The effect of prolonged spaceflight on cerebrospinal fluid and perivascular spaces of astronauts and cosmonauts.

Long-duration spaceflight induces changes to the brain and cerebrospinal fluid compartments and visual acuity problems known as spaceflight-associated neuro-ocular syndrome (SANS). The clinical relevance of these changes and whether they equally affect crews of different space agencies remain unknown. We used MRI to analyze the alterations occurring in the perivascular spaces (PVS) in NASA and European Space Agency astronauts and Roscosmos cosmonauts after a 6-mo spaceflight on the International Space Station (ISS). We found increased volume of basal ganglia PVS and white matter PVS (WM-PVS) after spaceflight, which was more prominent in the NASA crew than the Roscosmos crew. Moreover, both crews demonstrated a similar degree of lateral ventricle enlargement and decreased subarachnoid space at the vertex, which was correlated with WM-PVS enlargement. As all crews experienced the same environment aboard the ISS, the differences in WM-PVS enlargement may have been due to, among other factors, differences in the use of countermeasures and high-resistive exercise regimes, which can influence brain fluid redistribution. Moreover, NASA astronauts who developed SANS had greater pre- and postflight WM-PVS volumes than those unaffected. These results provide evidence for a potential link between WM-PVS fluid and SANS.

Nutrition as Fuel for Human Spaceflight.

History books are rife with examples of the role of nutrition in determining either the success or the failure of human exploration on Earth. With planetary exploration in our future, it is imperative that we understand the role of nutrition in optimizing health before humans can safely take the next giant leaps in space exploration.

Microgravity-induced ocular changes are related to body weight.

On Earth, tissue weight generates compressive forces that press on body structures and act on the walls of vessels throughout the body. In microgravity, tissues no longer have weight, and tissue compressive forces are lost, suggesting that individuals who weigh more may show greater effects from microgravity exposure. One unique effect of long-duration microgravity exposure is spaceflight-associated neuroocular syndrome (SANS), which can present with globe flattening, choroidal folds, optic disk edema, and a hyperopic visual shift. To determine whether weight or other anthropometric measures are related to ocular changes in space, we analyzed data from 45 individual long-duration astronauts (mean age 47, 36 male, 9 female, mean mission duration 165 days) who had pre- and postflight measures of disk edema, choroidal folds, and manifest ocular refraction. The mean preflight weights of astronauts who developed new choroidal folds [78.6 kg with no new folds vs. 88.6 kg with new folds ( F = 6.2, P = 0.02)] and disk edema [79.1 kg with no edema vs. 95 kg with edema ( F = 9.6, P = 0.003)] were significantly greater than those who did not. Chest and waist circumferences were also significantly greater in those who developed folds or edema. The odds of developing disk edema or new choroidal folds were 55% in the highest- and 9% in the lowest-weight quartile. In this cohort, no women developed disk edema or choroidal folds, although women also weighed significantly less than men [62.9 vs. 85.2 kg ( F = 53.2, P < 0.0001)]. Preflight body weight and anthropometric factors may predict microgravity-induced ocular changes.

How spaceflight challenges human cardiovascular health.

The harsh environmental conditions in space, particularly weightlessness and radiation exposure, can negatively affect cardiovascular function and structure. In the future, preventive cardiology will be crucial in enabling safe space travel. Indeed, future space missions destined to the Moon and from there to Mars will create new challenges to cardiovascular health while limiting medical management. Moreover, commercial spaceflight evolves rapidly such that older persons with cardiovascular risk factors will be exposed to space conditions. This review provides an overview on studies conducted in space and terrestrial models, particularly head-down bedrest studies. These studies showed that weightlessness elicits a fluid shift towards the head, which likely predisposes to the spaceflight-associated neuro-ocular syndrome, neck vein thrombosis, and orthostatic intolerance after return to Earth. Moreover, cardiovascular unloading produces cardiopulmonary deconditioning, which may be associated with cardiac atrophy. In addition to limiting physical performance, the mechanism further worsens orthostatic tolerance after return to Earth. Finally, space conditions may directly affect vascular health; however, the clinical relevance of these findings in terms of morbidity and mortality is unknown. Targeted preventive measures, which are referred to as countermeasures in aerospace medicine, and technologies to identify vascular risks early on will be required to maintain cardiovascular performance and health during future space missions.

Current concepts of cerebrospinal fluid dynamics and the translaminar cribrosa pressure gradient: a paradigm of optic disk disease.

Modern advances in measuring and studying cerebrospinal fluid dynamics have furthered our understanding of intracranial pressure and its pathophysiological effects on the eye. In particular, the cerebrospinal fluid pressure and composition within the optic nerve subarachnoid space are key factors in diseases of the optic disk. Intracranial pressure and intraocular pressure establish a pressure gradient across the lamina cribrosa. Alterations in this translaminar cribrosa pressure difference induce structural deformations in the lamina cribrosa manifested clinically by the appearance of optic disk edema or optic disk cupping. Much has been learned about papilledema (i.e., optic disk edema due to elevated intracranial pressure) from clinical observations and studies on patients with idiopathic intracranial hypertension. Furthermore, optic nerve subarachnoid space hydrodynamics and translaminar cribrosa pressure difference are postulated to contribute to the pathogenesis of optic disk edema observed in spaceflight-associated neuroocular syndrome. Recently, a substantial body of literature has accumulated suggesting low intracranial pressure may be a risk factor for the development of glaucomatous optic disk cupping within the context of the translaminar cribrosa pressure difference and posterior scleral biomechanics.