Biomedical Physiology and Kinesiology - Theses, Dissertations, and other Required Graduate Degree Essays

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Nonshivering thermogenesis: responses to acute cold exposure in obese males

Date created: 
2015-05-13
Abstract: 

The studies in this thesis were to assess whether obese relative to non-obese individuals have blunted metabolic and non-shivering thermogenic responses in acute mild cold exposure, possibly established by a higher capacity to activate brown adipose tissue in the non-obese, resulting in greater energy expenditure. It was hypothesised that the obese would demonstrate a reduced non-shivering thermogenesis during acute mild cold exposure despite having lower skin temperatures and the same core temperature. The first study resulted in obese individuals having lower mean rate of oxygen consumption (p < 0.05), lower mean skin temperatures (p < 0.05), and lower mean heat flux (p < 0.05) during a 19°C exposure. There was no difference, however, in carbohydrate (p = 0.14) or lipid (p = 0.46) oxidation rates. The second study resulted in obese having lower mean supraclavicular skin temperatures (p < 0.001), lower mean supraclavicular heat flux (p < 0.05), lower mean surface temperatures from FLIR thermography (p < 0.05) and a lower mean metabolic response (p < 0.05). Non- shivering thermogenesis was achieved as there was minimal and no significantly different skeletal muscle activity between the two groups (p = 0.94). In conclusion, during acute mild cold exposure, obese individuals displayed a significantly lower non- shivering thermogenesis despite having lower skin temperatures and the same core temperatures relative to non-obese individuals. This possibly originates from a decreased capacity to activate brown adipose tissue depots in the obese that contributes to their lower energy expenditure in these conditions.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Matthew White
Department: 
Science:
Thesis type: 
(Thesis) M.Sc.

The Effect of Glaucoma on Gaze Behaviour and Mobility While Walking in Cluttered Environments

Date created: 
2015-08-14
Abstract: 

Glaucoma causes loss of peripheral vision and is a leading cause of blindness worldwide. It primarily affects older adults, limiting their mobility and increasing their risk for falls. This thesis investigated the effects of visual field loss from glaucoma on gaze behaviour and mobility during two visually demanding walking tasks while multitasking; stepping to targets, and navigating around obstacles. Older adults with glaucoma had less precise foot placement, looked to the same target more often, and looked toward future targets sooner, compared to healthy older adults. Subjects with glaucoma also collided with obstacles more frequently, looked to obstacles more often, and looked more frequently toward their feet. Dual tasking also disrupted mobility and gaze during the walking tasks. For this population these findings provide the framework to design future walking and gaze training programs for people with glaucoma to improve their quality of life.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Dr. Daniel Marigold
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

KeyLabel Algorithms for Keyword Search in Large Graphs

Author: 
Date created: 
2015-08-24
Abstract: 

Graph keyword search is the process of extracting small subgraphs that contain a set of query keywords from a graph. This problem is challenging because there are many constraints, including distance constraint, keyword constraint, search time constraint, index size constraint, and memory constraint, while the size of data is inflating at a very high speed nowadays. Existing greedy algorithms guarantee good performance by sacrificing accuracy to generate approximate answers, and exact algorithms promise exact answers but require huge memory consumption for loading indices and advanced knowledge about the maximum distance constraint. We propose a new keyword search algorithm that finds exact answers with low memory consumption and without pre-defined maximum distance constraint. This algorithm builds a compact index structure offline based on a recent labeling index for shortest path queries. At the query time, it finds answers efficiently by examining a small portion of the index related to a query.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Ke Wang
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Internephron synchronization of renal blood flow autoregulation

Date created: 
2015-07-21
Abstract: 

Renal autoregulation is the system that maintains a constant renal blood flow when arterial pressure fluctuates. Failure of autoregulation leads to renal damage and subsequent failure. There are two mechanisms of autoregulation. First is the myogenic response, which is common to almost all microvascular beds. Second is tubuloglomerular feedback, which is a slower system that fine-tunes the delivery of solutes to each nephorn. Autoregulation is well studied. However, limitations in measurement techniques, and simplifying assumption, previously forced us to assume that all nephrons in the kidney act independently in response to local changes in blood pressure. The goal of this dissertation was to determine the presence, extent, and mechanism of network behaviour in renal autoregulation. In this dissertation I show that the mechanisms of renal autoregulation are synchronized over macroscopic regions of the renal surface, and that the spatial distribution of synchronization can be modulated by nitric oxide. Then I show that the patterns of synchronization of autoregulation on the surface of the kidney are governed by the underlying arterial anatomy. We show that the mechanism of internephron synchronization is chiefly dependent on gap junctional intercellular communication, and that removal of this communication pathway reduces the efficiency of autoregulation overall. Finally, impaired autoregulation in early diabetes is shown to coincide with a reduction in spatial smoothing of autoregulation. By the end, I have shown that internephron synchronization is present in the kidney, and 1) synchronization is modulated by an important hormonal modulator, nitric oxide, 2) that arterial anatomy determines divisions between synchronized clusters, 3) gap junctions mediate synchronization and contribute to autoregulation effectiveness, and 4) that network behaviour of autoregulation is reduced in early diabetes, linked with impaired autoregulation. Overall, this shows that internephron synchronization is an important aspect of renal autoregulation, and it must be considered in the future when studying this field.

Document type: 
Thesis
File(s): 
Senior supervisor: 
William Cupples
Department: 
Science:
Thesis type: 
(Dissertation) Ph.D.

Cardiovascular and cerebrovascular consequences of spinal cord injury

Date created: 
2015-06-08
Abstract: 

Spinal cord injury (SCI) has profound effects on motor, sensory, and autonomic function. The autonomic repercussions of SCI are widespread and demand life-long management and care. Cardiovascular problems are particularly common after high-level SCI that disrupts spinal sympathetic pathways to the heart and blood vessels. In this thesis I investigated the effect of damage to autonomic pathways on cardiovascular control during routine activities of daily living. In Chapter 2, I showed that moderate changes in wheelchair seating positions could challenge or bolster blood pressure and cerebral blood flow in individuals with damage to autonomic pathways. This shows that positional changes can be used as physical manoeuvres to maintain blood pressure. Chapter 3 documented the progression of autonomic function over time in the acute post-injury period, demonstrating the wide range of trajectories of cardiovascular function after injury. This work also highlighted how motor, sensory and autonomic function can be affected differently by SCI; damage to motor and sensory pathways cannot always predict autonomic deficits. Next, in Chapter 4, I examined cerebrovascular control, and found that individuals with damage to autonomic pathways have a reduced cerebral blood flow response to low oxygen. While the aetiology of this difference is unclear, the results suggest that exposure to low oxygen, for example during sleep apnea, may be particularly detrimental in this population. Finally, in Chapter 5, I conducted a survey examining bowel care and cardiovascular function after SCI that identified a significant need for ongoing support to improve bowel management. It also revealed the major limitations that bowel care can have on social participation and employment. A knowledge gap was also identified regarding blood pressure control and cardiovascular symptoms triggered by bowel care. This work reiterates the importance of autonomic assessment after SCI and the value of combining physiological recording with symptom assessments. Autonomic dysfunctions have significant ramifications for blood pressure control, cerebrovascular control, and quality of life after SCI. The integrity of the autonomic nervous system should be incorporated into research outcomes and stratification and be used to help guide clinical decision-making and self-management.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Victoria Claydon
Department: 
Science: Biomedical Physiology and Kinesiology
Thesis type: 
(Dissertation) Ph.D.

Diaphragm Pacing during Mechanical Ventilation: Development of a Control Algorithm and Analysis of Respiratory Mechanics

Date created: 
2013-04-23
Abstract: 

Prolonged totally controlled mechanical ventilation results in the complete absence of mechanical activity of the diaphragm leading to rapid loses in diaphragmatic function, a syndrome known as Ventilator-Induced Diaphragmatic Dysfunction VIDD. Electrical activation of the diaphragm by phrenic nerve stimulation may prevent diaphragm atrophy in sedated patients undergoing Controlled Mechanical Ventilation CMV. The aims of this thesis were to develop a control algorithm to pace the diaphragm in-synchrony with a ventilator during controlled mechanical ventilation in critically-ill patients and analyze the respiratory mechanics resulting from such co-ordinated inspiratory action of the diaphragm and the mechanical ventilator. The algorithm was verified through bench tests and evaluated in an animal model. In the animal study, the respiratory mechanics were also analyzed to better understand the effects of synchronous diaphragm pacing during mechanical ventilation and to identify an optimal level of pacing support during mechanical ventilation for clinical applications.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Andy Hoffer
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Transvascular nerve stimulation electrodes

Author: 
Date created: 
2012-05-30
Abstract: 

Patients in intensive care units (ICU) who require mechanical ventilation (MV) for more than a week have an increased risk of medical complications, such as ventilator acquired pneumonia and nosocomial infections, and are seven-times more likely to die in the ICU. The disused diaphragm muscle atrophies rapidly in ventilated patients, contributing to complications and frequent failure to wean from MV. Current phrenic nerve and diaphragm pacing systems require long, complicated, and risky surgery, unsuitable for those in the ICU. This study documents the prototype development of a simple, minimally invasive, transvascular device for electrically pacing the diaphragm intended to maintain diaphragm viability, reduce mortality, facilitate weaning from MV, shorten duration of ICU stay, and decrease hospitalization costs. Proof-of-concept, safety and stability data from acute and 3-week chronic pig experiments were analyzed. This thesis provides insight into endovascular electrode designs, fabrication, material selection, and configuration and orientation effects on phrenic nerve stimulation.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Andy Hoffer
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) M.Sc.

Sensitivity to Visuomotor Prediction Errors During Precision Walking

Date created: 
2015-04-20
Abstract: 

All human movements happen in the face of uncertainty. The objective of this thesis was to determine how the nervous system deals with sensorimotor uncertainty when adapting to visuomotor perturbations during walking. We asked subjects to walk and step on a target while wearing prism goggles that shifted the perception of the target’s location. We manipulated uncertainty by varying the strength and perturbation direction of the prism lenses on a trial-by-trial basis in three conditions: no, low and high noise. We measured lateral end-point errors of foot placement from the target in a visuomotor adaptation paradigm with baseline, adaptation and post-adaptation phases. Results showed increases in error variability, slower adaptation rates, and smaller errors in the first adaptation trial when increasing uncertainty. These results suggest that the nervous system relies on a predictive mechanism, which is sensitive to errors, and weights prior experiences to adapt walking.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Daniel Marigold
Department: 
Science:
Thesis type: 
(Thesis) M.Sc.

The association of perceived and objective built environment features with physical activity, adiposity and blood glucose

Author: 
Date created: 
2014-12-19
Abstract: 

Physical inactivity, obesity and diabetes are major public health problems and risk factors for cardiovascular disease, a number one cause of death globally. There is growing evidence to link built environment (BE) with physical inactivity, obesity and diabetes. However, published studies mostly focused on the macro-environment; perceived or objective BE measures; and self-reported rather than objectively assessed adiposity. There is also a lack of investigation of metabolic risk factors and lack of consideration for distinct demographic and socio-economic groups. Therefore, the objectives of this study were to explore the associations of both perceived and objective BE measures with distinct domains of physical activity (PA), objectively measured adiposity and fasting blood glucose (FBG); and to investigate the differences in environmental perceptions and the agreement between perceived and objective BE features based on gender, income level and ethnicity. Adults (n=356) between the ages of 35 and 70 years, from high- (median household income >$75,000) and low-income (<$55,000) areas in Vancouver were assessed for socio-demographics, PA (reported), adiposity (measured; body mass index, waist circumference, waist-to-hip ratio, and percentage of body fat), FBG, and environmental perceptions (Neighborhood Environment Walkability Scale). Neighbourhoods, a 500-meter buffer around a participant’s home, were directly assessed using the Irvine Minnesota Inventory (122 BE features). The study results indicate that more objective than perceived BE features were associated with PA; and associations were strongest for transportation PA followed with overall walking. Greatest effects were observed for features related to safety from traffic and presence of sidewalks. Associations of BE features with adiposity and FBG were limited. Additionally, environmental perceptions and the agreement between perceived and objective BE measures differed across gender, ethnicity, and income. The results suggest that improving pedestrian infrastructure and increasing safety from traffic may help residents engage more in transport PA and overall walking. Observed differences in BE perceptions may be used to direct the development of public health interventions aimed at increasing awareness about facilities in the neighbourhood whereby special consideration should be given to ethnic minorities and residents from low-income neighbourhoods.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Scott A. Lear
Department: 
Science:
Thesis type: 
(Dissertation) Ph.D.

Video Analysis of the Circumstances of Falls in Long-term Care

Author: 
Date created: 
2015-03-24
Abstract: 

Falls cause more than 95% of hip fractures and 65% of head injuries in older adults. A major barrier to prevention is lack of objective evidence of the circumstances of falls, especially in the high-risk long-term care (LTC) setting. My PhD research addresses this issue through the analysis of falls captured on video in two LTC facilities. My first study involved the development and validation of a 24-item video analysis questionnaire that probes key biomechanical aspects of fall initiation, descent, and impact from video footage. My results demonstrated good inter-rater and intra-rater reliability in 17 of the 24 questions (agreement≥80%, kappa≥0.6). My second study compared the circumstances of falls described in incident reports to information from video analysis (n=309, with 863 falls). I found poor agreement on the cause of imbalance and activity at time of fall (agreement=45%, kappa≤0.25), and moderate agreement on the use of mobility aids (agreement=79.5%, kappa=0.59). My third study examined how risk of head impact during falls was associated with biomechanical factors (from video analysis) and physiological factors (from Minimum Data Set) (n=160, with 520 falls). I found that 33% of falls involved head impact. Odds for head impact were increased more than 2-fold for female, impaired vision, and intact cognition. These trends were explained in part by women and individuals with relatively intact cognition who tend to fall during walking and fall forward (both increased the odds for head impact). Odds for head impact were not reduced by hand impact. Body rotation during descent from forward to sideways or backward decreased the odds of head impact nearly 3-fold. My fourth study used the same data set to examine how risk of hip impact during falls was influenced by biomechanical and physiological factors. I found falling forward was just as likely as falling sideways to cause hip impact. There was no association between physiological factors and odds for hip impact. Collectively, my findings should help guide the development of improved fall and injury prevention strategies, by providing new evidence on the circumstances of falls in LTC, and the risk factors for impact to the head and hip.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Stephen N. Robinovitch
Department: 
Science:
Thesis type: 
(Dissertation) Ph.D.