Computational assessment of hemodynamics-based diagnostic tools using a database of virtual subjects: Application to three case studies

AbstractMany physiological indexes and algorithms based on pulse wave analysis have been suggested in order to better assess cardiovascular function. Because these tools are often computed from in-vivo hemodynamic measurements, their validation is time-consuming, challenging, and biased by measurement errors.Recently, a new methodology has been suggested to assess theoretically these computed tools: a database of virtual subjects generated using numerical 1D-0D modeling of arterial hemodynamics. The generated set of simulations encloses a wide selection of healthy cases that could be encountered in a clinical study.We applied this new methodology to three different case studies that demonstrate the potential of our new tool, and illustrated each of them with a clinically relevant example: (i) we assessed the accuracy of indexes estimating pulse wave velocity; (ii) we validated and refined an algorithm that computes central blood pressure; and (iii) we investigated theoretical mechanisms behind the augmentation index.Our database of virtual subjects is a new tool to assist the clinician: it provides insight into the physical mechanisms underlying the correlations observed in clinical practice

Comment on 'Numerical assessment and comparison of pulse wave velocity methods aiming at measuring aortic stiffness'

A recent numerical study investigated the potential utility of peripheral PWV measurements for assessing aortic stiffness by simulating pulse wave propagation through the arterial tree. In this Comment we provide additional analysis of the simulations in which arterial compliances were changed. The analysis indicates that relationships between aortic and peripheral pulse transit times (PTTs) may not be constant when compliances change. Consequently, peripheral PWV measurements may have greatest utility in particular clinical settings in which either: an assumption can be made about possible changes in compliance, allowing aortic PTT to be estimated from peripheral PTT; or, one wishes to assess changes in peripheral PWV over time

Rapid manufacturing of color-based hemispherical soft tactile fingertips

Tactile sensing can provide access to information about the contact (i.e. slippage, surface feature, friction), which is out of reach of vision but crucial for manipulation. To access this information, a dense measurement of the deformation of soft fingertips is necessary. Recently, tactile sensors that rely on a camera looking at a deformable membrane have demonstrated that a dense measurement of the contact is possible. However, their manufacturing can be time-consuming and labor-intensive. Here, we show a new design method that uses multi-color additive manufacturing and silicone casting to efficiently manufacture soft marker-based tactile sensors that are able to capture with high-resolution the three-dimensional deformation field at the interface. Each marker is composed of two superimposed color filters. The subtractive color mixing encodes the normal deformation of the membrane, and the lateral deformation is found by centroid detection. With this manufacturing method, we can reach a density of 400 markers on a 21 mm radius hemisphere, allowing for regular and dense measurement of the deformation. We calibrated and validated the approach by finding the curvature of objects with a threefold increase in accuracy as compared to previous implementations. The results demonstrate a simple yet effective approach to manufacturing artificial fingertips for capturing a rich image of the tactile interaction at the location of contact

A "well-balanced" finite volume scheme for blood flow simulation

We are interested in simulating blood flow in arteries with a one dimensional model. Thanks to recent developments in the analysis of hyperbolic system of conservation laws (in the Saint-Venant/ shallow water equations context) we will perform a simple finite volume scheme. We focus on conservation properties of this scheme which were not previously considered. To emphasize the necessity of this scheme, we present how a too simple numerical scheme may induce spurious flows when the basic static shape of the radius changes. On contrary, the proposed scheme is "well-balanced": it preserves equilibria of Q = 0. Then examples of analytical or linearized solutions with and without viscous damping are presented to validate the calculations. The influence of abrupt change of basic radius is emphasized in the case of an aneurism.Comment: 36 page

Surgical Video Motion Magnification with Suppression of Instrument Artefacts

Video motion magnification could directly highlight subsurface blood vessels in endoscopic video in order to prevent inadvertent damage and bleeding. Applying motion filters to the full surgical image is however sensitive to residual motion from the surgical instruments and can impede practical application due to aberration motion artefacts. By storing the temporal filter response from local spatial frequency information for a single cardiovascular cycle prior to tool introduction to the scene, a filter can be used to determine if motion magnification should be active for a spatial region of the surgical image. In this paper, we propose a strategy to reduce aberration due to non-physiological motion for surgical video motion magnification. We present promising results on endoscopic transnasal transsphenoidal pituitary surgery with a quantitative comparison to recent methods using Structural Similarity (SSIM), as well as qualitative analysis by comparing spatio-temporal cross sections of the videos and individual frames.Comment: Early accept to the Internation Conference on Medical Imaging Computing and Computer Assisted Intervention (MICCAI) 2020 Presentation available here: https://www.youtube.com/watch?v=kKI_Ygny76Q Supplementary video available here: https://www.youtube.com/watch?v=8DUkcHI149

The importance of the altricial – precocial spectrum for social complexity in mammals and birds:A review

Various types of long-term stable relationships that individuals uphold, including cooperation and competition between group members, define social complexity in vertebrates. Numerous life history, physiological and cognitive traits have been shown to affect, or to be affected by, such social relationships. As such, differences in developmental modes, i.e. the ‘altricial-precocial’ spectrum, may play an important role in understanding the interspecific variation in occurrence of social interactions, but to what extent this is the case is unclear because the role of the developmental mode has not been studied directly in across-species studies of sociality. In other words, although there are studies on the effects of developmental mode on brain size, on the effects of brain size on cognition, and on the effects of cognition on social complexity, there are no studies directly investigating the link between developmental mode and social complexity. This is surprising because developmental differences play a significant role in the evolution of, for example, brain size, which is in turn considered an essential building block with respect to social complexity. Here, we compiled an overview of studies on various aspects of the complexity of social systems in altricial and precocial mammals and birds. Although systematic studies are scarce and do not allow for a quantitative comparison, we show that several forms of social relationships and cognitive abilities occur in species along the entire developmental spectrum. Based on the existing evidence it seems that differences in developmental modes play a minor role in whether or not individuals or species are able to meet the cognitive capabilities and requirements for maintaining complex social relationships. Given the scarcity of comparative studies and potential subtle differences, however, we suggest that future studies should consider developmental differences to determine whether our finding is general or whether some of the vast variation in social complexity across species can be explained by developmental mode. This would allow a more detailed assessment of the relative importance of developmental mode in the evolution of vertebrate social systems

Arterial pressure and flow wave analysis using time-domain 1-D hemodynamics

We reviewed existing methods for analyzing, in the time domain, physical mechanisms underlying the patterns of blood pressure and flow waveforms in the arterial system. These are wave intensity analysis and separations into several types of waveforms: (i) forward- and backward-traveling, (ii) peripheral and conduit, or (iii) reservoir and excess. We assessed the physical information provided by each method and showed how to combine existing methods in order to quantify contributions to numerically generated waveforms from previous cardiac cycles and from specific regions and properties of the numerical domain: the aortic root, arterial bifurcations and tapered vessels, peripheral reflection sites, and the Windkessel function of the aorta. We illustrated our results with numerical examples involving generalized arterial stiffening in a distributed one-dimensional model or localized changes in the model parameters due to a femoral stenosis, carotid stent or abdominal aortic aneurysm. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10439-014-1087-4) contains supplementary material, which is available to authorized users

Blood flow modeling for patient-specific bypass surgery in lower-limb arteries

Every day in Belgium, at least one or two people will undergo a bypass surgery in the lower-limb arteries. This medical procedure consists of replacing an occluded section of the leg arteries with an artificial vessel, in order to allow blood to flow downwards of this blockage. Even though this intervention is very common, failure of this treatment within five years reaches up to 60%. In order to improve our understanding of the causes of bypass failure, one approach is to study the local hemodynamics (i.e. the blood flow circulation) in these vessels, as this factor strongly influences the initiation and progression of arterial diseases. This thesis addresses this objective by modeling the patient-specific arterial hemodynamics. As each patient is characterized by his own physiology (e.g. morphology, severity of the disease) and is treated by a bypass graft of fixed characteristics (e.g. material, length, location of the anastomoses), each clinical case needs to be considered individually. In the first part of our work, blood pressure, velocity and flow rate in the network of arteries are modeled with a one-dimensional model of the arteries and lumped windkessel models of the secondary and distal vessels. The 18 parameters of this coupled model are then computed in order to reflect the pathological condition of the patient. Thanks to the set-up of an experimental protocol of data acquisition, in-vivo measurements of hemodynamics have been acquired on 25 patients operated with bypass surgery. The comparison of these in-vivo signals with simulations from the numerical model enabled us to improve and to validate our patient-specific numerical model. In the second part of this thesis, the dynamic of blood is considered as impulses of waves which are generated by the contractions of the heart, and which propagate throughout the arterial network. By using the wave intensity analysis method, we analyzed and characterized these waves in the pathological arteries of the leg, and emphasized the effects of the bypass.(FSA 3) -- UCL, 201

Biomécanique de la perception tactile du frottement

When manipulating objects, humans rely on their sense of touch to perceive subtle movements and micro slippages. This synergy between sensations and motion permits them to manipulate an impressive range of objects of different sizes, shapes, and surface properties. This incredible dexterity relies on fast and unconscious adjustments of the grip force by placing a 20% safety margin before slip that holds an object strong enough to avoid a catastrophic fall yet gentle enough not to damage it. In addition to being accurate, this regulation is swift: only a hundred milliseconds after first making contact, grip forces are already adjusted by taking into account the actual frictional strength of the contact. This astonishing performance is owed to the sense of touch, which informs on the physical properties of the surrounding world and contact state. Within the fingertip, thousands of mechanoreceptors convert the complex mechanical interaction into action potentials. However, how the brain copes with large amounts of data to infer the state of the contact is still debated.This thesis covers how the cutaneous tactile afferent made it possible for a swift and precise regulation of the grip. Firstly, I show that humans can assess friction without slippage, suggesting that the radial stretch of the skin can provide enough information to regulate grip at the contact initialization. Secondly, I show that the perceptual system uses a compact code to estimate the safety margin from the skin deformation during an incipient slip, suggesting a mechanism to explain the rapid reactions. Finally, I expose a new model based on contact mechanics to quantify the sensitivity of the mechanoreceptors to the patterns of skin deformation highlighted in the first two chapters. This model also correlates the spatial and temporal detection threshold to detect a moving stimulus, suggesting a persistence of touch that bridges discrete sensations into a continuous stimulus.Taken together, these results reveal how the perception of friction is encoded in the spatio-temporal deformation of the skin. The findings are useful for designing bio-inspired tactile sensors for robotics or prosthetics and for improving haptic human-machine interactions.Lorsque nous manipulons des objets, nous nous fions à notre sens du toucher pour percevoir les mouvements subtils et les micro glissements. Cette synergie entre sensations et mouvement nous permet de manipuler une grande variété d’objets de différentes tailles, formes ou matériaux. Cette remarquable dextérité repose sur une régulation rapide et inconsciente de notre force de préhension, en maintenant une marge de sécurité avant glissement de 20% nous permettant ainsi de serrer l’objet suffisamment fort pour éviter une perte d’adhérence, mais suffisamment délicatement pour ne pas l’endommager. En plus d’être précise, cette régulation est très rapide : après seulement une centaine de millisecondes après l’initialisation du contact, la force de préhension est déjà ajustée en fonction du frottement disponible à l’interface. Nous devons cette performance hors-du-commun au sens du toucher qui nous informe sur les propriétés physiques du monde qui nous entoure ainsi que de l’état de contact. Le doigt humain est équipé de milliers de mécanorécepteurs qui convertissent l’interaction mécanique complexe en potentiels d’actions. Cependant, comment le cerveau reconstruit l’état de contact à partir de ce volume considérable de données, continue à faire débat.Cette thèse explore comment les afférents tactiles cutanés rendent possible une régulation rapide et précise de la force de préhension. Tout d’abord, une expérience psychophysique a permis de montrer que les humains étaient capables d’apprécier le frottement à l’interface sans glissement, indiquant qu’une expansion radiale de la peau peut apporter suffisamment d’informations pour réguler la force de préhension à l’initialisation du contact. Dans un second temps, je propose un encodage compact qui pourrait être utilisé par le système perceptuel pour estimer la safety margin à partir de la déformation de la peau lors d’un glissement partiel, suggérant un mécanisme pour expliquer nos promptes réactions. Enfin, j’expose un nouveau modèle basé sur la mécanique du contact pour quantifier la sensibilité des mécanorécepteurs aux motifs de déformation mis en évidence dans les deux premières parties. Ce modèle corrobore également avec les seuils de détection spatial et temporel, évoquant la présence d’une persistance tactile comblant un signal discret en stimulus continu.Dans leur ensemble, ces travaux révèlent l’encodage de la perception du frottement dans la déformation spatio-temporelle de la peau. Ces résultats pourront être utiles pour le design de capteurs tactiles bio-inspirés pour la robotique ou les prothèses. Ils ont également vocation à améliorer les interactions haptiques homme-machine