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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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2
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McNicholas BA, Ibarra-Estrada M, Perez Y, Li J, Pavlov I, Kharat A, Vines DL, Roca O, Cosgrave D, Guerin C, Ehrmann S, Laffey JG. Awake prone positioning in acute hypoxaemic respiratory failure. Eur Respir Rev 2023; 32:32/168/220245. [PMID: 37137508 PMCID: PMC10155045 DOI: 10.1183/16000617.0245-2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Accepted: 02/22/2023] [Indexed: 05/05/2023] Open
Abstract
Awake prone positioning (APP) of patients with acute hypoxaemic respiratory failure gained considerable attention during the early phases of the coronavirus disease 2019 (COVID-19) pandemic. Prior to the pandemic, reports of APP were limited to case series in patients with influenza and in immunocompromised patients, with encouraging results in terms of tolerance and oxygenation improvement. Prone positioning of awake patients with acute hypoxaemic respiratory failure appears to result in many of the same physiological changes improving oxygenation seen in invasively ventilated patients with moderate-severe acute respiratory distress syndrome. A number of randomised controlled studies published on patients with varying severity of COVID-19 have reported apparently contrasting outcomes. However, there is consistent evidence that more hypoxaemic patients requiring advanced respiratory support, who are managed in higher care environments and who can be prone for several hours, benefit most from APP use. We review the physiological basis by which prone positioning results in changes in lung mechanics and gas exchange and summarise the latest evidence base for APP primarily in COVID-19. We examine the key factors that influence the success of APP, the optimal target populations for APP and the key unknowns that will shape future research.
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Affiliation(s)
- Bairbre A McNicholas
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospital, Saolta Hospital Group, Galway, Ireland
- School of Medicine, University of Galway, Galway, Ireland
| | - Miguel Ibarra-Estrada
- Unidad de Terapia Intensiva, Hospital Civil Fray Antonio Alcalde, Guadalajara, Jalisco, Mexico
| | - Yonatan Perez
- Clinical Investigation Center, INSERM 1415, CHRU Tours, Tours, France
- Médecine Intensive Réanimation, CHRU Tours, Tours, France
- Médecine Intensive Réanimation, Hôpital de Hautepierre, Hôpitaux universitaires de Strasbourg, Strasbourg, France
| | - Jie Li
- Department of Cardiopulmonary Sciences, Division of Respiratory Care, Rush University, Chicago, IL, USA
| | - Ivan Pavlov
- Department of Emergency Medicine, Hôpital de Verdun, Montréal, QC, Canada
| | - Aileen Kharat
- Department of Respiratory Medicine, Geneva University Hospital, Geneva, Switzerland
| | - David L Vines
- Department of Cardiopulmonary Sciences, Division of Respiratory Care, Rush University, Chicago, IL, USA
| | - Oriol Roca
- Servei de Medicina Intensiva, Parc Taulí Hospital Universitari, Sabadell, Spain
- Departament de Medicina, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - David Cosgrave
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospital, Saolta Hospital Group, Galway, Ireland
- School of Medicine, University of Galway, Galway, Ireland
| | - Claude Guerin
- University of Lyon, Lyon and INSERM 955, Créteil, France
| | - Stephan Ehrmann
- Clinical Investigation Center, INSERM 1415, CHRU Tours, Tours, France
- Médecine Intensive Réanimation, CHRU Tours, Tours, France
| | - John G Laffey
- Department of Anaesthesia and Intensive Care Medicine, Galway University Hospital, Saolta Hospital Group, Galway, Ireland
- School of Medicine, University of Galway, Galway, Ireland
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3
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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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4
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Trachsel D, Erb TO, Hammer J, von Ungern‐Sternberg BS. Developmental respiratory physiology. Paediatr Anaesth 2022; 32:108-117. [PMID: 34877744 PMCID: PMC9135024 DOI: 10.1111/pan.14362] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 12/02/2021] [Accepted: 12/05/2021] [Indexed: 12/25/2022]
Abstract
Various developmental aspects of respiratory physiology put infants and young children at an increased risk of respiratory failure, which is associated with a higher rate of critical incidents during anesthesia. The immaturity of control of breathing in infants is reflected by prolonged central apneas and periodic breathing, and an increased risk of apneas after anesthesia. The physiology of the pediatric upper and lower airways is characterized by a higher flow resistance and airway collapsibility. The increased chest wall compliance and reduced gas exchange surface of the lungs reduce the pulmonary oxygen reserve vis-à-vis a higher metabolic oxygen demand, which causes more rapid oxygen desaturation when ventilation is compromised. This review describes the various developmental aspects of respiratory physiology and summarizes anesthetic implications.
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Affiliation(s)
- Daniel Trachsel
- Pediatric Intensive Care and PulmonologyUniversity Children’s Hospital of Basel UKBBBaselSwitzerland
| | - Thomas O. Erb
- Department AnesthesiologyUniversity Children’s Hospital of Basel UKBBBaselSwitzerland
| | - Jürg Hammer
- Pediatric Intensive Care and PulmonologyUniversity Children’s Hospital of Basel UKBBBaselSwitzerland
| | - Britta S. von Ungern‐Sternberg
- Department of Anaesthesia and Pain ManagementPerth Children’s HospitalPerthWAAustralia,Division of Emergency Medicine, Anaesthesia and Pain MedicineMedical SchoolThe University of Western AustraliaPerthWAAustralia,Perioperative Medicine TeamTelethon Kids InstitutePerthWAAustralia
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5
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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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Chan ST, Evans KC, Song TY, Selb J, van der Kouwe A, Rosen BR, Zheng YP, Ahn AC, Kwong KK. Dynamic brain-body coupling of breath-by-breath O2-CO2 exchange ratio with resting state cerebral hemodynamic fluctuations. PLoS One 2020; 15:e0238946. [PMID: 32956397 PMCID: PMC7505589 DOI: 10.1371/journal.pone.0238946] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 08/26/2020] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND The origin of low frequency cerebral hemodynamic fluctuations (CHF) in the resting state remains unknown. Breath-by breath O2-CO2 exchange ratio (bER) has been reported to correlate with the cerebrovascular response to brief breath hold challenge at the frequency range of 0.008-0.03Hz in healthy adults. bER is defined as the ratio of the change in the partial pressure of oxygen (ΔPO2) to that of carbon dioxide (ΔPCO2) between end inspiration and end expiration. In this study, we aimed to investigate the contribution of respiratory gas exchange (RGE) metrics (bER, ΔPO2 and ΔPCO2) to low frequency CHF during spontaneous breathing. METHODS Twenty-two healthy adults were included. We used transcranial Doppler sonography to evaluate CHF by measuring the changes in cerebral blood flow velocity (ΔCBFv) in bilateral middle cerebral arteries. The regional CHF were mapped with blood oxygenation level dependent (ΔBOLD) signal changes using functional magnetic resonance imaging. Temporal features and frequency characteristics of RGE metrics during spontaneous breathing were examined, and the simultaneous measurements of RGE metrics and CHF (ΔCBFv and ΔBOLD) were studied for their correlation. RESULTS We found that the time courses of ΔPO2 and ΔPCO2 were interdependent but not redundant. The oscillations of RGE metrics were coherent with resting state CHF at the frequency range of 0.008-0.03Hz. Both bER and ΔPO2 were superior to ΔPCO2 in association with CHF while CHF could correlate more strongly with bER than with ΔPO2 in some brain regions. Brain regions with the strongest coupling between bER and ΔBOLD overlapped with many areas of default mode network including precuneus and posterior cingulate. CONCLUSION Although the physiological mechanisms underlying the strong correlation between bER and CHF are unclear, our findings suggest the contribution of bER to low frequency resting state CHF, providing a novel insight of brain-body interaction via CHF and oscillations of RGE metrics.
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Affiliation(s)
- Suk-tak Chan
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Karleyton C. Evans
- Department of Psychiatry, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Tian-yue Song
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Juliette Selb
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Andre van der Kouwe
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Bruce R. Rosen
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Yong-ping Zheng
- Department of Biomedical Engineering, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region, China
| | - Andrew C. Ahn
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Kenneth K. Kwong
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
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7
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Chan ST, Evans KC, Song TY, Selb J, van der Kouwe A, Rosen BR, Zheng YP, Ahn A, Kwong KK. Cerebrovascular reactivity assessment with O2-CO2 exchange ratio under brief breath hold challenge. PLoS One 2020; 15:e0225915. [PMID: 32208415 PMCID: PMC7092994 DOI: 10.1371/journal.pone.0225915] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2019] [Accepted: 02/27/2020] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Hypercapnia during breath holding is believed to be the dominant driver behind the modulation of cerebral blood flow (CBF). However, increasing evidence show that mild hypoxia and mild hypercapnia in breath hold (BH) could work synergistically to enhance CBF response. We hypothesized that breath-by-breath O2-CO2 exchange ratio (bER), defined as the ratio of the change in partial pressure of oxygen (ΔPO2) to that of carbon dioxide (ΔPCO2) between end inspiration and end expiration, would be able to better correlate with the global and regional cerebral hemodynamic responses (CHR) to BH challenge. We aimed to investigate whether bER is a more useful index than end-tidal PCO2 to characterize cerebrovascular reactivity (CVR) under BH challenge. METHODS We used transcranial Doppler ultrasound (TCD) to evaluate CHR under BH challenge by measuring cerebral blood flow velocity (CBFv) in the middle cerebral arteries. Regional changes in CHR to BH and exogenous CO2 challenges were mapped with blood oxygenation level dependent (BOLD) signal changes using functional magnetic resonance imaging (fMRI). We correlated respiratory gas exchange (RGE) metrics (bER, ΔPO2, ΔPCO2, end-tidal PCO2 and PO2, and time of breaths) with CHR (CBFv and BOLD) to BH challenge. Temporal features and frequency characteristics of RGE metrics and their coherence with CHR were examined. RESULTS CHR to brief BH epochs and free breathing were coupled with both ΔPO2 and ΔPCO2. We found that bER was superior to either ΔPO2 or ΔPCO2 alone in coupling with the changes of CBFv and BOLD signals under breath hold challenge. The regional CVR results derived by regressing BOLD signal changes on bER under BH challenge resembled those derived by regressing BOLD signal changes on end-tidal PCO2 under exogenous CO2 challenge. CONCLUSION Our findings provide a novel insight on the potential of using bER to better quantify CVR changes under BH challenge.
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Affiliation(s)
- Suk-tak Chan
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Karleyton C. Evans
- Department of Psychiatry, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Tian-yue Song
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
- Department of Psychiatry, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Juliette Selb
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Andre van der Kouwe
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Bruce R. Rosen
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Yong-ping Zheng
- Department of Biomedical Engineering, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region, China
| | - Andrew Ahn
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
| | - Kenneth K. Kwong
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States of America
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Dentice RL, Elkins MR, Verschuer J, Eberl S, Dwyer G, Bye PTP. Side lying during nebulisation can significantly improve apical deposition in healthy adults and adults with mild cystic fibrosis lung disease: a randomised crossover trial. BMC Pulm Med 2019; 19:128. [PMID: 31311524 PMCID: PMC6636004 DOI: 10.1186/s12890-019-0886-7] [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: 01/08/2019] [Accepted: 06/25/2019] [Indexed: 11/17/2022] Open
Abstract
Background In people with and without Cystic Fibrosis (CF), does side lying during nebulisation change: the proportion of the dose loaded in the nebuliser that is deposited in the lungs; the uniformity of deposition throughout the lungs; or the apical drug density as a percentage of the drug density in the remaining lung? Do these effects differ depending on the degree of lung disease present? Methods A randomised crossover trial with concealed allocation, intention-to-treat analysis and blinded assessors, involving 39 adults: 13 healthy, 13 with mild CF lung disease (FEV1 > 80%pred), and 13 with more advanced CF lung disease (FEV1 < 80%pred). In random order, 4 mL of nebulised radioaerosol was inhaled in upright sitting and in alternate right and left side lying at 2-min intervals, for 20 min. Results Compared to sitting upright, lung deposition and the uniformity of deposition were not significantly altered by side lying in any of the three groups. In sitting, the density of the deposition was significantly less in the apical regions than in the rest of the lung in all participants. Side lying significantly improved apical deposition in healthy adults (MD, 13%; 95% CI, 7 to 19), and in minimal CF lung disease (MD, 4%; 95% CI, 1 to 7) but not in advanced disease (MD, 4%; 95% CI, − 2 to 9). Conclusion Alternating between right and left side lying during nebulisation significantly improves apical deposition in healthy adults and in adults with mild CF lung disease, without substantial detriment to overall deposition. Trial registration ACTRN12611000674932 (Healthy), ACTRN12611000672954 (CF) Retrospectively registered 4/7/2011. Electronic supplementary material The online version of this article (10.1186/s12890-019-0886-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Ruth L Dentice
- Physiotherapy Department, Royal Prince Alfred Hospital, Sydney, Australia.
| | - Mark R Elkins
- Centre for Education & Workforce Development, Sydney Local Health District, Sydney, Australia.,Sydney Medical School, University of Sydney, Sydney, Australia
| | - Jordan Verschuer
- Department of Molecular Imaging, Royal Prince Alfred Hospital, Sydney, Australia
| | - Stefan Eberl
- Department of Molecular Imaging, Royal Prince Alfred Hospital, Sydney, Australia
| | - Genevieve Dwyer
- Physiotherapy Program, Western Sydney University, Sydney, Australia.
| | - Peter T P Bye
- Sydney Medical School, University of Sydney, Sydney, Australia.,Department of Respiratory Medicine, Royal Prince Alfred Hospital, Sydney, Australia
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9
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Dentice RL, Elkins MR, Dwyer GM, Bye PTP. The use of an alternate side lying positioning strategy during inhalation therapy does not prolong nebulisation time in adults with Cystic Fibrosis: a randomised crossover trial. BMC Pulm Med 2018; 18:3. [PMID: 29310638 PMCID: PMC5759805 DOI: 10.1186/s12890-017-0568-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 12/21/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Inhalation of nebulised medications is performed in upright sitting to maximise lung volumes. The pattern of deposition is poor for inhaled medications in people with Cystic Fibrosis. The pattern tends to be non-uniform and typically the upper lobes receive a reduced dose compared to the rest of the lung. One strategy that has been proposed as having the potential to improve homogeneity of deposition is to adopt an alternate side lying position for the inhalation procedure. This study sought to determine whether, among adults with Cystic Fibrosis, there is any disadvantage to delivery time of nebulised medications with a strategy of alternate side lying, compared to upright sitting. METHODS A randomised crossover trial with concealed allocation, intention-to-treat analysis and blinded assessors was undertaken. The participants were 24 adults with stable Cystic Fibrosis. They inhaled 4 mL of normal saline via an LC Star™ nebuliser twice within 24 h. In random order, participants sat upright throughout nebulisation, or alternated between left and right side lying at each minute during the nebulisation period. The nebuliser was stopped and weighed each minute until the residual volume was reached. The primary outcome was the time required for 3.5 mL to be delivered. The secondary outcomes were: respiratory rate; ratio of the volume delivered on right and left sides; and calculation of how long the periods in side lying can be extended without causing greater than 20% discrepancy in dose delivered in the two positions. RESULTS The delivery time did not significantly differ between sitting and side lying (mean difference 0.58 min, 95% confidence interval (CI) -1.40 to 0.24). There was no significant correlation between delivery time, lung function or subject height (all R2 < 0.4). Increasing side lying duration from 1 to 2 min did not significantly impact the dose delivered on each side. Turning each 3 min however, significantly worsened the disparity (mean ratio 1.32, 95% CI 1.24 to 1.40). CONCLUSION Side lying during inhalation therapy does not prolong nebulisation time. 2-min periods should provide an equal dose in the two side lying positions. TRIAL REGISTRATION Prospectively registered on 4 July 2011; ACTRN12611000672954 .
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Affiliation(s)
- Ruth L Dentice
- Physiotherapy Department, Royal Prince Alfred Hospital, Sydney, Australia
| | - Mark R Elkins
- Sydney Medical School, University of Sydney, Sydney, Australia.,Centre for Education & Workforce Development, Sydney Local Health District, Sydney, Australia
| | - Genevieve M Dwyer
- Physiotherapy Program, Western Sydney University, Sydney, Australia.
| | - Peter T P Bye
- Sydney Medical School, University of Sydney, Sydney, Australia.,Department of Respiratory & Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia
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10
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Felloni P, Duhamel A, Faivre JB, Giordano J, Khung S, Deken V, Remy J, Remy-Jardin M. Regional Distribution of Pulmonary Blood Volume with Dual-Energy Computed Tomography: Results in 42 Subjects. Acad Radiol 2017; 24:1412-1421. [PMID: 28711443 DOI: 10.1016/j.acra.2017.05.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 04/27/2017] [Accepted: 05/10/2017] [Indexed: 10/19/2022]
Abstract
RATIONALE AND OBJECTIVES The noninvasive approach of lung perfusion generated from dual-energy computed tomography acquisitions has entered clinical practice. The purpose of this study was to analyze the regional distribution of iodine within distal portions of the pulmonary arterial bed on dual-source, dual-energy computed tomography examinations in a cohort of subjects without cardiopulmonary pathologies. MATERIALS AND METHODS The study population included 42 patients without cardiorespiratory disease, enabling quantitative and qualitative analysis of pulmonary blood volume after administration of a 40% contrast agent. Qualitative analysis was based on visual assessment. Quantitative analysis was obtained after semiautomatic division of each lung into 18 areas. RESULTS The iodine concentration did not significantly differ between the right (R) and left (L) lungs (P = .49), with a mean attenuation of 41.35 Hounsfield units (HU) and 41.14 HU, respectively. Three regional gradients of attenuation were observed between: (a) lung bases and apices (P < .001), linked to the conditions of examination (mean Δ: 6.23 in the R lung; 5.96 in the L lung); (b) posterior and anterior parts of the lung (P < .001) due to gravity (mean Δ: 11.92 in the R lung ; 15.93 in the L lung); and (c) medullary and cortical lung zones (P < .001) (mean Δ: 9.35 in the R lung ; 8.37 in the L lung). The intensity of dependent-nondependent (r = 0.42; P < .001) and corticomedullary (r = 0.58; P < .0001) gradients was correlated to the overall iodine concentration. CONCLUSION Distribution of pulmonary blood volume is influenced by physiological gradients and scanning conditions.
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Trachsel D, Svendsen J, Erb T, von Ungern-Sternberg B. Effects of anaesthesia on paediatric lung function. Br J Anaesth 2016; 117:151-63. [DOI: 10.1093/bja/aew173] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
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12
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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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13
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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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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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15
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Abstract
Management of acute respiratory failure is an important component of intensive care. In this review, we analyze 21 original research articles published last year in Critical Care in the field of respiratory and critical care medicine. The articles are summarized according to the following topic categories: acute respiratory distress syndrome, mechanical ventilation, adjunctive therapies, and pneumonia.
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Clark AR, Tawhai MH, Hoffman EA, Burrowes KS. The interdependent contributions of gravitational and structural features to perfusion distribution in a multiscale model of the pulmonary circulation. J Appl Physiol (1985) 2011; 110:943-55. [PMID: 21292845 DOI: 10.1152/japplphysiol.00775.2010] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Recent experimental and imaging studies suggest that the influence of gravity on the measured distribution of blood flow in the lung is largely through deformation of the parenchymal tissue. To study the contribution of hydrostatic effects to regional perfusion in the presence of tissue deformation, we have developed an anatomically structured computational model of the pulmonary circulation (arteries, capillaries, veins), coupled to a continuum model of tissue deformation, and including scale-appropriate fluid dynamics for blood flow in each vessel type. The model demonstrates that both structural and the multiple effects of gravity on the pulmonary circulation make a distinct contribution to the distribution of blood. It shows that postural differences in perfusion gradients can be explained by the combined effect of tissue deformation and extra-acinar blood vessel resistance to flow in the dependent tissue. However, gravitational perfusion gradients persist when the effect of tissue deformation is eliminated, highlighting the importance of the hydrostatic effects of gravity on blood distribution in the pulmonary circulation. Coupling of large- and small-scale models reveals variation in microcirculatory driving pressures within isogravitational planes due to extra-acinar vessel resistance. Variation in driving pressures is due to heterogeneous large-vessel resistance as a consequence of geometric asymmetry in the vascular trees and is amplified by the complex balance of pressures, distension, and flow at the microcirculatory level.
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Affiliation(s)
- A R Clark
- Auckland Bioengineering Institute, Univ. of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand.
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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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Bein T, Ploner F, Ritzka M, Pfeifer M, Schlitt HJ, Graf BM. No change in the regional distribution of tidal volume during lateral posture in mechanically ventilated patients assessed by electrical impedance tomography. Clin Physiol Funct Imaging 2010; 30:234-40. [PMID: 20491842 PMCID: PMC2913102 DOI: 10.1111/j.1475-097x.2010.00933.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We assessed the distribution of regional lung ventilation during moderate and steep lateral posture using electrical impedance tomography (EIT) in mechanically ventilated patients. Seven patients were placed on a kinetic treatment table. An elastic belt containing 16 electrodes was placed around the chest and was connected to the EIT device. Patients were moved to left and right lateral positions in a stepwise (10°) mode up to 60°. EIT images [arbitrary units (AU)] were generated and scanned for assessment of relative ventilation distribution changes [tidal volume (VT)]. A calibration procedure of arbitrary units (AUs) versus ventilator-derived VT performed in all patients during three predefined positions (supine, 60°-left dependent and 60°-right-dependent) showed a significant correlation between VT in supine, left and right lateral positions with the corresponding AUs (r2 = 0·356, P<0·05). Changes in VT were calculated and compared to supine position, and specific regions of interest (ROIs) were analysed. In our study, in contrast to recent findings, a change in lateral positions did not induce a significant change in regional tidal volume distribution. In right lateral positions, a broader variation of VT with a trend towards an increase in the dependently positioned lung was observed in comparison with supine. Lateral positioning promotes the redistribution of ventilation to the ventral regions of the lung. The use of EIT technology might become a helpful tool for understanding and guiding posture therapy in mechanically ventilated patients.
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Affiliation(s)
- Thomas Bein
- Department of Anesthesiology, Regensburg University Hospital, Regensburg, Germany.
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19
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The effects of intraoperative positioning on patients undergoing early definitive care for femoral shaft fractures. J Orthop Trauma 2009; 23:615-21. [PMID: 19897981 DOI: 10.1097/bot.0b013e3181a6a941] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVES To determine if there is a difference in morbidity and mortality in orthopaedic trauma patients with femoral shaft fractures undergoing early definitive care with intramedullary (IM) nails in the supine versus the lateral position. DESIGN Retrospective cohort study, single centered. SETTING One level 1 trauma center. PATIENTS Nine hundred eighty-eight patients representing 1027 femoral shaft fractures treated with IM nails were identified through a prospectively gathered database between 1987 and 2006. INTERVENTION Antegrade IM nail insertion with reaming of the femoral canal in either the supine or lateral position. OUTCOME MEASURES Mortality was the primary outcome. Admission to intensive care unit (ICU) was the secondary outcome measure and a surrogate measure of morbidity. Literature review was performed to identify factors shown to contribute to morbidity and mortality in orthopaedic trauma patients. Intraoperative position in either the supine or lateral position was added to this list. Logistic regression analysis was performed to determine the magnitude and effect of the independent variables on each of the study end points. To determine if a more significant trend toward less favorable outcomes was observed with increasing severity of injury, particularly injuries of the chest and thorax, subgroup analysis was performed for all those with a femur fracture and an Injury Severity Score > or =18 and all those with a femur fracture and an Abbreviated Injury Score chest > or =3. RESULTS Intraoperative position in either the supine or lateral position was not a significant predictor of mortality or ICU admission for the original cohort or the subgroup of Injury Severity Score > or =18. However, for the subgroup of Abbreviated Injury Score chest > or =3, intraoperative positioning in the lateral position had a statistically significant protective effect against ICU admission (P = 0.044). CONCLUSIONS For polytrauma patients with femoral shaft fractures, surgical stabilization using IM nails inserted with reaming of the femoral canal in the lateral position is not associated with an increased risk of mortality or ICU admission.
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21
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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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Hopkins SR, Levin DL, Emami K, Kadlecek S, Yu J, Ishii M, Rizi RR. Advances in magnetic resonance imaging of lung physiology. J Appl Physiol (1985) 2006; 102:1244-54. [PMID: 17158249 DOI: 10.1152/japplphysiol.00738.2006] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This review presents an overview of some recent magnetic resonance imaging (MRI) techniques for measuring aspects of local physiology in the lung. MRI is noninvasive, relatively high resolution, and does not expose subjects to ionizing radiation. Conventional MRI of the lung suffers from low signal intensity caused by the low proton density and the large degree of microscopic field inhomogeneity that degrades the magnetic resonance signal and interferes with image acquisition. However, in recent years, there have been rapid advances in both hardware and software design, allowing these difficulties to be minimized. This review focuses on some newer techniques that measure regional perfusion, ventilation, gas diffusion, ventilation-to-perfusion ratio, partial pressure of oxygen, and lung water. These techniques include contrast-enhanced and arterial spin-labeling techniques for measuring perfusion, hyperpolarized gas techniques for measuring regional ventilation, and apparent diffusion coefficient and multiecho and gradient echo techniques for measuring proton density and lung water. Some of the major advantages and disadvantages of each technique are discussed. In addition, some of the physiological issues associated with making measurements are discussed, along with strategies for understanding large and complex data sets.
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Affiliation(s)
- Susan R Hopkins
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA.
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23
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Abstract
Functional lung imaging has the potential to offer many new insights into mechanisms of pulmonary disease. While the physiologist has access to a number of techniques to evaluate lung function, such as multiple inert gas elimination technique or the injection of microspheres, these techniques have significant disadvantages, including lack of spatial information or low spatial resolution and, in the case of microspheres, an inability to make measurements in humans. The functional imaging techniques based on magnetic resonance (MR), computed tomography (CT), or positron emission tomography (PET) hold substantial promise. In this article, specific issues related to the MR evaluation of pulmonary blood flow, including quantification of heterogeneity, reliability, and validity of the technique, are discussed to highlight some of the important physiologic issues that affect functional imaging. Additional physiologic considerations include the anatomic partitioning of blood flow, and the effects of posture, breath holding, and exercise. The relationships between these many factors and the collection of regional pulmonary perfusion data are explored.
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Affiliation(s)
- Susan R Hopkins
- Division of Physiology, University of California, San Diego, La Jolla, California, USA.
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24
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Abstract
Recent recognition that artificial ventilation may cause damage to the acutely injured lung has caused renewed interest in ventilation techniques that minimise this potential harm. Many ventilation techniques have proved beneficial in small trials of very specific patient groups, but most have subsequently failed to translate into improved patient outcome in larger trials. An exception to this is 'protective ventilation' using reduced tidal volumes (to lower airway pressure) and increased PEEP (to reduce pulmonary collapse). Results of trials of protective ventilation have been encouraging, and the technique should now be adopted more widely. High frequency ventilation, inverse ratio ventilation, prone positioning and inhaled nitric oxide are all techniques that may be considered when, in spite of optimal artificial ventilation, the patient's gas exchange remains dangerously poor. Under these circumstances, the choice of technique is dependent on their availability, local expertise and individual patient needs.
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Affiliation(s)
- N Malarkkan
- Department of Anaesthesia, St James's University Hospital, Leeds LS9 7TF, UK
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Nitz J, Burke B. A study of the facilitation of respiration in myotonic dystrophy. PHYSIOTHERAPY RESEARCH INTERNATIONAL 2003; 7:228-38. [PMID: 12528578 DOI: 10.1002/pri.262] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND AND PURPOSE Dystrophia myotonica or myotonic dystrophy is a progressive neuromuscular disorder in which patients demonstrate an irregular respiratory pattern and are particularly subject to cardiopulmonary compromise. The aim of the present study was to investigate the effects of both proprioceptive neuromuscular facilitation (PNF) and staged basal expansion (SBE) breathing exercises in subjects with myotonic dystrophy in two different positions: high support sitting and left side-lying. METHOD A randomized, double-blind study design was used. Seven non-congenital myotonic dystrophy subjects took part in the study. Six 'treatment' levels were applied to each subject: resting in high support sitting; resting in left side-lying; PNF of deep breathing in high support sitting; PNF of deep breathing in left side-lying; SBE in high support sitting and SBE in left side-lying. The outcome measures employed were arterial oxygen saturation (SpO2) and heart rate, as measured by oximetry and thoraco-abdominal motion (TAM), and respiratory rate, as measured by a pneumograph. RESULTS The PNF technique was found to be the main contributor to improvement in SpO2 for subjects with myotonic dystrophy, where a 2.2% increase was found in the high support sitting position and a 2.6% increase was found in the left side-lying position. There was an increase of between 377% and 556% in TAM during application of both treatment techniques, in either the high support sitting or left side-lying positions. Respiratory rate declined between 15% and 30% immediately after treatment application and heart rate dropped slightly by between 0.2% and 4.1%. CONCLUSION The present study provides objective evidence that application of these respiratory physiotherapy interventions elicits an improvement in respiratory function in subjects with myotonic dystrophy. Further research into the physiological effects of these techniques could explore the mechanisms responsible for improvement in respiratory indices.
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Affiliation(s)
- Jennifer Nitz
- Department of Physiotherapy, School of Health and Rehabilitation Sciences, University of Queensland, Australia
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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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Chang H, Lai-Fook SJ, Domino KB, Schimmel C, Hildebrandt J, Robertson HT, Glenny RW, Hlastala MP. Spatial distribution of ventilation and perfusion in anesthetized dogs in lateral postures. J Appl Physiol (1985) 2002; 92:745-62. [PMID: 11796689 DOI: 10.1152/japplphysiol.00377.2001] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We aimed to assess the influence of lateral decubitus postures and positive end-expiratory pressure (PEEP) on the regional distribution of ventilation and perfusion. We measured regional ventilation (VA) and regional blood flow (Q) in six anesthetized, mechanically ventilated dogs in the left (LLD) and right lateral decubitus (RLD) postures with and without 10 cmH(2)O PEEP. Q was measured by use of intravenously injected 15-microm fluorescent microspheres, and VA was measured by aerosolized 1-microm fluorescent microspheres. Fluorescence was analyzed in lung pieces approximately 1.7 cm(3) in volume. Multiple linear regression analysis was used to evaluate three-dimensional spatial gradients of Q, VA, the ratio VA/Q, and regional PO(2) (Pr(O(2))) in both lungs. In the LLD posture, a gravity-dependent vertical gradient in Q was observed in both lungs in conjunction with a reduced blood flow and Pr(O(2)) to the dependent left lung. Change from the LLD to the RLD or 10 cmH(2)O PEEP increased local VA/Q and Pr(O(2)) in the left lung and minimized any role of hypoxia. The greatest reduction in individual lung volume occurred to the left lung in the LLD posture. We conclude that lung distortion caused by the weight of the heart and abdomen is greater in the LLD posture and influences both Q and VA, and ultimately gas exchange. In this respect, the smaller left lung was the most susceptible to impaired gas exchange in the LLD posture.
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Affiliation(s)
- Hung Chang
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195, USA
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Keilholz SD, Knight-Scott J, Christopher JM, Mai VM, Berr SS. Gravity-dependent perfusion of the lung demonstrated with the FAIRER arterial spin tagging method. Magn Reson Imaging 2001; 19:929-35. [PMID: 11595364 DOI: 10.1016/s0730-725x(01)00416-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Magnetic resonance imaging of lung perfusion using an arterial spin tagging (AST) sequence called flow sensitive alternating inversion recovery with an extra RF pulse (FAIRER) was performed in the left and right lateral positions in five volunteers. Coronal slices were obtained and the average intensity of each lung was measured. In both positions, an increase in the intensity of the dependent lung was found (229% for left lateral, 40% for right lateral). No change was seen along an isogravitational plane. Lung volumes were measured in each position to account for the compression of the lungs by the heart. This effect was found to be symmetric and did not contribute to the perfusion gradient. This demonstrates that AST is sensitive to gravity-dependent perfusion gradients in the lung.
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Affiliation(s)
- S D Keilholz
- Engineering Physics Program, School of Engineering, University of Virginia, Charlottesville, VA 22908, USA
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Suga K, Ogasaware N, Matsunaga N, Sasai K. Perfusion characteristics of oleic acid--injured canine lung on Gd-DTPA--enhanced dynamic magnetic resonance imaging. Invest Radiol 2001; 36:386-400. [PMID: 11496094 DOI: 10.1097/00004424-200107000-00005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
RATIONALE AND OBJECTIVES We conducted an animal study to describe and interpret the perfusion characteristics of oleic acid (OA)-injured lungs on gadopentetate dimeglumine (Gd-DTPA)-enhanced dynamic perfusion magnetic resonance (MR) imaging. METHODS Fourteen dogs received an intravenous OA infusion in the supine (n = 4), prone (n = 4), and right lateral decubitus (n = 6) positions, and 10 minutes later these animals in the same postures underwent the dynamic MR study. Regional Gd-DTPA kinetics was analyzed by the time-signal intensity (SI) curves and by qualitative functional map images of the mean transit time that was representative of the mean circulation time in the vascular bed and the average cumulative sum of the relative increases in SI representative of Gd-DTPA distribution volume during Gd-DTPA first pass. The results were compared with those in six control animals and in another six animals that underwent the MR study 3 minutes (n = 3) and 60 minutes (n = 3) after OA infusion. The MR findings were correlated with the distribution of lung damage and the infused OA particles as assessed by histology. RESULTS The dynamic MR study showed postural shifts on the gravity-dependent perfusion map of normal lungs. Contrast enhancement during Gd-DTPA first pass in the lung was lower and more heterogeneous in the OA-injured lung models than in controls but was followed by conversely greater and persistent enhancement during the Gd-DTPA redistribution phase. Regardless of the postures for OA infusion, these abnormalities were predominant in the dependent lungs and became more pronounced with time after OA infusion, where more prominent capillary obstruction with OA droplets and alveolar/interstitial edema were histologically observed. On the functional map images, greater mean transit time and the average cumulative sum of the relative increases in SI values were also predominantly distributed in the dependent lungs. CONCLUSIONS Low and heterogeneous enhancement was observed during Gd-DTPA first pass but was followed by persistent enhancement during the Gd-DTPA redistribution phase, and predominant abnormalities in the dependent lungs may be characteristic features of the perfusion of OA-injured lungs. The histological correlations indicate that these abnormalities may reflect OA-induced pathophysiologies associated with capillary OA obstruction, increased vascular resistance, and capillary permeability/extravascular spaces and that lung damage may be gravity dependent.
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Affiliation(s)
- K Suga
- Department of Radiology, Yamaguchi University School of Medicine, Ube, Japan
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Mure M, Nyrén S, Jacobsson H, Larsson SA, Lindahl SG. High continuous positive airway pressure level induces ventilation/perfusion mismatch in the prone position. Crit Care Med 2001; 29:959-64. [PMID: 11378604 DOI: 10.1097/00003246-200105000-00010] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
OBJECTIVE Gas exchange in patients with adult respiratory distress syndrome is influenced by posture. The combined effect of continuous positive airway pressure and posture has not been investigated. We studied the effect of normal spontaneous breathing, and that of continuous positive airway pressure, on ventilation/perfusion distributions in healthy volunteers while they were in supine and prone positions. SETTING Nuclear medicine department in a university hospital. DESIGN Experimental study. SUBJECTS Sixteen healthy volunteers. INTERVENTIONS In the supine or prone position, the subjects inhaled a technetium-labeled aerosol (technetium-99m diethylenetriamine pentaacetic acid) through a tight-fitting mask. Single photon emission computed tomography images of the lungs were obtained. The subjects then received an intravenous injection of technetium-99m-labeled macroaggregates of albumin, and an identical single photon emission computed tomography imaging was performed. In the group that received continuous positive airway pressure, an end-expiratory pressure of 10 cm H2O was applied during both inhalation and injection. MEASUREMENTS AND MAIN RESULTS During spontaneous breathing, ventilation/perfusion distribution assessed by regression analysis was uniform (i.e., not significantly different from zero) both in supine and prone positions, with a slope of -1.5 +/- 3.5%/cm supine and 1.5 +/- 3.5%/cm prone. During continuous positive airway pressure breathing in the supine position, ventilation/perfusion had a slope of -3.4 +/- 2.4 compared with 8.3 +/- 1.1%/cm in the prone position according to analysis of spatial resolution. CONCLUSION There was a less favorable ventilation/perfusion ratio in the prone position when the subjects were exposed to continuous positive airway pressure of 10 cm H2O.
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Affiliation(s)
- M Mure
- Department of Anesthesiology and Intensive Care, Diagnostic Radiology, and Hospital Physics, Karolinska Hospital and Institute, Stockholm, Sweden
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Rice AJ, Scroop GC, Thornton AT, McNaughton NS, Rogers KJ, Chapman MJ, Greville HW, Scicchitano R, Gore CJ. Arterial hypoxaemia in endurance athletes is greater during running than cycling. RESPIRATION PHYSIOLOGY 2000; 123:235-46. [PMID: 11007990 DOI: 10.1016/s0034-5687(00)00174-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The effect of both training discipline and exercise modality on exercise-induced hypoxaemia (EIH) was examined in seven runners and six cyclists during 5 min high intensity treadmill and cycle exercise. There were no significant interactions between training discipline, exercise modality and arterial P(O(2)) (Pa(O(2))) when subject groups were considered separately but when pooled there were significant differences between exercise modalities. After min 2 of exercise arterial hydrogen ion concentration, minute ventilation, alveolar P(O(2)) (PA(O(2))) and Pa(O(2)) were all lower with treadmill running with the largest differential for the latter occurring at min 5 (treadmill, 80.8+/-1.8; cycle, 90.2+/-2.5, mmHg, N=13, P< or = 0.05). At every min of exercise, the differences in Pa(O(2)) between the ergometers were strongly associated with similar differences in PA(O(2)) and alveolar to arterial P(O(2)) (PA(O(2))-Pa(O(2))). It is concluded that the greater EIH with treadmill running is a consequence of the combined effect of a reduced lactic acidosis-induced hyperventilation and greater ventilation-perfusion inequality with this exercise mode.
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Affiliation(s)
- A J Rice
- Department of Thoracic Medicine, Royal Adelaide Hospital, 275 North Terrace, Adelaide, SA, Australia.
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Mure M, Domino KB, Lindahl SG, Hlastala MP, Altemeier WA, Glenny RW. Regional ventilation-perfusion distribution is more uniform in the prone position. J Appl Physiol (1985) 2000; 88:1076-83. [PMID: 10710406 DOI: 10.1152/jappl.2000.88.3.1076] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The arterial blood PO(2) is increased in the prone position in animals and humans because of an improvement in ventilation (VA) and perfusion (Q) matching. However, the mechanism of improved VA/Q is unknown. This experiment measured regional VA/Q heterogeneity and the correlation between VA and Q in supine and prone positions in pigs. Eight ketamine-diazepam-anesthetized, mechanically ventilated pigs were studied in supine and prone positions in random order. Regional VA and Q were measured using fluorescent-labeled aerosols and radioactive-labeled microspheres, respectively. The lungs were dried at total lung capacity and cubed into 603-967 small ( approximately 1.7-cm(3)) pieces. In the prone position the homogeneity of the ventilation distribution increased (P = 0.030) and the correlation between VA and Q increased (correlation coefficient = 0.72 +/- 0.08 and 0.82 +/- 0.06 in supine and prone positions, respectively, P = 0.03). The homogeneity of the VA/Q distribution increased in the prone position (P = 0.028). We conclude that the improvement in VA/Q matching in the prone position is secondary to increased homogeneity of the VA distribution and increased correlation of regional VA and Q.
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Affiliation(s)
- M Mure
- Department of Anesthesiology and Intensive Care, Karolinska Hospital and Institute, SE-171 76 Stockholm, Sweden
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Lamm WJ, Albert RK. Effect of zonal conditions and posture on pulmonary blood flow distribution to subpleural and interior lung. J Appl Physiol (1985) 2000; 88:120-5. [PMID: 10642371 DOI: 10.1152/jappl.2000.88.1.120] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Observations made on vessels seen directly beneath the pleura may not accurately reflect what occurs in vessels located deeper in the interior of the lung. We quantified flow to subpleural and deeper, interior regions under zone 1 or 2 conditions in excised (n = 5) and in vivo (n = 6) rabbit lungs, in the head-up or inverted position. After infusion of radiolabeled microspheres, lungs were dried at alveolar pressure of 25 cmH(2)O and sliced in 1-cm sections along the gravitational plane and in three planes in the dorsal-ventral axis. Regions located <1 mm from the pleural surface were dissected away from the remaining tissue. In both zonal conditions, 1) weight-normalized flow to the interior exceeded that found in subpleural regions; and 2) flow followed the gravitational gradient, with the correlation varying with the scale of measurement. We conclude that flow through subpleural vessels is less than that which occurs deeper in the interior, but the regional distributions of flow and the effects of zonal conditions are similar in the two regions.
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Affiliation(s)
- W J Lamm
- Department of Medicine, University of Washington, Seattle, Washington 98105, USA
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Nyrén S, Mure M, Jacobsson H, Larsson SA, Lindahl SG. Pulmonary perfusion is more uniform in the prone than in the supine position: scintigraphy in healthy humans. J Appl Physiol (1985) 1999; 86:1135-41. [PMID: 10194194 DOI: 10.1152/jappl.1999.86.4.1135] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The main purpose of this study was to find out whether the dominant dorsal lung perfusion while supine changes to a dominant ventral lung perfusion while prone. Regional distribution of pulmonary blood flow was determined in 10 healthy volunteers. The subjects were studied in both prone and supine positions with and without lung distension caused by 10 cmH2O of continuous positive airway pressure (CPAP). Radiolabeled macroaggregates of albumin, rapidly trapped by pulmonary capillaries in proportion to blood flow, were injected intravenously. Tomographic gamma camera examinations (single-photon-emission computed tomography) were performed after injections in the different positions. All data acquisitions were made with the subject in the supine position. CPAP enhanced perfusion differences along the gravitational axis, which was more pronounced in the supine than prone position. Diaphragmatic sections of the lung had a more uniform pulmonary blood flow distribution in the prone than supine position during both normal and CPAP breathing. It was concluded that the dominant dorsal lung perfusion observed when the subjects were supine was not changed into a dominant ventral lung perfusion when the subjects were prone. Lung perfusion was more uniformly distributed in the prone compared with in the supine position, a difference that was more marked during total lung distension (CPAP) than during normal breathing.
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Affiliation(s)
- S Nyrén
- Department of Diagnostic Radiology, Karolinska Hospital and Institute, SE-171 76 Stockholm, Sweden
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36
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Jolliet P, Bulpa P, Chevrolet JC. Effects of the prone position on gas exchange and hemodynamics in severe acute respiratory distress syndrome. Crit Care Med 1998; 26:1977-85. [PMID: 9875907 DOI: 10.1097/00003246-199812000-00023] [Citation(s) in RCA: 120] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVES To address the following issues regarding the use of prone position ventilation in patients with severe acute respiratory distress syndrome (ARDS): a) response rate; b) magnitude and duration of improved oxygenation in responders during a 12-hr trial and the consequences of returning to the supine position; c) effects of the prone position on gas exchange and hemodynamics; d) consequences of oxygenation in nonresponders; and e) effects of repeated prone position trials. DESIGN Prospective, nonrandomized interventional study. SETTING Medical intensive care unit, university tertiary care center. PATIENTS Nineteen consecutive, mechanically ventilated patients (age 45+/-20 yrs, mean+/-SD) with ARDS and severe hypoxemia, defined as PaO2/FiO2 of < or = 150 with FiO2 of > or = 0.6 persisting for < or =24 hrs, and a pulmonary artery occlusion pressure of <18 mm Hg. INTERVENTIONS Patients were turned prone for 2 hrs. Nonresponders were returned supine, but responders were maintained prone for 12 hrs before being returned to the supine position. The procedure was repeated on a daily basis in all patients, until inclusion criteria were no longer met or the patients died. MEASUREMENTS AND MAIN RESULTS Hemodynamic, blood gas, and gas exchange measurements were performed at the following time points: a) baseline supine; b) after 30 mins prone; and c) after 120 mins prone. Additional measurements for nonresponders were taken after 30 mins supine. For responders, additional measurements were taken after 12 hrs prone and 30 mins supine. Patients were considered responders if an increase in PaO2 of > or = 10 torr (> or =1.3 kPa), or increase in the PaO2/FiO2 ratio of >20 occurred within 120 mins. Eleven (57%) patients responded to the prone position. There was no difference in initial baseline parameters between responders and nonresponders. After 30 mins, the prone position in responders increased PaO2 and decreased calculated venous admixture (Qva/Qt). This improvement was the maximal obtained, and was maintained throughout the 12-hr prone period. After 12 hrs prone, mean FiO2 had been lowered from 0.85+/-0.16 to 0.66+/-0.18 (p < .05). Thirty minutes after the patients were returned supine, PaO2, PaO2/FiO2, and Qva/Qt were not different from 12-hr prone values, and were improved in comparison with baseline supine values. There was no worsening of gas exchange or hemodynamics in nonresponders. After the initial trial, a total of 28 additional episodes of prone position ventilation were performed in nine of the 19 patients. Of the 24 additional episodes in the responders, there was a response in 17 (71%) of 24 episodes. In the four additional episodes in nonresponders, there was a response in only one (25%) of four episodes. Response was accompanied by the same beneficial effects on gas exchange and Qva/Qt and absence of effect on hemodynamics as in the initial trial. There was no worsening in gas exchange or hemodynamics in nonresponder trials. CONCLUSIONS Based on the data from this study, the prone position can improve oxygenation in severely hypoxemic ARDS patients without deleterious effects on hemodynamics. This beneficial effect does not immediately disappear on return to the supine position. In our patients, an absence of response to this technique was not accompanied by worsening hypoxemia or hemodynamic instability. Repeated daily trials in the prone position should be considered in the management of ARDS patients with severe hypoxemia.
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Affiliation(s)
- P Jolliet
- Medical Intensive Care Unit Division, University Hospital, Geneva, Switzerland
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Abstract
Severe ULD presents a challenge in ventilator management because of the marked asymmetry in the mechanics of the two lungs. The asymmetry may result from significant decreases or increases in the compliance of the involved lung. Traditional ventilator support may fail to produce adequate gas exchange in these situations and has the potential to cause further deterioration. Fortunately, conventional techniques can be safely and effectively applied in the majority of cases without having to resort to less familiar and potentially hazardous forms of support. In those circumstances when conventional ventilation is unsuccessful in restoring adequate gas exchange, lateral positioning and ILV have proved effective at improving and maintaining gas exchange. Controlled trials to guide clinical decision making are lacking. In patients who have processes associated with decreased compliance in the involved lung, lateral positioning may be a simple method of improving gas exchange but is associated with many practical limitations. ILV in these patients is frequently successful when differential PEEP is applied with the higher pressure to the involved lung. In patients in whom the pathology results in distribution of ventilation favoring the involved lung, particularly BPF, ILV can be used to supply adequate support while minimizing flow through the fistula and allowing it to close. The application of these techniques should be undertaken with an understanding of the pathophysiology of the underlying process; the reported experience with these techniques, including indications and successfully applied methods; and the potential problems encountered with their use. Fortunately, these modalities are infrequently required, but they provide a critical means of support when conventional techniques fail.
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Affiliation(s)
- A R Thomas
- Department of Medicine, University of Arizona/Maricopa Medical Center, Phoenix, Arizona, USA
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Hlastala MP, Chornuk MA, Self DA, Kallas HJ, Burns JW, Bernard S, Polissar NL, Glenny RW. Pulmonary blood flow redistribution by increased gravitational force. J Appl Physiol (1985) 1998; 84:1278-88. [PMID: 9516194 DOI: 10.1152/jappl.1998.84.4.1278] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
This study was undertaken to assess the influence of gravity on the distribution of pulmonary blood flow (PBF) using increased inertial force as a perturbation. PBF was studied in unanesthetized swine exposed to -Gx (dorsal-to-ventral direction, prone position), where G is the magnitude of the force of gravity at the surface of the Earth, on the Armstrong Laboratory Centrifuge at Brooks Air Force Base. PBF was measured using 15-micron fluorescent microspheres, a method with markedly enhanced spatial resolution. Each animal was exposed randomly to -1, -2, and -3 Gx. Pulmonary vascular pressures, cardiac output, heart rate, arterial blood gases, and PBF distribution were measured at each G level. Heterogeneity of PBF distribution as measured by the coefficient of variation of PBF distribution increased from 0.38 +/- 0.05 to 0.55 +/- 0.11 to 0.72 +/- 0.16 at -1, -2, and -3 Gx, respectively. At -1 Gx, PBF was greatest in the ventral and cranial and lowest in the dorsal and caudal regions of the lung. With increased -Gx, this gradient was augmented in both directions. Extrapolation of these values to 0 G predicts a slight dorsal (nondependent) region dominance of PBF and a coefficient of variation of 0.22 in microgravity. Analysis of variance revealed that a fixed component (vascular structure) accounted for 81% and nonstructure components (including gravity) accounted for the remaining 19% of the PBF variance across the entire experiment (all 3 gravitational levels). The results are inconsistent with the predictions of the zone model.
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Affiliation(s)
- M P Hlastala
- Department of Physiology and Biophysics, University of Washington, Seattle 98195, USA
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Melsom MN, Flatebø T, Kramer-Johansen J, Aulie A, Sjaastad OV, Iversen PO, Nicolaysen G. Both gravity and non-gravity dependent factors determine regional blood flow within the goat lung. ACTA PHYSIOLOGICA SCANDINAVICA 1995; 153:343-53. [PMID: 7618481 DOI: 10.1111/j.1748-1716.1995.tb09872.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Distribution of pulmonary blood flow has traditionally been regarded as determined by gravity. This view has been challenged recently by reports describing marked gravity-independent distribution of flow. These reports were based on experiments in which local blood flow was measured by methods that have not been thoroughly evaluated. In the present study, we showed that in the goat lung regional trapping of i.v. infused microspheres (O = 15 microns) correlated to endothelial uptake of a simultaneously i.v. infused diamine (r = 0.99, region size approximately 1.5 cm3, dry weight approximately 40 mg). This indicates that the deposition of microspheres reflects true regional pulmonary blood flow. Using the microsphere method, we found a marked gravity-independent heterogeneity in blood flow (coefficient of variation approximately 40%) in the awake goat. We could find no pattern related to anatomy that could account for this variability. We re-examined the influence of gravity by analysing the distribution of pulmonary blood flow in anaesthetized goats both in prone and supine positions. The dorsal to sternal distribution of flow appeared to be inverted when the animals were turned from prone to supine recumbency, indicating that gravity influenced the distribution of pulmonary blood flow along this axis. However, along the gravitational axis, distribution of blood flow varied considerably from lung to lung. It appears that in awake goats the distribution of pulmonary blood flow is the result of several different determinants.
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Affiliation(s)
- M N Melsom
- Department of Physiology, University of Oslo, Norway
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Uren NG, Davies SW, Agnew JE, Irwin AG, Jordan SL, Hilson AJ, Lipkin DP. Reduction of mismatch of global ventilation and perfusion on exercise is related to exercise capacity in chronic heart failure. BRITISH HEART JOURNAL 1993; 70:241-6. [PMID: 8398494 PMCID: PMC1025303 DOI: 10.1136/hrt.70.3.241] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
BACKGROUND The inability to match lung perfusion to ventilation because of a reduced cardiac output on exercise contributes to reduced exercise capacity in chronic heart failure. OBJECTIVE To quantify ventilation to perfusion matching at rest and at peak exercise in patients with chronic heart failure and relate this to haemodynamic and ventilatory variables of exercise capacity. DESIGN Eight men in New York Heart Association class II underwent maximal bicycle ergometry with expired gas analysis. MAIN OUTCOME MEASURES On separate days, ventilation and perfusion gamma camera imaging was performed at rest, and at 80% of previous peak exercise heart rate during bicycle ergometry. The vertical distribution of mismatch between ventilation and perfusion (V/Q) was estimated from subtracted profiles of activity (ventilation and perfusion) to derive a numerical index of global mismatch. RESULTS Maximal mean (SD) oxygen consumption on bicycle ergometry was 16.0 (4.5) ml min-1 kg-1. There was a reduction in the global V/Q mismatch index from 23.96 (5.90) to 14.88 (7.90) units (p < 0.01) at rest and at peak exercise. Global V/Q mismatch index at peak exercise correlated negatively with maximal minute ventilation (R = -0.90, p < 0.01) and with maximal mean arterial pressure (R = -0.79, p < 0.05), although no relation was seen with maximal oxygen consumption. The reduction in global V/Q mismatch index from rest to peak exercise correlated with maximal oxygen consumption (R = 0.88, p < 0.01), and with maximal minute ventilation (R = 0.87, p < 0.01). CONCLUSIONS During exercise in patients with chronic heart failure, there is a reduction in the global V/Q mismatch index. A lower global V/Q mismatch index at peak exercise is associated with higher maximal ventilation. The reduction in global V/Q mismatch index on exercise correlates well with maximal exercise capacity. This may imply that the inability to perfuse adequately all regions of lung on exercise and match this to ventilation is a factor determining exercise capacity in chronic heart failure.
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Affiliation(s)
- N G Uren
- Department of Cardiology, Royal Free Hospital, London
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Abstract
Little information has been published concerning the pattern of regional ventilation in children, yet many differences in lung and chest wall mechanics in childhood, supported by clinical observation, have led to the hypothesis that the pattern of regional ventilation seen in children may not be the same as in adults. Forty-three children and 16 adult volunteers underwent Krypton (Kr) 81m radionuclide ventilation lung scans in the supine and right and left decubitus postures. In children aged 2-10 years mean fractional ventilation to the right lung (VfR) was 46.1%. This fell to 36% when dependent and rose to 56.1% in the uppermost position. Redistribution of ventilation away from the dependent towards the uppermost lung was seen in all children. In children aged 10-18 years VfR was 57.2% (supine), 48.0% (dependent), and 62.9% (uppermost). An identical pattern was seen in children with normal or abnormal pulmonary function tests (peak expiratory flow rate, and FEV1: FVC ratio). In subjects over 18 years of age a different pattern was seen: mean VfR was 52.4% (supine), rising to 53.4% (dependent), and falling to 48.9% (uppermost). Postural redistribution of ventilation, as assessed by Kr81m ventilation imaging, changes late in the second decade of life. This will have clinical consequences in the management of children with unilateral lung disease.
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Affiliation(s)
- H Davies
- Department of Paediatrics, Central Middlesex Hospital, London, England
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Abstract
Single photon emission computerized tomography (SPECT) of the lungs was used for topographical determination of V/Q ratios in anaesthetized-paralyzed subjects. Ventilation and perfusion were estimated from the distribution of an inhaled aerosol containing a radioactive isotope and injected macroaggregates of human albumin tagged with another isotope. There was a prominent gradient of V/Q ratios in the vertical direction. In the horizontal plane there were marked gradients of both ventilation and perfusion of similar appearance with maxima in central lung regions, resulting in only small gradients of V/Q ratios.
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Affiliation(s)
- L Tokics
- Department of Anaesthesiology and Intensive Care, Huddinge University Hospital, Sweden
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Abstract
We describe positional changes in oxygenation in two patients with respiratory failure due to massive pulmonary embolism. In both patients, oxygenation improved when the "sick" lung was dependent and deteriorated when the "healthy" lung was in the dependent position. These positional changes are different from previously reported changes in unilateral pulmonary disease. We speculate that a combination of unilateral pulmonary embolism and mechanical ventilation was responsible for the improvement in gas exchange when the "sick" lung was placed in the dependent position. The relative contribution of these two components to the development of this phenomenon is unclear.
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Affiliation(s)
- M S Badr
- Pulmonary Section, University of Wisconsin Hospitals and Clinics, Madison
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Bhuyan U, Peters AM, Gordon I, Davies H, Helms P. Effects of posture on the distribution of pulmonary ventilation and perfusion in children and adults. Thorax 1989; 44:480-4. [PMID: 2763258 PMCID: PMC1020808 DOI: 10.1136/thx.44.6.480] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
In the adult the distributions of ventilation and of perfusion show the same directional dependence on gravity. In children, however, the distribution of ventilation in response to gravity is the reverse of that seen in adults. The aim of the current study was to determine whether perfusion showed the same reversal in children or followed the adult pattern. Distribution of perfusion was measured with intravenous technetium-99m macroaggregated albumin and distribution of ventilation with inhaled krypton-81m. Eighteen children and seven adults were studied; they had been referred for lung scanning for various respiratory problems. The effect of gravity was examined by giving aliquots of macroaggregated albumin and 81mKr by inhalation to the subject in the supine and the lateral decubitus position. Counts in the dependent lung were compared with those in the upper lung. The dependent lung in the lateral decubitus position received more of the total perfusion than it did in the supine position in seven children with a normal chest radiograph (mean 7.0%, range 4.8-10.9% more) and in 11 children with an abnormal radiograph (mean 3.4%(0.1-10.0%)). Ventilation, however, changed in the opposite direction, falling by 7.1% (-3.2% to -12.8%) in five children with a normal chest radiograph and 11.2% (-2.8% to -19.3%) in eight children with an abnormal radiograph. Fractional V/fractional Q (an index of the ventilation:perfusion ratio) decreased in the dependent lung in the children when they moved from the supine to the decubitus position. The same directional change was recorded in adults, but it was significantly less than in the children, irrespective of whether the chest radiograph was abnormal. In children and adults with various respiratory problems the effect of posture on the distribution of perfusion is similar.
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Affiliation(s)
- U Bhuyan
- Department of Paediatric Radiology, Hospital for Sick Children, London
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Nelson RJ, Lovick AH, Pickard JD, Brice J, Saunders D, Horsey PJ. Changes in cerebral blood flow during anaesthesia and surgery in the sitting position. J Neurol Neurosurg Psychiatry 1987; 50:971-5. [PMID: 3655831 PMCID: PMC1032223 DOI: 10.1136/jnnp.50.8.971] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Serial measurements of global cerebral blood flow (CBF) were made in 15 patients undergoing elective neurosurgical procedures in the sitting position, using a modified intravenous 133Xenon technique. The mean supine CBF rose from 43 (+/-3) ml/100g/min to 62 (+/-6) ml/100g/min in the sitting position and remained elevated at the end of surgery at 62 (+/-5) ml/100g/min. Both increases in CBF were statistically significant with respect to baseline supine values.
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Affiliation(s)
- R J Nelson
- Wessex Neurological Centre, Southampton General Hospital, UK
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47
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Orphanidou D, Hughes JM, Myers MJ, Al-Suhali AR, Henderson B. Tomography of regional ventilation and perfusion using krypton 81m in normal subjects and asthmatic patients. Thorax 1986; 41:542-51. [PMID: 3491441 PMCID: PMC460388 DOI: 10.1136/thx.41.7.542] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Single photon emission computed tomography, a rotating gamma camera, and continuous inhalation or infusion of krypton 81m (half life 13 seconds) were used to measure regional ventilation (V), perfusion (Q), and ventilation-perfusion (V/Q) ratios in five normal subjects in supine, prone, and lateral decubitus postures and in three asthmatic patients (supine posture only) before and after inhalation of 2.5 mg nebulised salbutamol. Vertical and horizontal gradients of V, Q, and V/Q were examined at three levels in each lung in regions of 1.9 cm3 size. In normal subjects V and Q increased along the axis of gravity in all postures and at all levels in the lung except for V in the prone position. Smaller horizontal gradients were found with an increase in V and Q from caudal to cranial--again except in the prone posture, where the gradient was slightly reversed. Constraint to outward motion of the ventral chest and abdominal wall is the most likely explanation for the different behaviour in the prone posture. In chronic asthma the vertical gradients of V and V/Q were the reverse of normal, but the Q gradient was normal. Bronchodilator treatment did not affect the vertical or horizontal gradients significantly, but analysis of individual regions showed that, relatively, V/Q worsened in 42% of them; this was associated in two thirds with an increase in fractional Q. After inhalation of beta agonist local vasodilatation may influence V/Q ratios in some units more than bronchodilatation.
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Hughes JM. Regional lung function: physiology and clinical applications. CLINICAL PHYSIOLOGY (OXFORD, ENGLAND) 1985; 5 Suppl 3:19-31. [PMID: 3995885 DOI: 10.1111/j.1475-097x.1985.tb00598.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The current status of tests of regional lung function has been reviewed from the physiological and clinical standpoint. Recent technical innovations include the use of single photon and positron emission computerized tomography (SPECT and PET). For PET work, neon-19 (t 1/2 17 sec) has been introduced as a ventilation tracer, and fluorine-18 deoxyglucose as a marker of glucose metabolism. Indium-111 labelled neutrophils have been studied. Physiological measurements of the distribution of blood flow and ventilation are concentrating on non-gravitational influences such as the pattern of force generation by the respiratory muscles and vasomotor tone. Ventilation and perfusion imaging of the lung with the gamma camera has established itself as an essential screening test for the diagnosis of pulmonary embolic disease. Inhalation of a radio-labelled aerosol of small particle size (1 micron) may be an acceptable substitute for a radioactive gas ventilation scan. Mucociliary clearance has been investigated with radionuclide techniques. Measurements of regional lung water have been replaced by tracers sensitive to alterations of epithelial (inhaled 99Tcm-DTPA) or endothelial (i.v. 113Inm-transferrin) permeability. New techniques using positron emission tomography, such as measurements of extravascular lung density, regional ventilation (19Ne) and regional glucose metabolism (18F-deoxyglucose) have been discussed briefly.
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Amis TC, Jones HA, Hughes JM. Effect of posture on inter-regional distribution of pulmonary ventilation in man. RESPIRATION PHYSIOLOGY 1984; 56:145-67. [PMID: 6463423 DOI: 10.1016/0034-5687(84)90100-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Regional ventilation per unit alveolar volume (V/VA) and regional lung expansion (FRCR/TLCR) were measured in twelve normal male human subjects in seated, supine, lateral decubitus and prone postures using a gamma camera and inhalation of the radioactive gases 81Krm (half-life 13 sec) and 85Krm (half-life 4.4 h). FRCR/TLCR decreased from superior to inferior in all postures except prone where it was uniform; V/VA increased from superior to inferior except in the prone position where it was uniform. In the horizontal axis FRCR/TLCR and V/VA were uniformly distributed except for cranial to caudal gradients (with lower values caudally) in supine and lateral decubitus postures. In the prone posture V/VA tended to be higher in caudal lung zones.
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