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Atia L, Fredberg JJ. A life off the beaten track in biomechanics: Imperfect elasticity, cytoskeletal glassiness, and epithelial unjamming. BIOPHYSICS REVIEWS 2023; 4:041304. [PMID: 38156333 PMCID: PMC10751956 DOI: 10.1063/5.0179719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Accepted: 11/17/2023] [Indexed: 12/30/2023]
Abstract
Textbook descriptions of elasticity, viscosity, and viscoelasticity fail to account for certain mechanical behaviors that typify soft living matter. Here, we consider three examples. First, strong empirical evidence suggests that within lung parenchymal tissues, the frictional stresses expressed at the microscale are fundamentally not of viscous origin. Second, the cytoskeleton (CSK) of the airway smooth muscle cell, as well as that of all eukaryotic cells, is more solid-like than fluid-like, yet its elastic modulus is softer than the softest of soft rubbers by a factor of 104-105. Moreover, the eukaryotic CSK expresses power law rheology, innate malleability, and fluidization when sheared. For these reasons, taken together, the CSK of the living eukaryotic cell is reminiscent of the class of materials called soft glasses, thus likening it to inert materials such as clays, pastes slurries, emulsions, and foams. Third, the cellular collective comprising a confluent epithelial layer can become solid-like and jammed, fluid-like and unjammed, or something in between. Esoteric though each may seem, these discoveries are consequential insofar as they impact our understanding of bronchospasm and wound healing as well as cancer cell invasion and embryonic development. Moreover, there are reasons to suspect that certain of these phenomena first arose in the early protist as a result of evolutionary pressures exerted by the primordial microenvironment. We have hypothesized, further, that each then became passed down virtually unchanged to the present day as a conserved core process. These topics are addressed here not only because they are interesting but also because they track the journey of one laboratory along a path less traveled by.
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Affiliation(s)
- Lior Atia
- Ben Gurion University of the Negev, Beer Sheva, Israel
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2
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Donovan GM, Noble PB, Langton D. Therapeutic response to bronchial thermoplasty: toward feasibility of patient selection based on modeling predictions. J Appl Physiol (1985) 2022; 133:1341-1348. [PMID: 36356255 DOI: 10.1152/japplphysiol.00493.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Bronchial thermoplasty (BT) is a treatment for moderate-to-severe asthma in which the airway smooth muscle layer is targeted directly using thermal ablation. Although it has been shown to be safe and effective in long-term follow-up, questions remain about its mechanism of action, patient selection, and optimization of protocol based on structural phenotype. Using a cohort of 20 subjects who underwent thermoplasty and assessment by computed tomography (CT), we demonstrate that response to BT can be feasibly predicted based on pretreatment airway dimensions that inform a subject-specific computational model. Analysis revealed the need for CT assessment at total lung capacity, rather than functional residual capacity, which was less sensitive to the effects of BT. Final model predictions compared favorably with observed outcomes in terms of airway caliber and asthma control, suggesting that this approach could form the basis of improved clinical practice.NEW & NOTEWORTHY Bronchial thermoplasty is a treatment for asthma that targets the airway smooth muscle directly. We demonstrate the feasibility and constraints of predicting patient-specific response to thermoplasty using a computational model informed by pretreatment CT scans at different lung volumes. Predictions are compared with functional outcomes and posttreatment CT scans. This has the potential to form the basis for improved clinical practice.
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Affiliation(s)
- G M Donovan
- Department of Mathematics, The University of Auckland, Auckland, New Zealand
| | - P B Noble
- School of Human Sciences, The University of Western Australia, Crawley, Western Australia, Australia
| | - D Langton
- Faculty of Medicine, Nursing and Allied Health, Monash University, Melbourne, Victoria, Australia
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3
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Donovan GM, Noble PB. Small airways vs large airways in asthma: time for a new perspective. J Appl Physiol (1985) 2021; 131:1839-1841. [PMID: 34520278 DOI: 10.1152/japplphysiol.00403.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Graham M Donovan
- Department of Mathematics, University of Auckland, Auckland, New Zealand
| | - Peter B Noble
- School of Human Sciences, University of Western Australia, Crawley, Western Australia, Australia
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4
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Rampadarath AK, Donovan GM. Mathematical modelling of lung function — what have we learnt and where to next? CURRENT OPINION IN PHYSIOLOGY 2021. [DOI: 10.1016/j.cophys.2021.03.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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5
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Jamieson RR, Stasiak SE, Polio SR, Augspurg RD, McCormick CA, Ruberti JW, Parameswaran H. Stiffening of the extracellular matrix is a sufficient condition for airway hyperreactivity. J Appl Physiol (1985) 2021; 130:1635-1645. [PMID: 33792403 DOI: 10.1152/japplphysiol.00554.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The current therapeutic approach to asthma focuses exclusively on targeting inflammation and reducing airway smooth muscle force to prevent the recurrence of symptoms. However, even when inflammation is brought under control, airways in an asthmatic can still hyperconstrict when exposed to a low dose of agonist. This suggests that there are mechanisms at play that are likely triggered by inflammation and eventually become self-sustaining so that even when airway inflammation is brought back under control, these alternative mechanisms continue to drive airway hyperreactivity in asthmatics. In this study, we hypothesized that stiffening of the airway extracellular matrix is a core pathological change sufficient to support excessive bronchoconstriction even in the absence of inflammation. To test this hypothesis, we increased the stiffness of the airway extracellular matrix by photo-crosslinking collagen fibers within the airway wall of freshly dissected bovine rings using riboflavin (vitamin B2) and Ultraviolet-A radiation. In our experiments, collagen crosslinking led to a twofold increase in the stiffness of the airway extracellular matrix. This change was sufficient to cause airways to constrict to a greater degree, and at a faster rate when they were exposed to 10-5 M acetylcholine for 5 min. Our results show that stiffening of the extracellular matrix is sufficient to drive excessive airway constriction even in the absence of inflammatory signals.NEW & NOTEWORTHY Targeting inflammation is the central dogma on which current asthma therapy is based. Here, we show that a healthy airway can be made to constrict excessively and at a faster rate in response to the same stimulus by increasing the stiffness of the extracellular matrix, without the use of inflammatory agents. Our results provide an independent mechanism by which airway remodeling in asthma can sustain airway hyperreactivity even in the absence of inflammatory signals.
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Affiliation(s)
- Ryan R Jamieson
- Department of Bioengineering, Northeastern University, Boston, Massachusetts
| | - Suzanne E Stasiak
- Department of Bioengineering, Northeastern University, Boston, Massachusetts
| | - Samuel R Polio
- Department of Bioengineering, Northeastern University, Boston, Massachusetts
| | - Ralston D Augspurg
- Department of Bioengineering, Northeastern University, Boston, Massachusetts
| | | | - Jeffrey W Ruberti
- Department of Bioengineering, Northeastern University, Boston, Massachusetts
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6
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van den Bosch WB, James AL, Tiddens HA. Structure and function of small airways in asthma patients revisited. Eur Respir Rev 2021; 30:200186. [PMID: 33472958 PMCID: PMC9488985 DOI: 10.1183/16000617.0186-2020] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Accepted: 08/27/2020] [Indexed: 12/21/2022] Open
Abstract
Small airways (<2 mm in diameter) are probably involved across almost all asthma severities and they show proportionally more structural and functional abnormalities with increasing asthma severity. The structural and functional alterations of the epithelium, extracellular matrix and airway smooth muscle in small airways of people with asthma have been described over many years using in vitro studies, animal models or imaging and modelling methods. The purpose of this review was to provide an overview of these observations and to outline several potential pathophysiological mechanisms regarding the role of small airways in asthma.
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Affiliation(s)
- Wytse B. van den Bosch
- Dept of Paediatric Pulmonology and Allergology, Erasmus MC – Sophia Children’s Hospital, University Medical Center Rotterdam, Rotterdam, The Netherlands
- Dept of Radiology and Nuclear Medicine, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Alan L. James
- Dept of Pulmonary Physiology and Sleep Medicine, Sir Charles Gairdner Hospital, Perth, Australia
| | - Harm A.W.M. Tiddens
- Dept of Paediatric Pulmonology and Allergology, Erasmus MC – Sophia Children’s Hospital, University Medical Center Rotterdam, Rotterdam, The Netherlands
- Dept of Radiology and Nuclear Medicine, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
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7
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Foy BH, Natarajan S, Munawar A, Soares M, Thorpe J, Owers-Bradley J, Siddiqui S. Characterising the role of small airways in severe asthma using low frequency forced oscillations: A combined computational and clinical approach. Respir Med 2020; 170:106022. [PMID: 32843165 DOI: 10.1016/j.rmed.2020.106022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Revised: 03/18/2020] [Accepted: 05/11/2020] [Indexed: 10/24/2022]
Abstract
BACKGROUND Within asthma, the small airways (≤2 mm in diameter) play an important role in pathophysiology. Using a combined clinical-computational approach, we sought to more precisely evaluate the contribution of the small airways to deep-breath induced airway dilation (in the absence of bronchial challenge), which may be impaired in severe asthma. METHODS A patient-based computational model of the FOT was used to examine the sensitivity and specificity of FOT signals to small airways constriction at frequencies of 2 & 8 Hz. A clinical study of moderate to severe asthmatics (n = 24), and healthy volunteers (n = 10) was performed to evaluate correlations between baseline and post deep inspiration (following bronchodilator withhold and in the absence of prior bronchial challenge) forced oscillation technique (FOT) responses (at 2Hz and 8Hz) and asthma treatment intensity, spirometry, airway hyper-responsiveness and airway inflammation. RESULTS Computational modelling demonstrated that baseline resistance measures at 2Hz are both sensitive and specific to anatomical narrowing in the small airways. Furthermore, small airways resistance was significantly increased in asthmatics compared to health. Despite these differences, there were no noticeable differences between asthmatics and healthy volunteers in resistive measures following deep inspiration (DI) and DI responses of small airways were amplified in the presence of spirometry defined airflow limitation. CONCLUSIONS These results suggest that the small airways demonstrate increased resistance in moderate-to-severe asthma but dilate normally in response to deep inspirations in the absence of bronchial challenge. This suggests that effective targeting of the small airways is required to achieve functional improvements in moderate-severe asthmatic patients.
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Affiliation(s)
- Brody H Foy
- Computational Biology, Department of Computer Science, University of Oxford, Oxford, United Kingdom.
| | - Sushiladevi Natarajan
- Institute for Lung Health, Department of Respiratory Sciences, University of Leicester, United Kingdom
| | - Arham Munawar
- Cambridge University Hospitals, NHS Foundation Trust, Cambridge, United Kingdom
| | - Marcia Soares
- Institute for Lung Health, Department of Respiratory Sciences, University of Leicester, United Kingdom
| | - James Thorpe
- School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom
| | - John Owers-Bradley
- School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom
| | - Salman Siddiqui
- Institute for Lung Health, Department of Respiratory Sciences, University of Leicester, United Kingdom
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8
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Gazzola M, Khadangi F, Clisson M, Beaudoin J, Clavel MA, Bossé Y. Airway smooth muscle adapting in dynamic conditions is refractory to the bronchodilator effect of a deep inspiration. Am J Physiol Lung Cell Mol Physiol 2020; 318:L452-L458. [PMID: 31913645 DOI: 10.1152/ajplung.00270.2019] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Airway smooth muscle (ASM) is continuously strained during breathing at tidal volume. Whether this tidal strain influences the magnitude of the bronchodilator response to a deep inspiration (DI) is not clearly defined. The present in vitro study examines the effect of tidal strain on the bronchodilator effect of DIs. ASM strips from sheep tracheas were mounted in organ baths and then subjected to stretches (30% strain), simulating DIs at varying time intervals. In between simulated DIs, the strips were either held at a fixed length (isometric) or oscillated continuously by 6% (length oscillations) to simulate tidal strain. The contractile state of the strips was also controlled by adding either methacholine or isoproterenol to activate or relax ASM, respectively. Although the time-dependent gain in force caused by methacholine was attenuated by length oscillations, part of the acquired force in the oscillating condition was preserved postsimulated DIs, which was not the case in the isometric condition. Consequently, the bronchodilator effect of simulated DIs (i.e., the decline in force postsimulated versus presimulated DIs) was attenuated in oscillating versus isometric conditions. These findings suggest that an ASM operating in a dynamic environment acquired adaptations that make it refractory to the decline in contractility inflicted by a larger strain simulating a DI.
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Affiliation(s)
- Morgan Gazzola
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Laval University, Quebec City, Quebec, Canada
| | - Fatemeh Khadangi
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Laval University, Quebec City, Quebec, Canada
| | - Marine Clisson
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Laval University, Quebec City, Quebec, Canada
| | - Jonathan Beaudoin
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Laval University, Quebec City, Quebec, Canada
| | - Marie-Annick Clavel
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Laval University, Quebec City, Quebec, Canada
| | - Ynuk Bossé
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Laval University, Quebec City, Quebec, Canada
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9
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Ram-Mohan S, Bai Y, Schaible N, Ehrlicher AJ, Cook DP, Suki B, Stoltz DA, Solway J, Ai X, Krishnan R. Tissue traction microscopy to quantify muscle contraction within precision-cut lung slices. Am J Physiol Lung Cell Mol Physiol 2019; 318:L323-L330. [PMID: 31774304 DOI: 10.1152/ajplung.00297.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In asthma, acute bronchospasm is driven by contractile forces of airway smooth muscle (ASM). These forces can be imaged in the cultured ASM cell or assessed in the muscle strip and the tracheal/bronchial ring, but in each case, the ASM is studied in isolation from the native airway milieu. Here, we introduce a novel platform called tissue traction microscopy (TTM) to measure ASM contractile force within porcine and human precision-cut lung slices (PCLS). Compared with the conventional measurements of lumen area changes in PCLS, TTM measurements of ASM force changes are 1) more sensitive to bronchoconstrictor stimuli, 2) less variable across airways, and 3) provide spatial information. Notably, within every human airway, TTM measurements revealed local regions of high ASM contraction that we call "stress hotspots". As an acute response to cyclic stretch, these hotspots promptly decreased but eventually recovered in magnitude, spatial location, and orientation, consistent with local ASM fluidization and resolidification. By enabling direct and precise measurements of ASM force, TTM should accelerate preclinical studies of airway reactivity.
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Affiliation(s)
- Sumati Ram-Mohan
- Center for Vascular Biology Research, Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts
| | - Yan Bai
- Pulmonary and Critical Care Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts
| | - Niccole Schaible
- Center for Vascular Biology Research, Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts
| | - Allen J Ehrlicher
- Department of Bioengineering, McGill University, Montreal, Quebec, Canada
| | - Daniel P Cook
- Department of Internal Medicine, University of Iowa, Iowa City, Iowa
| | - Bela Suki
- Biomedical Engineering Department, Boston University, Boston, Massachusetts
| | - David A Stoltz
- Department of Internal Medicine, University of Iowa, Iowa City, Iowa
| | - Julian Solway
- Department of Medicine, University of Chicago, Chicago, Illinois
| | - Xingbin Ai
- Pulmonary and Critical Care Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts
| | - Ramaswamy Krishnan
- Center for Vascular Biology Research, Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts
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10
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Gazzola M, Khadangi F, Clisson M, Beaudoin J, Clavel MA, Bossé Y. Shortening of airway smooth muscle is modulated by prolonging the time without simulated deep inspirations in ovine tracheal strips. J Appl Physiol (1985) 2019; 127:1528-1538. [PMID: 31545157 DOI: 10.1152/japplphysiol.00423.2019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The shortening of airway smooth muscle (ASM) is greatly affected by time. This is because stimuli affecting ASM shortening, such as bronchoactive molecules or the strain inflicted by breathing maneuvers, not only alter quick biochemical processes regulating contraction but also slower processes that allow ASM to adapt to an ever-changing length. Little attention has been given to the effect of time on ASM shortening. The present study investigates the effect of changing the time interval between simulated deep inspirations (DIs) on ASM shortening and its responsiveness to simulated DIs. Excised tracheal strips from sheep were mounted in organ baths and either activated with methacholine or relaxed with isoproterenol. They were then subjected to simulated DIs by imposing swings in distending stress, emulating a transmural pressure from 5 to 30 cmH2O. The simulated DIs were intercalated by 2, 5, 10, or 30 min. In between simulated DIs, the distending stress was either fixed or oscillating to simulate tidal breathing. The results show that although shortening was increased by prolonging the interval between simulated DIs, the bronchodilator effect of simulated DIs (i.e., the elongation of the strip post- vs. pre-DI) was not affected, and the rate of re-shortening post-simulated DIs was decreased. As the frequency with which DIs are taken increases upon bronchoconstriction, our results may be relevant to typical alterations observed in asthma, such as an increased rate of re-narrowing post-DI.NEW & NOTEWORTHY The frequency with which patients with asthma take deep inspirations (DIs) increases during bronchoconstriction. This in vitro study investigated the effect of changing the time interval between simulated DIs on airway smooth muscle shortening. The results demonstrated that decreasing the interval between simulated DIs not only decreases shortening, which may be protective against excessive airway narrowing, but also increases the rate of re-shortening post-simulated DIs, which may contribute to the increased rate of re-narrowing post-DI observed in asthma.
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11
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Polio SR, Stasiak SE, Jamieson RR, Balestrini JL, Krishnan R, Parameswaran H. Extracellular matrix stiffness regulates human airway smooth muscle contraction by altering the cell-cell coupling. Sci Rep 2019; 9:9564. [PMID: 31267003 PMCID: PMC6606622 DOI: 10.1038/s41598-019-45716-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2018] [Accepted: 06/13/2019] [Indexed: 12/31/2022] Open
Abstract
For an airway or a blood vessel to narrow, there must be a connected path that links the smooth muscle (SM) cells with each other, and transmits forces around the organ, causing it to constrict. Currently, we know very little about the mechanisms that regulate force transmission pathways in a multicellular SM ensemble. Here, we used extracellular matrix (ECM) micropatterning to study force transmission in a two-cell ensemble of SM cells. Using the two-SM cell ensemble, we demonstrate (a) that ECM stiffness acts as a switch that regulates whether SM force is transmitted through the ECM or through cell-cell connections. (b) Fluorescent imaging for adherens junctions and focal adhesions show the progressive loss of cell-cell borders and the appearance of focal adhesions with the increase in ECM stiffness (confirming our mechanical measurements). (c) At the same ECM stiffness, we show that the presence of a cell-cell border substantially decreases the overall contractility of the SM cell ensemble. Our results demonstrate that connectivity among SM cells is a critical factor to consider in the development of diseases such as asthma and hypertension.
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Affiliation(s)
- Samuel R Polio
- Department of Bioengineering, Northeastern University, Boston, MA, 02115, USA
| | - Suzanne E Stasiak
- Department of Bioengineering, Northeastern University, Boston, MA, 02115, USA
| | - Ryan R Jamieson
- Department of Bioengineering, Northeastern University, Boston, MA, 02115, USA
| | - Jenna L Balestrini
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Ramaswamy Krishnan
- Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Boston, MA, 02115, USA
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12
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Bossé Y. The Strain on Airway Smooth Muscle During a Deep Inspiration to Total Lung Capacity. JOURNAL OF ENGINEERING AND SCIENCE IN MEDICAL DIAGNOSTICS AND THERAPY 2019; 2:0108021-1080221. [PMID: 32328568 PMCID: PMC7164505 DOI: 10.1115/1.4042309] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Revised: 11/06/2018] [Indexed: 02/05/2023]
Abstract
The deep inspiration (DI) maneuver entices a great deal of interest because of its ability to temporarily ease the flow of air into the lungs. This salutary effect of a DI is proposed to be mediated, at least partially, by momentarily increasing the operating length of airway smooth muscle (ASM). Concerningly, this premise is largely derived from a growing body of in vitro studies investigating the effect of stretching ASM by different magnitudes on its contractility. The relevance of these in vitro findings remains uncertain, as the real range of strains ASM undergoes in vivo during a DI is somewhat elusive. In order to understand the regulation of ASM contractility by a DI and to infer on its putative contribution to the bronchodilator effect of a DI, it is imperative that in vitro studies incorporate levels of strains that are physiologically relevant. This review summarizes the methods that may be used in vivo in humans to estimate the strain experienced by ASM during a DI from functional residual capacity (FRC) to total lung capacity (TLC). The strengths and limitations of each method, as well as the potential confounders, are also discussed. A rough estimated range of ASM strains is provided for the purpose of guiding future in vitro studies that aim at quantifying the regulatory effect of DI on ASM contractility. However, it is emphasized that, owing to the many limitations and confounders, more studies will be needed to reach conclusive statements.
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Affiliation(s)
- Ynuk Bossé
- Université Laval, Faculty of Medicine, Department of Medicine, IUCPQ, M2694, Pavillon Mallet, Chemin Sainte-Foy, Québec, QC G1V 4G5, Canada e-mail:
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13
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Lutchen KR, Paré PD, Seow CY. Hyperresponsiveness: Relating the Intact Airway to the Whole Lung. Physiology (Bethesda) 2018; 32:322-331. [PMID: 28615315 DOI: 10.1152/physiol.00008.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 05/10/2017] [Accepted: 05/10/2017] [Indexed: 11/22/2022] Open
Abstract
We relate changes of the airway wall to the response of the intact airway and the whole lung. We address how mechanical conditions and specific structural changes for an airway contribute to hyperresponsiveness resistant to deep inspiration. This review conveys that the origins of hyperresponsiveness do not devolve into an abnormality at single structural level but require examination of the complex interplay of all the parts.
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Affiliation(s)
- Kenneth R Lutchen
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts
| | - Peter D Paré
- Department of Medicine, Respiratory Division, University of British Columbia, Vancouver, British Columbia, Canada.,Centre for Heart Lung Innovation-St. Paul's Hospital, University of British Columbia, Vancouver, British Columbia, Canada; and
| | - Chun Y Seow
- Centre for Heart Lung Innovation-St. Paul's Hospital, University of British Columbia, Vancouver, British Columbia, Canada; and.,Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada
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14
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Donovan GM. Inter-airway structural heterogeneity interacts with dynamic heterogeneity to determine lung function and flow patterns in both asthmatic and control simulated lungs. J Theor Biol 2017; 435:98-105. [PMID: 28867222 DOI: 10.1016/j.jtbi.2017.08.024] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 08/23/2017] [Accepted: 08/28/2017] [Indexed: 01/10/2023]
Abstract
Asthma is a disease involving both airway remodelling (e.g. thickening of the airway wall) and acute, reversible airway narrowing driven by airway smooth muscle contraction. Both of these processes are known to be heterogeneous, and in this study we consider a new theoretical model which considers the interactions of both mechanisms: structural heterogeneity (variation in airway remodelling) and dynamic heterogeneity (emergent variation in airway narrowing and flow). By integrating both types of inter-airway heterogeneity in a full human lung geometry, we are able to draw several insights regarding the mechanisms underlying observed ventilation heterogeneity. We show that: (1) bimodal ventilation distributions are driven by paradoxical contraction/dilation patterns for airways of all sizes; (2) structural heterogeneity differences between asthmatic and control subjects significantly influences resulting lung function, and observed ventilation heterogeneity patterns; and (3) individual airway dilation probabilities are uncorrelated with prior airway remodelling of that airway.
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Affiliation(s)
- G M Donovan
- Department of Mathematics, University of Auckland, New Zealand.
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15
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Donovan GM. Airway Bistability Is Modulated by Smooth Muscle Dynamics and Length-Tension Characteristics. Biophys J 2017; 111:2327-2335. [PMID: 27851954 DOI: 10.1016/j.bpj.2016.10.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Revised: 10/03/2016] [Accepted: 10/05/2016] [Indexed: 12/11/2022] Open
Abstract
Airway closure has important implications for lung disease, especially asthma; in particular, the prospect of bistability between open and closed (or effectively closed) airway states has been thought to play a prominent role in airway closure associated with the formation of clustered ventilation defects in asthma. However, many existing analyses of closure consider only static airway equilibria; here we construct, to our knowledge, a new model wherein airway narrowing and closure dynamics are modulated by coupling the airway to cross-bridge models of airway smooth muscle dynamics and force generation. Using this model, we show that important qualitative features of airway pressure-radius hysteresis loops are highly dependent on both airway smooth muscle dynamics, and the length-tension relationship. Furthermore, we show that two recent experimental results from intact bronchial segments are both expressions of the same phenomenon: that a monotonically increasing length-tension relationship, with sharply higher tension at longer lengths, is needed to drive the observed changes in low-compliance regions of the baseline pressure-radius curve. We also explore the potential implications of this finding for airway closure in coupled airway models.
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Affiliation(s)
- Graham M Donovan
- Department of Mathematics, University of Auckland, Auckland, New Zealand.
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16
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Harvey BC, Lutchen KR, Barbone PE. Spatial distribution of airway wall displacements during breathing and bronchoconstriction measured by ultrasound elastography using finite element image registration. ULTRASONICS 2017; 75:174-184. [PMID: 27988462 PMCID: PMC5228632 DOI: 10.1016/j.ultras.2016.11.023] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Revised: 09/10/2016] [Accepted: 11/28/2016] [Indexed: 05/17/2023]
Abstract
With every breath, the airways within the lungs are strained. This periodic stretching is thought to play an important role in determining airway caliber in health and disease. Particularly, deep breaths can mitigate excessive airway narrowing in healthy subjects, but this beneficial effect is absent in asthmatics, perhaps due to an inability to stretch the airway smooth muscle (ASM) embedded within an airway wall. The heterogeneous composition throughout an airway wall likely modulates the strain felt by the ASM but the magnitude of ASM strain is difficult to measure directly. In this study, we optimized a finite element image registration method to measure the spatial distribution of displacements and strains throughout an airway wall during pressure inflation within the physiological breathing range before and after induced narrowing with acetylcholine (ACh). The method was shown to be repeatable, and displacements estimated from different image sequences of the same deformation agreed to within 5.3μm (0.77%). We found the magnitude and spatial distribution of displacements were radially and longitudinally heterogeneous. The region in the middle layer of the airway experienced the largest radial strain due to a transmural pressure (Ptm) increase simulating tidal breathing and a deep inspiration (DI), while the region containing the ASM (i.e., closest to the lumen) strained least. During induced narrowing with ACh, we observed temporal longitudinal heterogeneity of the airway wall. After constriction, the displacements and strain are much smaller than the relaxed airway and the pattern of strains changed, suggesting the airway stiffened heterogeneously.
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Affiliation(s)
- Brian C Harvey
- Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02215, USA.
| | - Kenneth R Lutchen
- Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02215, USA.
| | - Paul E Barbone
- Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA 02215, USA.
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Smooth muscle in human bronchi is disposed to resist airway distension. Respir Physiol Neurobiol 2016; 229:51-8. [PMID: 27095271 DOI: 10.1016/j.resp.2016.04.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 04/11/2016] [Accepted: 04/14/2016] [Indexed: 11/21/2022]
Abstract
Studying airway smooth muscle (ASM) in conditions that emulate the in vivo environment within which the bronchi normally operate may provide important clues regarding its elusive physiological function. The present study examines the effect of lengthening and shortening of ASM on tension development in human bronchial segments. ASM from each bronchial segment was set at a length approximating in situ length (Linsitu). Bronchial tension was then measured during a slow cyclical strain (0.004Hz, from 0.7Linsitu to 1.3Linsitu) in the relaxed state and at graded levels of activation by methacholine. In all cases, tension was greater at longer ASM lengths, and greater during lengthening than shortening. The threshold of methacholine concentration that was required for ASM to account for bronchial tension across the entire range of ASM lengths tested was on average smaller by 2.8 logs during lengthening than during shortening. The length-dependency of ASM tension, together with this lower threshold of methacholine concentration during lengthening versus shortening, suggest that ASM has a greater ability to resist airway dilation during lung inflation than to narrow the airways during lung deflation. More than serving to narrow the airway, as has long been thought, these data suggest that the main function of ASM contraction is to limit airway wall distension during lung inflation.
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18
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Dowie J, Ansell TK, Noble PB, Donovan GM. Airway compliance and dynamics explain the apparent discrepancy in length adaptation between intact airways and smooth muscle strips. Respir Physiol Neurobiol 2015; 220:25-32. [PMID: 26376002 DOI: 10.1016/j.resp.2015.09.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 08/27/2015] [Accepted: 09/11/2015] [Indexed: 11/16/2022]
Abstract
Length adaptation is a phenomenon observed in airway smooth muscle (ASM) wherein over time there is a shift in the length-tension curve. There is potential for length adaptation to play an important role in airway constriction and airway hyper-responsiveness in asthma. Recent results by Ansell et al., 2015 (JAP 2014 10.1152/japplphysiol.00724.2014) have cast doubt on this role by testing for length adaptation using an intact airway preparation, rather than strips of ASM. Using this technique they found no evidence for length adaptation in intact airways. Here we attempt to resolve this apparent discrepancy by constructing a minimal mathematical model of the intact airway, including ASM which follows the classic length-tension curve and undergoes length adaptation. This allows us to show that (1) no evidence of length adaptation should be expected in large, cartilaginous, intact airways; (2) even in highly compliant peripheral airways, or at more compliant regions of the pressure-volume curve of large airways, the effect of length adaptation would be modest and at best marginally detectable in intact airways; (3) the key parameters which control the appearance of length adaptation in intact airways are airway compliance and the relaxation timescale. The results of this mathematical simulation suggest that length adaptation observed at the level of the isolated ASM may not clearly manifest in the normal intact airway.
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Affiliation(s)
- Jackson Dowie
- Department of Mathematics, University of Auckland, New Zealand
| | - Thomas K Ansell
- School of Veterinary and Life Sciences, Murdoch University, Australia; School of Anatomy, Physiology and Human Biology, The University of Western Australia, Australia
| | - Peter B Noble
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Australia; Centre for Neonatal Research and Education, The University of Western Australia, Australia
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