Effects of Endurance Training on Aortic and Carotid Baroreflex Function

dc.contributor.advisorPeter B. Raven
dc.contributor.committeeMemberMichael Smith
dc.contributor.committeeMemberPatricia A. Gwirtz
dc.creatorSmith, Scott Alan
dc.description.abstractSmith, Scott Alan, Effects of Endurance Training on Aortic and Carotid Baroreflex Function. Doctor of Philosophy (Biomedical Sciences), June 1999; 122 pp; 8 tables; 10 figures; bibliography, 148 titles. Arterial bareflex control of cardiac function is dependent upon afferent input from both the aortic arch and carotid sinus bareceptors. Extensive research in animals has generated conflicting results as to the range of arterial pressures over which each baroreflex operates. Further, the complex integration of afferent signals within the medullary cardiovascular center, in reference to aortic and carotid baroreceptor input, has been characterized as additive, inhibitory, and facilitatory in nature. Such reports make it difficult to draw definitive conclusions about the behavior or central neural processing within the brainstem. In addition, these relationships have yet to be examined in humans. Therefore, the purpose of the investigations described herein, was to quantify the range of pressures over which the arterial aortic and carotid baroreflexes operate as well as to describe the interactive relationship between the aortic and carotid baroreceptors. In order to investigate these questions, we isolated the arterial, aortic, and carotid-cardiac baroreflexes in volunteer subjects generating sigmoidal stimulus-response curves for each reflex arc. Arterial and aortic baroreflex (ABR) control of heart rate (HR) was assessed by inducing graded increases and decreases in mean arterial pressure (MAP) by bolus infusion of the vasoactive agents phenylephrine (PE) and sodium nitroprusside (SN), respectively. Carotid baroreflex (CBR) function was determined utilizing ramped five second pulses of both pressure and suction applied to the carotid sinus via a neck chamber collar, independent of drug administration. The MAP at which the threshold and saturation were elicited did not differ among the reflexes examined indicating each reflex operated over a similar range of arterial pressures. Further, the simple sum of the independently driven HR response ranges of the CBR and ABR was significantly greater than that produced when both baroreceptor populations were concomitantly stimulated (i.e. arterial baroreflex) suggesting an inhibitory interaction. To investigate differential baroreflex control of HR in response to chronic endurance exercise training, a second investigation was designed implementing the reflex isolation techniques described previously. Stimulus-response relationships were compared between high fit (maximal oxygen uptake, VO2max [greater than] 60ml˖kg-1˖min-1) and average fit (VO2maxml˖kg-1˖min-1) individuals. Interestingly, neither the range of operating pressures for each reflex nor the integrative relationship between the ABR and CBR were altered as a result of aerobic training. However, the HR response range elicited from the aortic baroreceptors as a result of hypotensive and hypertensive insult was markedly attenuated in the aerobically trained population compared to their sedentary counterparts, exclusively causing a requisite reduction in arterial baroreflex sensitivity.
dc.subjectCardiovascular System
dc.subjectCell and Developmental Biology
dc.subjectCirculatory and Respiratory Physiology
dc.subjectLife Sciences
dc.subjectMedicine and Health Sciences
dc.subjectNervous System
dc.subjectNeuroscience and Neurobiology
dc.subjectSystems and Integrative Physiology
dc.subjectSystems Neuroscience
dc.subjectEndurance training
dc.subjectcarotid baroreflex function
dc.subjectaortic baroreflex
dc.subjectsodium nitroprusside
dc.subjectmean arterial pressure
dc.subjectcentral neural processing
dc.titleEffects of Endurance Training on Aortic and Carotid Baroreflex Function
thesis.degree.departmentGraduate School of Biomedical Sciences
thesis.degree.disciplineBiomedical Sciences
thesis.degree.grantorUniversity of North Texas Health Science Center at Fort Worth
thesis.degree.nameDoctor of Philosophy


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