. However, finding the best method to address a particular physical problem is often highly non-trivial and depends on the properties of the particles and the involved fluid(s) together. In this report we provide a short overview on a number of existing simulation methods and provide two state of the art examples in more detail. In both cases, the particles are described using a Discrete Element Method (DEM). The DEM solver is usually coupled to a fluid-solver, which can be classified as grid-based or mesh-free (one example for each is given). Fluid solvers feature different resolutions relative to the particle size and separation. First, a multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine resolution) is presented to study the behavior of particle stabilized fluid interfaces and second, a Smoothed Particle Hydrodynamics implementation (mesh-free, meso-scale resolution, similar to the particle size) is introduced to highlight a new player in the field, which is expected to be particularly suited for flows including free surfaces.Comment: 16 pages, 4 figure

About the influence of friction and polydispersityon the jamming behavior of bead assemblies

Abstract.: We study the jamming of bead assemblies placed in a cylindrical container whose bottom is pierced with a circular hole. Their jamming behavior is quantified here by the median jamming diameter, that is the diameter of the hole for which the jamming probability is 0.5. Median jamming diameters of monodisperse assemblies are obtained numerically using the Distinct Element Method and experimentally with steel beads. We obtain good agreement between numerical and experimental results. The influence of friction is then investigated. In particular, the formation of concentric bead rings is observed for low frictions. We identify this phenomenon as a boundary effect and study its influence on jamming. Relying on measures obtained from simulation runs, the median jamming diameter of bidisperse bead assemblies is finally found to depend only on the volume-average diameter of their constituting beads. We formulate this as a tentative law and validate it using bidisperse assemblies of steel bead