AGBRESA – you take everything with you into space, apart from gravity – training on the short-arm centrifuge
Strict bedrest and spinning – how do they fit together? Very easily – as a participant in the AGBRESA bed-rest study! The participants complete their training on the DLR short-arm human centrifuge every day during their 60 days of bedrest.##markend##
Since the earliest days of crewed spaceflight, human beings have been venturing out into the cosmos for increasingly long periods, where they are exposed to a weightless environment, or microgravity. Long-term stays on the International Space Station (ISS) lasting six months or more have become the norm. From an evolutionary perspective, though, human beings are adapted to Earth’s gravity. When this force is absent, the body experiences a large number of physiological responses as it adjusts to the new environment. Some of the effects are adverse and can even be harmful after returning to a gravitational environment, for instance on Earth or, in future, on Mars. At present, space travellers lose as much as two percent of their bone density each month and experience a significant drop in their muscle strength as well. The immune system is also compromised, and there seems to be a correlation between the length of time spent in space and a reduction in vision acuity.
In short, while prolonged space missions seem to be possible, they do present health risks. ISS crew members exercise for up to 90 minutes every day in order to prevent negative physiological changes – although they do so in a weightless environment. However successful this training may be, its effects are nevertheless limited, and the equipment requires significantly more space than would probably be available on a spaceship traveling to Mars. In addition, future missions to Mars are likely to last approximately 1000 days, which is considerably longer than any astronaut has spent on the ISS so far.
Research into suitable countermeasures is necessary in order to minimise the risk of mission-critical injuries, such as fractures due to inadequate bone density or an unstable circulatory system. Centrifuges might be a suitable way of compensating for the lack of gravity. The General Theory of Relativity suggests that the centrifugal forces generated by this method act in the same way as gravitation and therefore expose cells in the body to a comparable stimulus. The concept of rotating space stations or spaceships has been around for a long time and was first proposed by the Russian space pioneer Konstantin Eduardovich Tsiolkovsky. However, it is currently unknown which exact parameters are necessary or are tolerable for humans over a sustained period.
30 revolutions per minute
With AGBRESA, two different centrifuge profiles have been tested as possible countermeasures as part of a long-term bed-rest study for the first time. This involves treating eight of the 12 participants for 30 minutes every day. The other four belong to the control group and do not take part in the centrifuge training. Four of the participants are treated on the centrifuge for 30 minutes every day, while the others complete a type of interval training, during which they receive six five-minute treatments, each separated by a break of three minutes. The participants were randomly assigned to the various groups at the start of the study. They lie on the centrifuge with their head facing inwards and their feet pointing out, so that the centrifugal force generated by the ride takes effect in the direction of their feet. The participants riding the centrifuge are exposed to 1g (Earth gravity) at the centre of gravity of their body, and 2g – twice Earth’s gravity – at their feet. The rotational speed of the centrifuge is approximately 30 revolutions per minute, or once every two seconds. The body’s own weight presses the feet against the base plate. Participants who close their eyes and forget for a moment that they are actually lying down might almost feel like they are standing up.
By now, all of the participants have become old-hands on the centrifuge. They know that they are meant to ‘go’ to the toilet before starting (so they need to ask one of the study personnel to give them a urine bottle …) and that it is advisable not to eat a large meal any later than one hour before receiving treatment. The 30-minute rides themselves usually pass quickly – some of the participants listen to their favourite music or audio books, while others just lie there with their own thoughts. Many of the test participants were afraid they would become nauseous, but that has rarely been the case so far. Often, they are given real assignments during the treatment. There are frequently experiments scheduled for their time on the centrifuge, to which they must actively contribute. There are cognitive tests with arithmetical and concentration-endurance exercises, during which the participants use a microphone to give their answers to the test operators in the control room. The programme even includes ultrasound measurements to determine the blood flow, which the participants perform on themselves during the treatment session, following instructions from the experiment coordinators. These experiments are usually conducted at the beginning, in the middle and at the end of the bed-rest phase. Cardiovascular parameters, muscle metabolism data and muscular activity are recorded and then analysed on the other days of the study. Intraocular pressure is measured before and after the treatment, and a respiratory gas reading is also taken. So, boredom is rarely a factor during the centrifuge training.
Daily centrifuge treatment – 60 days in a row
The participants receive frequent instructions from the control room during the treatment session. The test operators maintain constant contact through audio and video links. There are times for the test participants to orient themselves, questions concerning their well-being or short chats if the experiment setup allows them to communicate freely. A certain routine has now been established, and the participants experience the treatments on the centrifuge as a welcome distraction from their days in bed.
For the DLR personnel, the AGBRESA study means approximately 10-hour working days with the centrifuge. They do more than just manage the treatment sessions themselves and are also responsible for preparations, follow-ups, medical checks and monitoring. Acceleration, deceleration and the pauses within the intermittent protocol take a lot of effort, as none of the treatment sessions are automated. Each one has to be accompanied on site by at least one doctor and a technical operator from the team. The treatments take place daily, so neither the study personnel nor the participants have the weekend off. The centrifuge team is at the facility seven days a week to spin the terrestrial astronauts in a circle. It is still astonishing how smoothly everything proceeds; there have been no problems whatsoever so far. The participants are all in good spirits and highly motivated, although they occasionally have to get over the odd phase of fatigue in the morning. None of them have suffered the nausea they feared during the treatments on the centrifuge, and all of the participants are pleased that the ambitious plan is being implemented.
Exposing the feet to 2g in 25 seconds
The eight participants are moved in and out for centrifuge training almost like on a conveyor belt – so the team needs to work smoothly. The first step is fitting electrodes to the participant and a safety belt around their hips in the preparation room. The participant is then moved from the stretcher to the centrifuge arm and the final arrangements are completed. The centrifuge team connects the medical monitoring devices and secures the belts. The doctor – an integral part of the centrifuge team and present during all the sessions – takes another quick look at the participant’s heart rate and measures their blood pressure. In addition, the centrifuge operator inspects the circular room with a critical eye one final time to make sure that all the devices are firmly attached and no objects have been left behind. The large door to the centrifuge room now closes, but the centrifuge itself cannot start until the door has been locked. A short tone indicates that the centrifuge is ready to start. The operator presses the start button to set it in motion; the direction of rotation changes each day to ensure that the gravitational effects on the participant’s legs are evenly distributed during the study. The acceleration phase before the participant reaches the final speed lasts around 25 seconds. The centrifuge slows to a stop after 30 minutes, and the team comes back to unbuckle the participant, remove the cables and electrodes and return the participant to the stretcher. It is just a short distance back through the doors of the centrifuge room and into the study ward. The participant encounters the next candidate along the way, and they high-five one another from stretcher to stretcher. This participant is all ready to go, and a new session can begin.
Over 500 centrifuge sessions will have been completed by the end of this first campaign, including the familiarisation ones at the beginning of the study. Each participant will have spent more than 30 hours on the device, completing far more than 54,000 rotations in the process.