On Earth, our bodies rely on convection to cool down: as liquids and gases heat up they become less dense and rise, and consequently moving heat away from our skin. There is no convection in weightlessness so it is surprising that astronauts’ bodies adapt and do not overheat in space. The body temperature control is particularly important during exercise which for astronatus during a long-duration stay is mandatory every day. It is hypothesized that heat balance, thermoregulation and circadian temperature rhythms are altered in humans during long-term space flights because of changes in:
i) The natural convective heat transfer from the body surface to the environment,
ii) Fluid shifts along the body axis from peripheral to central parts,
iii) The cardiovascular and,
iv) The autonomous nervous system as well as
v) Due to changes of body composition (fat mass, muscle mass, body water).
Since these factors are particularly cross-linked with each other during exercise, an integrative study of the topic under microgravity conditions is mandatory. However, such integrative studies combining exercise performance (NASA´s V02 Max experiment, PI: A. Moore) and thermoregulatory adaptations of humans in space have been very limited to date or even missing for long-term space flights due to methodological constraints.
Therefore, Thermolab aims to investigate the core temperature and heart rate during rest and exercise to determine the physiological strain index (PSI) in the course of a long-term micro-g exposure (ISS mission).
For this purpose a newly developed thermo-sensor (DoubleSensor, Draegerwerk AG) for core temperature will be applied. This technical device will enable us to study non-invasive and very convenient to the subject the core temperature during rest and exercise under long-term micro-g conditions.
Justification for the need of space experiment
During space flight, crewmembers are:
(1) Frequently exposed to hot or cold environments,
(2) Have to perform high physical work loads, and
(3) Must wear heavy armour protective clothing against cold stress or radiation during EVA´s.
Under these conditions the body core temperature can change rapidly, eventually reaching deleterious levels. Until now, body core temperatures measurements were quite difficult to achieve, and required insertion of a thermo sensor into the body.
The Double Sensor hardware will allow for the first time to monitor body core temperature during long-duration space flight, and will lead to a better understanding of heat transfer in humans under microgravity conditions. The two sensors are place on the astronaut´s forehead and chest that measure the temperature continuously. see Figure 2
Experiment specific goals and detailed objectives:
To investigate thermoregulatory and cardiovascular adaptations during rest and exercise in the course of a long-term microgravity exposure with a newly-developed thermo sensor (DoubleSensor) for core temperatures.
Previous flight experiments (human physiology experiments only)
The DoubleSensor which will be used during the BDC and in-flight recordings had already been used in experiments during parabolic flights with a related scientific objective. At the moment we are analysing the data that we collected during two Parabolic Flight Campaigns organised by the German Aerospace Center (DLR) in November 2007 and April 2008.
The Thermolab experiment should be performed in combination with NASA´s V02 Max experiment (PI: Moore) see Fig 1. The subject will be instrumented with the Thermolab hardware in the beginning of each session to allow for approximately 15-30 minutes of baseline core temperature reading while the subject is instrumented with other hardware required for V02 Max testing. Data collection continues during the V02 Max exercise protocol and it is requested that the Thermolab hardware is removed last to allow capturing the complete cool-down phase after exercises.
Estimated in-flight crew time for retaining the hardware and instrumentation is 15 minutes, plus 10 minutes for de-instrumentation and stowage of the hardware after testing; 25 minutes total per data collection session. During data collection the data are stored inside Thermolab control unit on a memory card. Data downlink should be scheduled after data collection is complete via USB interface. The required time is estimated at 2-3 minutes per data download (if data download possible via Portable PFS USB port). If multiple subjects are scheduled to perform VO2 Max testing within several days, one data download at the end of the last session is requested.
Pre- and post-flight data collections will include the L-270 Peak Cycle Test (MEDB 4.1) and all planned V02 Max BDC sessions (L-60, L-30*, R+1, R+10 and R+30*), plus two Bioelectrical Impedance Analysis (BIA) measurements performed once pre-flight (L-10 +/-10 days) and once past-flight (R+8 +/-5 days).
(* V02 Max team has indicated that L-30 and R+30 BDC´s will only be performed if required.)
see also: Table 1 Thermolab
- Body core temperature, in degrees Celsius
- Body composition (Body water content, body fat mass, lean body mass etc.)
Number of test subjects:
- Minimum: 8 subjects are required to allow for sufficient statistical analysis
- Desired: 12 objects
Ground reference experiment(s):
Thermolab will be implemented during a NASA bed-rest study. A minimum of 6 bed-rest subjects are requested.
Detailed Experiment Timeline and associated Functional Objectives
Thermo BDC sessions
L-10 +/- 10 days
R+8 +/- 5 days
Thermo In-flight Sessions
see also: Table 1 Thermolab
The information obtained by this study will lead to a better basic understanding of heat transfer and the thermal regulation in humans under microgravity conditions.
The core temperature is automatically calculated by the Themolab Control Unit according to the heat-flux-formula. The physiological strain index (PSI) will be calculated out of the core temperature values and the heart rate of the subject. So the PSI can be determined for certain levels of strain. The heart rate data will be requested from the
V02 Max experiment team via data sharing.
Core body temperature rises faster during exercise on the ISS than on Earth, probably caused by fluid shifts and modified heat flow away from the body. The graphs in Figure 4 highlight this adaptation in the core body temperature. Adaptation can be seen in the first six weeks on the ISS with an increase in core body temperature by around 1-1.5 deg C though this settles down to an increase of around 0.5-1 deg C above pre-flight core body temperature as the mission extends. With the core temperature rising faster on the ISS it is also noticeable that the body temperature takes longer to cool back down to core temperature after exercise.
The measurement of the core body temperature together with cardiovascular measurements during the NASA VO2 Max protocol can be used to evaluate the subject´s state of fatigue, which is very important for optimising mission success. The non-invasive double sensor could be a very useful diagnostic tool for recognising early warning signs of fatigue during, for example, spacewalks in orbit. On Earth firefighters (to recognise exhaustion/overheating) or jet pilots, steel workers, miners, soldiers in combat, divers etc. working in extreme conditions could all benefit from this technology. It could also be used for monitoring during critical hospital operations such as heart surgery or for monitoring babies in incubators.
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click on items to display
Figure 1: Exercise protocol performed during VO2 Max testing.
Figure 2: DoubleSensor positioning.
Figure 3: Schematic overview of Thermolab flight hardware.
Figure 4: Variation in core body temperature (measured at the forehead) before, during, after a graded exercise protocol before flight, in‐ flight and post‐flight. (Images: H‐C Gunga)
Table 1: Thermolab Functional Objectives for in-flight timetable.
13 May 2015: Web story on the ESA website about the experiment