An ergonomic driver workspace and interface design is essential to ensure a healthier and comfortable driving experience in terms of driver perceptions, postures, and interface pressures. Developing more effective methods for driver-side interior design and evaluation, hence, requires thorough investigation of: 1) which perceptual responses are more relevant to ensuring ergonomic quality of a design, 2) the interrelationships among perceptual responses and objective measures, and 3) whether current assumptions regarding driver behaviors, and tools for specifying these behaviors, are valid for the design and evaluation. Existing studies, however, have rarely addressed these topics comprehensively, and often have been conducted with unsubstantiated assumptions. In contrast, this work sought to address these topics in a way that jointly considers characteristics of driver perceptions, behaviors, and objective measures to develop an improved design and evaluation methodology for driver workspace and interface, and that can also investigate the validity of implicit assumptions regarding perceptual relevance and drivers' behaviors. The first part of this work investigated drivers' perceptions in relation to driver workspace design and evaluation. Specifically, it examined the efficacy of several perceptual ratings, when used for evaluating automobile interface design. Results showed that comfort ratings were more effective at distinguishing among interface designs, in contrast to the current common practice of using discomfort ratings for designing and evaluating interface designs. Two distinct decision processes to relate local to global perceptions were also identified (i.e., global comfort as an average of local comforts, and global discomfort predominantly influenced by maximal local discomforts). These findings were observed consistently across age and cultural groups. In addition, this work provided empirical support for an earlier hypothetical comfort/discomfort model, which posited comfort and discomfort are complementary, yet independent entities. In order to facilitate the integration of driver perceptions and dynamic behaviors into driver workspace design and evaluation, the second part of this work clarified the relationships between perceptual ratings and various types of driver-seat interface pressure. Interface pressure was found to be more strongly related to overall and comfort ratings than to discomfort ratings, which is also in marked contrast with existing work that has focused on identifying association between discomfort and interface pressure. Specific pressure interface requirements for comfortable driver workspace design and evaluation were also provided. Lastly, this work specified more rigorous driving postures for digital human models (DHMs), based on actual drivers' perceptions, postural sensitivity, and static behavioral characteristics, to facilitate proactive design and evaluation that enables cost/time efficient vehicle development. Drivers' behavioral characteristics observed in this work were applied to the driver workspace design. First, postural sensitivity obtained by using a psychophysics concept has been applied to determination of core seat track ranges. Second, postural data have been used: 1) to review relevant industry standards on driver accommodation, 2) to investigate whether driving postures are bilaterally asymmetric, 3) to provide comfortable joint ranges, and lastly 4) to identify drivers' postural strategies for interacting with a vehicle. Overall, this work identified three important behavioral characteristics, specifically a bilateral imbalance in terms of interface pressure, bilaterally asymmetric joint posture, and postural strategies identified by cluster analysis. Such characteristics can be embedded in DHMs to describe more accurately actual driver behaviors inside a driver workspace, which is deemed to be a fundamental step to improved virtual ergonomic vehicle design and evaluation. In addition, the strategy-based classification method used in this work can be extended to simulate and predict more complex human motions. Practical and fundamental findings of this work will facilitate efficient and proactive design and evaluation of driver workspace and interface, and will help provide a healthier driving experience for a broader range of individuals. / Ph. D.

Pressure ulcers and related skin integrity threats are a significant problem in current transfer/transport systems used for spinal cord injury patients. To understand this problem twenty-three different slings with varying type, material, and features were analyzed in hopes to identify at-risk areas for skin integrity threats such as pressure ulcers. Population samples included non-disabled (otherwise referred to as "healthy") volunteers as well as SCI patients from the James A. Haley Veterans Hospital. High resolution pressure interface mapping was utilized to directly measure the interface pressures between the patient and sling interface. Overall results provide relevant feedback on the systems used and to suggest a particular type of sling that might reduce and possibly minimize skin integrity threats as well as extend safe patient handling guidelines with sling use. It was found that the highest interface pressures convened along the seams of the sling, regardless of manufacturer or type.

It has been desirable for years to develop non-intrusive/non-invasiveprocedures to determine the pressures and stresses at various levels andinterfaces in the railroad track structure in order to optimize track designs andimprove subsequent track performance. Recent research has developedsatisfactory procedures for measuring pressures in the track structure at theballast/subballast/subgrade levels using earth pressure cells. The researchreported in this thesis documents the development of a technique for measuringthe pressures in the track, at the rail/tie plate/tie interfaces, using a very thinpressure sensitive Tekscan sensor. The Tekscan Measurement System uses asensor composed of a matrix-based array of force sensitive cells, similar to ministrain gauges, to obtain accurate pressure distributions between two surfaces inthe track. This thesis specifically describes: 1) the optimum procedure to installthe sensors into the track, 2) the recommended practices to effectively collectdata with the software, and 3) the accepted techniques for analyzing the results.Both laboratory calibration and in-track testing have been conducted and theresults are presented. The findings attest to the usefulness and practicality of theprocedure for accurately measuring pressures in railroad tracks. The proceduremay also be applicable for a wide variety of specific track related measurementssuch as validating curve geometric criteria, assessing crossing diamond impactpressures, and evaluating the advantages/disadvantages of various types of tieplates, fastenings and tie compositions.

The overall aim of this thesis was to combine optical methods into a system with the ability to simultaneously measure blood flow changes at different tissue depths. The goal of such a system was to reveal vascular mechanisms relevant to pressure ulcer etiology under clinically relevant conditions and in relation to the evaluation of pressure-redistribution support surfaces. This thesis consists of four quantitative, cross-sectional studies measuring blood flow responses before, during, and after pressure exposure of the sacral tissue. Two optical methods – photoplethysmography and laser Doppler flowmetry – were combined in a newly developed system that has the ability to discriminate blood flows at different tissue depths. Studies I and II explored blood flow responses at different depths in 17 individuals. In Study I the blood flow was related to tissue thickness and tissue compression during pressure exposure of ≥ 220 mmHg. In Study II, the sacral tissue was loaded with 37.5 mmHg and 50.0 mmHg, and the variation in blood flow was measured. Studies III and IV included 42 healthy individuals < 65 years, 38 healthy individuals ≥ 65 years, and 35 patients ≥ 65 years. Study III included between-subject comparisons of blood flow and pressure between individuals in the three study groups lying in supine positions on a standard hospital mattress. Study IV added within-subject comparisons while the individual was lying on four different types of mattress. The studies explored the vascular phenomena pressure-induced vasodilation (PIV) and reactive hyperemia (RH). The most common blood flow response to tissue exposure in this thesis was PIV, although a decrease in blood flow (a lack of PIV) was observed in some individuals. The patients tended to have higher interface pressure during pressure exposure than the healthy groups but no differences in blood flow responses were seen. Our results showed that pressure levels that are normally considered to be harmless could have a significant effect on the microcirculation in different tissue structures. Differences in individual blood flow responses in terms of PIV and RH were seen, and a larger proportion of individuals lacked these responses in the deeper tissue structures compared to more superficial tissue structures. This thesis identified PIV and RH that are important vascular mechanisms for pressure ulcer development and revealed for the first time that PIV and RH are present at different depths under clinically relevant conditions. The thesis also identified a population of individuals not previously identified who lack both PIV and RH and seem to be particularly vulnerable to pressure exposure. Further, this thesis has added a new perspective to the microcirculation in pressure ulcer etiology in terms of blood flow regulation and endothelial function that are anchored in clinically relevant studies. Finally, the evaluation of pressureredistribution support surfaces in terms of mean blood flow during and after tissue exposure was shown to be unfeasible, but the assessment of PIV and RH could provide a new possibility for measuring individual physiological responses that are known to be related to pressure ulcer development.

Les bandes de compression, couramment utilisées pour le traitement de l’insuffisance veineuse, appliquent une pression sur la jambe, appelée pression d’interface, qui est le principe actif du traitement. L'objectif était de mieux comprendre les mécanismes influençant la pression exercée par une bande de compression sur le membre inférieur.En lien avec des médecins et un industriel, l’approche biomécanique proposée était composée d’une part expérimentale (mesures de pression d'interface) et d'une part numérique (modélisation éléments-finis de la pose d'une bande). Deux études préliminaires, expérimentale et numérique, ont montré la limite de l'utilisation de la Loi de Laplace (standard actuel) pour le calcul des pressions d’interface. Ces études ont soulevé des interrogations concernant l'éventuel impact des propriétés de surface des bandes (coefficient de frottement bande-bande) sur la pression. Elles ont aussi montré l’importance des déformations des tissus mous de la jambe induite par l'application de la bande. Deux méthodes de caractérisation mécanique ont donc été mises en place pour l’identification personnalisée des propriétés mécaniques des tissus mous de la jambe et la mesure du coefficient de frottement bande-bande.Un nouvel outil de prédiction des pressions d’interface a été développé grâce à la combinaison de la simulation numérique de la pose d’une bande et de la paramétrisation géométrique de la jambe puis il a été confronté aux mesures expérimentales.Finalement, une étude clinique a été réalisée pour étudier la pression exercée par la superposition de deux bandes de compression (pratique clinique très courante pour le traitement de l'ulcère veineux). / Compression bandages are commonly used for the treatment of chronic venous insufficiency. They apply a pressure onto the leg, called interface pressure, which is one of the key aspects of the treatment. The objective was to better understand the mechanisms impacting interface pressure applied by compression bandage on the lower leg. In collaboration with clinicians and a medical devices manufacturer, a biomechanical approach was proposed. This approach was composed of experimental pressure measurements and the numerical simulation of bandage application. Two preliminary studies, experimental and numerical, showed the limitations of the use of Laplace’s Law (current standard) for interface pressure computation. These studies also questioned the possible impact of bandage surface properties (bandage-to-bandage friction coefficient) on interface pressure. They also showed the need to consider soft tissues deformation induced by bandage application. Two characterization methods were designed for the identification of patient-specific soft tissue mechanical properties and the measurement of bandage-to-bandage friction coefficient. A new methodology for the prediction of interface pressure was developed thanks to the combination of the numerical simulation of bandage application and the leg geometry parametrization. The results were then confronted to experimental measurements. Finally, a clinical study was designed to investigate the pressure applied by superimposed compression bandages (very common in clinical practice for the treatment of venous ulcers).

The magnitudes and relative pressure distributions transmitted to the crosstie-ballast interface of railroad track significantly influences the subsequent behavior and performance of the overall track structure. If the track structure is not properly designed to distribute the heavy-axle loads of freight cars and locomotives, deficiencies and inherent failures of the crossties, ballast, or underlying support layers can occur, requiring substantial and frequent maintenance activities to achieve requisite track geometrical standards. Incorporating an understanding of the pressure distribution at the crosstie-ballast interface, appropriate designs can be applied to adequately provide a high performing and long-lasting railroad track. Although this can be considered a simple concept, the magnitudes and distributions of pressures at the crosstie-ballast interface have historically proven to be difficult to quantifiably measure and assess over the years. This document describes the development and application of a method to measure average railroad track crosstie-ballast interfacial pressures using timber crossties and pressure cells specifically designed for granular materials. A procedure was specifically developed for recessing the cells in the bottoms of timber crossties. The validity of the test method was initially verified with a series of laboratory tests. These tests used controlled loads applied to sections of trackbed constructed in specifically designed resilient frames. The prototype trackbed section was intended to simulate typical in-track loading conditions and ballast response. Cells were subsequently installed at a test site on an NS Railway well-maintained mainline just east of Knoxville, TN. Six successive crossties were fitted with pressure cells at the ballast interface below the rail seat. Pressure cells were also installed at the center of two crossties where the ballast is typically not tamped or consolidated. Trackbed pressures at the crosstie-ballast interface were periodically measured for numerous revenue freight trains during a period of twenty-one months. After raising and surfacing the track, the ballast was permitted to further consolidate under normal train traffic before again measuring pressures. Having the ballast tightly and uniformly compacted under crossties is important to ensuring representative and reproducible pressure measurements. Measured maximum pressures under the rail at the crosstie-ballast interface ranged from 20 to 30 psi (140 to 210 kPa) for locomotives and loaded freight cars with smooth wheels producing negligible wheel/rail impacts. Crosstie-ballast interface pressures were typically 3 psi (20 kPa) maximum for empty freight cars with smooth wheels. Heavily loaded articulated intermodal car pressures for shared trucks tended to reach nearly 40 psi (280 kPa), actually higher than locomotive-produced pressures. The recorded pressures under the center of the ties were normally negligible, less than 1 psi (7 kPa) for locomotives and loaded freight cars. Wheel-Rail force parameters measured by nearby wheel-impact load detectors (WILD) were compared to crosstie-ballast pressure data for the same trains traversing the test site. Increases in peak WILD forces, either due to heavier wheel loads or increased impacts, were determined to relate favorably to increases in recorded trackbed pressures with a power relationship. The ratios between the peak and nominal wheel forces and trackbed pressures also have strong relationships.

La prise en charge de l’insuffisance veineuse chronique (IVC) et du lymphœdème repose, traditionnellement, sur des méthodes de compression fondées sur des concepts généralement admis mais insuffisamment éprouvés. Le Projet « Phlébosthène », initié en 2010, comporte le développement et l’application d’outils d’étude biomécanique quantitative de l’œdème et des troubles fonctionnels veineux. Les études n°1 et 2 reposaient sur la volumétrie par mesures étagées de circonférence du membre supérieur chez des patientes présentant un lymphœdème. Elles ont montré la valeur prédictive des variations de volume obtenues par la phase intensive du traitement décongestif quant à l’évolution du lymphœdème à moyen terme et au risque de phénomène de rebond. L’étude n°3 a validé la volumétrie de membre par caméra laser 3D chez des sujets sains et des patients souffrant d’insuffisance veineuse chronique du membre inférieur, en comparaison à la volumétrie par déplacement d’eau, méthode de référence, avec l’avantage majeur de quantifier le volume du pied et de la main. L’étude n°4 comportait, au membre inférieur, la mesure des pressions d’interface, intraveineuse, et intramusculaire sans et avec orthèse de compression dégressive de force 2 et 3, et avec orthèse de compression progressive, au repos, lors d’une manœuvre de flexion-extension du pied en position allongée, et lors d’une manœuvre de haussement sur la pointe des pieds en position debout. L’échographie avec mesure de la force d’appui sur la sonde et analyse automatique d’image calculant l’aire veineuse permettait de déterminer la courbe force / aire d’une veine superficielle et d’une veine profonde du mollet en position allongée et debout. Nous avons inclus 57 patients souffrant d’IVC (21 au stade C1s, 18 au stade C3, et 18 au stade C5 selon la classification CEAP), et 54 sujets sains témoins (18 sédentaires, 18 actifs, 18 sportifs) appariés. Les mesures de pression intraveineuse et intramusculaire ont été réalisées chez un tiers des patients et sujets sains. Le traitement des données échographiques (1776 séquences) étant en cours, nous ne pouvons présenter que des résultats préliminaires et partiels. Les pressions d’interface évoluaient conformément aux attentes, atteignant des valeurs plus élevées sous compression de force 2 que sans compression, sous compression de force 3 que de force 2, et sous compression progressive que sous compression de force 2 ou 3. La compression progressive ne se distinguait nettement des compressions dégressives qu’au niveau du mollet et non de la cheville. Les pressions d’interface étaient généralement plus élevées, sous compression, chez les témoins et les patients au stade C5, et, à un moindre degré, au stade C3, que chez les patients au stade C1s. La pression intraveineuse variait en fonction de la posture et du mouvement et était corrélée à la taille du sujet et sa longueur de jambe en orthostatisme ainsi qu’avec le stade clinique d’IVC. La pression intramusculaire évoluait parallèlement à la compression. Les boucles force / aire veineuse montraient une hystérésis caractéristique, décrivant donc la viscoélasticité des veines examinées. L’analyse complète des résultats permettra de comparer les différentes orthèses de compression et leur effet sur la biomécanique veineuse des sujets sains et pathologiques, avec des données quantitatives sur les caractéristiques viscoélastiques des veines. Nous pourrons évaluer l’effet de l’activité physique en comparant les sujets sédentaires, actifs, et sportifs. L’objectif est, à terme, de produire un modèle mathématique permettant, à partir d’un ensemble limité de données obtenues de façon non-vulnérante, de prédire l’effet des différentes modalités de compression sur la biomécanique veineuse de façon à pouvoir déterminer, grâce à la description géométrique tridimensionnelle du membre, les paramètres individuels optimaux de compression. / The conventional treatment of chronic venous insufficiency (CVI) and lymphedema is based upon mechanical compression, relying on generally admitted but insufficiently proven concepts. The " Phlebosthene " project, initiated in 2010, involves the development and implementation of innovative tools for the quantitative biomechanical evaluation of edema and venous disorders. Studies #1 and #2 were based on the calculation of the upper limb volume by serial circumference measurements in patients with lymphedema. They demonstrated the predictive value of volume variations during the intensive phase of decongestive therapy as for the medium-term outcome and the risk of rebound phenomenon. Study #3 validated segmental limb volumetry by 3D laser scanning in healthy subjects and in patients with lower limb CVI, in comparison with water displacement (reference method), with the major advantage of quantifying the volume of the foot and toes. Study #4 included the measurement, at the lower limb, of interface, intravenous, and intramuscular pressure without and with compression stockings, comparing force 2 and force 3 graduated stockings with so-called progressive compression. Measurements were performed at rest, during flexion-extension movements of the foot while the subject was lying supine, and during a tip-toe test in the standing position. Synchronously recorded B-mode sonography with automatic image analysis allowed calculating the venous area and provided force / area curves of superficial and deep calf veins in the supine and in the standing position. We included 57 patients with CVI (21 at the C1s, 18 at the C3 and 18 at the C5 stage of CVI according to the CEAP classification), and 54 matched healthy controls (18 sedentary, 18 active, 18 sportive). Intravenous and intramuscular pressure measurements were performed in one third of patients. As the processing of the 1776 B-mode sonographic sequences is still underway, we can only offer here partial and preliminary results. Interface pressures evolved as expected, reaching higher values under graduated force 2 compression stockings than without compression, under graduated force 3 than force 2 compression, and under progressive than under graduated compression. Progressive compression clearly distinguished itself from graduated compression only at the calf but not at the ankle level. Interface pressures were generally higher, under compression, in controls and in patients with IVC at the C5 stage, and, to a lesser degree, at the C3 stage, than in patients at the C1s stage. Intravenous pressure varied with posture and movement and correlated with the subject’s size and leg length in orthostatic position, and with the CVI stage. The force / area curves of superficial and deep calf veins exhibited a characteristic hysteresis, yielding viscoelasticity information. When the database will be complete and consolidated, we will be able to compare different compression stockings and their effect on the venous biomechanics of healthy and pathological subjects, providing quantitative data on the viscoelastic characteristics of superficial and deep veins. We will also be able to assess the effect of physical activity on venous biomechanics by comparing sedentary, active, and sportive subjects. The confrontation of interface, intravenous, and intramuscular pressures with these biomechanical data will provide a mathematical model using a limited set of data obtained by simple and non-invasive measurements to predict the effect of compression stockings on the biomechanics of superficial and deep veins, in order to determine, with the help of 3D laser scanning, the optimal individual compression settings.