Microgravity and the Microgravity and the Circulatory SystemCirculatory SystemMina Mina IscandarIscandar Kevin MorganKevin Morgan

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OutlineOutline

IntroductionIntroductionCirculatory System on EarthCirculatory System on EarthChanges Due to MicrogravityChanges Due to MicrogravitySide effects Upon Return to EarthSide effects Upon Return to EarthPossible CountermeasuresPossible CountermeasuresOngoing StudiesOngoing Studies

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IntroductionIntroduction

Exposure to microgravity during space flight Exposure to microgravity during space flight affects almost all human physiological systemsaffects almost all human physiological systems

Musculoskeletal System Musculoskeletal System NeurovestibularNeurovestibular SystemSystemCirculatory SystemCirculatory System

Understanding these affects are of the utmost Understanding these affects are of the utmost importance before longer mission and importance before longer mission and interplanetary travel are possibleinterplanetary travel are possibleWe will focus on microgravityWe will focus on microgravity’’s affects on the s affects on the circulatory systemcirculatory system

Circulatory System on EarthCirculatory System on Earth

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Terrestrial LifeTerrestrial Life

Gravity is always acting on the human bodyGravity is always acting on the human bodySome Systems work Some Systems work ““because ofbecause of”” and some and some work work ““in spite ofin spite of”” gravity gravity [1][1]

Circulatory System works Circulatory System works ““in spite ofin spite of”” gravitygravityblood to flows up from heart to the brainblood to flows up from heart to the brainLower body blood vessels constrict to push blood Lower body blood vessels constrict to push blood upwardsupwards

Blood Pressure normally higher in lower body than Blood Pressure normally higher in lower body than in the upper bodyin the upper body

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Terrestrial Life (contTerrestrial Life (cont’’d)d)

HumansHumansMaintain upright Maintain upright positionposition70% of blood below 70% of blood below heart level heart level [1][1]

QuadrupedsQuadrupeds““All foursAll fours”” body body positionposition70% of blood above 70% of blood above heart level heart level [1][1]

[8]

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Under PressureUnder Pressure

Blood Pressure = Cardiac Output (CO) * Blood Pressure = Cardiac Output (CO) * Total Peripheral Resistance (TPR)Total Peripheral Resistance (TPR)

Normally 100mmHg at the aortic bulbNormally 100mmHg at the aortic bulb2 other components to blood pressure2 other components to blood pressure

Static pressure (~7 mmHg)Static pressure (~7 mmHg)Due to elastic characteristic of vascular systemDue to elastic characteristic of vascular system

Hydrostatic (Hydrostatic (ρρ*g*h) where *g*h) where ρρ is blood densityis blood densityA negative value corresponds to pumping above the A negative value corresponds to pumping above the heart and a positive to pumping below the heartheart and a positive to pumping below the heart

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Blood Pressure RegulationBlood Pressure Regulation

BaroreceptorsBaroreceptorsdetect blood pressure and send orders to CNS detect blood pressure and send orders to CNS whether to increase or decrease TPR and COwhether to increase or decrease TPR and CO

ReninRenin--angiotensinangiotensin system (RAS)system (RAS)Allows kidneys to compensate for drops in blood Allows kidneys to compensate for drops in blood pressure by muscle constrictionpressure by muscle constriction

AldosteroneAldosterone releasereleaseRelease steroid hormone in response to decrease in Release steroid hormone in response to decrease in blood pressureblood pressureIncrease blood pressure in bodyIncrease blood pressure in body

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Factors Affecting Blood PressureFactors Affecting Blood Pressure

Rate of pumpingRate of pumpingVolume of fluidVolume of fluid

The more blood in the body the higher the The more blood in the body the higher the pressurepressure

ResistanceResistanceSmall diameter, higher resistanceSmall diameter, higher resistance

ViscosityViscosityHigh red blood cell concentration increases High red blood cell concentration increases viscosity which increases pressureviscosity which increases pressure

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Under Pressure (contUnder Pressure (cont’’d)d)Blood pools in the Blood pools in the lower body lower body ““because because ofof”” gravity causing a gravity causing a pressure gradientpressure gradientHeart must work Heart must work ““in in spite ofspite of”” gravity to gravity to return the blood return the blood upwardsupwardsWhat happens in the What happens in the absence of the absence of the pressure gradient?pressure gradient?

[7]

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Under Pressure (contUnder Pressure (cont’’d)d)

During long periods of bed rest, the heart, During long periods of bed rest, the heart, lower body, and head are all at the same lower body, and head are all at the same levellevelThe pressure gradient disappearsThe pressure gradient disappearsρρ*g*h goes to zero*g*h goes to zero

Most of the blood collects in the chest and Most of the blood collects in the chest and abdomenabdomenWhat about in microgravity?What about in microgravity?

Changes Due to MicrogravityChanges Due to Microgravity

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MicrogravityMicrogravity

As distance from the Earth increases, the As distance from the Earth increases, the affect of the gravity decreaseaffect of the gravity decreaseWithout the pull of gravity, the blood can Without the pull of gravity, the blood can no longer pool in the lower legs and feetno longer pool in the lower legs and feetInstead the blood collects in the head and Instead the blood collects in the head and thorax region of the bodythorax region of the bodyVessels in the legs must no longer Vessels in the legs must no longer constrict to push blood upwards to the rest constrict to push blood upwards to the rest of the body and become of the body and become ““lazylazy””

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““PuffyPuffy--Head Bird LegsHead Bird Legs”” SyndromeSyndrome

Sinuses swell because of blood shiftSinuses swell because of blood shiftLeg muscles weaken due to blood shift and because Leg muscles weaken due to blood shift and because they are no longer needed to support the body weightthey are no longer needed to support the body weightHeart increases blood flow per beat causing expanded Heart increases blood flow per beat causing expanded blood vesselsblood vesselsIncreased urine excretion by the kidneysIncreased urine excretion by the kidneys

[3]

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Changes in the Circulatory SystemChanges in the Circulatory System

The change in environment causes an The change in environment causes an homeostatic response by the Circulatory homeostatic response by the Circulatory SystemSystemTwo types of ChangesTwo types of Changes

Rapid ResponseRapid ResponseDelayed Adaptive ResponseDelayed Adaptive Response

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Changes in the Circulatory SystemChanges in the Circulatory System

Rapid ResponseRapid ResponseDecrease of plasma volumeDecrease of plasma volumeDecrease in circulating blood and interstitial Decrease in circulating blood and interstitial fluid volumesfluid volumesIncrease mass of red blood cells and Increase mass of red blood cells and hemoglobinhemoglobinDecrease of arterial blood diastolic pressureDecrease of arterial blood diastolic pressure

Blood pressure between heart beatsBlood pressure between heart beats

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Changes in the Circulatory SystemChanges in the Circulatory System

Delayed Adaptive ResponseDelayed Adaptive ResponseFurther decrease in blood volumeFurther decrease in blood volumeDecrease in red blood cell mass and Decrease in red blood cell mass and hemoglobin concentrationhemoglobin concentrationDecrease in blood pressureDecrease in blood pressureDecrease in stroke volumeDecrease in stroke volume

Blood pumped from the ventricle in one beatBlood pumped from the ventricle in one beat

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MicrogravityMicrogravity

Absence of Forces of Gravity

Increase Central VolumeDecrease in pressure gradientIncrease blood flow and blood

pressure in kidneys

Increase in excretion of fluids

Decrease activity of the sympathetic region of

the hypothalamus

Muscle system deconditioning

decrease activity of peripheral muscles

Decrease peripheral resistance

Pooling of blood in visceral organs

Decrease plasma and circulating bloodIncrease in mass of red blood cellsDecrease in arterial blood diastolic pressure

Further decrease in blood volumeDecreased mass of red blood cellsDecreased blood pressureDecrease in stroke volume

Rapid Delayed

[1] Adapted

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A New Set PointA New Set Point

The Circulatory System establishes a new The Circulatory System establishes a new set point that is different to that on Earthset point that is different to that on Earth

The new set point has a decreased tolerance The new set point has a decreased tolerance to gravityto gravity

The circulatory system is now The circulatory system is now ““deconditioneddeconditioned”” with respect to Earthwith respect to EarthBaroreceptorsBaroreceptors ““resetreset”” themselves to be in themselves to be in line with the new gravitational conditionsline with the new gravitational conditions

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Circulatory System AdaptationCirculatory System Adaptation

[2]

Returning To EarthReturning To Earth

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Returning to EarthReturning to Earth

Astronauts may not Astronauts may not feel the effects of their feel the effects of their changing circulatory changing circulatory system in spacesystem in spaceUpon returning to Upon returning to Earth the changes Earth the changes become very become very apparentapparent

[2]

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Returning to EarthReturning to EarthThe Circulatory System has reached a new The Circulatory System has reached a new equilibrium in microgravityequilibrium in microgravityUpon returning to Earth a sudden shift in gravity Upon returning to Earth a sudden shift in gravity causes a number of effects on the circulatory causes a number of effects on the circulatory systemsystemIt is difficult to quantitatively express these It is difficult to quantitatively express these changes as a great amount of factors come into changes as a great amount of factors come into playplay

Duration of space travelDuration of space travelDistance form EarthDistance form EarthMission activitiesMission activities

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Returning to EarthReturning to Earth

Qualitative Analysis of Returning Qualitative Analysis of Returning Astronauts and CosmonautsAstronauts and Cosmonauts

Sweaty and pale facesSweaty and pale facesDizzinessDizzinessIncreased Heart rateIncreased Heart rateInability to assume standing position Inability to assume standing position (Orthostatic intolerance)(Orthostatic intolerance)General impairment due to ineffective control General impairment due to ineffective control of bloodof bloodDecreased exercise capacityDecreased exercise capacity

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Return to EarthReturn to Earth

Quantitative Analysis of Returning Quantitative Analysis of Returning Astronauts and CosmonautsAstronauts and Cosmonauts

7 ~ 15% decline in plasma volume7 ~ 15% decline in plasma volume2 ~ 4% decline in total body water2 ~ 4% decline in total body water15 ~ 36% reduction in stroke volume15 ~ 36% reduction in stroke volume8 ~ 11% increase in heart rate8 ~ 11% increase in heart rate

Main findings that all of these factors Main findings that all of these factors contribute to lower exercise capacitycontribute to lower exercise capacity

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Orthostatic IntoleranceOrthostatic Intolerance

In ability to regulate blood pressureIn ability to regulate blood pressureOn Earth can be felt by standing up or On Earth can be felt by standing up or sitting up too fastsitting up too fastAstronautAstronaut’’s and Cosmonauts and Cosmonaut’’s blood s blood vessels have become accustom to being vessels have become accustom to being ““lazylazy””

In space they are not required to constrict to In space they are not required to constrict to push blood up to the upper bodypush blood up to the upper bodyThey stay in a dilated stateThey stay in a dilated state

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Orthostatic IntoleranceOrthostatic Intolerance

When returning to the Earth gWhen returning to the Earth g--forces act forces act on the body and all of a sudden the on the body and all of a sudden the pressure gradient repressure gradient re--appearsappearsThe blood is then forced from the head The blood is then forced from the head and chest to the lower limbsand chest to the lower limbsThe blood vessels have The blood vessels have ““forgottenforgotten”” how to how to contract and push the blood back towards contract and push the blood back towards the brainthe brain

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Orthostatic IntoleranceOrthostatic Intolerance

This causes a lack of blood to the brainThis causes a lack of blood to the brainResults in dizziness and faintingResults in dizziness and faintingSymptoms duration depends on the length of Symptoms duration depends on the length of time subject is exposed to microgravitytime subject is exposed to microgravity

4 4 –– 10 day mission requires 10 days recovery period10 day mission requires 10 days recovery period8 8 –– 12 month mission requires 4 12 month mission requires 4 –– 5 weeks recovery 5 weeks recovery periodperiod

Current studies are being performed to better Current studies are being performed to better understand factors causing Orthostatic understand factors causing Orthostatic IntoleranceIntolerance

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Effects on Returning AstronautsEffects on Returning Astronauts

Astronauts on short space missions Astronauts on short space missions (4 ~ 14 days)(4 ~ 14 days)Often have trouble walking and keeping balanceOften have trouble walking and keeping balanceMust be aided in movements and usually lie down Must be aided in movements and usually lie down after departing the shuttleafter departing the shuttle

Cosmonauts on long missionsCosmonauts on long missions(6 ~ 12 months)(6 ~ 12 months)Often capsules land in water because cosmonauts Often capsules land in water because cosmonauts are unable to properly land on the surfaceare unable to properly land on the surfaceTypically faint and have trouble movingTypically faint and have trouble moving

Possible CountermeasuresPossible Countermeasures

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Possible CountermeasuresPossible Countermeasures

Past CountermeasuresPast CountermeasuresDrinking Salt WaterDrinking Salt WaterG G –– SuitsSuits

Current CountermeasuresCurrent CountermeasuresUtilization of drugsUtilization of drugs

MidodrineMidodrine

Creation of artificial gravity on the shuttleCreation of artificial gravity on the shuttleTwin Bikes SystemTwin Bikes System

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Past CountermeasurePast Countermeasure

Drinking Salt WaterDrinking Salt WaterIncreases the viscosity of the bloodIncreases the viscosity of the bloodForces heart to work harder causing higher Forces heart to work harder causing higher blood pressureblood pressure

G G –– SuitsSuitsRubberized fullRubberized full--body suitsbody suitsApplies pressure on extremities and raises Applies pressure on extremities and raises blood pressureblood pressure

Both not sufficient solutionsBoth not sufficient solutions

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Current CountermeasuresCurrent Countermeasures

MidodrineMidodrineImproves blood pressure counteracting Improves blood pressure counteracting orthostatic intoleranceorthostatic intoleranceBinds to alphaBinds to alpha--1 receptors on arteries and 1 receptors on arteries and veinsveins

Sympathetic responseSympathetic responseConstricts blood vessels and increase blood Constricts blood vessels and increase blood pressurepressure

Increase blood pressure for a short period of Increase blood pressure for a short period of timetime

3 3 –– 4 hours approximately depending on dosage4 hours approximately depending on dosage

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Current CountermeasuresCurrent CountermeasuresCreation of Artificial Creation of Artificial GravityGravity

Twin Bikes System (TBS)Twin Bikes System (TBS)Two astronauts riding two Two astronauts riding two bicycles and counterbicycles and counter--rotating along the inner rotating along the inner wall of the cyclical space wall of the cyclical space shuttle shuttle [1][1]

Allows astronauts to Allows astronauts to experience the Earthexperience the Earth’’s s gravity while being in gravity while being in spacespaceEnables astronauts to Enables astronauts to perform physical exercisesperform physical exercises

[1]

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Current CountermeasuresCurrent Countermeasures

How Artificial Gravity is GeneratedHow Artificial Gravity is GeneratedAny object traveling in a circle will experience Any object traveling in a circle will experience an outward acceleration called centrifugal an outward acceleration called centrifugal acceleration ( aacceleration ( ac c ))aac c = v= v22 / R (for space shuttle R = 2 m)/ R (for space shuttle R = 2 m)aac c must be equal to 9.81 m/smust be equal to 9.81 m/s22 in order to in order to mimic Earthmimic Earth’’s gravitys gravity

v must be equal to approx. 4.5 m/s

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Current CountermeasuresCurrent Countermeasures

Centrifugal force due to the mass of the Centrifugal force due to the mass of the upper body is supported by the bikeupper body is supported by the bike’’s s frameframeThis is similar to Earth where the spine This is similar to Earth where the spine supports the mass of the upper bodysupports the mass of the upper bodyThe lower limbs will have a force equal to The lower limbs will have a force equal to the mass of the limbs multiplied by athe mass of the limbs multiplied by acc

This is similar to Earth where the lower limbs will This is similar to Earth where the lower limbs will be stimulated by their own weight and the force be stimulated by their own weight and the force of the muscle while pedalingof the muscle while pedaling

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Current CountermeasuresCurrent Countermeasures

aac c = = ωω2 * 2 * RRTaking the average acceleration between two Taking the average acceleration between two points yieldspoints yieldsaac c = = ωω2 2 * ( R* ( R11 + R+ R22) / 2) / 2Therefore PTherefore Paa = = ρρ * [* [ωω2 2 * ( R* ( R11 + R+ R22) / 2] * (R) / 2] * (R2 2 –– RR11))This enables us to measure the total pressure at This enables us to measure the total pressure at any desired point in the circulatory systemany desired point in the circulatory system

Ongoing StudiesOngoing Studies

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Blood Vessel Changes in RatsBlood Vessel Changes in RatsDr. Michael Dr. Michael DelpDelp at at Texas A&M UniversityTexas A&M UniversityAnimal Enclosure Animal Enclosure Model (AEM)Model (AEM)

8 rats in microgravity8 rats in microgravity8 control rats8 control rats

Experiment explores Experiment explores the affects of the affects of microgravity on blood microgravity on blood vessels and smooth vessels and smooth musclemuscle

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Blood Vessel Changes in RatsBlood Vessel Changes in Rats

ResultsResultsA and C are controlsA and C are controlsB and D experience B and D experience microgravitymicrogravity

Muscle cells around B Muscle cells around B and D weaken and and D weaken and shrinkshrinkThis results in the This results in the inability to constrict inability to constrict and force blood up to and force blood up to the brainthe brain

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Affects of Nitric OxideAffects of Nitric Oxide

Recent Studies by NASA and the Recent Studies by NASA and the University of CaliforniaUniversity of California

Rats kept in microgravity produce excessive Rats kept in microgravity produce excessive amounts of nitric oxide amounts of nitric oxide synthasesynthase (NOS) in the (NOS) in the heart, blood vessels, kidneys, and brain heart, blood vessels, kidneys, and brain [4][4]

NOS causes blood vessel dilationNOS causes blood vessel dilationOver production of nitric oxide may contribute Over production of nitric oxide may contribute to orthostatic intoleranceto orthostatic intolerancePreventing overproduction of nitric oxide may Preventing overproduction of nitric oxide may help to treat orthostatic intolerancehelp to treat orthostatic intoleranceAminoguanidineAminoguanidine blocks the action of NOSblocks the action of NOS

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ConclusionConclusion

Studies on the circulatory system in Studies on the circulatory system in microgravity have helped further us microgravity have helped further us understand how heart physiology works in understand how heart physiology works in gravitygravityBecause studies on the affects of Because studies on the affects of microgravity are very limited it is difficult to microgravity are very limited it is difficult to make progressmake progressHowever, progress must be made before However, progress must be made before we can venture further out into our solar we can venture further out into our solar systemsystem

Question?Question?

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Works CitedWorks Cited1.1. G. G. AntonuttoAntonutto, P.E. , P.E. PramperoPrampero, , Cardiovascular Cardiovascular deconditioningdeconditioning in microgravity: some in microgravity: some

possible countermeasures.possible countermeasures. 2003.2003.2.2. http://science.nasa.gov/headlines/y2002/25mar_dizzy.htmhttp://science.nasa.gov/headlines/y2002/25mar_dizzy.htm3.3. http://library.thinkquest.org/03oct/01581/SpaceTravelEnglish/danhttp://library.thinkquest.org/03oct/01581/SpaceTravelEnglish/dangers/puffy.htmlgers/puffy.html4.4. http://research.hq.nasa.gov/Spaceline_WEB/SpaceLine/nasa/pdf/Faihttp://research.hq.nasa.gov/Spaceline_WEB/SpaceLine/nasa/pdf/Fainting_Astronanting_Astrona

uts.pdfuts.pdf5.5. T. Trappe, T. Trappe, S.TrappeS.Trappe, , G.LeeG.Lee et., et., CardiorespiratoryCardiorespiratory response to physical work response to physical work

during and following 17 days of bed rest and spaceflight.during and following 17 days of bed rest and spaceflight. Journal of Applied Journal of Applied Physiology. pg. 951 Physiology. pg. 951 –– 956. 2006.956. 2006.

6.6. X. Xiao et. X. Xiao et. Effect of simulated microgravity on closedEffect of simulated microgravity on closed--loop cardiovascular loop cardiovascular regulation and orthostatic intolerance: analysis by means of sysregulation and orthostatic intolerance: analysis by means of system identification.tem identification.Journal of Applied Physiology. pg. 489 Journal of Applied Physiology. pg. 489 –– 496. 2004.496. 2004.

7.7. http://en.wikipedia.org/wiki/Image:Grafik_blutkreislauf.jpghttp://en.wikipedia.org/wiki/Image:Grafik_blutkreislauf.jpg8.8. http://www.huntington.org/LibraryDiv/LASKEREXHIBIT/Seabiscuit.jphttp://www.huntington.org/LibraryDiv/LASKEREXHIBIT/Seabiscuit.jpgg9.9. http://health.howstuffworks.com/definehttp://health.howstuffworks.com/define--heart.htmheart.htm10.10. http://en.wikipedia.org/wiki/Blood_pressurehttp://en.wikipedia.org/wiki/Blood_pressure11.11. http://www.nasa.gov/vision/earth/livingthings/arterial_remodel.hhttp://www.nasa.gov/vision/earth/livingthings/arterial_remodel.htmltml