To investigate cardiovascular impacts of short-term space travels.
Authors conducted a systematic review (following PRISMA protocol) of available literature on Pubmed, CINAHL, EBSCO, Cochrane Library databases through March 30, 2024, and included studies on the cardiovascular effects of short-term microgravity/commercial space travels, regardless of their design. (RCT, Quasi-experimental, Observational, Case reports, Systematic Reviews). Studies without available full text or non-English language were excluded. Search terms were Boolean combination of short-term microgravity, space travel, space tourism, acute microgravity, cardiovascular function, blood flow, cardiac output, heart rate, blood pressure. Crossed references and grey literature from relevant companies and NASA were also included. Two reviewers independently screened, reviewed the studies, extracted data, and any point of uncertainty was resolved by the 3rd reviewer. The quality of papers and risk of bias were evaluated by appropriate tool (PEDro, NIH tool, AMSTAR II).
Out of 436 results, 32 studies (7 RCTs, 22 quasi-experimental, 3 literature reviews) included for final review, representing total of 317 (M/F:227/82) healthy human participants (18-55 y/o, 22 studies) and 102 rats (6 animal studies). Flight protocols ranged from International Space Station, space beyond the Karman line, to space missions in simulated microgravity labs. Twenty-four studies reported changes in blood pressure, HR (with dispersed results), cardiac output (significant, up to 21%-29%), stroke volume (significant, up to 8%). Eight studies indicated unchanged cerebral blood flow velocity during brief microgravity exposure (30 seconds) but significant decrease with longer exposure. Three hematological studies showed significantly decreased hemoglobin and hematocrit but significantly increased myoglobin levels. Baroreflex sensitivity and endothelial resistance were reduced during microgravity, contributing to orthostatic intolerance. One study reported a reduction in plasma volume and no significant change in C-reactive protein and creatinine. Most studies had sources of bias, selection bias of participants, methodological shortcomings due to nonrandomization, non-blinding, quasi-experimental nature, and small sample size.
Short-term microgravity induced during commercial space travels can impose significant hemodynamic, vascular and hematologic changes; however, authors concluded that the current available evidence is insufficient to predict the titrating effects of microgravity in a standardized fashion and is inconclusive to establish health screening tools for specific populations with comorbidities due to low quality of studies and methodological shortcomings.
Foreseeing the future expansion of space tourism, its availability for ordinary citizens with potential cardiovascular comorbidities; there is a need to establish precise health screening tools and explore potential PT interventions corresponding to variable titration of gravity designed for appropriate populations with comorbidities.
Microgravity
Cardiovascular Performance
