Intraocular Pressure and Retinal Vascular Changes During Transient Exposure to Microgravity

Mader, Col. Thomas H.; Gibson, Charles R.; Caputo, Michael; Hunter, Norwood; Taylor, Gerald R.; Charles, John B.; Meehan, Richard T.

doi:10.1016/s0002-9394(14)73586-x

Cited by 78 publications

(53 citation statements)

References 6 publications

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“…The internal jugular veins are a major drainage pathway between the brain and the heart, although the percentage of blood draining through the internal jugular vein in relation to the vertebral veins is position dependent (Manuel Valdueza et al 2000;Cirovic et al 2003). Along with an increased IJVP and venous distension, intraocular pressure also is elevated with parabolic flight (Mader et al 1993;Anderson et al 2016). While this study only reports a finding during acute exposure to weightlessness, increased IJVP during long-duration spaceflight may promote cranial venous and lymphatic congestion chronically.…”

Section: Discussionmentioning

confidence: 63%

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Internal jugular pressure increases during parabolic flight

Martin

Lee

Matz

et al. 2016

Physiological Reports

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One hypothesized contributor to vision changes experienced by >75% of International Space Station astronauts is elevated intracranial pressure (ICP). While no definitive data yet exist, elevated ICP might be secondary to the microgravity‐induced cephalad fluid shift, resulting in venous congestion (overfilling and distension) and inhibition of cerebrospinal and lymphatic fluid drainage from the skull. The objective of this study was to measure internal jugular venous pressure (IJVP) during normo‐ and hypo‐gravity as an index of venous congestion. IJVP was measured noninvasively using compression sonography at rest during end‐expiration in 11 normal, healthy subjects (3 M, 8 F) during normal gravity (1G; supine) and weightlessness (0G; seated) produced by parabolic flight. IJVP also was measured in two subjects during parabolas approximating Lunar (1/6G) and Martian gravity (1/3G). Finally, IJVP was measured during increased intrathoracic pressure produced using controlled Valsalva maneuvers. IJVP was higher in 0G than 1G (23.9 ± 5.6 vs. 9.9 ± 5.1 mmHg, mean ± SD P < 0.001) in all subjects, and IJVP increased as gravity levels decreased in two subjects. Finally, IJVP was greater in 0G than 1G at all expiration pressures (P < 0.01). Taken together, these data suggest that IJVP is elevated during acute exposure to reduced gravity and may be elevated further by conditions that increase intrathoracic pressure, a strong modulator of central venous pressure and IJVP. However, whether elevated IJVP, and perhaps consequent venous congestion, observed during acute microgravity exposure contribute to vision changes during long‐duration spaceflight is yet to be determined.

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Section: Discussionmentioning

confidence: 63%

“…Along with an increased IJVP and venous distension, intraocular pressure also is elevated with parabolic flight (Mader et al. ; Anderson et al. ).…”

Section: Discussionmentioning

confidence: 99%

Internal jugular pressure increases during parabolic flight

Martin

Lee

Matz

et al. 2016

Physiological Reports

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“…Factors that could contribute to the ophthalmic changes observed in some crewmembers after long-duration spaceflight include microgravity-induced fluid shifts (7-9), increased intra-cranial pressure, optic nerve sheath changes, and/or changes in intraocular pressure (1,10). At this point, the unifying pathologic mechanism is hypothesized to be prolonged exposure to the effects of cephalad fluid shifts that occur during microgravity exposure.…”

Section: Discussionmentioning

confidence: 99%

Vision Changes after Spaceflight Are Related to Alterations in Folate- and Vitamin B-12-Dependent One-Carbon Metabolism,

Zwart

Gibson

Mader

et al. 2012

The Journal of Nutrition

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101

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Approximately 20% (7 of 38) of astronauts on International Space Station (ISS) missions have developed measurable ophthalmic changes after flight. This study was conducted to determine if the folate- and vitamin B-12-dependent 1-carbon metabolic pathway is altered in these individuals. Since 2006, we have conducted experiments on the ISS to evaluate nutritional status and related biochemical indices of astronauts before, during, and after flight. Data were modeled to evaluate differences between individuals with ophthalmic changes (n = 5) and those without them (n = 15), all of whom were on ISS missions of 48-215 d. We also determined whether mean preflight serum concentrations of the 1-carbon metabolites and changes in measured cycloplegic refraction after flight were associated. Serum homocysteine (Hcy), cystathionine, 2-methylcitric acid (2MCA), and methylmalonic acid concentrations were 25-45% higher (P < 0.001) in astronauts with ophthalmic changes than in those without them. These differences existed before, during, and after flight. Preflight serum concentrations of Hcy and cystathionine, and mean in-flight serum folate, were correlated with change (postflight relative to preflight) values in refraction (P < 0.05), and preflight serum concentrations of 2MCA tended to be associated (P = 0.06) with ophthalmic changes. The biochemical differences observed in crewmembers with vision issues strongly suggest that their folate- and vitamin B-12-dependent 1-carbon transfer metabolism was affected before and during flight. The consistent differences in markers of 1-carbon metabolism between those who did and those who did not develop changes in vision suggest that polymorphisms in enzymes of this pathway may interact with microgravity to cause these pathophysiologic changes.

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“…11,12 As reviewed by Manuel and Mader, short-duration microgravity studies suggest that the initial rise in IOP may decline to roughly preflight values within several hours. The evidence comes from parabolic flight, bed rest, and orbital flights.…”

Section: Vision Changes After Long-duration Space Flightmentioning

confidence: 99%