Representation of Somatosensory Afferents in the Cortical Autonomic Network

The relationship between somatosensory stimulation and the autonomic nervous system has been established with effects on heart rate (HR) and sympathetic tone. However, the involvement of the cortical autonomic network (CAN) during muscle sensory afferent stimulation has not been identified. The main objective of the research in this dissertation was to determine the representation of somatosensory afferents in the CAN and their physiologic impact on cardiovascular control. Somatosensory afferent activation was elicited by electrical stimulation of type I and II afferents (sub-motor threshold) and type III and IV afferents (motor threshold), and CAN patterns were assessed using blood-oxygenation level-dependent functional magnetic resonance imaging. Study 1 (Chapter 2) established CAN regions associated with sub-motor stimulation including the ventral medial prefrontal cortex (vMPFC), subgenual anterior cingulate cortex (sACC), and posterior insula, along with a trend towards increased heart rate variability (HRV). Motor threshold stimulation was associated with activation in the posterior insula. Having established the CAN regions affected by sensory afferent input, diffusion tensor imaging was used (Chapter 3) to establish structural connections between the cortical regions associated with functional cardiovascular control. We identified two discrete patterns of white matter connectivity between the anterior insula-sACC and posterior insula-posterior cingulate cortex, suggesting that a structural network may underlie functional roles in autonomic regulation and sensory processing. As somatosensory stimulation had modest impact on cardiovascular control under baseline conditions, Study 3 (Chapter 4) aimed to establish the effects of somatosensory stimulation during baroreceptor unloading (lower-body negative pressure, LBNP) on muscle sympathetic nerve activity (MSNA) and cortical activity. Sensory stimulation during LBNP led to an attenuated increase in MSNA burst frequency, as well as absent activity in the right insula and dorsal ACC, supporting the sympatho-excitatory role of these regions. No effect of somatosensory stimulation during chemoreflex-mediated sympatho-excitation was observed on MSNA, while right insular and dorsal ACC activities were maintained. Overall, the results of these studies provide evidence of somatosensory representation within the CAN regions that are anatomically linked, and highlight a role for type I and II sensory afferents in modulating autonomic outflow in a manner that depends upon baroreceptor loading

Forebrain neurocircuitry associated with human reflex cardiovascular control.

Physiological homeostasis depends upon adequate integration and responsiveness of sensory information with the autonomic nervous system to affect rapid and effective adjustments in end organ control. Dysregulation of the autonomic nervous system leads to cardiovascular disability with consequences as severe as sudden death. The neural pathways involved in reflexive autonomic control are dependent upon brainstem nuclei but these receive modulatory inputs from higher centers in the midbrain and cortex. Neuroimaging technologies have allowed closer study of the cortical circuitry related to autonomic cardiovascular adjustments to many stressors in awake humans and have exposed many forebrain sites that associate strongly with cardiovascular arousal during stress including the medial prefrontal cortex, insula cortex, anterior cingulate, amygdala and hippocampus. Using a comparative approach, this review will consider the cortical autonomic circuitry in rodents and primates with a major emphasis on more recent neuroimaging studies in awake humans. A challenge with neuroimaging studies is their interpretation in view of multiple sensory, perceptual, emotive and/or reflexive components of autonomic responses. This review will focus on those responses related to non-volitional baroreflex control of blood pressure and also on the coordinated responses to non-fatiguing, non-painful volitional exercise with particular emphasis on the medial prefrontal cortex and the insula cortex

Forebrain neurocircuitry associated with human reflex cardiovascular control

© 2015 Shoemaker and Goswami. Physiological homeostasis depends upon adequate integration and responsiveness of sensory information with the autonomic nervous system to affect rapid and effective adjustments in end organ control. Dysregulation of the autonomic nervous system leads to cardiovascular disability with consequences as severe as sudden death. The neural pathways involved in reflexive autonomic control are dependent upon brainstem nuclei but these receive modulatory inputs from higher centers in the midbrain and cortex. Neuroimaging technologies have allowed closer study of the cortical circuitry related to autonomic cardiovascular adjustments to many stressors in awake humans and have exposed many forebrain sites that associate strongly with cardiovascular arousal during stress including the medial prefrontal cortex, insula cortex, anterior cingulate, amygdala and hippocampus. Using a comparative approach, this review will consider the cortical autonomic circuitry in rodents and primates with a major emphasis on more recent neuroimaging studies in awake humans. A challenge with neuroimaging studies is their interpretation in view of multiple sensory, perceptual, emotive and/or reflexive components of autonomic responses. This review will focus on those responses related to non-volitional baroreflex control of blood pressure and also on the coordinated responses to non-fatiguing, non-painful volitional exercise with particular emphasis on the medial prefrontal cortex and the insula cortex

Does altering brachial artery tone with lower-body negative pressure and flow-mediated dilation affect arterial stiffness?

Although medium sized, muscular vessels normally respond to sympathetic stimulation by reducing compliance, it is unclear whether the large brachial artery is similarly affected by sympathetic stimulation induced via lower-body negative pressure (LBNP). Similarly, the impact of flow-mediated dilation (FMD) on brachial artery compliance and distensibility remains unresolved, hi addition, before such measures can be used as prognostic tools, it is important to investigate the reliability and repeatability of both techniques. Using a randomized order design, the effects of LBNP and FMD on the mechanical properties of the brachial artery were examined in nine healthy male subjects (mean age 24y). Non-invasive Doppler ultrasound and a Finometer were used to measure simultaneously the variation in systolic and diastolic diameter, and brachial blood pressure, respectively. These values were used to calculate compliance and distensibility values at baseline, and during both LBNP and FMD. The within-day and between-day repeatability of arterial diameter, compliance, distensibility, and FMD measures were assessed using the error coefficient and intra-class correlation coefficient (ICC). While heart rate (P<0.01) and peripheral resistance increased during LBNP (P<0.05), forearm blood flow and pulse pressure decreased (P<0.01). hi terms of mechanical properties, vessel diameters decreased (P<0.05), but both compliance and distensibility were not changed. On the other hand, FMD resulted in a significant increase in diameter (P<0.001), with no change in compliance or distensibility. hi summary, LBNP and FMD do not appear to alter brachial artery compliance or distensibility in young, healthy males. Whereas measures ofFMD were not found to be repeatable between days, the ICC indicated that compliance and distensibility were repeatable only within-day

Cardio-embolic stroke due to valve tissue embolization during Percutaneous Transseptal Mitral Commissurotomy (PTMC)

Percutaneous Transseptal Mitral Commissurotomy (PTMC) has replaced surgical commissurotomy as a treatment of choice in selected patients of rheumatic mitral stenosis. Various randomized trials have shown PTMC to be equal or superior to surgical commissurotomy in terms of hemodynamic improvement as well as long term survival. Systemic embolism is one of the dreaded complications of PTMC, which is reported in 0.5–5% of cases and involves cerebral circulation in 1% of cases. Most of the time, periprocedural embolism during PTMC is caused by the mobilization of preexisting thrombus in the left atrial appendage. We report an unusual case of acute stroke due embolization of mitral valve tissue during PTMC

The relationship between brain atrophy and cognitive-behavioural symptoms in retired Canadian football players with multiple concussions

Multiple concussions, particularly in contact sports, have been associated with cognitive deficits, psychiatric impairment and neurodegenerative diseases like chronic traumatic encephalopathy. We used volumetric and deformation-based morphometric analyses to test the hypothesis that repeated concussions may be associated with smaller regional brain volumes, poorer cognitive performance and behavioural symptoms among former professional football players compared to healthy controls. This study included fifty-three retired Canadian Football League players, 25 age- and education-matched healthy controls, and controls from the Cambridge Centre for Aging and Neuroscience database for validation. Volumetric analyses revealed greater hippocampal atrophy than expected for age in former athletes with multiple concussions than controls and smaller left hippocampal volume was associated with poorer verbal memory performance in the former athletes. Deformation-based morphometry confirmed smaller bilateral hippocampal volume that was associated with poorer verbal memory performance in athletes. Repeated concussions may lead to greater regional atrophy than expected for age. Keywords: Sport-related concussion, Mild traumatic brain injury, Deformation based morphometry, Agin