Physiological Responses to Microgravity in Human Spaceflight

Exposure to microgravity triggers systemic adaptations across multiple organ systems. In the cardiovascular domain, fluid redistributes cephalad, leading to increases in central venous pressure and cardiac preload which in turn may induce myocardial remodelling and endothelial dysfunction. Bone metabolism shifts towards resorption, resulting in rapid loss of bone mineral density, while skeletal muscle encounters unloading-driven atrophy accompanied by fibre-type transitions. Sensorimotor and vestibular systems undergo functional reorganisation to accommodate altered proprioceptive input, often manifesting as impaired balance and spatial orientation. Neuro-ocular challenges include increased intracranial pressure and changes in ocular biomechanics, which can culminate in optic disc oedema and visual acuity alterations. Metabolic shifts may mimic features of metabolic syndrome, with reductions in glucose tolerance and dyslipidaemia reported. Countermeasures such as resistive exercise, lower body negative pressure and pharmacological interventions aim to mitigate these responses, yet the interplay among systems under prolonged missions remains an active area of investigation.

Research from Nature Portfolio

A recent controlled study employing a five-day dry immersion model in healthy women has provided a comprehensive multi-system assessment of acute microgravity exposure. Participants exhibited a metabolic shift reminiscent of early metabolic syndrome, characterised by reduced glucose tolerance, unfavourable lipid profiles and heightened atherogenic indices. Simultaneously, bone remodelling markers indicated reduced formation and increased resorption, while fluid redistribution and muscle unloading contributed to diminished orthostatic tolerance, aerobic capacity and postural stability. These findings underscore the importance of sex-based analyses in the development of targeted countermeasures for long-duration missions.

Physiological Responses to Microgravity in Human Spaceflight publication trend

The graph below shows the total number of articles in physiological responses to microgravity in human spaceflight across all publications each year (not limited to Nature Index journals).

Technical terms

Microgravity: An environment with near-weightlessness, typically experienced in orbit, where gravitational forces are greatly reduced.

Dry immersion: A ground-based model of microgravity in which subjects are immersed in water while prevented from contacting it, simulating weightlessness and mechanical unloading.

Orthostatic tolerance: The capacity to maintain stable blood pressure and consciousness upon assuming an upright posture.

Endothelial dysfunction: Impaired function of the vascular endothelium, leading to altered blood vessel dilation and increased risk of cardiovascular pathology.

Bone resorption: The process by which osteoclast cells break down bone tissue, resulting in the release of minerals and decreased bone density.

References

1. Cardiovascular adaptations and pathological changes induced by spaceflight: from cellular mechanisms to organ-level impacts. Military Medical Research (2024).
2. Comprehensive assessment of physiological responses in women during the ESA dry immersion VIVALDI microgravity simulation. Nature Communications (2023).
3. Spaceflight associated neuro-ocular syndrome (SANS) and the neuro-ophthalmologic effects of microgravity: a review and an update. npj Microgravity (2020).
4. Assessment of Jugular Venous Blood Flow Stasis and Thrombosis During Spaceflight. JAMA Network Open (2019).