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Functions of carotid and aortic baroreflex control of heart rate (HR), cardiopulmonary baroreflex control of vascular resistance, adrenoreceptor responsiveness, indexes of baseline vagal and sympathetic tone, circulating blood volume, and venous compliance were compared in men and women to test the hypothesis that lower orthostatic tolerance in women would(More)
Compromised cardiovascular performance, occurrence of serious cardiac dysrhythmias, cardiac atrophy, orthostatic intolerance, reduced aerobic capacity, operational impacts of regular physical exercise, and space radiation are risks of space flight to the cardiovascular system identified in the 2007 NASA Human Integrated Research Program. An evidence-based(More)
High tolerance to progressive reductions in central blood volume has been associated with higher heart rate (HR), peripheral vascular resistance (PVR), sympathetic nerve activity (SNA), and vagally mediated cardiac baroreflex sensitivity (BRS). Using a database of 116 subjects classified as high tolerance to presyncopal-limited lower body negative pressure(More)
We tested the hypothesis that breathing through an inspiratory threshold device (ITD) during progressive central hypovolemia would protect cerebral perfusion and attenuate the reporting of presyncopal symptoms. Eight human subjects were exposed to lower-body negative pressure (LBNP) until the presence of symptoms while breathing through either an active ITD(More)
Twelve healthy men underwent measurement of their carotid-cardiac baroreflex response during varying conditions of vestibulo-oculomotor stimulation to test the hypothesis that vestibular and/or oculomotor stimulation associated with head movements in the yaw plane inhibit baroreflex control of heart rate. We assessed the carotid-cardiac baroreflex response(More)
We measured various hemodynamic responses and muscle sympathetic nerve activity (MSNA) in human subjects during a graded lower-body negative pressure (LBNP) protocol to test the hypotheses that: (1) reduced stroke volume (SV) is linearly related to increased MSNA; and (2) the onset of symptoms of impending cardiovascular collapse is associated with(More)
During 30 days (d) of bedrest, the practicality of using electromyostimulation (EMS) as a deterrent to atrophy and strength loss of lower limb musculature was examined. An EMS system was developed that provided variable but quantifiable levels of EMS, and measured torque. The dominant leg of three male subjects was stimulated twice daily in a 3-d on/1-d off(More)
The purpose of this study was to examine the effect of 30 d of 6 degrees headdown bedrest (BR) on the in vivo strength of skeletal muscle. Peak angle specific (0.78 rad below horizontal) torque of the knee extensor (KE) and flexor (KF) muscle groups of both limbs was assessed during unilateral efforts at four speeds (0.52, 1.74, 2.97 and 4.19 rad.s-1)(More)
Medics and first responders to emergencies are often faced with monitoring and assessing victims with very limited resources. Therefore, there is an inherent need for a real-time ambulatory monitoring capability that is portable and low power. This is particularly important for physiological monitoring of life-threatening conditions such as internal(More)
Hemorrhage remains a major cause of mortality following traumatic injury in both military and civilian settings. Lower body negative pressure (LBNP) has been used as an experimental model to study the compensatory phase of hemorrhage in conscious humans, as it elicits central hypovolemia like that induced by hemorrhage. One physiological compensatory(More)