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The Effect of Gravity and Upright Posture on Circulation

  • Branko Furst
Chapter

Abstract

Adaptation to gravity is an essential requirement for life on earth and plays a fundamental role in structuring musculoskeletal support and in the organizing of bodily fluids. About 60% of muscle mass is dedicated to opposing gravity. Moving blood possesses a significant momentum, and a change in posture requires a separate set of adaptive responses for its optimal distribution. Unlike the quadrupeds whose long bodily axis is parallel with the ground, humans spend over two thirds of their lives in the upright or sitting position in line with the gravitational pull. To counteract the effect of gravity, humans and tall vertebrates have developed a host of short-term neuronal and long-term humoral adjustments which correct and maintain a steady mean arterial pressure during change in posture or sudden acceleration. The aim of this chapter is first to examine the physiologic circulatory response to upright posture and the levels of organization responsible for its maintenance. The controversial issue of the siphon effect on perfusion of the brain is discussed in the context of environmental adaptations. Next, the salient features of cerebral blood supply and the dependence of brain function on buoyancy are examined. Human exposure to microgravity removes hydrostatic gradients and causes a headward shift of blood and extracellular body fluids. Microgravity experiments suggest the existence of body’s own “buoyancy field” (upthrust) generated by total body water (60% of total body weight) which bathes the water-free elements consisting of connective tissue, fat, tendons, and bone matrix. This buoyancy vector is parallel with the long axis of the body and works in opposition to gravitational loading. The heart is positioned at the fulcrum between the forces of gravity and levity (buoyancy).

Keywords

Upright posture Gravity Levity Venous valves Hydrostatic column Baroreceptors Medullary cardiovascular center Vestibulo-sympathetic reflex Vascular siphon Brain perfusion in giraffe Cerebral autoregulation Blood–brain barrier Archimedes principle Intracranial pressure curve Cerebrospinal fluid Choroid plexus Negative intracranial pressure Circulation in microgravity Visual impairment intracranial pressure syndrome Prolonged bed rest 

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Copyright information

© Springer Nature Switzerland AG 2020

Authors and Affiliations

  • Branko Furst
    • 1
  1. 1.Professor of AnesthesiologyAlbany Medical CollegeAlbanyUSA

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