The Digital Astronaut Project (DAP)
Applying computational models and
simulations to inform life science research
Lealem Mulugeta
DAP Project Scientist
mulugeta@dsls.usra.edu
lealem.mulugeta@nasa.gov
USRA DSLS Brown Bag Lunch Seminar - April 19th, 2012
Acknowledgments
Dr. Jean Sibonga, PhD
Christian Otto, MD
HACD Bone Discipline Lead
VIIP Project Scientist
Marlei Walton, PhD
IMM Project Scientist
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Overview
• Goals of the Digital Astronaut Project
• Processes DAP follows to accomplish its goals
• The modeling and simulation tools currently under
development
• Video demonstration of the ARED and exercise modules
• Our recent achievements
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Introduction
• Mars and NEO missions will expose astronaut to extended
durations of reduced-gravity, isolation and higher radiation
• These new operation conditions pose health risks that are
not well understood and perhaps unanticipated
• Advanced computational simulation environments can
beneficially augment research to predict, assess and
mitigate potential hazards to astronaut health
• The Digital Astronaut Project (DAP) strives to achieve this
goal
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DAP’s Model Development and
Implementation Process
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How Models Can be Applied to Enhance
Life Science Research
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Current Focus Areas
1. Exercise countermeasures modeling and simulation
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Advanced Resistive Exercise Device (ARED)
Biomechanics of exercise
Bone adaptation
Muscle adaptation
Advanced Exercise Concept Devices
2. Risk of bone fracture
– Bone adaptation
– Biomechanics of post-flight activities for bone load predictions
3. Visual Impairment and Intracranial Pressure (VIIP)
– Preliminary stages
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ARED Exercise Modeling
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ARED Exercise Modeling Kick-off Plan
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Exercise Countermeasures Modeling
• Human exercise simulation in micro-gravity
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Squat
Single-leg squat
Dead-lift
Heel-raise
• Prediction of:
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Muscle forces
Muscle adaptation
Ground reaction forces
Joint torque
Mechanical load bones/joints
Bone adaptation
• Influence of:
– Anthropometric variation
– Stance variation
– Range of motion
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Exercise Countermeasures Modeling
Targeted HRP risk knowledge gaps:
B15: (a) What exercise protocols are necessary to maintain skeletal health? And
(b) Can exercise hardware be designed to provide these?
M7: Can the current in-flight performance be maintained with reduced exercise
volume?
M8: What is the minimum exercise regimen needed to maintain fitness levels
for tasks?
M9: What is the minimum set of exercise hardware needed to maintain those
(M8) fitness levels?
M24: What is the time course of changes in muscle protein turnover, muscle
mass, and function during long-term spaceflight?
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ARED Hardware Model
• High fidelity dynamics
model of ARED/VIS
developed in MSC Adams™
– Mass and inertial properties
– Friction forces
– Gas laws
• Currently allows for
simulation of bar exercises
only
Modeler: Brad Humphreys
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ARED Hardware Model
NOT VALIDATED
Modeler: Brad Humphreys
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Force generated at the bar in 1-g
NOT VALIDATED
Modeler: Brad Humphreys
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Force generated at the bar in 0-g
NOT VALIDATED
Modeler: Brad Humphreys
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ARED Exercise Modeling Kick-off Plan
Developed in parallel
with ARED/VIS model
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ARED Exercise Models
• Developed with LifeMOD™ using motion capture data
acquired on the ARED ground unit at JSC
Normal Squat
Single-leg squat
Joint Module
Muscle Module
Dead lift
Modelers: Nate Newby and Erin Caldwell
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Integrated ARED-Dead Lift Exercise Model
NOT VALIDATED
Modelers: Nate Newby and Erin Caldwell
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Integrated ARED-Dead Lift Exercise Model
NOT VALIDATED
Modelers: Nate Newby and Erin Caldwell
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Integrated ARED-Squat Exercise Model
NOT VALIDATED
Modeler: Bill Thompson
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Integrated ARED-Exercise Squat Model
NOT VALIDATED
Modeler: Bill Thompson
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Integrated ARED-Exercise Squat Model
NOT VALIDATED
Modeler: Bill Thompson
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ARED Exercise Modeling and Implementation Process
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Muscle Adaptation Model
• Conceptual phase
• Enhance the fidelity of muscle representation
in the LifeMOD biomechanics models in terms
of space flight changes
• Gain insight on muscle adaptation factors:
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Neuromuscular drive and activation
Muscle atrophy and fiber morphology
Blood flow and intramuscular pressure
Metabolic processes
Fatigue
Modeler: Beth Lewandowski, PhD
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Bone Adaptation Model
• Predicted muscle force from biomechanics
models is an input to the bone adaptation
model
• Bone adaptation model factors :
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Cortical bone tissue rate of change
Bone fluid calcium rate of change
Biochemical equations
Mechanical stimulus
Cellular dynamics
Modeler: Jim Pennline, PhD
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Risk of Bone Fracture
Targeted HRP risk knowledge gaps:
B15: (a) What exercise protocols are necessary to maintain skeletal
health?
B1:
(a) Is there an increased lifetime risk of fragility
fractures/osteoporosis in astronauts?
(b) Is bone strength completely recovered post-flight, and does
BMD reflect it?
(c) What are the risk factors for poor recovery of BMD/bone
strength
B30: What are the loads applied to bone in-flight and during EVA
activities and do they increase fracture risk in light of expected
bone loss?
Modeler: Jim Pennline, PhD
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Risk of Bone Fracture
• Implement biomechanical modules to
predict the forces experienced at
specific bone sites during various
activities (not exercise)
• Enhance bone adaptation module to
determine changes in the macro- and
microstructure of bone during longduration spaceflight and implications on
long-term bone health risks
(Hewett et al., 2008)
Modeler: Jim Pennline, PhD
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Advanced Exercise Devices Modeling
• Develop device models for advanced exercise (AEC)
devices:
– Multi-mode Exercise Device (M-MED) – NSBRI / UC Irvine
– Gas spring device (ZIN)
– Streamline ergometer (SBIR)
Modeler: Brad Humphreys
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Advanced Exercise Devices Modeling
• Objectives:
1. Gain insight into the efficacy of AEC devices for exercise
countermeasures
2. Provide timely input for design, development, and
refinement of AEC devices
3. Help reduce the time and cost to develop the exercise
devices
4. Help reduce the time and cost to clinically test new exercise
devices
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Visual Impairment and Intracranial Pressure (VIIP)
Intracranial
Pressure
Intracranial
Compliance
Intracranial
Hemodynamics
Intra-ocular
Pressure
Cerebrospinal
Fluid Flow
(Adapted from Google Body –
http://bodybrowser.googlelabs.com)
Papilledema
Changes in visual acuity
Primary focus:
• biomechanical responses to the of
the intracranial and ocular structure
while microgravity environment that
may affect visual acuity
Model types under consideration:
• Lumped parameter models of the
intracranial and spinal compartments
• Finite element model of the eye
• Computational fluid dynamics of the
intracranial and spinal space
• High fidelity tissue models to capture
nonlinear/viscoelastic properties
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Current Status for VIIP Modeling
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VIIP Targeted Gaps
• VIIP6: How do changes in vascular compliance/ pressures
influence intraocular pressure or intracranial pressure?
• Gap VIIP2: Does exposure to microgravity cause changes in
visual acuity, intraocular pressure and/or intracranial
pressure? Are the effects related to mission duration?
• Gap VIIP4: Are changes in visual acuity related to changes
in:
1) deformation of the optic nerve head;
2) chronic choroidal engorgement;
3) elevated intraocular pressure; and/or
4) intracranial pressure?
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Recent Successes
ARED Model used for Flywheel
Preventative Maintenance
• The ARED flywheels were disengaged due to ground
evidence that suggested the flywheel set screws may
back out of their engagement to cause damage to the
ARED
• Substantiation was requested from the ISS Program
Office on whether or not crew time should be allocated
to re-torque the set-screws as a short term fix to buy
enough time to investigate a long-term fix
• The exercise lab at JSC leveraged the Beta ARED
hardware model to partially substantiate the benefit of
having the inertial wheels engaged during exercise
Analysts: Nate Newby, Erin Caldwell and Brad Humphreys
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ARED Model used for Flywheel
Preventative Maintenance
Analysts: Nate Newby, Erin Caldwell and Brad Humphreys
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ARED Model used for Exercise Envelope Analysis
Analysts: Nate Newby and Erin Caldwell
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ARED Model used for Exercise Envelope Analysis
• The ISS Program Office requested an analysis to assess if the
ISS operational envelope for ARED exercise to assess if the
envelope is being exceeded during exercise due to excess
stowage in the exercise area
• DAP modelers used the dead lift/ARED model within the
currently assigned ISS operational envelope for ARED exercise
to assess if the envelope is being exceeded during exercise
• DAP modelers developed a model of a 95th % male
performing a bench press on the ARED to perform the same
analysis
• The results were shared with the ISS Program Office to
determine the necessary operational envelope
Analysts: Nate Newby and Erin Caldwell
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Contributions to the Field for V&V of
Biomedical Models and Simulations
• The FDA is leveraging a lot of the methodologies DAP
and IMM have laid out for verification, validation and
credibility assessment of M&S
• Collaboration talks are currently underway with FDA
• The NIH Multiscale Modeling Working group meeting
in October 2012 is going to have a large emphasis on
V&V and credibility assent
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Synapses
• DAP has established a systematic process to closely
work with researchers to leverage computational
models inform HRP risk knowledge gaps
• Current areas of focus are exercise countermeasures,
risk of bone fracture and VIIP
• Substantial strides have been made in the past year in
biomechanical and exercise device modeling
• Making notable contributions to the field in verification
and validation, and credibility assessment of
computational models
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“All models are wrong, but some are useful.”
- George E. P. Box
The DAP Team
Beth Lewandowski, PhD – Muscle Model
Bill Thompson, MS – Squat Integration
Brad Humphreys – Exercise Device Modeling
Chris Sheehan – Exercise Device Modeling Task Lead
Chris Werner – ARED V&V
DeVon Griffin, PhD - Project Manager
Emily Nelson, PhD – VIIP M&S
Erin Caldwell , MS - Biomechanics Modeling and Dead Lift Integration
Jennifer Stein – Exercise Device V&V Processes
Jim Pennline, PhD – Bone Modeling Lead
Jerry Myers, PhD – M&S Advisor
Lealem Mulugeta, MS - Project Scientist
Nate Newby, MS – Biomechanics Modeling and Dead Lift integration
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Questions?
DAP Mission Statement
The DAP implements well-vetted computational models
to predict and assess spaceflight health and performance
risks, and enhance countermeasure development. The
DAP aims to accomplish these goals by:
1. Partnering with subject matter experts to address Human
Research Program (HRP) knowledge gaps and countermeasure
development decisions
2. Modeling, simulating, and analyzing the physiologic responses
to exposure to reduced gravity and analog environments
3. Providing timely input to mission architecture and operations
decisions in areas where clinical data are lacking
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NASA Standard 7009
A comprehensive set of requirements and
processes for developing and applying
models and simulations, while ensuring
appropriate verification, validation and
credibility of the M&S results
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NASA-STD-7009 Background
• NASA M&S that impact on the crew or mission will be
required to follow NASA-STD-7009, including biological
models
• It was initially developed for engineering systems
• DAP and Integrated Medical Model (IMM) have
adapted NASA-STD-7009 for biomedical models for
clinical and research applications
• Given the highly comprehensive nature of the
standard, DAP and IMM are working to establish a
systematic process to apply it to vet M&S
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