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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Th6CBr14 by Materials Project

Th6CBr14 crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. there are two inequivalent Th sites. In the first Th site, Th is bonded to one C and five Br atoms to form a mixture of distorted edge and corner-sharing ThCBr5 octahedra. The corner-sharing octahedra tilt angles range from 0–45°. The Th–C bond length is 2.56 Å. There are a spread of Th–Br bond distances ranging from 2.91–3.32 Å. In the second Th site, Th is bonded to one C and five Br atoms to form a mixture of edge and corner-sharing ThCBr5 octahedra. The corner-sharing octahedra tilt angles range from 0–45°. The Th–C bond length is 2.64 Å. There are a spread of Th–Br bond distances ranging from 2.90–3.04 Å. C is bonded in an octahedral geometry to six Th atoms. There are five inequivalent Br sites. In the first Br site, Br is bonded in an L-shaped geometry to two Th atoms. In the second Br site, Br is bonded in an L-shaped geometry to two Th atoms. In the third Br site, Br is bonded in a 3-coordinate geometry to three Th atoms. In the fourth Br site, Br is bonded in an L-shaped geometry to two equivalent Th atoms. In the fifth Br site, Br is bonded in a distorted bent 150 degrees geometry to two equivalent Th atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta3Br7 by Materials Project

Ta3Br7 crystallizes in the orthorhombic Cmce space group. The structure is two-dimensional and consists of two Ta3Br7 sheets oriented in the (0, 1, 0) direction. there are two inequivalent Ta sites. In the first Ta site, Ta is bonded in a distorted square co-planar geometry to four Br atoms. There are two shorter (2.60 Å) and two longer (2.61 Å) Ta–Br bond lengths. In the second Ta site, Ta is bonded to five Br atoms to form distorted corner-sharing TaBr5 square pyramids. There are a spread of Ta–Br bond distances ranging from 2.61–2.88 Å. There are five inequivalent Br sites. In the first Br site, Br is bonded in a 2-coordinate geometry to two equivalent Ta atoms. In the second Br site, Br is bonded in a 2-coordinate geometry to two equivalent Ta atoms. In the third Br site, Br is bonded in a 2-coordinate geometry to two Ta atoms. In the fourth Br site, Br is bonded in a distorted bent 150 degrees geometry to two equivalent Ta atoms. In the fifth Br site, Br is bonded in a 2-coordinate geometry to two Ta atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb6Br7 by Materials Project

Tb6Br7 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Tb sites. In the first Tb site, Tb is bonded in a distorted rectangular see-saw-like geometry to four Br atoms. There are a spread of Tb–Br bond distances ranging from 2.82–3.08 Å. In the second Tb site, Tb is bonded in a 3-coordinate geometry to three Br atoms. There are one shorter (3.00 Å) and two longer (3.02 Å) Tb–Br bond lengths. In the third Tb site, Tb is bonded to five Br atoms to form distorted edge-sharing TbBr5 square pyramids. There are a spread of Tb–Br bond distances ranging from 2.88–3.17 Å. There are four inequivalent Br sites. In the first Br site, Br is bonded in a square co-planar geometry to four equivalent Tb atoms. In the second Br site, Br is bonded in a 3-coordinate geometry to three Tb atoms. In the third Br site, Br is bonded in a distorted see-saw-like geometry to four Tb atoms. In the fourth Br site, Br is bonded in a 3-coordinate geometry to three Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb5Br8 by Materials Project

Tb5Br8 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Tb sites. In the first Tb site, Tb is bonded in a 5-coordinate geometry to five Br atoms. There are four shorter (2.92 Å) and one longer (3.46 Å) Tb–Br bond lengths. In the second Tb site, Tb is bonded in a rectangular see-saw-like geometry to four Br atoms. There are two shorter (2.88 Å) and two longer (3.05 Å) Tb–Br bond lengths. In the third Tb site, Tb is bonded to six Br atoms to form edge-sharing TbBr6 octahedra. There are four shorter (2.85 Å) and two longer (2.86 Å) Tb–Br bond lengths. There are four inequivalent Br sites. In the first Br site, Br is bonded in a 3-coordinate geometry to three Tb atoms. In the second Br site, Br is bonded in a distorted T-shaped geometry to three Tb atoms. In the third Br site, Br is bonded in a 2-coordinate geometry to three Tb atoms. In the fourth Br site, Br is bonded in a distorted T-shaped geometry to three Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs5Nb2S4Br9 by Materials Project

Cs5Nb2S4Br9 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 10-coordinate geometry to two equivalent S2- and eight Br+0.33- atoms. Both Cs–S bond lengths are 4.03 Å. There are a spread of Cs–Br bond distances ranging from 3.61–3.92 Å. In the second Cs1+ site, Cs1+ is bonded to six Br+0.33- atoms to form corner-sharing CsBr6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (3.59 Å) and two longer (3.86 Å) Cs–Br bond lengths. Nb3+ is bonded in a 8-coordinate geometry to four equivalent S2- and four Br+0.33- atoms. All Nb–S bond lengths are 2.51 Å. There are two shorter (2.72 Å) and two longer (2.83 Å) Nb–Br bond lengths. S2- is bonded in a 2-coordinate geometry to two equivalent Cs1+, two equivalent Nb3+, and two equivalent Br+0.33- atoms. Both S–Br bond lengths are 3.29 Å. There are three inequivalent Br+0.33- sites. In the first Br+0.33- site, Br+0.33- is bonded in a 1-coordinate geometry to four equivalent Cs1+ and one Nb3+ atom. In the second Br+0.33- site, Br+0.33- is bonded in a 7-coordinate geometry to four Cs1+, one Nb3+, and two equivalent S2- atoms. In the third Br+0.33- site, Br+0.33- is bonded to six Cs1+ atoms to form corner-sharing BrCs6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3Se5Br7 by Materials Project

Nb3Se5Br7 crystallizes in the monoclinic P2_1/m space group. The structure is one-dimensional and consists of one Nb3Se5Br7 ribbon oriented in the (0, 1, 0) direction. there are two inequivalent Nb+3.67+ sites. In the first Nb+3.67+ site, Nb+3.67+ is bonded in a 8-coordinate geometry to four Se2- and four Br+0.14- atoms. All Nb–Se bond lengths are 2.65 Å. There are a spread of Nb–Br bond distances ranging from 2.74–2.82 Å. In the second Nb+3.67+ site, Nb+3.67+ is bonded in a distorted octahedral geometry to one Se2- and five Br+0.14- atoms. The Nb–Se bond length is 2.30 Å. There are a spread of Nb–Br bond distances ranging from 2.49–2.96 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a single-bond geometry to one Nb+3.67+ atom. In the second Se2- site, Se2- is bonded in a 2-coordinate geometry to two equivalent Nb+3.67+ atoms. In the third Se2- site, Se2- is bonded in a 2-coordinate geometry to two equivalent Nb+3.67+ atoms. There are five inequivalent Br+0.14- sites. In the first Br+0.14- site, Br+0.14- is bonded in a distorted water-like geometry to two Nb+3.67+ atoms. In the second Br+0.14- site, Br+0.14- is bonded in a single-bond geometry to one Nb+3.67+ atom. In the third Br+0.14- site, Br+0.14- is bonded in a 3-coordinate geometry to three Nb+3.67+ atoms. In the fourth Br+0.14- site, Br+0.14- is bonded in an L-shaped geometry to two equivalent Nb+3.67+ atoms. In the fifth Br+0.14- site, Br+0.14- is bonded in a distorted L-shaped geometry to two equivalent Nb+3.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KZnBr3O2 by Materials Project

KZnO2Br3 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of one KZnO2Br3 sheet oriented in the (1, 0, 0) direction. K is bonded in a 2-coordinate geometry to two equivalent O and three Br atoms. There are one shorter (2.72 Å) and one longer (2.88 Å) K–O bond lengths. There are a spread of K–Br bond distances ranging from 3.22–3.64 Å. Zn is bonded to two equivalent O and two Br atoms to form distorted edge-sharing ZnBr2O2 tetrahedra. There are one shorter (2.05 Å) and one longer (2.08 Å) Zn–O bond lengths. There are one shorter (2.35 Å) and one longer (2.41 Å) Zn–Br bond lengths. There are two inequivalent O sites. In the first O site, O is bonded in a trigonal planar geometry to two equivalent Zn and one Br atom. The O–Br bond length is 1.80 Å. In the second O site, O is bonded in a trigonal planar geometry to two equivalent K and one Br atom. The O–Br bond length is 1.72 Å. There are three inequivalent Br sites. In the first Br site, Br is bonded in a distorted single-bond geometry to one K and one Zn atom. In the second Br site, Br is bonded in a 1-coordinate geometry to two equivalent K and one Zn atom. In the third Br site, Br is bonded in a water-like geometry to two O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho4RuBr5 by Materials Project

Ho4RuBr5 crystallizes in the tetragonal P4_2/nnm space group. The structure is three-dimensional. there are three inequivalent Ho sites. In the first Ho site, Ho is bonded to three equivalent Ru and three Br atoms to form a mixture of corner and edge-sharing HoRu3Br3 octahedra. The corner-sharing octahedra tilt angles range from 2–15°. There are two shorter (2.81 Å) and one longer (2.83 Å) Ho–Ru bond lengths. There are one shorter (3.06 Å) and two longer (3.19 Å) Ho–Br bond lengths. In the second Ho site, Ho is bonded to one Ru and five Br atoms to form distorted HoRuBr5 octahedra that share corners with three HoRu3Br3 octahedra and edges with eight HoRuBr5 octahedra. The corner-sharing octahedra tilt angles range from 2–15°. The Ho–Ru bond length is 2.68 Å. There are a spread of Ho–Br bond distances ranging from 2.90–3.22 Å. In the third Ho site, Ho is bonded to one Ru and five Br atoms to form distorted HoRuBr5 octahedra that share a cornercorner with one HoRu3Br3 octahedra and edges with eight HoRuBr5 octahedra. The corner-sharing octahedral tilt angles are 14°. The Ho–Ru bond length is 2.70 Å. There are a spread of Ho–Br bond distances ranging from 2.92–3.19 Å. Ru is bonded to six Ho atoms to form distorted edge-sharing RuHo6 octahedra. There are four inequivalent Br sites. In the first Br site, Br is bonded in a distorted see-saw-like geometry to four Ho atoms. In the second Br site, Br is bonded in a distorted see-saw-like geometry to four Ho atoms. In the third Br site, Br is bonded in a 3-coordinate geometry to three Ho atoms. In the fourth Br site, Br is bonded in a 3-coordinate geometry to three Ho atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta3Br7 by Materials Project

Ta3Br7 crystallizes in the orthorhombic Cmce space group. The structure is two-dimensional and consists of two Ta3Br7 sheets oriented in the (1, 0, 0) direction. there are two inequivalent Ta sites. In the first Ta site, Ta is bonded to five Br atoms to form distorted corner-sharing TaBr5 square pyramids. There are a spread of Ta–Br bond distances ranging from 2.60–2.92 Å. In the second Ta site, Ta is bonded in a distorted square co-planar geometry to four Br atoms. There are two shorter (2.60 Å) and two longer (2.61 Å) Ta–Br bond lengths. There are five inequivalent Br sites. In the first Br site, Br is bonded in a 2-coordinate geometry to two Ta atoms. In the second Br site, Br is bonded in a 2-coordinate geometry to two Ta atoms. In the third Br site, Br is bonded in a distorted bent 150 degrees geometry to two equivalent Ta atoms. In the fourth Br site, Br is bonded in a 2-coordinate geometry to two equivalent Ta atoms. In the fifth Br site, Br is bonded in a 2-coordinate geometry to two equivalent Ta atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2InBr5O by Materials Project

K2InOBr5 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. K is bonded in a 8-coordinate geometry to eight Br atoms. There are a spread of K–Br bond distances ranging from 3.41–3.79 Å. In is bonded in a 5-coordinate geometry to one O and five Br atoms. The In–O bond length is 2.15 Å. There are a spread of In–Br bond distances ranging from 2.64–3.02 Å. O is bonded in a distorted L-shaped geometry to one In and one Br atom. The O–Br bond length is 2.46 Å. There are four inequivalent Br sites. In the first Br site, Br is bonded in a 4-coordinate geometry to two equivalent K, one In, and one O atom. In the second Br site, Br is bonded to four equivalent K and one In atom to form a mixture of distorted corner, edge, and face-sharing BrK4In square pyramids. In the third Br site, Br is bonded to four equivalent K and one In atom to form a mixture of corner, edge, and face-sharing BrK4In square pyramids. In the fourth Br site, Br is bonded in a distorted rectangular see-saw-like geometry to three equivalent K and one In atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb4C2Br3 by Materials Project

Tb4C2Br3 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are four inequivalent Tb sites. In the first Tb site, Tb is bonded to two equivalent C and four Br atoms to form distorted TbC2Br4 octahedra that share corners with four TbC4Br2 octahedra and edges with ten TbC2Br4 octahedra. The corner-sharing octahedral tilt angles are 4°. Both Tb–C bond lengths are 2.43 Å. There are a spread of Tb–Br bond distances ranging from 2.78–3.19 Å. In the second Tb site, Tb is bonded to four C and two equivalent Br atoms to form a mixture of edge and corner-sharing TbC4Br2 octahedra. The corner-sharing octahedra tilt angles range from 0–4°. There are a spread of Tb–C bond distances ranging from 2.60–2.71 Å. Both Tb–Br bond lengths are 2.96 Å. In the third Tb site, Tb is bonded to three C and three Br atoms to form a mixture of distorted edge and corner-sharing TbC3Br3 octahedra. The corner-sharing octahedra tilt angles range from 1–21°. There are two shorter (2.51 Å) and one longer (2.55 Å) Tb–C bond lengths. There are one shorter (2.93 Å) and two longer (3.00 Å) Tb–Br bond lengths. In the fourth Tb site, Tb is bonded to three C and three Br atoms to form a mixture of distorted edge and corner-sharing TbC3Br3 octahedra. The corner-sharing octahedra tilt angles range from 1–21°. There are two shorter (2.46 Å) and one longer (2.56 Å) Tb–C bond lengths. There are one shorter (2.91 Å) and two longer (3.16 Å) Tb–Br bond lengths. There are two inequivalent C sites. In the first C site, C is bonded to six Tb atoms to form a mixture of edge and corner-sharing CTb6 octahedra. The corner-sharing octahedral tilt angles are 6°. In the second C site, C is bonded to six Tb atoms to form edge-sharing CTb6 octahedra. There are three inequivalent Br sites. In the first Br site, Br is bonded in a distorted square co-planar geometry to four Tb atoms. In the second Br site, Br is bonded in a 3-coordinate geometry to three Tb atoms. In the third Br site, Br is bonded in a 5-coordinate geometry to five Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nd(BrO6)3 by Materials Project

Nd(O6Br)3 crystallizes in the orthorhombic Cmc2_1 space group. The structure is zero-dimensional and consists of four Nd(O6Br)3 clusters. Nd is bonded in a 12-coordinate geometry to twelve O atoms. There are a spread of Nd–O bond distances ranging from 2.38–3.13 Å. There are eleven inequivalent O sites. In the first O site, O is bonded in a water-like geometry to one Nd and one Br atom. The O–Br bond length is 1.72 Å. In the second O site, O is bonded in a water-like geometry to one Nd and one Br atom. The O–Br bond length is 1.72 Å. In the third O site, O is bonded in a distorted water-like geometry to one Nd and one Br atom. The O–Br bond length is 1.72 Å. In the fourth O site, O is bonded in a single-bond geometry to one Br atom. The O–Br bond length is 1.65 Å. In the fifth O site, O is bonded in a single-bond geometry to one Br atom. The O–Br bond length is 1.65 Å. In the sixth O site, O is bonded in a water-like geometry to two equivalent O atoms. Both O–O bond lengths are 1.45 Å. In the seventh O site, O is bonded in a water-like geometry to two O atoms. There is one shorter (1.45 Å) and one longer (1.46 Å) O–O bond length. In the eighth O site, O is bonded in a single-bond geometry to one Nd atom. In the ninth O site, O is bonded in a single-bond geometry to one Nd atom. In the tenth O site, O is bonded in a distorted water-like geometry to one Nd and two equivalent O atoms. In the eleventh O site, O is bonded in a distorted trigonal non-coplanar geometry to one Nd and two O atoms. There are two inequivalent Br sites. In the first Br site, Br is bonded in a trigonal non-coplanar geometry to three O atoms. In the second Br site, Br is bonded in a trigonal non-coplanar geometry to three O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce2Br5 by Materials Project

Ce2Br5 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are two inequivalent Ce sites. In the first Ce site, Ce is bonded to seven Br atoms to form distorted edge-sharing CeBr7 pentagonal bipyramids. There are a spread of Ce–Br bond distances ranging from 2.99–3.18 Å. In the second Ce site, Ce is bonded in a 7-coordinate geometry to eight Br atoms. There are a spread of Ce–Br bond distances ranging from 3.02–3.61 Å. There are five inequivalent Br sites. In the first Br site, Br is bonded in a trigonal non-coplanar geometry to three equivalent Ce atoms. In the second Br site, Br is bonded in a distorted T-shaped geometry to three Ce atoms. In the third Br site, Br is bonded in a distorted T-shaped geometry to three Ce atoms. In the fourth Br site, Br is bonded in a trigonal non-coplanar geometry to three equivalent Ce atoms. In the fifth Br site, Br is bonded in a distorted L-shaped geometry to three Ce atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sc4FeBr5 by Materials Project

Sc4FeBr5 crystallizes in the tetragonal P4_2/nnm space group. The structure is three-dimensional. there are three inequivalent Sc sites. In the first Sc site, Sc is bonded to three equivalent Fe and three Br atoms to form edge-sharing ScFe3Br3 octahedra. There are two shorter (2.58 Å) and one longer (2.61 Å) Sc–Fe bond lengths. There are one shorter (2.83 Å) and two longer (2.95 Å) Sc–Br bond lengths. In the second Sc site, Sc is bonded in a 6-coordinate geometry to one Fe and five Br atoms. The Sc–Fe bond length is 2.44 Å. There are a spread of Sc–Br bond distances ranging from 2.74–3.26 Å. In the third Sc site, Sc is bonded in a 6-coordinate geometry to one Fe and five Br atoms. The Sc–Fe bond length is 2.47 Å. There are a spread of Sc–Br bond distances ranging from 2.75–3.19 Å. Fe is bonded to six Sc atoms to form distorted edge-sharing FeSc6 octahedra. There are four inequivalent Br sites. In the first Br site, Br is bonded in a 4-coordinate geometry to four Sc atoms. In the second Br site, Br is bonded in a distorted see-saw-like geometry to four Sc atoms. In the third Br site, Br is bonded in a 3-coordinate geometry to three Sc atoms. In the fourth Br site, Br is bonded in a 3-coordinate geometry to three Sc atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y4RuBr5 by Materials Project

Y4RuBr5 crystallizes in the tetragonal P4_2/nnm space group. The structure is three-dimensional. there are three inequivalent Y sites. In the first Y site, Y is bonded to one Ru and five Br atoms to form distorted YRuBr5 octahedra that share a cornercorner with one YRu3Br3 octahedra and edges with eight YRuBr5 octahedra. The corner-sharing octahedral tilt angles are 13°. The Y–Ru bond length is 2.72 Å. There are a spread of Y–Br bond distances ranging from 2.93–3.20 Å. In the second Y site, Y is bonded to three equivalent Ru and three Br atoms to form a mixture of edge and corner-sharing YRu3Br3 octahedra. The corner-sharing octahedra tilt angles range from 2–14°. There are two shorter (2.83 Å) and one longer (2.86 Å) Y–Ru bond lengths. There are one shorter (3.06 Å) and two longer (3.20 Å) Y–Br bond lengths. In the third Y site, Y is bonded to one Ru and five Br atoms to form distorted YRuBr5 octahedra that share corners with three YRu3Br3 octahedra and edges with eight YRuBr5 octahedra. The corner-sharing octahedra tilt angles range from 2–14°. The Y–Ru bond length is 2.69 Å. There are a spread of Y–Br bond distances ranging from 2.91–3.24 Å. Ru is bonded to six Y atoms to form edge-sharing RuY6 octahedra. There are four inequivalent Br sites. In the first Br site, Br is bonded in a 3-coordinate geometry to three Y atoms. In the second Br site, Br is bonded in a distorted see-saw-like geometry to four Y atoms. In the third Br site, Br is bonded in a distorted see-saw-like geometry to four Y atoms. In the fourth Br site, Br is bonded in a 3-coordinate geometry to three Y atoms.

36 MATERIALS SCIENCE↗
NASA NTRS2008

Arterial Structure and Function in Women and Men Following Long Duration Bed Rest

Orthostatic intolerance is a well-recognized consequence of space flight and bed rest (BR), with a greater incidence reported in women. We hypothesized that leg, but not arm, arterial structure and function would be altered following prolonged BR, as a model of space flight, and that women would be more susceptible to BR-induced deconditioning than men. METHODS: Ten volunteers (5 males, 5 females) completed 90 d of 6 head-down BR. Subjects participated in tests of brachial (BA) and anterior tibial (AT) artery endothelium-dependent (flow mediated dilation [FMD] following 5-7 min of arterial occlusion) and endothelium-independent (0.4 mg sublingual nitroglycerin [SN]) vasodilation before BR (PRE) and on days 7 (BR7), 21 (BR21), and 90 (BR90) of BR. Vessel diameter and intimal medial thickness (IMT) were measured by ultrasound. IMT, baseline diameter, and percent change in diameter from baseline during FMD and SN tests were compared across BR and between genders using repeated measures two-way ANOVA with Bonferroni post-hoc tests in which PRE and women were control conditions. RESULTS: Baseline vessel diameter was lower in women than in men in both the BA (p=0.005) and AT (p=0.01) across all days. Baseline AT diameter decreased during BR (p=0.01) and tended to be more profound in women (interaction, p=0.06). AT diameter was reduced in women at BR21 and BR90 (p<0.01) but not in men. In contrast, there was no BR effect on baseline BA diameter. IMT also decreased in the AT (p<0.001) but not in the BA during BR; AT IMT was reduced by BR21 (p<0.05). As a group, there was no effect of BR on AT FMD, BA FMD, and AT SN-dilation, although BA SN-dilation was significantly reduced on BR21 (p=0.01). Across all BR days, women exhibited higher AT FMD (p=0.03), BA FMD (p=0.02), and BA SN-dilation (p=0.01) and tended to demonstrate greater AT SN-dilation (p=0.11). CONCLUSIONS: These preliminary results suggest that arterial remodeling occurs during BR in the leg (decreased diameter and IMT), but not in the arm, and that women appear to be more responsive to BR than men. These changes in the leg, coupled with larger responses to direct and indirect stimulation of the arterial smooth muscle, may be related to the greater incidence of orthostatic intolerance in women after BR and space flight.

Lee, Stuart M. C.↗
NASA NTRS2013

Association Between Cardiovascular and Intraocular Pressure Changes in a 14-Day 6 deg Head Down Tilt (HDT) Bed Rest Study: Possible Implications in Retinal Anatomy

Visual symptoms and intracranial pressure increase reported in astronauts returning from long duration missions in low Earth-orbit are thought to be related to fluid shifts within the body due to microgravity exposure. Because of this possible relation to fluid shifts, studies conducted in head-down tilt (HDT) bed rest are being monitored for potential changes in ocular health. These measures will also serve to determine whether HDT is a suitable ground-based analog to model subclinical cardiovascular and ocular changes that could shed light on the etiology of the VIIP syndrome observed in spaceflight. Sixteen healthy normotensive (12M, 4F, age range 29-54 years), non-smoker and normal weight subjects, volunteered to participate in a 14 day 6 deg head HDT study conducted at the NASA Flight Analogs Research Unit (FARU). This facility provides standard bed rest conditions (diet, wake/sleep time, time allowed in sunlight) during the time that the subjects stay at the FARU. Cardiovascular parameters were obtained in supine posture at BR-5, BR+0, and BR+3 and ocular monitoring was performed weekly. Intraocular pressure (IOP) increased from pre-bed rest BR-3) to the third day into bed rest (BR+3). Values reached a plateau towards the end of the bed rest phase (BR10) and decreased within the first three days of recovery (BR+2) returning to levels comparable to baseline at BR-3. As expected, most cardiovascular parameters were affected by 14 days of HDT bed rest. Plasma volume decreased as a result of bed rest but recovered to baseline levels by BR+3. Indications of cardiovascular deconditioning included increase in both systolic and diastolic blood pressure and heart rate, and a decrease in stroke volume and cardiac output between BR-5 and BR+3. Due to the experimental design of this study, we were not able to test the hypothesis that fluid shifts might be involved in the IOP increase during the bed rest phase, since cardiovascular measures were not available for those time points. There was no correlation between the largest change in IOP (BR-3 versus BR3) and cardiovascular measure changes between baseline (BR-5) and post bed rest (BR+2). While no clinically relevant visual changes were observed during the study, measurement of various retinal parameters was performed with optical coherence tomography (OCT). A decrease in central subfield retinal thickness was observed between BR+2 and baseline at BR-10, but no association was observed with IOP changes. This work investigates the time course of changes in IOP during 14-day HDT bed rest in an attempt to characterize HDT bed rest as a model of the VIIP syndrome and delve into its etiology.

Cromwell, Ronita↗
NASA NTRS2014

High Intensity Exercise Countermeasures does not Prevent Orthostatic Intolerance Following Prolonged Bed Rest

Approximately 20% of Space Shuttle astronauts became presyncopal during operational stand and 80deg head‐up tilt tests, and the prevalence of orthostatic intolerance increases after longer missions. Greater than 60% of the US astronauts participating in Mir and early International Space Station missions experienced presyncope during post‐flight tilt tests, perhaps related to limitations of the exercise hardware that prevented high intensity exercise training until later ISS missions. The objective of this study was to determine whether an intense resistive and aerobic exercise countermeasure program designed to prevent cardiovascular and musculoskeletal deconditioning during 70 d of bed rest (BR), a space flight analog, would protect against post‐BR orthostatic intolerance. METHODS Twenty‐six subjects were randomly assigned to one of three groups: non‐exercise controls (n=11) or one of two exercise groups (ExA, n=8; ExB, n=7). Both ExA and ExB groups performed the same resistive and aerobic exercise countermeasures during BR, but one exercise group received testosterone supplementation while the other received a placebo during BR in a double‐blinded fashion. On 3 d/wk, subjects performed lower body resistive exercise and 30 min of continuous aerobic exercise (≥75% max heart rate). On the other 3 d/wk, subjects performed only highintensity, interval‐style aerobic exercise. Orthostatic intolerance was assessed using a 15‐min 80 head‐up tilt test performed 2 d (BR‐2) before and on the last day of BR (BR70). Plasma volume was measured using carbon monoxide rebreathing on BR‐3 and before rising on the first recovery day (BR+0). The code for the exercise groups has not been broken, and results are reported here without group identification. RESULTS Only one subject became presyncopal during tilt testing on BR‐2, but 7 of 11 (63%) controls, 3 of 8 (38%) ExA, and 4 of 7 (57%) ExB subjects were presyncopal on BR70. Survival analysis of post‐BR tilt tests revealed no differences (p=0.77) between groups. Plasma volume (absolute or relative to body mass index) decreased (p<0.001) from pre to post‐BR, with no differences between groups. CONCLUSIONS These preliminary results corroborate previous reports that the performance of a vigorous exercise countermeasure protocol during BR, even with testosterone supplementation, does not protect against orthostatic intolerance or plasma volume loss. Preventing post‐BR orthostatic intolerance may require additional countermeasures, such as orthostatic stress during BR or end‐of‐BR fluid infusion.

Platts, Steven H.↗