Arterial Remodeling and Functional Adaptations
Understanding How Space Travel Affects Blood Vessels
Ever rise quickly from the couch to get something from the kitchen and suddenly
feel dizzy? With a low heart rate and relaxed muscles, the cardiovascular system
does not immediately provide the resistance necessary to keep enough blood going
to your head. Gravity wins, at least for a short time, before your heart and blood
vessels can respond to the sudden change in position and correct the situation.
 
 
These figures show feed arteries and first-order arterioles
from control rats and from rats that have experienced simulated microgravity.
After flight, the small blood vessels in hindlimb skeletal muscles that provide
blood pressure resistance will be analyzed for their responses to chemical signals
and pressure changes, and for changes in vessel structure and gene expression.
A - Feed Artery/Control, B - Feed Artery/Simulated Microgravity,
C - First-order arterioles/Control, D - First-order arterioles/Simulated
Microgravity. Photo credit - Delp
Actually, the human cardiovascular system is quite well adapted to the constant
gravitational force of the Earth. When standing, vessels in the legs constrict
to prevent blood from collecting in the lower extremities. In the space environment,
the usual head-to-foot blood pressure and tissue fluid gradients that exist during
the upright posture on Earth are removed. 
The subsequent shift in fluids from the lower to the upper portions of the
body triggers adaptations within the cardiovascular system to accommodate the
new pressure and fluid gradients. In animal models that simulate microgravity,
the vessels in the head become more robust while those in the lower limbs become
thin and lax. Similar changes may also occur in humans during spaceflight and
while these adaptations are appropriate for a microgravity environment, they can
cause problems when the astronauts return to Earth or perhaps another planet.
Astronauts often develop orthostatic intolerance which means they become dizzy
or faint when standing upright.
This dizziness can persist for a number of days making routine activities difficult.
In an effort to understand the physiological details of these cardiovascular adaptations,
Dr. Michael Delp at Texas A&M University, uses the rat as a model for his
studies. For the experiment flown on STS–107, he will test the hypothesis
that blood vessels in the rats’ hindlimbs become thinner, weaker, and constrict
less in response to pressure changes and to chemical signals when exposed to microgravity.
In addition, he will test the hypothesis that arteries in the brain become thicker
as a result of microgravity-induced fluid shifts toward the head.
Background Information
From previous studies using models that simulate microgravity, it is now evident
that the shift of fluid toward the head and the unloading of postural muscles
together alter the mechanical forces exerted on arteries, the vessels responsible
for regulating blood flow and arterial blood pressure. The purpose of the present
study is to determine whether the fluid shifts and muscle unloading that occur
in actual microgravity, similarly alter rodent arterial vessel structure and function.
Earth Benefits and Applications
This experiment will contribute toward attaining a better understanding of
how fundamental biological systems, such as the cardiovascular system, respond
to the microgravity environment.The detailed study of the resulting vascular adaptations
triggered by microgravity will yield essential information on the basic physiological
responses of individual blood vessels involved in blood flow and pressure regulation.
This information will also support the development of treatments or countermeasures
to improve crew health and performance following their return to a gravitational
environment.
Science Discipline Supported
This experiment supports NASA’s priorities for research aimed at understanding
fundamental biological processes in which gravity is known to play a direct role
and alleviating problems that may limit astronauts’ ability to survive and/or
function during prolonged spaceflight.
This experiment will address the effects of microgravity on vascular smooth
muscle and vascular endothelial cell function and structure in resistance arteries
and arterioles isolated from skeletal muscle and the brain. Three groups of rats
will be studied. These will consist of 8 rats flown in microgravity, 8 rats from
a ground-based vivarium cage control group, and 8 rats from a ground-based AEM
control group. Resistance arteries or arterioles will be isolated and used for
physiology experiments, in gene expression studies, and structural analyses. This
work will provide potentially important information about the mechanisms underlying
the orthostatic intolerance experienced by astronauts returning to Earth.
Above: A cross section of the basilar artery
from the brain of a control rat (A) and a rat that experienced simulated microgravity
(B). Photo credit - Delp
Hardware
The Animal Enclosure Module (AEM) is a rodent habitat that provides ventilation,
continuous filtered air flow to control waste and odor, timed lighting, food in
the form of foodbars attached to the side of the cage, and a water supply which
can be refilled as required. Rodents in the cage compartment of the AEM are not
accessible but can be viewed through the clear lexan cover. This also allows for
viewing of water level remaining in the AEM water box.
The AEM has been designed for minimum crew interaction and the animals adapt
very well to this virtually self-contained system. The only nominal operations
required are a daily hardware check, a daily visual animal health check, and periodic
water refills.
Above: This experiment is part of the Fundamental Rodent
Experiments Supporting Health (FRESH)-02 payload which consists of 13 rats housed
in 3 AEMs. The animals, which will be shared among several different investigators,
will experience microgravity for 16 days on board the Shuttle Columbia. The AEMs
have been used successfully on many previous shuttle flights. Photo credit - Ames
Research Center
Principal Investigator: Dr. Michael Delp,
Texas A&M University, College Station, TX
Project Scientist: Marilyn Vasques,
NASA Ames Research Center, Mountain View, CA
Project Manager: Rudy Aquilina,
NASA Ames Research Center, Mountain View, CA
Visit Arterial Remodeling
for a printable PDF version of this research.
Visit http://spaceresearch.nasa.gov/sts-107/overview.html
to learn more about the other OBPR investigations flying on STS-107.
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