ROOM
49
Astronautics
The real importance of gravity
on physiological systems is
seen when gravity is reduced or
taken away
of spaceflight. Here, the impact of microgravity
is seen on many physiological systems including
cardiovascular function, cerebral autoregulation,
musculoskeletal and sensorimotor systems.
For instance, cardiovascular deconditioning
remains a persistent problem associated with
the time spent in microgravity during spaceflight
(Antonutto et al., 2003). In addition, the re-entry
to Earth has many important effects including
increased heart rate, dizziness symptoms 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 immobilisation.
A variety of conditions and diseases such as
cerebral or peripheral vascular disease, metabolic
or endocrine disorders, autonomic neuropathy,
or cardiac arrhythmias may result in syncope
(dizziness and loss of consciousness), especially
during changes in posture from lying/sitting to
standing up.
Illness or injury in older people frequently
requires hospital-based care and the
immobilisation that occurs during hospitalisation
is itself a major factor in physiological
deconditioning and functional decline which, in
older people can further contribute to a downward
spiral of increasing frailty, dizziness upon standing
up and increased risk and incidence of falls
(Mühlberg and Sieber, 2004).
Bedrest is used as a ground-based analogue
for studying the effects of weightlessness on
physiological systems as seen during spaceflight
(Goswami et al., 2015; Jost, 2008; Pavy Le Traon
et al., 2007). The bedrest study protocol, in which
subjects lie in supine position over variable time
periods, is a highly controllable experimental setup
routinely used by space agencies and providing
excellent possibilities to investigate physiological
function changes during lowered gravitational
stress (Arzeno et al., 2013; Cvirn et al., 2015; Oshea
et al., 2015).
As older people spend up to 80 percent of their
time in hospital confined to bed, bedrest studies
can also help in furthering our understanding of
the deconditioning process during hospital stays.
Astronauts in space spend a substantial amount
of time doing physical training to counteract the
deconditioning due to the effects of microgravity
and to alleviate orthostatic intolerance on return
to Earth. They also complement their training
regimes with nutrition and other measures to
ensure optimal health. Pedersen and colleagues
(2016) recently reported that since the advanced
resistive exercise device (ARED) was introduced on
the International Space Station (ISS) eight years
Right: Astronauts
exercising on the ISS, with
NASA’s Ron Garan in the
foreground.
NASA
