A theory for why the spaceflight-associated neuro-ocular syndrome develops

Buckey, Jay C.; Lan, Mimi; Phillips, Scott; Archambault‐Léger, Véronique; Fellows, Abigail

doi:10.1152/japplphysiol.00854.2021

Cited by 9 publications

(14 citation statements)

References 12 publications

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“…IOP and ICP have also been shown to be susceptible to other factors such as ambient CO2 levels 9 , 13 , 15 , 27 or body and tissue weight 67 , 68 , which are not simulated by our model. Given the role of CO2 as a cerebrovascular vasodilator promoting ICP and IOP increase 9 , 13 , 15 , 27 , this parameter should be accounted for in future HDT numerical investigations and represents thus a limitation of our current model.…”

Section: Discussionmentioning

confidence: 93%

“…Given the role of CO2 as a cerebrovascular vasodilator promoting ICP and IOP increase 9 , 13 , 15 , 27 , this parameter should be accounted for in future HDT numerical investigations and represents thus a limitation of our current model. Additionally, body and tissue weight—completely removed in actual 0 g conditions 67 , 68 though not accounted for in our modeling layout—should be included in the modeling framework as an additional posture-dependent parameter influencing vascular and ocular variables during HDT 36 , 69 , 70 . Moreover, while HDT is a reasonable microgravity model for many applications, it is important to acknowledge the physiological differences between HDT and true microgravity.…”

Section: Discussionmentioning

confidence: 99%

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Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework

Fois,

Diaz-Artiles,

Zaman

et al. 2024

npj Microgravity

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Head-down tilt (HDT) has been widely proposed as a terrestrial analog of microgravity and used also to investigate the occurrence of spaceflight-associated neuro-ocular syndrome (SANS), which is currently considered one of the major health risks for human spaceflight. We propose here an in vivo validated numerical framework to simulate the acute ocular-cerebrovascular response to 6° HDT, to explore the etiology and pathophysiology of SANS. The model links cerebral and ocular posture-induced hemodynamics, simulating the response of the main cerebrovascular mechanisms, as well as the relationship between intracranial and intraocular pressure to HDT. Our results from short-term (10 min) 6° HDT show increased hemodynamic pulsatility in the proximal-to-distal/capillary-venous cerebral direction, a marked decrease (-43%) in ocular translaminar pressure, and an increase (+31%) in ocular perfusion pressure, suggesting a plausible explanation of the underlying mechanisms at the onset of ocular globe deformation and edema formation over longer time scales.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework

Fois,

Diaz-Artiles,

Zaman

et al. 2024

npj Microgravity

View full text Add to dashboard Cite

show abstract

“…Given the role of CO 2 as cerebrovascular vasodilator promoting ICP and IOP increase [7,11,13,24], this parameter should be accounted for in future HDT numerical investigations. Additionally, body and tissue weight -completely removed in actual 0g conditions [61,62] -should be included in the modeling framework as an additional posture-dependent parameter influencing vascular and ocular variables during HDT. [31,63,64].…”

Section: Discussionmentioning

confidence: 99%

Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework

Fois

Diaz‐Artiles

Zaman

et al. 2023

Preprint

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Head-down tilt (HDT) has been widely proposed as terrestrial analogue of microgravity and used also to investigate the occurrence of the spaceflight associated neuro-ocular syndrome (SANS), which is currently considered one of the major health risks for human spaceflight. We propose here a novel, in vivo validated numerical framework to simulate the acute ocular-cerebrovascular response to 6° HDT and to explore the etiology and pathophysiology of SANS. The model links cerebral and ocular posture-induced hemodynamics, simulating the response of the main cerebrovascular mechanisms, as well as the relationship between intracranial and intraocular pressure to HDT. Our results from short-term (10 min) 6° HDT show increased hemodynamic pulsatility in the proximal-to-distal/capillary-venous cerebral direction, a marked decrease (-43%) in ocular translaminar pressure, and an increase (+31%) in ocular perfusion pressure, suggesting a plausible explanation of the underlying mechanisms at the onset of ocular globe deformation and edema formation over longer time scales.

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“…The removal of axial hydrostatic gradients was recently documented to decrease cardiac mass in an extreme duration swimmer, who spent 9–17 h per day in the supine or prone posture, and a long duration spaceflight astronaut, adding evidence that gravitational loading is important to consider in SANS pathology ( MacNamara et al, 2021 ). Also, the loss in hydrostatic gradients that occur in space may create a pressure environment conducive to developing SANS ( Buckey et al, 2022 ). Table 3 indicates the anticipated effects of fluid shift, tissue weight, and hydrostatic gradients for the conditions in this study in addition to head-down tilt (HDT) and microgravity.…”

Section: Discussionmentioning

confidence: 99%

Acute effects of postural changes and lower body positive and negative pressure on the eye

et al. 2022

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Introduction: Entry into weightlessness results in a fluid shift and a loss of hydrostatic gradients. These factors are believed to affect the eye and contribute to the ocular changes that occur in space. We measured eye parameters during fluid shifts produced by lower body negative pressure (LBNP) and lower body positive pressure (LBPP) and changes in hydrostatic gradient direction (supine-prone) in normal subjects to assess the relative effects of fluid shifts and hydrostatic gradient changes on the eye.Methods: Ocular parameters (intraocular pressure (IOP), ocular geometry, and optical coherence tomography measures) were measured in the seated, supine, and prone positions. To create a fluid shift in the supine and prone positions, the lower body chamber pressure ranged from -40 mmHg to +40 mmHg. Subjects maintained each posture and LBNP/LBPP combination for 15 min prior to data collection. A linear mixed-effects model was used to determine the effects of fluid shifts (as reflected by LBNP/LBPP) and hydrostatic gradient changes (as reflected by the change from seated to supine and from seated to prone) on eye parameters.Results: Chamber pressure was positively correlated with both increased choroidal thickness (β = 0.11 ,p = 0.01) and IOP (β = 0.06 p < 0.001). The change in posture increased IOP compared to seated IOP (supine β = 2.1, p = 0.01, prone β = 9.5, p < 0.001 prone) but not choroidal thickness. IOP changes correlated with axial length (R = 0.72, p < 0.001).Discussion: The effects of hydrostatic gradients and fluids shifts on the eye were investigated by inducing a fluid shift in both the supine and prone postures. Both hydrostatic gradients (posture) and fluid shifts (chamber pressure) affected IOP, but only hydrostatic gradients affected axial length and aqueous depth. Changes in choroidal thickness were only significant for the fluid shifts. Changes in hydrostatic gradients can produce significant changes in both IOP and axial length. Fluid shifts are often cited as important factors in the pathophysiology of SANS, but the local loss of hydrostatic gradients in the head may also play an important role in these ocular findings.

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A theory for why the spaceflight-associated neuro-ocular syndrome develops

Cited by 9 publications

References 12 publications

Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework

Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework

Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework

Acute effects of postural changes and lower body positive and negative pressure on the eye

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