Microgravity and Weightlessness Pathophysiological Effects; A Systematic Review of the Literature
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Rosemary Kimball
CoPIs:
Kayley Brooks
College:
The Dorothy and George Hennings College of Science, Mathematics, and Technology
Major:
Biology
Faculty Research Advisor(s):
Rana Zeine
Abstract:
OBJECTIVE: Numerous studies have demonstrated that weightlessness, microgravity or zero gravity, has physiological and pathological effects on multiple organ systems in humans and animals. Clinicopathological changes have been observed in the cardiovascular, musculoskeletal, endocrine, digestive, nervous, and immune systems in individuals who completed either short-term or extended space flight missions. This study reviews the growing scientific data on the effects of microgravity by organ system.
METHODS: We conducted a systematic review by literature search using PubMed, ProQuest and EBSCOHost electronic databases. The text words, “microgravity”, “weightlessness”, and “spaceflight”, with the use of the Boolean operator “AND” the terms “respiratory system”, “cardiovascular”, “heart”, “brain”, “nervous system”, “digestion”, “reproduction”, “hormones”, “endocrine”, “immune system”, “immunological”, “muscle”, “musculoskeletal system”, “bone”, “skin”, and “integumentary system” were used to identify relevant studies discussing the physiologic changes and pathologic manifestations following exposure to short term microgravity and longterm spaceflight. Inclusion criteria were the following: 1) must be a scholarly or peer-reviewed source, 2) a relevant article within the last 13 years, and 3) articles published in the English language only. Outcome measures included any changes in tissues and cells in the risk groups.
RESULTS: 65 studies were included on both human cosmonauts, astronauts, animal models and cell lines. Weightlessness effects on the cardiovascular system included decreased heart size, increased incidence of negative EKG events, arrhythmias, and intimal thickening in blood vessel. In the skeletal system, exposure to weightlessness in combination with radiation decreased bone minerals, decreased bone density, impaired osteoclast differentiation and decreased osteoblasts, thus, accelerating bone degeneration and diminishing bone size. Microgravity induced muscle atrophy and decreased volume of transverse abdominus and multifidus muscle at L5, while resulting in hypertrophy of internal oblique muscles. Immune function was also adversely impacted by weightlessness, which impaired T-cell-mediated responses, increases levels of harmful reactive oxygen species (ROS), impaired macrophage cytoskeletal structure, CD68 and MHC-II surface expression, reduced lymphocyte activation in response to mitogenic stimuli, reduced cytotoxicity of natural killer cells, reactivation of latent viruses and reduced delayed-type hypersensitivity reactions in response to common recall antigens. In the reproductive system, microgravity damaged sperm DNA, induced spermatogenic cell apoptosis, diminished testicular weight and tubular diameter. Endocrinological effects of weightlessness included increased levels of epinephrine, decreased levels of cortisol, morphological and functional changes within the thyroid gland. Digestive effects of weightlessness included disturbances in gut microbiome. Neurologic impairment included increased glioma cell death by apoptosis, decreased glioma cell migration, increased disorganization of microtubules, decreased brain activity in the left cerebellum, paracentral, anterior cingulate, superior frontal gyrus, and limbic lobe, right lingual, post-central, and middle temporal gyri.
CONCLUSION: Exposure to microgravity was associated with physiological changes that may represent accelerated aging. Although some of the microgravity-induced physiologic changes were reversible and preventable by exercise regimens in space, other changes raised concerns of tissue damage and clinicopathological manifestations. Therefore, long-term exposure to zero-gravity conditions could have adverse consequences if not addressed. Further studies with larger sample size are warranted, in preparation for the new era of space tourism.