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

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A human iPSC-CM model for type 1 catecholaminergic polymorphic ventricular tachycardia (CPVT1)

Author: 
Date created: 
2019-07-05
Abstract: 

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a devastating, heritable cardiac arrhythmia and often a cause of sudden cardiac death. Greater than 50% of cases of CPVT are due to genetic variants in the cardiac ryanodine receptor (RyR2). CPVT-associated RyR2 variants often result in gain-of-function phenotypes, producing a dominantly inherited and difficult to treat disease. Human induced pluripotent stem cells (hiPSCs) have been used to generate patient-specific hiPSC-derived cardiomyocytes (hiPSC-CM) to study CPVT phenotypes and pharmacological approaches, however generating hiPSCs from patients is low through-put and lacks true isogenic controls. Therefore, this thesis aimed to use CRIPSR/Cas9 genome-editing technology to generate hiPSC cells lines harbouring a CPVT-associated variant. Genome-edited hiPSCs were differentiated into 2D tissue-like monolayers of hiPSC-CMs, and voltage and calcium dynamics were measured. This thesis indicates that CRISPR/Cas9 is a useful technology for studying CPVT in an in vitro human model, and that the R417L mutant disrupts hiPSC-CM calcium handling.

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

Molecular determinants of voltage sensor movement and its transduction to pore opening by the S4-S5 linker in the hERG potassium channel

Author: 
Date created: 
2019-04-15
Abstract: 

The hERG potassium channel, found in cardiac tissues, is an important contributor to cardiac repolarization. Loss of function of hERG channels is associated with long QT syndrome, a condition linked to sudden cardiac death. Unlike other Shaker-like voltage-gated potassium (Kv) channels, hERG channel activation (opening) and deactivation (closing) kinetics are unusually slow and this is critical to their unique role in repolarization. Despite this, the mechanistic basis for slow gating kinetics in hERG remains unclear. In Shaker-like Kv channels movement of the voltage sensor upon depolarization is mechanically transduced by the alpha-helical S4-S5 linker to S6 pore opening. Given the unique gating properties of hERG channels, the details of voltage sensor movement and its coupling with the S6 activation gate are of significant interest. My thesis examines the mechanistic basis to S4 voltage sensor movement and its transduction to pore opening. In my first study, I use a flexibility removed hERG mutant (G546L) to examine the role of S4-S5 linker flexibility in the activation gating of hERG channels. The flexibility removed channels are stabilized in the open conformation and when flexibility is reintroduced elsewhere in the S4-S5 linker there is a restoration of WT-like activation gating. This suggest flexibility of the S4-S5 linker regulates hERG channel closed-state stabilization. I then examine the role of the S4 voltage sensor and the S4-S5 linker in slow deactivation. To do this I examined charge conserving mutations within the S4 voltage sensor, single glycine substitutions in the S4-S5 linker and an N-terminally deleted channel. These data suggest that the intrinsic relaxation transition of the voltage sensor causes the slow deactivation kinetics characteristic of hERG. They also suggest that both the S4 voltage sensor and S4-S5 linker are attractive targets for hERG modifying compounds. In my final study, I investigate the utility of the adult zebrafish whole heart translational model in the screening of hERG modifying compounds. Using the oocyte expression system, I conducted a pharmacological characterization of the zebrafish paralog of hERG, zkcnh6a, and using optical mapping of the zebrafish whole heart, I show that this model may serve as a valuable tool in the screening of hERG modifying compounds.

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

Cardio-postural control and cerebral autoregulation in older adults after ischemic stroke

Author: 
Date created: 
2019-04-09
Abstract: 

Acute ischemic strokes are a common cause of death within the world’s population. Older adults affected by cerebral infarctions, often experience orthostatic hypotension which can be associated with autonomic dysfunctions. By using a method to identify the bi-directional relationship between cardiovascular control and postural control, as well as cerebral autoregulation, new insight into orthostatic hypotension associated with ischemic stroke can be provided. This thesis compared acute stroke patients with healthy controls as well as females and males to examine the relationships within the cardio-postural model and included the new aspect of involving the cerebral autoregulatory system and their correlation. It was hypothesized that stroke patients show impairment within the autonomic system and the cerebral autoregulation. A decrease in cardiovascular baroreflex, muscle-pump baroreflex, and cerebral autoregulatory impairment was shown in stroke patients compared to the healthy controls. Furthermore, the impairment was greater in female stroke patients.

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

Implantable Transducers for Neurokinesiological Research and Neural Prostheses

Author: 
Peer reviewed: 
No, item is not peer reviewed.
Date created: 
1998-02
Abstract: 

The objective of this thesis was to develop a family of advanced electrical and mechanical interfaces to record activity of nerves and muscles during natural movements. These interfaces have applications in basic research and may eventually be refined for used in restoring voluntary control of movement in paralyzed persons.

I) A muscle length gauge was designed that is based on piezoelectric crystals attached at the ends of a fluid filled extensible tubing. The in-vivo performance of these gauges was equal to previous length gauge designs. In addition, the ultrasound based design provided for the first time a direct muscle length calibration method.

2) An innovative nerve cuff closing technique was devised that does not reqmre suture closures. The new design uses interdigitated tubes to lock the opening and fix the lumen of a nerve cuff. The cuffs were tested in long-term mammalian implants and their performance matched or surpassed previous closure designs. The nerve cuff was further redesigned to include a more compliant cuff wall and wire electrodes.

3) Floating microelectrodes previously used for central nervous system recordings were adapted for chronic use in the peripheral nervous system. These electrodes proved disappointing in terms of signal quality and longevity. The reasons for failure are thought to be of both electrical and mechanical origin.

4) An innovative silicon micromachined peripheral single unit electrode was designed and tested. In the in-vivo tests, a limited number of recording sites successfully established short-term neural interfaces. However, the quality of the electrode performance, in terms of signal amplitude and ability to discriminate single unit potentials, was insufficient.

5) Using a finite difference model, a numerical simulation of static and dynamic electrical interactions between peripheral axons and microelectrode interfaces was derived. The model consisted of resistive and capacitive elements arranged in a 3-dimensional conductive universe (two spatial dimensions and time). Models of intrafascicular fine wire or silicon based electrodes were used to record simulated propagating action potentials. It was confirmed that electrode movement affected the recorded signal amplitude and that a dielectric layer on a silicon electrode accentuated the recorded potential field. A conducting back plane facing away from axon sources did not have a significant effect on the electrode recording properties.

In conclusion, several novel implantable transducers were developed for use in neurokinesiological research. A numerical simulation of the axonal potentials recorded by intrafascicular electrodes helped interpret various shortcomings found in the in-vivo electrode performance. Although not attempted in the present thesis some of the developed technologies may have potential of transferring to clinical neural prostheses applications.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Joaquin Andres Hoffer
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

A model of health: Using business analytics to identify older Canadian adults with heart disease

Author: 
Date created: 
2018-12-14
Abstract: 

Nearly 90% of older Canadians have at least one chronic disease; 65% have two or more. The aims of my thesis were to apply business analytics techniques to predict the presence of an exemplar chronic disease, heart disease, among older Canadians, and to calculate the corresponding expected healthcare costs. I used neural networks to develop logistic regression models of heart disease using demographic, lifestyle, and health information for 15,599 older adults from the Canadian Longitudinal Study on Aging. The Economic Burden of Illness in Canada provided healthcare cost data. The best model identified 65.8% of heart disease cases from 40% of participants with the highest predicted probabilities of heart disease, accounting for $2.7 million more expected annual healthcare costs than a randomly sampled 40%. Among all older Canadians, this difference would be $1.1 billion. These methods could assist healthcare decision makers to optimize the delivery of chronic disease prevention interventions.

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

Activity monitor reliability and validity in community-dwelling older adults

Author: 
Date created: 
2018-11-20
Abstract: 

Monitoring older adult physical activity is central to surveillance of individual and population health as well as delivery and evaluation of health promotion programs, and it requires reliable and valid measurement tools. I investigated step count test-retest reliability and criterion validity across consumer-grade activity monitors in community-dwelling older adults with and without self-reported mobility limitations during over-ground walking (n = 36; mean 71.4 years). I evaluated six activity monitors (Fitbit Charge, Fitbit One, Garmin vívofit 2, Jawbone UP2, Misfit Shine, and New-Lifestyles NL-1000) during two 100-step walks, one continuous 400-metre walk, and one interrupted 400-metre walk. On average, all monitors undercounted steps. Step counts from hip-worn monitors generally exhibited better reliability and validity than from wrist-worn monitors. Mobility status did not affect monitor step count errors, but interruptions to walking negatively impacted criterion validity. The hip-worn Fitbit One was the only monitor with sufficiently high test-retest reliability and criterion validity.

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

The mechanism of action of external protons on hERG potassium channels

Author: 
Date created: 
2018-11-19
Abstract: 

Myocardial ischemia occurs when there is a reduction of blood flow to the heart due to blockage of an artery, causing inefficient delivery of oxygen and nutrients to the heart muscle. Acidosis is one of the major consequences during myocardial ischemia and affects a wide array of ion channels in the heart that may predispose individuals to cardiac arrhythmia. The human ether-à-go-go (hERG) related gene encodes the potassium channel that conducts the IKr current, which is responsible for the repolarization phase of the cardiac action potential and is particularly sensitive to external acidosis. External acidosis had been well observed to reduce hERG channel overall conductance, right-shift the voltage-dependence of activation, and accelerate deactivation rate, all of which lead to a loss-of-function effect on the hERG channels. We hypothesized that this can prolong action potential duration, increase susceptibility of individuals to long QT syndrome and reduce the protective current against premature ectopic beat. My first study aimed to determine the site and mechanism for the right-shift in the voltage-dependence of activation. I found that external protons disrupt stable interactions formed by the cation binding pocket, compose of three acidic residues: D456, D460 in S2, and D509 in S3, with positive charges in S4 to destabilize the activated voltage sensor. My second study aims to determine the site and mechanism for the acceleration of deactivation induced by external protons. Using voltage-clamp fluorimetry and gating current measurement with long duration protocols to measure voltage sensor mode-shift, we determined that external protons reduced the voltage sensor mode-shift by right shifting the voltage-dependence of deactivation suggesting that the relaxed conformation of the voltage sensor is destabilized and that D509 is a critical protonation site. In my last study, I used zebrafish heart as a translational model, with the optical mapping technique to investigate the effect of external protons on the overall cardiac action potential. We discovered that at low pH, the cardiac action potential is significantly prolonged, triangulation is increased, and the electrical restitution curve is flattened, which are all predictors for arrhythmogenicity.

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

Transverse expansion of muscle fascicles during dynamic tasks: experimental and modelling approaches to study human gastrocnemii

Author: 
Date created: 
2018-10-26
Abstract: 

Force generation is influenced by transverse shape changes of a muscle. Recent studies suggest that muscle fascicles may bulge in an anisotropic manner, and this may affect the relation between internal architecture and muscle deformations; however, to date fascicle bulging has not been quantified during active contractions. Understanding the nature and extent of the transverse deformations is necessary to explore the mechanisms driving the changes in internal geometry of whole muscle during contraction. The goal of this thesis is to quantify transverse deformations in muscles and fascicles using novel modelling and experimental techniques. The first study tested the accuracy with which 1D, 2D or 3D structural models of muscle could predict the pennation and muscle thickness for the medial gastrocnemius (MG) and lateral gastrocnemius (LG) in man during ankle plantarflexions. The second study acquired images from the MG and LG during cyclic contractions, and the transverse fascicle strains were calculated from their wavelengths within B-mode ultrasound images. For the third study, fascicle deformations were measured from two orthogonal ultrasound scans to provide 3D information of muscle geometry for the MG and LG. The results from the modelling study showed that a 1D model established a good relation between fascicle length and pennation; however, 3D models are necessary to understand the mechanisms underlying 3D structural changes. The second study found increases in the transverse fascicle strain while the longitudinal fascicle length decreased, however, the extent of these strains was smaller than expected. In the third study, transverse deformations in the MG were similar for the two transverse directions. However, the data for the LG confirm that transverse anisotropy in strain can occur in the muscle fascicles: as the LG fascicle length shortened, the fascicles bulged transversally in one direction while thinned in the other orthogonal direction. These results highlight that muscle fascicles do not bulge uniformly during contraction, and the implications for this behaviour on muscle function remain largely unexplored. This thesis provides a novel 3D perspective to enhance our understanding of the deformations of muscle fascicles during contraction, which in turn affect contractile performance and muscle function.

Document type: 
Thesis
File(s): 
Senior supervisor: 
James Wakeling
Department: 
Science: Department of Biomedical Physiology and Kinesiology
Thesis type: 
(Thesis) Ph.D.

Electrophysiology of inhibitory control in the context of emotion processing in children with Autism Spectrum Disorder

Author: 
Date created: 
2018-11-08
Abstract: 

Autism Spectrum Disorder (ASD) is an increasingly common developmental disorder that affects 1 in 59 children. Despite this high prevalence of ASD, knowledge regarding the biological basis of its associated cognitive deficits, including emotion processing and inhibitory control abnormalities, remains scant. In this study, I aimed to identify altered neurophysiological responses underlying inhibitory control difficulties in the context of emotion processing in ASD, together with their associations with various domains of cognitive and social function, and age. This was accomplished by assessing electroencephalographic recordings during an emotional go/nogo task alongside various parent rating scales of behaviour. Event related potential N2 component amplitudes were reduced in children with ASD compared to typically developing (TD) children. Consistent with previous findings, increased age correlated with improved behavioural accuracy and reduced N2 amplitude in the TD group, indicating that as these children develop, their neural systems underlying inhibition become more efficient. However, these associations were not observed in the ASD group. Relations between various behavioural scores and N2 amplitude were also only significant in the TD group, revealing an association between increased N2 amplitudes and improved executive control abilities and decreased autism traits in these children. The newly discovered findings of differences in neural processing between children with ASD and TD children during an emotional inhibitory control task, alongside a lack of correlation between these neural responses, age and various behavioural scores in the ASD group, provide a potential neurophysiological indicator of atypical development of inhibitory control mechanisms in children with ASD.

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

Measuring the baroreflex: equivalency, repeatability, and its relationship with sex, age, and orthostatic tolerance

Author: 
Date created: 
2018-08-17
Abstract: 

The lifetime prevalence of fainting is estimated at 20-40%. Fainting, or syncope, is caused by reduced cerebral perfusion, often secondary to a reduction in blood pressure. During standing, the movement of blood into the lower limbs stimulates the arterial baroreflex to increase cardiac output and constrict peripheral blood vessels to maintain blood pressure and blood flow to the brain. Syncope is more common in older adults and women; however, it is unclear whether this might relate to age- and/or sex-related changes in baroreflex function. Different methods of baroreflex stimulation and measurement may not be comparable, and the repeatability of these techniques is uncertain. In Chapter 3, I quantify the agreement and repeatability of different baroreflex testing methods. Cardiac baroreflex tests have higher agreement and repeatability than sympathetic vascular tests, highlighting the need for better methods of vascular baroreflex measurement. In Chapter 4, I examine the relationship between aging, sex and both the cardiac and vascular arms of the baroreflex using novel sympathetic vascular baroreflex measurement techniques. In Chapter 5, I examine the influence of carotid sinus massage (CSM) methodology on the cardiovascular responses, and recommend that CSM be applied to the area of maximal pulsatility when ultrasound-guidance is unavailable. Lastly, in Chapter 6, I refute the hypothesis that large responses to carotid baroreceptor stimulation in older adults are related to chronic denervation of the sternocleidomastoid muscles. Thus, the pathophysiology of hypersensitive responses to CSM remains unknown. This work demonstrates that careful consideration should be taken when selecting baroreflex measurement techniques. Our novel sympathetic vascular baroreflex testing methods are critical for a thorough description of baroreflex control of blood pressure in younger and older men and women. While the vascular responses to orthostasis are large in older individuals, the vascular responses to acute carotid baroreceptor stimulation with the neck collar decline with age. The standard clinical methodology of CSM may not accurately deliver mechanical stimulation to the carotid baroreceptors. We have shown that the previously reported association with sternocleidomastoid denervation is likely coincidental, not causal. Overall, this thesis reiterates the importance of sympathetic vascular baroreflex function in the maintenance of blood pressure.

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