Browsing by Subject "central command"
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Item Influence of Thermoregulatory and Nonthermoregulatory Control Mechanisms of Arterial Blood Pressure During Recivert from Exercise in Humans(2001-05-10) Carter, Robert; Michael L. Smith; Robert L. Kaman; Thomas YorioCarter, III Robert, Thermoregulatory and nonthermoregulatory control of arterial pressure during recovery from exercise in humans. Doctor of Philosophy (Biomedical Sciences). May 2001; 153p; 4 tables, 17 figures; 100 titles. The mechanisms of arterial blood pressure control during exercise is well established; however, much less is known about the regulation of arterial blood pressure immediately after intense or prolonged dynamic exercise. Inactive recovery from dynamic exercise is associated with cessation of the primary exercise stimuli from the brain (central command), Skeletal muscle pumping, which contributes to increases in venous return during exercise is also stopped during inactive recovery from exercise. Thus, the skeletal muscle pump and central command each contribute importantly to elevation and maintenance of arterial blood pressure regulation and cerebral blood flow during exercise. When exercise is intense and/or prolonged, the resulting thermal load exacerbates the challenge to maintain arterial blood pressure and cerebral blood flow both during exercise and particularly during recovery from exercise and thereby increases the risk of syncope. Recently, we found that the skeletal muscle pump plays a major role in arterial blood pressure control during recovery from brief (3 min), mild (60% of maximal HR) exercise in which there was no thermal load. However, how the mechanisms of arterial pressure regulation operate during recovery from intense or prolonged exercise when a thermal load occurs is unknown. Therefore, the purpose of the investigations described herein, was to quantify the mechanisms of the carotid baroreflex function, central command, and the skeletal muscle pump when a thermal stress occurs on arterial blood pressure regulation during recovery from exercise in humans. In addition, differences in arterial blood pressure regulation in women and men during recovery from exercise were addressed in women and men. To investigate these mechanisms, we investigated the carotid-cardiac baroreflex function, cardiovascular, and thermoregulatory responses in volunteer subjects during inactive and active recovery from prolonged exercise improved the function of the baroreflex by increasing the functional reserve of the reflex to buffer against hypotensive stimuli. Our data also suggest that thermoregulatory factors contribute to decreases in MAP after inactive recovery from exercise. In addition, the metabolic state of skeletal muscle during longer duration exercise (15 min) may contribute to these responses during inactive recovery from exercise. These results support the hypothesis that thermal stress contributes to the rapid decreases in arterial blood pressure during inactive recovery following dynamic exercise. To investigate gender differences in arterial pressure regulation during recovery from exercise, we compared 11 women and 8 men during 3 min of exercise and 5 min of inactive and active recovery from exercise. Interestingly, at 1 minute after exercise, MAP decreased less during inactive recovery in men when compared to women. This difference was due to greater decreases in SV and less increase in TPR during inactive recovery from exercise in women compared to men. MAP decreased less during active recovery in men when compared to women. These findings suggest that women may have increased risk of post-exercise orthostatic hypotension and that active recovery from exercise may reduce this risk.Item Regulation of Carotid Baroreflex Resetting During Arm Exercise(1999-06-01) Querry, Ross G.; Peter B. Raven; Patricia Gwirtz; Michael SmithQuerry, Ross G., Regulation of Carotid Baroreflex Resetting during Arm Exercise. Doctor of Philosophy (Biomedical Sciences), June 1999, 100 pp., 4 tables, 12 figures, bibliography, 56 titles. Cardiovascular responses to exercise are modulated by the integration of the central nervous system and afferent information from arterial baroreflexes and working skeletal muscle. Investigations have shown that during exercise, the carotid baroreflex (CBR) is reset in proportion to the exercise intensity. The role of the central nervous system contribution to the CBR resetting has not been elucidated. Investigations of CBR function in the animal model consistently report CBR variables such as maximal gain that are different than those reported in humans. These discrepancies may be due in part to methodological limitations in the neck pressure/neck suction (NP-NS) technique used to investigate the isolated CBR function in humans. To accurately examine the internal stimulus from the NP-NS maneuver, subjects were instrumented with a percutaneous catheter to record tissue pressure at the carotid sinus during five-second and rapid pulse NP-NS protocols. Carotid baroreflex function curves were analyzed with and without transmission correction of the carotid sinus pressure (CSP). Results indicated that positive pressure was more fully transmitted (~83%) than negative pressure (~65%) during the five-second-pulse, but not the rapid pulse protocol. Correction of the CSP in either protocol resulted in significant increases in CBR maximal gain and threshold and a reduced saturation pressure. These methodological refinements were then utilized to investigate the role of central command on CBR function during exercise. Subjects performed static and rhythmic handgrip exercise before and after regional anesthesia. Carotid baroreflex curves were analyzed at rest and during exercise before and after blockade at the same absolute workload. Muscle weakness from the blockade required an increased effort to maintain control tension. Heart rate, arterial pressure and perceived exertion during exercise were increased following blockade. During control exercise the CBR function curves were reset upward and rightward compared to rest with a further parallel shift during exercise with blockade. The operating point of the CBR was reset along with the centering point, but did not show the divergence toward the threshold pressure that had been previously described during dynamic exercise. The results support the proposal that central command was a primary mechanism for the resetting of the carotid baroreflex during exercise, but may not be the primary mechanism in the resetting of the operating point of the reflex.