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MCGILL-TRAINED MD, EXPERIMENT GIVE JUNE 20

SHUTTLE FLIGHT STRONG CANADLIN FLAVOUR

Robert Thirsk, MD, CM, PEng

The US National Aeronautics andSpace Administration (NASA) is

completing final preparations for theLife and Microgravity Spacelab(LMS) mission. Also known as STS-78, this space shuttle flight is sched-uled to lift off from the KennedySpace Center in Florida June 20. Lastyear I had the good fortune to bechosen to fly as a payload specialist-a highlight of my career with theCanadian Space Agency and the ful-filment of a personal dream.

This dream began in 1983 when Iwas named one of the original mem-bers of the Canadian Astronaut Pro-gram. At the time I was a second-year resident in family medicine at

Family physician Robert Thirsk is an astronaut with the Cana-dian Space Agency.

0 1996 Canadian Space Agency

the Queen Elizabeth Hospital inMontreal. A year later, as backup as-tronaut for shuttle mission 41 -G, Igot a taste of what it would be like toparticipate in a space mission. How-ever, training is not the same as ac-tual flying. I am delighted and feelvery fortunate to be chosen for amission that seems uniquely de-signed for my interests and abilities.My six LMS crewmates, our two

backups and I represent five interna-tional space agencies - NASA andthe French, European, Italian andCanadian agencies. We have beentraining for the last 15 months toprepare for 16 days in space aboardthe space shuttle Columbia. On behalfof scientists from the US, Europe andCanada, we will perform 43 investi-gations devoted to the study of lifeand materials sciences. The life-sci-

ences experiments will probechanges in plants, animals and hu-mans under spaceflight conditions.The materials-science investigationswill examine protein crystallization,fluid physics and high-temperaturesolidification of multiphase materialsin a microgravity environment. (Mi-crogravity describes experimentalconditions in the shuttle, which arenot perfectly weightless. As the shut-tle orbits Earth, it is subjected tosmall decelerations from atmosphericdrag. Other factors, such as the loca-tion of experiments relative to theshuttle's centre of gravity and vibra-tions from spacecraft machinery in-duce small accelerations on the orderof one millionth the force of Earth'sgravity, or one microgravity.)

Our initial training took place inthe investigators' laboratories and atNASA centres, where we were in-structed in the theory, hardware andoperations involved in the experi-ments. Training for the flight tookplace at the Marshall (Alabama) andJohnson (Texas) space centres, wherein-flight operations involving groundcontrollers were realistically simu-lated in high-fidelity spacecraft train-ers. Everyone involved in the mission- scientists, ground controllers, as-tronauts - participated in severalmultiday simulations to rehearseplanned operations, communicationprocedures and problem-solvingtechniques. Thorough training is es-sential, because in human spaceflight we have only one in-orbitchance to perform the experimentsproperly.

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Due to my clinical background Ihave also trained as one of the desig-nated crew medical officers, and willdiagnose and treat any in-flight med-ical problems in consultation withthe flight surgeon on the ground.

Fortunately, significant illness andinjury have been uncommon onshuttle flights. Rigorous medicalscreening of candidates ensures thatastronauts are in good health. Fur-thermore, a 7-day quarantine periodprior to launch minimizes crew expo-sure to infectious diseases, and therelatively short duration of shuttlemissions - it ranges from 7 to 16days- reduces the probability of in-flight illness.

Minor illnesses such as space mo-tion sickness, nasal congestion,headache and backache are com-mon. More serious problems, such asrenal colic, chronic prostatitis, pneu-monitis, cardiac arrhythmias, decom-pression sickness and corneal abra-

sions have been rare occurrences onother spacecraft and have had a seri-ous impact on mission objectives.A well-stocked medical kit will al-

low me to deliver ambulatory care,first aid and basic life support. It con-tains oral, topical and injectabledrugs, intravenous fluids, bandagesand the equipment and suppliesneeded to treat routine medical anddental problems. A contaminantclean-up kit contains equipment toprotect crew members from toxicsubstances and a pair of eye gogglesthat can be used to flush contami-nants from the eyes.

I am eagerly anticipating thebone-rattling launch, the tranquillityof weightlessness and gazing in aweat vast regions of our planet. I amequally excited by the broad range ofhuman physiological investigationswe will conduct, which will occupymost of our work time. Spaceflightresults in significant physiological

NAS4 photos

and biochemical changes in every or-gan system. My crewmates and I willbe both onboard researchers andsubjects for several experiments in-vestigating these changes. Most LMSscientific investigations will be con-ducted in the Spacelab laboratory.This cylindrical pressurized modulein the cargo bay provides a shirt-sleeve working environment that in-cludes work stations, experiment fa-cilities, freezers, storage compart-ments and other support equipment.I have an interest in all these experi-ments and feel I am part of the pio-neering effort to understand mecha-nisms behind the adaptive changes. Iwill outline a few of these LMS ex-periments.

TORSO-ROTATIONEXPERIMENT

The torso-rotation experiment(TRE) is the only one from Canada;Dr. Douglas Watt of McCill Univer-sity's Aerospace Medical ResearchUnit is the principal investigator.The idea was hatched several yearsago when one of Watt's colleaguessuffered an injury that required himto wear a rigid neck brace. He beganto feel nauseated after several min-utes moving about his laboratorywith his head braced to his torso.

Voluntarily fixing the head to thetorso, as with a neck brace, has beentermed "torso rotation," since the up-per body must move to turn thehead. On the ground this graduallyleads to motion sickness in most sub-jects. Torso rotation is an example ofa deliberate "egocentric" motor strat-egy, in which the subject concen-trates on a body frame of referencerather than an external world refer-ence. A motor strategy similar totorso rotation is often inadvertentlyadopted by astronauts during theearly days of a space mission. Whilethis may be a means of reducinghead movement to combat motionsickness, it might actually exacerbate

Dr. Robert Thirsk: the fulfilment of a personal dream the symptoms.

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Watt's aim is to monitor our eye,head and torso movements for evi-dence of egocentric motor strategiesas we perform typical in-orbit activi-ties. Eye movements will be mea-sured with electro-oculogram (EOG)electrodes, and head and torsomovements with angular velocitytransducer units securely mounted onthe top of the head and upper back.Each of us will perform the TREthree times during the mission - afew hours after launch, halfwaythrough the mission and near theend of the flight.

The data will be analysed for evi-dence of unusual gaze control duringcoordinated eye-head movements.As well, head rotation will be com-pared with torso rotation to assessour overall motor strategy and how itmight change during the mission. Ifmotor activities similar to torso rota-tion contribute to motion sickness inspace, it would be relatively easy to

train future astronauts to avoid suchmovements or to pre-adapt them bymimicking the provocative move-ments under controlled conditions.

SKELETAL-MUSCLEEXPERIMENTS

Previous missions have shownthat microgravity produces signifi-cant skeletal muscle wasting, particu-larly in the postural muscles. The ex-tent and responsible mechanisms areonly partially understood, and this isa medical concern during extendedstays aboard space stations or for fu-ture missions to the inner planets.Crews returning from long missionslikely will show decreased musclestrength and endurance, which willpose health and safety concerns.

This will be the first space missionto investigate comprehensively thechanges in human skeletal musclestructure and function induced by

the weightless environment. TheLMS work is actually an aggressiveand coordinated effort involving sixresearch teams from the US and Eu-rope. They will investigate bothflexor and extensor muscle groupsacting at the ankle, knee, wrist andelbow. They will provide a detailedanalysis of the relative importance ofweightlessness-induced changes inmotor perception, recruitment andhormonal and cellular factors in me-diating the reduced performance ofthese limb muscle groups.A sophisticated torque-velocity

dynamometer facility has been de-veloped to support the in-flight in-vestigations. It measures the torqueand the angular velocity producedduring predefined types of contrac-tions of the flexor and extensor mus-cles of the elbow and the ankle.These two measurements enable in-vestigators to quantitate several mus-cle-performance and function prop-erties.We will test the hypothesis that

the primary factors reducing limb-muscle function can be attributed toalterations at the cellular level,specifically a selective loss in thecontractile proteins. We expect thatspace flight will result in increasedmuscle fatigability due to preferentialatrophy of slow-twitch muscle fibres,coupled with a percentage increasein the more fatigable fast-twitch fi-bres and an inhibition in the abilityof muscle cells to metabolize fats.Furthermore, a greater atrophy ofpredominantly slow-twitch musclessuch as the soleus compared with fastmuscles such as the gastrocnemiusmay be detected by changes in mus-cle volume when postflight magneticresonance images of our muscles arecompared with preflight images.

Data from earlier spaceflights sug-gest that the decrease in limb-musclestrength is out of proportion to thecorresponding degree of muscle atro-phy, so other mechanisms also mayplay a role. We will examine the pos-sibility that at least a portion of the

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decline in muscular strength iscaused by alterations in motoneuronfunction or motor-fibre recruitment.

Muscle biopsy samples will be ob-tained from the gastrocnemius andsoleus muscle of each participatingcrew member. The mechanical, mor-phologic and metabolic properties ofthe muscle fibres that are biopsiedpostflight will be compared withthose obtained preflight.

Because of the electromyograph(EMG) and percutaneous-stimulationelectrodes that we will be wearingand the number of blood and tissuesamples that will be taken to supportthe muscle physiology investigation,we lightheartedly refer to ourselvesas the "rat crew" (as in laboratoryrats)! However, the LMS investiga-tors hope to gain a deeper under-standing of the effect of weightless-

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Medical experiments are nothing new on space shuttle flights. In this 1993 flight, David Wolfdrew blood from Martin Fettman. Regular blood tests played a critical role in several experi-

ments during that flight.

ness on muscle function and to pro-vide useful recommendations to im-prove both rehabilitation programsin clinical situations where muscu-loskeletal unloading is a componentand countermeasures for preventingspaceflight deconditioning.

PULMONARY FUNCTION

Our lungs are also sensitive togravity. The mass of lungparenchyma, airways, chest wall anddiaphragm causes them to deformunder their own weight. As well, hy-drostatic gradients within the bodyinfluence intrathoracic blood vol-ume, the distribution of pulmonaryblood flow and the return of bloodto the right side of the heart. Duringthe LMS mission we will perform aseries of noninvasive pulmonary-function tests to gain understandingof the intrinsic behaviour of the lungin a unique laboratory setting unaf-fected by the force of gravity.We will utilize a computerized

pulmonary-function-testing systembuilt around three inspiration and ex-halation bags, a variety of test gases,flow and volume measurement sys-tems and a respiratory mass spec-trometer. Specific tests designed atthe University of California at SanDiego will evaluate resting gas ex-change, distribution of ventilationand perfusion, diffusing capacity,lung volumes and fluid content, car-diac output, mechanisms of gas mix-ing in the lungs, ventilatory controlmechanisms and respiratory mechan-ics.

Little is known about the car-diopulmonary system's response toheavy exercise in microgravity.Such knowledge is important whenastronauts work hard during spacewalks and while performing otherduties during extended tours inspace. For this reason we will per-form the pulmonary-function testsat rest and shortly after completinga session of heavy exercise on a cy-cle ergometer.

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SLEEP AND CIRCADIANSTUDIES

Humans have a biological clockthat ensures we are physiologicallyand psychologically prepared for ac-tive wakefulness or restful sleep atappropriate times. Our preparation isaccomplished by circadian rhythmsthat are generated, at least in part, bya self-sustaining master oscillator lo-cated near the suprachiasmatic nu-clei. However, abrupt changes in en-vironmental factors or daily routinecan result in misalignment of our bio-logical clock relative to our activities.

The environment and routine as-sociated with life in space are quitedifferent from those on Earth. Space-flight is characterized by weightless-ness, 16 sunsets and sunrises per day,social isolation, cramped living con-ditions and the absence of the Earth's24-hour temporal structure. Over theduration of a mission astronautsmight experience a progressive ten-dency towards circadian dysfunction,with resulting decrements in sleepand performance.

The aim of the sleep and circadianstudies experiment from the Univer-sity of Pittsburgh is to evaluate oursleep, circadian rhythms and task per-formance. For several nights the qual-ity and quantity of our sleep will beevaluated by electroencephalograms,EOGs and EMGs, and computerizedsleep diaries. Circadian rhythms will

be measured by core body tempera-ture and urinary variables (volume,sodium, potassium, melatonin, corti-sol), and performance by cognitive-function tests and subjective reportsof mood, vigilance, stress and work-load. As human spaceflights becomelonger, the results from this experi-ment may have operational signifi-cance. Modification of work sched-ules and the provision of time cuesmay be recommended to maintain as-tronaut performance levels and feel-ings of well-being.We will participate in several

other physiological studies of neu-rovestibular adjustment, regulatoryphysiology, bone demineralizationand cognitive function. On behalf ofbiologists, we will collect data on theadaptation of other living systems(plants, fish embryos and rats) to themicrogravity environment. Togetherthese experiments complement eachother to provide a comprehensiveview of the effects of space travel onliving systems.

MATERIALS SCIENCE

The materials-science experi-ments are less crew intensive becausemostly they will be controlled auto-matically or commanded from theground during the night while wesleep. During the day, we willchange samples and film for these in-vestigations.

Of interest to the biotechnologyindustry is the Advanced ProteinCrystallization Facility (APCF). Withrecent refinements in the techniqueof x-ray crystallography, biochemistsand molecular biologists now have apowerful tool for probing the struc-ture of complicated macromoleculesin three dimensions at the atomiclevel. The limiting factor in x-raycrystallography is no longer the tech-nique itself but the availability ofmacromolecular crystals. Most of thethousands of known proteins and nu-cleic acids do not crystallize readily.Failure to obtain these crystals for vi-

sualization hinders basic understand-ing of macromolecular structure aswell as the rational, systematic designof drugs intended to interact with tar-get proteins and nucleic acids.

Protein crystallization on Earth isdisturbed by gravity effects such asconvection and sedimentation, re-sulting in the production of defectsand reduced crystal size and quality.Small, inhomogeneous crystals arepoor candidates for x-ray diffractionanalysis. The APCF experiment willattempt to determine whethermacromolecular crystals nucleate andgrow larger and more uniformly inmicrogravity. Ninety-six separate ex-periments under controlled tempera-ture conditions are accommodated inthe facility. A video microscopy sys-tem will allow the facility's multipleusers to observe the crystallizationprocess in 24 of the reactor cells.The long-term goal is not to estab-lish a protein crystallization facilityin space, but to better understandcrystal growth on Earth. Improve-ments in the crystallization processin conventional terrestrial labs maythen accelerate advances in biotech-nology, medicine and agriculture.

POSTSCRIPT

Since 1984 1 have put my clinicalcareer partially on hold. My work asan astronaut is a full-time commit-ment that focuses primarily on oper-ational training, medical research andflight payload design. My employer,the Canadian Space Agency, recog-nizes that my clinical skills benefitthe goals of the Canadian space pro-gram, and has facilitated my contin-ued involvement in part-time med-ical practice and continuing medicaleducation.

I miss contact with my patientsand the challenges of diagnosis andtreatment, but I am doing what I en-joy. My return to clinical medicine ispostponed while I pursue present andfuture opportunities that are simplyout of this world. a

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