Modelling the Response of Intracranial Pressure to Microgravity Environments

Lakin, W. D.; Stevens, Scott A.

doi:10.1007/978-3-7643-8591-0_11

Cited by 4 publications

(25 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…No data exist on the response of a healthy blood-brain 311 barrier to microgravity conditions. However, [20] suggested that such a barrier could be 312 weakened by gravity unloading and showed, with the lumped parameter model of the 313 brain that we also have adopted, that this is a relevant ingredient to reproduce the 314 observed increase in ICP.…”

Section: Simulation Of Microgravity Conditions 305mentioning

confidence: 92%

“…Simulations are 344 performed for π c ∈ (18.5, 25) mmHg. Decreases of 3.3 mmHg and 6.3 mmHg have been 345 associated with LHDT and microgravity conditions, respectively, leading to π c values of 346 21.7 mmHg and 18.7 mmHg, respectively [20], which are indeed included in the 347 simulated interval.…”

mentioning

confidence: 94%

“…• blood (5 compartments: retina (r ), choroid (ch), central retinal artery (cra), 99 central retinal vein (crv ), ciliary body circulation (cl )); 100 • aqueous humor (ah) (1 compartment: anterior and posterior chamber); 101 and in the eye-brain coupling: The lumped parameter circuit for the brain adopted in the present work was 106 described and validated by Lakin and Stevens in [20] for microgravity simulations. The 107 eye block combines a model for the retinal circulation and a model for the dynamics of 108 aqueous humor that have been proposed by some of the authors of this paper in [21] 109 and [22], respectively, and extends them to account also for the choroidal and ciliary 110 body vascular beds [23].…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we describe the brain via an electrical analogue representation of the production is externally imposed and kept constant at the production rate Q CF . Unlike 164 the choice adopted in [20] to impose a constant flux Q IC between the intracranial this circuit is important since the balance between aqueous production and drainage 179 governs the levels of IOP. The light blue-shaded area in the figure represents the interior 180 of the eye globe, where the pressure equals IOP.…”

mentioning

confidence: 99%

“…In the present paper, microgravity conditions are simulated following the same 316 approach as in [20], namely: (i) we impose zero hydrostatic pressure distribution; (ii) we 317 set the central venous pressure to zero; (iii) we decrease blood colloid osmotic pressure 318 as a consequence of fluid shift towards the head; (iv) we weaken the blood-brain barrier 319 by modifying the Starling-Landis equation coefficients (see Eq (1)). In particular, we 320 increase the filtration coefficient K CB between capillaries in the brain and the brain 321 tissue and correspondingly decrease the reflection coefficient σ CB as suggested by [20]. 322 We also consider long head-down tilt (LHDT) conditions that are the most common 323 earth clinical model used to mimic the effects of microgravity on body fluids shift.…”

mentioning

confidence: 99%

See 4 more Smart Citations

Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions

Salerni

Repetto

Harris

et al. 2019

Preprint

View full text Add to dashboard Cite

This work aims at investigating the interactions between the flow of fluids in the eyes and the brain and their potential implications in the development of visual impairment in astronauts, a condition also known as spaceflight associated neuro-ocular syndrome (SANS). To this end, we propose a reduced (0-dimensional) mathematical model of fluid flow in the eyes and brain, which is embedded into a simplified whole-body circulation model. In particular, the model accounts for: (i) the flows of blood and aqueous humor in the eyes; (ii) the flows of blood, cerebrospinal fluid and interstitial fluid in the brain; and (iii) their interactions. The model is used to simulate variations in intraocular pressure, intracranial pressure and blood flow due to microgravity conditions, which are thought to be critical factors in SANS. Specifically, the model predicts that both intracranial and intraocular pressures increase in microgravity, even though their respective trends may be different. In such conditions, ocular blood flow is predicted to decrease in the choroid and ciliary body circulations, whereas retinal circulation is found to be less susceptible to microgravity-induced alterations, owing to a purely mechanical component in perfusion control associated with the venous segments. These findings indicate that the particular anatomical architecture of venous drainage in the retina may be one of the reasons why most of the SANS alterations are not observed in the retina but, rather, in other vascular beds, particularly the choroid. Thus, clinical assessment of ocular venous function may be considered as a determinant SANS factor, for which astronauts could be screened on earth and in-flight. April 1, 2019 1/22 1 Microgravity conditions have been observed to induce visual function alterations in 2 many astronauts that pose serious challenges for both astronauts and their missions in 3 space [1, 2]. This syndrome, also known as spaceflight associated neuro-ocular syndrome 4 (SANS), is characterized by a large number of apparently unrelated and often not 5 concurrent symptoms. These include choroidal folds, cotton wool spots, optic nerve 6 distension and/or kinking, optic disc protrusion, posterior globe flattening, refractive 7 deficits and elevated intracranial pressure [3]. Added to the complexity of the range of 8 symptoms are the problems of susceptibility and genetic predisposition to develop visual 9problems. 10The current understanding of how weightlessness environment affects the human 11 body and may lead to SANS development is still quite rudimentary. Various studies of 12 the symptoms experienced by astronauts during long-term missions (four to six months) 13 have been performed [1], but their validity is hampered by the small size of the subjects 14 cohort. To overcome this difficulty, ground-based microgravity laboratory models have 15 been proposed, the most significant of which is the long head down tilt (LHDT) 16 experimental procedure that is used to simulate the effects of microgravity on the 17 cardiovas...

show abstract

Section: Simulation Of Microgravity Conditions 305mentioning

confidence: 92%

mentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions

Salerni

Repetto

Harris

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

Optic Disc Edema and Choroidal Engorgement in Astronauts During Spaceflight and Individuals Exposed to Bed Rest

et al. 2020

View full text Add to dashboard Cite

IMPORTANCE Optic disc edema develops in astronauts during long-duration spaceflight and is a risk for all future astronauts during spaceflight. Having a ground-based analogue of weightlessness that reproduces critical features of spaceflight-associated neuro-ocular syndrome will facilitate understanding, preventing, and/or treating this syndrome. OBJECTIVE To determine whether the ocular changes in individuals exposed to an analogue of weightlessness are similar to the ocular changes in astronauts exposed to a duration of spaceflight comparable to this analogue of weightlessness. DESIGN, SETTING, AND PARTICIPANTS This cohort study, conducted from 2012 to 2018, investigated 11 healthy test participants before, during, and after 30 days of strict 6°h ead-down tilt bed rest as well as 20 astronauts before and during approximately 30 days of spaceflight. Data were collected at NASA Johnson Space Center, the German Aerospace Center, and on board the International Space Station. Statistical analysis was performed from February 13 to April 24, 2019. MAIN OUTCOMES AND MEASURES Peripapillary total retinal thickness and peripapillary choroid thickness quantified from optical coherence tomography images. RESULTS Peripapillary total retinal thickness increased to a greater degree among 11 individuals (6 men and 5 women; mean [SD] age, 33.4 [8.0 years]) exposed to bed rest than among 20 astronauts (17 men and 3 women; mean [SD] age, 46.0 [6.0] years), with a mean difference between groups of 37 μm (95% CI, 13-61 μm; P = .005). Conversely, choroid thickness did not increase among the individuals exposed to bed rest but increased among the astronauts, resulting in a mean difference between groups of 27 μm (95% CI, 14-41 μm; P < .001). CONCLUSIONS AND RELEVANCE These findings suggest that strict head-down tilt bed rest produces a different magnitude of edema than occurs after a similar duration of spaceflight, and no change in choroid thickness. It is possible that a mild, long-term elevation in intracranial pressure experienced by individuals exposed to bed rest is greater than the intracranial pressure experienced by astronauts during spaceflight, which may explain the different severity of optic disc edema between the cohorts. Gravitational gradients that remain present during bed rest may explain the lack of increase in choroid thickness during bed rest, which differs from the lack of gravitational gradients during spaceflight. Despite the possibility that different mechanisms may underlie optic disc edema development in modeled and real spaceflight, use of this terrestrial model of spaceflight-associated neuro-ocular syndrome will be assistive in the development of effective countermeasures that will protect the eyes of astronauts during future space missions.

show abstract