Physiology Commons^™

The Effect Of Central Chemoreceptors On The Peripheral Respiratory Chemoreflex Response To Hypoxia In Humans, Nasimi A. Guluzade

Electronic Thesis and Dissertation Repository

We measured the peripheral chemoreflex sensitivity to hypoxia (PChS) at various isocapnic carbon dioxide tensions (PCO₂) to determine the form of the relationship between PChS and central PCO₂. Twenty participants completed three repetitions of modified rebreathing tests with end-tidal PO₂ (P_ETO₂) clamped at 150, 70, 60, and 45 mmHg. PChS was computed at 1-mmHg intervals of P_ETCO₂ as follows: the differences in V̇_E between the three hypoxic profiles and the hyperoxic profile (∆V̇_E) were calculated; three ∆V̇_E values were plotted against corresponding calculated oxyhemoglobin …

The Sympathetic Neural Control Of The Circulation At Rest And During Exercise: Effects Of Age, Biological Sex, And Sex Hormones, Andrew W. D'Souza

Electronic Thesis and Dissertation Repository

The overall objective of this dissertation was to determine the impact of age, sex, and sex hormones on the discharge behaviours of muscle sympathetic action potentials (APs) as well as the corresponding changes in peripheral vasoconstriction and blood pressure at rest and during exercise. The microneurographic technique was employed to record multi-unit muscle sympathetic nerve activity (MSNA), with a continuous wavelet transform applied post-hoc to evaluate APs within the recorded neurogram. Study One examined the impact of aging on the central and peripheral arcs of the sympathetic baroreflex under resting conditions. This study revealed that middle-aged-to-older adults demonstrated heightened sympathetic …

Plantar Flexor Dynamic Contractile Rates Are Not Dependent On Calcaneal Tendon Stiffness, Sohum Kulkarni

Electronic Thesis and Dissertation Repository

The ability to rapidly generate muscular torque and velocity is important in specialized activities and daily tasks of living. Tendon stiffness is one factor in the neuromuscular system that influences musculoskeletal torque transmission. Previous studies have reported weak-to-moderate correlations between tendon stiffness and rate of torque development (RTD). However, these correlations have been reported only for isometric contractions which may not be relevant to contractions involving joint rotation (i.e., dynamic). The purpose was to investigate the effect of calcaneal tendon stiffness on the dynamic rates of torque (RTD) and velocity (RVD) development in plantar flexor muscles. Young adult males (n=13) …

Prefrontal Coding Of Naturalistic Working Memory: Mechanisms During Normal Maintenance And Modelled Disease, Megan P. Roussy

Electronic Thesis and Dissertation Repository

Neural activity in the primate lateral prefrontal cortex (LPFC) has been causally linked to working memory (WM) ⁠— the brief maintenance and mental manipulation of information. Primates use WM to perform tasks in complex contexts; however, neural mechanisms of WM and the pathophysiology related to WM deficits have traditionally been studied using simple tasks that deviate from naturalistic conditions. This raises the question, how is WM processed in naturalistic conditions? To explore this, I trained two macaque monkeys on a spatial WM task set in a naturalistic virtual environment. During the task, a target was presented in 1 of 9 …

The Effect Of Breathing Patterns Common To Competitive Swimming On Gas Exchange And Muscle Deoxygenation During Heavy-Intensity Fartlek Exercise, Kevin J. Grossman

Electronic Thesis and Dissertation Repository

The purpose of this study was to compare the respiratory and muscle deoxygenation (HHb) responses of regulated breathing versus free-breathing, during continuous exercise (CONLD) and intermittent 5s breath holds (BH) (CONLD-BH), intermittent 5s sprint (FLK) and combined 5s BH and sprint (FLK-BH) followed by 25s of free-breathing. Oxygen uptake(V̇O₂)was unchanged between CONLD (2.12±0.35L/min) and CONLD-BH (2.15±0.42L/min; p=0.116), and FLK (2.24±0.40L/min) and FLK-BH (2.20±0.45L/min; p=0.861). Δ[Hb_tot]: CONLD (3.3±1.6µM) > CONLD-BH (-2.5±1.2µM; ∆177%; p<0.001), but unchanged between FLK (2.0±1.6µM) and FLK-BH (0.82±1.4µM; p=0.979). Δ[HHb]: CONLD (7.3±1.8µM) > CONLD-BH (7.0±2.0µM; ∆4%; p=0.011), and FLK (6.7±1.8µM) < FLK-BH (8.7±2.4µM; p<0.001). It is suggested that the unchanged V̇O₂ between CONLD and CONLD-BH was supported by increased deoxygenation, reflected by decreased ∆[Hb_tot] and blunted …

Increased Corticospinal Inhibition Following Submaximal And Maximal Muscle Activation In Humans, Alexander D. Paish

Electronic Thesis and Dissertation Repository

Following short duration, high intensity muscle activation, there is an enhancement of muscle contractile properties, termed postactivation potentiation (PAP). Corticospinal inhibition, assessed by an increased silent period (SP), was shown previously to increase following voluntary or electrically evoked PAP. Although these changes coexist, the direct effect of PAP on corticospinal inhibition has not been systematically evaluated. In 10 participants, SP duration was measured pre and post 10s maximal and submaximal, voluntary and electrically stimulated contractions. Following maximal contractions, mean twitch torque was enhanced ~180% with no enhancement at submaximal levels (~102%). The SP duration was prolonged following all conditions: ~12% …

Mechanisms Of Diapause And Cold Tolerance In The Colorado Potato Beetle, Jacqueline E. Lebenzon

Electronic Thesis and Dissertation Repository

Many temperate insects enter diapause (a state of dormancy) and enhance their cold tolerance to survive the winter. During diapause, the Colorado potato beetle (CPB, Leptinotarsa decemlineata, Coleoptera: Chrysomelidae) stops developing, lowers its metabolism, and changes its physiology to avoid freezing. The extent to which diapause confers cold tolerance in CPB is currently unknown. In my thesis, I used CPB to improve our understanding of the mechanisms underlying metabolic suppression during diapause and cellular protection at sub-zero temperatures in insects. First, I used RNA-sequencing (RNA-seq) to compare gene expression in two metabolically important tissues (the fat body and flight muscle) …

Direct Electrical Stimulation Of Prefrontal Cortex Modulates The Transient Heart Rate Response To Exercise In Conscious Humans, Bartek Kulas

Electronic Thesis and Dissertation Repository

Prefrontal cortical regions play an essential role in generating appropriate cardiovascular adjustments, particularly in cardio-vagally mediated heart rate (HR) responses to active tasks. Functional imaging studies provide correlational evidence that this region coordinates HR responses to exercise, however, direct experimental evidence of prefrontal cortical HR regulation in humans is not available. Seven persons with epilepsy implanted with intracranial electroencephalography (iEEG) completed 2-second isometric handgrip (IHG) contractions at no-stimulation (NO-STIM) or sham-stimulation (SHAM) conditions, and during direct electrical stimulation (STIM) of the orbitofrontal and medial prefrontal cortex. HR responses to IHG during NO-STIM and SHAM increased HR by Δ4.9±2.7 bpm, compared …

Post-Activation Potentiation & Aging, Sohum Kulkarni

Undergraduate Student Research Internships Conference

No abstract provided.

Cerebrovascular Compliance In Humans, Marcy Erin Moir

Electronic Thesis and Dissertation Repository

Pulsatile blood flow consists of two components: steady flow and oscillatory flow. Steady blood flow is primarily regulated by vascular resistance while vascular compliance represents a key mediator of oscillatory blood flow. However, most studies investigating the regulation of cerebral blood flow in humans have focused on vascular resistance. Recently, emerging evidence has implicated vascular compliance as an important contributor to the regulation of cerebral perfusion. Therefore, the research contained herein aimed to i) quantify cerebrovascular compliance responses to blood pressure alterations and ii) explore mechanisms regulating cerebrovascular compliance in humans. The studies employed a Windkessel modelling approach to calculate …

Spinal Excitability Changes Following Sensory Electrical Stimulation Of The Forearm, Devin K. Box

Electronic Thesis and Dissertation Repository

Sensory electrical stimulation can be used to suppress tremor in Parkinson’s disease. This study investigated the central mechanism underlying this suppression in healthy participants. Reciprocal inhibition (RI) of the wrist flexors before and after a session of sensory electrical stimulation (SES) applied to the antagonistic extensor muscles was assessed using electromyography. It was hypothesized that a 15-minute session of SES, rated by participants as a 3 on a 0-10 pain scale, would produce an increase in RI. Seven of the 18 participants experienced an increase in RI at 0-5 minutes post stimulation, which returned to baseline at 10-15 minutes. The …

Regulators Of Ectopic Calcification In A Mouse Model Of Dish: A Multi-Omics Perspective, Matthew A. Veras

Electronic Thesis and Dissertation Repository

Diffuse idiopathic skeletal hyperostosis (DISH) is a non-inflammatory spondyloarthropathy and the second most common form of arthritis characterized by formation of ectopic mineral along the spine. Pathological findings in DISH include regional calcification of the anterior longitudinal ligament, paraspinal connective tissues, and annulus fibrosus (AF) of the intervertebral disc (IVD). Clinical symptoms of DISH include increased spine stiffness, decreased spinal range of motion, and in severe cases dysphagia and spinal cord/nerve root compression. The molecular pathways responsible for DISH have not been delineated and as such, there are no disease-modifying treatments. Clinical treatment for DISH is limited to surgical resection …

Investigating The Role Of Nuclear Receptor Peroxisome Proliferator-Activated Receptor Δ In Obesity-Associated Osteoarthritis, Bethia C. To

Electronic Thesis and Dissertation Repository

Osteoarthritis (OA) is a heterogeneous disease, differentiated based by risk factors that drive joint damage. Peroxisome proliferator-activated receptor delta (PPARd) is a nuclear receptor previously implicated in cartilage damage in OA. Given its deleterious role in post-traumatic OA and in regulating metabolism, we hypothesized that PPARd inhibition will protect against obesity-associated OA. Diet-induced obesity was used to induce OA in mice. Mice fed the western diet for 40 weeks exhibited mild OA, with subchondral bone remodelling occurring alongside cartilage damage. Cartilage-specific Ppard knockout (KO) mice were generated to study its role in metabolic OA. Both wildtype and PPARd KO mice …

Action Potential Subpopulations In Human Muscle Sympathetic Nerve Activity: Discharge Properties And Governing Mechanisms, Stephen A. Klassen

Electronic Thesis and Dissertation Repository

What discharge properties are expressed by varying-sized sympathetic action potential (AP) subpopulations active under baseline conditions in humans and what are the governing mechanisms? To address this overall question the microneurographic approach was employed to record multi-unit muscle sympathetic nerve activity (MSNA), after which a continuous wavelet transform exposed APs in the recorded neurogram. Study One examined the role of the paravertebral ganglia on sympathetic neural discharge patterns. Through trimethaphan infusion under baseline conditions, this study revealed ordered de-recruitment of larger to smaller AP clusters, suggesting that the paravertebral ganglia contribute to the distribution of firing probabilities expressed by differently-sized …

Is Professional Breath-Hold Diving Associated With Endothelial Dysfunction?, Emilie Woehrle

Electronic Thesis and Dissertation Repository

Professional breath-hold diving has been linked to acute dangers; however, the long-term impacts on vascular health are unknown. The endothelium releases vasodilator substances and its functionality is an indicator of vascular health. We are testing the hypothesis that chronic exposure to severe hypoxia may alter endothelial function in breath hold divers. Divers and controls completed a flow-mediated dilation (FMD) protocol, where brachial blood flow velocity was measured following blood flow occlusion. Percent FMD was calculated as the primary measure of endothelial function. T-tests assessed the statistical significance of between-group differences. The %FMD were similar between groups (p >0.05); however, divers …

Cardiodynamic Associations With Resilience In Undergraduate Students And The Effect Of A Mentorship Intervention, Rachel J. Knetsch

Electronic Thesis and Dissertation Repository

The National College Health Assessment (NCHA) indicates that a majority of Canadian university students report feeling overwhelmed, stressed, and anxious during their undergraduate studies. Resilience refers to positive adaptation, or the ability to maintain or regain mental health, despite experiencing adversity (Herrman et al., 2011). While autonomic indices have been used to describe chronic physiological stress, the role of heart rate variability (HRV) as an index of resilience remains unclear. This research tested the hypotheses that (1) there is a relationship between HRV and resilience scoresand (2) a mentorship intervention will improve HRV and resilience outcomes. Fifty-seven first year students …

Pilot Study: Heart Rate Variability Analysis And Mental Health Outcomes In University Female Hockey Players, Kaitlyn Jacobs

Electronic Thesis and Dissertation Repository

Exercise improves anxiety and depression, both of which are associated with impaired autonomic regulation of heart rate (HR). In turn, HR variability (HRV) is a reliable physiological indicator of external stressors. The following research tested the hypothesis that HRV is indicative of chronic resilience towards mental stress in female varsity hockey players. Seventeen varsity hockey players (HOCK, age 21 ± 1.5) and fifteen healthy controls (CTRL, age 21 ± 2.2) at Western University participated three times throughout a 7-month season. Participants completed questionnaires (brief resilience scale, BRS; generalized anxiety scale, GAD-7; mental health inventory, MHI; visual analog scale, VAS; short …

The Effect Of Diet On Midgut And Resulting Changes In Infectiousness Of Acmnpv Baculovirus In Trichoplusia Ni, Elizabeth Chen

Electronic Thesis and Dissertation Repository

The cabbage looper, Trichoplusia ni, a global generalist lepidopteran pest, has developed resistance to many synthetic and biological insecticides, requiring effective and environmentally acceptable alternatives. One possibility is the Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). This baculovirus is highly infectious for T. ni, with potential as a biocontrol agent, however, its effectiveness is strongly influenced by dietary context. In this study, microscopy and transcriptomics were used to examine how the efficacy of this virus was affected when T. ni larvae were raised on different diets. Larvae raised on potato host plants had lower chitinase and chitin deacetylase transcript levels …

Impaired Dynamic Cerebrovascular Autoregulation In Adolescent Concussion, Marcy Erin Moir

Electronic Thesis and Dissertation Repository

Although cerebrovascular impairments are believed to contribute to concussion symptoms, little information exists regarding brain vasomotor control in adolescent concussion, particularly during changes in arterial blood pressure (ABP). This research tested the hypothesis that adolescent concussion is marked by impaired dynamic cerebral autoregulation (dCA). Thirty concussed adolescents and thirty healthy controls completed two sit-to-stand trials. Cerebral blood flow velocity and ABP were measured continuously. Cerebrovascular resistance (CVR) was calculated and the rate of drop in CVR relative to the change in ABP provided the rate of regulation (RoR). The concussed adolescents were followed through rehabilitation for up to 12-weeks. At …

Recruitment Strategies In Human Sympathetic Nerve Activity, Mark B. Badrov

Electronic Thesis and Dissertation Repository

The overall objectives of the current dissertation were to 1) establish the neural coding principles employed by the sympathetic nervous system (SNS) in response to acute physiological stress; and 2) to determine the various mechanisms of control underlying these sympathetic neural recruitment strategies. This research tested the working hypothesis that efferent post-ganglionic muscle sympathetic nerve activity exhibits neural coding patterns reflecting increased firing of lower-threshold axons, recruitment of latent sub-populations of higher-threshold axons, as well as malleable synaptic delays, and further, that these strategies are governed by factors such as reflex-specificity, stress severity, perception of effort or stress, age, and …

Role Of Anterior Cingulate Cortex In Saccade Control, Sahand Babapoor-Farrokhran

Electronic Thesis and Dissertation Repository

Cognitive control is referred to the guidance of behavior based on internal goals rather than external stimuli. It has been postulated that prefrontal cortex is mainly involved in higher order cognitive functions. Specifically, anterior cingulate cortex (ACC), which is part of the prefrontal cortex, is suggested to be involved in performance monitoring and conflict monitoring that are considered to be cognitive control functions.

Saccades are the fast eye movements that align the fovea on the objects of interest in the environment. In this thesis, I have explored the role of ACC in control of saccadic eye movements. First, I performed …

The Neuroprotective Effects Of Endurance Training On The Aging Brain, Katelyn Norton

Electronic Thesis and Dissertation Repository

Dysregulation of autonomic control often develops with advancing age, favoring a chronic state of heightened sympathetic outflow with parasympathetic withdrawal. However, the mechanisms of this age-related autonomic impairment are not known and may relate to alterations in brain structure (e.g. cortical atrophy) and/or altered neural function, particularly in regions related to the cortical autonomic network, namely, the medial prefrontal cortex (MPFC), insula cortex (IC), and hippocampus (HC). Exercise exerts beneficial effects on brain structure and, in the case of cognition, neurologic function; however, how exercise affects regions of the brain related to autonomic function are not known. This thesis tested …

Non-Invasive Determination Of Vascular Reactivity: A New Approach To An Important Measure, Kaitlin M. Mclay

Electronic Thesis and Dissertation Repository

Vascular impairments at both the macro- and the micro-circulatory level are known to be associated with cardiovascular disease (CVD) and may be one of the earlier signs of disease. As such, it is important to have a means of non-invasively assessing vascular reactivity, however accurate assessment remains challenging. Tests of flow-mediated dilation (FMD) have been widely used to non-invasively determine endothelium-dependent vasodilation in humans; however, the use of this technique poses some challenges. Thus, the purpose of this thesis was to explore new strategies to non-invasively determine the magnitude and dynamic adjustment of vascular responses in humans. Using near-infrared spectroscopy …

Brain Injury And Inflammation And Placental Inflammation In Response To Repetitive Umbilical Cord Occlusions In The Near Term Ovine Fetus, Alex Xu

Electronic Thesis and Dissertation Repository

We hypothesized that repetitive umbilical cord occlusions (UCOs) leading to severe acidemia will stimulate a placental and fetal inflammatory response associated with brain injury, which will be exacerbated by chronic hypoxemia and low-grade infection. Chronically instrumented fetal sheep served as controls or underwent repetitive UCOs for up to 4 hours or until fetal arterial pH was2saturation pre-UCOs of >55% and

Freeze Tolerance In The Spring Field Cricket, Gryllus Veletis, Alexander H. Mckinnon

Electronic Thesis and Dissertation Repository

Many insects are able to survive internal ice formation. However, the mechanisms underlying freeze tolerance are not well-understood, perhaps because of a lack of suitable model organisms. I found that the spring field cricket, Gryllus veletis, seasonally acquires freeze tolerance in the fall when kept outside in London, Ontario. Moreover, individuals acquired freeze tolerance in the laboratory in response to a simulated fall thermophotoperiod. Lab-acclimated G. veletis freeze at -6.1 ± 0.7 ºC and the acquisition of freeze tolerance is accompanied by the accumulation of proline and trehalose. Crickets survived temperatures as low as -12 ºC (1.5 h), and …

The Implications Of Altered Cholinergic Signaling In Cardiac Health And Disease, Ashbeel Roy

Electronic Thesis and Dissertation Repository

­Cardiac remodeling and dysfunction occur prior to the onset of heart failure. Altered regulation of cardiac function by the autonomic nervous system has been implicated in the progression of heart disease. Both altered sympathetic and parasympathetic tone contribute to cardiac disease; however, the role of the parasympathetic nervous system, and specifically acetylcholine (ACh), in cardiac dysfunction has not been fully elucidated. In these studies, we sought to determine whether changes in neuronal and/or non-neuronal ACh release regulate cardiac activity and alter the progression of cardiac remodeling and dysfunction. A systemic decrease in the expression of the vesicular acetylcholine transporter …

Niacin And Microvascular Endothelial Cell Response To Fatty Acid Excess And Hypoxia, Dominic Pang

Electronic Thesis and Dissertation Repository

Niacin can reduce vascular disease risk, but its mechanism of action is controversial, and may not be dependent on systemic lipid modifying effects. This thesis tested the hypothesis that niacin directly improves endothelial cell function under lipotoxic and low oxygen conditions, as seen in ischemic conditions during metabolic syndrome, and investigated the potential mechanism involved. Human microvascular endothelial cell (HMVEC) survival was reduced by exposure to excess fatty acids under both normoxic and low oxygen conditions. Angiogenic function, as determined by tube formation on Matrigel, was impaired during fatty acid overload under either normoxic or low oxygen conditions. These effects …

Sex Hormones And Sympathetic Nerve Activity, Charlotte W. Usselman

Electronic Thesis and Dissertation Repository

The purpose of this thesis was to test the hypothesis that changes in circulating sex hormone levels are associated with changes in muscle sympathetic nerve activity. The hypothesis was tested through the comparison of low- (early follicular [EF]) and high-hormone (midluteal [ML]) phases of the menstrual cycle and of hormonal contraceptive use (low hormone [LH] versus high hormone [HH]). The microneurography technique was used to compare both the frequency and size of bursts in muscle sympathetic nerve activity (MSNA) at baseline and during two sympatho-excitatory maneuvers: baroreceptor unloading elicited through lower body negative pressure, and chemoreflex stimulation elicited through a …

Role Of Adenylyl Cyclase S674 In Central And Forearm Vasomotor Control, James Corkal

Electronic Thesis and Dissertation Repository

This study examined the cardiac and vasomotor responses to submaximal handgrip exercise and beta-adrenergic control in carriers (n = 6) and non-carriers (n = 4) of a genetic variant of adenylyl cyclase 6 (AC S674). Rhythmic handgrip contractions (1 minute bout; 2 second contraction-relaxation period) were performed at three different intensities (20, 40, and 60% of maximal voluntary contraction force) to test the vasodilatory response to exercise. Additionally, two 5 minute infusions of isoproterenol (0.01 and 0.02 µg·kg^-1·min^-1 diluted in 5% dextrose) and one 10 minute infusion of propranolol (0.1 mg·kg^-1 diluted in 0.9% saline) were …

Ionic And Osmotic Mechanisms Of Insect Chill-Coma And Chilling Injury, Heath A. Macmillan

Electronic Thesis and Dissertation Repository

A mechanistic understanding of how temperature limits insect performance is needed to accurately model insect distribution and abundance. Upon crossing the temperature of their critical thermal minimum (CT_min), insects enter a state of paralysis (chill-coma). Chill-susceptible insects accumulate injuries (termed chilling injury) during prolonged exposure to low temperatures. My objective was to determine the mechanisms by which both chill-coma and chilling injury manifest in chill-susceptible insects. In aquatic animals, critical thermal limits are associated with a temperature-induced failure of oxygen supply relative to demand (oxygen- and capacity- limitation of thermotolerance; OCLT), which leads to reliance on anaerobic metabolism …