Vasopressin and blood pressure in humans.
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Adult↗
Biomedical subjects
A Diedrich
Publications and source records attributed to A Diedrich.
Orthostatic intolerance: emerging genetic and environmental etiologies.
Orthostatic intolerance (OI) is common after space flight and resembles the disabling idiopathic orthostatic intolerance commonly observed in otherwise healthy young individuals. OI can arise from reduced sympathetic nervous system activity and, paradoxically, also from increased sympathetic nervous system activity. Patients with early manifestations of pure autonomic failure demonstrate an etiology based upon reduced sympathetic nervous system activity. Patients with hyperadrenergia demonstrate an etiology based on increased sympathetic nervous activity. For many years, we have recognized that the microgravity environment induces adaptation in the cardiovascular system and its autonomic control mechanisms that lead to the presence of OI on return to gravity. Understanding the nature of OI in astronauts returning from space as well as in the relevant patient population on earth has been a priority of Vanderbilt's Center for Space Physiology and Medicine in recent years. A major purpose of the autonomic experiment in the Neurolab mission was to identify whether the OI experienced by astronauts on return to earth was best explained by a hypoadrenergic or hyperadrenergic state. To address this question, we analyzed sympathetic nervous system activity inflight by 1) measurement of plasma catecholamines; 2) assessment of peroneal microneurographic sympathetic nerve traffic; and 3) assessment of norepinephrine spillover and clearance during infusion of tritiated norepinephrine. These studies documented a slight (five bursts per minute) increase in muscle sympathetic nerve activity, a 200 pg/ml increase in plasma norepinephrine level, and a 350 ng/min increase in norepinephrine clearance. Plasma norepinephrine and norepinephrine spillover and clearance were also raised on recovery day. These data indicate that enhanced sympathetic activation, rather than reduced sympathetic activation, accompanies the orthostatic intolerance following microgravity.
Autonomic Nervous System Diseases↗
[Long-term monitoring of psychophysiologic values in flight physiology].
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Aircraft↗
Forehead skin microcirculation during tilt table testing and lower body negative pressure.
Noninvasive skin microcirculation measurements based on a new Near Infrared sensor technique (NIR/Fa. Silicon Sensor GmbH; Berlin) were embeded in a tilt table experiment for simulation of acute effects of weightlessness (HDT -6 degrees) and active standing with the Russian Tschibis-LBNP device. The phenomenon of orthostatic intolerance depends on complex interactions among functional characteristics of central and peripheral cardiovascular control. The purpose of this study was to assess the blood volume and flow motion changes as well as pulsatile spectral pattern during orthostatic and antiorthostatic stress.
Adult↗
Heart rate variability during head down tilt and lower body negative pressure in the Russian Tschibis.
The cardiovascular function in space seems to be normal. However, abnormalities of cardiovascular responses have been found during lower body negative pressure suction in space. The etiology of the cardiovascular deconditioning in space is still unknown. A previous study showed, that short periods of head down tilt (HDT-6 degrees) induce changes in the spectral pattern of heart rate variabilty (HRV) and an increase in the sympathethic activation caused by orthostatic stress. The aim of this study was to test following hypotheses: 1. The dynamic of heart rate variability is different in the head down tilt and supine positions. 2. The application of lower body negative pressure (LBNP) during head down tilt induces similar heart rate variability patterns like the standing position. 3. After short term head down tilt the cardiovascular response to lower body negative pressure stressor is altered.
Adult↗
Acute effects of simulated microgravity on heart rate variability.
Microgravity is known to stress the heart and blood vessels and to perturb the normal neural regulation of the cardiovascular system. In an effort to gain greater insight into the adjustments of neural control of the cardiovascular system in space, we have used a model of simulated microgravity, the -6 degrees head-down tilt body position (HDT). As a common method for the description of the functional state of the cardiovascular system the power spectral analysis of the heart rate can be used. The following working hypotheses were postulated: 1. HDT causes an acute activation of the parasympathetic nerve traffic to the heart, which is detectable by a reduction in heart rate and by the spectral power distribution of the heart rate variability. 2. HDT induces changes in the autonomic nervous response to upright posture which can be detected after a 45-minute period of head-down tilt.
Adult↗