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Effect of Microgravity on the Peripheral Subcutaneous Veno-Arteriolar Reflex in Humans

Effect of Microgravity on the Peripheral Subcutaneous Veno-Arteriolar Reflex in Humans. Principal Investigator: Anders Gabrielsen, M.D. Danish Aerospace Medical Center of Research Co-Investigator: Peter Norsk, M.D., D.M.Sc. Local vascular reflexes in lower leg. On ground.

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Effect of Microgravity on the Peripheral Subcutaneous Veno-Arteriolar Reflex in Humans

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  1. Effect of Microgravity on the Peripheral Subcutaneous Veno-Arteriolar Reflex in Humans Principal Investigator: Anders Gabrielsen, M.D. Danish Aerospace Medical Center of Research Co-Investigator: Peter Norsk, M.D., D.M.Sc.

  2. Local vascular reflexes in lower leg

  3. On ground Vasoconstriction: Blood flow Gravity Flow detector

  4. In space No gravitational stress No vasoconstriction

  5. After flight Vasoconstriction ? Gravity Flow detector

  6. Background • Astronauts might faint after spaceflight (orthostatic intolerance) • Several mechanisms might account for this: • - Low blood volume. • - Weak pressure reflexes. • - Attenuated muscle strength. • - Increased distensibility of veins (compliance). • - Weak local vascular reflexes?

  7. Hypothesis The local vascular reflexes in the lower leg are attenuated after spaceflight.

  8. Purpose of experiment • 1. To measure: • arm blood pressure and • blood flow under the skin (subcutaneous tissue) in the lower leg before and after spaceflight. 2. Local vascular resistance is calculated by blood pressure/flow.

  9. Possible Risks or Discomforts • Subcutaneous injection: Minimal risk • - Some pain and discomfort during needle insertion. • - Possibility of infection. Aseptic technique and sterile disposable equipment will minimize this possibility.

  10. Possible Risks or Discomforts • Radioactive Isotope Injection (133Xe; inert gas in sterile isotonic saline solution): Minimal Risk • - 80 µCi in 0.2 ml saline. • - No evidence of effects on normal physiology.

  11. Experimental Flow • Preflight • L-TBD: Flexible • Supine: • - Leg horizontal 7 min • - Lower leg down 7 min • Leg horizontal 7 min • Blood pressure • Blood flow in the leg • Postflight • R+0 • Supine: • - Leg horizontal 7 min • - Lower leg down 7 min • Leg horizontal 7 min • Blood pressure • Blood flow in the leg

  12. Sessions – Pre/Postflight Injection of tracer

  13. Sessions – Pre/Postflight 7 min 7 min 7 min

  14. Crew Requirements For Each Study Day (L-X (TBD) and R+0): • No physical exercise on study day • before experiment. • Notes on orthostatic feelings (postflight). • Crew time: 1 hr.

  15. Experimental Success • Accurate blood flow detection in • totally resting leg. • Postflight measurements as early • as possible.

  16. Experimental Benefits • Understanding mechanisms of postflight fainting. • Understanding local vascular reflexes (basic physiology). • Correlations to disease (e.g. heart failure).

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