UBC Theses and Dissertations
Cardiovascular and metabolic function after thoracic spinal cord injury Inskip, Jessica Ann
Spinal cord injury (SCI) has the potential to disrupt autonomic pathways in the spinal cord leading to a range of autonomic dysfunctions. The cardiovascular (CV) and metabolic sequelae can restrict the lives of individuals with SCI and contribute to the deterioration of their cardiometabolic health. Here I investigated the whole-body CV and metabolic ramifications of experimental SCI in rats. Complete thoracic SCI was performed at two different levels in order to determine whether these outcomes demonstrated a level dependence. High-(T3) and low-(T10) thoracic SCI both result in flaccid hindlimb paralysis, but have different effects on the level of supraspinal autonomic control. CV and metabolic function were assessed at several times post-injury to investigate changes over time. Animals with acute high-thoracic SCI displayed resting hypotension that resolved with time post-injury. However, their capacity to control blood pressure (BP) in response to physiological stimuli remained deficient; animals with high-thoracic SCI displayed pronounced orthostatic hypotension (OH) and severe episodes of sensory stimulation-induced hypertension known as autonomic dysreflexia (AD). The resting BP and heart rate of animals with low-thoracic SCI, and their ability to respond to orthostatic stress, was indistinguishable from sham controls. Lipid metabolism was also disordered by SCI in a level-dependent pattern. Animals with high-thoracic SCI carried increased white adipose tissue and had higher circulating triacylglycerol levels compared to animals with low-thoracic SCI and sham controls. However, there was no difference in the distribution of cholesterol-carrying lipoproteins. Carbohydrate metabolism in animals with SCI did not support the diabetic profile suggested by the lipid results. Overall, animals with SCI were more sensitive to glucose and insulin than sham-injured animals. The pronounced ketone response to fasting in animals with high-thoracic SCI suggests that there are diverse effects on substrate metabolism. This work introduces simple tests that can be performed to investigate several important and understudied autonomic outcomes of SCI. The results reveal the importance of the intact autonomic nervous system in regulating CV and metabolic function. The disparity between motor and autonomic function encourages modifying our current conventions so that we stratify subjects by their autonomic injury level and their motor deficits.
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