Fast Pace On Board Blurrolab

The intense pace of the mission, and the additional free time given up to care for the sick rodents - which meant most of the astronauts averaged three or four hours of sleep each night - had turned it into something of a blur for Linnehan. ''I started calling it 'Blurrolab', instead of 'Neurolab','' he said, ''because I just could never remember what day it was or where we were, we just kept on going.'' Nevertheless, despite the neonatal fatalities, the mission was shaping up to be a superb scientific success.

''We went into this mission facing a number of challenges,'' said Homick. ''We knew we had a difficult timeline to work with, we knew that we had a number of complex hardware systems . . . to acquire the data and we knew we were going to be implementing a number of very difficult experimental procedures using cutting-edge technologies. With all of that in mind, we did expect to achieve a great deal of success with this mission and I'm pleased to report that I think we've exceeded our expectations.''

Although the astronauts had averaged only a few hours of sleep each night during the rodent crisis, Dave Williams at least was able to sleep fitfully, which aided another of Neurolab's investigations: a series of comprehensive measurements of brainwaves, eye movement, respiration, heart rates, internal body temperatures and snoring while at rest. As well as helping to improve the performance of astronauts in space, such experiments were also expected to improve the sleep-wake cycles of people on Earth. ''We are really a sleep-deprived society,'' said Charles Czeisler of Harvard Medical School, ''in which people burn the candle at both ends.''

Not only does the hectic workload of astronauts affect their performance, but they also experience a 'sunrise' and 'sunset' during every 90-minute orbit of Earth and regularly take sleeping medication during missions. ''Twenty percent of the

Unusual 'fisheye' view of the cramped middeck. Rick Linnehan pokes his head through the airlock from the tunnel leading into Neurolab as Jim Pawelczyk (left) and Rick Searfoss (lower) enjoy off-duty time. An unidentified crew member (top) is floating through the hatch to the flight deck. Above and slightly to the right of Pawelczyk are the crew's sleep stations and on the far left are a row of storage lockers.

Unusual 'fisheye' view of the cramped middeck. Rick Linnehan pokes his head through the airlock from the tunnel leading into Neurolab as Jim Pawelczyk (left) and Rick Searfoss (lower) enjoy off-duty time. An unidentified crew member (top) is floating through the hatch to the flight deck. Above and slightly to the right of Pawelczyk are the crew's sleep stations and on the far left are a row of storage lockers.

crews on single-shift missions like this one take some sort of sleeping pill while they're in the space environment,'' said Czeisler. ''So they do have a problem. That's three to eight times the rate of the general population.'' During STS-90, Linnehan, Williams, Buckey and Pawelczyk also donned body suits and sensor-laden skullcaps before going to bed to monitor their sleep patterns.

''Over four or five days,'' continued Czeisler, ''if you lose two or three hours of sleep per night, it's the equivalent of losing a full night of sleep, and that causes a lot of detriments in our ability to perform effectively. It impairs the ability to consolidate short-term memory, causes a slowing of reaction time and it increases the probability of lapses of attention that may occur when you're carrying out a routine, highly over-learned task, such as on Earth driving a car. NASA is concerned about the potential impact of this cumulative sleep deprivation on mission safety and success.''

During the mission, although Williams admitted that his sleep had been reduced, he was nevertheless still able to rest adequately. He added, interestingly, that although he was weightless and had no 'pressure points' - such as a bed to lie on - ''I

still turn over in my sleep. I don't know why I do this, but it still happens.'' Referring to what was essentially a mini-sleep laboratory that he donned before bedtime, he felt its potential spinoffs on Earth could lead to patients doing studies of sleep phenomena at home, rather than in hospital.

Williams' inclusion on the STS-90 crew was fortuitous, as two of the medical experiments were Canadian. The Visuo-Motor Coordination Facility (VCF) studied changes in movement during weightlessness that affect astronauts' pointing and grasping abilities, while the Role of Visual Cues in Spatial Orientation - shortened to 'Visual Cues' - created 'fake gravity' by applying pressure to the soles of the feet to find out if it 'overrode' visual cues and allowed them to readapt to a terrestrial-type environment. This was expected to aid research into the causes and treatments for motion sickness.

Developed by the Canadian Space Agency, the VCF was a particularly interesting device that projected visual targets onto a screen; as these appeared, one of the science crew members grasped and pointed at them, and tracked them as they moved, using a special, instrumented glove. The motor skills thus demonstrated, at various stages throughout the 16-day mission, were used to record changes in the astronauts' nervous systems as they adapted to the microgravity environment. Other associated experiments on board Neurolab could, it was hoped, one day enable engineers to build advanced robots capable of performing incredibly intricate tasks.

Tasks such as catching a ball are second-nature to most of us, but to train a robot to do it involves sophisticated stereo vision, a powerful computer to calculate the

Jay Buckey 'wires up' Rick Linnehan with a special skullcap for a sleep study.

object's flight path, mass and estimate its time of arrival and, of course, position itself appropriately to capture it without causing damage. ''During the few hundred milliseconds when the ball first appears in the field-of-view of the subject, the brain apparently computes the velocity and acceleration of the ball and also, from its surface appearance and texture and volume, it infers a mass,'' said investigator Alain Berthoz.

''The third thing the brain does - which is what is of interest to us here - is that it applies an internal representation of the effect of gravity on such a mass and therefore predicts the effect of gravity.'' Berthoz's team was also intrigued by the question of how the brain computes the distance to the incoming ball, although some psychologists have speculated that our brain actually works out the time-to-impact based on how fast the ball's image on our retina changes as it gets closer. In humans, this is all learned at a very early age.

''Probably during the first year of life, the brain constructs these internal representations of the laws of mechanics - of Newtonian mechanics,'' said Berthoz. ''This is done not only for our limbs. The brain has to know not only the impact of the ball, but also it has to somehow know in advance the properties of our limbs. This apparently is done in the first year of life.'' To understand the motor-sensory processes that control these actions, Berthoz's team flew a spring-propelled ball on board Neurolab, which the astronauts - their arm, heads and bodies outfitted with sensors - were obliged to catch.

''The ball will go with a constant velocity; it will not be accelerated as it is on Earth,'' explained Berthoz. ''So the muscular contractions that the brains of the astronauts will produce, if they use the internal model of gravity, will be nonfunctional. Therefore, in flight, the brain has to recognise this very basic, fundamental prediction and organisation. That's the idea.'' Elsewhere, other experiments used a rotating chair, mounted in the centre aisle of the Spacelab module, to stimulate the astronauts' vestibular systems with spinning and tilting sensations.

Known as the Visual and Vestibular Integration System (WIS), the chair was expected to yield data on how the nervous system 'rewires' itself to account for the lack of'normal' gravity. Performed by each of the science crew members - Searfoss, Altman and Hire, as the orbiter crew, were exempt from the tests - the experiment was done six times during the 16-day mission. As each VVIS run started, the astronauts' eyes were shielded from external stimuli, giving their nervous systems no visual references, and a video camera was trained on their faces to capture their reactions to the spinning motion.

The orbiter crew did have a number of scientific tasks to perform, however. One of Hire's responsibilities was a device in the middeck known as the Bioreactor Demonstration Experiment (BDE) which, on STS-90, grew cultures of renal tissue and bone marrow. Both of these were widely anticipated to yield substances that might be of use for kidney disease, AIDS and other immune-system ailments, as well as for the chemotherapy treatment of cancer sufferers.

As well as proving somewhat dizzying, a few Neurolab investigations were potentially 'stinging' for the crew: one demonstrated an innovative technique known as 'microneurography', whereby a very fine needle - about the same size as an acupuncture needle - was inserted into a nerve just below the knee. This allowed nerve signals travelling from the brain to the blood vessels to be measured directly, while the crew's cardiovascular systems were monitored using the Lower Body Negative Pressure (LBNP) device. All of this data allowed investigators to carefully track how well the nervous system controlled cardiovascular function in the astronauts' bodies.

Results were expected to aid sufferers of autonomic blood pressure disorders, particularly 'orthostatic intolerance' - an inability to maintain proper blood pressure while standing for long periods. ''This is a multifaceted problem,'' said Pawelczyk, ''but it shares many features similar to those experienced by astronauts after flight. The experiments we'll be conducting really focus at the crux of the matter: how it is that nerve signals travel from the brain to blood vessels and cause the process called 'basal constriction'. Basal constriction, the narrowing of blood vessels in the lower body, has the effect of boosting pressure elsewhere in the system.

''The way to think of this is like thinking of a garden hose. If you want to get more pressure out of a garden hose, you can do one of two things. You can either turn up the faucet and increase the flow or you can put your thumb over the end of the hose and increase the pressure that way. That process of placing your thumb over the end of the hose is just like the process of basal constriction that occurs in vasculature. All our blood vessels are surrounded by muscle that's fed by 'sympathetic nerves'.

''What we'll actually be doing in flight is recording from those nerves in flight. This will be the first time we've ever done neural recording in humans in flight. We'll be looking for specific fibres that feed blood vessels that travel to skeletal muscles. Skeletal muscle is about half our body mass. Changes that we can elicit there in skeletal muscle have a profound impact on blood pressure regulation. We'll be asking the questions whether or not the signals sent from the brain to blood vessels to cause basal constriction are appropriate for the kinds of stresses we'll be applying.''

To prepare for the microneurography procedure, Linnehan, Williams, Buckey and Pawelczyk spent two months at Vanderbilt University training with the hardware. The insertion of the needle, which all four typically achieved within about 40 minutes during several runs in orbit, was both delicate and difficult. ''Finding a nerve'', said Principal Investigator David Robertson, ''is a lot more difficult than finding a vein. This is a very difficult thing to do on Earth, and the idea that it can be done in space is a little bit astounding to many people.''

As the mission drew towards its conclusion, on 29 April a problem arose with a blockage in Columbia's waste water dump line, which flight controllers speculated may have been caused by a clogged filter. An initial attempt by Searfoss and Altman to bypass the line by routeing a hose through a spare filter and venting waste water overboard did not resolve the problem. Meanwhile, the following day the Mission Management Team opted not to extend STS-90 to 17 days, after the Neurolab scientists indicated that they already had enough data and additional time in space would not be necessary.

This was a pity, because the conservation efforts of the crew had added enough

Was this article helpful?

0 0

Post a comment