NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Mechanism of Headward Fluid Shift During Exposure To MicrogravityA prominent feature of early cardiovascular adaptation to the microgravity of space flight is a shift of blood and tissue fluid from the lower body to the upper body. Symptoms of this fluid shift include facial edema, nasal congestion, and headache. Normally on Earth, the human body is exposed to hydrostatic (gravitational) blood pressure gradients during upright posture. In this posture, mean arterial pressures at head, heart, and foot levels are approximately 70, 100, and 200 mm Hg, respectively. Theoretically, all hydrostatic pressures within arteries and veins are lost during exposure to microgravity so that mean arterial pressure in all regions of the body is uniform and approximately equal to that at heart level (100 mm Hg). Acute studies of 60 head-down tilt (simulated microgravity on Earth) indicate that facial edema is caused by: 1) elevation of capillary blood pressure from 28 to 34 mm Hg, 2) reduction of blood colloid osmotic pressure 22 to 18 mm Hg, and 3) 50% increase of blood perfusion in tissues of the head. Furthermore, as compared to microvasculature in the feet, microvessels of the head have a low capacity to constrict and diminish local perfusion. Elevation of blood and tissue fluid pressures/flow in the head may also explain the higher headward bone density associated with long-term head-down tilt. These mechanistic studies of head-down tilt, along with a better understanding of the relative stresses involved with upright posture and lower body negative pressure, have facilitated development of physiologic countermeasures to maintain astronaut health during microgravity. Presently no exercise hardware is available to provide a blood pressure gradient from head to feet in space. However, recent studies in our laboratory suggest that treadmill exercise within lower body negative pressure provides equivalent or greater physiologic stress as compared to similar upright exercise on Earth.
Document ID
20010124103
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Hargens, Alan R.
(NASA Ames Research Center Moffett Field, CA United States)
Parazynski, Scott E.
(NASA Johnson Space Center Houston, TX United States)
Watenpaugh, Donald E.
(NASA Ames Research Center Moffett Field, CA United States)
Aratow, Michael
(NASA Ames Research Center Moffett Field, CA United States)
Murthy, Gita
(NASA Ames Research Center Moffett Field, CA United States)
Kawai, Yasuaki
(Tottori Univ. Japan)
Date Acquired
August 20, 2013
Publication Date
January 1, 1994
Subject Category
Aerospace Medicine
Meeting Information
Meeting: 2nd International Congress of Pathophysiology
Location: Kyoto
Country: Japan
Start Date: November 19, 1994
End Date: November 24, 1994
Funding Number(s)
PROJECT: RTOP 199-14-12-04
PROJECT: RTOP 199-26-12-38
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

Available Downloads

There are no available downloads for this record.
No Preview Available