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Sato A, Ajimi A, Omiya Y, Shimizu JI. Interventional study of comparing body pressure in different prone positions in healthy young women. J Phys Ther Sci 2024; 36:571-576. [PMID: 39239414 PMCID: PMC11374175 DOI: 10.1589/jpts.36.571] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2024] [Accepted: 06/16/2024] [Indexed: 09/07/2024] Open
Abstract
[Purpose] Although prone positioning is used to increase oxygenation in various respiratory conditions, this positioning can lead to facial and limb pressure ulcers. The aim in this study was to investigate body pressure variations in the prone position for different facial orientations and upper extremity positions. [Participants and Methods] Nineteen healthy young women participated in this study. Body pressure (maximum body pressure on the face, chest, elbows, and knees) was measured in six different prone positions with different face orientations and upper extremity positions, and the median value of each body pressure measurement was compared among postures. [Results] Face pressure tended to decrease when face orientation coincided with the raised side of the upper limb. In contrast, elbow pressure tended to be lower when the orientation of the face did not coincide with that of the raised side of the upper limb. [Conclusion] Pressure on the face and elbows can be reduced by placing the upper limbs in the prone position. This suggests that targeted and specific positioning may be useful for limiting the incidence and severity of pressure ulcers in these areas.
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Affiliation(s)
- Akihiro Sato
- Department of Occupational Therapy, Mejiro University: 320 Ukiya, Iwatsuki-ku, Saitama-shi, Saitama 339-8501, Japan
- Doctoral Program in Human Life Science, Tokyo Kasei University, Japan
| | - Akiko Ajimi
- Department of Physical Therapy, Mejiro University, Japan
| | - Yuko Omiya
- Department of Nursing, Mejiro University, Japan
| | - Jun-Ichi Shimizu
- Graduate School of Human Life Science, Tokyo Kasei University, Japan
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2
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Hopkins SR, Stickland MK. The Pulmonary Vasculature. Semin Respir Crit Care Med 2023; 44:538-554. [PMID: 37816344 PMCID: PMC11192587 DOI: 10.1055/s-0043-1770059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/12/2023]
Abstract
The pulmonary circulation is a low-pressure, low-resistance circuit whose primary function is to deliver deoxygenated blood to, and oxygenated blood from, the pulmonary capillary bed enabling gas exchange. The distribution of pulmonary blood flow is regulated by several factors including effects of vascular branching structure, large-scale forces related to gravity, and finer scale factors related to local control. Hypoxic pulmonary vasoconstriction is one such important regulatory mechanism. In the face of local hypoxia, vascular smooth muscle constriction of precapillary arterioles increases local resistance by up to 250%. This has the effect of diverting blood toward better oxygenated regions of the lung and optimizing ventilation-perfusion matching. However, in the face of global hypoxia, the net effect is an increase in pulmonary arterial pressure and vascular resistance. Pulmonary vascular resistance describes the flow-resistive properties of the pulmonary circulation and arises from both precapillary and postcapillary resistances. The pulmonary circulation is also distensible in response to an increase in transmural pressure and this distention, in addition to recruitment, moderates pulmonary arterial pressure and vascular resistance. This article reviews the physiology of the pulmonary vasculature and briefly discusses how this physiology is altered by common circumstances.
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Affiliation(s)
- Susan R. Hopkins
- Department of Radiology, University of California, San Diego, California
| | - Michael K. Stickland
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta
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3
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Xin Y, Kim T, Winkler T, Brix G, Gaulton T, Gerard SE, Herrmann J, Martin KT, Victor M, Reutlinger K, Amato M, Berra L, Kalra MK, Cereda M. Improving pulmonary perfusion assessment by dynamic contrast-enhanced computed tomography in an experimental lung injury model. J Appl Physiol (1985) 2023; 134:1496-1507. [PMID: 37167261 PMCID: PMC10228674 DOI: 10.1152/japplphysiol.00159.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 04/24/2023] [Accepted: 05/11/2023] [Indexed: 05/13/2023] Open
Abstract
Pulmonary perfusion has been poorly characterized in acute respiratory distress syndrome (ARDS). Optimizing protocols to measure pulmonary blood flow (PBF) via dynamic contrast-enhanced (DCE) computed tomography (CT) could improve understanding of how ARDS alters pulmonary perfusion. In this study, comparative evaluations of injection protocols and tracer-kinetic analysis models were performed based on DCE-CT data measured in ventilated pigs with and without lung injury. Ten Yorkshire pigs (five with lung injury, five healthy) were anesthetized, intubated, and mechanically ventilated; lung injury was induced by bronchial hydrochloric acid instillation. Each DCE-CT scan was obtained during a 30-s end-expiratory breath-hold. Reproducibility of PBF measurements was evaluated in three pigs. In eight pigs, undiluted and diluted Isovue-370 were separately injected to evaluate the effect of contrast viscosity on estimated PBF values. PBF was estimated with the peak-enhancement and the steepest-slope approach. Total-lung PBF was estimated in two healthy pigs to compare with cardiac output measured invasively by thermodilution in the pulmonary artery. Repeated measurements in the same animals yielded a good reproducibility of computed PBF maps. Injecting diluted isovue-370 resulted in smaller contrast-time curves in the pulmonary artery (P < 0.01) and vein (P < 0.01) without substantially diminishing peak signal intensity (P = 0.46 in the pulmonary artery) compared with the pure contrast agent since its viscosity is closer to that of blood. As compared with the peak-enhancement model, PBF values estimated by the steepest-slope model with diluted contrast were much closer to the cardiac output (R2 = 0.82) as compared with the peak-enhancement model. DCE-CT using the steepest-slope model and diluted contrast agent provided reliable quantitative estimates of PBF.NEW & NOTEWORTHY Dynamic contrast-enhanced CT using a lower-viscosity contrast agent in combination with tracer-kinetic analysis by the steepest-slope model improves pulmonary blood flow measurements and assessment of regional distributions of lung perfusion.
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Affiliation(s)
- Yi Xin
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States
- Department of Anesthesia, Critical Care and Pain Medicine, Harvard Medical School, Boston, Massachusetts, United States
| | - Taehwan Kim
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States
| | - Tilo Winkler
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States
- Department of Anesthesia, Critical Care and Pain Medicine, Harvard Medical School, Boston, Massachusetts, United States
| | - Gunnar Brix
- Department of Medical and Occupational Radiation Protection, Federal Office for Radiation Protection, Salzgitter, Germany
| | - Timothy Gaulton
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States
- Department of Anesthesia, Critical Care and Pain Medicine, Harvard Medical School, Boston, Massachusetts, United States
| | - Sarah E Gerard
- Roy J. Carver Department of Biomedical Engineering, University of Iowa, Iowa City, Iowa, United States
| | - Jacob Herrmann
- Roy J. Carver Department of Biomedical Engineering, University of Iowa, Iowa City, Iowa, United States
| | - Kevin T Martin
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States
| | - Marcus Victor
- Disciplina de Pneumologia, Instituto do Coração, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil
- Electronics Engineering Division, Aeronautics Institute of Technology, Sao Paulo, Brazil
| | - Kristan Reutlinger
- Department of Anesthesiology and Critical Care, University of Pennsylvania, Philadelphia, Pennsylvania, United States
| | - Marcelo Amato
- Disciplina de Pneumologia, Instituto do Coração, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil
| | - Lorenzo Berra
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States
- Department of Anesthesia, Critical Care and Pain Medicine, Harvard Medical School, Boston, Massachusetts, United States
| | - Mannudeep K Kalra
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, United States
- Department of Radiology, Harvard Medical School, Boston, Massachusetts, United States
| | - Maurizio Cereda
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts, United States
- Department of Anesthesia, Critical Care and Pain Medicine, Harvard Medical School, Boston, Massachusetts, United States
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4
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Rampon GL, Simpson SQ, Agrawal R. Prone Positioning for Acute Hypoxemic Respiratory Failure and ARDS: A Review. Chest 2023; 163:332-340. [PMID: 36162482 DOI: 10.1016/j.chest.2022.09.020] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 09/11/2022] [Accepted: 09/12/2022] [Indexed: 01/14/2023] Open
Abstract
Prone positioning is an immediately accessible, readily implementable intervention that was proposed initially as a method for improvement in gas exchange > 50 years ago. Initially implemented clinically as an empiric therapy for refractory hypoxemia, multiple clinical trials were performed on the use of prone positioning in various respiratory conditions, cumulating in the landmark Proning Severe ARDS Patients trial, which demonstrated mortality benefit in patients with severe ARDS. After this trial and the corresponding meta-analysis, expert consensus and societal guidelines recommended the use of prone positioning for the management of severe ARDS. The ongoing COVID-19 pandemic has brought prone positioning to the forefront of medicine, including widespread implementation of prone positioning in awake, spontaneously breathing, nonintubated patients with acute hypoxemic respiratory failure. Multiple clinical trials now have been performed to investigate the safety and effectiveness of prone positioning in these patients and have enhanced our understanding of the effects of the prone position in respiratory failure. In this review, we discuss the physiologic features, clinical outcome data, practical considerations, and lingering questions of prone positioning.
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Affiliation(s)
- Garrett L Rampon
- Division of Pulmonary, Critical Care, and Sleep Medicine, University of Kansas Medical Center, Kansas City, KS
| | - Steven Q Simpson
- Division of Pulmonary, Critical Care, and Sleep Medicine, University of Kansas Medical Center, Kansas City, KS.
| | - Ritwick Agrawal
- Pulmonary Critical Care and Sleep Medicine Section, Medical Care Line, Michael E. DeBakey Veteran Affairs Medical Center, Houston, TX; Pulmonary Critical Care and Sleep Medicine Section, Department of Medicine, Baylor College of Medicine, Houston, TX
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5
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Lee HJ, Wanderley M, Rubin VCDS, Rodrigues ACT, Diniz AR, Parga JR, Amato MBP. Lobar pulmonary perfusion quantification with dual-energy CT angiography: Interlobar variability and relationship with regional clot burden in pulmonary embolism. Eur J Radiol Open 2022; 9:100428. [PMID: 35712646 PMCID: PMC9192795 DOI: 10.1016/j.ejro.2022.100428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2022] [Revised: 05/18/2022] [Accepted: 05/28/2022] [Indexed: 11/29/2022] Open
Abstract
Purpose Semi-automated lobar segmentation tools enable an anatomical assessment of regional pulmonary perfusion with Dual-Energy CTA (DE-CTA). We aimed to quantify lobar pulmonary perfusion with DE-CTA, analyze the perfusion distribution among the pulmonary lobes in subjects without cardiopulmonary diseases and assess the correlation between lobar perfusion and regional endoluminal clots in patients with acute pulmonary embolism (PE). Methods We evaluated 151 consecutive subjects with suspected PE and without cardiopulmonary comorbidities. DE-CTA derived perfused blood volume (PBV) of each pulmonary lobe was measured applying a semi-automated lobar segmentation technique. In patients with PE, blood clot location was assessed, and CT-based vascular obstruction index of each lobe (CTOIlobe) was calculated and classified into three groups: CTOIlobe= 0, low CTOIlobe (1–50%) and high CTOIlobe (>50%). Results Among patients without PE (103/151, 68.2%), median lobar PBV was 13.7% (IQR 10.2–18.0%); the right middle lobe presented lower PBV when compared to all the other lobes (p < .001). In patients with PE (48/151, 31.8%), lobar PBV was 12.6% (IQR 9.6–15.7%), 13.7% (IQR 10.1–16.7%) and 6.5% (IQR 5.1–10.2%) in the lobes with CTOIlobe= 0, low CTOIlobe and high CTOIlobe scores, respectively, with a significantly decreased PBV in the lobes with high CTOIlobe score (p < .001). ROC analysis of lobar PBV for prediction of high CTOIlobe score revealed AUC of 0.847 (95%CI 0.785–0.908). Conclusion Pulmonary perfusion was heterogeneously distributed along the pulmonary lobes in patients without cardiopulmonary diseases. In patients with PE, the lobes with high vascular obstruction score (CTOIlobe> 50%) presented a decreased lobar perfusion. Semi-automated tools enable assessment of lobar perfusion with Dual-Energy CTA. The pulmonary perfusion is heterogeneously distributed along the pulmonary lobes. Lobar perfusion was decreased only in the lobes with high vascular obstruction index.
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Affiliation(s)
- Hye Ju Lee
- Department of Radiology, Hospital das Clinicas, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil
| | - Mark Wanderley
- Department of Radiology, Hospital das Clinicas, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil
| | | | - Ana Clara Tude Rodrigues
- Echocardiography Laboratory, Department of Radiology, Hospital das Clinicas, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil
| | - Amanda Rocha Diniz
- Echocardiography Laboratory, Department of Radiology, Hospital das Clinicas, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil
| | - Jose Rodrigues Parga
- Department of Radiology, Hospital das Clinicas, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil
| | - Marcelo Britto Passos Amato
- Pneumology Division, Instituto do Coracao, Hospital das Clinicas, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil
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6
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Berg RMG, Hartmann JP, Iepsen UW, Christensen RH, Ronit A, Andreasen AS, Bailey DM, Mortensen J, Moseley PL, Plovsing RR. Therapeutic benefits of proning to improve pulmonary gas exchange in severe respiratory failure: focus on fundamentals of physiology. Exp Physiol 2021; 107:759-770. [PMID: 34242438 PMCID: PMC9290689 DOI: 10.1113/ep089405] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 07/06/2021] [Indexed: 12/27/2022]
Abstract
New Findings What is the topic of this review? The use of proning for improving pulmonary gas exchange in critically ill patients. What advances does it highlight? Proning places the lung in its ‘natural’ posture, and thus optimises the ventilation‐perfusion distribution, which enables lung protective ventilation and the alleviation of potentially life‐threatening hypoxaemia in COVID‐19 and other types of critical illness with respiratory failure.
Abstract The survival benefit of proning patients with acute respiratory distress syndrome (ARDS) is well established and has recently been found to improve pulmonary gas exchange in patients with COVID‐19‐associated ARDS (CARDS). This review outlines the physiological implications of transitioning from supine to prone on alveolar ventilation‐perfusion (V˙A--Q˙) relationships during spontaneous breathing and during general anaesthesia in the healthy state, as well as during invasive mechanical ventilation in patients with ARDS and CARDS. Spontaneously breathing, awake healthy individuals maintain a small vertical (ventral‐to‐dorsal) V˙A/Q˙ ratio gradient in the supine position, which is largely neutralised in the prone position, mainly through redistribution of perfusion. In anaesthetised and mechanically ventilated healthy individuals, a vertical V˙A/Q˙ ratio gradient is present in both postures, but with better V˙A--Q˙ matching in the prone position. In ARDS and CARDS, the vertical V˙A/Q˙ ratio gradient in the supine position becomes larger, with intrapulmonary shunting in gravitationally dependent lung regions due to compression atelectasis of the dorsal lung. This is counteracted by proning, mainly through a more homogeneous distribution of ventilation combined with a largely unaffected high perfusion dorsally, and a consequent substantial improvement in arterial oxygenation. The data regarding proning as a therapy in patients with CARDS is still limited and whether the associated improvement in arterial oxygenation translates to a survival benefit remains unknown. Proning is nonetheless an attractive and lung protective manoeuvre with the potential benefit of improving life‐threatening hypoxaemia in patients with ARDS and CARDS.
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Affiliation(s)
- Ronan M G Berg
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Department of Clinical Physiology, Nuclear Medicine & PET, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark.,Centre for Physical Activity Research, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark.,Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Jacob Peter Hartmann
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Centre for Physical Activity Research, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark.,Department of Emergency Medicine, North Zealand Hospital, Hillerød, Denmark
| | - Ulrik Winning Iepsen
- Centre for Physical Activity Research, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark.,Department of Anaesthesia and Intensive Care, Copenhagen University Hospital - Hvidovre Hospital, Hvidovre, Denmark
| | | | - Andreas Ronit
- Department of Infectious Diseases, Copenhagen University Hospital - Hvidovre Hospital, Hvidovre, Denmark
| | - Anne Sofie Andreasen
- Department of Anaesthesia and Intensive Care, Copenhagen University Hospital - Herlev Hospital, Herlev, Denmark.,Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Jann Mortensen
- Department of Clinical Physiology, Nuclear Medicine & PET, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark.,Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Pope L Moseley
- Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Ronni R Plovsing
- Department of Anaesthesia and Intensive Care, Copenhagen University Hospital - Hvidovre Hospital, Hvidovre, Denmark.,Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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7
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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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8
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McNicholas B, Cosgrave D, Giacomini C, Brennan A, Laffey JG. Prone positioning in COVID-19 acute respiratory failure: just do it? Br J Anaesth 2020; 125:440-443. [PMID: 32571573 PMCID: PMC7280095 DOI: 10.1016/j.bja.2020.06.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 06/03/2020] [Indexed: 01/09/2023] Open
Affiliation(s)
- Bairbre McNicholas
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospitals, Galway, Ireland; Anaesthesia and Intensive Care Medicine, School of Medicine, National Unversity of Ireland, Galway, Ireland
| | - David Cosgrave
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospitals, Galway, Ireland; Anaesthesia and Intensive Care Medicine, School of Medicine, National Unversity of Ireland, Galway, Ireland
| | - Camilla Giacomini
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospitals, Galway, Ireland
| | - Aoife Brennan
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospitals, Galway, Ireland; Anaesthesia and Intensive Care Medicine, School of Medicine, National Unversity of Ireland, Galway, Ireland
| | - John G Laffey
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospitals, Galway, Ireland; Anaesthesia and Intensive Care Medicine, School of Medicine, National Unversity of Ireland, Galway, Ireland; Regenerative Medicine Institute at the CURAM Centre for Medical Devices, National University of Ireland, Galway, Ireland.
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9
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Abstract
The pulmonary blood-gas barrier represents a remarkable feat of engineering. It achieves the exquisite thinness needed for gas exchange by diffusion, the strength to withstand the stresses and strains of repetitive and changing ventilation, and the ability to actively maintain itself under varied demands. Understanding the design principles of this barrier is essential to understanding a variety of lung diseases, and to successfully regenerating or artificially recapitulating the barrier ex vivo. Many classical studies helped to elucidate the unique structure and morphology of the mammalian blood-gas barrier, and ongoing investigations have helped to refine these descriptions and to understand the biological aspects of blood-gas barrier function and regulation. This article reviews the key features of the blood-gas barrier that enable achievement of the necessary design criteria and describes the mechanical environment to which the barrier is exposed. It then focuses on the biological and mechanical components of the barrier that preserve integrity during homeostasis, but which may be compromised in certain pathophysiological states, leading to disease. Finally, this article summarizes recent key advances in efforts to engineer the blood-gas barrier ex vivo, using the platforms of lung-on-a-chip and tissue-engineered whole lungs. © 2020 American Physiological Society. Compr Physiol 10:415-452, 2020.
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Affiliation(s)
- Katherine L. Leiby
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
- Yale School of Medicine, Yale University, New Haven, Connecticut, USA
| | - Micha Sam Brickman Raredon
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
- Yale School of Medicine, Yale University, New Haven, Connecticut, USA
| | - Laura E. Niklason
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
- Yale School of Medicine, Yale University, New Haven, Connecticut, USA
- Department of Anesthesiology, Yale University, New Haven, Connecticut, USA
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10
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Quantitative Dual-Energy Computed Tomography Predicts Regional Perfusion Heterogeneity in a Model of Acute Lung Injury. J Comput Assist Tomogr 2018; 42:866-872. [PMID: 30371620 PMCID: PMC6250290 DOI: 10.1097/rct.0000000000000815] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Objective The aims of this study were to investigate the ability of contrast-enhanced dual-energy computed tomography (DECT) for assessing regional perfusion in a model of acute lung injury, using dynamic first-pass perfusion CT (DynCT) as the criterion standard and to evaluate if changes in lung perfusion caused by prone ventilation are similarly demonstrated by DECT and DynCT. Methods This was an institutional review board–approved study, compliant with guidelines for humane care of laboratory animals. A ventilator-induced lung injury protocol was applied to 6 landrace pigs. Perfused blood volume (PBV) and pulmonary blood flow (PBF) were respectively quantified by DECT and DynCT, in supine and prone positions. The lungs were segmented in equally sized regions of interest, namely, dorsal, middle, and ventral. Perfused blood volume and PBF values were normalized by lung density. Regional air fraction (AF) was assessed by triple-material decomposition DECT. Per-animal correlation between PBV and PBF was assessed with Pearson R. Regional differences in PBV, PBF, and AF were evaluated with 1-way analysis of variance and post hoc linear trend analysis (α = 5%). Results Mean correlation coefficient between PBV and PBF was 0.70 (range, 0.55–0.98). Higher PBV and PBF values were observed in dorsal versus ventral regions. Dorsal-to-ventral linear trend slopes were −10.24 mL/100 g per zone for PBV (P < 0.001) and −223.0 mL/100 g per minute per zone for PBF (P < 0.001). Prone ventilation also revealed higher PBV and PBF in dorsal versus ventral regions. Dorsal-to-ventral linear trend slopes were −16.16 mL/100 g per zone for PBV (P < 0.001) and −108.2 mL/100 g per minute per zone for PBF (P < 0.001). By contrast, AF was lower in dorsal versus ventral regions in supine position, with dorsal-to-ventral linear trend slope of +5.77%/zone (P < 0.05). Prone ventilation was associated with homogenization of AF distribution among different regions (P = 0.74). Conclusions Dual-energy computed tomography PBV is correlated with DynCT-PBF in a model of acute lung injury, and able to demonstrate regional differences in pulmonary perfusion. Perfusion was higher in the dorsal regions, irrespectively to decubitus, with more homogeneous lung aeration in prone position.
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11
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Abstract
The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.
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Affiliation(s)
- Karthik Suresh
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland, USA
| | - Larissa A. Shimoda
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland, USA
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12
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Bein T, Bischoff M, Brückner U, Gebhardt K, Henzler D, Hermes C, Lewandowski K, Max M, Nothacker M, Staudinger T, Tryba M, Weber-Carstens S, Wrigge H. S2e guideline: positioning and early mobilisation in prophylaxis or therapy of pulmonary disorders : Revision 2015: S2e guideline of the German Society of Anaesthesiology and Intensive Care Medicine (DGAI). Anaesthesist 2015; 64 Suppl 1:1-26. [PMID: 26335630 PMCID: PMC4712230 DOI: 10.1007/s00101-015-0071-1] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The German Society of Anesthesiology and Intensive Care Medicine (DGAI) commissioneda revision of the S2 guidelines on "positioning therapy for prophylaxis or therapy of pulmonary function disorders" from 2008. Because of the increasing clinical and scientificrelevance the guidelines were extended to include the issue of "early mobilization"and the following main topics are therefore included: use of positioning therapy and earlymobilization for prophylaxis and therapy of pulmonary function disorders, undesired effects and complications of positioning therapy and early mobilization as well as practical aspects of the use of positioning therapy and early mobilization. These guidelines are the result of a systematic literature search and the subsequent critical evaluation of the evidence with scientific methods. The methodological approach for the process of development of the guidelines followed the requirements of evidence-based medicine, as defined as the standard by the Association of the Scientific Medical Societies in Germany. Recently published articles after 2005 were examined with respect to positioning therapy and the recently accepted aspect of early mobilization incorporates all literature published up to June 2014.
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Affiliation(s)
- Th Bein
- Clinic for Anaesthesiology, University Hospital Regensburg, 93042, Regensburg, Germany.
| | - M Bischoff
- Clinic for Anaesthesiology, University Hospital Regensburg, 93042, Regensburg, Germany
| | - U Brückner
- Physiotherapy Department, Clinic Donaustauf, Centre for Pneumology, 93093, Donaustauf, Germany
| | - K Gebhardt
- Clinic for Anaesthesiology, University Hospital Regensburg, 93042, Regensburg, Germany
| | - D Henzler
- Clinic for Anaesthesiology, Surgical Intensive Care Medicine, Emergency Care Medicine, Pain Management, Klinikum Herford, 32049, Herford, Germany
| | - C Hermes
- HELIOS Clinic Siegburg, 53721, Siegburg, Germany
| | - K Lewandowski
- Clinic for Anaesthesiology, Intensive Care Medicine and Pain Management, Elisabeth Hospital Essen, 45138, Essen, Germany
| | - M Max
- Centre Hospitalier, Soins Intensifs Polyvalents, 1210, Luxembourg, Luxemburg
| | - M Nothacker
- Association of Scientific Medical Societies (AWMF), 35043, Marburg, Germany
| | - Th Staudinger
- University Hospital for Internal Medicine I, Medical University of Wien, General Hospital of Vienna, 1090, Vienna, Austria
| | - M Tryba
- Clinic for Anaesthesiology, Intensive Care Medicine and Pain Management, Klinikum Kassel, 34125, Kassel, Germany
| | - S Weber-Carstens
- Clinic for Anaesthesiology and Surgical Intensive Care Medicine, Charité Universitätsmedizin Berlin, Campus Virchow Klinikum, 13353, Berlin, Germany
| | - H Wrigge
- Clinic and Policlinic for Anaesthesiology and Intensive Care Medicine, University Hospital Leipzig, 04103, Leipzig, Germany
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Siev M, Motamedinia P, Leavitt D, Fakhoury M, Barcohana K, Hoenig D, Smith AD, Okeke Z. Does Peak Inspiratory Pressure Increase in the Prone Position? An Analysis Related to Body Mass Index. J Urol 2015; 194:1302-6. [PMID: 25983193 DOI: 10.1016/j.juro.2015.05.015] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/05/2015] [Indexed: 11/30/2022]
Abstract
PURPOSE Percutaneous nephrolithotomy is commonly performed with the patient prone. There is concern that the prone position, especially in obese patients, negatively affects ventilation due to the restriction of chest compliance and respiratory mechanics. We analyzed the change in airway resistance between supine and prone positioning of patients undergoing percutaneous nephrolithotomy. MATERIALS AND METHODS We retrospectively reviewed the intraoperative respiratory parameters of 101 patients who underwent prone percutaneous nephrolithotomy. Peak inspiratory pressure was assessed with the patient supine, at several time points after being turned prone and at the end of the case. The change in peak inspiratory pressure with time was calculated. Results were stratified based on body mass index and data were compared using the paired t-test and Spearman ρ. RESULTS Of 101 patients 50 (50%) were obese (body mass index 30 kg/m(2) or greater). Median body mass index was 25.6 kg/m(2) in the nonobese cohort and 38.3 kg/m(2) in the obese cohort. Average peak inspiratory pressure while supine and prone was 18.0 and 18.5 cm H2O in the nonobese cohort, and 25.5 and 26.6 cm H2O, respectively, in the obese cohort. Obese patients had significantly higher peak inspiratory pressure in the supine and the prone positions relative to nonobese patients (p <0.0001). However, there was no change in peak inspiratory pressure from the supine to the prone position in either cohort. CONCLUSIONS Obese patients have higher baseline peak inspiratory pressure regardless of position. However, prone positioning does not impact peak inspiratory pressure in either cohort. It remains a safe and viable option.
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Affiliation(s)
- Michael Siev
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York
| | - Piruz Motamedinia
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York
| | - David Leavitt
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York
| | - Mathew Fakhoury
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York
| | - Kevin Barcohana
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York
| | - David Hoenig
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York
| | - Arthur D Smith
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York
| | - Zeph Okeke
- Smith Institute for Urology and Department of Anesthesia (KB), NorthShore-LIJ Health System, New Hyde Park, New York.
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14
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Hall ET, Sá RC, Holverda S, Arai TJ, Dubowitz DJ, Theilmann RJ, Prisk GK, Hopkins SR. The effect of supine exercise on the distribution of regional pulmonary blood flow measured using proton MRI. J Appl Physiol (1985) 2013; 116:451-61. [PMID: 24356515 DOI: 10.1152/japplphysiol.00659.2013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The Zone model of pulmonary perfusion predicts that exercise reduces perfusion heterogeneity because increased vascular pressure redistributes flow to gravitationally nondependent lung, and causes dilation and recruitment of blood vessels. However, during exercise in animals, perfusion heterogeneity as measured by the relative dispersion (RD, SD/mean) is not significantly decreased. We evaluated the effect of exercise on pulmonary perfusion in six healthy supine humans using magnetic resonance imaging (MRI). Data were acquired at rest, while exercising (∼27% of maximal oxygen consumption) using a MRI-compatible ergometer, and in recovery. Images were acquired in most of the right lung in the sagittal plane at functional residual capacity, using a 1.5-T MR scanner equipped with a torso coil. Perfusion was measured using arterial spin labeling (ASL-FAIRER) and regional proton density using a fast multiecho gradient-echo sequence. Perfusion images were corrected for coil-based signal heterogeneity, large conduit vessels removed and quantified (in ml·min(-1)·ml(-1)) (perfusion), and also normalized for density and quantified (in ml·min(-1)·g(-1)) (density-normalized perfusion, DNP) accounting for tissue redistribution. DNP increased during exercise (11.1 ± 3.5 rest, 18.8 ± 2.3 exercise, 13.2 ± 2.2 recovery, ml·min(-1)·g(-1), P < 0.0001), and the increase was largest in nondependent lung (110 ± 61% increase in nondependent, 63 ± 35% in mid, 70 ± 33% in dependent, P < 0.005). The RD of perfusion decreased with exercise (0.93 ± 0.21 rest, 0.73 ± 0.13 exercise, 0.94 ± 0.18 recovery, P < 0.005). The RD of DNP showed a similar trend (0.82 ± 0.14 rest, 0.75 ± 0.09 exercise, 0.81 ± 0.10 recovery, P = 0.13). In conclusion, in contrast to animal studies, in supine humans, mild exercise decreased perfusion heterogeneity, consistent with Zone model predictions.
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Affiliation(s)
- E T Hall
- Department of Medicine, University of California, San Diego, La Jolla, California
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15
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Abstract
The primary function of the pulmonary circulation is to deliver blood to the alveolar capillaries to exchange gases. Distributing blood over a vast surface area facilitates gas exchange, yet the pulmonary vascular tree must be constrained to fit within the thoracic cavity. In addition, pressures must remain low within the circulatory system to protect the thin alveolar capillary membranes that allow efficient gas exchange. The pulmonary circulation is engineered for these unique requirements and in turn these special attributes affect the spatial distribution of blood flow. As the largest organ in the body, the physical characteristics of the lung vary regionally, influencing the spatial distribution on large-, moderate-, and small-scale levels.
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Affiliation(s)
- Robb W Glenny
- Department of Medicine, University of Washington, Seattle, Washington, USA.
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16
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Glenny RW, Robertson HT. Spatial distribution of ventilation and perfusion: mechanisms and regulation. Compr Physiol 2013; 1:375-95. [PMID: 23737178 DOI: 10.1002/cphy.c100002] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
With increasing spatial resolution of regional ventilation and perfusion, it has become more apparent that ventilation and blood flow are quite heterogeneous in the lung. A number of mechanisms contribute to this regional variability, including hydrostatic gradients, pleural pressure gradients, lung compressibility, and the geometry of the airway and vascular trees. Despite this marked heterogeneity in both ventilation and perfusion, efficient gas exchange is possible through the close regional matching of the two. Passive mechanisms, such as the shared effect of gravity and the matched branching of vascular and airway trees, create efficient gas exchange through the strong correlation between ventilation and perfusion. Active mechanisms that match local ventilation and perfusion play little if no role in the normal healthy lung but are important under pathologic conditions.
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Affiliation(s)
- Robb W Glenny
- Department of Medicine, University of Washington, USA.
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17
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Abstract
Efficient gas exchange in the lung depends on the matching of ventilation and perfusion. However, the human lung is a readily deformable structure and as a result gravitational stresses generate gradients in both ventilation and perfusion. Nevertheless, the lung is capable of withstanding considerable change in the applied gravitational load before pulmonary gas exchange becomes impaired. The postural changes that are part of the everyday existence for most bipedal species are well tolerated, as is the removal of gravity (weightlessness). Increases in the applied gravitational load result only in a large impairment in pulmonary gas exchange above approximately three times that on the ground, at which point the matching of ventilation to perfusion is so impaired that efficient gas exchange is no longer possible. Much of the tolerance of the lung to alterations in gravitation stress comes from the fact that ventilation and perfusion are inextricably coupled. Deformations in the lung that alter ventilation necessarily alter perfusion, thus maintaining a degree of matching and minimizing the disruption in ventilation to perfusion ratio and thus gas exchange.
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Affiliation(s)
- G Kim Prisk
- Departments of Medicine and Radiology, University of California, San Diego, USA.
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18
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Abstract
Local driving pressures and resistances within the pulmonary vascular tree determine the distribution of perfusion in the lung. Unlike other organs, these local determinants are significantly influenced by regional hydrostatic and alveolar pressures. Those effects on blood flow distribution are further magnified by the large vertical height of the human lung and the relatively low intravascular pressures in the pulmonary circulation. While the distribution of perfusion is largely due to passive determinants such as vascular geometry and hydrostatic pressures, active mechanisms such as vasoconstriction induced by local hypoxia can also redistribute blood flow. This chapter reviews the determinants of regional lung perfusion with a focus on vascular tree geometry, vertical gradients induced by gravity, the interactions between vascular and surrounding alveolar pressures, and hypoxic pulmonary vasoconstriction. While each of these determinants of perfusion distribution can be examined in isolation, the distribution of blood flow is dynamically determined and each component interacts with the others so that a change in one region of the lung influences the distribution of blood flow in other lung regions.
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Affiliation(s)
- Robb Glenny
- Departments of Medicine, University of Washington, Seattle, Washington, USA.
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19
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Henderson AC, Sá RC, Theilmann RJ, Buxton RB, Prisk GK, Hopkins SR. The gravitational distribution of ventilation-perfusion ratio is more uniform in prone than supine posture in the normal human lung. J Appl Physiol (1985) 2013; 115:313-24. [PMID: 23620488 DOI: 10.1152/japplphysiol.01531.2012] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The gravitational gradient of intrapleural pressure is suggested to be less in prone posture than supine. Thus the gravitational distribution of ventilation is expected to be more uniform prone, potentially affecting regional ventilation-perfusion (Va/Q) ratio. Using a novel functional lung magnetic resonance imaging technique to measure regional Va/Q ratio, the gravitational gradients in proton density, ventilation, perfusion, and Va/Q ratio were measured in prone and supine posture. Data were acquired in seven healthy subjects in a single sagittal slice of the right lung at functional residual capacity. Regional specific ventilation images quantified using specific ventilation imaging and proton density images obtained using a fast gradient-echo sequence were registered and smoothed to calculate regional alveolar ventilation. Perfusion was measured using arterial spin labeling. Ventilation (ml·min(-1)·ml(-1)) images were combined on a voxel-by-voxel basis with smoothed perfusion (ml·min(-1)·ml(-1)) images to obtain regional Va/Q ratio. Data were averaged for voxels within 1-cm gravitational planes, starting from the most gravitationally dependent lung. The slope of the relationship between alveolar ventilation and vertical height was less prone than supine (-0.17 ± 0.10 ml·min(-1)·ml(-1)·cm(-1) supine, -0.040 ± 0.03 prone ml·min(-1)·ml(-1)·cm(-1), P = 0.02) as was the slope of the perfusion-height relationship (-0.14 ± 0.05 ml·min(-1)·ml(-1)·cm(-1) supine, -0.08 ± 0.09 prone ml·min(-1)·ml(-1)·cm(-1), P = 0.02). There was a significant gravitational gradient in Va/Q ratio in both postures (P < 0.05) that was less in prone (0.09 ± 0.08 cm(-1) supine, 0.04 ± 0.03 cm(-1) prone, P = 0.04). The gravitational gradients in ventilation, perfusion, and regional Va/Q ratio were greater supine than prone, suggesting an interplay between thoracic cavity configuration, airway and vascular tree anatomy, and the effects of gravity on Va/Q matching.
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Affiliation(s)
- A Cortney Henderson
- Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
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20
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Robak O, Schellongowski P, Bojic A, Laczika K, Locker GJ, Staudinger T. Short-term effects of combining upright and prone positions in patients with ARDS: a prospective randomized study. Crit Care 2011; 15:R230. [PMID: 21955757 PMCID: PMC3334777 DOI: 10.1186/cc10471] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Revised: 08/17/2011] [Accepted: 09/29/2011] [Indexed: 11/24/2022] Open
Abstract
Introduction Prone position is known to improve oxygenation in patients with acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). Supine upright (semirecumbent) position also exerts beneficial effects on gas exchange in this group of patients. We evaluated the effect of combining upright and prone position on oxygenation and respiratory mechanics in patients with ALI or ARDS in a prospective randomized cross-over study. Methods After turning them prone from a supine position, we randomized the patients to a prone position or combined prone and upright position. After 2 hours, the position was changed to the other one for another 6 hours. The gas exchange and static compliance of the respiratory system, lungs, and chest wall were assessed in the supine position as well as every hour in the prone position. Results Twenty patients were enrolled in the study. The PaO2/FiO2 ratio improved significantly from the supine to the prone position and further significantly increased with additional upright position. Fourteen (70%) patients were classified as responders to the prone position, whereas 17 (85%) patients responded to the prone plus upright position compared with the supine position (P = n.s.). No statistically significant changes were found with respect to compliance. Conclusions Combining the prone position with the upright position in patients with ALI or ARDS leads to further improvement of oxygenation. Trial registration Clinical Trials No. NCT00753129
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Affiliation(s)
- Oliver Robak
- Department of Internal Medicine I, Intensive Care Unit, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria
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21
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Chung F, Mueller D. Physical therapy management of ventilated patients with acute respiratory distress syndrome or severe acute lung injury. Physiother Can 2011; 63:191-8. [PMID: 22379259 DOI: 10.3138/ptc.2010-10] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Frank Chung
- Frank Chung, BSc(PT), MSc: Section Head, Physiotherapy Department, Burnaby Hospital, Burnaby, British Columbia
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22
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Mogensen ML, Steimle KS, Karbing DS, Andreassen S. A model of perfusion of the healthy human lung. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2011; 101:156-165. [PMID: 20667619 DOI: 10.1016/j.cmpb.2010.06.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Revised: 06/18/2010] [Accepted: 06/28/2010] [Indexed: 05/29/2023]
Abstract
This study presents a model that simulates the pulmonary capillary perfusion. The model describes the lungs as divided into horizontal layers and includes: capillary geometry; capillary wall elasticity; pressure at the pulmonary artery; blood viscosity; the effect of the chest wall; the change in lung height and hydrostatic effects of the lung tissue and of the blood during breathing. The model simulates pulsatile blood perfusion with an increasing blood distribution down the lungs, in agreement with previous experimental studies. Moreover the model is in agreement with experimentally measured total capillary perfusion, total capillary volume, total capillary surface area and transition time of red blood cells passing through the pulmonary capillary network. The presented model is the first to be validated against the mentioned experimental data and to model the link between airway pressure, lung volume and perfusion.
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Affiliation(s)
- M L Mogensen
- Aalborg University, Center for Model-Based Medical Decision Support, Fredrik Bajersvej 7, DK 9220 Aalborg, Denmark.
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23
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Grant CA, Pham T, Hough J, Riedel T, Stocker C, Schibler A. Measurement of ventilation and cardiac related impedance changes with electrical impedance tomography. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2011; 15:R37. [PMID: 21266025 PMCID: PMC3222074 DOI: 10.1186/cc9985] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 11/03/2010] [Accepted: 01/25/2011] [Indexed: 11/10/2022]
Abstract
INTRODUCTION Electrical impedance tomography (EIT) has been shown to be able to distinguish both ventilation and perfusion. With adequate filtering the regional distributions of both ventilation and perfusion and their relationships could be analysed. Several methods of separation have been suggested previously, including breath holding, electrocardiograph (ECG) gating and frequency filtering. Many of these methods require interventions inappropriate in a clinical setting. This study therefore aims to extend a previously reported frequency filtering technique to a spontaneously breathing cohort and assess the regional distributions of ventilation and perfusion and their relationship. METHODS Ten healthy adults were measured during a breath hold and while spontaneously breathing in supine, prone, left and right lateral positions. EIT data were analysed with and without filtering at the respiratory and heart rate. Profiles of ventilation, perfusion and ventilation/perfusion related impedance change were generated and regions of ventilation and pulmonary perfusion were identified and compared. RESULTS Analysis of the filtration technique demonstrated its ability to separate the ventilation and cardiac related impedance signals without negative impact. It was, therefore, deemed suitable for use in this spontaneously breathing cohort.Regional distributions of ventilation, perfusion and the combined ΔZV/ΔZQ were calculated along the gravity axis and anatomically in each position. Along the gravity axis, gravity dependence was seen only in the lateral positions in ventilation distribution, with the dependent lung being better ventilated regardless of position. This gravity dependence was not seen in perfusion.When looking anatomically, differences were only apparent in the lateral positions. The lateral position ventilation distributions showed a difference in the left lung, with the right lung maintaining a similar distribution in both lateral positions. This is likely caused by more pronounced anatomical changes in the left lung when changing positions. CONCLUSIONS The modified filtration technique was demonstrated to be effective in separating the ventilation and perfusion signals in spontaneously breathing subjects. Gravity dependence was seen only in ventilation distribution in the left lung in lateral positions, suggesting gravity based shifts in anatomical structures. Gravity dependence was not seen in any perfusion distributions.
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Affiliation(s)
- Caroline A Grant
- Paediatric Critical Care Research Group, Paediatric Intensive Care Unit, Mater Children's Hospital, 550 Stanley Street, South Brisbane, Queensland 4101, Australia.
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Richter T, Bergmann R, Pietzsch J, Közle I, Hofheinz F, Schiller E, Ragaller M, van den Hoff J. Effects of posture on regional pulmonary blood flow in rats as measured by PET. J Appl Physiol (1985) 2009; 108:422-9. [PMID: 19926822 DOI: 10.1152/japplphysiol.91257.2008] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using small animal PET with (68)Ga-radiolabeled human albumin microspheres (Ga-68-microspheres), we investigated the effect of posture on regional pulmonary blood flow (PBF) in normal rats. This in vivo method is noninvasive and quantitative, and it allows for repeated longitudinal measurements. The purpose of the experiment was to quantify spatial differences in PBF in small animals in different postures. Two studies were performed in anesthetized, spontaneously breathing Wistar rats. Study 1 was designed to determine PBF in the prone and supine positions. Ga-68-microspheres were given to five prone and eight supine animals. We found that PBF increased in dorsal regions of supine animals (0.75) more than in prone animals (0.70; P = 0.037), according to a steeper vertical gradient of flow in supine than in prone animals. No differences in spatial heterogeneity were detected. Study 2 was designed to determine the effects of tissue distribution on PBF measurements. Because microspheres remained fixed in the lung, PET was performed on animals in the position in which they received Ga-68-microsphere injections and thereafter in the opposite posture. The distribution of PBF showed a preference for dorsal regions in both positions, but the distribution was dependent on the position during administration of the microspheres. We conclude that PET using Ga-68-microspheres can detect and quantify regional PBF in animals as small as the rat. PBF distributions differed between the prone and supine postures and were influenced by the distribution of lung tissue within the thorax.
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Affiliation(s)
- Torsten Richter
- Department of Anesthesia and Critical Care, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany.
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Redistribution of pulmonary blood flow impacts thermodilution-based extravascular lung water measurements in a model of acute lung injury. Anesthesiology 2009; 111:1065-74. [PMID: 19809280 DOI: 10.1097/aln.0b013e3181bc99cf] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Studies using transthoracic thermodilution have demonstrated increased extravascular lung water (EVLW) measurements attributed to progression of edema and flooding during sepsis and acute lung injury. The authors hypothesized that redistribution of pulmonary blood flow can cause increased apparent EVLW secondary to increased perfusion of thermally silent tissue, not increased lung edema. METHODS Anesthetized, mechanically ventilated canines were instrumented with PiCCO (Pulsion Medical, Munich, Germany) catheters and underwent lung injury by repetitive saline lavage. Hemodynamic and respiratory physiologic data were recorded. After stabilized lung injury, endotoxin was administered to inactivate hypoxic pulmonary vasoconstriction. Computed tomographic imaging was performed to quantify in vivo lung volume, total tissue (fluid) and air content, and regional distribution of blood flow. RESULTS Lavage injury caused an increase in airway pressures and decreased arterial oxygen content with minimal hemodynamic effects. EVLW and shunt fraction increased after injury and then markedly after endotoxin administration. Computed tomographic measurements quantified an endotoxin-induced increase in pulmonary blood flow to poorly aerated regions with no change in total lung tissue volume. CONCLUSIONS The abrupt increase in EVLW and shunt fraction after endotoxin administration is consistent with inactivation of hypoxic pulmonary vasoconstriction and increased perfusion to already flooded lung regions that were previously thermally silent. Computed tomographic studies further demonstrate in vivo alterations in regional blood flow (but not lung water) and account for these alterations in shunt fraction and EVLW.
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Determinants of regional ventilation and blood flow in the lung. Intensive Care Med 2009; 35:1833-42. [DOI: 10.1007/s00134-009-1649-3] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Accepted: 08/12/2009] [Indexed: 11/26/2022]
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Arai TJ, Henderson AC, Dubowitz DJ, Levin DL, Friedman PJ, Buxton RB, Prisk GK, Hopkins SR. Hypoxic pulmonary vasoconstriction does not contribute to pulmonary blood flow heterogeneity in normoxia in normal supine humans. J Appl Physiol (1985) 2008; 106:1057-64. [PMID: 19057006 DOI: 10.1152/japplphysiol.90759.2008] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
We hypothesized that some of the heterogeneity of pulmonary blood flow present in the normal human lung in normoxia is due to hypoxic pulmonary vasoconstriction (HPV). If so, mild hyperoxia would decrease the heterogeneity of pulmonary perfusion, whereas it would be increased by mild hypoxia. To test this, six healthy nonsmoking subjects underwent magnetic resonance imaging (MRI) during 20 min of breathing different oxygen concentrations through a face mask [normoxia, inspired O(2) fraction (Fi(O(2))) = 0.21; hypoxia, Fi(O(2)) = 0.125; hyperoxia, Fi(O(2)) = 0.30] in balanced order. Data were acquired on a 1.5-T MRI scanner during a breath hold at functional residual capacity from both coronal and sagittal slices in the right lung. Arterial spin labeling was used to quantify the spatial distribution of pulmonary blood flow in milliliters per minute per cubic centimeter and fast low-angle shot to quantify the regional proton density, allowing perfusion to be expressed as density-normalized perfusion in milliliters per minute per gram. Neither mean proton density [hypoxia, 0.46(0.18) g water/cm(3); normoxia, 0.47(0.18) g water/cm(3); hyperoxia, 0.48(0.17) g water/cm(3); P = 0.28] nor mean density-normalized perfusion [hypoxia, 4.89(2.13) ml x min(-1) x g(-1); normoxia, 4.94(1.88) ml x min(-1) x g(-1); hyperoxia, 5.32(1.83) ml x min(-1) x g(-1); P = 0.72] were significantly different between conditions in either imaging plane. Similarly, perfusion heterogeneity as measured by relative dispersion [hypoxia, 0.74(0.16); normoxia, 0.74(0.10); hyperoxia, 0.76(0.18); P = 0.97], fractal dimension [hypoxia, 1.21(0.04); normoxia, 1.19(0.03); hyperoxia, 1.20(0.04); P = 0.07], log normal shape parameter [hypoxia, 0.62(0.11); normoxia, 0.72(0.11); hyperoxia, 0.70(0.13); P = 0.07], and geometric standard deviation [hypoxia, 1.88(0.20); normoxia, 2.07(0.24); hyperoxia, 2.02(0.28); P = 0.11] was also not different. We conclude that HPV does not affect pulmonary perfusion heterogeneity in normoxia in the normal supine human lung.
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Affiliation(s)
- T J Arai
- Department of Medicine, University of California, San Diego, La Jolla, California , CA 92093, USA
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Tawhai MH, Burrowes KS. Modelling pulmonary blood flow. Respir Physiol Neurobiol 2008; 163:150-7. [PMID: 18434260 PMCID: PMC2593627 DOI: 10.1016/j.resp.2008.02.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 02/27/2008] [Accepted: 02/28/2008] [Indexed: 11/17/2022]
Abstract
Computational model analysis has been used widely to understand and interpret complexity of interactions in the pulmonary system. Pulmonary blood transport is a multi-scale phenomenon that involves scale-dependent structure and function, therefore requiring different model assumptions for the microcirculation and the arterial or venous flows. The blood transport systems interact with the surrounding lung tissue, and are dependent on hydrostatic pressure gradients, control of vasoconstriction, and the topology and material composition of the vascular trees. This review focuses on computational models that have been developed to study the different mechanisms contributing to regional perfusion of the lung. Different models for the microcirculation and the pulmonary arteries are considered, including fractal approaches and anatomically-based methods. The studies that are reviewed illustrate the different complementary approaches that can be used to address the same physiological question of flow heterogeneity.
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Affiliation(s)
- Merryn H Tawhai
- Auckland Bioengineering Institute, University of Auckland, Private Bag 92019, Auckland 1010, New Zealand.
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Burrowes KS, Swan AJ, Warren NJ, Tawhai MH. Towards a virtual lung: multi-scale, multi-physics modelling of the pulmonary system. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2008; 366:3247-63. [PMID: 18593661 PMCID: PMC3268218 DOI: 10.1098/rsta.2008.0073] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The essential function of the lung, gas exchange, is dependent on adequate matching of ventilation and perfusion, where air and blood are delivered through complex branching systems exposed to regionally varying transpulmonary and transmural pressures. Structure and function in the lung are intimately related, yet computational models in pulmonary physiology usually simplify or neglect structure. The geometries of the airway and vascular systems and their interaction with parenchymal tissue have an important bearing on regional distributions of air and blood, and therefore on whole lung gas exchange, but this has not yet been addressed by modelling studies. Models for gas exchange have typically incorporated considerable detail at the level of chemical reactions, with little thought for the influence of structure. To date, relatively little attention has been paid to modelling at the cellular or subcellular level in the lung, or to linking information from the protein structure/interaction and cellular levels to the operation of the whole lung. We review previous work in developing anatomically based models of the lung, airways, parenchyma and pulmonary vasculature, and some functional studies in which these models have been used. Models for gas exchange at several spatial scales are briefly reviewed, and the challenges and benefits from modelling cellular function in the lung are discussed.
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Affiliation(s)
- K S Burrowes
- Oxford University Computing Laboratory, Parks Road, Oxford OX1 3QD, UK.
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Dakin JH, Evans TW, Hansell DM, Hoffman EA. Regional pulmonary blood flow in humans and dogs by 4D computed tomography. Acad Radiol 2008; 15:844-52. [PMID: 18572119 DOI: 10.1016/j.acra.2007.12.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2007] [Revised: 12/19/2007] [Accepted: 12/20/2007] [Indexed: 11/28/2022]
Abstract
RATIONALE AND OBJECTIVES Pulmonary vascular control mechanisms are complex and likely to differ between species. We wish to quantify regional perfusion and the effects of gravity using computed tomography. MATERIALS AND METHODS Sequential density measurements following the administration of a bolus of iodinated contrast medium were acquired from four healthy human subjects and four dogs. RESULTS In humans, perfusion (Q) was linear throughout most of the range of vertical height, with an overall gradient of -2.6% cm(-1). However, when perfusion was normalized to "tissue" density (blood plus tissue: sQt), maximum perfusion occurred around the mid-range of vertical height, being 9% (range 1-22%) greater than either the dorsal or ventral extreme. Within discrete transverse axial sections, concentric zones of perfusion centered on blood vessels were demonstrated. The relationship between sQt and vertical height in dogs was distinctly linear, with a gradient of -7.2% cm(-1). In dogs, the median gradient of Q was -13.6% cm(-1) (range -9.7 to -17.1%). CONCLUSIONS Differences in regional pulmonary perfusion, particularly the vertical gradient observed in humans and dogs, may in part reflect anatomic differences between the symmetric dichotomous branching structure of the human pulmonary vasculature and the more asymmetrical structure found in dogs.
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Affiliation(s)
- Jonathan H Dakin
- Imperial College of Science, Technology & Medicine, Unit of Critical Care, National Heart & Lung Institute, Royal Brompton Hospital, Dovehouse St, London SW3 6LY UK.
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Glenny R. Counterpoint: Gravity is not the major factor determining the distribution of blood flow in the healthy human lung. J Appl Physiol (1985) 2008; 104:1533-5; discussion 1535-6. [PMID: 18450991 DOI: 10.1152/japplphysiol.01092.2007a] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Robb Glenny
- Division of Pulmonary and Critical Care Medicine, University of Washington, Seattle, WA 98195, USA.
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32
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Tsai LL, Mair RW, Li CH, Rosen MS, Patz S, Walsworth RL. Posture-dependent human 3He lung imaging in an open-access MRI system: initial results. Acad Radiol 2008; 15:728-39. [PMID: 18486009 PMCID: PMC2474800 DOI: 10.1016/j.acra.2007.10.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Revised: 09/24/2007] [Accepted: 10/17/2007] [Indexed: 11/28/2022]
Abstract
RATIONALE AND OBJECTIVES The human lung and its functions are extremely sensitive to orientation and posture, and debate continues as to the role of gravity and the surrounding anatomy in determining lung function and heterogeneity of perfusion and ventilation. However, study of these effects is difficult. The conventional high-field magnets used for most hyperpolarized (3)He magnetic resonance imaging (MRI) of the human lung, and most other common radiologic imaging modalities including positron emission tomography and computed tomography, restrict subjects to lying horizontally, minimizing most gravitational effects. MATERIALS AND METHODS In this article, we review the motivation for posture-dependent studies of human lung function and present initial imaging results of human lungs in the supine and vertical body orientations using inhaled hyperpolarized (3)He gas and an open-access MRI instrument. The open geometry of this MRI system features a "walk-in" capability that permits subjects to be imaged in vertical and horizontal positions and potentially allows for complete rotation of the orientation of the imaging subject in a two-dimensional plane. RESULTS Initial results include two-dimensional lung images acquired with approximately 4 x 8 mm in-plane resolution and three-dimensional images with approximately 2-cm slice thickness. CONCLUSIONS Effects of posture variation are observed, including posture-related effects of the diaphragm and distension of the lungs while vertical.
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Affiliation(s)
- Leo L Tsai
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St, MS 59, Cambridge, MA 02138, USA
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33
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Wagner PD. Gravity is/is not the major factor determining the distribution of blood flow in the human lung. J Appl Physiol (1985) 2008; 104:1538. [DOI: 10.1152/japplphysiol.90402.2008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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34
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Hughes M, West JB. Point:Counterpoint: Gravity is/is not the major factor determining the distribution of blood flow in the human lung. J Appl Physiol (1985) 2008; 104:1531-3. [DOI: 10.1152/japplphysiol.01092.2007] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Abstract
Prone positioning of patients during anaesthesia is required to provide operative access for a wide variety of surgical procedures. It is associated with predictable changes in physiology but also with a number of complications, and safe use of the prone position requires an understanding of both issues. We have reviewed the development of the prone position and its variants and the physiological changes which occur on prone positioning. The complications associated with this position and the published techniques for various practical procedures in this position will be discussed. The aim of this review is to identify the risks associated with prone positioning and how these risks may be anticipated and minimized.
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Affiliation(s)
- H Edgcombe
- Royal Berkshire NHS Foundation Trust, London Road, Reading RG1 5AN, UK
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36
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Suzuki H, Sato Y, Shindo M, Yoshioka H, Mizutani T, Onizuka M, Sakakibara Y. Prone positioning improves distribution of pulmonary perfusion: noninvasive magnetic resonance imaging study in healthy humans. Eur Radiol 2007; 18:522-8. [DOI: 10.1007/s00330-007-0808-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2007] [Revised: 09/19/2007] [Accepted: 10/22/2007] [Indexed: 11/28/2022]
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37
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Prisk GK, Yamada K, Henderson AC, Arai TJ, Levin DL, Buxton RB, Hopkins SR. Pulmonary perfusion in the prone and supine postures in the normal human lung. J Appl Physiol (1985) 2007; 103:883-94. [PMID: 17569767 PMCID: PMC2399900 DOI: 10.1152/japplphysiol.00292.2007] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Prone posture increases cardiac output and improves pulmonary gas exchange. We hypothesized that, in the supine posture, greater compression of dependent lung limits regional blood flow. To test this, MRI-based measures of regional lung density, MRI arterial spin labeling quantification of pulmonary perfusion, and density-normalized perfusion were made in six healthy subjects. Measurements were made in both the prone and supine posture at functional residual capacity. Data were acquired in three nonoverlapping 15-mm sagittal slices covering most of the right lung: central, middle, and lateral, which were further divided into vertical zones: anterior, intermediate, and posterior. The density of the entire lung was not different between prone and supine, but the increase in lung density in the anterior lung with prone posture was less than the decrease in the posterior lung (change: +0.07 g/cm(3) anterior, -0.11 posterior; P < 0.0001), indicating greater compression of dependent lung in supine posture, principally in the central lung slice (P < 0.0001). Overall, density-normalized perfusion was significantly greater in prone posture (7.9 +/- 3.6 ml.min(-1).g(-1) prone, 5.1 +/- 1.8 supine, a 55% increase; P < 0.05) and showed the largest increase in the posterior lung as it became nondependent (change: +71% posterior, +58% intermediate, +31% anterior; P = 0.08), most marked in the central lung slice (P < 0.05). These data indicate that central posterior portions of the lung are more compressed in the supine posture, likely by the heart and adjacent structures, than are central anterior portions in the prone and that this limits regional perfusion in the supine posture.
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Affiliation(s)
- G Kim Prisk
- Department of Medicine, University of California, San Diego, La Jolla, California 92093-0931, USA.
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38
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Petersson J, Rohdin M, Sánchez-Crespo A, Nyrén S, Jacobsson H, Larsson SA, Lindahl SGE, Linnarsson D, Neradilek B, Polissar NL, Glenny RW, Mure M. Posture primarily affects lung tissue distribution with minor effect on blood flow and ventilation. Respir Physiol Neurobiol 2007; 156:293-303. [PMID: 17169620 DOI: 10.1016/j.resp.2006.11.001] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2006] [Revised: 10/13/2006] [Accepted: 11/01/2006] [Indexed: 11/30/2022]
Abstract
We used quantitative single photon emission computed tomography to estimate the proportion of the observed redistribution of blood flow and ventilation that is due to lung tissue shift with a change in posture. Seven healthy volunteers were studied awake, breathing spontaneously. Regional blood flow and ventilation were marked using radiotracers that remain fixed in the lung after administration. The radiotracers were administered in prone or supine at separate occasions, at both occasions followed by imaging in both postures. Images showed greater blood flow and ventilation to regions dependent at the time of imaging, regardless of posture at radiotracer administration. The results suggest that a shift in lung parenchyma has a major influence on the imaged distributions. We conclude that a change from the supine to the prone posture primarily causes a change in the vertical distribution of lung tissue. The effect on the vertical distribution of blood flow and ventilation within the lung parenchyma is much less.
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Affiliation(s)
- Johan Petersson
- Department of Anesthesiology and Intensive Care Medicine, Karolinska University Hospital Solna, 171 76 Stockholm, Sweden.
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Galvin I, Drummond GB, Nirmalan M. Distribution of blood flow and ventilation in the lung: gravity is not the only factor. Br J Anaesth 2007; 98:420-8. [PMID: 17347182 DOI: 10.1093/bja/aem036] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Current textbooks in anaesthesia describe how gravity affects the regional distribution of ventilation and blood flow in the lung, in terms of vertical gradients of pleural pressure and pulmonary vascular pressures. This concept fails to explain some of the clinical features of disturbed lung function. Evidence now suggests that gravity has a less important role in the variation of regional distribution than structural features of the airways and blood vessels. We review more recent studies that used a variety of methods: external radioactive counters, measurements using inhaled and injected particles, and computer tomography scans. These give a higher spatial resolution of regional blood flow and ventilation. The matching between ventilation and blood flow in these small units of lung is considered; the effects of microgravity, increased gravity, and different postures are reviewed, and the application of these findings to conditions such as acute lung injury is discussed. Down to the scale of the acinus, there is considerable heterogeneity in the distribution of both ventilation and blood flow. However, the matching of blood flow with ventilation is well maintained and may result from a common pattern of asymmetric branching of the airways and blood vessels. Disruption of this pattern may explain impaired gas exchange after acute lung injury and explain how the prone position improves gas exchange.
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Affiliation(s)
- I Galvin
- University Department of Anaesthesia and Critical Care Medicine, Manchester Royal Infirmary, Manchester, UK
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40
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Hopkins SR, Henderson AC, Levin DL, Yamada K, Arai T, Buxton RB, Prisk GK. Vertical gradients in regional lung density and perfusion in the supine human lung: the Slinky effect. J Appl Physiol (1985) 2007; 103:240-8. [PMID: 17395757 PMCID: PMC2399899 DOI: 10.1152/japplphysiol.01289.2006] [Citation(s) in RCA: 150] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In vivo radioactive tracer and microsphere studies have differing conclusions as to the magnitude of the gravitational effect on the distribution of pulmonary blood flow. We hypothesized that some of the apparent vertical perfusion gradient in vivo is due to compression of dependent lung increasing local lung density and therefore perfusion/volume. To test this, six normal subjects underwent functional magnetic resonance imaging with arterial spin labeling during breath holding at functional residual capacity, and perfusion quantified in nonoverlapping 15 mm sagittal slices covering most of the right lung. Lung proton density was measured in the same slices using a short echo 2D-Fast Low-Angle SHot (FLASH) sequence. Mean perfusion was 1.7 +/- 0.6 ml x min(-1) x cm(-3) and was related to vertical height above the dependent lung (slope = -3%/cm, P < 0.0001). Lung density averaged 0.34 +/- 0.08 g/cm3 and was also related to vertical height (slope = -4.9%/cm, P < 0.0001). By contrast, when perfusion was normalized for regional lung density, the slope of the height-perfusion relationship was not significantly different from zero (P = 0.2). This suggests that in vivo variations in regional lung density affect the interpretation of vertical gradients in pulmonary blood flow and is consistent with a simple conceptual model: the lung behaves like a Slinky (Slinky is a registered trademark of Poof-Slinky Incorporated), a deformable spring distorting under its own weight. The greater density of lung tissue in the dependent regions of the lung is analogous to a greater number of coils in the dependent portion of the vertically oriented spring. This implies that measurements of perfusion in vivo will be influenced by density distributions and will differ from excised lungs where density gradients are reduced by processing.
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Affiliation(s)
- Susan R Hopkins
- Department of Medicine, University of California, San Diego, La Jolla, California 92093, USA.
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41
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Chon D, Beck KC, Larsen RL, Shikata H, Hoffman EA. Regional pulmonary blood flow in dogs by 4D-X-ray CT. J Appl Physiol (1985) 2006; 101:1451-65. [PMID: 16825517 DOI: 10.1152/japplphysiol.01131.2005] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
ECG-triggered computed tomography (CT) was used during passage of iodinated contrast to determine regional pulmonary blood flow (PBF) in anesthetized prone/supine dogs. PBF was evaluated as a function of height within the lung (supine and prone) as a function of various normalization methods: raw unit volume data (PBFraw) or PBF normalized to regional fraction air (PBFair), fractional non-air (PBFgm), or relative number of alveoli (PBFalv). The coefficient of variation of PBFraw, PBFair, PBFalv, and PBFgm ranged between 30 and 50% in both lungs and both body postures. The position of maximal flow along the height of the lung (MFP) was calculated for PBFraw, PBFair, PBFalv, and PBFgm. Only PBFgm showed a significantly different MFP height supine vs. prone (whole lung: 2.60 +/- 1.08 cm supine vs. 5.08 +/- 1.61 cm prone, P < 0.01). Mean slopes (ml/min/gm water content/cm) of PBFgm were steeper supine vs. prone in the right (RL) but not left lung (LL) (RL: -0.65 +/- 0.29 supine vs. -0.26 +/- 0.25 prone, P < 0.02; LL: -0.47 +/- 0.21 supine vs. -0.32 +/- 0.26 prone, P > 0.10). Mean slopes of PBFgm vs. vertical lung height were not different prone vs. supine above this vertical height of MFP (VMFP), but PBFgm slopes were steeper in the supine position below the VMFP in the RL. We conclude that PBFgm distribution was posture dependent in RL but not LL. Support of the heart may play a role. We demonstrate that normalization factors can lead to differing attributions of gravitational effects on PBF heterogeneity.
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Affiliation(s)
- Deokiee Chon
- Department of Radiology, University of Iowa College of Medicine, Iowa City, IA 52242, USA
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42
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Burrowes KS, Tawhai MH. Computational predictions of pulmonary blood flow gradients: gravity versus structure. Respir Physiol Neurobiol 2005; 154:515-23. [PMID: 16386472 DOI: 10.1016/j.resp.2005.11.007] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2005] [Revised: 11/17/2005] [Accepted: 11/19/2005] [Indexed: 11/28/2022]
Abstract
A computational model of blood flow through the human pulmonary arterial tree has been developed to investigate the mechanisms contributing to regional pulmonary perfusion in the isolated network when the lung is in different orientations. The arterial geometric model was constructed using a combination of computed tomography and a volume-filling branching algorithm. Equations governing conservation of mass, momentum, and vessel distension, incorporating gravity, were solved to predict pressure, flow, and vessel radius. Analysis of results in the upright posture, with and without gravity, and in the inverted, prone, and supine postures reveals significant flow heterogeneity and a persistent decrease in flow in the cranial and caudal regions for all postures suggesting that vascular geometry makes a major contribution to regional flow with gravity having a lesser role. Results in the isolated arterial tree demonstrate that the vascular path lengths and therefore the positioning of the pulmonary trunk relative to the rest of the network play a significant role in the determination of flow.
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Affiliation(s)
- Kelly S Burrowes
- Bioengineering Institute, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
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43
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Burrowes KS, Hunter PJ, Tawhai MH. Investigation of the relative effects of vascular branching structure and gravity on pulmonary arterial blood flow heterogeneity via an image-based computational model. Acad Radiol 2005; 12:1464-74. [PMID: 16253859 DOI: 10.1016/j.acra.2005.06.004] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Revised: 06/07/2005] [Accepted: 06/07/2005] [Indexed: 11/22/2022]
Abstract
RATIONALE AND OBJECTIVES A computational model of blood flow through the human pulmonary arterial tree has been developed to investigate the relative influence of branching structure and gravity on blood flow distribution in the human lung. MATERIALS AND METHODS Geometric models of the largest arterial vessels and lobar boundaries were first derived using multidetector row x-ray computed tomography (MDCT) scans. Further accompanying arterial vessels were generated from the MDCT vessel endpoints into the lobar volumes using a volume-filling branching algorithm. Equations governing the conservation of mass and momentum were solved within the geometric model to calculate pressure, velocity, and vessel radius. Blood flow results in the anatomically based model, with and without gravity, and in a symmetric geometric model were compared to investigate their relative contributions to blood flow heterogeneity. RESULTS Results showed a persistent blood flow gradient and flow heterogeneity in the absence of gravitational forces in the anatomically based model. Comparison with flow results in the symmetric model revealed that the asymmetric vascular branching structure was largely responsible for producing this heterogeneity. Analysis of average results in varying slice thicknesses illustrated a clear flow gradient because of gravity in "lower resolution" data (thicker slices), but on examination of higher resolution data, a trend was less obvious. CONCLUSIONS Results suggest that although gravity does influence flow distribution, the influence of the tree branching structure is also a dominant factor. These results are consistent with high-resolution experimental studies that have demonstrated gravity to be only a minor determinant of blood flow distribution.
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Affiliation(s)
- Kelly S Burrowes
- Bioengineering Institute, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
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Montmerle S, Sundblad P, Linnarsson D. Residual heterogeneity of intra- and interregional pulmonary perfusion in short-term microgravity. J Appl Physiol (1985) 2005; 98:2268-77. [PMID: 15718403 DOI: 10.1152/japplphysiol.01268.2004] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We hypothesized that the perfusion heterogeneity in the human, upright lung is determined by nongravitational more than gravitational factors. Twelve and six subjects were studied during two series of parabolic flights. We used cardiogenic oscillations of O2/SF6 as an indirect estimate of intraregional perfusion heterogeneity ( series 1) and phase IV amplitude (P4) as a indirect estimate of interregional perfusion heterogeneity ( series 2). A rebreathing-breath holding-expiration maneuver was performed. In flight, breath holding and expiration were performed either in microgravity (0 G) or in hypergravity. Controls were performed at normal gravity (1 G). In series 1, expiration was performed at 0 G. Cardiogenic oscillations of O2/SF6 were 19% lower when breath holding was performed at 0 G than when breath holding was performed at 1 G [means (SD): 1.7 (0.3) and 2.3 (0.6)% units] ( P = 0.044). When breath holding was performed at 1.8 G, values did not differ from 1-G control [2.6 (0.8)% units, P = 0.15], but they were 17% larger at 1.8 G than at 1 G. In series 2, expiration was performed at 1.7 G. P4 changed with gravity ( P < 0.001). When breath holding was performed at 0 G, P4 values were 45 (46)% of control. When breath holding was performed at 1.7 G, P4 values were 183 (101)% of control. We conclude that more than one-half of indexes of perfusion heterogeneity at 1 G are caused by nongravitational mechanisms.
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Affiliation(s)
- Stéphanie Montmerle
- Dept. of Physiology and Pharmacology, Section of Environmental Physiology, Karolinska Institutet, Berzelius väg 13, SE-171 77 Stockholm, Sweden.
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45
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Hoste EAJ, Roosens CDVK, Bracke S, Decruyenaere JMA, Benoit DD, Vandewoude KHDK, Colardyn FA. Acute effects of upright position on gas exchange in patients with acute respiratory distress syndrome. J Intensive Care Med 2005; 20:43-9. [PMID: 15665259 DOI: 10.1177/0885066604271616] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Patients with acute respiratory distress syndrome (ARDS) have dorsal atelectasis of the lungs. This is probably caused by several mechanisms: compression on dependent lung zones, purulent secretions in alveoli, and upward shift of the diaphragm. An upright position (UP) of the patient (the whole body in a straight line at 40 to 45 degrees) can theoretically ameliorate these mechanisms. The objective was to evaluate whether there was an improvement of gas exchange during UP of ARDS patients and to evaluate the hemodynamic effects. A prospective interventional study was performed in the surgical and medical ICUs and the burn unit of the Ghent University Hospital, a tertiary care center. Included were ARDS patients with onset of ARDS within 48 hours before start of the study. Patients were excluded when there was hemodynamic instability or when the PaO2/FiO2 ratio deteriorated during the 2 hours preceding UP. After a 2-hour observation period in a semirecumbent position, patients were put in UP for 12 hours. Respiration and hemodynamic data were recorded at the start and end of the 2-hour observation period, and after 1, 4, and 12 hours in UP. Eighteen patients were included in the study. There was a significant increase of the PaO2/FiO2 ratio during UP (P < .001). Except for the need for volume resuscitation in 5 patients (27.8%), there was no significant change in the hemodynamic profile of the patients. Upright positioning of patients with ARDS, a relatively simple maneuver, resulted in an improvement of gas exchange and was tolerated hemodynamically relatively well during a 12-hour observation period.
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Affiliation(s)
- Eric A J Hoste
- Intensive Care Unit, Ghent University Hospital, Ghent, Belgium.
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46
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Peces-Barba G, Rodríguez-Nieto MJ, Verbanck S, Paiva M, González-Mangado N. Lower pulmonary diffusing capacity in the prone vs. supine posture. J Appl Physiol (1985) 2004; 96:1937-42. [PMID: 15075314 DOI: 10.1152/japplphysiol.00255.2003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We evaluated the effect of prone positioning on gas-transfer characteristics in normal human subjects. Single-breath (SB) and rebreathing (RB) maneuvers were employed to assess carbon monoxide diffusing capacity (DlCO), its components related to capillary blood volume (Vc) and membrane diffusing capacity (Dm), pulmonary tissue volume (Vti), and cardiac output (Qc). Alveolar volume (Va) was significantly greater prone than supine, irrespective of the test maneuver used. Nevertheless, Dl(CO) was consistently lower prone than supine, a difference that was enhanced when appropriately corrected for the higher Va prone. When adequately corrected for Va, diffusing capacity significantly decreased by 8% from supine to prone [SB: Dl(CO,corr) supine vs. prone: 32.6 +/- 2.3 (SE) vs. 30.0 +/- 2 ml x min(-1) x mmHg(-1) stpd; RB: Dl(CO,corr) supine vs. prone: 30.2 +/- 2.2 (SE) vs. 27.8 +/- 2.0 ml x min(-1) x mmHg(-1) stpd]. Both Vc and Dm showed a tendency to decrease from supine to prone, but neither reached significance. Finally, there were no significant differences in Vti or Qc between supine and prone. We interpret the lower diffusing capacity of the healthy lung in the prone posture based on the relatively larger space occupied by the heart in the dependent lung zones, leaving less space for zone 3 capillaries, and on the relatively lower position of the heart, leaving the zone 3 capillaries less engorged.
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Affiliation(s)
- G Peces-Barba
- Pulmonary Department, Fundación Jiménez Díaz, Universidad Autónoma, 28040 Madrid, Spain
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47
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Petersson J, Sánchez-Crespo A, Rohdin M, Montmerle S, Nyrén S, Jacobsson H, Larsson SA, Lindahl SGE, Linnarsson D, Glenny RW, Mure M. Physiological evaluation of a new quantitative SPECT method measuring regional ventilation and perfusion. J Appl Physiol (1985) 2003; 96:1127-36. [PMID: 14617523 DOI: 10.1152/japplphysiol.00092.2003] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have developed a new quantitative single-photon-emission computed tomography (SPECT) method that uses (113m)In-labeled albumin macroaggregates and Technegas ((99m)Tc) to estimate the distributions of regional ventilation and perfusion for the whole lung. The multiple inert-gas elimination technique (MIGET) and whole lung respiratory gas exchange were used as physiological evaluations of the SPECT method. Regional ventilation and perfusion were estimated by SPECT in nine healthy volunteers during awake, spontaneous breathing. Radiotracers were administered with subjects sitting upright, and SPECT images were acquired with subjects supine. Whole lung gas exchange of MIGET gases and arterial Po(2) and Pco(2) gases was predicted from estimates of regional ventilation and perfusion. We found a good agreement between measured and SPECT-predicted exchange of MIGET and respiratory gases. Correlations (r(2)) between SPECT-predicted and measured inert-gas excretions and retentions were 0.99. The method offers a new tool for measuring regional ventilation and perfusion in humans.
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Affiliation(s)
- Johan Petersson
- Department of Anesthesiology and Intensive Care, Karolinska Hospital, Stockholm, Sweden.
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Won C, Chon D, Tajik J, Tran BQ, Robinswood GB, Beck KC, Hoffman EA. CT-based assessment of regional pulmonary microvascular blood flow parameters. J Appl Physiol (1985) 2003; 94:2483-93. [PMID: 12588787 DOI: 10.1152/japplphysiol.00688.2002] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To determine regional pulmonary microvascular mean transit times (MTTs), we used electrocardiogram-gated X-ray computed tomographic imaging to follow bolus radiopaque contrast material through the lungs in anesthetized animals (7 dogs and 1 pig, prone and supine). By deconvolution/reconvolution of regional time-attenuation curves obtained from parenchyma and large lobar arteries, we estimated the microvascular residue function and reconstituted the regional microvascular time-attenuation curves and, thus, regional microvascular MTTs. The mean microvascular MTTs in the supine and prone postures were 3.94 +/- 1.0 and 3.40 +/- 0.84 (mean +/- SD), respectively. The dependent-nondependent vertical gradient of MTT was greater in the supine [slope = 0.25 +/- 0.10 (SD), P < 0.001 by t-test] than in the prone (-0.03 +/- 0.06 in 6 of 8 animals; 2 outliers had positive slopes) posture. In both postures, there was a trend toward faster transit times in the dorsal-basal lung region in six of the eight animals, suggesting gravity-independent higher vascular conductance dorsocaudally. We conclude that deconvolution methods, in association with electrocardiogram-gated high-speed X-ray computed tomography, can provide insights into regional heterogeneity of pulmonary microvascular MTT in vivo.
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Affiliation(s)
- Chulho Won
- Department of Radiology, University of Iowa, Iowa City, Iowa 52241, USA
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Musch G, Layfield JDH, Harris RS, Melo MFV, Winkler T, Callahan RJ, Fischman AJ, Venegas JG. Topographical distribution of pulmonary perfusion and ventilation, assessed by PET in supine and prone humans. J Appl Physiol (1985) 2002; 93:1841-51. [PMID: 12381773 DOI: 10.1152/japplphysiol.00223.2002] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Using positron emission tomography (PET) and intravenously injected (13)N(2), we assessed the topographical distribution of pulmonary perfusion (Q) and ventilation (V) in six healthy, spontaneously breathing subjects in the supine and prone position. In this technique, the intrapulmonary distribution of (13)N(2), measured during a short apnea, is proportional to regional Q. After resumption of breathing, regional specific alveolar V (sVA, ventilation per unit of alveolar gas volume) can be calculated from the tracer washout rate. The PET scanner imaged 15 contiguous, 6-mm-thick, slices of lung. Vertical gradients of Q and sVA were computed by linear regression, and spatial heterogeneity was assessed from the squared coefficient of variation (CV(2)). Both CV and CV were corrected for the estimated contribution of random imaging noise. We found that 1) both Q and V had vertical gradients favoring dependent lung regions, 2) vertical gradients were similar in the supine and prone position and explained, on average, 24% of Q heterogeneity and 8% of V heterogeneity, 3) CV was similar in the supine and prone position, and 4) CV was lower in the prone position. We conclude that, in recumbent, spontaneously breathing humans, 1) vertical gradients favoring dependent lung regions explain a significant fraction of heterogeneity, especially of Q, and 2) although Q does not seem to be systematically more homogeneous in the prone position, differences in individual behaviors may make the prone position advantageous, in terms of V-to-Q matching, in selected subjects.
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Affiliation(s)
- Guido Musch
- Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
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50
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Cordingley JJ, Keogh BF. The pulmonary physician in critical care. 8: Ventilatory management of ALI/ARDS. Thorax 2002; 57:729-34. [PMID: 12149536 PMCID: PMC1746415 DOI: 10.1136/thorax.57.8.729] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Current data relating to ventilation in ARDS are reviewed. Recent studies suggest that reduced mortality may be achieved by using a strategy which aims at preventing overdistension of lungs.
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Affiliation(s)
- J J Cordingley
- Department of Anaesthesia and Intensive Care, Royal Brompton Hospital, London SW3 6NP, UK
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