During the 1973-74 Skylab missions, when crews stayed in space up to 84 days, many astronauts experienced ”the beanpole effect.”
In one extreme case, an astronaut gained two inches in height while losing four inches around his stomach and buttocks. Another began the mission noticeably shorter than his wife, and returned to Earth taller.
After a hiatus of 17 years, the American space program has resumed an intensive effort to understand the changes that occur when the human body enters the near-zero gravity of space. The mission of the space shuttle Columbia, which roared into orbit Wednesday, is the vehicle.
Its ultimate objective is to pave the way for future flights-Mars, extended stays in a permanent space station and other missions that would require astronauts to stay in space for months or years.
The National Aeronautics and Space Administration has given Columbia an unusual ”crew” for the nine-day flight, the first space shuttle mission devoted to biomedical research. There are seven astronauts (including three physicians and a cell biologist), 2,478 jellyfish and 29 rats. They will work in Spacelab, a module the size of a small bus secured inside the shuttle`s payload bay.
A few hours after launch Wednesday, the astronauts began collecting urine and blood samples and taking blood pressure readings. They also turned on specimen incubators and other equipment in the laboratory module, and assembled a bicycle exercise machine that they will use.
Some of Spacelab`s 18 life sciences experiments have been performed individually on previous shuttle flights. But they never have they been performed on four different astronauts in an integrated fashion that would indicate how the body coordinates its response to space flight.
Other experiments are being conducted for the first time in space. One of those involves Dr. Francis Gaffney, a cardiologist.
Before blast-off, a physician opened a vein in the crook of Gaffney`s right arm. He then threaded a catheter-a thin, soft plastic tube-through the vein to a few inches from Gaffney`s heart.
At the catheter`s tip is a probe that measures central venous pressure, the driving force in blood pressure. The system is attached to monitors that measure and record these critical blood pressure changes.
The system operates during blast-off, when astronauts experience enormous gravitational forces, and for the first 24 hours of the mission.
During this period the cardiovascular system changes its mode of operation, making critical adaptations to weightlessness.
Blood pressure in the arteries rises, the body eliminates fluids and salts, and other changes occur.
Weightlessness also contributes to the ”beanpole effect,” decreasing abdominal girth. Astronauts gain in height because weightlessness decreases pressure on the intervertebral discs, which separate and cushion bones of the spine. The discs expand, but they return to normal size once astronauts are back on Earth.
Although the fluid shifts and related changes apparently do not impair astronauts` health or ability to perform, they do cause problems upon return to Earth and normal gravitational pull.
When a person stands on Earth, blood tends to pool in the lower part of the body. The cardiovascular system normally adapts quickly, and blood pressure remains constant.
But the system has difficulty after a space flight. Standing causes the heart to beat rapidly. Blood pressure falls, sometimes resulting in fainting. The system usually returns to normal within a few days after landing.
NASA says the mechanisms involved in the fluid shifts and other changes have never been identified. Likewise, there is little information about how cardiovascular system function might be affected by lengthy space flights.
Spacelab is the first of three shuttle life sciences flights, scheduled for completion by 1996. The flights are expected to substantially advance scientific knowledge about space medicine.
Knowledge about the physiological effects of low gravity has improved greatly since the 1950s, when some people feared space might harbor dangerous organisms or turn astronauts into monster-like mutants.
The shuttle mission also hopes to resolve what many experts regard as the single most serious problem: space motion sickness.
NASA says that it has affected about 50 percent of all American astronauts. Symptoms include extremely unpleasant stomach discomfort, pallor, cold sweats, nausea and vomiting that can incapacitate an astronaut.
The symptoms tend to disappear after a few days in orbit. But officials are concerned that space motion sickness could prevent a crew from performing critical duties shortly after reaching orbit. These include deploying military reconnaissance satellites.
Human beings rely on several mechanisms to orient their bodies. Nerves constantly perceive gravity as muscles contract and relax. The eyes sense the body`s relationship to the environment.
Some of the most critical information comes from a collection of structures located in the inner ear. Known as the neurovestibular system, the mechanisms are extremely sensitive to gravity.
These include tiny organs called otoliths (literally, ”ear stones”)
that are made from calcite and look like a patch of white sand. As a person changes position, gravity pulls on the otoliths, bending tiny hairs and sending information to more than 20,000 nerve cells in the inner ear.
A constant stream of positioning data flows from the nerve cells to the brain, which senses the body`s relationship to other objects.
In space, however, gravity no longer pulls on the otoliths. Information sent to the brain from the inner ear and other sense organs conflicts with cues expected from past experience.
The result is disorientation and space sickness.
NASA put jellyfish and rats on Columbia`s crew as part of an effort to determine if weightlessness results in changes in the vestibular system.
Rats, like humans, have otoliths. After Columbia lands, scientists will compare otoliths from the space rats with those from a group of controls. Scientists suspect that changes in the body`s calcium levels that occur during space flight may result in otolith degeneration.
Jellyfish and other invertebrates also have gravity receptors, termed rhophalia, that help to maintain the animal`s proper orientation in water. Rhophalia contain statoliths that are similar to human otoliths.
Scientists will study how the microgravity of space affects the development and structure of jellyfish statoliths. They will compare the space jellyfish to a control group kept on Earth.
