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Pollock RD, Hodkinson PD, Smith TG. Oh G: The x, y and z of human physiological responses to acceleration. Exp Physiol 2021; 106:2367-2384. [PMID: 34730860 DOI: 10.1113/ep089712] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2021] [Accepted: 10/18/2021] [Indexed: 01/06/2023]
Abstract
NEW FINDINGS What is the topic of this review? This review focuses on the main physiological challenges associated with exposure to acceleration in the Gx, Gy and Gz directions and to microgravity. What advances does it highlight? Our current understanding of the physiology of these environments and latest strategies to protect against them are discussed in light of the limited knowledge we have in some of these areas. ABSTRACT The desire to go higher, faster and further has taken us to environments where the accelerations placed on our bodies far exceed or are much lower than that attributable to Earth's gravity. While on the ground, racing drivers of the fastest cars are exposed to high degrees of lateral acceleration (Gy) during cornering. In the air, while within the confines of the lower reaches of Earth's atmosphere, fast jet pilots are routinely exposed to high levels of acceleration in the head-foot direction (Gz). During launch and re-entry of suborbital and orbital spacecraft, astronauts and spaceflight participants are exposed to high levels of chest-back acceleration (Gx), whereas once in space the effects of gravity are all but removed (termed microgravity, μG). Each of these environments has profound effects on the homeostatic mechanisms within the body and can have a serious impact, not only for those with underlying pathology but also for healthy individuals. This review provides an overview of the main challenges associated with these environments and our current understanding of the physiological and pathophysiological adaptations to them. Where relevant, protection strategies are discussed, with the implications of our future exposure to these environments also being considered.
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Affiliation(s)
- Ross D Pollock
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK
| | - Peter D Hodkinson
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK
| | - Thomas G Smith
- Centre for Human and Applied Physiological Sciences, King's College London, London, UK.,Department of Anaesthesia, Guy's and St Thomas' NHS Foundation Trust, London, UK
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Pollock RD, Jolley CJ, Abid N, Couper JH, Estrada-Petrocelli L, Hodkinson PD, Leonhardt S, Magor-Elliott S, Menden T, Rafferty G, Richmond G, Robbins PA, Ritchie GAD, Segal MJ, Stevenson AT, Tank HD, Smith TG. Pulmonary Effects of Sustained Periods of High-G Acceleration Relevant to Suborbital Spaceflight. Aerosp Med Hum Perform 2021; 92:633-641. [PMID: 34503616 DOI: 10.3357/amhp.5790.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
AbstractBACKGROUND: Members of the public will soon be taking commercial suborbital spaceflights with significant Gx (chest-to-back) acceleration potentially reaching up to 6 Gx. Pulmonary physiology is gravity-dependent and is likely to be affected, which may have clinical implications for medically susceptible individuals.METHODS: During 2-min centrifuge exposures ranging up to 6 Gx, 11 healthy subjects were studied using advanced respiratory techniques. These sustained exposures were intended to allow characterization of the underlying pulmonary response and did not replicate actual suborbital G profiles. Regional distribution of ventilation in the lungs was determined using electrical impedance tomography. Neural respiratory drive (from diaphragm electromyography) and work of breathing (from transdiaphragmatic pressures) were obtained via nasoesophageal catheters. Arterial blood gases were measured in a subset of subjects. Measurements were conducted while breathing air and breathing 15 oxygen to simulate anticipated cabin pressurization conditions.RESULTS: Acceleration caused hypoxemia that worsened with increasing magnitude and duration of Gx. Minimum arterial oxygen saturation at 6 Gx was 86 1 breathing air and 79 1 breathing 15 oxygen. With increasing Gx the alveolar-arterial (A-a) oxygen gradient widened progressively and the relative distribution of ventilation reversed from posterior to anterior lung regions with substantial gas-trapping anteriorly. Severe breathlessness accompanied large progressive increases in work of breathing and neural respiratory drive.DISCUSSION: Sustained high-G acceleration at magnitudes relevant to suborbital flight profoundly affects respiratory physiology. These effects may become clinically important in the most medically susceptible passengers, in whom the potential role of centrifuge-based preflight evaluation requires further investigation.Pollock RD, Jolley CJ, Abid N, Couper JH, Estrada-Petrocelli L, Hodkinson PD, Leonhardt S, Mago-Elliott S, Menden T, Rafferty G, Richmond G, Robbins PA, Ritchie GAD, Segal MJ, Stevenson AT, Tank HD, Smith TG. Pulmonary effects of sustained periods of high-G acceleration relevant to suborbital spaceflight. Aerosp Med Hum Perform. 2021; 92(7):633641.
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Hopkins SR. Ventilation/Perfusion Relationships and Gas Exchange: Measurement Approaches. Compr Physiol 2020; 10:1155-1205. [PMID: 32941684 DOI: 10.1002/cphy.c180042] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Ventilation-perfusion ( V ˙ A / Q ˙ ) matching, the regional matching of the flow of fresh gas to flow of deoxygenated capillary blood, is the most important mechanism affecting the efficiency of pulmonary gas exchange. This article discusses the measurement of V ˙ A / Q ˙ matching with three broad classes of techniques: (i) those based in gas exchange, such as the multiple inert gas elimination technique (MIGET); (ii) those derived from imaging techniques such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI), computed tomography (CT), and electrical impedance tomography (EIT); and (iii) fluorescent and radiolabeled microspheres. The focus is on the physiological basis of these techniques that provide quantitative information for research purposes rather than qualitative measurements that are used clinically. The fundamental equations of pulmonary gas exchange are first reviewed to lay the foundation for the gas exchange techniques and some of the imaging applications. The physiological considerations for each of the techniques along with advantages and disadvantages are briefly discussed. © 2020 American Physiological Society. Compr Physiol 10:1155-1205, 2020.
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Affiliation(s)
- Susan R Hopkins
- Departments of Medicine and Radiology, University of California, San Diego, California, USA
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Doganay O, Matin T, Chen M, Kim M, McIntyre A, McGowan DR, Bradley KM, Povey T, Gleeson FV. Time-series hyperpolarized xenon-129 MRI of lobar lung ventilation of COPD in comparison to V/Q-SPECT/CT and CT. Eur Radiol 2018; 29:4058-4067. [PMID: 30552482 PMCID: PMC6610266 DOI: 10.1007/s00330-018-5888-y] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Revised: 10/08/2018] [Accepted: 11/13/2018] [Indexed: 12/23/2022]
Abstract
Purpose To derive lobar ventilation in patients with chronic obstructive pulmonary disease (COPD) using a rapid time-series hyperpolarized xenon-129 (HPX) magnetic resonance imaging (MRI) technique and compare this to ventilation/perfusion single-photon emission computed tomography (V/Q-SPECT), correlating the results with high-resolution computed tomography (CT) and pulmonary function tests (PFTs). Materials and methods Twelve COPD subjects (GOLD stages I–IV) participated in this study and underwent HPX-MRI, V/Q-SPECT/CT, high-resolution CT, and PFTs. HPX-MRI was performed using a novel time-series spiral k-space sampling approach. Relative percentage ventilations were calculated for individual lobe for comparison to the relative SPECT lobar ventilation and perfusion. The absolute HPX-MRI percentage ventilation in each lobe was compared to the absolute CT percentage emphysema score calculated using a signal threshold method. Pearson’s correlation and linear regression tests were performed to compare each imaging modality. Results Strong correlations were found between the relative lobar percentage ventilation with HPX-MRI and percentage ventilation SPECT (r = 0.644; p < 0.001) and percentage perfusion SPECT (r = 0.767; p < 0.001). The absolute CT percentage emphysema and HPX percentage ventilation correlation was also statistically significant (r = 0.695, p < 0.001). The whole lung HPX percentage ventilation correlated with the PFT measurements (FEV1 with r = − 0.886, p < 0.001*, and FEV1/FVC with r = − 0.861, p < 0.001*) better than the whole lung CT percentage emphysema score (FEV1 with r = − 0.635, p = 0.027; and FEV1/FVC with r = − 0.652, p = 0.021). Conclusion Lobar ventilation with HPX-MRI showed a strong correlation with lobar ventilation and perfusion measurements derived from SPECT/CT, and is better than the emphysema score obtained with high-resolution CT. Key Points • The ventilation hyperpolarized xenon-129 MRI correlates well with ventilation and perfusion with SPECT/CT with the advantage of higher temporal and spatial resolution. • The hyperpolarized xenon-129 MRI correlates with the PFT measurements better than the high-resolution CT with the advantage of avoiding the use of ionizing radiation. Electronic supplementary material The online version of this article (10.1007/s00330-018-5888-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Ozkan Doganay
- Department of Oncology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, OX3 7DQ, Oxford, UK.
- Department of Radiology, Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, OX3 7LE, Oxford, UK.
| | - Tahreema Matin
- Department of Radiology, Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, OX3 7LE, Oxford, UK
| | - Mitchell Chen
- Department of Radiology, Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, OX3 7LE, Oxford, UK
| | - Minsuok Kim
- Department of Engineering Science, University of Oxford, OX1 3PJ, Oxford, UK
| | - Anthony McIntyre
- Department of Radiology, Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, OX3 7LE, Oxford, UK
| | - Daniel R McGowan
- Department of Oncology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, OX3 7DQ, Oxford, UK
- Radiation Physics and Protection, Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, OX3 7LE, Oxford, UK
| | - Kevin M Bradley
- Department of Radiology, Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, OX3 7LE, Oxford, UK
| | - Thomas Povey
- Department of Engineering Science, University of Oxford, OX1 3PJ, Oxford, UK
| | - Fergus V Gleeson
- Department of Oncology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, OX3 7DQ, Oxford, UK
- Department of Radiology, Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, OX3 7LE, Oxford, UK
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Jang TY, Jung AY, Kwon S, Kim YH. Hypergravity enhances the therapeutic effect of dexamethasone in allergic asthma and rhinitis animal model. PLoS One 2018; 13:e0197594. [PMID: 29772010 PMCID: PMC5957331 DOI: 10.1371/journal.pone.0197594] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Accepted: 05/04/2018] [Indexed: 12/16/2022] Open
Abstract
We investigated whether the therapeutic effects of dexamethasone for allergic asthma and rhinitis were enhanced in mice when exposed to hypergravity. Forty mice were divided into 5 groups (n = 8/group): Control group received saline intraperitoneally (i.p.) and intranasally (i.n.); Asthma group received i.p./i.n. ovalbumin (OVA) for inducing allergic asthma/rhinitis; Dexa group received i.n. dexamethasone (0.75 mg/kg) 30 minutes before each OVA challenge; Hypergravity group was subjected to allergic asthma/rhinitis as well as exposed to 5 G hypergravity for 30 days; Finally in Dexa/Hypergravity group, hypergravity and dexamethasone were used simultaneously during induction of allergic asthma/rhinitis. Dexa group and Hypergravity group showed a significant decrease in serum total IgE levels compared to the Asthma group (p<0.05). Dexa/Hypergravity group showed greater IgE decrease compared with Dexa group (p = 0.040). Compared with the monotherapy groups, Dexa/Hypergravity group showed significantly fewer eosinophils in BAL fluid (p<0.05). Dexa/Hypergravity group showed significantly decreased eosinophilic infiltration into the lungs and nasal cavity (p<0.05). EC-SOD (extracellular superoxide dismutase) expression was significantly upregulated in the Hypergravity group and Dexa/Hypergravity group, compared with the Dexa group (p<0.05). In conclusion, hypergravity enhanced the therapeutic effect of dexamethasone in a murine model of allergic asthma and rhinitis. Therefore, combination could be a promising strategy, and one of its mechanisms could be up-regulation of EC-SOD expression.
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Affiliation(s)
- Tae Young Jang
- Department of Otorhinolaryngology, Head and Neck Surgery, Inha University College of Medicine, Incheon, Republic of Korea
| | - Ah-Yeoun Jung
- Department of Otorhinolaryngology, Head and Neck Surgery, Inha University College of Medicine, Incheon, Republic of Korea
| | - Soonjo Kwon
- Department of Biological Engineering, Inha University, Incheon, Republic of Korea
| | - Young Hyo Kim
- Department of Otorhinolaryngology, Head and Neck Surgery, Inha University College of Medicine, Incheon, Republic of Korea
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Norberg P, Persson HL, Schmekel B, Carlsson GA, Wahlin K, Sandborg M, Gustafsson A. Does quantitative lung SPECT detect lung abnormalities earlier than lung function tests? Results of a pilot study. EJNMMI Res 2014; 4:39. [PMID: 26055938 PMCID: PMC4884006 DOI: 10.1186/s13550-014-0039-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 07/02/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Heterogeneous ventilation in lungs of individuals with allergies, cigarette smokers, asthmatics and chronic obstructive pulmonary disease (COPD) patients has been demonstrated using imaging modalities such as positron emission tomography (PET), magnetic resonance imaging (MRI) and single-photon emission computed tomography (SPECT). These individuals suffer from narrow and/or closed airways to various extents. By calculating regional heterogeneity in lung ventilation SPECT images as the coefficient of variation (CV) in small elements of the lung, heterogeneity maps and CV-density curves can be generated and used to quantitatively measure heterogeneity. This work explores the potential to use such measurements to detect mild ventilation heterogeneities in lung-healthy subjects. METHOD Fourteen healthy subjects without documented lung disease or respiratory symptoms, and two patients with documented airway disease, inhaled on average approximately 90 MBq (99m)Tc-Technegas immediately prior to the 20-min SPECT acquisition. Variation in activity uptake between subjects was compensated for in resulting CV values. The area under the compensated CV density curve (AUC), for CV values greater than a threshold value CVT, AUC(CV > CVT), was used as the measure of ventilation heterogeneity. RESULTS Patients with lung function abnormalities, according to lung function tests, generated higher AUC(CV > 20%) values compared to healthy subjects (p = 0.006). Strong linear correlations with the AUC(CV > 20%) values were found for age (p = 0.006) and height (p = 0.001). These demonstrated that ventilation heterogeneities increased with age and that they depend on lung size. Strong linear correlations were found for the lung function value related to indices of airway closure/air trapping, residual volume/total lung capacity (RV/TLC; p = 0.009), and diffusion capacity of the lung for carbon monoxide adjusted for haemoglobin concentration in the blood (DLCOc; p = 0.009), a value partly related to supposed ventilation/perfusion mismatch. These findings support the association between conventional lung function tests and the AUC(CV > 20%) value. CONCLUSIONS Among the healthy subjects, there is a group with increased AUC(CV > 20%) values, but with normal lung function tests, which implies that it might be possible to differentiate ventilation heterogeneities earlier in a disease process than by lung function tests.
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Affiliation(s)
- Pernilla Norberg
- />Medical Radiation Physics, County Council of Östergötland, Linköping, 581 85 Sweden
- />Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, 581 83 Sweden
- />Department of Medical and Health Sciences, Linköping University, Linköping, 581 83 Sweden
| | - Hans Lennart Persson
- />Department of Respiratory Medicine and Department of Medical and Health Sciences, Linköping University, Linköping, 581 83 Sweden
| | - Birgitta Schmekel
- />Department of Clinical Physiology and Department of Medical and Health Sciences, Linköping University, Linköping, 581 83 Sweden
| | - Gudrun Alm Carlsson
- />Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, 581 83 Sweden
- />Department of Medical and Health Sciences, Linköping University, Linköping, 581 83 Sweden
| | - Karl Wahlin
- />Department of Computer and Information Science, Linköping University, Linköping, 581 83 Sweden
| | - Michael Sandborg
- />Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, 581 83 Sweden
- />Department of Medical and Health Sciences, Linköping University, Linköping, 581 83 Sweden
| | - Agnetha Gustafsson
- />Department of Medical Physics, Karolinska University Hospital, Huddinge, Stockholm 141 86 Sweden
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