Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 109
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
JAMA Netw Open ; 2(11): e1915011, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31722025

RESUMO

Importance: Exposure to a weightless environment during spaceflight results in a chronic headward blood and tissue fluid shift compared with the upright posture on Earth, with unknown consequences to cerebral venous outflow. Objectives: To assess internal jugular vein (IJV) flow and morphology during spaceflight and to investigate if lower body negative pressure is associated with reversing the headward fluid shift experienced during spaceflight. Design, Setting, and Participants: This prospective cohort study included 11 International Space Station crew members participating in long-duration spaceflight missions . Internal jugular vein measurements from before launch and approximately 40 days after landing were acquired in 3 positions: seated, supine, and 15° head-down tilt. In-flight IJV measurements were acquired at approximately 50 days and 150 days into spaceflight during normal spaceflight conditions as well as during use of lower body negative pressure. Data were analyzed in June 2019. Exposures: Posture changes on Earth, spaceflight, and lower body negative pressure. Main Outcomes and Measures: Ultrasonographic assessments of IJV cross-sectional area, pressure, blood flow, and thrombus formation. Results: The 11 healthy crew members included in the study (mean [SD] age, 46.9 [6.3] years, 9 [82%] men) spent a mean (SD) of 210 (76) days in space. Mean IJV area increased from 9.8 (95% CI, -1.2 to 20.7) mm2 in the preflight seated position to 70.3 (95% CI, 59.3-81.2) mm2 during spaceflight (P < .001). Mean IJV pressure increased from the preflight seated position measurement of 5.1 (95% CI, 2.5-7.8) mm Hg to 21.1 (95% CI, 18.5-23.7) mm Hg during spaceflight (P < .001). Furthermore, stagnant or reverse flow in the IJV was observed in 6 crew members (55%) on approximate flight day 50. Notably, 1 crew member was found to have an occlusive IJV thrombus, and a potential partial IJV thrombus was identified in another crew member retrospectively. Lower body negative pressure was associated with improved blood flow in 10 of 17 sessions (59%) during spaceflight. Conclusions and Relevance: This cohort study found stagnant and retrograde blood flow associated with spaceflight in the IJVs of astronauts and IJV thrombosis in at least 1 astronaut, a newly discovered risk associated with spaceflight. Lower body negative pressure may be a promising countermeasure to enhance venous blood flow in the upper body during spaceflight.

2.
J Trauma Acute Care Surg ; 87(1S Suppl 1): S59-S66, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31246908

RESUMO

Acute compartment syndrome (ACS) is a serious medical condition that can occur following traumatic injury to an extremity. If left undiagnosed, ACS can eventuate in amputation of the limb or even death. Because of this, fasciotomy to release the pressure within the muscle and restore tissue perfusion is often performed upon suspicion of ACS, as the sequelae to fasciotomy are less severe than those associated with not performing the fasciotomy. Currently, the "gold standard" of diagnosis is based on clinical assessment of such symptoms as pain out of proportion to the injury, obvious high pressure and swelling, pain on passive stretch of the muscles in the affected compartment, and deficits in sensory and/ormotor functions. Diagnosis is often confirmed using invasive measurements of intramuscular pressure (IMP); however, controversy exists as to how direct IMP measurement should be accomplished and threshold pressures for accurate diagnosis. Because of this and the attendant issues with invasive measurements, investigators have been searching over the last 25 years for a noninvasive means to quantitatively measure IMP or perfusion to the limb. The purpose of this review is to summarize the current state of the art of noninvasive devices that could potentially be used to diagnose ACS accurately and objectively. To do this, we divide the discussion into those medical devices that primarily measure mechanical surrogates of IMP (e.g., tissue hardness or myofascial displacement) and those that primarily measure indices of tissue perfusion (e.g., tissue oxygen saturation via near-infraredspectroscopy). While near-infrared spectroscopy-basedtechnologies have shown the most promise, whether such technologies will be of diagnostic benefit await the completion of ongoing clinical trials. LEVEL OF EVIDENCE: Systematic Review, level II.

3.
Artigo em Inglês | MEDLINE | ID: mdl-30939585

RESUMO

Acute compartment syndrome (ACS) is a serious medical condition that can occur following traumatic injury to an extremity. If left undiagnosed, ACS can eventuate in amputation of the limb or even death. Because of this, fasciotomy to release the pressure within the muscle and restore tissue perfusion is often performed upon suspicion of ACS, as the sequelae to fasciotomy are less severe than those associated with not performing the fasciotomy. Currently, the "gold standard" of diagnosis is based on clinical assessment of such symptoms as pain out of proportion to the injury, obvious high pressure and swelling, pain on passive stretch of the muscles in the affected compartment, and deficits in sensory and/or motor functions. Diagnosis is often confirmed using invasive measurements of intramuscular pressure (IMP), however, controversy exists as to how direct IMP measurement should be accomplished and threshold pressures for accurate diagnosis. Because of this and the attendant issues with invasive measurements, investigators have been searching over the last 25 years for a noninvasive means to quantitatively measure IMP or perfusion to the limb. The purpose of this review is to summarize the current state of the art of noninvasive devices that could potentially be used to diagnose ACS accurately and objectively. To do this, we divide the discussion into those medical devices that primarily measure mechanical surrogates of IMP (e.g., tissue hardness or myofascial displacement) and those that primarily measure indices of tissue perfusion (e.g., tissue oxygen saturation via near-infrared technology (NIRS)). While NIRS-based technologies have shown the most promise, whether such technologies will be of diagnostic benefit await the completion of ongoing clinical trials.

4.
Science ; 364(6436)2019 04 12.
Artigo em Inglês | MEDLINE | ID: mdl-30975860

RESUMO

To understand the health impact of long-duration spaceflight, one identical twin astronaut was monitored before, during, and after a 1-year mission onboard the International Space Station; his twin served as a genetically matched ground control. Longitudinal assessments identified spaceflight-specific changes, including decreased body mass, telomere elongation, genome instability, carotid artery distension and increased intima-media thickness, altered ocular structure, transcriptional and metabolic changes, DNA methylation changes in immune and oxidative stress-related pathways, gastrointestinal microbiota alterations, and some cognitive decline postflight. Although average telomere length, global gene expression, and microbiome changes returned to near preflight levels within 6 months after return to Earth, increased numbers of short telomeres were observed and expression of some genes was still disrupted. These multiomic, molecular, physiological, and behavioral datasets provide a valuable roadmap of the putative health risks for future human spaceflight.


Assuntos
Adaptação Fisiológica , Astronautas , Voo Espacial , Imunidade Adaptativa , Peso Corporal , Artérias Carótidas/diagnóstico por imagem , Espessura Intima-Media Carotídea , Dano ao DNA , Metilação de DNA , Microbioma Gastrointestinal , Instabilidade Genômica , Humanos , Masculino , Homeostase do Telômero , Fatores de Tempo , Estados Unidos , United States National Aeronautics and Space Administration
5.
Aerosp Med Hum Perform ; 89(4): 357-364, 2018 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-29562965

RESUMO

BACKGROUND: We compared microvascular and macrovascular blood flows of the tibia and anterior tibial artery during graded whole-body tilt. We hypothesized equal responses for bone microvascular and macrovascular blood flows during varying angles of tilt. METHODS: There were 18 volunteers who were randomly positioned in the following postures: supine, 15° head-up tilt, 6° head-up tilt, 6° head-down tilt, and 15° head-down tilt using an inversion table with reference to seated posture (baseline control). Ultrasonography quantified anterior tibial arterial diameter and peak systolic velocity, enabling calculation of macrovascular blood flow to the tibia. Tibial bone microvascular blood flow was measured noninvasively using photoplethysmography in the same leg. RESULTS: Transitioning from a seated position to a supine position, macrovascular blood flow did not change significantly (1.81 ± 1.18 to 2.80 ± 1.74cm 3 · s-1). However, bone microvascular flow increased significantly (0.36 ± 0.23 to 1.11 ± 0.79 V) from the seated to the supine position. Transitioning from a seated posture to 15° head-down tilt, both arterial macrovascular and bone microvascular flows increased significantly (1.81 ± 1.18 to 3.32 ± 2.08 cm3 · s-1 and 0.36 ± 0.23 V to 2.99 ± 2.71 V, respectively). The normalized flow for microvascular blood flow as a function of body tilt was significantly greater than that for macrovascular blood flow at 6° and 15° head-down tilt. DISCUSSION: These data do not support our hypothesis that bone microvascular flow and arterial macrovascular flow share equal responses to altered body tilt. Therefore, for a given decrease in local blood pressure in the leg with head-down body tilt, the magnitude of increase in blood flow is greater in the microcirculation as compared to the feeding artery.Becker RL, Siamwala JH, Macias BR, Hargens AR. Tibia bone microvascular flow dynamics as compared to anterior tibial artery flow during body tilt. Aerosp Med Hum Perform. 2018; 89(4):357-364.


Assuntos
Velocidade do Fluxo Sanguíneo/fisiologia , Decúbito Inclinado com Rebaixamento da Cabeça/fisiologia , Microcirculação/fisiologia , Tíbia/irrigação sanguínea , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Voo Espacial , Tíbia/diagnóstico por imagem , Ultrassonografia , Ausência de Peso , Simulação de Ausência de Peso
6.
Front Physiol ; 9: 72, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29491839

RESUMO

Hands may show early signs of aging with altered skin texture, skin permeability and vascular properties. In clinics, a hand volumeter is used to measure swelling of hands due to edema, carpal tunnel syndrome or drug interventions. The hand volume measurements are generally taken without taking age into consideration. We hypothesized that age affects hand volumeter measurements and that the younger age group (≤40 years) records a greater change in hand volume as compared to the older group (>40 years). Four volumetric measurements were taken at 5 min intervals during 20 min of water immersion using a clinically-approved hand volumeter. After 20 min of immersion, the hand volume changes of the younger age group were significantly higher than the older age group (p < 0.001). Specifically, the right-hand volume of the younger age group (≤40 years, n = 30) increased by 4.3 ± 2%, and the left hand increased by 3.4 ± 2.1%. Conversely, the right-hand volume of the older age group (>40 years, n = 10) increased by 2.2 ± 2.0%, and the left hand decreased by 0.6 ± 2.4% after 20 min of water immersion. The data are presented as Mean ± SD. Hand volume changes were not correlated with body mass index (BMI) or gender, and furthermore, neither of these two variables affected the relationship between age and hand volume changes with water immersion. We conclude that the younger age group has a higher increase in hand volume with water immersion as compared to the older age group.

8.
Spine J ; 18(1): 7-14, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-28962911

RESUMO

BACKGROUND CONTEXT: Prolonged microgravity exposure is associated with localized low back pain and an elevated risk of post-flight disc herniation. Although the mechanisms by which microgravity impairs the spine are unclear, they should be foundational for developing in-flight countermeasures for maintaining astronaut spine health. Because human spine anatomy has adapted to upright posture on Earth, observations of how spaceflight affects the spine should also provide new and potentially important information on spine biomechanics that benefit the general population. PURPOSE: This study compares quantitative measures of lumbar spine anatomy, health, and biomechanics in astronauts before and after 6 months of microgravity exposure on board the International Space Station (ISS). STUDY DESIGN: This is a prospective longitudinal study. SAMPLE: Six astronaut crewmember volunteers from the National Aeronautics and Space Administration (NASA) with 6-month missions aboard the ISS comprised our study sample. OUTCOME MEASURES: For multifidus and erector spinae at L3-L4, measures include cross-sectional area (CSA), functional cross-sectional area (FCSA), and FCSA/CSA. Other measures include supine lumbar lordosis (L1-S1), active (standing) and passive (lying) flexion-extension range of motion (FE ROM) for each lumbar disc segment, disc water content from T2-weighted intensity, Pfirrmann grade, vertebral end plate pathology, and subject-reported incidence of chronic low back pain or disc injuries at 1-year follow-up. METHODS: 3T magnetic resonance imaging and dynamic fluoroscopy of the lumbar spine were collected for each subject at two time points: approximately 30 days before launch (pre-flight) and 1 day following 6 months spaceflight on the ISS (post-flight). Outcome measures were compared between time points using paired t tests and regression analyses. RESULTS: Supine lumbar lordosis decreased (flattened) by an average of 11% (p=.019). Active FE ROM decreased for the middle three lumbar discs (L2-L3: -22.1%, p=.049; L3-L4: -17.3%, p=.016; L4-L5: -30.3%, p=.004). By contrast, no significant passive FE ROM changes in these discs were observed (p>.05). Disc water content did not differ systematically from pre- to post-flight. Multifidus and erector spinae changed variably between subjects, with five of six subjects experiencing an average decrease 20% for FCSA and 8%-9% for CSA in both muscles. For all subjects, changes in multifidus FCSA strongly correlated with changes in lordosis (r2=0.86, p=.008) and active FE ROM at L4-L5 (r2=0.94, p=.007). Additionally, changes in multifidus FCSA/CSA correlated with changes in lordosis (r2=0.69, p=.03). Although multifidus-associated changes in lordosis and ROM were present among all subjects, only those with severe, pre-flight end plate irregularities (two of six subjects) had post-flight lumbar symptoms (including chronic low back pain or disc herniation). CONCLUSIONS: We observed that multifidus atrophy, rather than intervertebral disc swelling, associated strongly with lumbar flattening and increased stiffness. Because these changes have been previously linked with detrimental spine biomechanics and pain in terrestrial populations, when combined with evidence of pre-flight vertebral end plate insufficiency, they may elevate injury risk for astronauts upon return to gravity loading. Our results also have implications for deconditioned spines on Earth. We anticipate that our results will inform new astronaut countermeasures that target the multifidus muscles, and research on the role of muscular stability in relation to chronic low back pain and disc injury.


Assuntos
Degeneração do Disco Intervertebral/diagnóstico por imagem , Deslocamento do Disco Intervertebral/diagnóstico por imagem , Região Lombossacral/diagnóstico por imagem , Ausência de Peso/efeitos adversos , Adulto , Astronautas , Feminino , Humanos , Degeneração do Disco Intervertebral/etiologia , Degeneração do Disco Intervertebral/patologia , Deslocamento do Disco Intervertebral/etiologia , Deslocamento do Disco Intervertebral/patologia , Região Lombossacral/patologia , Imagem por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Músculos Paraespinais/diagnóstico por imagem , Músculos Paraespinais/patologia , Postura
9.
Physiol Rev ; 98(1): 59-87, 2018 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-29167331

RESUMO

Visual impairment intracranial pressure (VIIP) syndrome is considered an unexplained major risk for future long-duration spaceflight. NASA recently redefined this syndrome as Spaceflight-Associated Neuro-ocular Syndrome (SANS). Evidence thus reviewed supports that chronic, mildly elevated intracranial pressure (ICP) in space (as opposed to more variable ICP with posture and activity on Earth) is largely accounted for by loss of hydrostatic pressures and altered hemodynamics in the intracranial circulation and the cerebrospinal fluid system. In space, an elevated pressure gradient across the lamina cribrosa, caused by a chronic but mildly elevated ICP, likely elicits adaptations of multiple structures and fluid systems in the eye which manifest themselves as the VIIP syndrome. A chronic mismatch between ICP and intraocular pressure (IOP) in space may acclimate the optic nerve head, lamina cribrosa, and optic nerve subarachnoid space to a condition that is maladaptive to Earth, all contributing to the pathogenesis of space VIIP syndrome. Relevant findings help to evaluate whether artificial gravity is an appropriate countermeasure to prevent this seemingly adverse effect of long-duration spaceflight.


Assuntos
Hipertensão Intracraniana/fisiopatologia , Pressão Intracraniana/fisiologia , Pressão Intraocular/fisiologia , Postura/fisiologia , Voo Espacial , Transtornos da Visão/fisiopatologia , Animais , Humanos , Hipertensão Intracraniana/etiologia , Hipertensão Intracraniana/patologia , Transtornos da Visão/etiologia , Transtornos da Visão/patologia
10.
Bone Rep ; 7: 57-62, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28875158

RESUMO

Previously our laboratory documented increases in calvaria bone volume and thickness in mice exposed to 15 days of spaceflight aboard the NASA Shuttle mission STS-131. However, the tissues were not processed for gene expression studies to determine what bone formation pathways might contribute to these structural adaptations. Therefore, this study was designed to investigate both the structural and molecular changes in mice calvariae after a longer duration of spaceflight. The primary purpose was to determine the calvaria bone volume and thickness of mice exposed to 30 days of spaceflight using micro-computed tomography for comparison with our previous findings. Because sclerostin, the secreted glycoprotein of the Sost gene, is a potent inhibitor of bone formation, our second aim was to quantify Sost mRNA expression using quantitative PCR. Calvariae were obtained from six mice aboard the Russian 30-day Bion-M1 biosatellite and seven ground controls. In mice exposed to 30 days of spaceflight, calvaria bone structure was not significantly different from that of their controls (bone volume was about 5% lower in spaceflight mice, p = 0.534). However, Sost mRNA expression was 16-fold (16.4 ± 0.4, p < 0.001) greater in the spaceflight group than that in the ground control group. Therefore, bone formation may have been suppressed in mice exposed to 30 days of spaceflight. Genetic responsiveness (e.g. sex or strain of animals) or in-flight environmental conditions other than microgravity (e.g. pCO2 levels) may have elicited different bone adaptations in STS-131 and Bion-M1 mice. Although structural results were not significant, this study provides biochemical evidence that calvaria mechanotransduction pathways may be altered during spaceflight, which could reflect vascular and interstitial fluid adaptations in non-weight bearing bones. Future studies are warranted to elucidate the processes that mediate these effects and the factors responsible for discordant calvaria bone adaptations between STS-131 and Bion-M1 mice.

11.
J Bone Joint Surg Am ; 99(17): 1453-1459, 2017 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-28872527

RESUMO

BACKGROUND: The current gold standard for diagnosing acute compartment syndrome (ACS) is an assessment of clinical signs, invasive measurement of intramuscular pressure (IMP), and measurement of local perfusion pressure. However, IMP measurements have several shortcomings, including pain, risk of infection, risk of technique error, plugging of the catheter tip, lack of consensus on the diagnostic pressure threshold, and lack of specificity and sensitivity. The objective of this study was to evaluate muscle hemodynamics, oxygenation, and pH as diagnostic parameters in a human model of ACS. We hypothesized that as IMP increases, muscle microvascular blood flow, oxygenation, and pH decrease in the anterior compartment of a leg at heart level and that they decrease significantly more when the leg is elevated further. METHODS: An external pneumatic leg pressure chamber, combined with a venous stasis thigh cuff, was used to increase IMP and simulate ACS. Eight healthy subjects (5 males and 3 females; mean age, 26 years) had photoplethysmography and near-infrared spectroscopy-pH sensors placed over the middle aspect of the tibialis anterior muscle of the right (experimental) and left (control) legs. Leg chamber pressure conditions (40, 50, and 60 mm Hg) were applied in a randomized order after baseline measurements were taken. Data were collected continuously for each 11-minute pressure condition, with an 11-minute recovery period after each condition, and the average of the last 6 minutes was used for data analyses. The same protocol was repeated with each subject's legs elevated 12 cm above heart level. Data were analyzed using repeated-measures analysis of variance (ANOVA). RESULTS: As IMP increased, muscle microvascular blood flow (p = 0.01), oxygenation (p < 0.001), and pH (p < 0.001) all decreased significantly in the experimental leg compared with the control leg. At all IMP levels, leg elevation significantly decreased muscle oxygenation (p = 0.013) and perfusion pressure (p = 0.03) compared with the control leg at heart level. CONCLUSIONS: These results indicate that muscle microvascular blood flow, oxygenation, pH, and perfusion pressure decrease significantly as IMP increases in a human model of ACS. CLINICAL RELEVANCE: This study identifies hemodynamic and metabolic parameters as potential noninvasive diagnostic tools for ACS.


Assuntos
Síndrome do Compartimento Anterior/fisiopatologia , Músculo Esquelético/irrigação sanguínea , Adulto , Síndrome do Compartimento Anterior/etiologia , Pressão Sanguínea/fisiologia , Feminino , Humanos , Concentração de Íons de Hidrogênio , Masculino , Microcirculação/fisiologia , Modelos Cardiovasculares , Simulação de Paciente , Fluxo Sanguíneo Regional/fisiologia
12.
J Appl Physiol (1985) ; 123(4): 860-866, 2017 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-28663380

RESUMO

Loss of hydrostatic pressures in microgravity may alter skin and bone microvascular flows in the lower extremities and potentially reduce wound healing and bone fracture repair. The purpose of this study was to determine the rate at which skin and bone microvascular flows respond to head-down tilt (HDT). We hypothesized that microvascular flows in tibial bone and overlying skin would increase at different rates during HDT. Tibial bone and skin microvascular flows were measured simultaneously using photoplethysmography (PPG) in a total of 17 subjects during sitting (control posture), supine, 6° HDT, 15° HDT, and 30° HDT postures in random order. With greater angles of HDT, bone microvascular flow increased significantly, but skin microvascular flow did not change. Tibial bone microvascular flow increased from the sitting control posture (0.77 ± 0.41 V) to supine (1.95 ± 1.01 V, P = 0.001) and from supine posture to 15° HDT (3.74 ± 2.43 V, P = 0.004) and 30° HDT (3.91 ± 2.68 V, P = 0.006). Skin microvascular flow increased from sitting (0.703 ± 0.75 V) to supine (2.19 ± 1.72 V, P = 0.02) but did not change from supine posture to HDT (P = 1.0). We show for the first time that microcirculatory flows in skin and bone of the leg respond to simulated microgravity at different rates. These altered levels of blood perfusion may affect rates of wound and bone fracture healing in spaceflight.NEW & NOTEWORTHY Our data show that bone microvascular flow increases more than cutaneous blood flow with greater degrees of head-down tilt. A higher level of perfusion in bone may give insight into the bone mineral density loss in lower extremities of astronauts and why similar tissue degradation is not observed in the skin of the same areas.


Assuntos
Decúbito Inclinado com Rebaixamento da Cabeça , Microcirculação/fisiologia , Pele/irrigação sanguínea , Tíbia/irrigação sanguínea , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Fotopletismografia , Postura , Simulação de Ausência de Peso , Adulto Jovem
13.
J Appl Physiol (1985) ; 123(1): 260-266, 2017 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-28495841

RESUMO

Long-term spaceflight induces a near visual acuity change in ~50% of astronauts. In some crew members, postflight cerebrospinal fluid (CSF) opening pressures by lumbar puncture are as high as 20.9 mmHg; these members demonstrated optic disc edema. CSF communicates through the cochlear aqueduct to affect perilymphatic pressure and tympanic membrane motion. We hypothesized that 50 mmHg of lower-body negative pressure (LBNP) during 15° head-down tilt (HDT) would mitigate elevations in internal jugular vein cross-sectional area (IJV CSA) and intracranial pressure (ICP). Fifteen healthy adult volunteers were positioned in sitting (5 min), supine (5 min), 15° HDT (5 min), and 15° HDT with LBNP (10 min) postures for data collection. Evoked tympanic membrane displacements (TMD) quantified ICP noninvasively. IJV CSA was measured using standard ultrasound techniques. ICP and IJV CSA increased significantly from the seated upright to the 15° HDT posture (P < 0.05), and LBNP mitigated these increases. LBNP at 25 mmHg reduced ICP during HDT (TMD of 322.13 ± 419.17 nl) to 232.38 ± 445.85 nl, and at 50 mmHg ICP was reduced further to TMD of 199.76 ± 429.69 nl. In addition, 50 mmHg LBNP significantly reduced IJV CSA (1.50 ± 0.33 cm2) during 15° HDT to 0.83 ± 0.42 cm2 LBNP counteracts the headward fluid shift elevation of ICP and IJV CSA experienced during microgravity as simulated by15° HDT. These data provide quantitative evidence that LBNP shifts cephalic fluid to the lower body, reducing IJV CSA and ICP.NEW & NOTEWORTHY The current study provides new evidence that 25 or 50 mmHg of lower body negative pressure reduces jugular venous pooling and intracranial pressure during simulated microgravity. Therefore, spaceflight countermeasures that sequester fluid to the lower body may mitigate cephalic venous congestion and vision impairment.


Assuntos
Decúbito Inclinado com Rebaixamento da Cabeça/fisiologia , Pressão Intracraniana/fisiologia , Veias Jugulares/fisiologia , Adulto , Pressão Sanguínea/fisiologia , Feminino , Frequência Cardíaca/fisiologia , Humanos , Pressão Negativa da Região Corporal Inferior/métodos , Masculino , Pessoa de Meia-Idade , Postura/fisiologia , Voo Espacial/métodos , Ausência de Peso , Simulação de Ausência de Peso/métodos , Adulto Jovem
14.
Physiol Rep ; 5(4)2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28242824

RESUMO

The purpose of the investigation was to study lower body negative pressure recovery in response to head down tilt position in men and women. The study examined the primary hypothesis that tibial bone microvascular flow responses to HDT and lower body negative pressure (LBNP) differ in women and men. Nine women and nine men between 20 to 30 years of age participated in the study. Tibial microvascular flow, head and tibial oxygenation and calf circumference were measured using photoplethysmography (PPG), near-infrared spectroscopy (NIRS) and strain gauge plethysmography (SGP), respectively, during sitting (control baseline), supine, 15° HDT, and 15° HDT with 25 mmHg LBNP Tibial microvascular flow with HDT increased by 57% from supine position (from 1.4V ± 0.7 to 2.2V ± 1.0 HDT; ANOVA P < 0.05) in men but there is no significant difference between supine and HDT in women. Ten minutes of LBNP during 15o HDT restored tibial bone microvascular flows to supine levels, (from 2.2V±1.0 HDT to 1.1V ± 0.7 supine; ANOVA P < 0.05) in men but not in women. These data support the concept that there are gender specific microvascular responses to a fluid-shift countermeasure such as LBNP Thus, gender differences should be considered while developing future countermeasure strategies to headward fluid shifts in microgravity.


Assuntos
Decúbito Inclinado com Rebaixamento da Cabeça , Pressão Negativa da Região Corporal Inferior , Microvasos/fisiologia , Fluxo Sanguíneo Regional/fisiologia , Caracteres Sexuais , Tíbia/irrigação sanguínea , Adulto , Pressão Sanguínea/fisiologia , Feminino , Frequência Cardíaca/fisiologia , Humanos , Masculino , Fotopletismografia , Espectroscopia de Luz Próxima ao Infravermelho , Adulto Jovem
15.
Spine (Phila Pa 1976) ; 41(24): 1917-1924, 2016 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-27779600

RESUMO

STUDY DESIGN: Prospective case series. OBJECTIVE: Evaluate lumbar paraspinal muscle (PSM) cross-sectional area and intervertebral disc (IVD) height changes induced by a 6-month space mission on the International Space Station. The long-term objective of this project is to promote spine health and prevent spinal injury during space missions and here on Earth. SUMMARY OF BACKGROUND DATA: National Aeronautics and Space Administration (NASA) crewmembers have a 4.3 times higher risk of herniated IVDs, compared with the general and military aviator populations. The highest risk occurs during the first year after a mission. Microgravity exposure during long-duration spaceflights results in approximately 5 cm lengthening of body height, spinal pain, and skeletal deconditioning. How the PSMs and IVDs respond during spaceflight is not well described. METHODS: Six NASA crewmembers were imaged supine with a 3 Tesla magnetic resonance imaging. Imaging was conducted preflight, immediately postflight, and then 33 to 67 days after landing. Functional cross-sectional area (FCSA) measurements of the PSMs were performed at the L3-4 level. FCSA was measured by grayscale thresholding within the posterior lumbar extensors to isolate lean muscle on T2-weighted scans. IVD heights were measured at the anterior, middle, and posterior sections of all lumbar levels. Repeated measures analysis of variance was used to determine significance at P < 0.05, followed by post-hoc testing. RESULTS: Paraspinal lean muscle mass, as indicated by the FCSA, decreased from 86% of the total PSM cross-sectional area down to 72%, immediately after the mission. Recovery of 68% of the postflight loss occurred during the next 6 weeks, still leaving a significantly lower lean muscle fractional content compared with preflight values. In contrast, lumbar IVD heights were not appreciably different at any time point. CONCLUSION: The data reveal lumbar spine PSM atrophy after long-duration spaceflight. Some FCSA recovery was seen with 46 days postflight in a terrestrial environment, but it remained incomplete compared with preflight levels. LEVEL OF EVIDENCE: 4.


Assuntos
Astronautas , Disco Intervertebral/patologia , Vértebras Lombares/patologia , Região Lombossacral/patologia , Músculos Paraespinais/fisiologia , Feminino , Humanos , Imagem por Ressonância Magnética/métodos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Voo Espacial/métodos , Fatores de Tempo
16.
Physiol Rep ; 4(15)2016 08.
Artigo em Inglês | MEDLINE | ID: mdl-27495299

RESUMO

Leg muscle mass and strength are decreased during reduced activity and non-weight-bearing conditions such as bed rest (BR) and spaceflight. Supine treadmill exercise within lower body negative pressure (LBNPEX) provides full-body weight loading during BR and may prevent muscle deconditioning. We hypothesized that a 40-min interval exercise protocol performed against LBNPEX 6 days week(-1) would attenuate losses in leg lean mass (LLM), strength, and endurance during 6° head-down tilt BR, with similar benefits for men and women. Fifteen pairs of healthy monozygous twins (8 male and 7 female pairs) completed 30 days of BR with one sibling of each twin pair assigned randomly as the non-exercise control (CON) and the other twin as the exercise subject (EX). Before and after BR, LLM and isokinetic leg strength and endurance were measured. Mean knee and ankle extensor and flexor strength and endurance and LLM decreased from pre- to post-BR in the male CON subjects (P < 0.01), but knee extensor strength and endurance, ankle extensor strength, and LLM were maintained in the male EX subjects. In contrast, no pre- to post-BR changes were significant in the female subjects, either CON or EX, likely due to their lower pre-BR values. Importantly, the LBNPEX countermeasure prevents or attenuates declines in LLM as well as extensor leg strength and endurance. Individuals who are stronger, have higher levels of muscular endurance, and/or have greater LLM are likely to experience greater losses during BR than those who are less fit.


Assuntos
Repouso em Cama/efeitos adversos , Terapia por Exercício/métodos , Perna (Membro)/fisiologia , Pressão Negativa da Região Corporal Inferior , Força Muscular , Resistência Física , Adulto , Teste de Esforço , Feminino , Humanos , Contração Isométrica , Masculino , Voo Espacial , Adulto Jovem
17.
J Appl Physiol (1985) ; 120(10): 1215-22, 2016 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-26893030

RESUMO

Microgravity-induced lumbar paraspinal muscle deconditioning may contribute to back pain commonly experienced by astronauts and may increase the risk of postflight injury. We hypothesized that a combined resistive and aerobic exercise countermeasure protocol that included spinal loading would mitigate lumbar paraspinal muscle deconditioning during 60 days of bed rest in women. Sixteen women underwent 60-day, 6° head-down-tilt bed rest (BR) and were randomized into control and exercise groups. During bed rest the control group performed no exercise. The exercise group performed supine treadmill exercise within lower body negative pressure (LBNP) for 3-4 days/wk and flywheel resistive exercise for 2-3 days/wk. Paraspinal muscle cross-sectional area (CSA) was measured using a lumbar spine MRI sequence before and after BR. In addition, isokinetic spinal flexion and extension strengths were measured before and after BR. Data are presented as means ± SD. Total lumbar paraspinal muscle CSA decreased significantly more in controls (10.9 ± 3.4%) than in exercisers (4.3 ± 3.4%; P < 0.05). The erector spinae was the primary contributor (76%) to total lumbar paraspinal muscle loss. Moreover, exercise attenuated isokinetic spinal extension loss (-4.3 ± 4.5%), compared with controls (-16.6 ± 11.2%; P < 0.05). In conclusion, LBNP treadmill and flywheel resistive exercises during simulated microgravity mitigate decrements in lumbar paraspinal muscle structure and spine function. Therefore spaceflight exercise countermeasures that attempt to reproduce spinal loads experienced on Earth may mitigate spinal deconditioning during long-duration space travel.


Assuntos
Repouso em Cama/efeitos adversos , Exercício/fisiologia , Músculos Paraespinais/fisiologia , Ausência de Peso/efeitos adversos , Astronautas , Teste de Esforço/métodos , Feminino , Decúbito Inclinado com Rebaixamento da Cabeça/fisiologia , Humanos , Pressão Negativa da Região Corporal Inferior/métodos , Vértebras Lombares/fisiologia , Região Lombossacral/fisiologia , Treinamento de Resistência/métodos , Voo Espacial/métodos , Contramedidas de Ausência de Peso , Simulação de Ausência de Peso/métodos
18.
J Appl Physiol (1985) ; 120(8): 891-903, 2016 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-26893033

RESUMO

Long-duration bed rest is widely employed to simulate the effects of microgravity on various physiological systems, especially for studies of bone, muscle, and the cardiovascular system. This microgravity analog is also extensively used to develop and test countermeasures to microgravity-altered adaptations to Earth gravity. Initial investigations of bone loss used horizontal bed rest with the view that this model represented the closest approximation to inactivity and minimization of hydrostatic effects, but all Earth-based analogs must contend with the constant force of gravity by adjustment of the G vector. Later concerns about the lack of similarity between headward fluid shifts in space and those with horizontal bed rest encouraged the use of 6 degree head-down tilt (HDT) bed rest as pioneered by Russian investigators. Headward fluid shifts in space may redistribute bone from the legs to the head. At present, HDT bed rest with normal volunteers is the most common analog for microgravity simulation and to test countermeasures for bone loss, muscle and cardiac atrophy, orthostatic intolerance, and reduced muscle strength/exercise capacity. Also, current physiologic countermeasures are focused on long-duration missions such as Mars, so in this review we emphasize HDT bed rest studies with durations of 30 days and longer. However, recent results suggest that the HDT bed rest analog is less representative as an analog for other important physiological problems of long-duration space flight such as fluid shifts, spinal dysfunction and radiation hazards.


Assuntos
Repouso em Cama , Decúbito Inclinado com Rebaixamento da Cabeça/fisiologia , Descanso/fisiologia , Ausência de Peso , Adaptação Fisiológica/fisiologia , Animais , Humanos , Voo Espacial , Fatores de Tempo , Simulação de Ausência de Peso
19.
NPJ Microgravity ; 2: 16022, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-28725733

RESUMO

Spaceflight causes sensorimotor adaptations that result in balance deficiencies on return to a gravitational environment. Treadmill exercise within lower-body negative pressure (LBNP) helps protect physiological function during microgravity as simulated by bed rest. Therefore, we hypothesized that treadmill exercise within LBNP would prevent balance losses in both male and female identical twins during 30 days of 6° head-down tilt bed rest. Fifteen (seven female and eight male) identical twin sets participated in this simulation of microgravity. Within each twin pair, one twin was randomly assigned to an exercise group that performed 40 min of supine treadmill exercise within LBNP set to generate 1.0-1.2 body weight, followed by 5 min of static feet-supported LBNP, 6 days per week. Their identical sibling was assigned to a non-exercise control group with all other bed rest conditions equivalent. Before and immediately after bed rest, subjects completed standing and walking rail balance tests with eyes open and eyes closed. In control subjects, standing rail balance times (men: -42%, women: -40%), rail walk distances (men: -44%, women: -32%) and rail walk times (men: -34%, women: -31%) significantly decreased after bed rest. Compared with controls, treadmill exercise within LBNP significantly attenuated losses of standing rail balance time by 63% in men, but the 41% attenuation in women was not significant. Treadmill exercise within LBNP did not affect rail walk abilities in men or women. Treadmill exercise within LBNP during simulated spaceflight attenuates loss of balance control in men but not in women.

20.
J Orthop Res ; 34(1): 48-57, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26285046

RESUMO

Intervertebral disc herniation rates are quadrupled in astronauts following spaceflight. While bending motions are main contributors to herniation, the effects of microgravity on the bending properties of spinal discs are unknown. Consequently, the goal of this study was to quantify the bending properties of tail discs from mice with or without microgravity exposure. Caudal motion segments from six mice returned from a 30-day Bion M1 mission and eight vivarium controls were loaded to failure in four-point bending. After testing, specimens were processed using histology to determine the location of failure, and adjacent motion segments were scanned with micro-computed tomography (µCT) to quantify bone properties. We observed that spaceflight significantly shortened the nonlinear toe region of the force-displacement curve by 32% and reduced the bending strength by 17%. Flight mouse spinal segments tended to fail within the growth plate and epiphyseal bone, while controls tended to fail at the disc-vertebra junction. Spaceflight significantly reduced vertebral bone volume fraction, bone mineral density, and trabecular thickness, which may explain the tendency of flight specimens to fail within the epiphyseal bone. Together, these results indicate that vertebral bone loss during spaceflight may degrade spine bending properties and contribute to increased disc herniation risk in astronauts.


Assuntos
Reabsorção Óssea/etiologia , Ausência de Peso/efeitos adversos , Animais , Reabsorção Óssea/diagnóstico por imagem , Reabsorção Óssea/patologia , Reabsorção Óssea/fisiopatologia , Osso e Ossos/patologia , Masculino , Camundongos Endogâmicos C57BL , Voo Espacial , Cauda , Suporte de Carga , Microtomografia por Raio-X
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA