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The effects of lower body negative pressure on the cardiovascular system: the relationships of gender and aerobic fitness

Description: Sixteen males and sixteen females were recruited for this study; eight of each gender were aerobically trained athletes; the remaining eight were untrained control subjects. Each subject performed a maximal exercise stress test for aerobic capacity (VO2max). On a separate day the blood volume and the cardiovascular responses to progressive (0 to -50 torr) lower body negative pressure (LBNP) were determined.
Date: 1986
Creator: Hudson, Donna Louise
Partner: UNT Libraries

Alterations in Human Baroreceptor Reflex Regulation of Blood Pressure Following 15 Days of Simulated Microgravity Exposure

Description: Prolonged exposure to microgravity is known to invoke physiological changes which predispose individuals to orthostatic intolerance upon readaptation to the earth's gravitational field. Attenuated baroreflex responsiveness has been implicated in contributing to this inability to withstand orthostatic stress. To test this hypothesis, eight individuals were exposed to 15 days of simulated microgravity exposure using the 6° head-down bed rest model. Prior to, and after the simulated microgravity exposure, the following were assessed: a) aortic baroreflex function; b) carotid baroreflex function; c) cardiopulmonary baroreflex function; and d) the degree of interaction between the cardiopulmonary and carotid baroreflexes.
Date: August 1993
Creator: Crandall, Craig G. (Craig Gerald)
Partner: UNT Libraries

Aortic Baroreceptor Reflex Control of Blood Pressure: Effect of Fitness

Description: Aortic baroreflex (ABR) control of blood pressure was examined in 7 untrained (UT) and 8 endurance exercise trained (EET) young men. ABR control of blood pressure was determined during a steady state phenylephrine infusion to increase mean arterial pressure 10-15 mmHg, combined with positive neck pressure to counteract the increased carotid sinus transmural pressure, and low levels of lower body negative pressure to counteract the increased central venous pressure. Functioning alone, the ABR was functionally adequate to control blood pressure. However, ABR control of HR was significantly diminished in the EET subjects due solely to the decrease in the ABR sensitivity. The persistent strain from an increased stroke volume resulting from endurance exercise training could be the responsible mechanism.
Date: May 1992
Creator: Andresen, Jean M.
Partner: UNT Libraries

Blood Pressure Regulation During Simulated Orthostatism Prior to and Following Endurance Exercise Training

Description: Cardiovascular responses and tolerance to an orthostatic stress were examined in eight men before and after eight months of endurance exercise training. Following training, maximal oxygen consumption and blood volume were increased, and resting heart rate reduced. Orthostatic tolerance was reduced following training in all eight subjects. It was concluded that prolonged endurance training decreased orthostatic tolerance and this decrease in tolerance appeared associated with attenuated baroreflex sensitivity and alterations in autonomic balance secondary to an increased parasympathetic tone noted with training.
Date: May 1992
Creator: Stevens, Glen Harold John
Partner: UNT Libraries

A Comparison of Biofeedback and Cognitive Therapy in the Control of Blood Pressure Under Stress and No-Stress Conditions

Description: This study evaluated the efficacy of cognitive therapy and biofeedback training in lowering Dlood pressures of normotensives under no-stress and stress conditions. A cognitive therapy group was compared to biofeedback and habituation control groups with 32 normotensives. Subjects were taught to use the electronic sphygmomanometer that served as the device to measure blood pressure during pretreatment and posttreatment phases of the study. These measurement phases each consisted of three 19 minute periods. Trie first period consisted of no-stress, and then a stress period followed. Return-to-no-stress was the final period. Subjects in the cognitive therapy and biofeedbacK groups received five sessions of self-control training of 66 minutes each between the pre- and posttreatment phases. The cold pressor was the analogue stressor used to induce bxood pressure elevations,
Date: August 1982
Creator: Dafter, Roger E. (Roger Edwin)
Partner: UNT Libraries

Biofeedback Treatment of Systolic and Diastolic Blood Pressure Under Stress and No-Stress Conditions

Description: This study compares the relative efficacy of systolic and diastolic biofeedback in lowering the systolic and diastolic blood pressures of normotensives. The importance of testing these biofeedback procedures lies in assessment of their potential as blood pressure self-control techniques for the treatment of essential hypertension.
Date: May 1982
Creator: Dafter, Roger E. (Roger Edwin)
Partner: UNT Libraries

Interactions between Carotid and Cardiopulmonary Baroreceptor Populations in Men with Varied Levels of Maximal Aerobic Power

Description: Reductions in baroreflex responsiveness have been thought to increase the prevalence of orthostatic hypotension in endurance trained athletes. To test this hypothesis, cardiovascular responses to orthostatic stress, cardiopulmonary and carotid baroreflex responsiveness, and the effect of cardiopulmonary receptor deactivation on carotid baroreflex responses were examined in 24 men categorized by maximal aerobic power (V02max) into one of three groups: high fit (HF, V0-2max=67.0±1.9 ml•kg^-1•min^-1), moderately fit (MF, V0-2max=50.9±1.4 ml•kg^-1•min^-1), and low fit (LF, V0-2max=38.9±1.5 ml•kg^-1•min^-1). Orthostatic stress was induced using lower body negative pressure (LBNP) at -5, -10, -15, -20, -35, and -50 torr. Cardiopulmonary baroreflex responsiveness was assessed as the slope of the relationship between forearm vascular resistance (FVR, strain gauge plethysmography) and central venous pressure (CVP, dependent arm technigue) during LBNP<-35 torr. Carotid baroreflex responsiveness was assessed as the change in heart rate (HR, electrocardiography) or mean arterial pressure (MAP, radial artery catheter) elicited by 600 msec pulses of neck pressure and neck suction (NP/NS) from +40 to -70 torr. Pressures were applied using a lead collar wrapped about the subjects' necks during held expiration. Stimulus response data were fit to a logistic model and the parameters describing the curve were compared using two-factor ANOVA. The reductions CVP, mean (MAP), systolic, and pulse pressures during LBNP were similar between groups (P<0.05). However, diastolic blood pressure increased during LBNP m all but the HF group. (P<0.05). The slope of the FVR/CVP relationship did not differ between groups, nor did the form of the carotid-cardiac baroreflex stimulus response curve change during LBNP. changes in HR elicited with NP/NS were not different between groups (£>0.05). The range of the MAP stimulus response curve, however, was significantly less in the HP group compared to either the MP or LF group (£<0.05). These data imply that carotid baroreflex control of HR is unaltered ...
Date: August 1989
Creator: Pawelczyk, James A. (James Anthony)
Partner: UNT Libraries

Fitness-Related Alterations in Blood Pressure Control: The Role of the Autonomic Nervous System

Description: Baroreflex function and cardiovascular responses to lower body negative pressure during selective autonomic blockade were evaluated in endurance exercise trained (ET) and untrained (UT) men. Baroreflex function was evaluated using a progressive intravenous infusion of phenylephrine HCL (PE) to a maximum of 0.12 mg/min. Heart rate, arterial blood pressure, cardiac output and forearm blood flow were measured at each infusion rate of PE. The reduction in forearm blood flow and concomitant rise in forearm vascular resistance was the same for each subject group. However, the heart rate decreases per unit increase of systolic or mean blood pressure were significantly (P<.05) less in the ET subjects (0.91 ± 0.30 versus 1.62 ± 0.28 for UT). During progressive lower body negative pressure with no drug intervention, the ET subjects had a significantly (P<.05) greater fall in systolic blood pressure (33.8 ± 4.8 torr versus 16.7 ± 3.9 torr). However, the change in forearm blood flow or resistance was not significantly different between groups. Blockade of parasympathetic receptors with atropine (0.04 mg/kg) eliminated the differences in response to lower body negative pressure. Blockade of cardiac sympathetic receptors with metoprolol (0.02 mg/kg) did not affect the differences observed during the control test. It was concluded that the ET subjects were less effective in regulating blood pressure than the UT subjects, because of 1) an attenuated baroreflex sensitivity, and 2) parasympathetic-mediated depression of cardiac and vasoconstrictive responses to the hypotensive stress.
Date: December 1986
Creator: Smith, Michael Lamar, 1957-
Partner: UNT Libraries