1. Rodent Research in Microgravity: Anesthesia Recovery System
Tian Shi1,2, Joshua Danny3, Michael Levy4, Victor Niego4, and Brandon Hagerty5
1UC San Diego, La Jolla, CA 92093, 2Advanced Studies Laboratories, Moffett Field, CA 94035, 3Kansas Space Grant, 4Education Associates Program,
5NASA Ames Research Center, Moffett Field, CA 94035
ABSTRACT
The Rodent Habitat is hardware that
safely transports mice to the International
Space Station (ISS) and provides long-term
accommodation aboard the station. The
Habitat allows researchers to study the
long-term effects of microgravity on various
mammalian body systems. Such knowledge
can be used to prevent and treat adverse
effects of spaceflight, and to improve health
on Earth. In support of the Rodent Habitat,
a team of interns is redesigning the
Anesthesia Recovery System (ARS), which
will minimize the risk of hypothermia and
death associated with anesthetized mice. To ensure the survival of the mice during
the studies, the ARS will maintain a body temperature of 35.5 to 38 degrees Celsius
for a minimum of 5 hours, withstand the g-force during launch, and comply with other
science and animal welfare requirements. The preliminary heating system includes
heating pads with a power source that recharges through solar panels. The team
conducted numerous tests to gauge the effectiveness of the heating pads and the
required amount of energy, concluding that it is a viable design that requires more
testing to be finalized. The ARS will be a critical step in extending the scope and
capabilities of research onboard the ISS.
INTRODUCTION
Onboard the ISS, the mice must undergo anesthesia for procedures such as a bone
density scan . Under the effects of anesthesia, the brain does not function properly
and cannot detect temperature drop. The mice experience the inability to regulate
heat, inability to shiver, and vasodilatation in extremities. Combined with their large
surface to volume ratio, which causes increased metabolism and heat loss, these
factors greatly increase the risk of hypothermia and even death.
In order to minimize the risk, the ARS provides a holding area where the mice will
fall asleep from anesthesia before they are scanned and where they will wake from
anesthesia after. It fulfills the following requirements:
•Maintain mouse body temperature of 35.5 to 38 degrees Celsius for a minimum
of 5 hours
•Withstand g-force during launch
•Comply with other requirements of ARC Science and animal welfare to ensure
the safety of the mice
Our goal is to redesign the first prototype ARS, which fails to meet science
requirements and is heavy and large. It is an aluminum block with slots, into which
cylinders containing the mice can slide in. A thermocouple probe inside the block
allows for temperature feedback and control. It has the following pros and cons.
Our design aims to address these disadvantages, to not only meet the science
requirements but also be energy and space efficient. The proposed design utilizes
the Mouse Transfer Box (MTB), an existing piece of hardware designed for the safe
transportation of mice between holding areas.
SUMMARY AND CONCLUSIONS
Tests 1-3:
The use of a space blanket to retain heat significantly increased the ambient
temperature, from 85˚F to ~95˚F, which is in the required range.
The surface temperatures of S3 vary by up to 56.5˚F, which is a problem
considering that the range 70.5-127˚F is dangerously outside the required range 95.9-
100.4˚F. Factors that contribute to this include: heating pad inconsistency, varying wall
thickness of the container, and poor thermal conductivity of the container. We plan to
obtain better designed heating pads and install a mesh barrier within the plastic
container to keep the mice in a safe temperature zone. Another possible solution is to
make the MTB with a transparent thermally conductive material, such as ceramic.
Tests 4-5:
The purpose of power source tests was to assess the energy required for the
proposed design. The NiMH batteries linked in parallel lasted for ~75 minutes whereas
the USB battery lasted for ~237 minutes. In addition, the USB battery was far more
consistent in performance, maintaining constant power output and constant ambient
temperature. Since the ARS must operate for 1-5 hours, the USB battery is the better
option. However, not all lithium ion batteries are allowed on ISS, so we must either
conduct further testing for flight certification or find an alternative.
DISCUSSION
Our design also includes three solar panels intended to trickle charge the battery during
and after use. We plan to run tests in the MSG Simulator, which mimics the light
conditions the ARS will be in. We also must continue to validate the safety and efficiency
of our design and possibly explore other heating methods, such as forced air.
REFERENCES
“Prototype Mouse Warming System.” Center for the Advancement of Science in Space (CASIS), n.d. PDF file. 8 July 2014.
Hart, Dominic. “Rodent Habitat.” Photograph. “Rodent Research Hardware System.” National Aeronautics and Space
Administration, 9 March 2014. PDF file. 21 July 2014.
“Mouse Anesthesia Warming Support Hardware Requirements Interpretation Letter.” National Aeronautics and Space
Administration, n.d. doc file. 24 June 2014.
“Mouse Warming Box: Derivation of Requirements.” National Aeronautics and Space Administration, 12 Nov. 2013. pptx file.
23 June 2014.
Pletcher, David. “Rodent Habitat Project: Overview and Concept of Operations.” 15 January 2014. PowerPoint. 2 June 2014.
“Science Requirements Document for Mouse Warming Box.” National Aeronautics and Space Administraction, 25 Nov. 2013.
doc file. 23 June 2014.
ACKNOWLEDGEMENTS
I would like to thank my mentor Kevin Stube for his guidance and support. This research has
been supported by the Rodent Research Project and the ASL Internship Program. Special
thanks to Joshua Danny, Michael Levy, Victor Nieto, Brandon Hagerty, Dennis Leveson, and
Michael Hines for providing their gracious, collaborative approach to this project.
www.asl.ucsc.edu
Rodent Habitat
Image credit: NASA / Dominic Hart
Pros:
• Aluminum block uniformly distributes the heat.
• Temperature can be set, and controller relays
actual temperature.
Cons:
• Mouse is in a confined space, which may cause
stress when it awakes.
• The cylinder containers do not allow for
appropriate air exchange and waste containment.
• Mouse is not observable inside warming device.
Vital signs cannot be verified.
• The controller and warming device are very large,
and therefore expensive to transport and reduces
usable space in the Microgravity Sciences Glovebox
(MSG).
Temperature controller and power supply
Image credit: CASIS
Mouse container slides in and out
Image credit: CASIS
MATERIALS AND METHODS
We conducted multiple tests to optimize the heating method and the power source, using the
following configurations:
S1
S2
S3
h1
h2
RESULTS (cont.)
Configuration A:
• 5V heating pads attached to surfaces S1, S2, and S3.
• Plastic lid drilled with two holes h1 and h2 for temperature
measurements, and one hole covered with PVC pipe as a
thermocouple holder. The thermocouple is positioned to measure
the ambient temperature at the center of the container.
• Set up container on stand to focus solely on the effectiveness of
the heating pads.
Test 1: Determine ambient temperature curve caused by heating pads
• Use Configuration A, and set AC power source at 5V
• Measure current, ambient temperature with the thermocouple, and surface temperatures with
the infrared thermometer
Test 2: Determine ambient temperature curve caused by heating pads and space blanket
• Use Configuration B, and set AC power source at 5V
• Measure current, and ambient temperature with the thermocouple
• At maximum ambient temperature, open the lid and use a thermal imaging camera to assess
uniformity of S3’s internal surface temperature
Test 3: Test product consistency of heating pad
• Use Configuration B with different set of heating pads, and set AC power source at 5V
• Measure current, and ambient temperature with the thermocouple
• At maximum ambient temperature, open the lid and use a thermal imaging camera to assess
uniformity of inside S3 surface temperature
Configuration B:
• Setup is identical to Configuration A except that a space
blanket covers surfaces S1, S2, and S3. This is to retain heat
better by reflecting it back to the container.
Test 4: Test energy density of first power source
• Use Configuration B
• Power source is two 2000mAh, 4.8V NiMH batteries wired in parallel
to maintain same voltage but greater current
• Measure current with ammeter, voltage with voltmeter, and ambient
temperature with the thermocouple
Test 5: Test energy density of second power source
• Use Configuration B
• Power source is a USB charger with a lithium ion battery, at 12Ah
and 5V
• Measure current with ammeter, voltage with voltmeter, and ambient
temperature with the thermocouple
RESULTS
S1
S2
S3
Test 1: Ambient temperature
plateaus at 85.4˚F at around
27 minutes.
Test 2: Ambient temperature
reaches 85˚F much quicker,
and plateaus at 97.3˚F at
around 51 minutes.
Test 3: Ambient temperature
plateaus at 93.7˚F at around
51 minutes.
Test 2: At plateaued ambient temperature,
inside S3 temperature peaks at 127˚F. The
minimum is 70.5˚F and the average is 98.4˚F.
Test 3: At plateaued ambient temperature,
inside S3 temperature peaks at 126˚F. The
minimum is 72.3˚F and the average is 102˚F.
Test 4 ambient temperature
plateaus at 93˚F at ~46 minutes
and begins to drop at ~121
minutes. Test 5 ambient
temperature plateaus at 93˚F at
~89 minutes and begins to drop at
~326 minutes.
Test 4 power plateaus at ~7.4 W and
displays constant and gradual
decreasing. Test 5 power remains
constant around ~7.35 W and displays
abrupt changes.
Electrical circuit used for Test 4 and 5