Brandon R. Macias
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View article: Differential regulation of mitochondrial quality control in skeletal muscle by HZE radiation exposure and partial weightbearing in mice
Differential regulation of mitochondrial quality control in skeletal muscle by HZE radiation exposure and partial weightbearing in mice Open
Spaceflight places astronauts under both reduced mechanical loading and ionizing radiation, each of which can compromise skeletal muscle health. We investigated whether 21 days of simulated lunar gravity (one sixth G) with or without a sin…
View article: Daily use of countermeasures to prevent headward fluid shifts throughout 30 days of strict head-down tilt bed rest
Daily use of countermeasures to prevent headward fluid shifts throughout 30 days of strict head-down tilt bed rest Open
We demonstrate that daily use of lower body negative pressure or venoconstrictive thigh cuffs following aerobic exercise is well tolerated throughout 30 days of exposure to the spaceflight analog strict head-down tilt bed rest. Both counte…
View article: Normal variation in brain volumetrics, CSF dynamics, and ocular structures from magnetic resonance images of healthy participants over two years
Normal variation in brain volumetrics, CSF dynamics, and ocular structures from magnetic resonance images of healthy participants over two years Open
We report estimated thresholds of normal variability from methodological and physiological sources in brain and ocular outcomes in healthy participants. Outcomes that exceed these thresholds have less than a 5% probability of occurring due…
View article: Cardiovascular responses to standing with and without lower body compression garments after long-duration spaceflight
Cardiovascular responses to standing with and without lower body compression garments after long-duration spaceflight Open
Cardiovascular adaptations during long-duration spaceflight increase the likelihood of orthostatic intolerance upon re-exposure to gravity, and thus, countermeasures have been developed. Here we report findings derived across four National…
View article: Brain and cerebrospinal fluid 3D center of mass shift after spaceflight
Brain and cerebrospinal fluid 3D center of mass shift after spaceflight Open
A subset of long-duration spaceflight astronauts at the International Space Station has been documented to develop spaceflight associated neuro-ocular syndrome (SANS). Researchers have sought to understand SANS by quantification of ocular …
View article: Arterial structure and function in the years after long-duration spaceflight
Arterial structure and function in the years after long-duration spaceflight Open
Previous investigations focused on in- and immediate postflight cardiovascular health indices. Here we report that in the 5 years after long-duration spaceflight in low Earth orbit, there was no evidence of increased carotid artery intima-…
View article: Mechanical countermeasures for spaceflight-associated neuro-ocular syndrome during 30-days of head down tilt bed rest: design, implementation, and tolerability
Mechanical countermeasures for spaceflight-associated neuro-ocular syndrome during 30-days of head down tilt bed rest: design, implementation, and tolerability Open
After longer duration space missions, some astronauts experience structural and functional changes in the eye and structural changes in the brain, termed Spaceflight-Associated Neuro-Ocular Syndrome (SANS). Countermeasures against SANS are…
View article: Impact of Daily Lower‐Body Negative Pressure or Cycling Followed by Venous Constrictive Thigh Cuffs on Bedrest‐Induced Orthostatic Intolerance
Impact of Daily Lower‐Body Negative Pressure or Cycling Followed by Venous Constrictive Thigh Cuffs on Bedrest‐Induced Orthostatic Intolerance Open
Background Orthostatic intolerance occurs following immobilization in patients on Earth and in astronauts after spaceflight. Head‐down tilt bedrest is a terrestrial model for weightlessness and induces orthostatic intolerance. We hypothesi…
View article: Severe Spaceflight-Associated Neuro-Ocular Syndrome in an Astronaut With 2 Predisposing Factors
Severe Spaceflight-Associated Neuro-Ocular Syndrome in an Astronaut With 2 Predisposing Factors Open
Importance Understanding potential predisposing factors associated with spaceflight-associated neuro-ocular syndrome (SANS) may influence its management. Objective To describe a severe case of SANS associated with 2 potentially predisposin…
View article: Spaceflight Associated Neuro-Ocular Syndrome in a Predisposed Astronaut With B-Vitamin Supplementation as a Potential Countermeasure
Spaceflight Associated Neuro-Ocular Syndrome in a Predisposed Astronaut With B-Vitamin Supplementation as a Potential Countermeasure Open
View article: Self-Generated Lower Body Negative Pressure Exercise: A Low Power Countermeasure for Acute Space Missions
Self-Generated Lower Body Negative Pressure Exercise: A Low Power Countermeasure for Acute Space Missions Open
Microgravity in spaceflight produces headward fluid shifts which probably contribute to Spaceflight-Associated Neuro-Ocular Syndrome (SANS). Developing new methods to mitigate these shifts is crucial for preventing SANS. One possible strat…
View article: Cardiopulmonary deconditioning and plasma volume loss are not sufficient to provoke orthostatic hypertension
Cardiopulmonary deconditioning and plasma volume loss are not sufficient to provoke orthostatic hypertension Open
View article: Jugular venous flow dynamics during acute weightlessness
Jugular venous flow dynamics during acute weightlessness Open
The absence of hydrostatic pressure gradients in the vascular system and loss of tissue weight during weightlessness results in altered flow dynamics in the left internal jugular vein in some astronauts that may contribute to an increased …
View article: Optic disc edema during strict 6° head-down tilt bed rest is related to one-carbon metabolism pathway genetics and optic cup volume
Optic disc edema during strict 6° head-down tilt bed rest is related to one-carbon metabolism pathway genetics and optic cup volume Open
Some astronauts on International Space Station missions experience neuroophthalmological pathologies as part of spaceflight associated neuro-ocular syndrome (SANS). Strict head-down tilt bed rest (HDTBR) is a spaceflight analog that replic…
View article: P11-057-23 Genetics of One-Carbon Metabolism Are Associated With Optic Disc Edema in a Ground-Based Model of Spaceflight
P11-057-23 Genetics of One-Carbon Metabolism Are Associated With Optic Disc Edema in a Ground-Based Model of Spaceflight Open
View article: Author Response: The Posterior Displacement of the Bruch's Membrane Opening: A Surprising Finding in Spaceflight-Associated Neuro-Ocular Syndrome
Author Response: The Posterior Displacement of the Bruch's Membrane Opening: A Surprising Finding in Spaceflight-Associated Neuro-Ocular Syndrome Open
View article: Ocular Deformations in Spaceflight-Associated Neuro-Ocular Syndrome and Idiopathic Intracranial Hypertension
Ocular Deformations in Spaceflight-Associated Neuro-Ocular Syndrome and Idiopathic Intracranial Hypertension Open
This study showed substantial differences in the degree of disc edema and the pattern of ocular deformations between IIH and SANS. The precise cause for these differences is unknown but suggests that there may be fundamental differences in…
View article: Error in Author Affiliations
Error in Author Affiliations Open
In Reply We thank Waisberg et al for their interest in our article 1 and agree that optical coherence tomography angiography (OCTA) may provide new insight into the pathophysiology of spaceflight-associated neuro-ocular syndrome (SANS).The…
View article: Incidence and Progression of Chorioretinal Folds During Long-Duration Spaceflight
Incidence and Progression of Chorioretinal Folds During Long-Duration Spaceflight Open
Importance The primary contributing factor for development of chorioretinal folds during spaceflight is unknown. Characterizing fold types that develop and tracking their progression may provide insight into the pathophysiology of spacefli…
View article: MRI-based quantification of posterior ocular globe flattening during 60 days of strict 6° head-down tilt bed rest with and without daily centrifugation
MRI-based quantification of posterior ocular globe flattening during 60 days of strict 6° head-down tilt bed rest with and without daily centrifugation Open
Head-down tilt (HDT) bed rest is commonly used as a spaceflight analog for investigating spaceflight associated neuro-ocular syndrome (SANS). Posterior ocular globe flattening has been identified in astronauts with SANS but until now has n…
View article: Identification of Factors Associated With the Development of Optic Disc Edema During Spaceflight
Identification of Factors Associated With the Development of Optic Disc Edema During Spaceflight Open
Importance Approximately 70% of crew members who complete long-duration missions to the International Space Station develop signs of optic disc edema, a hallmark finding of spaceflight-associated neuro-ocular syndrome. The onset and magnit…
View article: Noninvasive indicators of intracranial pressure before, during, and after long-duration spaceflight
Noninvasive indicators of intracranial pressure before, during, and after long-duration spaceflight Open
The current study provides new evidence that intracranial pressure (ICP), as assessed with noninvasive measures, may not be elevated during long-duration spaceflight. In addition, the acute use of lower body negative pressure did not signi…
View article: Changes in Optic Nerve Head and Retinal Morphology During Spaceflight and Acute Fluid Shift Reversal
Changes in Optic Nerve Head and Retinal Morphology During Spaceflight and Acute Fluid Shift Reversal Open
Importance Countermeasures that reverse the headward fluid shift experienced in weightlessness have the potential to mitigate spaceflight-associated neuro-ocular syndrome. This study investigated whether use of the countermeasure lower-bod…
View article: Spaceflight-Associated Vascular Remodeling and Gene Expression in Mouse Calvaria
Spaceflight-Associated Vascular Remodeling and Gene Expression in Mouse Calvaria Open
Astronauts suffer from a loss of bone mass at a rate of 1.5% per month from lower regions of the body during the course of long-duration (>30 days) spaceflight, a phenomenon that poses important risks for returning crew. Conversely, a g…
View article: Error in Author Name
Error in Author Name Open
appreciate the importance of determining the association between intracranial compliance and other brain and ocular outcomes and the need to directly measure intracranial pressure during spaceflight to characterize this complex physiology.…
View article: Optic disc edema and chorioretinal folds develop during strict 6° head‐down tilt bed rest with or without artificial gravity
Optic disc edema and chorioretinal folds develop during strict 6° head‐down tilt bed rest with or without artificial gravity Open
Spaceflight associated neuro-ocular syndrome (SANS) is hypothesized to develop as a consequence of the chronic headward fluid shift that occurs in sustained weightlessness. We exposed healthy subjects (n = 24) to strict 6° head-down tilt b…
View article: Lower body negative pressure reduces jugular and portal vein volumes and counteracts the elevation of middle cerebral vein velocity during long-duration spaceflight
Lower body negative pressure reduces jugular and portal vein volumes and counteracts the elevation of middle cerebral vein velocity during long-duration spaceflight Open
Microgravity-induced fluid shifts markedly enlarge jugular and portal veins and increase cerebral vein velocity. These findings demonstrate a marked flow engorgement at neck and splanchnic levels and may suggest compression of the cerebral…
View article: Intraocular pressure and choroidal thickness respond differently to lower body negative pressure during spaceflight
Intraocular pressure and choroidal thickness respond differently to lower body negative pressure during spaceflight Open
Spaceflight induces a chronic headward fluid shift that is believed to underlie ocular changes observed in astronauts. The present study demonstrates, for the first time, that reversing this headward fluid shift via application of lower bo…
View article: Optic disc edema and chorioretinal folds develop during strict head-down tilt bedrest with and without artificial gravity
Optic disc edema and chorioretinal folds develop during strict head-down tilt bedrest with and without artificial gravity Open
View article: Association of Structural Changes in the Brain and Retina After Long-Duration Spaceflight
Association of Structural Changes in the Brain and Retina After Long-Duration Spaceflight Open
These results help characterize spaceflight-associated neuro-ocular syndrome and the physiologic associations of headward fluid shifts with outcomes during spaceflight on the central nervous system. The possibly weak association between in…