Influence of long-term head-down body position on innervation density in extremity blood vessels

The aim of the present study was to quantitate and compare the density of nerve terminals (NTD), as well as of their synaptic vesicle population (SyVD) in saphenous and brachial vein and artery, obtained from rats maintained in the horizontal or head-down tilted (HDT) position for two weeks. The same technique was applied as that for the head-up tilt study.     

Quantitative analysis of the density and pattern of adrenergic innervation of blood vessels

Summary Automated quantitative image analysis (QIAF) was used to measure and compare the adrenergic nerve plexuses of 4 blood vessels from the guinea pig, demonstrated by glyoxylic acid fluorescence (GAF). The results showed considerable quantitative variation of plexus density, size of bundles, and numbers of varicosities. A range of alternative procedural and anatomical sources of variability were investigated and assessed. The carotid artery was found to have a dense plexus with more nerves than that of the mesenteric artery; the mesenteric vein and abdominal aorta had sparse plexuses. The carotid artery plexus, despite the density of its nerves, possessed only half the number of varicosities of the mesenteric artery plexus. This sparse varicosity population was shown to have a similar density to the varicosities demonstrated by QIAF in the scattered nerves of the mesenteric vein and abdominal aorta. QIAF confirmed visual estimates of adrenergic plexus density, and was able to demonstrate less obvious differences of nerve density and size, and varicosity populations, between the different plexuses studied. The method is applicable to stretch preparations and transverse sections of many adrenergically innervated tissues.     

Adrenergic innervation of the umbilical vessels

Summary The intra- and extrafetal portions of the umbilical vessels in the guinea-pig and the umbilical cord of man, mouse and rabbit have been investigated by means of the Falck-Hillarp method for the fluorescence microscopical demonstration of catecholamines.The umbilical cord was found to be devoid of nerves in all species investigated. Adrenergic nerves are present only in the immediate vicinity of the umbilicus.The intrafetal portions of the umbilical artery and umbilical vein receive adrenergic nerves, the distribution pattern of which is different for each vessel. In the guinea-pig the ductus venosus is an intrahepatic branch of the vena umbilicalis. No adrenergically innervated sphincter has been detected in the initial segment of the ductus venosus. Regional variations in the pattern of innervation of the intrafetal portion of the umbilical vein are paralleled by regional differences in the construction pattern of the vessel's wall. Regional differences in the noradrenaline concentration (measured by fluorometry) which correspond to the fluorescence microscopical findings have been detected in umbilical vessels: low noradrenaline content of the umbilical cord, high concentrations in the intrafetal sections of the umbilical vessels. The noradrenaline concentration of the guinea-pig umbilical artery is three times that of the umbilical vein.Supported by the Joachim Jungius-Gesellschaft der Wissenschaften, Hamburg.For continuous advice and constructive criticism I am indebted to Prof. Dr. Dr. E. Horstmann.     

Influence of adaptation to horizontal body position on pointing errors and visual estimation of a target position in humans

The central program of a targeted movement includes a component intended for to compensate for the weight of the arm; this is why the accuracy of pointing to a memorized position of the visual target in darkness depends on orientation of the moving limb in relation to the vertical axis. Transition from the vertical to the horizontal body position is accompanied by a shift of the final hand position along the body axis towards the head. We studied how pointing errors and visual localization of the target are modified due to adaptation to the horizontal body position; targeted movements to a real target were repeatedly performed during the adaptation period. Three types of experiments were performed: a basic experiment, and two different experiments with adaptation realized under somewhat dissimilar conditions. In the course of the first adaptation experiment, subjects received no visual information on the hand’s position in space, and targeted movements of the arm to a luminous target could be corrected using proprioceptive information only. With such a paradigm, the accuracy of pointing to memorized visual targets showed no adaptation-related changes. In the second adaptation experiment, subjects were allowed to continuously view a marker (a light-emitting diode taped to the fingertip). After such adaptation practice, the accuracy of pointing movements to memorized targets increased: both constant and variational errors, as well as both components of constant error (i.e.,X andY errors) significantly dropped. Testing the accuracy of visual localization of the targets by visual/verbal adjustment, performed after this adaptation experiment, showed that the pattern of errors did not change compared with that in the basic experiment. Therefore, we can conclude that sensorimotor adaptation to the horizontal position develops much more successfully when the subject obtains visual information about the working point position; such adaptation is not related to modifications in the system of visual localization of the target.     

Influence of body position on pulmonary diffusing capacity in yound and old men.

Steady-state diffusing capacity (DLCOSS2), studied in healthy nonsmokers, was significantly higher in five old men when seated than when supine, but was unchanged in five young men. However, "corrected" for the increased ventilation, it decreased in the young--but not in the old--when erect compared with when supine. The change of DLCOSS2 in the young during the first 20 min when seated was related to a change of the fractional dead space ventilation (VD/VT)mThe old showed less venous admixture when seated than when supine, whereas VD/VT and regional ventilation-perfusion index of the lung bases was the same in both positions. The decrease in venous admixture was probably due to the closing capacity (CC) being less than the functional residual capacity (FRC) when seated. The elimination of closed off regions when seated made more pulmonary capillaries available for diffusion.     

Influence of body position on the urinary output of adrenaline and noradrenaline]

In normal subjects in basal conditions, urinary excretion of noradrenaline is directly related to the hydrostatic pressure changes induced by the body posture in the dependant parts of the venous system. Adrenaline elimination is no influenced by these factors.     

Adrenergic innervation of human mesenteric blood vessels.

A fluorescent histochemical technique has been applied to study the adrenergic innervation of human superior mesenteric arteries obtained at autopsy. Specific catecholamine fluorescence was demonstrated in the smaller branches of this artery taken from three infants and one child. No specific fluorescence was seen in arteries from three adult subjects.     

Influence of body position on cortical pain-related somatosensory processing: an ERP study

Background

Despite the consistent information available on the physiological changes induced by head down bed rest, a condition which simulates space microgravity, our knowledge on the possible perceptual-cortical alterations is still poor. The present study investigated the effects of 2-h head-down bed rest on subjective and cortical responses elicited by electrical, pain-related somatosensory stimulation.

Methodology/Principal Findings

Twenty male subjects were randomly assigned to two groups, head-down bed rest (BR) or sitting control condition. Starting from individual electrical thresholds, Somatosensory Evoked Potentials were elicited by electrical stimuli administered randomly to the left wrist and divided into four conditions: control painless condition, electrical pain threshold, 30% above pain threshold, 30% below pain threshold. Subjective pain ratings collected during the EEG session showed significantly reduced pain perception in BR compared to Control group. Statistical analysis on four electrode clusters and sLORETA source analysis revealed, in sitting controls, a P1 component (40–50 ms) in the right somatosensory cortex, whereas it was bilateral and differently located in BR group. Controls'' N1 (80–90 ms) had widespread right hemisphere activation, involving also anterior cingulate, whereas BR group showed primary somatosensory cortex activation. The P2 (190–220 ms) was larger in left-central locations of Controls compared with BR group.

Conclusions/Significance

Head-down bed rest was associated to an overall decrease of pain sensitivity and an altered pain network also outside the primary somatosensory cortex. Results have implications not only for astronauts'' health and spaceflight risks, but also for the clinical aspects of pain detection in bedridden patients at risk of fatal undetected complications.