Dry immersion, which is a ground-based model of prolonged conditions of microgravity, is widely used in Russia but is less well known elsewhere. Dry immersion involves immersing the subject in thermoneutral water covered with an elastic waterproof fabric. As a result, the immersed subject, who is freely suspended in the water mass, remains dry. For a relatively short duration, the model can faithfully reproduce most physiological effects of actual microgravity, including centralization of body fluids, support unloading, and hypokinesia. Unlike bed rest, dry immersion provides a unique opportunity to study the physiological effects of the lack of a supporting structure for the body (a phenomenon we call 'supportlessness'). In this review, we attempt to provide a detailed description of dry immersion. The main sections of the paper discuss the changes induced by long-term dry immersion in the neuromuscular and sensorimotor systems, fluid-electrolyte regulation, the cardiovascular system, metabolism, blood and immunity, respiration, and thermoregulation. The long-term effects of dry immersion are compared with those of bed rest and actual space flight. The actual and potential uses of dry immersion are discussed in the context of fundamental studies and applications for medical support during space flight and terrestrial health care.

A sedentary lifestyle has adverse effects on the cardiovascular system, including impaired endothelial functions. Subjecting healthy men to 7 days of dry immersion (DI) presented a unique opportunity to analyze the specific effects of enhanced inactivity on the endothelium. We investigated endothelial properties before, during, and after 7 days of DI involving eight subjects. Microcirculatory functions were assessed with laser Doppler in the skin of the calf. We studied basal blood flow and endotheliumdependent and -independent vasodilation. We also measured plasma levels of microparticles, a sign of cellular dysfunction, and soluble endothelial factors, reflecting the endothelial state. Basal flow and endothelium-dependent vasodilation were reduced by DI (22 Ϯ 4 vs. 15 Ϯ 2 arbitrary units and 29 Ϯ 6% vs. 12 Ϯ 6%, respectively, P Ͻ 0.05), and this was accompanied by an increase in circulating endothelial microparticles (EMPs), which was significant on day 3 (42 Ϯ 8 vs. 65 Ϯ 10 EMPs/l, P Ͻ 0.05), whereas microparticles from other cell origins remained unchanged. Plasma soluble VEGF decreased significantly during DI, whereas VEGF receptor 1 and soluble CD62E were unchanged, indicating that the increase in EMPs was associated with a change in antiapoptotic tone rather than endothelial activation. Our study showed that extreme physical inactivity in humans induced by 7 days of DI causes microvascular impairment with a disturbance of endothelial functions, associated with a selective increase in EMPs. Microcirculatory endothelial dysfunction might contribute to cardiovascular deconditioning as well as to hypodynamia-associated pathologies. In conclusion, the endothelium should be the focus of special care in situations of acute limitation of physical activity. dry immersion; weightlessness; microcirculation; endothelial dysfunction; soluble endothelial markers THE VASCULAR ENDOTHELIUM is a key element in the control of local blood flow (12,46). It is now widely recognized that alterations of endothelial integrity and physiological functions represent pivotal mechanisms in the initiation and development of vascular diseases. A decrease in endothelial vasomotor function (endothelium-dependent vasodilation), which correlates with a risk of cardiovascular events, has been demonstrated in patients with atherosclerosis, hypertension, and peripheral vascular diseases (49). Physical inactivity and a sedentary lifestyle are known to cause cardiovascular deconditioning and increase the risk of cardiovascular disease (5). Endothelial dysfunction seems to be intimately linked to this deconditioning. A chronic decrease in shear stress forces during physical inactivity, especially significant in small vessels of the microcirculatory bed (8), may impair endothelial functions.Experimental physical inactivity of varying duration and intensity in healthy humans can be achieved through confinement (altitude chambers), partial immobilization, bedrest, and "dry" water immersion (33, 34). Dry immersion (DI) induces extreme physical inac...

A new method for the activation of spinal locomotor networks (SLN) in humans by transcutane ous electrical spinal cord stimulation (tESCS) has been described. The tESCS applied in the region of the T11-T12 vertebrae with a frequency of 5-40 Hz elicited involuntary step like movements in healthy subjects with their legs suspended in a gravity neutral position. The amplitude of evoked step like movements increased with increasing tESCS frequency. The frequency of evoked step like movements did not depend on the frequency of tESCS. It was shown that the hip, knee, and ankle joints were involved in the evoked move ments. It has been suggested that tESCS activates the SPG (SLN) through in part, via the dorsal roots that enter the spinal cord. tESCS can be used as a noninvasive method in rehabilitation of spinal pathology.

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