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Spaceflight meets Geriatrics!

Nandu Goswami1*
  • 1 Medical University of Graz, Austria

Introduction This paper presents a general overview of important physiological effects induced by spaceflight, the aging process in humans on Earth, and important connections between these physiological states. Developing an understanding of links between spaceflight physiology and the physiology of the aging process can provide insights and methods that improve both human health in older persons on Earth and the health and effectiveness of astronauts living in microgravity. Ever since our ancestors started walking upright, our body has adapted to the impact of gravity. During standing, for example, although the human heart is positioned below the brain, it is able to pump enough blood to the brain against the force of gravity to maintain proper brain function. Furthermore, during standing, gravity induces blood pooling in the legs. This is counteracted by several mechanisms including muscle activity in the lower limbs which together with one way valves in the veins acts as a muscle pump to return blood to the heart which is further supported by the act of breathing. Additionally, the weight-bearing bones and anti-gravity muscles have adapted during evolution to ensure adequate support during standing. Thus humans can stand up without any real problems. The real importance of gravity on physiological systems is, however, revealed in the reduced gravitational environment (microgravity) encountered during spaceflight. The impact of microgravity can be in many important physiological systems, including the cerebral autoreglatory control system, the cardiovascular and cardipostural systems, as well as sensorimotor and musculoskeletal systems. For instance, cardiovascular deconditioning remains a persistent problem associated with the time spent in microgravity during spaceflight (Antonutto et al., 2003). The return to to Earth and normal gravity, results in a number of important reactions which can include increased heart rate, dizziness upon standing up (decreased orthostatic tolerance) and a reduction in exercise capacity (Buckey et al., 1996). Physiological deconditioning as seen in spaceflight also occurs on Earth, especially as a consequence of the aging process and also due to bed-confinement and/ or immobilization. Many conditions and diseases including metabolic or endocrine disorders, cerebral or peripheral vascular disease, cardiac arrhythmias, and autonomic neuropathy, can lead to orthostatic intolerance (dizziness and loss of consciousness upon standing up), especially during changes in posture from lying/ sitting. Furthermore, illness or injury in older persons frequently requires hospitalized based care which often includes bed confinement and immobilization. It is important to observe that immobilization during hospitalization also represents a significant source of deconditioning and decline in physiological function, which in older persons ca be an important additional factor contributing to a continiuing negative spiral of increasing frailty, orthostatic intolerance and greater risk and occurrence of falls (Mühlberg and Sieber, 2004). Bedrest is a ground-based model for weightlessness that has been applied to investigate the effects of spaceflight on the functioning of human physiological systems as observed during the microgravity of space flight (Goswami et al., 2015; Jost, 2008; Pavy Le Traon et al., 2007). In the bedrest study protocol, subjects are restricted to the supine position over various durations of time which can be days or weeks. The bedrest protocol provides an experimental set up which is highly controllable and allows for investigating changes in physiological function during reduced gravitational stress and has frequently been employed by space research agencies (Arzeno et al., 2013; Cvirn et al., 2015; Oshea et al., 2015). Since older persons in hospital can spend as much as 80% of their time confined to bed, bedrest studies can also help in furthering our understanding of the deconditioning process during hospitalization in older persons (Figure 1). During spaceflight, astronauts devote a substantial amount of time to physical training with the goal to both reduce deconditioning due to microgravity during flight but also to reduce the problem of orthostatic intolerance after return to normal gravity on Earth after flight. They also complement their training regimes with nutrition and other measures to ensure optimal health. Pedersen and colleagues (2016) have reported recently that, following the introduction of the advanced resistive exercise device (ARED), 8 years ago at the ISS, resistance exercise has increased as a component of the planned exercise regimen during space flight. Could such physical activity programs carried out by astronauts in space be used during bedrest immobilization in older persons to counteract deconditioning as well? Early intervention in bed-confined older persons is vital, as typically, without such intervention, rapid declines in bone and muscle mass as well as functionality are experienced (Singh et al., 2008). Started early enough, remobilization interventions can overcome the decline of physiological function, leading to complete recovery. However, delayed intervention often results in incomplete recovery where patients can be left with reduced physiological functionality. Unfortunately, re-mobilization is started too late in many cases and patients suffer a permanent loss of their functionality, leading as well to a loss of autonomy and the ability to lead an independent life, and resulting to increased risk of mortality (Singh et al., 2008). Intervention combinations in older persons confined to bed could incorporate physical exercise and/ or nutrition (Figure 2). While some evidence exists indicting that physical activity is beneficial for maintenance of physical functionality as well as mental health in older persons (Olanrewaju et al., 2016), there is limited literature that has examined the effectiveness of various forms of physical activity in combating the negative consequences of bed-confinement in older persons. Recent data generated from bedrest campaigns related to space research suggest that resistive vibration exercises can maintain muscle strength and function. Even though these data were obtained in young subjects confined to bedrest, resistive vibration exercise could provide an important method to address the problems of deconditioning in bed-confined older persons. This illustrates how data generated from ground based analogs of microgravity could have application in geriatrics. There is increasing evidence that inadequate food intake and nutrition in general is strongly associated with risk of frailty in older persons (Martone et al., 2013). The consequences of malnutrition include increased morbidity, functional decline, increased/ early dependency and institutionalisation, increased re-admission following hospital discharge as well as greater mortality. However, evidence is limited on the degree of benefit that improved nutrition alone can provide in older persons (Muscaritoli et al., 2016). In this regard, Strandberg et al. (1985) found that nutritional therapy, combined with resistive exercise training, can improve muscle mass in older persons. Moreover, another study indicated that a diet high in protein inceases both muscle strength and lean tissue mass in older women when combined with resistive training (Daly et al., 2014). Similarly, spaceflight data have also shown that resistance exercise, together with proper nutrition, including Vitamin D, is effective in maintaining physiological functionality in astronauts during spaceflights of up to six months duration (Smith et al., 2012). These observations indicate that knowledge obtained from space research can provide guidance regarding supplementing and optimizing the effects of physical exercises by including nutritional supplementations and/or pharmacological interventions in an integrated approach to therapy, which could represent key innovations in tackling bed-confined deconditioning, especially in older persons (see Hackney et al., 2015). The call-out box summarizes the important aspects of this paper: • Integrating what is known about deconditioning due to minimal gravitation stress in the microgravity of space and deconditioning induced by bed rest, provides an opportunity to develop a more comprehensive understanding of deconditioning (Figure 1) and lead to the development of countermeasures. • To reduce the deconditioning effects of microgravity, astronauts during spaceflight schedule regular sessions of specialized exercise trainng. • Could these exercises carried out by astronauts be used to counteract deconditioning in bedconfined older persons? • Additional countermeasures can incorporate nutrition, and innovative training methods to improve muscle function and strength, as well as cardiovascular and cardio-postural functions (Figure 2). • Early remobilization after a period of confinement to bed in older persons can prevent orthostatic intolerance, falls and injuries related to falls. Conclusions and Future Perspectives Developing an understanding of parallels and sharred aspects between the physiology of humans in reduced gravity and the physiology of aging provides the opportunity of deriving new insights and new strategies of intervenation relevant for both spaceflight physioslogy and the physiology of aging. For example, studies involving bedrest, in addition to simulating spaceflight induced deconditioning, can also provide information on deconditiong during confinement in bed, for example during hospitalization, a common occurrence with special impact in older persons who undergo surgery or must be treated for injury or are subject to debilitating diseases. Indeed the potential exists for a powerful convergence of knowledge between microgravity induced deconditioning and bed rest induced deconditioning in older persons, which could be useful in the development of countermeasures in both conditions. The parallels between the physiological consequences of aging and microgravity, and strategies that apply spaceflight technology to help life on Earth, especially in relation to bed-confined older persons should be further explored and recommendations developed that incorporate the important aspects of deconditioning and muscle loss, nutrition, and cardiovascular/ cardio-postural functions, which are involved in the aging process and/ or the effects of long term bed confinement.

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References

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Keywords: spaceflight, Aging, falls, Orthostatic Intolerance, Immobilazation, Bedrest

Conference: 39th ISGP Meeting & ESA Life Sciences Meeting, Noordwijk, Netherlands, 18 Jun - 22 Jun, 2018.

Presentation Type: Extended abstract

Topic: Astronaut health

Citation: Goswami N (2019). Spaceflight meets Geriatrics!. Front. Physiol. Conference Abstract: 39th ISGP Meeting & ESA Life Sciences Meeting. doi: 10.3389/conf.fphys.2018.26.00022

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Received: 02 Dec 2018; Published Online: 16 Jan 2019.

* Correspondence: Dr. Nandu Goswami, Medical University of Graz, Graz, Austria, nandu.goswami@medunigraz.at