A change in vision is the number one health risk for astronauts who spend
extended periods of time on the International Space Station.
This vision deterioration in astronauts is
likely due to the lack of a day-night cycle in intracranial pressure.
But using a vacuum device to lower pressure for part of each day might
prevent the problem, UT Southwestern Medical Center researchers said.
Their study appears in the Journal of Physiology
‘Vision problems in astronauts who spend a long time in space can be prevented by using a vacuum device to lower pressure for part of each day.’
research showed that intracranial pressure in zero-gravity conditions,
such as exists in space, is higher than when people are standing or
sitting on Earth, but lower than when people are sleeping on Earth. The
researcher's finding suggests that the constancy of pressure on the back
of the eye causes the vision problems astronauts experience over time.
To study how zero-gravity conditions affect intracranial pressure,
UT Southwestern researchers recruited volunteer patients who had had a
port (called an Ommaya reservoir) permanently placed in their head as
part of treatment for cancer. The ports provided a way for researchers
to measure intracranial pressure.
NASA flights then flew the eight
volunteers one by one on steep up-and-down maneuvers (parabolic flights)
that created 20-second intervals of weightlessness. The researchers
measured intracranial pressure during the zero-gravity intervals and
compared these with intracranial pressure during standard times of
sitting, lying face upward (supine), and lying with head inclined
"These challenging experiments were among the most ambitious human
studies ever attempted as part of the Flight Operations parabolic flight
program, and changed the way we think about the effect of gravity - and
its absence - on pressure inside the brain," said senior author Dr.
Benjamin Levine, Professor of Internal Medicine at UT Southwestern
Medical Center and Director of the Institute for Exercise and
Environmental Medicine (IEEM), jointly run by UT Southwestern and Texas
"The information from these studies is already leading to novel
partnerships with companies to develop tools to simulate the upright
posture in space while astronauts sleep, thereby normalizing the
circadian variability in intracranial pressure, and hopefully
eliminating the remodeling behind the eye," said Dr. Levine, who holds
the Distinguished Professorship in Exercise Sciences.
The researchers have continued studying whether it is possible to
lower intracranial pressure by means of a vacuum device that pulls blood
away from the head. They previously showed that a negative pressure box
that snuggly fits the lower body can lower intracranial pressure when
applied for 20-minute periods. They will soon be testing the effect of
the lower body negative pressure device on eye remodeling when negative
pressure is applied for eight-hour periods.
"Astronauts are basically supine the entire time they are in space.
The idea is that the astronauts would wear negative pressure clothing or
a negative pressure device while they sleep, creating lower
intracranial pressure for part of each 24 hours," said first author Dr.
Justin Lawley, Instructor in Internal Medicine at UT Southwestern and a
researcher at the IEEM.
The negative pressure device research was also used with patients with Ommaya ports.
"We are extremely grateful to these brave men and women from around
the country who volunteered to let us make these critical measurements
on them during parabolic flight. They have been through a lot of medical
procedures in their lives, and were nonetheless extremely altruistic,
desiring to give something back to medical science," Dr. Levine said of
the cancer patient volunteers.