Central hemodynamics in a baboon model during microgravity induced by parabolic flight

Latham, R. D.; Fanton, John W.; Vernalis, Marina; Gaffney, F. Andrew; Crisman, R. P.

doi:10.1016/0273-1177(94)90422-7

Cited by 11 publications

(4 citation statements)

References 5 publications

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“…These changes in gravity occur quickly (in about 1 s). For a hydrostatic gradient in a subject seated upright in this plane, this pressure gradient suddenly nearly doubles for 30 s (from 1 to 1.8 G), then equally suddenly drops to zero for 20 s (from 1.8 G to 0 G), only to rapidly return to double for another 30 s (from 0 to 1.8 G), after which it returns to normal (176,310,330,415,600). For autoregulation, these conditions create a series of step-wise, very fast changes in perfusion pressure (under the hypothesis that the gradient affects perfusion pressure) of 30 mmHg.…”

Section: Iid On Dynamic Autoregulation)mentioning

confidence: 97%

“…Parabolic flight experiments offer the unique opportunity to modify effects of gravity without changing posture (176,330). In a parabola following normal gravity (1 G), a period of  22 s of 0 G is preceded and followed by  30 s of hypergravity (1.8 G).…”

Section: Iid On Dynamic Autoregulation)mentioning

confidence: 99%

“…Unfortunately (yet unsurprisingly), the sudden changes in gravity affect multiple physiological processes (176,309,330,415,600). For example, hypergravity increases BP whereas zero gravity reduces BP, but also ICP, and PaCO2 (332).…”

Section: Iid On Dynamic Autoregulation)mentioning

confidence: 99%

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Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Claassen

Thijssen

Panerai

et al. 2021

Physiological Reviews

482

418

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Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure, 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)], 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans), and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the inter-relationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.

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Section: Iid On Dynamic Autoregulation)mentioning

confidence: 97%

Section: Iid On Dynamic Autoregulation)mentioning

confidence: 99%

See 1 more Smart Citation

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Claassen

Thijssen

Panerai

et al. 2021

Physiological Reviews

482

418

View full text Add to dashboard Cite

show abstract

“…Third, we did not specifically control or measure fluid intake or hydration of our subjects, which may have contributed to the between-subject variability of the response to partial gravity. Hydration had a graded effect on right and left atrial pressures and volumes during weightlessness in instrumented non-human primates in parabolic flight (Latham et al, 1994), particularly right atrial pressure in the upright posture when the animals were volume depleted. Finally, these analyses do not control for the seated height of our test subjects, which could contribute to differences in hydrostatic pressure gradients across individuals, although in our statistical design subjects served as their own controls.…”

Section: Limitationsmentioning

confidence: 95%

Venous and Arterial Responses to Partial Gravity

et al. 2020

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Introduction: Chronic exposure to the weightlessness-induced cephalad fluid shift is hypothesized to be a primary contributor to the development of spaceflight-associated neuro-ocular syndrome (SANS) and may be associated with an increased risk of venous thrombosis in the jugular vein. This study characterized the relationship between gravitational level (G z-level) and acute vascular changes. Methods: Internal jugular vein (IJV) cross-sectional area, inferior vena cava (IVC) diameter, and common carotid artery (CCA) flow were measured using ultrasound in nine subjects (5F, 4M) while seated when exposed to 1.00-G z , 0.75-G z , 0.50-G z , and 0.25-G z during parabolic flight and while supine before flight (0-G analog). Additionally, IJV flow patterns were characterized. Results: IJV cross-sectional area progressively increased from 12 (95% CI: 9-16) mm 2 during 1.00-G z seated to 24 (13-35), 34 (21-46), 68 (40-97), and 103 (75-131) mm 2 during 0.75-G z , 0.50-G z , and 0.25-G z seated and 1.00-G z supine, respectively. Also, IJV flow pattern shifted from the continuous forward flow observed during 1.00-G z and 0.75-G z seated to pulsatile flow during 0.50-G z seated, 0.25-G z seated, and 1.00-G z supine. In contrast, we were unable to detect differences in IVC diameter measured during 1.00-G seated and any level of partial gravity or during 1.00-G z supine. CCA blood flow during 1.00-G seated was significantly less than 0.75-G z and 1.00-G z supine but differences were not detected at partial gravity levels 0.50-G z and 0.25-G z. Conclusions: Acute exposure to decreasing G z-levels is associated with an expansion of the IJV and flow patterns that become similar to those observed in supine subjects and in astronauts during spaceflight. These data suggest that G z-levels greater than 0.50-G z may be required to reduce the weightlessness-induced headward fluid shift that may contribute to the risks of SANS and venous thrombosis during spaceflight.

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Pulmonary Circulation in Extreme Environments

Prisk

2011

Comprehensive Physiology

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The pulmonary circulation is subject to direct challenge from both altered pressure and altered gravity. To efficiently exchange gas, the pulmonary capillaries must be extremely thin-walled and directly exposed to the alveolar space. Thus, alterations in ambient pressure are directly transmitted to the capillaries with the potential to alter pulmonary blood flow. To produce ventilation, the mammalian lung must expand and contract, and so it is a highly compliant structure. Thus, because the capillaries are contained in the alveolar walls, alterations in the apparent gravitational force deform the lung and directly affect pulmonary blood flow both through lung deformation and through changes in the hydrostatic pressure distribution in the lung. High gravitational forces are encountered in the aviation environment, while gravity is absent in spaceflight. Diving subjects the lung to large increases in ambient pressure, while large reductions in pressure occur, often associated with alterations in oxygen level and airway pressure, in aviation. This article reviews the effects of alterations in both gravity and ambient pressure on the pulmonary circulation.

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Central hemodynamics in a baboon model during microgravity induced by parabolic flight

Cited by 11 publications

References 5 publications

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Venous and Arterial Responses to Partial Gravity

Pulmonary Circulation in Extreme Environments

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