title: [Hemodynamic shifts in humans under the conditions of prolonged microgravity and the role of hypovolemia].
abstract: Purpose of this work was to elicit the role of hypovolemia in the development of hemodynamic shifts and loss of orthostatic tolerance in humans during prolonged space flights (PSF). Correlation analysis of the data of in-flight ultrasonic investigations of hemodynamics in resting cosmonauts and bio-impedance measurements of body liquids in different periods during PSF pointed out that changes in the left ventricle filling and renal artery resistance (Rren) reflect the degree of hypovolemia with r = 0.95. The dependence of orthostatic tolerance on hypovolemia fell short of this ambiguity. Lower body negative pressure tests (LBNP) performed by 15 cosmonauts in different periods of PSF typically correlated with the body hydration status at r = 0.94; however, several cosmonauts showed a substantial loss of LBNP tolerance despite a moderate hypovolemia. Therefore, we may hypothesize that hypovolemia is a significant yet not the sole factor in orthostatic disorders. Deconditioning, altered control of hemodynamics, decreased vasoconstriction of arterial vessels and increased compliance of the leg veins have an important, in some cases decisive role in degradation of orthostatic tolerance.
authors: G A
authors: GA
authors: Fomina
authors: A R
authors: AR
authors: Kotovskaia
mesh_terms: D018480:Astronauts; D001810:Blood Volume; D004244:Dizziness; D018495:Fluid Shifts; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D020896:Hypovolemia / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D008150:Lower Body Negative Pressure; D012146:Rest; D013026:Space Flight; D013997:Time Factors; D014893:Weightlessness / Q000009:adverse effects