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INTRODUCTION Bed rest is a valuable ground-based model for many of the physiological changes that are associated with spaceflight. Nutritional changes during and after 60 or 90 d of head-down bed rest were evaluated. METHODS A total of 13 subjects (8 men, 5 women; ages 26-54 yr) participated in either 60 or 90 d of bed rest. Blood and urine were collected(More)
We studied the relationship between aortic baroreceptor function and aortic wall properties in normotensive (NTR) and spontaneously hypertensive (SHR) rats 10-20 weeks old. Baroreceptor discharge, static pressure-volume (P-V), and pressure-radius relationships were measured in excised aortic segments. Histological studies of wall thickness and receptor(More)
The ultrastructure of fibres and sensory terminals of the aortic nerve innervating the aorta between the left common carotid and left subclavian arteries was investigated in the rat. This is the region from which most baroreceptor responses are recorded electrophysiologically. The fibres of the aortic nerve enter the adventitia and separate into bundles(More)
Biochemical variables in blood were measured in venous blood samples from 38 to 72 Space Shuttle astronauts before and immediately after flights of 2 to 11 days. Mean pre- and postflight values were compared using the paired t-test or the Wilcoxon signed-rank test. The largest change in serum enzymes was a 21% increase (P = .0014) in(More)
The fluid and electrolyte regulation experiment with seven subjects was designed to describe body fluid, renal, and fluid regulatory hormone responses during the Spacelab Life Sciences-1 (9 days) and -2 (14 days) missions. Total body water did not change significantly. Plasma volume (PV; P < 0.05) and extracellular fluid volume (ECFV; P < 0.10) decreased 21(More)
The three-dimensional branching pattern and ultrastructure of afferent myelinated fibers and their terminals located in the trachealis muscle of the dog are described. The afferent endings are believed to be those of the slowly adapting stretch receptors of the trachea. They have structural features typical of mechanoreceptors: distal to the loss of myelin,(More)
The adventitia of the rat aortic arch, with the depressor nerve intact, was separated from the underlying media to obtain a preparation in which the direct effects of norepinephrine on baroreceptor discharge could be examined free of smooth muscle effects. Cyclic stretch was applied to the adventitia to evoke discharge in single aortic baroreceptor fibers.(More)
Despite a number of difficulties in performing experiments during weightlessness, a great deal of information has been obtained concerning the effects of spaceflight on the regulation of body fluid and electrolytes. Many paradoxes and questions remain, however. Although body mass, extracellular fluid volume, and plasma volume are reduced during spaceflight(More)
Study of metabolic alterations that occur during space flight can provide insight into mechanisms of physiologic regulation. Results of medical experiments with astronauts reveal rapid loss of volume (2 L) from the legs and a transient early increase in left ventricular volume index. These findings indicate that, during space flight, fluid is redistributed(More)