Structured Exercise Training as Countermeasure to Space Flight-Induced Orthostatic Intolerance (Exerc-Orthostatic Tolerance) - 07.15.14
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Structured Exercise Training as Countermeasure to Space Flight-Induced Orthostatic Intolerance (Exerc-Orthostatic Tolerance) tests crewmembers' ability to stand before and after a space mission, during which they perform a structured, individualized treadmill exercise program. Astronauts lose bone and muscle density in microgravity, and undergo alterations in the neural regulation of cardiovascular responses to orthostatic stress, leading to orthostatic intolerance, or the inability to stand, when they return to Earth. Results from the investigation could improve countermeasures to prevent this problem.
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OpNom Orthostatic Tolerance
IRCCS San Raffaele Pisana, Rome, , Italy
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Italian Space Agency (ASI)
Earth Benefits, Scientific Discovery, Space Exploration
ISS Expedition Duration
September 2014 - October 2015
Previous ISS Missions
- The study in the development of specific countermeasures to prevent major health issues after space flight, such as orthostatic intolerance.
- Accelerating rehabilitation of crews on exploration missions could find clinical applications in preventing inactivity, or other gravity-related disorders, and disability on Earth.
- These countermeasures can be used to prevent autonomic dysfunctions related to gravitational stress, such those encountered in bedridden subjects, like orthostatic hypotension. This is particularly important in the present aged-society with many bedridden elderly people.
The knowledge accumulated from studies on autonomic neural functions in space should be very useful to establish effective countermeasures and preventive methods for gravity-dependent autonomic dysfunctions.
Astronauts adapt to the microgravity environment of space appropriately and effectively. However, on return to the Earth they have reduced orthostatic tolerance and exercise capacity. Even after short duration flights approximately 20% of the astronauts experience light-headedness and muscular weakness when standing on landing day, and as many as 83% after long-duration spaceflights. The underlying mechanisms are not completely defined and are probably dependent on many factors. Alterations in the autonomic nervous system and neuromuscular function induced by spaceflight are the most likely contributors to this problem.
Many countermeasures have been tested against orthostatic intolerance. Among these, physical exercise has been the most obvious countermeasure employed during space flight because of its predictable capability to positively affect exercise capacity, autonomic nervous system regulation, muscle strength, power, and endurance, all of which are impaired as a consequence of weightlessness. Physical exercise is an important component of the routine work during flight, and could have positive effects on various microgravity induced disturbances, inclusive of muscle-skeletal impairment and post-flight orthostatic intolerance. Accordingly it has been always considered as a potentially important countermeasure. Yet, despite widespread in-flight utilization, physical exercise has proven only partially effective in counteracting orthostatic intolerance after space flight.
To date, physical activity of astronauts during space flights has been mainly self-selected using daily conventional one level of dynamic exercise (according to general recommendations) with the general aim to maintain functional capacity and muscle strength and power. To our knowledge, no structured exercise training program has been performed by astronauts specifically targeted at addressing the autonomic adaptations to a specific exercise training, as defined by the type of exercise performed, and its relationship with prevention or reduction of orthostatic intolerance upon return to earth after space flight. Accordingly, the objective of this project is to assess the effectiveness of a structured aerobic, individually tailored exercise training in preventing orthostatic intolerance and its underlying, mainly neural, mechanisms in astronauts.
Orthostatic (in)tolerance is assessed both before launch, and after landing, by means of an Orthostatic Tolerance test consisting of ten minutes of supine rest, followed by 20 minutes of unaided standing. During this time, blood pressure andheart rate are continuously and non- invasively recorded. Heart Rate is recorded by means of three electrodes positioned on the chest. and blood pressure is measured continuously at the finger of a hand by means of a photoplethysmographic device (Portapres) connected to a small pneumatic cuff placed around a finger. During standing, the arm with the instrumented finger is maintained at the heart level by the aid of an elastic band supporting the arm at the wrist.
The hardware needed for this investigation consists of a biological signal (analogic) data acquisition system that has been used in several previous space flights investigations sponsored by NASA.
Analysis heart rate (HR) and blood pressure (BP) variability and baroreflex sensitivity (BRS), with dedicated software, will be used in a consolidated methodology to assess the neural control of the cardiovascular system during orthostatic stress before and after flight. Exercise training during flight is performed by crew member(s) on the treadmill, according to a program individually-tailored on the basis of an incremental treadmill exercise test performed before flight by means of the individualized TRaining IMPulse (TRIMPi) methodology.
TRIMPi is an individually determined, integrated measure of response to physical load, that permits for both intensity and volume effects of endurance exercise training programs. The TRIMPi method considers the change in Heart Rate (ΔHR =HRexercise- HRrest /HRmax-HRrest), as main exercise variable. The duration of any specific training session is multiplied by the average ΔHR achieved during that session. To avoid giving a disproportionate importance to long-duration activity at low ΔHR levels, compared with intense but short-duration activity, the ΔHR is weighted by a multiplying individual factor (yi), in a way that reflects the intensity of effort. This y factor is based upon the exponential rise of blood lactate levels with the fractional elevation of exercise above resting HR. This factor served to equate the TRIMPi scores of exercises of long duration and light HR, with exercises of short duration and high HR.
In order to plan a TRIMPi-based training program, the crew members perform before flight, a progressive exercise test on a treadmill to volitional fatigue with recording of HR and blood lactate levels (25µL capillary blood samples taken from the earlobe) at pre-defined time intervals. During in-flight exercise sessions the astronauts wear a cardiotachograph, which is capable of storing HR values to be transferred to a PC, and analysed using dedicated software.
Astronauts have difficulty standing or walking when they return to Earth, partly because of reduced bone density, muscle mass, and alterations in the neural regulation of cardiovascular responses to orthostatic stress caused by exposure to microgravity. Countering this problem requires developing exercises that maintain muscle and bone strength in space, and also preserves neural cardiovascular regulation. A standing test before and after the flight with simultaneous, non invasive, evaluation of neural cardiovascular regulation can assess the effectiveness of the exercise regimen.
More effective countermeasures that address neural cardiovascular regulation in addition to bone and muscle density loss could also improve rehabilitation methods for people on Earth. Patients with limited mobility, including people on bed rest, also experience alterations in neural cardiovascular regulation, cardiovascular deconditioning in addition to bone and muscle degeneration.
Within two months prior to launch, the crew members perform a progressive exercise test on a treadmill to volitional fatigue, with recording of HR and blood lactate levels (25µL capillary blood samples taken from the earlobe) for determination of individualized TRIMPi, in order to plan an individually-tailored exercise training program. Also, crewmembers should undergo an Orthostatic Tolerance test consisting of 10 minutes supine rest, followed by 20 minutes of unaided standing during which blood pressure, and heart rate are continuously and non- invasively recorded. Optionally, this test should be repeated in the week preceding launch. This test should also be repeated by returning crewmembers within ten days of landing (R+6±4).
Investigating 4 crewmembers would be ideal. Downlink of data during flight experiments is essential. The only specific constraint is for no meals other than breakfast should be eaten within two hours before the orthostatic tolerance test, and no exercise test or strenuous physical activity in the 24 hours preceding the orthostatic tolerance test, both before launch (BDC) and after reentry after space flight.
On orbit, the crew members perform a structured, individually tailored aerobic exercise training program on the treadmill, as planned before flight, according to the schedule foreseen for their usual physical activity on board, which consists of approximately 1 hour per day. During the aerobic exercise sessions, the crewmembers wear a cardiotachograph, which is capable of storing HR values every 5 seconds to be transferred to a PC, and analysed using Microsoft Excel Spreadsheet.