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Neder JA, Santyr G, Zanette B, Kirby M, Pourafkari M, James MD, Vincent SG, Ferguson C, Wang CY, Domnik NJ, Phillips DB, Porszasz J, Stringer WW, O'Donnell DE. Beyond Spirometry: Linking Wasted Ventilation to Exertional Dyspnea in the Initial Stages of COPD. COPD 2024; 21:2301549. [PMID: 38348843 DOI: 10.1080/15412555.2023.2301549] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Accepted: 12/29/2023] [Indexed: 02/15/2024]
Abstract
Exertional dyspnea, a key complaint of patients with chronic obstructive pulmonary disease (COPD), ultimately reflects an increased inspiratory neural drive to breathe. In non-hypoxemic patients with largely preserved lung mechanics - as those in the initial stages of the disease - the heightened inspiratory neural drive is strongly associated with an exaggerated ventilatory response to metabolic demand. Several lines of evidence indicate that the so-called excess ventilation (high ventilation-CO2 output relationship) primarily reflects poor gas exchange efficiency, namely increased physiological dead space. Pulmonary function tests estimating the extension of the wasted ventilation and selected cardiopulmonary exercise testing variables can, therefore, shed unique light on the genesis of patients' out-of-proportion dyspnea. After a succinct overview of the basis of gas exchange efficiency in health and inefficiency in COPD, we discuss how wasted ventilation translates into exertional dyspnea in individual patients. We then outline what is currently known about the structural basis of wasted ventilation in "minor/trivial" COPD vis-à-vis the contribution of emphysema versus a potential impairment in lung perfusion across non-emphysematous lung. After summarizing some unanswered questions on the field, we propose that functional imaging be amalgamated with pulmonary function tests beyond spirometry to improve our understanding of this deeply neglected cause of exertional dyspnea. Advances in the field will depend on our ability to develop robust platforms for deeply phenotyping (structurally and functionally), the dyspneic patients showing unordinary high wasted ventilation despite relatively preserved FEV1.
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Affiliation(s)
- J Alberto Neder
- Respiratory Investigation Unit, Division of Respirology, Department of Medicine, Queen's University and Kingston Health Sciences Centre, Kingston, Canada
| | - Giles Santyr
- Translational Medicine Department, Faculty of Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Canada
| | - Brandon Zanette
- Translational Medicine Department, Faculty of Physiology and Experimental Medicine, Hospital for Sick Children, Toronto, Canada
| | - Miranda Kirby
- Department of Physics, Faculty of Science, Toronto Metropolitan University, Toronto, Canada
| | - Marina Pourafkari
- Department of Radiology and Diagnostic Imaging, Kingston Health Sciences Centre, Kingston, Canada
| | - Matthew D James
- Respiratory Investigation Unit, Division of Respirology, Department of Medicine, Queen's University and Kingston Health Sciences Centre, Kingston, Canada
| | - Sandra G Vincent
- Respiratory Investigation Unit, Division of Respirology, Department of Medicine, Queen's University and Kingston Health Sciences Centre, Kingston, Canada
| | - Carrie Ferguson
- The Lundquist Institute for Biomedical Innovation, Harbor U.C.L.A Medical Centre, Torrance, CA, USA
| | - Chu-Yi Wang
- The Lundquist Institute for Biomedical Innovation, Harbor U.C.L.A Medical Centre, Torrance, CA, USA
| | - Nicolle J Domnik
- Respiratory Investigation Unit, Division of Respirology, Department of Medicine, Queen's University and Kingston Health Sciences Centre, Kingston, Canada
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Canada
| | - Devin B Phillips
- School of Kinesiology and Health Science, York University, Toronto, Canada
| | - Janos Porszasz
- The Lundquist Institute for Biomedical Innovation, Harbor U.C.L.A Medical Centre, Torrance, CA, USA
| | - William W Stringer
- The Lundquist Institute for Biomedical Innovation, Harbor U.C.L.A Medical Centre, Torrance, CA, USA
| | - Denis E O'Donnell
- Respiratory Investigation Unit, Division of Respirology, Department of Medicine, Queen's University and Kingston Health Sciences Centre, Kingston, Canada
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Kizhakke Puliyakote AS, Tedjasaputra V, Petersen GM, Sá RC, Hopkins SR. Assessing the pulmonary vascular responsiveness to oxygen with proton MRI. J Appl Physiol (1985) 2024; 136:853-863. [PMID: 38385182 DOI: 10.1152/japplphysiol.00747.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Revised: 02/05/2024] [Accepted: 02/19/2024] [Indexed: 02/23/2024] Open
Abstract
Ventilation-perfusion matching occurs passively and is also actively regulated through hypoxic pulmonary vasoconstriction (HPV). The extent of HPV activity in humans, particularly normal subjects, is uncertain. Current evaluation of HPV assesses changes in ventilation-perfusion relationships/pulmonary vascular resistance with hypoxia and is invasive, or unsuitable for patients because of safety concerns. We used a noninvasive imaging-based approach to quantify the pulmonary vascular response to oxygen as a metric of HPV by measuring perfusion changes between breathing 21% and 30%O2 using arterial spin labeling (ASL) MRI. We hypothesized that the differences between 21% and 30%O2 images reflecting HPV release would be 1) significantly greater than the differences without [Formula: see text] changes (e.g., 21-21% and 30-30%O2) and 2) negatively associated with ventilation-perfusion mismatch. Perfusion was quantified in the right lung in normoxia (baseline), after 15 min of 30% O2 breathing (hyperoxia) and 15 min normoxic recovery (recovery) in healthy subjects (7 M, 7 F; age = 41.4 ± 19.6 yr). Normalized, smoothed, and registered pairs of perfusion images were subtracted and the mean square difference (MSD) was calculated. Separately, regional alveolar ventilation and perfusion were quantified from specific ventilation, proton density, and ASL imaging; the spatial variance of ventilation-perfusion (σ2V̇a/Q̇) distributions was calculated. The O2-responsive MSD was reproducible (R2 = 0.94, P < 0.0001) and greater (0.16 ± 0.06, P < 0.0001) than that from subtracted images collected under the same [Formula: see text] (baseline = 0.09 ± 0.04, hyperoxia = 0.08 ± 0.04, recovery = 0.08 ± 0.03), which were not different from one another (P = 0.2). The O2-responsive MSD was correlated with σ2V̇a/Q̇ (R2 = 0.47, P = 0.007). These data suggest that active HPV optimizes ventilation-perfusion matching in normal subjects. This noninvasive approach could be applied to patients with different disease phenotypes to assess HPV and ventilation-perfusion mismatch.NEW & NOTEWORTHY We developed a new proton MRI method to noninvasively quantify the pulmonary vascular response to oxygen. Using a hyperoxic stimulus to release HPV, we quantified the resulting redistribution of perfusion. The differences between normoxic and hyperoxic images were greater than those between images without [Formula: see text] changes and negatively correlated with ventilation-perfusion mismatch. This suggests that active HPV optimizes ventilation-perfusion matching in normal subjects. This approach is suitable for assessing patients with different disease phenotypes.
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Affiliation(s)
- Abhilash S Kizhakke Puliyakote
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, La Jolla, California, United States
- Department of Radiology, University of California, San Diego, La Jolla, California, United States
| | - Vincent Tedjasaputra
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, La Jolla, California, United States
- Department of Medicine, University of California, San Diego, La Jolla, California, United States
| | - Gregory M Petersen
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, La Jolla, California, United States
| | - Rui Carlos Sá
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, La Jolla, California, United States
- Department of Medicine, University of California, San Diego, La Jolla, California, United States
| | - Susan R Hopkins
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, La Jolla, California, United States
- Department of Radiology, University of California, San Diego, La Jolla, California, United States
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Balczon R, Lin MT, Voth S, Nelson AR, Schupp JC, Wagener BM, Pittet JF, Stevens T. Lung endothelium, tau, and amyloids in health and disease. Physiol Rev 2024; 104:533-587. [PMID: 37561137 DOI: 10.1152/physrev.00006.2023] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Revised: 06/26/2023] [Accepted: 08/04/2023] [Indexed: 08/11/2023] Open
Abstract
Lung endothelia in the arteries, capillaries, and veins are heterogeneous in structure and function. Lung capillaries in particular represent a unique vascular niche, with a thin yet highly restrictive alveolar-capillary barrier that optimizes gas exchange. Capillary endothelium surveys the blood while simultaneously interpreting cues initiated within the alveolus and communicated via immediately adjacent type I and type II epithelial cells, fibroblasts, and pericytes. This cell-cell communication is necessary to coordinate the immune response to lower respiratory tract infection. Recent discoveries identify an important role for the microtubule-associated protein tau that is expressed in lung capillary endothelia in the host-pathogen interaction. This endothelial tau stabilizes microtubules necessary for barrier integrity, yet infection drives production of cytotoxic tau variants that are released into the airways and circulation, where they contribute to end-organ dysfunction. Similarly, beta-amyloid is produced during infection. Beta-amyloid has antimicrobial activity, but during infection it can acquire cytotoxic activity that is deleterious to the host. The production and function of these cytotoxic tau and amyloid variants are the subject of this review. Lung-derived cytotoxic tau and amyloid variants are a recently discovered mechanism of end-organ dysfunction, including neurocognitive dysfunction, during and in the aftermath of infection.
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Affiliation(s)
- Ron Balczon
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, Alabama, United States
- Center for Lung Biology, University of South Alabama, Mobile, Alabama, United States
| | - Mike T Lin
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, Alabama, United States
- Center for Lung Biology, University of South Alabama, Mobile, Alabama, United States
| | - Sarah Voth
- Department of Cell Biology and Physiology, Edward Via College of Osteopathic Medicine, Monroe, Louisiana, United States
| | - Amy R Nelson
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, Alabama, United States
- Center for Lung Biology, University of South Alabama, Mobile, Alabama, United States
| | - Jonas C Schupp
- Pulmonary and Critical Care Medicine, Department of Internal Medicine, Yale University, New Haven, Connecticut, United States
- Department of Respiratory Medicine, Hannover Medical School, Hannover, Germany
- German Center for Lung Research (DZL), Hannover, Germany
| | - Brant M Wagener
- Department of Anesthesiology and Perioperative Medicine, University of Alabama-Birmingham, Birmingham, Alabama, United States
| | - Jean-Francois Pittet
- Department of Anesthesiology and Perioperative Medicine, University of Alabama-Birmingham, Birmingham, Alabama, United States
| | - Troy Stevens
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, Alabama, United States
- Department of Internal Medicine, University of South Alabama, Mobile, Alabama, United States
- Center for Lung Biology, University of South Alabama, Mobile, Alabama, United States
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Huang YH, Teng X, Zhang J, Chen Z, Ma Z, Ren G, Kong FMS, Ge H, Cai J. Respiratory Invariant Textures From Static Computed Tomography Scans for Explainable Lung Function Characterization. J Thorac Imaging 2023; 38:286-296. [PMID: 37265243 DOI: 10.1097/rti.0000000000000717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
PURPOSE The inherent characteristics of lung tissue independent of breathing maneuvers may provide fundamental information for function assessment. This paper attempted to correlate textural signatures from computed tomography (CT) with pulmonary function measurements. MATERIALS AND METHODS Twenty-one lung cancer patients with thoracic 4-dimensional CT, DTPA-single-photon emission CT ventilation ( VNM ) scans, and available spirometry measurements (forced expiratory volume in 1 s, FEV 1 ; forced vital capacity, FVC; and FEV 1 /FVC) were collected. In subregional feature discovery, function-correlated candidates were identified from 79 radiomic features based on the statistical strength to differentiate defected/nondefected lung regions. Feature maps (FMs) of selected candidates were generated on 4-dimensional CT phases for a voxel-wise feature distribution study. Quantitative metrics were applied for validations, including the Spearman correlation coefficient (SCC) and the Dice similarity coefficient for FM- VNM spatial agreement assessments, intraclass correlation coefficient for FM interphase robustness evaluations, and FM-spirometry comparisons. RESULTS At the subregion level, 8 function-correlated features were identified (effect size>0.330). The FMs of candidates yielded moderate-to-strong voxel-wise correlations with the reference VNM . The FMs of gray level dependence matrix dependence nonuniformity showed the highest robust (intraclass correlation coefficient=0.96 and P <0.0001) spatial correlation, with median SCCs ranging from 0.54 to 0.59 throughout the 10 breathing phases. Its phase-averaged FM achieved a median SCC of 0.60, a median Dice similarity coefficient of 0.60 (0.65) for high (low) functional lung volumes, and a correlation of 0.565 (0.646) between the spatially averaged feature values and FEV 1 (FEV 1 /FVC). CONCLUSIONS The results provide further insight into the underlying association of specific pulmonary textures with both local ( VNM ) and global (FEV 1 /FVC, FEV 1 ) functions. Further validations of the FM generalizability and the standardization of implementation protocols are warranted before clinically relevant investigations.
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Affiliation(s)
- Yu-Hua Huang
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University
| | - Xinzhi Teng
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University
| | - Jiang Zhang
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University
| | - Zhi Chen
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University
| | - Zongrui Ma
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University
| | - Ge Ren
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University
| | - Feng-Ming Spring Kong
- Department of Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR
- Department of Clinical Oncology, The University of Hong Kong-Shenzhen Hospital, Shenzhen
| | - Hong Ge
- Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University & Henan Cancer Hospital, Zhengzhou, China
| | - Jing Cai
- Department of Health Technology and Informatics, The Hong Kong Polytechnic University
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Kizhakke Puliyakote AS, Prisk GK, Elliott AR, Kim NH, Pazar B, Sá RC, Asadi AK, Hopkins SR. The spatial-temporal dynamics of pulmonary blood flow are altered in pulmonary arterial hypertension. J Appl Physiol (1985) 2023; 134:969-979. [PMID: 36861672 PMCID: PMC10085549 DOI: 10.1152/japplphysiol.00463.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 02/16/2023] [Accepted: 02/27/2023] [Indexed: 03/03/2023] Open
Abstract
Global fluctuation dispersion (FDglobal), a spatial-temporal metric derived from serial images of the pulmonary perfusion obtained with MRI-arterial spin labeling, describes temporal fluctuations in the spatial distribution of perfusion. In healthy subjects, FDglobal is increased by hyperoxia, hypoxia, and inhaled nitric oxide. We evaluated patients with pulmonary arterial hypertension (PAH, 4F, aged 47 ± 15, mean pulmonary artery pressure 48 ± 7 mmHg) and healthy controls (CON, 7F, aged 47 ± 12) to test the hypothesis that FDglobal is increased in PAH. Images were acquired at ∼4-5 s intervals during voluntary respiratory gating, inspected for quality, registered using a deformable registration algorithm, and normalized. Spatial relative dispersion (RD = SD/mean) and the percent of the lung image with no measurable perfusion signal (%NMP) were also assessed. FDglobal was significantly increased in PAH (PAH = 0.40 ± 0.17, CON = 0.17 ± 0.02, P = 0.006, a 135% increase) with no overlap in values between the two groups, consistent with altered vascular regulation. Both spatial RD and %NMP were also markedly greater in PAH vs. CON (PAH RD = 1.46 ± 0.24, CON = 0.90 ± 0.10, P = 0.0004; PAH NMP = 13.4 ± 6.1%; CON = 2.3 ± 1.4%, P = 0.001 respectively) consistent with vascular remodeling resulting in poorly perfused regions of lung and increased spatial heterogeneity. The difference in FDglobal between normal subjects and patients with PAH in this small cohort suggests that spatial-temporal imaging of perfusion may be useful in the evaluation of patients with PAH. Since this MR imaging technique uses no injected contrast agents and has no ionizing radiation it may be suitable for use in diverse patient populations.NEW & NOTEWORTHY Using proton MRI-arterial spin labeling to obtain serial images of pulmonary perfusion, we show that global fluctuation dispersion (FDglobal), a metric of temporal fluctuations in the spatial distribution of perfusion, was significantly increased in female patients with pulmonary arterial hypertension (PAH) compared with healthy controls. This potentially indicates pulmonary vascular dysregulation. Dynamic measures using proton MRI may provide new tools for evaluating individuals at risk of PAH or for monitoring therapy in patients with PAH.
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Affiliation(s)
- Abhilash S Kizhakke Puliyakote
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, San Diego, California, United States
- Department of Radiology, University of California, San Diego, California, United States
| | - G Kim Prisk
- Department of Radiology, University of California, San Diego, California, United States
- Department of Medicine, University of California, San Diego, California, United States
| | - Ann R Elliott
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, San Diego, California, United States
- Department of Medicine, University of California, San Diego, California, United States
| | - Nick H Kim
- Department of Medicine, University of California, San Diego, California, United States
| | - Beni Pazar
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, San Diego, California, United States
- Department of Radiology, University of California, San Diego, California, United States
| | - Rui Carlos Sá
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, San Diego, California, United States
- Department of Medicine, University of California, San Diego, California, United States
| | - Amran K Asadi
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, San Diego, California, United States
- Department of Radiology, University of California, San Diego, California, United States
| | - Susan R Hopkins
- Pulmonary Imaging Laboratory, UC San Diego Health Sciences, San Diego, California, United States
- Department of Radiology, University of California, San Diego, California, United States
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Li Z, Le Roux PY, Callahan J, Hardcastle N, Hofman MS, Siva S, Yamamoto T. Quantitative assessment of ventilation-perfusion relationships with gallium-68 positron emission tomography/computed tomography imaging in lung cancer patients. Phys Imaging Radiat Oncol 2022; 22:8-12. [PMID: 35465222 PMCID: PMC9018442 DOI: 10.1016/j.phro.2022.03.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 03/30/2022] [Accepted: 03/31/2022] [Indexed: 11/30/2022] Open
Abstract
Voxel-wise correlations between gallium-68 (68Ga) positron emission tomography/computed tomography (PET/CT)-measured ventilation and perfusion varied widely among 19 patients with lung cancer (range: 0.26–0.88). 68Ga PET/CT-measured percent gas exchanging lung volume was moderately correlated with diffusing capacity of the lung for carbon monoxide (DLCO) as the reference standard, with the highest correlation coefficient of 0.59 (P < 0.01). 68Ga PET/CT ventilation/perfusion imaging may provide a reasonable surrogate for regional gas exchange.
Pulmonary functional imaging has demonstrated potential to improve thoracic radiotherapy. The purpose of this study was twofold: 1) to quantify ventilation/perfusion relationships in lung cancer patients using a new functional imaging approach, gallium-68 (68Ga)-positron emission tomography/computed tomography (PET/CT); and 2) to compare ventilation/perfusion matching with diffusing capacity of the lung for carbon monoxide (DLCO). Voxel-wise correlations between ventilation and perfusion varied widely among 19 patients (range: 0.26–0.88). 68Ga-PET/CT-measured percent gas exchanging lung volume was moderately correlated with DLCO (≤0.59). Our findings suggested that 68Ga-PET/CT ventilation/perfusion imaging provided complementary information and a reasonable surrogate for gas exchange in lung cancer patients.
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Affiliation(s)
- Zhuorui Li
- Department of Biomedical Engineering, University of California Davis, Davis, CA, USA
| | - Pierre-Yves Le Roux
- Department of Nuclear Medicine, Brest University Hospital, EA3878 (GETBO), Brest, France
| | - Jason Callahan
- Molecular Imaging and Therapeutic Nuclear Medicine, Peter MacCallum Cancer Centre, Melbourne, Australia
| | - Nicholas Hardcastle
- Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, Australia
- Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, Australia
| | - Michael S. Hofman
- Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, Australia
- Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, Australia
| | - Shankar Siva
- Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, Australia
- Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia
| | - Tokihiro Yamamoto
- Department of Radiation Oncology, University of California Davis School of Medicine, Sacramento, CA, USA
- Corresponding author at: Department of Radiation Oncology, University of California Davis School of Medicine, 4501 X St., Sacramento, CA 95817, USA.
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A century of exercise physiology: key concepts on coupling respiratory oxygen flow to muscle energy demand during exercise. Eur J Appl Physiol 2022; 122:1317-1365. [PMID: 35217911 PMCID: PMC9132876 DOI: 10.1007/s00421-022-04901-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Accepted: 01/25/2022] [Indexed: 12/26/2022]
Abstract
After a short historical account, and a discussion of Hill and Meyerhof’s theory of the energetics of muscular exercise, we analyse steady-state rest and exercise as the condition wherein coupling of respiration to metabolism is most perfect. The quantitative relationships show that the homeostatic equilibrium, centred around arterial pH of 7.4 and arterial carbon dioxide partial pressure of 40 mmHg, is attained when the ratio of alveolar ventilation to carbon dioxide flow (\documentclass[12pt]{minimal}
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\begin{document}$${\dot{V}}_{A}/{\dot{V}}_{R}{CO}_{2}$$\end{document}V˙A/V˙RCO2) is − 21.6. Several combinations, exploited during exercise, of pertinent respiratory variables are compatible with this equilibrium, allowing adjustment of oxygen flow to oxygen demand without its alteration. During exercise transients, the balance is broken, but the coupling of respiration to metabolism is preserved when, as during moderate exercise, the respiratory system responds faster than the metabolic pathways. At higher exercise intensities, early blood lactate accumulation suggests that the coupling of respiration to metabolism is transiently broken, to be re-established when, at steady state, blood lactate stabilizes at higher levels than resting. In the severe exercise domain, coupling cannot be re-established, so that anaerobic lactic metabolism also contributes to sustain energy demand, lactate concentration goes up and arterial pH falls continuously. The \documentclass[12pt]{minimal}
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\begin{document}$${\dot{V}}_{A}/{\dot{V}}_{R}{CO}_{2}$$\end{document}V˙A/V˙RCO2 decreases below − 21.6, because of ensuing hyperventilation, while lactate keeps being accumulated, so that exercise is rapidly interrupted. The most extreme rupture of the homeostatic equilibrium occurs during breath-holding, because oxygen flow from ambient air to mitochondria is interrupted. No coupling at all is possible between respiration and metabolism in this case.
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Bayat S, Broche L, Dégrugilliers L, Porra L, Paiva M, Verbanck S. Fractal analysis reveals functional unit of ventilation in the lung. J Physiol 2021; 599:5121-5132. [PMID: 34647325 DOI: 10.1113/jp282093] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 10/06/2021] [Indexed: 12/14/2022] Open
Abstract
Ventilation is inhomogeneous in the lungs across species. It has been hypothesized that ventilation inhomogeneity is largely determined by the design of the airway branching network. Because exchange of gases at the alveolar barrier is more efficient when gas concentrations are evenly distributed at subacinar length scales, it is assumed that a 'functional unit' of ventilation exists within the lung periphery, where gas concentration becomes uniform. On the other hand, because the morphology of pulmonary airways and alveoli, and the distribution of inhaled fluorescent particles show self-similar fractal properties over a wide range of length scales, it has been predicted that fractal dimension of ventilation approaches unity within an internally homogeneous functional unit of ventilation. However, the existence of such a functional unit has never been demonstrated experimentally due to lack of in situ gas concentration measurements of sufficient spatial resolution in the periphery of a complex bifurcating network. Here, using energy-subtractive synchrotron radiation tomography, we measured the distribution of an inert gas (Xe) in the in vivo rabbit lung during Xe wash-in breathing manoeuvres. The effects of convective flow rate, diffusion and cardiac motion were also assessed. Fractal analysis of resulting gas concentration and tissue density maps revealed that fractal dimension was always smaller for Xe than for tissue density, and that only for the gas, a length scale existed where fractal dimension approached unity. The length scale where this occurred was seen to correspond to that of a rabbit acinus, the terminal structure comprising only alveolated airways. KEY POINTS: Gas ventilation is inhomogeneous in the lung of many species. However, it is not known down to what length scales this inhomogeneity persists. It is generally assumed that ventilation becomes homogeneous at subacinar length scales, beyond the spatial resolution of commonly available imaging techniques, hence this has not been demonstrated experimentally. Here we measured the distribution of inhaled Xe gas in the rabbit lung using synchrotron radiation energy-subtractive imaging and used fractal analysis to show that ventilation becomes internally uniform within regions about the size of rabbit lung acini.
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Affiliation(s)
- Sam Bayat
- Department of Pulmonology and Physiology, Grenoble University Hospital, Grenoble, France.,Univ. Grenoble Alpes, STROBE Laboratory Inserm UA07, Grenoble, France
| | - Ludovic Broche
- Biomedical Beamline, European Synchrotron Radiation Facility, Grenoble, France
| | - Loïc Dégrugilliers
- Department of Paediatric Intensive Care, Amiens University Hospital, Amiens, France
| | - Liisa Porra
- Department of Physics, University of Helsinki, Helsinki University Central Hospital, Helsinki, Finland
| | - Manuel Paiva
- University Hospital Erasme, Université Libre de Bruxelles, Brussels, Belgium
| | - Sylvia Verbanck
- Respiratory Division, University Hospital UZ Brussel, Vrije Universiteit Brussel, Brussels, Belguim
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Regional Gas Transport During Conventional and Oscillatory Ventilation Assessed by Xenon-Enhanced Computed Tomography. Ann Biomed Eng 2021; 49:2377-2388. [PMID: 33948747 DOI: 10.1007/s10439-021-02767-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Accepted: 03/12/2021] [Indexed: 01/16/2023]
Abstract
Enhanced intrapulmonary gas transport enables oscillatory ventilation modalities to support gas exchange using extremely low tidal volumes at high frequencies. However, it is unknown whether gas transport rates can be improved by combining multiple frequencies of oscillation simultaneously. The goal of this study was to investigate distributed gas transport in vivo during multi-frequency oscillatory ventilation (MFOV) as compared with conventional mechanical ventilation (CMV) or high-frequency oscillatory ventilation (HFOV). We hypothesized that MFOV would result in more uniform rates of gas transport compared to HFOV, measured using contrast-enhanced CT imaging during wash-in of xenon gas. In 13 pigs, xenon wash-in equilibration rates were comparable between CMV and MFOV, but 21 to 39% slower for HFOV. By contrast, the root-mean-square delivered volume was lowest for MFOV, increased by 70% during HFOV and 365% during CMV. Overall gas transport heterogeneity was similar across all modalities, but gravitational gradients and regional patchiness of specific ventilation contributed to regional ventilation heterogeneity, depending on ventilator modality. We conclude that MFOV combines benefits of low lung stretch, similar to HFOV, but with fast rates of gas transport, similar to CMV.
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Barisione G, Brusasco V. Lung diffusing capacity for nitric oxide and carbon monoxide following mild-to-severe COVID-19. Physiol Rep 2021; 9:e14748. [PMID: 33625799 PMCID: PMC7903940 DOI: 10.14814/phy2.14748] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Revised: 01/07/2021] [Accepted: 01/13/2021] [Indexed: 02/06/2023] Open
Abstract
A decreased lung diffusing capacity for carbon monoxide (DLCO ) has been reported in a variable proportion of subjects over the first 3 months of recovery from severe coronavirus disease 2019 (COVID-19). In this study, we investigated whether measurement of lung diffusing capacity for nitric oxide (DLNO ) offers additional insights on the presence and mechanisms of gas transport abnormalities. In 94 subjects, recovering from mild-to-severe COVID-19 pneumonia, we measured DLNO and DLCO between 10 and 266 days after each patient was tested negative for severe acute respiratory syndrome coronavirus 2. In 38 subjects, a chest computed tomography (CT) was available for semiquantitative analysis at six axial levels and automatic quantitative analysis of entire lungs. DLNO was abnormal in 57% of subjects, independent of time of lung function testing and severity of COVID-19, whereas standard DLCO was reduced in only 20% and mostly within the first 3 months. These differences were not associated with changes of simultaneous DLNO /DLCO ratio, while DLCO /VA and DLNO /VA were within normal range or slightly decreased. DLCO but not DLNO positively correlated with recovery time and DLCO was within the normal range in about 90% of cases after 3 months, while DLNO was reduced in more than half of subjects. Both DLNO and DLCO inversely correlated with persisting CT ground glass opacities and mean lung attenuation, but these were more frequently associated with DLNO than DLCO decrease. These data show that an impairment of DLNO exceeding standard DLCO may be present during the recovery from COVID-19, possibly due to loss of alveolar units with alveolar membrane damage, but relatively preserved capillary volume. Alterations of gas transport may be present even in subjects who had mild COVID-19 pneumonia and no or minimal persisting CT abnormalities. TRIAL REGISTRY: ClinicalTrials.gov PRS: No.: NCT04610554 Unique Protocol ID: SARS-CoV-2_DLNO 2020.
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Affiliation(s)
- Giovanni Barisione
- Struttura Semplice Fisiopatologia Respiratoria, Clinica Malattie Respiratorie e Allergologia, Dipartimento di Medicina Interna e Specialità Mediche, Università di Genova, IRCCS Ospedale Policlinico San Martino, Genova, Italy
| | - Vito Brusasco
- Centro Polifunzionale di Scienze Motorie, Dipartimento di Medicina Sperimentale, Università di Genova, IRCCS Ospedale Policlinico San Martino, Genova, Italy
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11
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Clark AR, Burrowes KS, Tawhai MH. Integrative Computational Models of Lung Structure-Function Interactions. Compr Physiol 2021; 11:1501-1530. [PMID: 33577123 DOI: 10.1002/cphy.c200011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Anatomically based integrative models of the lung and their interaction with other key components of the respiratory system provide unique capabilities for investigating both normal and abnormal lung function. There is substantial regional variability in both structure and function within the normal lung, yet it remains capable of relatively efficient gas exchange by providing close matching of air delivery (ventilation) and blood delivery (perfusion) to regions of gas exchange tissue from the scale of the whole organ to the smallest continuous gas exchange units. This is despite remarkably different mechanisms of air and blood delivery, different fluid properties, and unique scale-dependent anatomical structures through which the blood and air are transported. This inherent heterogeneity can be exacerbated in the presence of disease or when the body is under stress. Current computational power and data availability allow for the construction of sophisticated data-driven integrative models that can mimic respiratory system structure, function, and response to intervention. Computational models do not have the same technical and ethical issues that can limit experimental studies and biomedical imaging, and if they are solidly grounded in physiology and physics they facilitate investigation of the underlying interaction between mechanisms that determine respiratory function and dysfunction, and to estimate otherwise difficult-to-access measures. © 2021 American Physiological Society. Compr Physiol 11:1501-1530, 2021.
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Affiliation(s)
- Alys R Clark
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Kelly S Burrowes
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Merryn H Tawhai
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
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12
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Hopkins SR, Sá RC, Prisk GK, Elliott AR, Kim NH, Pazar BJ, Printz BF, El-Said HG, Davis CK, Theilmann RJ. Abnormal pulmonary perfusion heterogeneity in patients with Fontan circulation and pulmonary arterial hypertension. J Physiol 2020; 599:343-356. [PMID: 33026102 DOI: 10.1113/jp280348] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Accepted: 10/06/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The distribution of pulmonary perfusion is affected by gravity, vascular branching structure and active regulatory mechanisms, which may be disrupted by cardiopulmonary disease, but this is not well studied, particularly in rare conditions. We evaluated pulmonary perfusion in patients who had undergone Fontan procedure, patients with pulmonary arterial hypertension (PAH) and two groups of controls using a proton magnetic resonance imaging technique, arterial spin labelling to measure perfusion. Heterogeneity was assessed by the relative dispersion (SD/mean) and gravitational gradients. Gravitational gradients were similar between all groups, but heterogeneity was significantly increased in both patient groups compared to controls and persisted after removing contributions from large blood vessels and gravitational gradients. Patients with Fontan physiology and patients with PAH have increased pulmonary perfusion heterogeneity that is not explainable by differences in mean perfusion, gravitational gradients, or large vessel anatomy. This probably reflects vascular remodelling in PAH and possibly in Fontan physiology. ABSTRACT Many factors affect the distribution of pulmonary perfusion, which may be disrupted by cardiopulmonary disease, but this is not well studied, particularly in rare conditions. An example is following the Fontan procedure, where pulmonary perfusion is passive, and heterogeneity may be increased because of the underlying pathophysiology leading to Fontan palliation, remodelling, or increased gravitational gradients from low flow. Another is pulmonary arterial hypertension (PAH), where gravitational gradients may be reduced secondary to high pressures, but remodelling may increase perfusion heterogeneity. We evaluated regional pulmonary perfusion in Fontan patients (n = 5), healthy young controls (Fontan control, n = 5), patients with PAH (n = 6) and healthy older controls (PAH control) using proton magnetic resonance imaging. Regional perfusion was measured using arterial spin labelling. Heterogeneity was assessed by the relative dispersion (SD/mean) and gravitational gradients. Mean perfusion was similar (Fontan = 2.50 ± 1.02 ml min-1 ml-1 ; Fontan control = 3.09 ± 0.58, PAH = 3.63 ± 1.95; PAH control = 3.98 ± 0.91, P = 0.26), and the slopes of gravitational gradients were not different (Fontan = -0.23 ± 0.09 ml min-1 ml-1 cm-1 ; Fontan control = -0.29 ± 0.23, PAH = -0.27 ± 0.09, PAH control = -0.25 ± 0.18, P = 0.91) between groups. Perfusion relative dispersion was greater in both Fontan and PAH than controls (Fontan = 1.46 ± 0.18; Fontan control = 0.99 ± 0.21, P = 0.005; PAH = 1.22 ± 0.27, PAH control = 0.91 ± 0.12, P = 0.02) but similar between patient groups (P = 0.13). These findings persisted after removing contributions from large blood vessels and gravitational gradients (all P < 0.05). We conclude that patients with Fontan physiology and PAH have increased pulmonary perfusion heterogeneity that is not explained by differences in mean perfusion, gravitational gradients, or large vessel anatomy. This probably reflects the effects of remodelling in PAH and possibly in Fontan physiology.
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Affiliation(s)
- Susan R Hopkins
- Department of Radiology, University of California, San Diego, CA, USA.,Department of Medicine, University of California, San Diego, CA, USA
| | - Rui C Sá
- Department of Medicine, University of California, San Diego, CA, USA
| | - G Kim Prisk
- Department of Radiology, University of California, San Diego, CA, USA.,Department of Medicine, University of California, San Diego, CA, USA
| | - Ann R Elliott
- Department of Medicine, University of California, San Diego, CA, USA
| | - Nick H Kim
- Department of Medicine, University of California, San Diego, CA, USA
| | - Beni J Pazar
- Department of Radiology, University of California, San Diego, CA, USA
| | - Beth F Printz
- Department of Radiology, University of California, San Diego, CA, USA.,Rady Children's Hospital-San Diego, San Diego, CA, USA.,Department of Pediatrics, University of California, San Diego, CA, USA
| | - Howaida G El-Said
- Rady Children's Hospital-San Diego, San Diego, CA, USA.,Department of Pediatrics, University of California, San Diego, CA, USA
| | - Christopher K Davis
- Rady Children's Hospital-San Diego, San Diego, CA, USA.,Department of Pediatrics, University of California, San Diego, CA, USA
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13
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Barisione G, Garlaschi A, Occhipinti M, Baroffio M, Pistolesi M, Brusasco V. Value of lung diffusing capacity for nitric oxide in systemic sclerosis. Physiol Rep 2020; 7:e14149. [PMID: 31264386 PMCID: PMC6603284 DOI: 10.14814/phy2.14149] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Accepted: 06/01/2019] [Indexed: 01/08/2023] Open
Abstract
A decreased lung diffusing capacity for carbon monoxide (DLCO ) in systemic sclerosis (SSc) is considered to reflect losses of alveolar membrane diffusive conductance for CO (DMCO ), due to interstitial lung disease, and/or pulmonary capillary blood volume (VC ), due to vasculopathy. However, standard DLCO does not allow separate DMCO from VC . Lung diffusing capacity for nitric oxide (DLNO ) is considered to be more sensitive to decrement of alveolar membrane diffusive conductance than DLCO . Standard DLCO and DLNO were compared in 96 SSc subjects with or without lung restriction. Data showed that DLNO was reduced in 22% of subjects with normal lung volumes and DLCO , whereas DLCO was normal in 30% of those with decreased DLNO . In 30 subjects with available computed tomography of the chest, both DLCO and DLNO were negatively correlated with the extent of pulmonary fibrosis. However, DLNO but not DLCO was always reduced in subjects with ≥ 5% fibrosis, and also decreased in some subjects with < 5% fibrosis. DMCO and VC partitioning and Doppler ultrasound-determined systolic pulmonary artery pressure could not explain individual differences in DLCO and DLNO . DLNO may be of clinical value in SSc because it is more sensitive to DMCO loss than standard DLCO , even in nonrestricted subjects without fibrosis, whereas DLCO partitioning into its subcomponents does not provide information on whether diffusion limitation is primarily due to vascular or interstitial lung disease in individual subjects. Moreover, decreased DLCO in the absence of lung restriction does not allow to suspect pulmonary arterial hypertension without fibrosis.
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Affiliation(s)
- Giovanni Barisione
- Unità Operativa Fisiopatologia Respiratoria, Dipartimento di Medicina Interna, Università di Genova, Genova, Italy
| | - Alessandro Garlaschi
- Dipartimento della Diagnostica per Immagini e Radioterapia, Ospedale Policlinico San Martino - IRCCS, Genova, Italy
| | - Mariaelena Occhipinti
- Dipartimento di Medicina Sperimentale e Clinica, Azienda Ospedaliero-Universitaria Careggi, Firenze, Italy
| | - Michele Baroffio
- Unità Operativa Fisiopatologia Respiratoria, Dipartimento di Medicina Interna, Università di Genova, Genova, Italy
| | - Massimo Pistolesi
- Dipartimento di Medicina Sperimentale e Clinica, Azienda Ospedaliero-Universitaria Careggi, Firenze, Italy
| | - Vito Brusasco
- Unità Operativa Fisiopatologia Respiratoria, Dipartimento di Medicina Interna, Università di Genova, Genova, Italy
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14
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Abstract
The pulmonary circulation carries deoxygenated blood from the systemic veins through the pulmonary arteries to be oxygenated in the capillaries that line the walls of the pulmonary alveoli. The pulmonary circulation carries the cardiac output with a relatively low driving pressure, and so differs considerably in structure and function from the systemic circulation to maintain a low-resistance vascular system. The pulmonary circulation is often considered to be a quasi-static system in both experimental and computational studies of pulmonary perfusion and its matching to ventilation (air flow) for exchange. However, the system is highly dynamic, with cardiac output and regional perfusion changing with posture, exercise, and over time. Here we review this dynamic system, with a focus on understanding the physiology of pulmonary vascular dynamics across spatial and temporal scales, and the changes to these dynamics that are reflective of disease. © 2019 American Physiological Society. Compr Physiol 9:1081-1100, 2019.
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Affiliation(s)
- Alys Clark
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Merryn Tawhai
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
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15
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Cieri RL. Pulmonary Smooth Muscle in Vertebrates: A Comparative Review of Structure and Function. Integr Comp Biol 2019; 59:10-28. [DOI: 10.1093/icb/icz002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Abstract
Although the airways of vertebrates are diverse in shape, complexity, and function, they all contain visceral smooth muscle. The morphology, function, and innervation of this tissue in airways is reviewed in actinopterygians, lungfish, amphibians, non-avian reptiles, birds, and mammals. Smooth muscle was likely involved in tension regulation ancestrally, and may serve to assist lung emptying in fishes and aquatic amphibians, as well as maintain internal lung structure. In certain non-avian reptiles and anurans antagonistic smooth muscle fibers may contribute to intrapulmonary gas mixing. In mammals and birds, smooth muscle regulates airway caliber, and may be important in controlling the distribution of ventilation at rest and exercise, or during thermoregulatory and vocal hyperventilation. Airway smooth muscle is controlled by the autonomic nervous system: cranial cholinergic innervation generally causes excitation, cranial non-adrenergic, non-cholinergic innervation causes inhibition, and spinal adrenergic (SA) input causes species-specific, often heterogeneous contractions and relaxations.
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Affiliation(s)
- Robert L Cieri
- School of Biological Sciences, The University of Utah, 247 South 1400 East, 201 South Biology, Salt Lake City, UT 84112, USA
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16
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Myziuk N, Guerrero T, Sakthivel G, Solis D, Nair G, Guerra R, Castillo E. Pulmonary blood mass dynamics on 4DCT during tidal breathing. ACTA ACUST UNITED AC 2019; 64:045014. [DOI: 10.1088/1361-6560/aaff7b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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17
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Holanda MA, Sousa NPD, Melo LT, Marinho LS, Ribeiro-Filho HV, Troncon LEDA, Bastos VPD, Santos AAD, Siqueira RJBD. Helping students to understand physiological aspects of regional distribution of ventilation in humans: a experience from the electrical impedance tomography. ADVANCES IN PHYSIOLOGY EDUCATION 2018; 42:655-660. [PMID: 30387699 DOI: 10.1152/advan.00086.2018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Undergraduate biomedical students often have difficulties in understanding basic concepts of respiratory physiology, particularly respiratory mechanics. In this study, we report the use of electrical impedance tomography (EIT) to improve and consolidate the knowledge about physiological aspects of normal regional distribution of ventilation in humans. Initially, we assessed the previous knowledge of a group of medical students ( n = 39) about regional differences in lung ventilation. Thereafter, we recorded the regional distribution of ventilation through surface electrodes on a healthy volunteer adopting four different decubitus positions: supine, prone, and right and left lateral. The recordings clearly showed greater pulmonary ventilation in the dependent lung, mainly in the lateral decubitus. Considering the differences in pulmonary ventilation between right and left lateral decubitus, only 33% of students were able to notice it correctly beforehand. This percentage increased to 84 and 100%, respectively ( P < 0.01), after the results of the ventilation measurements obtained with EIT were examined and discussed. A self-assessment questionnaire showed that students considered the practical activity as an important tool to assist in the understanding of the basic concepts of respiratory mechanics. Experimental demonstration of the physiological variations of regional lung ventilation in volunteers by using EIT is feasible, effective, and stimulating for undergraduate medical students. Therefore, this practical activity may help faculty and students to overcome the challenges in the field of respiratory physiology learning.
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Affiliation(s)
- Marcelo Alcantara Holanda
- Department of Internal Medicine, School of Medicine, Federal University of Ceará , Fortaleza, Ceará , Brazil
| | - Nathalia Parente de Sousa
- Department of Internal Medicine, School of Medicine, Federal University of Ceará , Fortaleza, Ceará , Brazil
| | - Luana Torres Melo
- Department of Internal Medicine, School of Medicine, Federal University of Ceará , Fortaleza, Ceará , Brazil
| | - Liégina Silveira Marinho
- Department of Internal Medicine, School of Medicine, Federal University of Ceará , Fortaleza, Ceará , Brazil
| | - Helder Veras Ribeiro-Filho
- Department of Physiology and Pharmacology, School of Medicine, Federal University of Ceará , Fortaleza, Ceará , Brazil
| | - Luiz Ernesto de Almeida Troncon
- Department of Clinical Medicine, Ribeirão Preto Medical School, University of São Paulo , Ribeirão Preto, São Paulo , Brazil
| | | | - Armênio Aguiar Dos Santos
- Department of Physiology and Pharmacology, School of Medicine, Federal University of Ceará , Fortaleza, Ceará , Brazil
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18
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Abstract
Respiratory disease is a significant problem worldwide, and it is a problem with increasing prevalence. Pathology in the upper airways and lung is very difficult to diagnose and treat, as response to disease is often heterogeneous across patients. Computational models have long been used to help understand respiratory function, and these models have evolved alongside increases in the resolution of medical imaging and increased capability of functional imaging, advances in biological knowledge, mathematical techniques and computational power. The benefits of increasingly complex and realistic geometric and biophysical models of the respiratory system are that they are able to capture heterogeneity in patient response to disease and predict emergent function across spatial scales from the delicate alveolar structures to the whole organ level. However, with increasing complexity, models become harder to solve and in some cases harder to validate, which can reduce their impact clinically. Here, we review the evolution of complexity in computational models of the respiratory system, including successes in translation of models into the clinical arena. We also highlight major challenges in modelling the respiratory system, while making use of the evolving functional data that are available for model parameterisation and testing.
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Affiliation(s)
- Alys R Clark
- 1 Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
| | - Haribalan Kumar
- 1 Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
| | - Kelly Burrowes
- 2 Department of Chemical and Materials Engineering, The University of Auckland, Auckland, New Zealand
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19
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Kang W, Clark AR, Tawhai MH. Gravity outweighs the contribution of structure to passive ventilation-perfusion matching in the supine adult human lung. J Appl Physiol (1985) 2017; 124:23-33. [PMID: 29051337 DOI: 10.1152/japplphysiol.00791.2016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gravity and matched airway/vascular tree geometries are both hypothesized to be key contributors to ventilation-perfusion (V̇/Q̇) matching in the lung, but their relative contributions are challenging to quantify experimentally. We used a structure-based model to conduct an analysis of the relative contributions of tissue deformation (the "Slinky" effect), other gravitational mechanisms (weight of blood and gravitational gradient in tissue elastic recoil), and matched airway and arterial tree geometry to V̇/Q̇ matching and therefore to total lung oxygen exchange. Our results showed that the heterogeneity in V̇ and Q̇ were lowest and the correlation between V̇ and Q̇ was highest when the only mechanism for V̇/Q̇ matching was either tissue deformation or matched geometry. Heterogeneity in V̇ and Q̇ was highest and their correlation was poorest when all mechanisms were active (that is, at baseline). Eliminating the contribution of matched geometry did not change the correlation between V̇ and Q̇ at baseline. Despite the much larger heterogeneities in V̇ and Q̇ at baseline, the contribution of in-common (to V̇ and Q̇) gravitational mechanisms provided sufficient compensatory V̇/Q̇ matching to minimize the impact on oxygen transfer. In summary, this model predicts that during supine normal breathing under gravitational loading, passive V̇/Q̇ matching is predominantly determined by shared gravitationally induced tissue deformation, compliance distribution, and the effect of the hydrostatic pressure gradient on vessel and capillary size and blood pressures. Contribution from the matching airway and arterial tree geometries in this model is minor under normal gravity in the supine adult human lung. NEW & NOTEWORTHY We use a computational model to systematically analyze contributors to ventilation-perfusion matching in the lung. The model predicts that the multiple effects of gravity are the predominant mechanism in providing passive ventilation-perfusion matching in the supine adult human lung under normal gravitational loads, while geometric matching of airway and arterial trees plays a minor role.
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Affiliation(s)
- W Kang
- Auckland Bioengineering Institute, University of Auckland , Auckland , New Zealand
| | - A R Clark
- Auckland Bioengineering Institute, University of Auckland , Auckland , New Zealand
| | - M H Tawhai
- Auckland Bioengineering Institute, University of Auckland , Auckland , New Zealand
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20
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Guérin C. Prone positioning acute respiratory distress syndrome patients. ANNALS OF TRANSLATIONAL MEDICINE 2017; 5:289. [PMID: 28828364 DOI: 10.21037/atm.2017.06.63] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Prone position has been used in acute respiratory distress syndrome (ARDS) patients for more than 40 years in ICU. After having demonstrated its capability to significantly improve oxygenation in a large number of patients, sometimes dramatically, this procedure has been found to prevent ventilator-induced lung injury, the primary concern for the intensivists managing ARDS patients. Over the time, several trials have been done, which regularly improved and refined from each other. At the end, significant improvement in survival has been demonstrated in the most severe ARDS patients, at a threshold of 100-150 mmHg PaO2/FiO2 ratio. The effect of proning on survival cannot be predicted and seems unrelated with both severity of oxygenation impairment and oxygenation response to proning. The rate of complication is declining with the increase in centers expertise. The pressure sores are more frequent in prone and require a special attention. Prone position is a key component of lung protective mechanical ventilation and should be used as a first line therapy in association with low tidal volume and neuromuscular blocking agents in patients with severe ARDS.
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Affiliation(s)
- Claude Guérin
- Medical ICU, Croix Rousse Hospital, Lyon, France.,University of Lyon, Lyon, France.,INSERM 955, Créteil, France
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21
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Sá RC, Henderson AC, Simonson T, Arai TJ, Wagner H, Theilmann RJ, Wagner PD, Prisk GK, Hopkins SR. Measurement of the distribution of ventilation-perfusion ratios in the human lung with proton MRI: comparison with the multiple inert-gas elimination technique. J Appl Physiol (1985) 2017; 123:136-146. [PMID: 28280105 DOI: 10.1152/japplphysiol.00804.2016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 02/23/2017] [Accepted: 03/07/2017] [Indexed: 11/22/2022] Open
Abstract
We have developed a novel functional proton magnetic resonance imaging (MRI) technique to measure regional ventilation-perfusion (V̇A/Q̇) ratio in the lung. We conducted a comparison study of this technique in healthy subjects (n = 7, age = 42 ± 16 yr, Forced expiratory volume in 1 s = 94% predicted), by comparing data measured using MRI to that obtained from the multiple inert gas elimination technique (MIGET). Regional ventilation measured in a sagittal lung slice using Specific Ventilation Imaging was combined with proton density measured using a fast gradient-echo sequence to calculate regional alveolar ventilation, registered with perfusion images acquired using arterial spin labeling, and divided on a voxel-by-voxel basis to obtain regional V̇A/Q̇ ratio. LogSDV̇ and LogSDQ̇, measures of heterogeneity derived from the standard deviation (log scale) of the ventilation and perfusion vs. V̇A/Q̇ ratio histograms respectively, were calculated. On a separate day, subjects underwent study with MIGET and LogSDV̇ and LogSDQ̇ were calculated from MIGET data using the 50-compartment model. MIGET LogSDV̇ and LogSDQ̇ were normal in all subjects. LogSDQ̇ was highly correlated between MRI and MIGET (R = 0.89, P = 0.007); the intercept was not significantly different from zero (-0.062, P = 0.65) and the slope did not significantly differ from identity (1.29, P = 0.34). MIGET and MRI measures of LogSDV̇ were well correlated (R = 0.83, P = 0.02); the intercept differed from zero (0.20, P = 0.04) and the slope deviated from the line of identity (0.52, P = 0.01). We conclude that in normal subjects, there is a reasonable agreement between MIGET measures of heterogeneity and those from proton MRI measured in a single slice of lung.NEW & NOTEWORTHY We report a comparison of a new proton MRI technique to measure regional V̇A/Q̇ ratio against the multiple inert gas elimination technique (MIGET). The study reports good relationships between measures of heterogeneity derived from MIGET and those derived from MRI. Although currently limited to a single slice acquisition, these data suggest that single sagittal slice measures of V̇A/Q̇ ratio provide an adequate means to assess heterogeneity in the normal lung.
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Affiliation(s)
- Rui Carlos Sá
- Department of Medicine, University of California, San Diego, La Jolla, California.,The Pulmonary Imaging Laboratory, University of California, San Diego, La Jolla, California
| | - A Cortney Henderson
- Department of Medicine, University of California, San Diego, La Jolla, California.,The Pulmonary Imaging Laboratory, University of California, San Diego, La Jolla, California
| | - Tatum Simonson
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Tatsuya J Arai
- Department of Medicine, University of California, San Diego, La Jolla, California.,The Pulmonary Imaging Laboratory, University of California, San Diego, La Jolla, California
| | - Harrieth Wagner
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Rebecca J Theilmann
- Department of Radiology, University of California, San Diego, La Jolla, California; and.,The Pulmonary Imaging Laboratory, University of California, San Diego, La Jolla, California
| | - Peter D Wagner
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - G Kim Prisk
- Department of Medicine, University of California, San Diego, La Jolla, California.,Department of Radiology, University of California, San Diego, La Jolla, California; and.,The Pulmonary Imaging Laboratory, University of California, San Diego, La Jolla, California
| | - Susan R Hopkins
- Department of Medicine, University of California, San Diego, La Jolla, California; .,Department of Radiology, University of California, San Diego, La Jolla, California; and.,The Pulmonary Imaging Laboratory, University of California, San Diego, La Jolla, California
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22
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Abstract
As pulmonary functional imaging moves beyond the realm of the radiologist and physicist, it is important that imagers have a common language and understanding of the relevant physiology of the lung. This review will focus on key physiological concepts and pitfalls relevant to functional lung imaging.
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23
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Barisione G, Brusasco C, Garlaschi A, Baroffio M, Brusasco V. Lung diffusing capacity for nitric oxide as a marker of fibrotic changes in idiopathic interstitial pneumonias. J Appl Physiol (1985) 2016; 120:1029-38. [DOI: 10.1152/japplphysiol.00964.2015] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Accepted: 02/12/2016] [Indexed: 02/07/2023] Open
Abstract
Lung diffusing capacity for carbon monoxide (DLCO) is decreased in both usual interstitial pneumonia-idiopathic pulmonary fibrosis (UIP-IPF) and nonspecific interstitial pneumonia (NSIP), but is moderately related to computed tomography (CT)-determined fibrotic changes. This may be due to the relative insensitivity of DLCO to changes in alveolar membrane diffusive conductance (DMCO). The purpose of this study was to determine whether measurement of lung diffusing capacity for nitric oxide (DLNO) better reflects fibrotic changes than DLCO. DLNO-DLCO were measured simultaneously in 30 patients with UIP-IPF and 30 with NSIP. Eighty-one matched healthy subjects served as a control group. The amount of pulmonary fibrosis was estimated by CT volumetric analysis of visually bounded areas showing reticular opacities and honeycombing. DMCO and pulmonary capillary volume (VC) were calculated. DLNO was below the lower limit of normal in all patients irrespective of extent and nature of disease, whereas DLCO was within the normal range in a nonnegligible number of patients. Both DLNO and DLCO were significantly correlated with visual assessment of fibrosis but DLNO more closely than DLCO. DMCO was also below the lower limit of normal in all UIP-IPF and NSIP patients and significantly correlated with fibrosis extent in both diseases, whereas VC was weakly correlated with fibrosis in UIP-IPF and uncorrelated in NSIP, with normal values in half of patients. In conclusion, measurement of DLNO may provide a more sensitive evaluation of fibrotic changes than DLCO in either UIP-IPF or NSIP, because it better reflects DMCO.
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Affiliation(s)
- Giovanni Barisione
- Unità Operativa Fisiopatologia Respiratoria, Dipartimento di Medicina Interna e Specialità Mediche, Università di Genova, Genoa, Italy; and
| | - Claudia Brusasco
- Unità Operativa Fisiopatologia Respiratoria, Dipartimento di Medicina Interna e Specialità Mediche, Università di Genova, Genoa, Italy; and
| | - Alessandro Garlaschi
- Dipartimento di Diagnostica della Patologia e delle Cure ad Alta Complessità Tecnologica, IRCCS Azienda Ospedaliera Universitaria San Martino-IST, Genoa, Italy
| | - Michele Baroffio
- Unità Operativa Fisiopatologia Respiratoria, Dipartimento di Medicina Interna e Specialità Mediche, Università di Genova, Genoa, Italy; and
| | - Vito Brusasco
- Unità Operativa Fisiopatologia Respiratoria, Dipartimento di Medicina Interna e Specialità Mediche, Università di Genova, Genoa, Italy; and
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24
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Abstract
Structural and functional complexities of the mammalian lung evolved to meet a unique set of challenges, namely, the provision of efficient delivery of inspired air to all lung units within a confined thoracic space, to build a large gas exchange surface associated with minimal barrier thickness and a microvascular network to accommodate the entire right ventricular cardiac output while withstanding cyclic mechanical stresses that increase several folds from rest to exercise. Intricate regulatory mechanisms at every level ensure that the dynamic capacities of ventilation, perfusion, diffusion, and chemical binding to hemoglobin are commensurate with usual metabolic demands and periodic extreme needs for activity and survival. This article reviews the structural design of mammalian and human lung, its functional challenges, limitations, and potential for adaptation. We discuss (i) the evolutionary origin of alveolar lungs and its advantages and compromises, (ii) structural determinants of alveolar gas exchange, including architecture of conducting bronchovascular trees that converge in gas exchange units, (iii) the challenges of matching ventilation, perfusion, and diffusion and tissue-erythrocyte and thoracopulmonary interactions. The notion of erythrocytes as an integral component of the gas exchanger is emphasized. We further discuss the signals, sources, and limits of structural plasticity of the lung in alveolar hypoxia and following a loss of lung units, and the promise and caveats of interventions aimed at augmenting endogenous adaptive responses. Our objective is to understand how individual components are matched at multiple levels to optimize organ function in the face of physiological demands or pathological constraints.
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Affiliation(s)
- Connie C.W. Hsia
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Dallas M. Hyde
- California National Primate Research Center, University of California at Davis, Davis, California, USA
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Ishii M, Hamedani H, Clapp JT, Kadlecek SJ, Xin Y, Gefter WB, Rossman MD, Rizi RR. Oxygen-weighted Hyperpolarized (3)He MR Imaging: A Short-term Reproducibility Study in Human Subjects. Radiology 2015; 277:247-58. [PMID: 26110668 DOI: 10.1148/radiol.2015142038] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To determine whether hyperpolarized helium 3 magnetic resonance (MR) imaging to measure alveolar partial pressure of oxygen (Pao2) shows sufficient test-retest repeatability and between-cohort differences to be used as a reliable technique for detection of alterations in gas exchange in asymptomatic smokers. MATERIALS AND METHODS The protocol was approved by the local institutional review board and was HIPAA compliant. Informed consent was obtained from all subjects. Two sets of MR images were obtained 10 minutes apart in 25 subjects: 10 nonsmokers (five men, five women; mean ± standard deviation age, 50 years ± 6) and 15 smokers (seven women, eight men; mean age, 50 years ± 8). A mixed-effects model was developed to identify the regional repeatability of Pao2 measurements as an intraclass correlation coefficient. Ten smokers were matched with the 10 nonsmokers on the basis of signal-to-noise ratio (SNR). Three separate models were generated: one for nonsmokers, one for the SNR-matched smokers, and one for the five remaining smokers, who were imaged with a significantly higher SNR. RESULTS Short-term back-to-back regional reproducibility was assessed by using intraclass correlation coefficients, which were 0.67 and 0.65 for SNR case-matched nonsmokers and smokers, respectively. Repeatability was a strong function of SNR; a 50% increase in SNR in the remaining smokers improved the intraclass correlation coefficient to 0.82. Although repeatability was not significantly different between the SNR-matched cohorts (P = .44), the smoker group showed higher spatial and temporal variability in Pao2. CONCLUSION The short-term test-retest repeatability of hyperpolarized gas MR imaging of regional Pao2 was good. Asymptomatic smokers exhibited greater spatial and temporal variability in Pao2 than did the nonsmokers, which suggests that this parameter allows detection of small functional alterations associated with smoking.
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Affiliation(s)
- Masaru Ishii
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
| | - Hooman Hamedani
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
| | - Justin T Clapp
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
| | - Stephen J Kadlecek
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
| | - Yi Xin
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
| | - Warren B Gefter
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
| | - Milton D Rossman
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
| | - Rahim R Rizi
- From the Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University, Baltimore, Md (M.I., R.R.R.); Department of Radiology (H.H., J.T.C., S.J.K., Y.X., W.G.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104
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26
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Torday JS. Pleiotropy as the Mechanism for Evolving Novelty: Same Signal, Different Result. BIOLOGY 2015; 4:443-59. [PMID: 26103090 PMCID: PMC4498309 DOI: 10.3390/biology4020443] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Revised: 06/02/2015] [Accepted: 06/10/2015] [Indexed: 11/22/2022]
Abstract
In contrast to the probabilistic way of thinking about pleiotropy as the random expression of a single gene that generates two or more distinct phenotypic traits, it is actually a deterministic consequence of the evolution of complex physiology from the unicellular state. Pleiotropic novelties emerge through recombinations and permutations of cell-cell signaling exercised during reproduction based on both past and present physical and physiologic conditions, in service to the future needs of the organism for its continued survival. Functional homologies ranging from the lung to the kidney, skin, brain, thyroid and pituitary exemplify the evolutionary mechanistic strategy of pleiotropy. The power of this perspective is exemplified by the resolution of evolutionary gradualism and punctuated equilibrium in much the same way that Niels Bohr resolved the paradoxical duality of light as Complementarity.
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Affiliation(s)
- John S Torday
- Harbor-UCLA Medical Center, 1124 West Carson Street, Torrance, CA 90502-2006, USA.
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27
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Cardona PJ. The key role of exudative lesions and their encapsulation: lessons learned from the pathology of human pulmonary tuberculosis. Front Microbiol 2015; 6:612. [PMID: 26136741 PMCID: PMC4468931 DOI: 10.3389/fmicb.2015.00612] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 06/02/2015] [Indexed: 12/31/2022] Open
Abstract
A review of the pathology of human pulmonary TB cases at different stages of evolution in the pre-antibiotic era suggests that neutrophils play an instrumental role in the progression toward active TB. This progression is determined by the type of lesion generated. Thus, exudative lesions, in which neutrophils are the major cell type, are both triggered by and induce local high bacillary load, and tend to enlarge and progress toward liquefaction and cavitation. In contrast, proliferative lesions are triggered by low bacillary loads, mainly comprise epithelioid cells and fibroblasts and tend to fibrose, encapsulate and calcify, thus controlling the infection. Infection of the upper lobes is key to the progression toward active TB for two main reasons, namely poor breathing amplitude, which allows local bacillary accumulation, and the high mechanical stress to which the interlobular septae (which enclose secondary lobes) are submitted, which hampers their ability to encapsulate lesions. Overall, progressing factors can be defined as internal (exudative lesion, local bronchogenous dissemination, coalescence of lesions), with lympho-hematological dissemination playing a very limited role, or external (exogenous reinfection). Abrogating factors include control of the bacillary load and the local encapsulation process, as directed by interlobular septae. The age and extent of disease depend on the quality and speed with which lesions liquefy and disseminate bronchially, the volume of the slough, and the amount and distribution of the sloughing debris dispersed.
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Affiliation(s)
- Pere-Joan Cardona
- Unitat de Tuberculosi Experimental, Fundació Institut d'Investigació en Ciències de la Salut Germans Trias i Pujol, Universitat Autònoma de Barcelona, Centro de Investigación Biomédica en Red de Enfermedades Respiratorias Badalona, Spain
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28
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Asadi AK, Sá RC, Kim NH, Theilmann RJ, Hopkins SR, Buxton RB, Prisk GK. Inhaled nitric oxide alters the distribution of blood flow in the healthy human lung, suggesting active hypoxic pulmonary vasoconstriction in normoxia. J Appl Physiol (1985) 2014; 118:331-43. [PMID: 25429099 DOI: 10.1152/japplphysiol.01354.2013] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hypoxic pulmonary vasoconstriction (HPV) is thought to actively regulate ventilation-perfusion (V̇a/Q̇) matching, reducing perfusion in regions of alveolar hypoxia. We assessed the extent of HPV in the healthy human lung using inhaled nitric oxide (iNO) under inspired oxygen fractions (FiO2 ) of 0.125, 0.21, and 0.30 (a hyperoxic stimulus designed to abolish HPV without the development of atelectasis). Dynamic measures of blood flow were made in a single sagittal slice of the right lung of five healthy male subjects using an arterial spin labeling (ASL) MRI sequence, following a block stimulus pattern (3 × 60 breaths) with 40 ppm iNO administered in the central block. The overall spatial heterogeneity, spatiotemporal variability, and regional pattern of pulmonary blood flow was quantified as a function of condition (FiO2 × iNO state). While spatial heterogeneity did not change significantly with iNO administration or FiO2 , there were statistically significant increases in Global Fluctuation Dispersion, (a marker of spatiotemporal flow variability) when iNO was administered during hypoxia (5.4 percentage point increase, P = 0.003). iNO had an effect on regional blood flow that was FiO2 dependent (P = 0.02), with regional changes in the pattern of blood flow occurring in hypoxia (P = 0.007) and normoxia (P = 0.008) tending to increase flow to dependent lung at the expense of nondependent lung. These findings indicate that inhaled nitric oxide significantly alters the distribution of blood flow in both hypoxic and normoxic healthy subjects, and suggests that some baseline HPV may indeed be present in the normoxic lung.
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Affiliation(s)
- Amran K Asadi
- Department of Medicine, University of California, San Diego, La Jolla, California; and
| | - Rui Carlos Sá
- Department of Medicine, University of California, San Diego, La Jolla, California; and
| | - Nick H Kim
- Department of Medicine, University of California, San Diego, La Jolla, California; and
| | - Rebecca J Theilmann
- Department of Radiology, University of California, San Diego, La Jolla, California
| | - Susan R Hopkins
- Department of Medicine, University of California, San Diego, La Jolla, California; and Department of Radiology, University of California, San Diego, La Jolla, California
| | - Richard B Buxton
- Department of Radiology, University of California, San Diego, La Jolla, California
| | - G Kim Prisk
- Department of Medicine, University of California, San Diego, La Jolla, California; and Department of Radiology, University of California, San Diego, La Jolla, California
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29
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Glenny RW, Bauer C, Hofmanninger J, Lamm WJ, Krueger MA, Beichel RR. Heterogeneity and matching of ventilation and perfusion within anatomical lung units in rats. Respir Physiol Neurobiol 2013; 189:594-606. [PMID: 23942308 DOI: 10.1016/j.resp.2013.07.027] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 07/24/2013] [Accepted: 07/30/2013] [Indexed: 11/30/2022]
Abstract
Prior studies exploring the spatial distributions of ventilation and perfusion have partitioned the lung into discrete regions not constrained by anatomical boundaries and may blur regional differences in perfusion and ventilation. To characterize the anatomical heterogeneity of regional ventilation and perfusion, we administered fluorescent microspheres to mark regional ventilation and perfusion in five Sprague-Dawley rats and then using highly automated computer algorithms, partitioned the lungs into regions defined by anatomical structures identified in the images. The anatomical regions ranged in size from the near-acinar to the lobar level. Ventilation and perfusion were well correlated at the smallest anatomical level. Perfusion and ventilation heterogeneity were relatively less in rats compared to data previously published in larger animals. The more uniform distributions may be due to a smaller gravitational gradient and/or the fewer number of generations in the distribution trees before reaching the level of gas exchange, making regional matching of ventilation and perfusion less extensive in small animals.
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30
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31
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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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32
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Stickland MK, Lindinger MI, Olfert IM, Heigenhauser GJF, Hopkins SR. Pulmonary gas exchange and acid-base balance during exercise. Compr Physiol 2013; 3:693-739. [PMID: 23720327 PMCID: PMC8315793 DOI: 10.1002/cphy.c110048] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
As the first step in the oxygen-transport chain, the lung has a critical task: optimizing the exchange of respiratory gases to maintain delivery of oxygen and the elimination of carbon dioxide. In healthy subjects, gas exchange, as evaluated by the alveolar-to-arterial PO2 difference (A-aDO2), worsens with incremental exercise, and typically reaches an A-aDO2 of approximately 25 mmHg at peak exercise. While there is great individual variability, A-aDO2 is generally largest at peak exercise in subjects with the highest peak oxygen consumption. Inert gas data has shown that the increase in A-aDO2 is explained by decreased ventilation-perfusion matching, and the development of a diffusion limitation for oxygen. Gas exchange data does not indicate the presence of right-to-left intrapulmonary shunt developing with exercise, despite recent data suggesting that large-diameter arteriovenous shunt vessels may be recruited with exercise. At the same time, multisystem mechanisms regulate systemic acid-base balance in integrative processes that involve gas exchange between tissues and the environment and simultaneous net changes in the concentrations of strong and weak ions within, and transfer between, extracellular and intracellular fluids. The physicochemical approach to acid-base balance is used to understand the contributions from independent acid-base variables to measured acid-base disturbances within contracting skeletal muscle, erythrocytes and noncontracting tissues. In muscle, the magnitude of the disturbance is proportional to the concentrations of dissociated weak acids, the rate at which acid equivalents (strong acid) accumulate and the rate at which strong base cations are added to or removed from muscle.
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Affiliation(s)
- Michael K. Stickland
- Division of Pulmonary Medicine, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada
| | - Michael I. Lindinger
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - I. Mark Olfert
- Robert C. Byrd Health Sciences Center, Center for Cardiovascular and Respiratory Sciences, Division of Exercise Physiology, West Virginia University School of Medicine, Morgantown, West Virginia
| | | | - Susan R. Hopkins
- Departments of Medicine and Radiology, University of California, San Diego, San Diego, California
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