J Kevin Shoemaker's research while affiliated with University of the Western Cape and other places

Publications (390)

Article
We examined the influence of sex and age on the relationship between aerobic fitness and muscle sympathetic nerve activity (MSNA) in healthy adults. Data were assessed from 224 volunteers (88 females), aged 18-76 yrs, in whom resting MSNA (microneurography) and peak oxygen uptake (V̇O 2 peak; incremental exercise test) were evaluated. When separate...
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Background Targeted exercise training is a promising strategy for promoting cognitive function and preventing dementia in older age. Despite the utility of exercise as an intervention, variation still exists in exercise-induced cognitive gains and questions remain regarding the type of training (i.e., what), as well as moderators (i.e., for whom) a...
Article
Background: We tested the hypothesis that women who develop gestational hypertension (GH) display abnormal sympathetic action potential (AP) discharge patterns during late pregnancy (32-36 weeks), both at supine rest and during postural stress. Methods: Thirteen nonpregnant, female controls (nonpregnant controls [CTRL]) and 32 pregnant women par...
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Near-infrared spectroscopy (NIRS) measurements of tissue oxygen saturation (StO2) are frequently used during vascular and cardiac surgeries as a non-invasive means of assessing brain health; however, signal contamination from extracerebral tissues remains a concern. As an alternative, hyperspectral (hs)NIRS can be used to measure changes in the oxi...
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Maintaining standing balance is vital to completing activities in daily living. Recent findings suggest an interaction between cardiovascular and postural control systems. Volitional slow breathing can modulate the cardiovascular response and affect postural control during quiet standing. However, the effects of slow breathing during threats to sta...
Preprint
Background: Targeted exercise training is a promising strategy for promoting cognitive function and preventing dementia in older age. Despite the utility of exercise as an intervention, variation still exists in exercise-induced cognitive gains and questions remain regarding the type of training ( i.e. , what), as well as moderators ( i.e. , for wh...
Article
We tested the hypothesis that the baroreflex control of action potential (AP) subpopulations would be blunted in older compared to young adults. Integrated muscle sympathetic nerve activity (MSNA) and the underlying sympathetic APs were obtained using microneurography and a continuous wavelet analysis approach, respectively, during 5 minutes of sup...
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This article describes the forebrain neurocircuitry associated with rapid heart rate response at the exercise onset with attention to ascending somatosensory information from the Type I and II afferents from the contracting muscle and potential influence of sensory information related to blood pressure and changes in heart rate.
Conference Paper
During transient reductions in blood pressure induced by standing upright, a rapid increase in cerebrovascular compliance represents a fundamental response in addition to reductions in cerebrovascular resistance. Age-related reductions in central arterial compliance are known but how ageing affects the cerebrovascular compliance response to standin...
Article
Introduction: The occlusion of the common carotid artery (CCA) during carotid endarterectomy (CEA) is associated with a risk of cerebral ischemia due to inadequate collateral blood flow1 . By monitoring tissue oxygen saturation (StO2 ), near-infrared spectroscopy (NIRS) is frequently employed during CEA2 to determine sufficient oxygen delivery. Ho...
Article
Posttraumatic stress disorder (PTSD) is a debilitating psychiatric disorder that is more prevalent in women than men and has been linked to an elevated risk of developing cardiovascular disease. Although the physiological mechanisms are unclear, it is thought that exaggerated neuro-cardiovascular reactivity is partially responsible. Indeed, women w...
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The ability to regain control of balance is vital in limiting falls and injuries. Little is known regarding how the autonomic nervous system responds during recovery from balance perturbations of different intensities. The purpose of this study was to examine the cardiovascular response following a standing balance perturbation of varying intensiti...
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The study of vascular regulation often omits important information about the elastic properties of arteries under conditions of pulsatile flow. The purpose of this study was to examine the relationship between muscle sympathetic nerve activity (MSNA), vascular bed compliance, and peripheral blood flow responses in humans. We hypothesized that incre...
Article
Irregular heartbeats are often considered benign in isolation, but individuals who experience them frequently have a higher prevalence of cerebrovascular and/or cognitive associated disorders How irregular heartbeats affect blood pressure and cerebral hemodynamics in healthy and cardiovascular disease patients, those with and without reduced ejecti...
Article
The sympathetic nervous system exhibits patterns of action potential (AP) discharge in human muscle sympathetic nerve activity that suggest coding strategies express reflex specificity. This study explored the interactive effects of baroreceptor unloading using lower body negative pressure (LBNP) and volitional end-expiratory apnea (APN) on sympath...
Article
Muscle sympathetic nerve activity (MSNA) increases during isometric exercise via increased firing of low-threshold action potentials (AP), recruitment of larger, higher-threshold APs, and synaptic delay modifications. Recent work found that women with post-traumatic stress disorder (PTSD) demonstrate exaggerated early-onset MSNA responses to exerci...
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Sport concussions can be difficult to diagnose and if missed, they can expose athletes to greater injury risk and long-lasting neurological disabilities. Discovery of objective biomarkers to aid concussion diagnosis is critical to protecting athlete brain health. To this end, we performed targeted proteomics on plasma obtained from adolescent athle...
Article
There is a need for improved understanding of how different cerebrovascular reactivity (CVR) protocols affect vascular cross-sectional area (CSA) to reduce error in CVR calculations when measures of vascular CSA are not feasible. In human participants, we delivered ∼±4 mm Hg end-tidal partial pressure of CO 2 (P ET CO 2 ) relative to baseline throu...
Article
The current study evaluated the hypothesis that six months of exercise-based cardiac rehabilitation (CR) would improve sympathetic neural recruitment in patients with ischemic heart disease (IHD). Microneurography was used to evaluate action potential (AP) discharge patterns within bursts of muscle sympathetic nerve activity (MSNA), in eleven patie...
Article
New findings: What is the central question of this study? Vascular compliance importantly contributes to the regulation of cerebral perfusion and complex mechanisms are known to influence compliance of a vascular bed. While vasodilation mediates changes in vascular resistance, it remains unknown whether it may also affect compliance, particularly...
Preprint
Full-text available
There is a need for improved understanding of how different cerebrovascular reactivity (CVR) protocols affect vascular cross-sectional area (CSA) when measures of vascular CSA are not feasible. In human participants, we delivered ~±4mmHg end-tidal partial pressure of CO 2 (PETCO 2 ) relative to baseline through controlled delivery, and measured cha...
Article
Concussions are frequent in sports and can contribute to significant and long-lasting neurological disability. Adolescents are particularly susceptible to concussions, with accurate determination of the injury challenging. Our previous study demonstrated that concussion diagnoses could be aided by metabolomics profiling and machine learning, with p...
Article
Sympathetic emissions directed towards the skeletal muscle circulation — muscle sympathetic nerve activity (MSNA) — represent a key mechanism for maintaining homeostasis and supporting human survival during physiological stress. Pulse-rhythmic bursts formed by the synchronous discharge of differently-sized sympathetic action potentials (APs) repres...
Article
As with blood pressure, age-related changes in muscle sympathetic nerve activity (MSNA) may differ nonlinearly between sexes. Data acquired from 398 male (age: 39±17; range: 18-78 years [mean±SD]) and 260 female (age: 37±18; range: 18-81 years) normotensive healthy nonmedicated volunteers were analyzed using linear regression models with resting MS...
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Intervertebral discs (IVDs) are often referred to as the largest avascular structures of the human body, yet a collective resource characterizing the vascularization of the IVD does not exist. To address this gap, the objective of this study was to conduct a comprehensive search of the literature to review and summarize current knowledge of the pre...
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A single bout of aerobic exercise improves executive function; however, the mechanism for the improvement remains unclear. One proposal asserts that an exercise-mediated increase in cerebral blood flow (CBF) enhances the efficiency of executive-related cortical structures. Here, participants completed separate 10-min sessions of moderate to heavy i...
Article
This case study reports the efferent muscle sympathetic nerve activity (MSNA) discharge patterns during a sinus pause observed during a maximal end-expiratory apnea in a young healthy male (age = 26 years). During a 15.3-second end-expiratory apnea following a bout of intermittent hypercapnic hypoxia we observed a 5.2-second (R-R interval) sinus pa...
Article
Characterization of dynamic cerebral autoregulation has focused primarily on adjustments in cerebrovascular resistance in response to blood pressure (BP) alterations. However, the role of vascular compliance in dynamic autoregulatory processes remains elusive. The present study examined changes in cerebrovascular compliance and resistance during st...
Article
The survival rate of ischemic heart disease (IHD) patients is increasing. However, survivors experience increased risk for neurological complications. The mechanisms for this increased risk are unknown. We tested the hypothesis that IHD patients have greater carotid and cerebrovascular stiffness and these indices predict white matter small vessel d...
Article
Background: We examined the effect of acute intermittent hypoxia (IH) on sympathetic neural firing patterns and the role of the carotid chemoreceptors. We hypothesized exposure to acute IH would increase muscle sympathetic nerve activity (MSNA) via an increase in action potential (AP) discharge rates and within-burst firing. We further hypothesize...
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Post-traumatic stress disorder (PTSD) is more prevalent in women and associated with greater risk of major forms of cardiovascular disease but physiological mechanisms underlying this association remain unknown. We hypothesized that abnormal sympathetic responses to sympatho-excitatory stimuli might predispose PTSD patients to a greater risk of car...
Article
Key points: Emission patterns in muscle sympathetic nerve activity (MSNA) stem from differently sized action potential (AP) subpopulations that express varying discharge probabilities. The mechanisms governing these firing behaviours are unclear. This study investigated the hypothesis that the arterial baroreflex exerts varying control over the di...
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In this commentary, we respond to Bowen and colleagues’ empirical study of research partnerships between Canadian health organizations and university-based investigators. We draw on our experiences of university and health-services partnerships to elaborate on some of the misalignments between researchers and health services leaders identified by B...
Article
Objectives: We systemically reviewed published studies that evaluated aerobic exercise interventions in patients with knee osteoarthritis (OA) to: (1) report the frequency, intensity, type and time (FITT) of exercise prescriptions and (2) quantify the changes in markers of cardiovascular health and systemic inflammation. Data sources: PubMed, CI...
Article
This study tested the hypothesis that older hypertensive women display augmented pressor responses and aberrant sympathetic neural discharge patterning in response to orthostatic stress versus older hypertensive men. We evaluated, in older hypertensive and normotensive men and women (n=12 each group), blood pressure, heart rate, cardiac index (acet...
Article
Insulin modulates vasomotor tone through vasodilator and vasoconstrictor signaling pathways. The purpose of the present work was to determine whether insulin-stimulated vasoconstriction is a pathophysiological phenomenon that can result from a combination of persistent insulin signaling, suppressed PI3K activation and an ensuing relative increase i...
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Individuals with osteoarthritis (OA) are at greater risk of cardiovascular and cerebrovascular incidents; yet, cerebrovascular control remains uncharacterized. Our primary outcome was to acquire cerebrovascular control metrics in patients with OA and compare measures to healthy control adults (CTL) without OA or cardiovascular complications. Our pr...
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Background Autonomic dysregulation represents a hallmark of coronary artery disease ( CAD ). Therefore, we investigated the effects of exercise‐based cardiac rehabilitation ( CR ) on autonomic function and neuro‐cardiovascular stress reactivity in CAD patients. Methods and Results Twenty‐two CAD patients (4 women; 62±8 years) were studied before a...
Article
We sought to examine the effect of varying chemoreflex stress on sympathetic neural recruitment strategies during end-expiratory apnea. We hypothesized increases in the firing frequency and probability of low-threshold axons at the asphyxic "break point" would be exaggerated during hypoxia and attenuated during hyperoxia. Multi-unit MSNA (microneur...
Article
What strategies are employed by the sympathetic system to communicate with the circulation? Muscle sympathetic nerve activity (MSNA) occurs in bursts of synchronous action potential (AP) discharge, yet whether between-burst asynchronous AP firing exists remains unknown. Using multi-unit microneurography and a continuous wavelet transform to isolate...
Article
Breath-hold divers (BHD) experience repeated bouts of severe hypoxia and hypercapnia with large increases in blood pressure. However, the impact of long-term breath-hold diving on cerebrovascular control remains poorly understood. The ability of cerebral blood vessels to respond rapidly to changes in blood pressure represent the property of dynamic...
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Objective: To study autonomic responses to postural changes in concussed adolescents. The influence of sex was also studied. Design: Longitudinal cohort observational study. Participants: Concussed adolescents (CONC; n = 65; 26 male adolescents; age 15 ± 1 years, range = 12-18 years) and a control (CTRL) group of nonconcussed adolescents of si...
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Objective: To assess the predictive capability of the postconcussion symptom scale (PCSS) of the sport concussion assessment tool (SCAT) III to differentiate concussed and nonconcussed adolescents. Design: Retrospective. Setting: Tertiary. Participants: Sixty-nine concussed (15.2 ± 1.6 years old) and 55 control (14.4 ± 1.7 years old) adolesc...
Article
Objective: Test the hypotheses that (1) concussion in adolescents impairs autonomic neural control of heart rate (HR), and (2) HR reactivity improves with symptom resolution. Design: Observational, case-control. Participants: Nineteen concussed adolescents (8 female adolescents; age 15 ± 2 years) and 16 healthy controls (6 female adolescents,...
Article
The autonomic nervous system elicits continuous beat-by-beat homeostatic adjustments to cardiovascular control. These modifications are mediated by sensory inputs (e.g., baroreceptors, metaboreceptors, pulmonary, thermoreceptors, and chemoreceptors afferents), integration at the brainstem control centres (i.e., medulla), and efferent autonomic neur...
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Pulsatile blood flow is generally mediated by the compliance of blood vessels whereby they distend locally and momentarily to accommodate the passage of the pressure wave. This freedom of the blood vessels to exercise their compliance may be suppressed within the confines of the rigid skull. The effect of this on the mechanics of pulsatile blood fl...
Article
This perspective document summarizes discussions held at the CSEP Annual Meeting in Winnipeg on October 27, 2017 when an expert panel was assembled to discuss the key questions and challenges for future research in cardiovascular exercise physiology. We were inspired by the example of the late Dr. Mike Sharratt, an accomplished and impactful Profes...
Article
Key points summary: The mechanisms affecting recruitment patterns of postganglionic sympathetic nerves remain unclear. The divergent and convergent preganglionic innervation patterns of postganglionic neurons, and presence of differently-sized postganglionic nerves, suggest that the ganglia may participate in modifying the discharge patterns of si...
Article
Purpose: Although cerebrovascular impairments are believed to contribute to concussion symptoms, little information exists regarding brain vasomotor control in adolescent concussion, particularly autoregulatory control that forms a fundamental response mechanism during changes in blood pressure. This research tested the hypothesis that adolescent...
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Background: Although the increased prevalence and severity of clinical depression and elevated cardiovascular disease risk represent 2 vexing public health issues, the growing awareness of their combined presentation compounds the challenge. The obese Zucker rat, a model of the metabolic syndrome, spontaneously develops significant depressive symp...