Research Description
The decision of Mark Shuttleworth to travel to space has provided South Africa with a unique opportunity to promote and share our unique scientific research and technology with the rest of the world. The Exercise Science and Sports Medicine Department of the University of Cape Town together with BODY iQ have proposed a study entitled 'The effect of a microgravity environment on autonomic cardiovascular control, energy expenditure and muscle characteristics'. The rationale and aims of the study are discussed below.
Both heart rate and blood pressure are controlled by the autonomic nervous system. This nervous system is an unconscious, or 'automatic' nervous system, which consists of 2 parts - the parasympathetic nervous system and the sympathetic nervous system. These 2 systems have opposing roles and are activated according to the different needs of the individual. The parasympathetic nervous system is activated during rest and assists in energy restoration. During rest, the parasympathetic nervous system assists in the digestion and absorption of food and causes a decrease in heart rate. The sympathetic nervous system, on the other hand, prepares the body for an emergency and counteracts the parasympathetic nervous system in order to maintain the required energy supply. During any emotional or physical stress, adrenaline is released by the sympathetic nervous system, which acts to increase heart rate and blood pressure. Accordingly, heart rate is controlled by the balance between parasympathetic (PNS) and sympathetic nervous system (SNS) activity. On a beat-to-beat basis, however, it has been observed that heart rate is not constant and there are periodical fluctuations indicative of the relative contributions of each of these 2 components of the autonomic nervous system. There have been various methods employed in an attempt to quantify the relative contributions of each of these systems. On of the most commonly used methods is the frequency domain analysis of heart rate variability method. This method uses highly sophisticated techniques to determine different frequencies of heart rate and from this analysis can identify which nervous system is predominantly active.
There have been very few studies conducted during space flights that have measured this component of physiology, and those that have been done have yielded conflicting results. Besides this, these studies have used on board electrocardiographic (ECG) equipment. Therefore, the first aim of this study will be to determine whether the relative contributions of the parasympathetic and sympathetic nervous system remain the same in space when compared to earth. This will be measured using an electrocardiograph (ECG), after which, the collected heart rate data will be transmitted to earth, via satellite, where it will be analyzed and interpreted by by UCT’s Human Biology (HUB) department. For this part of the study, Mark will be required to perform the same exercise test 4 times on earth before the launch. This exercise test involves a series of stages on a stationary bike that increase in intensity with an increase in time. Each stage lasts for 2 minutes and is separated by 1 minute of rest. Mark will then be required to perform the same test while in space. On each occasion, resting, exercising and recovery heart rate and blood pressure will be recorded. After each exercise session, Mark will be asked to record how he is feeling based on a 10 point scale. After landing, we will ask Mark to repeat these same tests in order to compare physiological responses on earth and in space.
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