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. 2024 Jun 11;10(1):64.
doi: 10.1038/s41526-024-00374-8.

Characterizing dehydration in short-term spaceflight using evidence from Project Mercury

Robert J Reynolds  1 , Mark Shelhamer  2 , Erik L Antonsen  3 , William R Carpentier
Affiliations

Characterizing dehydration in short-term spaceflight using evidence from Project Mercury

Robert J Reynolds et al. NPJ Microgravity. .

Abstract

Short-term spaceflight is commonly perceived as posing minimal risk to human health and performance. However, despite their duration, short-term flights potentially induce acute physiological changes that create risk to crews. One such change is dehydration (primarily body water loss) due to a heat-stressed environment. Such loss, if severe and prolonged, can lead to decrements in performance as well as increase the risk of more serious medical conditions. Though the general mechanisms of dehydration are broadly understood, the rate and extent of dehydration in short-term spaceflight has not been characterized. Combining data from the six spaceflights of the US Mercury program with a causal diagram illustrating the mechanisms of dehydration, we fit a path model to estimate the causal effects for all pathways in the causal model. Results demonstrate that Mercury astronauts experienced some degree of dehydration across the range of suited time and that the relationship between suited time and dehydration appears to be logarithmic. We discuss causal interpretations of the results and how the results from this and similar analyses can inform countermeasure development for short-term spaceflight.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Assumed causal diagram for dehydration during Mercury flights.
PV reduction plasma volume reduction, HCT hematocrit, Hb hemoglobin.
Fig. 2
Fig. 2. Observed data points and model predictions for the total effect of suited time on dehydration outcomes.
a Body mass reduction (%); b HCT (%); c Hb (g/dL); d PV reduction (%). In each plot, points represent individual values obtained after the various Mercury flights; solid lines are the estimated values derived from the path models; dashed lines represent estimated values obtained through the linear regression models.
See this image and copyright information in PMC

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References

    1. Lacey J, et al. A multidisciplinary consensus on dehydration: definitions, diagnostic methods and clinical implications. Ann. Med. 2019;51:232–251. doi: 10.1080/07853890.2019.1628352. - DOI - PMC - PubMed
    1. Harrison’s Principles of Internal Medicine, 21e | AccessMedicine | McGraw Hill Medical https://accessmedicine.mhmedical.com/book.aspx?bookID=3095 (2022).
    1. Cheuvront SN, Kenefick RW, Montain SJ, Sawka MN. Mechanisms of aerobic performance impairment with heat stress and dehydration. J. Appl. Physiol. Dec. 2010;109:1989–1995. doi: 10.1152/japplphysiol.00367.2010. - DOI - PubMed
    1. Norsk P, Asmar A, Damgaard M, Christensen NJ. Fluid shifts, vasodilatation and ambulatory blood pressure reduction during long duration spaceflight. J. Physiol. 2015;593:573–584. doi: 10.1113/jphysiol.2014.284869. - DOI - PMC - PubMed
    1. Leach CS, et al. Regulation of body fluid compartments during short-term spaceflight. J. Appl. Physiol. 1996;81:105–116. doi: 10.1152/jappl.1996.81.1.105. - DOI - PubMed