Flight Analogs Project:
A Testbed for Flight
Ronita L. Cromwell, Ph.D.
Universities Space Research Association
Flight Analogs Project Scientist
NASA Johnson Space Center
Overview
„
Head Down Tilt Bed Rest
History
„ Purpose
„ Standard conditions
„ Standard Measures
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Results of Standard Measures
Head Up Tilt Lunar Analog Model
Current and Future Studies
Testbed
„
„
A testbed is a platform for experimentation for
large development projects. Testbeds allow for
rigorous, transparent and replicable testing of
scientific theories, computational tools, and other
new technologies.
The term is used across many disciplines to
describe a development environment that is
shielded from the hazards of testing in a live or
production environment.
Bed Rest as a Testbed
„
„
Bed rest serves as an experimental
platform for rigorous examination of the
physiological affects of spaceflight.
Bed rest provides a controlled
environment to examine countermeasures
to mitigate these affects.
History of Bed Rest as a Flight Analog
„
„
1961: human spaceflight begins and bed
rest is used as a ground-based analog of
inactivity.
Early 1970s: cosmonauts return from
longer duration missions
difficulty sleeping due to sensation of slipping
off the end of the bed
„ Foot of the bed was raised to compensate,
then gradually lowered to horizontal
„
History of Bed Rest as a Flight Analog
„
Soviets tested a variety of tilt angles
„
„
„
6º of head down tilt (HDT) optimized comfort
and provided sufficient magnitude of
physiological responses.
HDT position provides the added benefit of
studying fluid shifts
6º HDT bed rest is an accepted model for
studying physiological affects of
spaceflight on bone, muscle and
cardiovascular systems.
Purpose
„
HDT bed rest
serves as a model for studying the
physiological changes that occur during
spaceflight under controlled conditions;
„ provides a platform for comparison between
bed rest and space flight;
„ provides a mechanism for testing
countermeasures prior to being used in flight.
„
NASA Flight Analogs Research
Unit
UTMB
Children’s
Hospital
Flight Analogs
Research Unit
Standard Conditions
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„
6º HDT bed rest
Room Temperature: 70-74º
Study duration ~117 days
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13-15 days pre-bed rest
90 days in bed
14 days recovery
Sleep/Wake cycle
„
„
Wake at 0600 hrs
Lights out at 2200 hrs
Standard Conditions
„
Monitored 24 hrs/day
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Daily Vital signs
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Subject monitors
cameras
Blood pressure
Heart rate
Body temperature
Respiratory rate
Body weight (bed scale)
Fluid intake and output is measured
Psychological support provided
Standard Conditions
„
„
Stretching twice each
day
Physiotherapy
(massage therapy)
„
„
„
every other day during
bed rest
daily for 1st week post
bed rest
No exercise permitted
Standard Diet
„
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Isocaloric diet based on NASA
spaceflight nutritional requirements
Caloric intake 35.7 kcal/kg body
weight (2500 calories/70 kg subject)
Fluid intake 28.5 ml/kg body weight
(2000 ml/70 kg subject)
Carbohydrate:Fat:Protein ratio
55:30:15
No caffine, cocoa, chocolate, tea or
herbal beverages
All food must be consumed
Caloric intake adjusted to weight
within 5%
Isocaloric Diet Body Mass
Maintenance
BW (% Δ from BR3)
7.5
C1 (n=3)
C3A (n=4)
C3B (n=5)
5.0
2.5
0.0
-2.5
-5.0
-7.5
-10.0
0
25
50
Day of Study
75
100
Purpose of Standard Measures
„
„
„
Characterize human responses to head
down tilt bed rest.
Provide a basis for comparison between
bed rest and spaceflight
Provide a mechanism to assess candidate
countermeasures in a multidisciplinary
manner to determine outcomes on nontargeted systems.
Standard Measures
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Neurocognitive
Assessment
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Nutrition
„
Pharmacokinetics
WinSCAT – Psychological
test of cognitive function
Clinical Laboratory
Assessment
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Blood and urine studies to
monitor subject health
Immune Status
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General immune status
Viral specific immunity
Latent Viral Reactivation
Physiological stress
ƒ Nutritional analysis
ƒ Markers of bone resorption
and bone formation
ƒ Circulating bone and
calcium regulatory factors
ƒ Antioxidants and oxidative
damage
„
Lactulose/acetaminophen
studies to assess
gastrointestinal motility
Standard Measures
„
Bone Assessment
Dual Energy X-Ray
Absorptiometry (DXA) –
Bone Density
„ Peripheral Quantitative
Computerized
Tomography (pQCT) –
lower extremity bone
mass and structure
„
Standard Measures
ƒ
Physical Fitness
ƒ
ƒ
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Isokinetic Testing –
muscle
strength/endurance
Cycle Ergometry –
maximum aerobic
capacity
Functional Fitness –
strength, endurance,
flexibility
Standard Measures
ƒ
Functional
Neurological
Assessment
ƒ
ƒ
Posturography
testing – standing
posture
Stretch Reflex –
monosynaptic,
functional
Standard Measures
ƒ
Cardiovascular
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Operational Tilt Test – orthostatic tolerance
Blood volume – carbon monoxide rebreathing
Echocardiography – hemodynamic assessment
Results from Standard Measures
„ Bone
„ Consistent
„ bone
with spaceflight:
loss during bed rest is most
pronounced in weight bearing regions: hip,
pelvis and heel.
„ average monthly bone loss is 1-1.5% for
the hip and pelvis
„ greatest rate of bone loss occurs in the
trochanter
„ Bone biomarkers show elevated resorption
with no changes in formation
Sibonga, et al, ASEM in press
Results from Standard Measures
„
Cardiovascular
Similar to spaceflight, plasma volume losses
up to 15% occur early in bed rest (day 7).
„ Orthostatic tolerance is reduced in bed rest,
showing trends similar to spaceflight.
„
Plasma Volume Losses during Bed Rest
Plasma Volume Index (L/BSA)
1.8
1.6
1.4
*
*
(n=13)
*
1.2
(n=3)
(n=12)
*
*
(n=6)
(n=9)
(n=12)
(n=5)
(n=7)
1.0
0.8
0
20
40
Bed Rest Day
60
80
100
Platts et al., ASEM, in press
Tilt Test
Survival Analyses
Pre-Bed Rest
Bed Rest Day 60
1.0
1.0
Survival Probability
n = 9, P = 0.1
0.8
Survival Probability
0.8
0.6
0.4
0.6
0.4
Long Duration R+0 n=10
0.2
0.2
Shuttle n=44
p<0.02
0.0
0.0
0
2
4
6
Time
8
10
0
5
10
15
Time
20
25
30
Muscle
„
Similar to spaceflight, long duration bed
rest produces losses in muscle strength.
„
Strength loss is more pronounced in the
extensor (antigravity) muscles.
Strength & Endurance
Lee et al, ASEM, in revision
Lunar Bed Rest Model
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As NASA prepares to return to the moon,
development of a ground based lunar
analog is necessary.
Previous missions to the moon have not
returned enough information to fully
understand how the human body performs
in lunar gravity.
Currently there is no basis to determine if
the 1/6 g lunar environment provides some
degree of protection against physiological
changes associated with spaceflight.
Lunar Analog Feasibility Study
„
Currently underway to assess the
feasibility of using the lunar analog bed as
a model for exploring the whole body
physiological effects of a lunar mission.
1/6 g Bed Rest Model
F = W sin (9.5deg)
= 0.165 W
9.5 deg
9.5 deg
W
Angle required to achieve lunar gravity loads at the feet.
Lunar Gravity Simulator Bed
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9.5º tilt
Linear bearings
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Counterweight system
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allow sled/mattress to
travel on rails
balance the mattress
weight allowing subject
to experience the true
1/6 g load
Standing and seated
positions permitted
LAFS Protocol
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11-day study
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3 days pre-bed rest
6 days in bed
2 days post bed rest rehabilitation
Jobst® stockings worn to simulate cardiovascular load of
lunar gravity.
Isocaloric Diet
Feasibility determined by:
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Subject’s comfort assessment
Foot force profiles using instrumented insoles
Data comparisons against Digital Astronaut
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Muscle Volume
Plasma Volume
Urine Calcium
Lunar Analog Pilot Study
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Successful completion of LAFS will
provide the background needed to further
test the platform as a long-duration model
Lunar Analog Pilot Study (LAPS) –
planning stages
90 days
„ Standard conditions
„ Standard measures
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Verification through Digital Astronaut until
data are obtained from the lunar surface
Bed Design for LAPS
Adjustable Foot Support
Slider Plate Assembly
Floor-mounted force
plate serves as a seat.
Scissor jack to adjust
force plate operated by
subject
Current Studies in HDT
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Gender Differences in Bed Rest: Autonomic and
Neuroendocrine Changes and Vascular Response in Lower
and Upper Extremities
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S. Platts, NASA
Examination of mechanisms controlling orthostatic tolerance to
determine differences between men and women
Validation of Near Infrared
Spectroscopy (NIRS) Measures
following Bed Rest
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B. Soller, University Massachusetts,
NSBRI, ExMC
Validation of NIRS device as a noninvasive mechanism to continuously
measure VO2 during exercise.
Upcoming Studies in HDT
„
Methods for the Assessment of
Gastrointestinal (GI) Physiology
and Function in a Reduced Gravity
Analog
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L. Putcha, NASA
Pharmacokinetics assessment of
GI function using SmartPill®
technology to measure pH,
temperature and pressure
Non-invasive Device for Measuring Core Temperature during
Maximal Exercise
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H. Gunga, ESA, ECP
Non-invasive device for estimating core temperature during
maximal exercise
Upcoming Studies in HDT
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A Quantitative Test of On-Orbit
Exercise Countermeasures for Bone
Demineralization Using a Bed Rest
Analog
„ P. Cavanagh, University of
Washington, NASA, ECP
„ Examination of an individualized,
intermittent load replacement to
protect against losses in bone
mineral density, bone quality and
muscle atrophy
Rapid Measurements of bone loss using Tracer-less Calcium
Isotope Analysis of Blood and Urine
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A. Anbar, Arizona State University, NASA, NxPCM
Development of methods for early detection of changes in bone
mineral balance through measures of calcium isotope composition
in blood and urine
Upcoming Studies for LAPS
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Determination of the Magnitude and time course of
Cardiovascular Alterations during a Simulated Extended
Stay Lunar Mission
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S. Platts, NASA
Examination of the cardiovascular response to simulated lunar
gravity through measures of compartmental fluid shifts, plasma
volume changes and load-independent changes in cardiac
function
Thermoregulatory Capacity and Exercise Responses
following Prolonged Lunar Analog Bed Rest
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D. Keller, University of Texas at Arlington, NASA, ECP
Examination of thermal and cardiovascular responses to
submaximal exercise
Upcoming Studies for LAPS
„
Methods for the Assessment of
Gastrointestinal (GI) Physiology
and Function in a Reduced
Gravity Analog
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Validation of Near Infrared
Spectroscopy (NIRS) Measures
following Bed Rest
„
„
B. Soller, University
Massachusetts, NSBRI, ExMC
Validation of NIRS device as a
non-invasive mechanism to
continuously measure VO2 during
exercise.
L. Putcha, NASA
Pharmacokinetics assessment of
GI function using SmartPill®
technology to measure pH,
temperature and pressure
Flight Analogs Team
„
J. Neigut, Project
Manager
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J. McFather, Deputy
Project Manager
R. Cromwell, Project
Scientist
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R. Buccello-Stout, Deputy
Project Scientist
P. Yarbough, Deputy
Project Scientist
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S. Stranges,
Bioastronautics Project
Manager
D. Ware, UTMB
Attending Physician
D. Powell, UTMB GCRC
Program Director
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L. Wiseman, UTMB GCRC
Administrator
M. Ottenbacher, UTMB
Head Nurse/Nurse
Manager