Human Gait Model Development for Objective Analysis of Pre/Post Gait Characteristics Following Lumbar Spine Surgery

Although multiple advanced tools and methods are available for gait analysis, the gait and its related disorders are usually assessed by visual inspection in the clinical environment. This thesis aims to introduce a gait analysis system that provides an objective method for gait evaluation in clinics and overcomes the limitations of the current gait analysis systems. Early identification of foot drop, a common gait disorder, would become possible using the proposed methodology

Age, Sex, and Head Position Effects on Swallowing Accelerometry and Sounds

Accelerometry (the measurement of vibrations) and auscultation (the measurement of sounds) are both noninvasive techniques that have been explored for detecting abnormalities in swallowing. The differences between these techniques and the information they capture about swallowing have not previously been explored in a direct comparison. In this study, we investigated the differences between dual-axis swallowing accelerometry and swallowing sounds by recording data from adult participants and calculating a number of time and frequency domain features. During the experiment, 55 participants (ages 18-65) were asked to complete five saliva swallows with a neutral head position and then five saliva swallows in a 'chin-tuck' position. The resulting data was processed by previously designed techniques utilizing wavelet denoising, spline filtering, and fuzzy means segmentation. The pre-processed signals were then used to calculate nine time, frequency, and time-frequency domain features for each independent signal. In addition to finding a number of features that varied with the participant's age, sex, and head position, our statistical analysis determined that the majority of our chosen features were significantly different for different transducers. We conclude that swallowing accelerometry and swallowing sounds provide different information about deglutition despite utilizing similar transduction methods

Rehabilitation Engineering in Parkinson's disease

Impairment of postural control is a common consequence of Parkinson's disease (PD) that becomes more and more critical with the progression of the disease, in spite of the available medications. Postural instability is one of the most disabling features of PD and induces difficulties with postural transitions, initiation of movements, gait disorders, inability to live independently at home, and is the major cause of falls. Falls are frequent (with over 38% falling each year) and may induce adverse consequences like soft tissue injuries, hip fractures, and immobility due to fear of falling. As the disease progresses, both postural instability and fear of falling worsen, which leads patients with PD to become increasingly immobilized. The main aims of this dissertation are to: 1) detect and assess, in a quantitative way, impairments of postural control in PD subjects, investigate the central mechanisms that control such motor performance, and how these mechanism are affected by levodopa; 2) develop and validate a protocol, using wearable inertial sensors, to measure postural sway and postural transitions prior to step initiation; 3) find quantitative measures sensitive to impairments of postural control in early stages of PD and quantitative biomarkers of disease progression; and 4) test the feasibility and effects of a recently-developed audio-biofeedback system in maintaining balance in subjects with PD. In the first set of studies, we showed how PD reduces functional limits of stability as well as the magnitude and velocity of postural preparation during voluntary, forward and backward leaning while standing. Levodopa improves the limits of stability but not the postural strategies used to achieve the leaning. Further, we found a strong relationship between backward voluntary limits of stability and size of automatic postural response to backward perturbations in control subjects and in PD subjects ON medication. Such relation might suggest that the central nervous system presets postural response parameters based on perceived maximum limits and this presetting is absent in PD patients OFF medication but restored with levodopa replacement. Furthermore, we investigated how the size of preparatory postural adjustments (APAs) prior to step initiation depend on initial stance width. We found that patients with PD did not scale up the size of their APA with stance width as much as control subjects so they had much more difficulty initiating a step from a wide stance than from a narrow stance. This results supports the hypothesis that subjects with PD maintain a narrow stance as a compensation for their inability to sufficiently increase the size of their lateral APA to allow speedy step initiation in wide stance. In the second set of studies, we demonstrated that it is possible to use wearable accelerometers to quantify postural performance during quiet stance and step initiation balance tasks in healthy subjects. We used a model to predict center of pressure displacements associated with accelerations at the upper and lower back and thigh. This approach allows the measurement of balance control without the use of a force platform outside the laboratory environment. We used wearable accelerometers on a population of early, untreated PD patients, and found that postural control in stance and postural preparation prior to a step are impaired early in the disease when the typical balance and gait intiation symptoms are not yet clearly manifested. These novel results suggest that technological measures of postural control can be more sensitive than clinical measures. Furthermore, we assessed spontaneous sway and step initiation longitudinally across 1 year in patients with early, untreated PD. We found that changes in trunk sway, and especially movement smoothness, measured as Jerk, could be used as an objective measure of PD and its progression. In the third set of studies, we studied the feasibility of adapting an existing audio-biofeedback device to improve balance control in patients with PD. Preliminary results showed that PD subjects found the system easy-to-use and helpful, and they were able to correctly follow the audio information when available. Audiobiofeedback improved the properties of trunk sway during quiet stance. Our results have many implications for i) the understanding the central mechanisms that control postural motor performance, and how these mechanisms are affected by levodopa; ii) the design of innovative protocols for measuring and remote monitoring of motor performance in the elderly or subjects with PD; and iii) the development of technologies for improving balance, mobility, and consequently quality of life in patients with balance disorders, such as PD patients with augmented biofeedback paradigms

Mechanisms of Fatigue with Aging: Evidence from the Whole-Limb to the Single Cell in Humans

Aging is accompanied by a loss of muscle mass and increased fatigability of limb muscles making it difficult for old adults to generate the force and power necessary to perform daily activities, such as ascending a flight of stairs. The mechanisms for the age-related increase in fatigability in old and very old adults (≥80 yrs) and whether there are differences between men and women are unknown. The purpose of this dissertation was to determine the mechanisms for the age-related increase in fatigability in men and women by studying fatigue at the level of the whole-limb and within the muscle cells. Study one compared the fatigability of the knee extensor muscles and determined the mechanisms of fatigue in young, old, and very old men and women elicited by high-velocity exercise. Fatigability of the whole-limb increased across age groups, with no sex differences observed in any age cohort. The age-related increase in power loss was strongly associated with changes in involuntary muscle contractile properties, with minimal contribution from age differences in neural drive. These data suggest the increased fatigability with aging is determined primarily by mechanisms within the muscle for both sexes. To test whether cross-bridge mechanisms could explain the age-related losses in whole-muscle power and increased fatigability, muscle cells from vastus lateralis biopsies were exposed to conditions mimicking quiescent muscle and fatiguing levels of hydrogen (H+) and phosphate (Pi). The fatigue-mimicking conditions revealed that H+ and Pi act synergistically to cause marked reductions in human cross-bridge function. However, other than severe atrophy of fast fibers in old men and women, the effects of the fatigue conditions on cross-bridge function with either severe (study 2) or a range of elevated H+ and Pi (study 3) did not differ with age. These data suggest that age-related losses in whole-muscle power are due primarily to atrophy of fast fibers, but the age-related increase in fatigability cannot be explained by an increased sensitivity of the cross-bridge to H+ and Pi. Combined, these studies suggest that interventions targeting the muscle are necessary to mitigate age-related declines in power and increased fatigability in men and women

Wearable Sensors in the Evaluation of Gait and Balance in Neurological Disorders

The aging population and the increased prevalence of neurological diseases have raised the issue of gait and balance disorders as a major public concern worldwide. Indeed, gait and balance disorders are responsible for a high healthcare and economic burden on society, thus, requiring new solutions to prevent harmful consequences. Recently, wearable sensors have provided new challenges and opportunities to address this issue through innovative diagnostic and therapeutic strategies. Accordingly, the book “Wearable Sensors in the Evaluation of Gait and Balance in Neurological Disorders” collects the most up-to-date information about the objective evaluation of gait and balance disorders, by means of wearable biosensors, in patients with various types of neurological diseases, including Parkinson’s disease, multiple sclerosis, stroke, traumatic brain injury, and cerebellar ataxia. By adopting wearable technologies, the sixteen original research articles and reviews included in this book offer an updated overview of the most recent approaches for the objective evaluation of gait and balance disorders

Mechanisms and Mitigation of Skeletal Muscle Fatigue in Single Fibers from Older Adults

Skeletal muscle fatigue is the contraction-induced decline in whole muscle force or power, and can be greater in older versus young adults. Fatigue primarily results from increased metabolism elevating phosphate (Pi) and hydrogen (H+), which alters myosin-actin interactions; however, which steps of the myosin-actin cross-bridge cycle are changed and their reversibility are unclear. PURPOSE: This study sought to: 1) Examine the effects of elevated Pi and H+ on molecular and cellular function, and 2) Test the ability of deoxyadenosine triphosphate (dATP), an alternative energy to adenosine triphosphate (ATP), to reverse the contractile changes induced with high Pi and H+. METHODS: Maximal tension (force/cross-sectional area), myofilament mechanics and myosin-actin cross-bridge kinetics were measured in 214 single fibers (104 type 1) from the vastus lateralis of eight (4 men) healthy, sedentary older adults (71±1.3 years) under normal (5 mM Pi, pH 7.0), simulated fatigue (30 mM Pi, pH 6.2) and simulated fatigue with dATP conditions. RESULTS: Tension declined with high Pi and H+ in slow- (type I, 23%) and fast-contracting (type II, 28%) fibers due to fewer strongly bound myosin heads (28-48%) and slower cross-bridge kinetics (longer myosin attachment times (ton) (18-40%) and reduced rates of force production (18-30%)). Type I myofilaments became stiffer with high Pi and H+ (48%), which may have partially mitigated fatigue-induced tension reduction. Elevated Pi and H+ with dATP moderately improved force production similarly in both fiber types (8-11%) compared to high Pi and H+ with ATP. In type I fibers, high Pi and H+ with dATP returned the number of myosin heads strongly bound and ton to normal, while the rate of force production became faster than normal (16%). In type II fibers, high Pi and H+ with dATP did not change the number of myosin heads bound, but cross-bridge kinetics were 16-23% faster than normal. CONCLUSION: These results identified novel fiber-type specific changes in myosin-actin cross-bridge kinetics and myofilament stiffness that help explain fatigue-related force reduction in human single skeletal muscle fibers as well as an alternative energy source that partially to fully reverses contractile changes of elevated Pi and H+ that occur with fatigue