Human Physiology Theses and Dissertations

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Open Access
3D COACHING: SPORTS BIOMECHANICAL ANALYSIS OF COLLEGIATE ATHLETICS (TRACK & FIELD)
(University of Oregon, 2024-01-09) ADENIJI, OLA; Halliwill, John
Athletic (Track & Field) championships have showcased globally the great strength, power, and speed of athletes in a myriad of disciplines. Notably over the last 30 years, steady improvements in championship performances have intrigued the Athletics community—athletes, coaches, spectators—sparking interest to look further into how this caliber of athletes perform and what the training demands are to continue the pace of progress. Coaches, by nature, focus on what is familiar to them until the next ‘phenomenon’ in development and training becomes recognizable. In consequence, sports science research sources are perceived with complexity, and unused or misused by the Athletic community. Efforts led by leading sports scientists have been made in the live capture of world-class competitors during world championships to better understand, discuss, and use science within the current state of Athletics in published biomechanical reports. Although athletes have a critical role in whether achievements are met, coaching efforts are to serve the athlete's needs within the demands of each discipline. Balancing what an athlete can do biomechanically and the mechanism within a discipline is the challenge. Coaches often turn to the experiences that have built their coaching philosophy for guidance on the best approaches. With a focus on the NCAA collegiate championship, this project served as a biomechanical-driven evidence-based collection to better understand championship performance. The results justified achieving season-best sprint times and jump marks for higher seeding purposes. Furthermore, results underscored the high individuality in step characteristics during the development of acceleration and velocity of sprinters and jumpers. NCAA championships feature arguably the best collegiate and world-class competitors in Athletics. When the coaching and scientific views are taken into consideration at this level, an improved attempt at defining and appropriately applying mechanical principles to the technique and skills used can be established. Assessing kinematic parameters captured during these championships provides insight into biomechanical contributions in performances for coaches to evaluate and improve training design that will shape an athlete’s performance. An opportunity is available to add to the sports science narratives on the mechanics of Athletic disciplines using a biomechanics lens to magnify the coaches’ eye.
Embargo
A Comparison of Exercise Training and Heat Therapy for Improving Blood Pressure in Adults with Untreated Hypertension
(University of Oregon, 2024-08-07) Kaiser, Brendan; Minson, Christopher
Hypertension, or high blood pressure, represents a primary yet preventable risk factor for cardiovascular disease, kidney dysfunction, and cognitive impairment that impacts nearly 50% of United States adults. Physical activity is the primary lifestyle recommendation to lower blood pressure, but many people are unwilling or unable to engage in exercise training. Heat therapy, in the form of hot water immersion, dry sauna, or far-infrared sauna, has gained attention in recent years as a potential therapeutic alternative to exercise for improving blood pressure and cardiovascular disease risk, with secondary benefits for multiple organ systems, including the renal and cerebral circulation. While both exercise and heat therapy have been demonstrated as effective in a variety of populations, there are no studies that have directly compared these interventions for lowering blood pressure in adults with untreated hypertension. Therefore, the purpose of this study was to compare the efficacy of heat therapy and exercise training for improving blood pressure, renal function, and biomarkers of Alzheimer’s disease among adults with untreated hypertension. 41 adults were randomized to complete either 30 sessions of aerobic exercise training (n=20) or hot water immersion (n=21) over 8-10 weeks, with a battery of in-clinic and ambulatory assessments at baseline (PRE), after 15 sessions (MID), and after 30 sessions (POST). The impact of both interventions in this population was equivocal among outcome variables of interest, including both ambulatory and in-clinic blood pressure, pulse wave velocity, as well as biomarkers of renal function, cognitive function, and Alzheimer’s Disease. These findings help to inform future lifestyle interventions aimed at improving blood pressure and cardiovascular disease risk among adults with untreated hypertension.
Open Access
A Simulation-Based Framework for Informing Design of Prosthetic Feet
(University of Oregon, 2021-04-27) McGeehan, Michael; Hahn, Mike
Individuals with lower limb amputation face a variety of conditions associated with decreased quality of life, including elevated metabolic cost during ambulation, gait asymmetry, and a variety of psychological disorders. Sustained prosthesis use may also induce overloading of joints, leading to orthopedic injuries. These issues may be attenuated by improving user specificity in the design characteristics of foot prostheses. However, the effects of varied design parameters (e.g. stiffness) are not well characterized, and thus achieving meaningful improvements in gait mechanics has proven elusive. In order to achieve improvements, a robust understanding of the relationship between anthropometry, gait mechanics, and prosthesis design is necessary. Simulations based on computational gait models are powerful tools for evaluating potential biomechanical interventions, such as implementing a novel prosthesis. However, the utility of simulations to evaluate the effects of varied prosthesis design parameters on gait mechanics has not been fully realized due to lack of a readily-available limb loss-specific gait model and methods for efficiently simulating the mechanics of passive foot prostheses. The purpose of this dissertation was to develop computational models of a semi-active variable-stiffness foot prosthesis (VSF) and a limb loss-specific gait model to elucidate the relationships between anthropometry, gait mechanics, and variable prosthesis stiffness.This dissertation was divided into three distinct, yet related projects. Project 1 consisted of developing and validating a computational model of a VSF, a model of VSF-ground contact dynamics, and an optimization algorithm for programmatically deriving model parameters. In Project 2, a limb loss-specific gait model was developed and validated. Project 3 entailed developing a spatial contact model for the interface between the prosthetic socket and residual limb, and using that model for a simulation-based analysis of the effects of variable prosthesis stiffness on residual limb-socket dynamics. Projects 1 and 2 resulted in models and code for simulating gait with a VSF. Project 3 resulted in a reduced order spatial contact model of residual limb-socket interface dynamics. Simulated interfacial pressure and shear stress, as well as residual limb kinematics were similar to values previously reported in the literature. The effects of variable prosthesis stiffness on these outcomes were subject-dependent.
Open Access
Analysis of Unique Myoelectric Characteristics in Lower-Extremity Musculature During Locomotive State Transitions
(University of Oregon, 2016-10-27) Nakamura, Bryson; Hahn, Michael
Lower-extremity amputees face numerous challenges when returning to daily activities. Amongst these challenges is the ability to safely and dynamically transition from one locomotor state to another. Switching between level-ground, ramp, and stair locomotion poses an increased risk as lower-extremity functionality is compromised. Powered prosthetics have been proposed as a solution to this problem. Hypothetically, powered prosthetics would be able to return full functional to the amputated limb. The most common and successful source of information used in algorithms for lower-extremity prosthetics has been electromyography. However, in practice, amputees remain unable to easily actuate the mechanized joints of powered prostheses. Therefore, the current project aimed to identify myoelectric activation differences in lower-extremity musculature during the gait cycles preceding locomotor transition in able-bodied, trans-tibial, and trans-femoral subjects to assist efforts in developing robust classification algorithms for locomotor transitions. Analysis of electromyography was completed to determine if there were periods of activation where classification algorithms could utilize differences in myoelectric activation to appropriately control joint actuation in a subset of eight transitions that included level-ground locomotion and switching to either ramp or stair locomotion and vice versa. Ramp transitions were fundamentally similar to level-ground locomotion and elicited no differences in myoelectric activation. Stair transitions were found to alter muscle activation patterns in able-body and trans-tibial subjects. Trans-femoral subjects differentiated from able-bodied and trans-tibial subjects due to increased recruitment pattern variability. These patterns are distinct and may suggest individual learning patterns within the trans-femoral amputee population. Further investigation of these patterns may be warranted. Findings within able-bodied and trans-tibial subjects suggest common transition based differences within each respective population. Trans-tibial classification algorithms may be developed to utilize this information, using schemes that are focused on important areas during the gait cycle.
Open Access
Assessing Inter-joint Coordination during Walking
(University of Oregon, 2012) Chiu, Shiu-Ling; Chiu, Shiu-Ling; Chou, Li-Shan
Coordination indicates the ability to assemble and maintain a series of proper relations between joints or segments during motions. In Dynamical Systems Theory (DST), movement patterns are results of a synergistic organization of the neuromuscular system based on the constraints of anatomical structures, environmental factors, and movement tasks. Human gait requires the high level of neuromuscular control to regulate the initiation, intensity and adaptability of movements. To better understand how the neuromuscular system organizes and coordinates movements during walking, examination of single joint kinematics and kinetics alone may not be sufficient. Studying inter-joint coordination will provide insights into the essential timing and sequencing of neuromuscular control over biomechanical degrees of freedom, and the variability of inter-joint coordination would reflect the adaptability of such control. Previous studies assessing inter-joint coordination were mainly focused on neurological deficiencies, such as stroke or cerebral palsy. However, information on how inter-joint coordination is modulated with different constraints, such as walking speeds, aging, brain injury or joint dysfunctions, are limited. This knowledge could help us in identifying the potential risks during walking and improve the performance of individuals with movement impairments. The purpose of the present study was to investigate the properties of inter-joint coordination pattern and variability during walking with different levels of neuromuscular system perturbations using a DST approach, including an overall neuromuscular systemic degeneration, a direct insult to the brain, and a joint disease. We found that aging seemed to reduce the pattern adaptability of neuromuscular control. Isolated brain injury and joint disease altered the coordination pattern and exaggerated the variability, indicating a poor neuromuscular control. To improve gait performances for different populations, clinical rehabilitation should be carefully designed as different levels of neuromuscular system constraints would lead to different needs for facilitating appropriate coordinative movement. This dissertation includes both previously published/unpublished and coauthored material.
Open Access
Attention and gait performance following a concussion
(University of Oregon, 2008-06) Catena, Robert David, 1981-
Currently the information on attention-balance control interactions following concussion is incomplete and not given particular consideration during clinical examinations of concussion. The purposes of this dissertation were to (1) test different gait paradigms for their sensitivity of identifying concussion symptoms and to (2) test how individual components of attention interact with gait performance. The long-term goal of this study is to establish more functional and succinct protocols for return-to-play decisions. Grade II (AAN guidelines) concussed individuals were recruited to participate in testing at 2, 6, 14, and 28 days post-injury. Gait and components of attention were analyzed during each session through a number of different paradigms. Control subjects were matched by stature, age, and athletic participation. The results indicate that the dynamic balance deficits following a concussion are immediately identified with an attention dividing gait task. Obstacle crossing identified more conservative adaptations 2 weeks after injury. A task combining the two did not clearly identify concussion deficits. Two components of attention showed promise as interacting with gait to cause balance deficits. The spatial orientation component showed an interaction with obstacle avoidance indicating that the same concussed individuals that had poor spatial orientation of attention also came closer to hitting the obstacle during crossings. An analysis of divided attention showed that concussed individuals performing poorly in one task also performed poorly in the other during a dual-task paradigm, but during any one particular trial there was a trade-off between task performances, which was not present in control individuals. The findings of this dissertation point to the use of a divided attention task to distinguish concussed individuals from healthy individuals immediately after a possible injurious event. How several different components of attention interact with gait performance is identified. Finally, if a concussion has occurred, an obstacle crossing task might be suitable for a long-term analysis of full recovery of balance control. Ultimately, it is my hope that the information provided here will lead to functionally relevant and clinically executable tests of concussed individuals before they are placed in harm's way due purely to an incomplete diagnosis of their injuries.
Open Access
Balance Control and Stability during Gait - An Evaluation of Fall Risk among Elderly Adults
(University of Oregon, 2011-09) Lugade, Vipul Anand, 1980-
Falls are a significant source of physical, social, and psychological suffering among elderly adults. Falls lead to morbidity and even mortality. Over one-third of adults over the age of 65 years will fall within a calendar year, with almost 10,000 deaths per year attributed to falls. The direct cost of falls exceeds $10 billion a year in the United States. Fall incidents have been linked to multiple risk factors, including cognitive function, muscle strength, and balance control. The ability to properly identify balance impairment is a tremendous challenge to the medical community, with accurate assessment of fall risk lacking. Therefore, the purpose of this study was to assess balance control during gait among young adults, elderly adults, and elderly fallers; determine which biomechanical measures can best identify fallers retrospectively; demonstrate longitudinal changes in elderly adults and prospectively assess fall risk; and provide a method for mapping clinical variables to sensitive balance control measures using artificial neural networks. The interaction of the whole body center of mass (CoM) in relation to the base of support (BoS) assessed static and dynamic balance control throughout gait. Elderly fallers demonstrated reduced balance control ability, specifically a decreased time to contact with the boundary of the BoS, when compared to young adults at heel strike. This decreased time might predispose older adults to additional falls due to an inability to properly respond to perturbations or slips. Inclusion of these balance control measures along with the Berg Balance Scale and spatiotemporal measures demonstrated sensitivity and specificity values of up to 90% when identifying 98 elderly fallers and non-fallers, respectively. Additionally, 27 older adults were followed longitudinally over a period of one year, with only the interaction of the CoM with the BoS demonstrating an ability to differentiate fallers and non-fallers prospectively. As the collection and analysis of these biomechanics measures can be time consuming and expensive, an artificial neural network demonstrated that clinical measures can accurately predict balance control during ambulation. This model approached a solution quickly and provides a means for assessing longitudinal changes, intervention effects, and future fall risk. This dissertation includes both previously published and unpublished co-authored material.
Embargo
Blood Flow Through Intrapulmonary Arteriovenous Anastomoses: Reconciliation of Inconsistent Data Obtained in Hypobaria and Body Position Studies
(University of Oregon, 2018-04-10) Petrassi, Frank; Lovering, Andrew
Intrapulmonary arteriovenous anastomoses (IPAVA) are vascular conduits through which blood flow bypasses the pulmonary circulation, and does not participate in pulmonary gas exchange. Blood flow through IPAVA (QIPAVA) is known to increase with increasing cardiac output, such as exercise, and while breathing normobaric, hypoxic gas at rest or during exercise. Previous studies demonstrate that QIPAVA is decreased at rest and during exercise in hypobaria compared to equivalent normobaric conditions. Studies involving postural changes have shown that QIPAVA may change with body position. In human studies, QIPAVA is measured either by transthoracic saline contrast echocardiography (TTSCE) or by injection of 99mTc-labeled macroaggregates of albumin (99mTc-MAA). It is unknown if discrepancies in measuring QIPAVA in normobaria and hypobaria, and in different body positions, represent real physiological changes or if they are methodological artifacts. In Chapter IV, the effect of hypobaria on QIPAVA was investigated. QIPAVA was reduced during exercise in hypobaria in normoxia and hypoxia compared to normobaric conditions, however gas exchange efficiency was unimpaired. This suggests that pulmonary blood flow may change in hypobaria such that blood flow is directed away from IPAVA. Alternatively, it may suggest that saline contrast is less stable at high altitude and not detected by TTSCE. In Chapter V, the effect of changing body position on QIPAVA as detected by TTSCE was investigated in human subjects at rest. No significant changes were observed in QIPAVA with postural changes. In Chapter VI, a perfusion model was used to investigate behavior of saline contrast microbubbles, MAA, and microspheres (20 µm and 50 µm diameter) encountering a vertical bifurcation. The results indicated that microbubbles and 20 µm microspheres tend to enter the upper branch of the bifurcation, whereas MAA and 50 µm microspheres tend to enter the lower branch. In Chapter VII, the effect of atmospheric pressure on the initial microbubble radius (Ro) of agitated saline contrast microbubbles was investigated. The results of this study demonstrated that the Ro of microbubbles created at sea level pressure was significantly smaller than Ro of microbubbles created at higher altitudes (1,668 m and 5,260 m).
Open Access
Chronic Passive Heat Exposure and Cardiometabolic Health in Obese Women with Polycystic Ovary Syndrome
(University of Oregon, 2018-09-06) Ely, Brett; Minson, Christopher
Polycystic Ovary Syndrome (PCOS) is a complex endocrine disorder that increases a woman’s risk of developing cardiovascular disease and diabetes. Women with PCOS have extremely high rates of obesity, insulin resistance, cardiovascular morbidity and mortality. Obese women with PCOS also tend to have elevated sympathetic nerve activity and systemic markers of inflammation, which likely contribute to cardiometabolic risk and PCOS pathogenesis. While few medication or lifestyle intervention options for women with PCOS target elevated sympathetic nerve activity, inflammation, and insulin resistance, passive heat exposure shows promise as a novel intervention for improving cardiovascular and metabolic health in this population. Therefore, the purpose of this study was to examine changes in inflammation, cardiovascular, autonomic, and metabolic health in obese women with PCOS following a 30-session, 8-10 week chronic passive heat intervention (termed ‘heat therapy’). Eighteen obese women with PCOS (Age: 27±1y, BMI 41.3±1.1 kg·m2) were matched for age and body mass index (BMI), then divided into heat therapy (HT) or time control (CON). At the beginning (Pre), middle (Mid), and end (Post) of 8-10 weeks, subjects participated in study days to assess vascular, autonomic, and metabolic function, and additionally underwent a subcutaneous fat biopsy in Pre and Post. HT subjects took part in 30 one-hour hot tub sessions over 8-10 weeks (3-4 per week) in 40.5˚C water, while CON subjects completed all other testing but were not exposed to heat. No change in BMI was observed over the study in HT or CON; however; HT subjects exhibited dramatically improved vascular and metabolic function, as well as reduced sympathetic nerve activity and circulating inflammatory markers. In fat biopsies, insulin signaling was improved in HT subjects, while CON subjects remained stable over time. These findings show promise for HT as a treatment option for obese women with PCOS to improve cardiovascular and metabolic risk profiles. This dissertation includes previously published co-authored material.
Open Access
Chronic passive heat therapy as a novel means of improving vascular function in sedentary humans
(University of Oregon, 2016-10-27) Brunt, Vienna; Minson, Christopher
Cardiovascular disease is the leading cause of death in the developed world. The majority of cardiovascular diseases are characterized by disorders of the arteries, predominantly caused by endothelial dysfunction and arterial stiffening. Passive heat stress results in elevations in core temperature (inducing heat shock protein expression) and changes in cardiovascular hemodynamics, such as increased cardiac output and shear stress, that are similar to exercise. Thus, repeated passive heat stress (“heat therapy”) may provide an alternative means of improving cardiovascular health, particularly for patients with limited exercise tolerance and/or capabilities. Therefore, the goal of this dissertation was to perform integrative studies to determine the effects of heat therapy on vascular function and the associated cellular pathways in young, sedentary humans. Twenty subjects were assigned to participate in 8 weeks (4-5x/week) of heat therapy (N=10; immersion in a 40.5°C bath sufficient to maintain rectal temperature ≥38.5°C for 60 min/session) or thermoneutral water immersion (N=10; sham). As discussed in Chapter V, we found that heat therapy improved numerous well-established biomarkers of conduit vessel/macrovascular function, including flow-mediated dilation (a measure of endothelial function), arterial stiffness, intima media thickness, and blood pressure. Heat therapy also improved microvascular function, as discussed in Chapter VI, measured as improved cutaneous thermal hyperemia and nitric oxide-dependent dilation (the difference between microdialysis sites receiving Lactated Ringer’s [control] and nitric oxide synthase inhibition). No changes were observed in any variables in sham subjects. In Chapter VII, we showed that both direct cellular heating and serum collected from human subjects following heat therapy improved nitric oxide bioavailability and angiogenesis in cultured endothelial cells, providing potential mechanisms by which heat therapy improves vascular function in vivo. Therefore, the studies described herein provide comprehensive evidence that passive heat therapy improves vascular health and insight into the mechanisms involved. Our data presented in Chapters IV-VII, combined with pilot data we conducted in spinal cord injured individuals (Chapter VIII), strongly indicate that passive heat therapy could be used as a simple and effective tool to improve cardiovascular health in a variety of patient populations. This dissertation includes published and unpublished co-authored material.
Open Access
Clinical and Laboratory Balance Assessment in the Elderly
(University of Oregon, 2013-07-11) Chen, Tzurei; Chou, Li-Shan
Falls can have severe consequences for elderly adults. In 2000, nearly 10,300 people aged 65 years or older died as a result of falls, and 2.6 million individuals were treated for non-fatal fall-related injuries. In order to reduce fall incidences, it is important to identify possible causes of falls, such as muscle weakness and imbalance. In this study, we examined balance control in the elderly during task transitions while performing the Timed Up and Go test (TUG). The TUG is a commonly used clinical balance test that includes transition phases between three daily activity tasks: sit-to-stand, walking and turning. Our findings suggested that elderly adults, especially fallers, have reduced balance control ability while making transitions during TUG. During sit-to-walk (STW), when compared to young adults, elderly adults demonstrated a smaller forward center of mass (COM) velocity, a smaller anterior-posterior (A-P) COM-Ankle angle, and a larger upward kinetic energy ratio at seat-off. Additionally, the medial-lateral COM control in elderly fallers was also perturbed due to their significant reduction in forward COM velocity. The reduced initial hip extensor moment and increased ankle plantarflexor moment in elderly fallers was associated with their reduced generation of horizontal momentum during STW. Smaller A-P COM-Ankle angles and taking more steps when making a turn demonstrated a reduction in balance control ability in elderly adults. Our analyses suggest that balance control is an important factor contributing to longer STW and turning durations of TUG. Furthermore, lower extremity muscle strength at hip and knee joints demonstrated a stronger association with STW than turning duration. To enhance the early detection of fall risk, we also assessed the ability of balance tests to predict future risk of falling in elderly adults. Our results indicated that biomechanical balance parameters measured during TUG were associated with future fall status. Among all biomechanical parameters investigated, frontal plane balance control parameters appear to be the most significant predictors for future falls. This dissertation includes unpublished co-authored material.
Open Access
Comprehensive examination of the differences in thermoregulatory and ventilatory responses between humans with and without a PFO under different environmental conditions
(University of Oregon, 2016-11-21) Davis, James; Lovering, Andrew
The existence of a patent foramen ovale (PFO) has been known about for nearly 2,000 years. The prevalence of a PFO has been shown to be 25-40% in the general population. Despite the fact that blood flowing through a PFO acts as a shunt, there has been little research looking at the effect a PFO has on physiology in otherwise healthy humans. In Chapter IV, the effect of a PFO on core temperature (Tcore) prior to, and during exercise, was investigated. The design of this experiment included appropriate controls for a thermoregulatory study (i.e. measuring at same time of day, appropriate hydration and food intake, etc.). Results from this study indicate that subjects with a PFO (PFO+) have a Tcore that is ~0.4°C higher at rest and during exercise than subjects without a PFO (PFO–). Additionally, this study showed that PFO– subjects do not increase Tcore to the same extent breathing cold air as they do breathing ambient air during a 10-minute exercise bout, whereas there was no difference in Tcore increase between these two conditions for PFO+ subjects. These findings suggest that the difference in Tcore between PFO+ and PFO– subjects is potentially due to differences in respiratory heat loss. The studies for Chapter V examined differences in thermoregulatory and ventilatory responses during hot water (40°C) and cold water (20°C) immersion. This study found that compared to PFO– subjects, PFO+ subjects 1) increase Tcore at the same rate during hot water immersion and 2) do not cool off as quickly during cold water immersion. Additionally, in subjects who reached a ventilatory threshold, PFO+ subjects had blunted ventilatory responses to increased Tcore compared to PFO– subjects. Finally, in Chapter VI it was shown that PFO+ subjects have blunted ventilatory responses during acute exposure to hyperoxic and normoxic hypercapnia. However, there were no differences in ventilatory responses between PFO+ and PFO– subjects during exposure to either isocapnic or poikilocapnic hypoxia. These findings suggest that PFO+ subjects have a blunted central chemoreflex. This dissertation contains previously, unpublished co-authored material.
Open Access
Contribution of spinal segments to control of posture during typical and atypical development
(University of Oregon, 2010-03) Saavedra, Sandra Lee, 1952-
Trunk control is critical for all functional movement, yet little is known about the development of trunk stability. Previous research considered the trunk to be one rigid segment ignoring the complexity of multiple spinal segments. In healthy adults spinal control is so well orchestrated that this assumption is reasonable; however during development and more specifically in pathological conditions in which spinal control is immature or compromised, this assumption may prevent accurate analysis and/or treatment of the condition. This dissertation investigates the mechanisms used by typical infants in gaining postural control of spinal segments for independent sitting. Infant data were compared to data from children with cerebral palsy (CP). The contribution of spinal segments was assessed by stabilizing the trunk in vertical alignment with four levels of support (axillae, mid-ribs, waist or hips). Documentation of postural sway of the head reflected the motor control available in the free segments of the spine. Kinematic data were collected bimonthly from 3 to 9 months of age in typically developing infants and 3-4 times over a 4 month time span in children with CP. The infants' response to external support changed in a non-linear, stage-like fashion as they transitioned from immature to mature spinal control. Head stability emerged first at higher levels of trunk support and gradually progressed in a cephalocaudal pattern to lower levels of support. Emergence of functional sitting was associated with mastery of postural control in the lower lumbar and pelvic regions of the spine. The severity of CP was related to the level of spinal control achieved. Children with severe CP had control in the cervical or upper thoracic spine while those with moderate CP had control into the mid to lower thoracic spine. In addition, behavioral patterns seen in children with CP were consistent with developmental stages seen in typical infants during acquisition of vertical alignment. These findings challenge the existing clinical practice of evaluating and treating the trunk as a single segment, offer intermediate measures of progression of spinal control and propose that a more specific approach may create the foundation for improved motor outcomes in pathological populations.
Open Access
Contributions of Distinct Trunk Segments to Control of Posture and Reaching During Typical Development
(University of Oregon, 2015-01-14) Rachwani Parshotam, Jaya; Karduna, Andrew
The relationship between the development of sitting postural control and of reaching during infancy has not been addressed in detail. It has recently been shown that trunk control develops starting with the head, then the upper trunk and subsequently the lower/pelvic regions. However, previous studies on infant reaching evaluated infants during supported supine or reclined sitting positions, failing to address the contributions of distinct regions of the trunk to reaching. This dissertation explores the relationship between the progression of trunk control and reaching performance in healthy infants. The effects of stabilizing the upper and lower regions of the trunk were assessed by providing vertical trunk fixation at two levels of support (thoracic and pelvic). Documentation of postural and reaching performance reflected how control of the free regions of the trunk modulated both behaviors. First, kinematic data were collected in infants aged 4-6 months who were grouped according to their sitting ability and extent of trunk control. Second, a longitudinal study was implemented in which kinematic and electromyographic recordings were collected bi-monthly from 2.5-8 months. Results from the cross-sectional study showed that postural stability and reaching kinematics of the two groups were similar when they received support at the thoracic level but differed when the support was limited to the pelvic level. Infants who were able to sit independently outperformed the infants who were unable to sit without help. These data were further expanded with the results obtained from the longitudinal study, showing that during the months prior to independent sitting, infant reaches were impoverished and were associated with a lack of postural stability when provided with pelvic, in comparison to thoracic, support. In addition, infants displayed inefficient muscle patterns in response to the instability. Differences between levels of support were not observed once infants acquired independent sitting. Taken together, these results offer detailed measures of the progression of trunk control and its relation to reaching. This raises important questions regarding whether this more specific approach may create the foundation for evaluating and improving trunk control in atypically developing populations. This dissertation includes previously published and unpublished co-authored material.
Open Access
Cutaneous vasodilation at simulated high altitude: Impacts on human thermoregulation and vasoconstrictor function
(University of Oregon, 2008-12) Simmons, Grant H., 1981-
During acute altitude exposure, humans maintain higher skin temperature and lower core body temperature. However, the role of cutaneous vascular regulation in these thermoregulatory differences is unclear. Therefore, the purpose of these studies was to investigate the impact of altitude exposure on reflex control of skin blood flow and core temperature during cold exposure. In Chapter IV, the effects of hypoxia and hypocapnia on cutaneous vasoconstriction during mild cold exposure were investigated. We found that hypoxia stimulates cutaneous vasodilation in men whereas skin blood flow is unaltered in women. However, during whole body cooling skin blood flow is upward shifted in both sexes. The development of hypocapnia does not affect the vascular response to hypoxia in either sex, but reduces the magnitude of cutaneous vasoconstriction during cold exposure by 50% in women. In Chapter V, we studied the timecourse of α-adrenergic blockade by yohimbine in the cutaneous circulation and how the duration of cold exposure modulates cotransmitter-mediated vasoconstriction during cold stress. We found that yohimbine produces functional α-adrenergic blockade within 30 minutes of initial delivery and completely abolishes reflex cutaneous vasoconstriction during mild cold stress. This latter finding was surprising, and an additional protocol demonstrated that cotransmitter-mediated vasoconstriction only participates in the vascular response to cold stress when the exposure is more prolonged. In Chapter VI, the effects of hypoxia on cutaneous vasoconstrictor mechanisms and core cooling rate were tested during more prolonged and severe cold stress. In contrast to our findings during brief cold exposure, we showed that cutaneous vasoconstriction during prolonged cold stress is potentiated by hypoxia and abolishes hypoxic vasodilation. Moreover, increased cotransmitter-mediated vasoconstriction appears to account for this response. Hypoxia had no effect on core cooling rate during severe cold exposure. The selective potentiation of cotransmitter-mediated vasoconstriction observed during hypoxia in Chapter VI provided the basis for Chapter VII. This study was designed to test the effect of hypoxia on cutaneous vascular responsiveness to peripherally stimulated sympathetic vasoconstriction. The results demonstrated that α-adrenergic vasoconstrictor transduction is not affected by hypoxia, and that stimulation of adrenergic nerves with tyramine does not elicit cotransmitter-mediated vasoconstriction in skin.
Open Access
Detecting Gait Imbalance Following Concussion Using an Inertial Measurement Unit
(University of Oregon, 2020-02-27) Pitt, William; Chou, Li-Shan
Concussion injury is shown to result in acutely impaired dynamic balance control. This impairment can last as long as two months post injury as evidenced by biomechanical metrics derived from data collected during dual-task (DT) gait using camera-based motion capture system. However, clinical application of such DT gait balance control with advanced kinematic analysis is yet limited. To advance the clinical translation of the laboratory findings to clinical practice, four studies were conducted to assess the utility of an inertial measurement unit (IMU) to detect gait imbalance following concussion. In the first study, a highly consistent and reliable DT assessment was developed using off the shelf hardware and software. Acceleration based kinematic markers collected from a single IMU placed over the fifth lumbar vertebra (L5) demonstrated potential for detecting subtle changes in gait balance control at a university sport medicine facility. In the second study the DT gait balance control of individuals sustaining an acute concussion was analyzed with the assessment and compared to that of healthy matched controls over a two month post injury period. Multiple-gait event specific accelerations and angular velocities collected from the L5 sensor were capable of detecting impaired gait balance control. In the third study, logistic regression models including groups of between three and six kinematic and neurocognitive metrics collected from both straight and turning gait were shown to have high sensitivity (Sn) and specificity (Sp) in distinguishing acutely concussed from healthy individuals. Furthermore, these models maintained moderate Sn and Sp throughout the two month post injury period suggesting they are capable of identifying individuals with lingering balance control deficits. In the fourth study, the utility of dual-task cost (DTC) metrics derived from the kinematic and neurocognitive measures was assessed for post-concussion gait imbalance detection. It was determined that due to high levels of variability inherent to the metrics in this application, their utility in gait imbalance detection is limited, and are similarly unable to be used to describe differences or changes in task prioritization. This dissertation includes co-authored work either previously published or unpublished.
Open Access
Development of postural control during gait in typically developing children and children with cerebral palsy: The effects of dual task conditions
(University of Oregon, 2010-03) Boonyong, Sujitra, 1973-
The purpose of this dissertation was (1) to investigate the effects of dual task conditions on the development of postural control during gait in typically developing children while walking and obstacle crossing, and (2) to investigate the attentional requirements of gait in children with cerebral palsy (CP). Forty younger and older typically developing (YTD and OTD) children and 10 children with CP performed a gait task with and without a concurrently auditory Stroop task. Gait and cognitive performance were measured. In study 1, dual task interference with gait performance was found in YTD and OTD children, but not in healthy young adults (HYA). In general, gait performance decrements under dual task contexts were greater in YTD than OTD children, whereas cognitive performance decrements during dual tasking were not different between the two groups of children. Dual task interference was lowest in HYA and highest in YTD children when compared among groups. As the difficulty of the gait task was increased, dual task affects on cognitive performance were now found in YTD and OTD children, but not HYA. In study 2, there were significant differences in dual task interference affecting gait performance in all groups of children. When performing the gait task with a concurrent auditory Stroop task, OTD children showed greater dual-task costs than children with CP for accuracy, but children with CP demonstrated greater dual-task costs than OTD and YTD children for medial Center of Mass-Ankle-joint-center inclination angle. This increased medio-lateral inclination angle in dual task situations has also been seen in older adults with balance deficits and may be associated with an increased risk for falls. YTD children showed dual-task costs in a slowing of gait velocity and stride time, a safer strategy than that used by children with CP. The lower cognitive performance during dual tasking for OTD children suggests that they allocate greater attention to maintain gait stability, whereas YTD children and children with CP do not. In addition, children with CP use a behavior that may increase their risk of falls in complex environments. This dissertation includes unpublished co-authored material.
Open Access
Disruption of Neurorespiratory Control by Acute Inflammation, Neonatal Inflammation, and Perinatal Opioids
(University of Oregon, 2020-02-27) Hocker, Austin; Huxtable, Adrianne
Adequate respiratory control is vital, but is disrupted by stressors such as inflammation or opioids. Additionally, early-life stressors may have long-lasting consequences for adult breathing, increasing the risk of disease. This dissertation focuses on how acute inflammation impairs adult respiratory control mechanisms and explores the consequences of two early life stressors, neonatal inflammation and perinatal opioids. Respiratory plasticity is a key feature of respiratory control, commonly studied in the form of phrenic long-term facilitation (LTF), evoked by acute intermittent hypoxia. Two distinct molecular pathways evoke LTF: the Q-pathway which is impaired by low-level inflammation, and the S-pathway which is inflammation-resistant. Chapters II and III further our mechanistic understanding of how inflammation impacts respiratory plasticity. Chapter II demonstrates spinal activation of the interleukin-1 (IL-1) receptor is necessary for impairing Q-pathway LTF after inflammation. However, IL-1beta, the endogenous ligand of IL-1R, is not sufficient to impair LTF in healthy animals, suggesting other inflammatory signals are required. While LPS or simulated sleep apnea induces inflammation and impairs Q-pathway-evoked LTF, chapter III demonstrates these impairments are generalizable to viral-mimetic induced inflammation which impairs Q-pathway, but not S-pathway-evoked pLTF. Chapter IV demonstrates the long-lasting impairment of adult respiratory plasticity following a single bout of LPS-induced early-life inflammation. Early-life inflammation impaired both Q-pathway and S-pathway-evoked LTF in male and female rats. Despite a lack of adult pro-inflammatory gene expression, Q-pathway LTF was restored by adult anti-inflammatory treatment, demonstrating ongoing inflammatory signaling after neonatal inflammation. S-pathway-evoked LTF was revealed by adenosine receptor agonism, suggesting upstream impairment in adenosine release. Chapter V investigates the impact of maternal opioid use, another common perinatal stressor. Maternal methadone increases neonatal apneas and mitigates acute methadone-induced respiratory depression, demonstrating perinatal opioids destabilize neonatal respiratory control in rats. These studies demonstrate neurorespiratory control is disrupted by acute inflammation, neonatal inflammation, and perinatal opioids. The research contributes to our fundamental understanding of how inflammation impairs adult respiratory plasticity, both acutely and after a single early-life exposure. Further, it lays the foundation for future studies investigating how perinatal opioids alter the developing respiratory control system. This dissertation includes previously published, coauthored material.
Open Access
Dynamic Limits of Balance Control during Daily Functional Activities Associated with Falling
(University of Oregon, 2012) Fujimoto, Masahiro; Fujimoto, Masahiro; Chou, Li-Shan
Falls are one of the most serious problems among the elderly, resulting in fatal physical injuries. Early identification of people at a high risk of falling is needed to facilitate rehabilitation to reduce future fall risk. The overall goal of this dissertation was to develop biomechanical models that identify dynamic limits of balance control in daily functional activities associated with falling, including sit-to-stand (STS) movement, standing (stance perturbation), and walking. Poor performance of STS movement has been identified as one of the risk factors of falls among elderly individuals. We proposed a novel method to identify dynamic limits of balance control during STS movement using whole body center of mass (COM) acceleration and assessed its feasibility to differentiate individuals with difficulty in STS movement from healthy individuals. The results demonstrated that our model with COM acceleration could better differentiate individuals with difficulty in STS movement from healthy individuals than the traditional model with COM velocity. Poor postural control ability is also a risk factor of falls. Postural recovery responses to backward support surface translations during quiet standing were examined for healthy young and elderly adults. The results demonstrated that functional base of support (FBOS) and ankle dorsiflexor strength could be sensitive measures to detect elderly individuals with declined balance control. Our biomechanical model, which determines a set of balance stability boundaries, showed a better predictive capability than the statistical model for identifying unstable balance recovery trials, while the statistical model better predicted stable recovery trials. Lastly, walking requires a fine momentum control where COM acceleration could play an important role. Differences in control of dynamic stability during walking were examined with our proposed boundaries of dynamic stability. Elderly fallers adapted a more conservative gait strategy than healthy individuals, demonstrating significantly slower forward COM velocity and acceleration with their COM significantly closer to the base of support at toe-off, which could be indicative of a poor momentum control ability. Overall, this study demonstrated that COM acceleration would provide further information on momentum control, which could better reveal underlying mechanisms causing imbalance and provide an insightful evaluation of balance dysfunction. This dissertation includes unpublished co-authored material.
Open Access
Effect of the Long-Term Health Practices of Tai Chi, Meditation and Aerobics on Adult Human Executive Attention: A Cross-Sectional Study
(University of Oregon, 2012) Hawkes, Teresa; Hawkes, Teresa; Woollacott, Marjorie
Meditation, Tai Chi, and moderate aerobic exercise have been shown to positively affect executive attention. We compared the executive attention efficiency and aerobic capacity of long-term Tai Chi, meditation plus exercise, aerobic fitness, and sedentary participants. We hypothesized that because meditation and Tai Chi include moderate aerobic exertion and executive attention training, these groups would show significantly greater executive attention efficiency compared to aerobic exercisers or sedentary control groups. Our results support this. Tai Chi and meditation but not aerobic fitness practitioners significantly outperformed sedentary controls on key executive measures: percent switch costs and P3b ERP switch amplitude (Tai Chi, p = .001; p = .031, respectively; meditation, p = .006; p = .003, respectively). This suggests participation in chronic health practices requiring moderate aerobic exertion and attentional focus may offset declines in aerobic, neuromotor, and executive attention capacity often seen in normal aging.