Neural Control of the Carotid Baroreflex During Exercise

Gallagher, Kevin Matthew, Neural Control of the Carotid Baroreflex During Exercise. Doctor of Osteopathic Medicine/Doctor of Philosophy (Biomedical Sciences), May 2000; 151 pages; 13 tables; 19 figures; bibliography; 161 titles. Carotid baroreflex (CBR) function is reset upward and rightward to the prevailing blood pressure during dynamic and static exercise. Feedforward central neural inputs (central command) and negative feedback from skeletal muscle (exercise pressor reflex) both contribute to the resetting. The purpose of this investigation was to identify the individual roles of central command and the exercise pressor reflex in the resetting of the CBR during dynamic and static exercise. First, it was necessary to determine which receptor group that comprises the exercise pressor reflex, chemically-sensitive (chemoreceptors) or mechanically-sensitive (mechanoreceptors) receptors, was primarily involved in the regulation of the cardiovascular system. We observed the cardiovascular responses during exercise to individual action of the chemoreceptors and the mechanoreceptors. We demonstrated an increased mean arterial pressure (MAP) response to mechanoreceptor activation that was not identified during chemoreceptor stimulation. This finding suggested that the mechanoreflex was the primary exercise pressor mediated of arterial blood pressure during exercise. To identify the role of central command on CBR resetting, a second investigation increased central command by partial neuromuscular blockade during dynamic and static exercise. Resetting of CBR control of heart rate (carotid-cardiac; CSP-HR) and MAP (carodtid-vasomotor; CSP-MAP) during control exercise was further reset upward and rightward by increased central command without alterations in sensitivity. In conclusion, central command, a feedforward mechanism, was actively involved in the resetting of the CBR during exercise. To investigate the role of the exercise pressor reflex on CBR function, a third investigation activated by the exercise pressor reflex with the application of medical anti-shock trousers (MAS) during dynamic and static exercise. From control exercise, carotid-vasomotor function was further reset upward and rightward by the application of MAS trousers while CSP-HR function was only reset rightward. Sensitivity of the CSP-MAP and CSP-HR function curves were unaltered. The negative feedback mechanism of exercise pressor reflex, primarily mediated by mechanoreceptors, appeared to act as a modulator of CBR resetting during exercise.