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Hall EA, Whittle RS, Diaz-Artiles A. Ocular perfusion pressure is not reduced in response to lower body negative pressure. NPJ Microgravity 2024; 10:67. [PMID: 38851800 PMCID: PMC11162494 DOI: 10.1038/s41526-024-00404-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2023] [Accepted: 05/16/2024] [Indexed: 06/10/2024] Open
Abstract
Lower body negative pressure (LBNP) has been proposed as a countermeasure to mitigate the cephalad fluid shift occurring during spaceflight, which may be associated with the development of Spaceflight Associated Neuro-ocular Syndrome (SANS). This study quantifies the effect of LBNP on intraocular pressure (IOP), mean arterial pressure at eye level (MAPeye), and ocular perfusion pressure (OPP). Twenty-four subjects (12 male, 12 female) were subjected to graded LBNP in 0° supine and 15° head-down tilt (HDT) postures from 0 mmHg to -50 mmHg in 10 mmHg increments. IOP decreased significantly with LBNP pressure in 0° supine (by 0.7 ± 0.09 mmHg per 10 mmHg LBNP pressure, p < 0.001) and in 15° HDT (by 1.0 ± 0.095 mmHg per 10 mmHg of LBNP pressure, p < 0.001). MAPeye significantly decreased by 0.9 ± 0.4 mmHg per 10 mmHg of LBNP pressure in 0° supine (p = 0.016) but did not significantly change with LBNP in 15° HDT (p = 0.895). OPP did not significantly change with LBNP in 0° supine (p = 0.539) but it significantly increased in 15° HDT at 1.0 ± 0.3 mmHg per 10 mmHg of LBNP pressure (p = 0.010). Sex did not have a significant effect on OPP, MAPeye, or IOP in any condition. In 15° HDT, the reduction in IOP during increasing negative pressure, combined with the relatively constant MAPeye, led to the increase in OPP. Furthermore, results suggest that LBNP, while effective in reducing IOP, is not effective in reducing OPP across all postures investigated.
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Affiliation(s)
- Eric A Hall
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA
- School of Engineering Medicine (EnMed), Texas A&M University, Houston, TX, USA
| | - Richard S Whittle
- Department of Mechanical and Aerospace Engineering, University of California Davis, Davis, CA, USA
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, USA
| | - Ana Diaz-Artiles
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, USA.
- Department of Kinesiology and Sport Management, Texas A&M University, College Station, TX, USA.
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2
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Wang Y, Neto OP, Weinrich M, Abbott R, Diaz-Artiles A, Kennedy DM. The effect of inherent and incidental constraints on bimanual force control in simulated Martian gravity. Hum Mov Sci 2024; 95:103199. [PMID: 38518737 DOI: 10.1016/j.humov.2024.103199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 02/23/2024] [Accepted: 03/04/2024] [Indexed: 03/24/2024]
Abstract
The ability to coordinate actions between the limbs is important for many operationally relevant tasks associated with space exploration. A future milestone in space exploration is sending humans to Mars. Therefore, an experiment was designed to examine the influence of inherent and incidental constraints on the stability characteristics associated with the bimanual control of force in simulated Martian gravity. A head-up tilt (HUT)/head-down tilt (HDT) paradigm was used to simulate gravity on Mars (22.3° HUT). Right limb dominant participants (N = 11) were required to rhythmically coordinate patterns of isometric forces in 1:1 in-phase and 1:2 multifrequency patterns by exerting force with their right and left limbs. Lissajous displays were provided to guide task performance. Participants performed 14 twenty-second practice trials at 90° HUT (Earth). Following a 30-min rest period, participants performed 2 test trials for each coordination pattern in both Earth and Mars conditions. Performance during the test trials were compared. Results indicated very effective temporal performance of the goal coordination tasks in both gravity conditions. However, results indicated differences associated with the production of force between Earth and Mars. In general, participants produced less force in simulated Martian gravity than in the Earth condition. In addition, force production was more harmonic in Martian gravity than Earth gravity for both limbs, indicating that less force distortions (adjustments, hesitations, and/or perturbations) occurred in the Mars condition than in the Earth condition. The force coherence analysis indicated significantly higher coherence in the 1:1 task than in the 1:2 task for all force frequency bands, with the highest level of coherence in the 1-4 Hz frequency band for both gravity conditions. High coherence in the 1-4 Hz frequency band is associated with a common neural drive that activates the two arms simultaneously and is consistent with the requirements of the two tasks. The results also support the notion that neural crosstalk stabilizes the performance of the 1:1 in-phase task. In addition, significantly higher coherence in the 8-12 Hz frequency bands were observed for the Earth condition than the Mars condition. Force coherence in the 8-12 Hz bands is associated with the processing of sensorimotor information, suggesting that participants were better at integrating visual, proprioceptive, and/or tactile feedback in Earth than for the Mars condition. Overall, the results indicate less neural interference in Martian gravity; however, participants appear to be more effective at using the Lissajous displays to guide performance under Earth's gravity.
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Affiliation(s)
- Yiyu Wang
- Department of Kinesiology and Sport Management, Texas A&M University, TX, USA
| | - Osmar P Neto
- Department of Biomedical Engineering, Anhembi Morumbi University, SP, Brazil
| | - Madison Weinrich
- Department of Kinesiology and Sport Management, Texas A&M University, TX, USA
| | - Renee Abbott
- Department of Aerospace Engineering, Texas A&M University, TX, USA
| | - Ana Diaz-Artiles
- Department of Kinesiology and Sport Management, Texas A&M University, TX, USA; Department of Aerospace Engineering, Texas A&M University, TX, USA
| | - Deanna M Kennedy
- Department of Kinesiology and Sport Management, Texas A&M University, TX, USA.
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3
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Whittle RS, Diaz-Artiles A. Gravitational effects on carotid and jugular characteristics in graded head-up and head-down tilt. J Appl Physiol (1985) 2023; 134:217-229. [PMID: 36476158 PMCID: PMC9870583 DOI: 10.1152/japplphysiol.00248.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2022] [Revised: 11/23/2022] [Accepted: 12/06/2022] [Indexed: 12/13/2022] Open
Abstract
Altered gravity affects hemodynamics and blood flow in the neck. At least one incidence of jugular venous thrombosis has been reported in an astronaut on the International Space Station. This investigation explores the impact of changes in the direction of the gravitational vector on the characteristics of the neck arteries and veins. Twelve subjects underwent graded tilt from 45° head-up to 45° head-down in 15° increments in both supine and prone positions. At each angle, the cross-sectional area of the left and right common carotid arteries (ACCA) and internal jugular veins (AIJV) were measured by ultrasound. Internal jugular venous pressure (IJVP) was also measured by compression sonography. Gravitational dose-response curves were generated from experimental data. ACCA did not show any gravitational dependence. Conversely, both AIJV and IJVP increased in a nonlinear fashion with head-down tilt. AIJV was significantly larger on the right side than the left side at all tilt angles. In addition, IJVP was significantly elevated in the prone position compared with the supine position, most likely because of raised intrathoracic pressure while prone. Dose-response curves were compared with existing experimental data from parabolic flight and spaceflight studies, showing good agreement on an acute timescale. The quantification of jugular hemodynamics as a function of changes in the gravitational vector presented here provides a terrestrial model to reference spaceflight-induced changes, contributes to the assessment of the pathogenesis of spaceflight venous thromboembolism events, and informs the development of countermeasures.NEW & NOTEWORTHY Flow stasis and thrombosis have been identified in the jugular vein during spaceflight. We measured the area and pressure of the internal jugular vein and the area of the common carotid artery in graded head-up and head-down tilt. Experimental data are used to generate gravitational dose-response curves for the measured variables, demonstrating that jugular vein area and pressure exhibit a nonlinear response to altered gravity. Gravitational dose-response curves show good agreement with spaceflight and parabolic flight studies.
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Affiliation(s)
- Richard S Whittle
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas
| | - Ana Diaz-Artiles
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas
- Department of Kinesiology & Sport Management, Texas A&M University, College Station, Texas
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4
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Keller N, Whittle RS, McHenry N, Johnston A, Duncan C, Ploutz-Snyder L, Torre GGDL, Sheffield-Moore M, Chamitoff G, Diaz-Artiles A. Virtual Reality "exergames": A promising countermeasure to improve motivation and restorative effects during long duration spaceflight missions. Front Physiol 2022; 13:932425. [PMID: 36304582 PMCID: PMC9593063 DOI: 10.3389/fphys.2022.932425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 09/21/2022] [Indexed: 11/13/2022] Open
Abstract
Long duration spaceflight missions will require novel exercise systems to protect astronaut crew from the detrimental effects of microgravity exposure. The SPRINT protocol is a novel and promising exercise prescription that combines aerobic and resistive training using a flywheel device, and it was successfully employed in a 70-day bed-rest study as well as onboard the International Space Station. Our team created a VR simulation to further augment the SPRINT protocol when using a flywheel ergometer training device (the Multi-Mode Exercise Device or M-MED). The simulation aspired to maximal realism in a virtual river setting while providing real-time biometric feedback on heart rate performance to subjects. In this pilot study, five healthy, male, physically-active subjects aged 35 ± 9.0 years old underwent 2 weeks of SPRINT protocol, either with or without the VR simulation. After a 1-month washout period, subjects returned for a subsequent 2 weeks in the opposite VR condition. We measured physiological and cognitive variables of stress, performance, and well-being. While physiological effects did not suggest much difference with the VR condition over 2 weeks, metrics of motivation, affect, and mood restoration showed detectable differences, or trended toward more positive outcomes than exercise without VR. These results provide evidence that a well-designed VR "exergaming" simulation with biometric feedback could be a beneficial addition to exercise prescriptions, especially if users are exposed to isolation and confinement.
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Affiliation(s)
- Nathan Keller
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Richard S. Whittle
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Neil McHenry
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Adam Johnston
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Colton Duncan
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Lori Ploutz-Snyder
- Movement Science Program, School of Kinesiology, University of Michigan, Ann Arbor, MI, United States
| | | | - Melinda Sheffield-Moore
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, TX, United States
| | - Gregory Chamitoff
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Ana Diaz-Artiles
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
- Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
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5
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Whittle RS, Keller N, Hall EA, Vellore HS, Stapleton LM, Findlay KH, Dunbar BJ, Diaz‐Artiles A. Gravitational Dose‐Response Curves for Acute Cardiovascular Hemodynamics and Autonomic Responses in a Tilt Paradigm. J Am Heart Assoc 2022; 11:e024175. [PMID: 35861832 PMCID: PMC9707822 DOI: 10.1161/jaha.121.024175] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background
The cardiovascular system is strongly dependent on the gravitational environment. Gravitational changes cause mechanical fluid shifts and, in turn, autonomic effectors influence systemic circulation and cardiac control. We implemented a tilt paradigm to (1) investigate the acute hemodynamic response across a range of directions of the gravitational vector, and (2) to generate specific dose‐response relationships of this gravitational dependency.
Methods and Results
Twelve male subjects were tilted from 45° head‐up tilt to 45° head‐down tilt in 15° increments, in both supine and prone postures. We measured the steady‐state hemodynamic response in a range of variables including heart rate, stroke volume, cardiac output, oxygen consumption, total peripheral resistance, blood pressure, and autonomic indices derived from heart rate variability analysis. There is a strong gravitational dependence in almost all variables considered, with the exception of oxygen consumption, whereas systolic blood pressure remained controlled to within ≈3% across the tilt range. Hemodynamic responses are primarily driven by differential loading on the baroreflex receptors, combined with differences in venous return to the heart. Thorax compression in the prone position leads to reduced venous return and increased sympathetic nervous activity, raising heart rate, and systemic vascular resistance while lowering cardiac output and stroke volume.
Conclusions
Gravitational dose‐response curves generated from these data provide a comprehensive baseline from which to assess the efficacy of potential spaceflight countermeasures. Results also assist clinical management of terrestrial surgery in prone posture or head‐down tilt positions.
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Affiliation(s)
- Richard S. Whittle
- Department of Aerospace Engineering Texas A&M University College Station TX
| | - Nathan Keller
- Department of Health and Kinesiology Texas A&M University College Station TX
| | - Eric A. Hall
- Department of Biomedical Engineering Texas A&M University College Station TX
| | | | | | | | - Bonnie J. Dunbar
- Department of Aerospace Engineering Texas A&M University College Station TX
| | - Ana Diaz‐Artiles
- Department of Aerospace Engineering Texas A&M University College Station TX
- Department of Health and Kinesiology Texas A&M University College Station TX
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6
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Diaz-Artiles A, Wang Y, Davis MM, Abbott R, Keller N, Kennedy DM. The Influence of Altered-Gravity on Bimanual Coordination: Retention and Transfer. Front Physiol 2022; 12:794705. [PMID: 35069255 PMCID: PMC8777123 DOI: 10.3389/fphys.2021.794705] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Accepted: 12/03/2021] [Indexed: 11/13/2022] Open
Abstract
Many of the activities associated with spaceflight require individuals to coordinate actions between the limbs (e.g., controlling a rover, landing a spacecraft). However, research investigating the influence of gravity on bimanual coordination has been limited. The current experiment was designed to determine an individual's ability to adapt to altered-gravity when performing a complex bimanual force coordination task, and to identify constraints that influence coordination dynamics in altered-gravity. A tilt table was used to simulate gravity on Earth [90° head-up tilt (HUT)] and microgravity [6° head-down tilt (HDT)]. Right limb dominant participants (N = 12) were required to produce 1:1 in-phase and 1:2 multi-frequency force patterns. Lissajous information was provided to guide performance. Participants performed 14, 20 s trials at 90° HUT (Earth). Following a 30-min rest period, participants performed, for each coordination pattern, two retention trials (Earth) followed by two transfer trials in simulated microgravity (6° HDT). Results indicated that participants were able to transfer their training performance during the Earth condition to the microgravity condition with no additional training. No differences between gravity conditions for measures associated with timing (interpeak interval ratio, phase angle slope ratio) were observed. However, despite the effective timing of the force pulses, there were differences in measures associated with force production (peak force, STD of peak force mean force). The results of this study suggest that Lissajous displays may help counteract manual control decrements observed during microgravity. Future work should continue to explore constraints that can facilitate or interfere with bimanual control performance in altered-gravity environments.
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Affiliation(s)
- Ana Diaz-Artiles
- Bioastronautics and Human Performance Lab, Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Yiyu Wang
- Neuromuscular Coordination Lab, Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
| | - Madison M. Davis
- Neuromuscular Coordination Lab, Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
| | - Renee Abbott
- Bioastronautics and Human Performance Lab, Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Nathan Keller
- Bioastronautics and Human Performance Lab, Department of Aerospace Engineering, Texas A&M University, College Station, TX, United States
| | - Deanna M. Kennedy
- Neuromuscular Coordination Lab, Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
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7
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Petersen LG, Whittle RS, Lee JH, Sieker J, Carlson J, Finke C, Shelton CM, Petersen JCG, Diaz-Artiles A. Gravitational effects on intraocular pressure and ocular perfusion pressure. J Appl Physiol (1985) 2022; 132:24-35. [PMID: 34762525 DOI: 10.1152/japplphysiol.00546.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Changes in the gravitational vector by postural changes or weightlessness induce fluid shifts, impacting ocular hemodynamics and regional pressures. This investigation explores the impact of changes in the direction of the gravitational vector on intraocular pressure (IOP), mean arterial pressure at eye level (MAPeye), and ocular perfusion pressure (OPP), which is critical for ocular health. Thirteen subjects underwent 360° of tilt (including both prone and supine positions) at 15° increments. At each angle, steady-state IOP and MAPeye were measured, and OPP calculated as MAPeye - IOP. Experimental data were also compared to a six-compartment lumped-parameter model of the eye. Mean IOP, MAPeye, and OPP significantly increased from 0° supine to 90° head-down tilt (HDT) by 20.7 ± 1.7 mmHg (P < 0.001), 38.5 ± 4.1 mmHg (P < 0.001), and 17.4 ± 3.2 mmHg (P < 0.001), respectively. Head-up tilt (HUT) significantly decreased OPP by 16.5 ± 2.5 mmHg (P < 0.001). IOP was significantly higher in prone versus supine position for much of the tilt range. Our study indicates that OPP is highly gravitationally dependent. Specifically, data show that MAPeye is more gravitationally dependent than IOP, thus causing OPP to increase during HDT and to decrease during HUT. In addition, IOP was elevated in prone position compared with supine position due to the additional hydrostatic column between the base of the rostral globe to the mid-coronal plane, supporting the notion that hydrostatic forces play an important role in ocular hemodynamics. Changes in OPP as a function of changes in gravitational stress and/or weightlessness may play a role in the pathogenesis of spaceflight-associated neuro-ocular syndrome.NEW & NOTEWORTHY Maintaining appropriate ocular perfusion pressure (OPP) is critical for ocular health. We measured the relative changes in intraocular and mean arterial pressures during 360° tilt and calculated OPP, which was elevated during head-down tilt and decreased during head-up tilt. Experimental data are also explained by our computational model. We demonstrate that OPP is more gravitationally dependent than previously recognized and may be a factor in the overall patho-etiology behind the weightlessness-induced spaceflight-associated neuro-ocular syndrome.
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Affiliation(s)
- Lonnie G Petersen
- Mechanical and Aerospace Engineering, Jacobs School of Engineering, University of California, San Diego, California.,Department of Radiology, School of Medicine, University of California, San Diego, California
| | - Richard S Whittle
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas
| | - Justin H Lee
- Department of Radiology, School of Medicine, University of California, San Diego, California
| | - Jeremy Sieker
- Department of Radiology, School of Medicine, University of California, San Diego, California
| | - Joseph Carlson
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas
| | - Colton Finke
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas
| | - Cody M Shelton
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas
| | - Johan C G Petersen
- Department of Anesthesiology, UC-Health, University of California, San Diego, California
| | - Ana Diaz-Artiles
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas.,Department of Health and Kinesiology, Texas A&M University, College Station, Texas
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Salvetti A, Degl'Innocenti A, Gambino G, van Loon JJ, Ippolito C, Ghelardoni S, Ghigo E, Leoncino L, Prato M, Rossi L, Ciofani G. Artificially altered gravity elicits cell homeostasis imbalance in planarian worms, and cerium oxide nanoparticles counteract this effect. J Biomed Mater Res A 2021; 109:2322-2333. [PMID: 33960131 PMCID: PMC8518838 DOI: 10.1002/jbm.a.37215] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 04/12/2021] [Accepted: 04/26/2021] [Indexed: 01/17/2023]
Abstract
Gravity alterations elicit complex and mostly detrimental effects on biological systems. Among these, a prominent role is occupied by oxidative stress, with consequences for tissue homeostasis and development. Studies in altered gravity are relevant for both Earth and space biomedicine, but their implementation using whole organisms is often troublesome. Here we utilize planarians, simple worm model for stem cell and regeneration biology, to characterize the pathogenic mechanisms brought by artificial gravity alterations. In particular, we provide a comprehensive evaluation of molecular responses in intact and regenerating specimens, and demonstrate a protective action from the space-apt for nanotechnological antioxidant cerium oxide nanoparticles.
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Affiliation(s)
- Alessandra Salvetti
- Università di Pisa, Department of Clinical and Experimental MedicineBiology and Genetics unitPisaItaly
| | - Andrea Degl'Innocenti
- Istituto Italiano di TecnologiaCenter for Materials Interfaces, Smart Bio‐InterfacesPisaItaly
| | - Gaetana Gambino
- Università di Pisa, Department of Clinical and Experimental MedicineBiology and Genetics unitPisaItaly
| | - Jack J.W.A. van Loon
- Dutch Experiment Support Center (DESC), Department of Oral and Maxillofacial Surgery/Oral PathologyAmsterdam UMC location VU University Medical Center & Academic Centre for Dentistry Amsterdam (ACTA)AmsterdamThe Netherlands
- TEC‐MMG LIS labEuropean Space Agency (ESA), European Space Research and Technology Center (ESTEC)NoordwijkThe Netherlands
| | - Chiara Ippolito
- Department of Clinical and Experimental Medicine, Biology and Genetics UnitUniversità di PisaPisaItaly
| | - Sandra Ghelardoni
- Department of Pathology, Biochemistry UnitUniversità di PisaPisaItaly
| | - Eric Ghigo
- Institut Hospitalo‐Universitaire Méditerranée InfectionMarseilleFrance
- Techno JouvenceMarseilleFrance
| | - Luca Leoncino
- Istituto Italiano di TecnologiaElectron Microscopy FacilityGenoaItaly
| | - Mirko Prato
- Istituto Italiano di TecnologiaMaterials Characterization FacilityGenoaItaly
| | - Leonardo Rossi
- Università di Pisa, Department of Clinical and Experimental MedicineBiology and Genetics unitPisaItaly
| | - Gianni Ciofani
- Istituto Italiano di TecnologiaCenter for Materials Interfaces, Smart Bio‐InterfacesPisaItaly
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9
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Whittle RS, Stapleton LM, Petersen LG, Diaz-Artiles A. Indirect measurement of absolute cardiac output during exercise in simulated altered gravity is highly dependent on the method. J Clin Monit Comput 2021; 36:1355-1366. [PMID: 34677821 DOI: 10.1007/s10877-021-00769-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Accepted: 10/13/2021] [Indexed: 10/20/2022]
Abstract
PURPOSE Altered gravity environments introduce cardiovascular changes that may require continuous hemodynamic monitoring in both spaceflight and terrestrial analogs. Conditions in such environments are often prohibitive to direct/invasive methods and therefore, indirect measurement techniques must be used. This study compares two common cardiac measurement techniques used in the human spaceflight domain, pulse contour analysis (PCA-Nexfin) and inert gas rebreathing (IGR-Innocor), in subjects completing ergometer exercise under altered gravity conditions simulated using a tilt paradigm. METHODS Seven subjects were tilted to three different angles representing Martian, Lunar, and microgravity conditions in the rostrocaudal direction. They completed a 36-min submaximal cardiovascular exercise protocol in each condition. Hemodynamics were continuously monitored using Nexfin and Innocor. RESULTS Linear mixed-effects models revealed a significant bias of [Formula: see text] ml ([Formula: see text]) in stroke volume and [Formula: see text] l/min ([Formula: see text]) in cardiac output, with Nexfin measuring greater than Innocor in both variables. These values are in agreement with a Bland-Altman analysis. The correlation of stroke volume and cardiac output measurements between Nexfin and Innocor were [Formula: see text] ([Formula: see text]) and [Formula: see text] ([Formula: see text]) respectively. CONCLUSION There is a poor agreement in absolute stroke volume and cardiac output values between measurement via PCA (Nexfin) and IGR (Innocor) in subjects who are exercising in simulated altered gravity environments. These results suggest that the chosen measurement method and device greatly impacts absolute measurements of cardiac output. However, there is a good level of agreement between the two devices when measuring relative changes. Either of these devices seem adequate to capture cardiac changes, but should not be solely relied upon for accurate measurement of absolute cardiac output.
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Affiliation(s)
- Richard S Whittle
- Department of Aerospace Engineering, Texas A&M University, 3141 TAMU, College Station, TX, 77843, USA
| | - Lindsay M Stapleton
- Department of Aerospace Engineering, Texas A&M University, 3141 TAMU, College Station, TX, 77843, USA
| | - Lonnie G Petersen
- Department of Radiology, University of California San Diego, 8929 University Center Lane, La Jolla, CA, 92122, USA
| | - Ana Diaz-Artiles
- Department of Aerospace Engineering, Texas A&M University, 3141 TAMU, College Station, TX, 77843, USA. .,Department of Health and Kinesiology, Texas A&M University, 4243 TAMU, College Station, TX, 77843, USA.
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10
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Whittle RS, Diaz-Artiles A. Modeling individual differences in cardiovascular response to gravitational stress using a sensitivity analysis. J Appl Physiol (1985) 2021; 130:1983-2001. [PMID: 33914657 DOI: 10.1152/japplphysiol.00727.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The human cardiovascular (CV) system elicits a physiological response to gravitational environments, with significant variation between different individuals. Computational modeling can predict CV response, however model complexity and variation of physiological parameters in a normal population makes it challenging to capture individual responses. We conducted a sensitivity analysis on an existing 21-compartment lumped-parameter hemodynamic model in a range of gravitational conditions to 1) investigate the influence of model parameters on a tilt test CV response and 2) to determine the subset of those parameters with the most influence on systemic physiological outcomes. A supine virtual subject was tilted to upright under the influence of a constant gravitational field ranging from 0 g to 1 g. The sensitivity analysis was conducted using a Latin hypercube sampling/partial rank correlation coefficient methodology with subsets of model parameters varied across a normal physiological range. Sensitivity was determined by variation in outcome measures including heart rate, stroke volume, central venous pressure, systemic blood pressures, and cardiac output. Results showed that model parameters related to the length, resistance, and compliance of the large veins and parameters related to right ventricular function have the most influence on model outcomes. For most outcome measures considered, parameters related to the heart are dominant. Results highlight which model parameters to accurately value in simulations of individual subjects' CV response to gravitational stress, improving the accuracy of predictions. Influential parameters remain largely similar across gravity levels, highlighting that accurate model fitting in 1 g can increase the accuracy of predictive responses in reduced gravity.NEW & NOTEWORTHY Computational modeling is used to predict cardiovascular responses to altered gravitational environments. However, considerable variation between subjects and model complexity makes accurate parameter assignment for individuals challenging. This computational effort studies sensitivity in cardiovascular model outcomes due to varying parameters across a normal physiological range. This allows determination of which parameters have the largest influence on outcomes, i.e., which parameters must be most carefully selected to give accurate predictions of individual responses.
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Affiliation(s)
- Richard S Whittle
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas
| | - Ana Diaz-Artiles
- Department of Aerospace Engineering, Texas A&M University, College Station, Texas.,Department of Health and Kinesiology, Texas A&M University, College Station, Texas
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11
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Diaz-Artiles A, Heldt T, Young LR. Computational model of cardiovascular response to centrifugation and lower body cycling exercise. J Appl Physiol (1985) 2019; 127:1453-1468. [PMID: 31343946 DOI: 10.1152/japplphysiol.00314.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Short-radius centrifugation combined with exercise has been suggested as a potential countermeasure against spaceflight deconditioning. Both the long-term and acute physiological responses to such a combination are incompletely understood. We developed and validated a computational model to study the acute cardiovascular response to centrifugation combined with lower body ergometer exercise. The model consisted of 21 compartments, including the upper body, renal, splanchnic, and leg circulation, as well as a four-chamber heart and pulmonary circulation. It also included the effects of gravity gradient and ergometer exercise. Centrifugation and exercise profiles were simulated and compared with experimental data gathered on 12 subjects exposed to a range of gravitational levels (1 and 1.4G measured at the feet) and workload intensities (25-100 W). The model was capable of reproducing cardiovascular changes (within ± 1 SD from the group-averaged behavior) due to both centrifugation and exercise, including dynamic responses during transitions between the different phases of the protocol. The model was then used to simulate the hemodynamic response of hypovolemic subjects (blood volume reduced by 5-15%) subjected to similar gravitational stress and exercise profiles, providing insights into the physiological responses of experimental conditions not tested before. Hypovolemic results are in agreement with the limited available data and the expected responses based on physiological principles, although additional experimental data are warranted to further validate our predictions, especially during the exercise phases. The model captures the cardiovascular response for a range of centrifugation and exercise profiles, and it shows promise in simulating additional conditions where data collection is difficult, expensive, or infeasible.NEW & NOTEWORTHY Artificial gravity combined with exercise is a potential countermeasure for spaceflight deconditioning, but the long-term and acute cardiovascular response to such gravitational stress is still largely unknown. We provide a novel mathematical model of the cardiovascular system that incorporates gravitational stress generated by centrifugation and lower body cycling exercise, and we validate it with experimental measurements from human subjects. Simulations of experimental conditions not used for model development corroborate the model's predictive capabilities.
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Affiliation(s)
- Ana Diaz-Artiles
- Department of Aerospace Engineering, Texas A & M University, College Station, Texas
| | - Thomas Heldt
- Institute for Medical Engineering and Science, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts
| | - Laurence R Young
- Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts
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