1
|
Hai CM. Prestrain and cholinergic receptor-dependent differential recruitment of mechanosensitive energy loss and energy release elements in airway smooth muscle. J Appl Physiol (1985) 2019; 126:823-831. [PMID: 30653417 DOI: 10.1152/japplphysiol.01008.2018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We tested the hypothesis that oscillatory airway smooth muscle (ASM) mechanics is governed by mechanosensitive energy loss and energy release elements that can be recruited by prestrain and cholinergic stimulation. We measured mechanical energy loss and mechanical energy release in unstimulated and carbachol-stimulated bovine ASM held at prestrains ranging from 0.3 to 1.0 Lo (reference length) and subjected to sinusoidal length oscillation at 1 hz with oscillatory strain amplitudes ranging from 0.1 to 1.5% Lo. We found that oscillatory ASM mechanics during sinusoidal length oscillation is governed predominantly by one class of nonlinear mechanosensitive energy loss element and one class of nonlinear mechanosensitive energy release element with differential mechanosensitivities to oscillatory strain amplitude. The greater mechanosensitivity of the energy loss element than energy release element may explain the bronchodilatory effect of deep inspiration. Prestrain, an important determinant of ASM responsiveness, differentially increased energy loss and energy release in unstimulated and carbachol-stimulated ASM. Cholinergic stimulation, an important cause of bronchoconstriction and airway inflammation, also differentially increased energy loss and energy release. When prestrain and cholinergic stimulation were combined, we found that prestrain and cholinergic stimulation synergistically increased energy loss and energy release by ASM. The relationship between recruitment of energy loss elements and recruitment of energy release elements was nonlinear, suggesting that energy loss and energy release elements are not coupled in ASM cells. These findings imply that large lung volume and cholinergic ASM activation would synergistically increase mechanical energy expenditure during inspiration and mechanical recoil of ASM during expiration. NEW & NOTEWORTHY We report for the first time that oscillatory airway smooth muscle mechanics is governed predominantly by one class of nonlinear mechanosensitive energy loss element and one class of nonlinear mechanosensitive energy release element with differential mechanosensitivities to oscillatory strain amplitude. Prestrain and cholinergic stimulation synergistically and differentially recruit energy loss and energy release elements. The greater mechanosensitivity of the energy loss element than the energy release element may explain the bronchodilatory effect of deep inspiration.
Collapse
Affiliation(s)
- Chi-Ming Hai
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University , Providence, Rhode Island
| |
Collapse
|
2
|
Zhang W, Gunst SJ. Molecular Mechanisms for the Mechanical Modulation of Airway Responsiveness. ACTA ACUST UNITED AC 2019; 2. [PMID: 32270135 PMCID: PMC7141576 DOI: 10.1115/1.4042775] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
The smooth muscle of the airways is exposed to continuously changing mechanical
forces during normal breathing. The mechanical oscillations that occur during
breathing have profound effects on airway tone and airway responsiveness both in
experimental animals and humans in vivo and in isolated airway tissues in vitro.
Experimental evidence suggests that alterations in the contractile and
mechanical properties of airway smooth muscle tissues caused by mechanical
perturbations result from adaptive changes in the organization of the
cytoskeletal architecture of the smooth muscle cell. The cytoskeleton is a
dynamic structure that undergoes rapid reorganization in response to external
mechanical and pharmacologic stimuli. Contractile stimulation initiates the
assembly of cytoskeletal/extracellular matrix adhesion complex proteins into
large macromolecular signaling complexes (adhesomes) that undergo activation to
mediate the polymerization and reorganization of a submembranous network of
actin filaments at the cortex of the cell. Cortical actin polymerization is
catalyzed by Neuronal-Wiskott–Aldrich syndrome protein (N-WASP) and the
Arp2/3 complex, which are activated by pathways regulated by paxillin and the
small GTPase, cdc42. These processes create a strong and rigid cytoskeletal
framework that may serve to strengthen the membrane for the transmission of
force generated by the contractile apparatus to the extracellular matrix, and to
enable the adaptation of smooth muscle cells to mechanical stresses. This model
for the regulation of airway smooth muscle function can provide novel
perspectives to explain the normal physiologic behavior of the airways and
pathophysiologic properties of the airways in asthma.
Collapse
Affiliation(s)
- Wenwu Zhang
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN 46202
| | - Susan J Gunst
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN 46202
| |
Collapse
|
3
|
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.
Collapse
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
| |
Collapse
|
4
|
Wong WD, Wang L, Paré PD, Seow CY. Bronchodilatory effect of deep inspiration in freshly isolated sheep lungs. Am J Physiol Lung Cell Mol Physiol 2016; 312:L178-L185. [PMID: 27913423 DOI: 10.1152/ajplung.00321.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 11/28/2016] [Accepted: 12/01/2016] [Indexed: 11/22/2022] Open
Abstract
Taking a big breath is known to reverse bronchoconstriction induced by bronchochallenge in healthy subjects; this bronchodilatory effect of deep inspiration (DI) is diminished in asthmatics. The mechanism underlying the DI effect is not clear. Observations from experiments using isolated airway smooth muscle (ASM) preparations and airway segments suggest that straining of ASM due to DI could lead to bronchodilation, possibly due to strain-induced reduction in ASM contractility. However, factors external to the lung cannot be excluded as potential causes for the DI effect. Neural reflex initiated by stretch receptors in the lung are known to inhibit the broncho-motor tone and enhance vasodilatation; the former directly reduces airway resistance, and the latter facilitates removal of contractile agonists through the bronchial circulation. If the DI effect is solely mediated by factors extrinsic to the lung, the DI effect would be absent in isolated, nonperfused lungs. Here we examined the DI effect in freshly isolated, nonperfused sheep lungs. We found that imposition of DI on isolated lungs resulted in significant bronchodilation, that this DI effect was present only after the lungs were challenged with a contractile agonist (acetylcholine or histamine), and that the effect was independent of the difference in lung volume observed pre- and post-DI. We conclude that a significant portion of the bronchodilatory DI effect stems from factors internal to the lung related to the activation of ASM.
Collapse
Affiliation(s)
- William D Wong
- The Centre for Heart Lung Innovation, University of British Columbia, Vancouver, British Columbia, Canada
| | - Lu Wang
- Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.,The Centre for Heart Lung Innovation, University of British Columbia, Vancouver, British Columbia, Canada
| | - Peter D Paré
- Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.,The Centre for Heart Lung Innovation, University of British Columbia, Vancouver, British Columbia, Canada
| | - Chun Y Seow
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada; and .,The Centre for Heart Lung Innovation, University of British Columbia, Vancouver, British Columbia, Canada
| |
Collapse
|
5
|
Ansell TK, McFawn PK, Mitchell HW, Noble PB. Bronchodilatory response to deep inspiration in bronchial segments: the effects of stress vs. strain. J Appl Physiol (1985) 2013; 115:505-13. [PMID: 23722712 DOI: 10.1152/japplphysiol.01286.2012] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During deep inspirations (DI), a distending force is applied to airway smooth muscle (ASM; i.e., stress) and the muscle is lengthened (i.e., strain), which produces a transient reversal of bronchoconstriction (i.e., bronchodilation). The aim of the present study was to determine whether an increase in ASM stress or the accompanying increase in strain mediates the bronchodilatory response to DI. We used whole porcine bronchial segments in vitro and a servo-controlled syringe pump that applied fixed-transmural pressure (Ptm) or fixed-volume oscillations, simulating tidal breathing and DI. The relationship between ASM stress and strain during oscillation was altered by increasing doses of acetylcholine, which stiffened the airway wall, or by changing the rate of inflation during DI, which utilized the viscous properties of the intact airway. Bronchodilation to DI was positively correlated with ASM strain (range of r values from 0.81 to 0.95) and negatively correlated with stress (range of r values from -0.42 to -0.98). Fast fixed-Ptm DI produced greater bronchodilation than slow DI, despite less ASM strain. Fast fixed-volume DI produced greater bronchodilation than slow DI, despite identical ASM strain. We show that ASM strain, rather than stress, is the critical determinant of bronchodilation and, unexpectedly, that the rate of inflation during DI also impacts on bronchodilation, independent of the magnitudes of either stress or strain.
Collapse
Affiliation(s)
- Thomas K Ansell
- School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, Australia.
| | | | | | | |
Collapse
|
6
|
Bullimore SR, Siddiqui S, Donovan GM, Martin JG, Sneyd J, Bates JHT, Lauzon AM. Could an increase in airway smooth muscle shortening velocity cause airway hyperresponsiveness? Am J Physiol Lung Cell Mol Physiol 2011; 300:L121-31. [PMID: 20971805 PMCID: PMC3023289 DOI: 10.1152/ajplung.00228.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2010] [Accepted: 10/19/2010] [Indexed: 11/22/2022] Open
Abstract
Airway hyperresponsiveness (AHR) is a characteristic feature of asthma. It has been proposed that an increase in the shortening velocity of airway smooth muscle (ASM) could contribute to AHR. To address this possibility, we tested whether an increase in the isotonic shortening velocity of ASM is associated with an increase in the rate and total amount of shortening when ASM is subjected to an oscillating load, as occurs during breathing. Experiments were performed in vitro using 27 rat tracheal ASM strips supramaximally stimulated with methacholine. Isotonic velocity at 20% isometric force (Fiso) was measured, and then the load on the muscle was varied sinusoidally (0.33 ± 0.25 Fiso, 1.2 Hz) for 20 min, while muscle length was measured. A large amplitude oscillation was applied every 4 min to simulate a deep breath. We found that: 1) ASM strips with a higher isotonic velocity shortened more quickly during the force oscillations, both initially (P < 0.001) and after the simulated deep breaths (P = 0.002); 2) ASM strips with a higher isotonic velocity exhibited a greater total shortening during the force oscillation protocol (P < 0.005); and 3) the effect of an increase in isotonic velocity was at least comparable in magnitude to the effect of a proportional increase in ASM force-generating capacity. A cross-bridge model showed that an increase in the total amount of shortening with increased isotonic velocity could be explained by a change in either the cycling rate of phosphorylated cross bridges or the rate of myosin light chain phosphorylation. We conclude that, if asthma involves an increase in ASM velocity, this could be an important factor in the associated AHR.
Collapse
|
7
|
Brown RH, Kaczka DW, Mitzner W. Effect of parenchymal stiffness on canine airway size with lung inflation. PLoS One 2010; 5:e10332. [PMID: 20436667 PMCID: PMC2859932 DOI: 10.1371/journal.pone.0010332] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2009] [Accepted: 02/25/2010] [Indexed: 11/18/2022] Open
Abstract
Although airway patency is partially maintained by parenchymal tethering, this structural support is often ignored in many discussions of asthma. However, agonists that induce smooth muscle contraction also stiffen the parenchyma, so such parenchymal stiffening may serve as a defense mechanism to prevent airway narrowing or closure. To quantify this effect, specifically how changes in parenchymal stiffness alter airway size at different levels of lung inflation, in the present study, we devised a method to separate the effect of parenchymal stiffening from that of direct airway narrowing. Six anesthetized dogs were studied under four conditions: baseline, after whole lung aerosol histamine challenge, after local airway histamine challenge, and after complete relaxation of the airways. In each of these conditions, we used High resolution Computed Tomography to measure airway size and lung volume at five different airway pressures (0, 12, 25, 32, and 45 cm H(2)O). Parenchymal stiffening had a protective effect on airway narrowing, a fact that may be important in the airway response to deep inspiration in asthma. When the parenchyma was stiffened by whole lung aerosol histamine challenge, at every lung volume above FRC, the airways were larger than when they were directly challenged with histamine to the same initial constriction. These results show for the first time that a stiff parenchyma per se minimizes the airway narrowing that occurs with histamine challenge at any lung volume. Thus in clinical asthma, it is not simply increased airway smooth muscle contraction, but perhaps a lack of homogeneous parenchymal stiffening that contributes to the symptomatic airway hyperresponsiveness.
Collapse
Affiliation(s)
- Robert H. Brown
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Environmental Health Sciences, Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Radiology, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - David W. Kaczka
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Wayne Mitzner
- Department of Environmental Health Sciences, Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America
| |
Collapse
|
8
|
An S, Bai T, Bates J, Black J, Brown R, Brusasco V, Chitano P, Deng L, Dowell M, Eidelman D, Fabry B, Fairbank N, Ford L, Fredberg J, Gerthoffer W, Gilbert S, Gosens R, Gunst S, Halayko A, Ingram R, Irvin C, James A, Janssen L, King G, Knight D, Lauzon A, Lakser O, Ludwig M, Lutchen K, Maksym G, Martin J, Mauad T, McParland B, Mijailovich S, Mitchell H, Mitchell R, Mitzner W, Murphy T, Paré P, Pellegrino R, Sanderson M, Schellenberg R, Seow C, Silveira P, Smith P, Solway J, Stephens N, Sterk P, Stewart A, Tang D, Tepper R, Tran T, Wang L. Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma. Eur Respir J 2007; 29:834-60. [PMID: 17470619 PMCID: PMC2527453 DOI: 10.1183/09031936.00112606] [Citation(s) in RCA: 279] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not "cure" asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.
Collapse
Affiliation(s)
- S.S. An
- Division of Physiology, Dept of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health
| | - T.R. Bai
- James Hogg iCAPTURE Centre, University of British Columbia, Vancouver
| | - J.H.T. Bates
- Vermont Lung Center, University of Vermont College of Medicine, Burlington, VT
| | - J.L. Black
- Dept of Pharmacology, University of Sydney, Sydney
| | - R.H. Brown
- Dept of Anesthesiology and Critical Care medicine, Johns Hopkins Medical Institutions, Baltimore, MD
| | - V. Brusasco
- Dept of Internal Medicine, University of Genoa, Genoa
| | - P. Chitano
- Dept of Paediatrics, Duke University Medical Center, Durham, NC
| | - L. Deng
- Program in Molecular and Integrative Physiological Sciences, Dept of Environmental Health, Harvard School of Public Health
- Bioengineering College, Chongqing University, Chongqing, China
| | - M. Dowell
- Section of Pulmonary and Critical Care Medicine
| | - D.H. Eidelman
- Meakins-Christie Laboratories, Dept of Medicine, McGill University, Montreal
| | - B. Fabry
- Center for Medical Physics and Technology, Erlangen, Germany
| | - N.J. Fairbank
- School of Biomedical Engineering, Dalhousie University, Halifax
| | | | - J.J. Fredberg
- Program in Molecular and Integrative Physiological Sciences, Dept of Environmental Health, Harvard School of Public Health
| | - W.T. Gerthoffer
- Dept of Pharmacology, University of Nevada School of Medicine, Reno, NV
| | | | - R. Gosens
- Dept of Physiology, University of Manitoba, Winnipeg
| | - S.J. Gunst
- Dept of Physiology, Indiana University School of Medicine, Indianapolis, IN
| | - A.J. Halayko
- Dept of Physiology, University of Manitoba, Winnipeg
| | - R.H. Ingram
- Dept of Medicine, Emory University School of Medicine, Atlanta, GA
| | - C.G. Irvin
- Vermont Lung Center, University of Vermont College of Medicine, Burlington, VT
| | - A.L. James
- West Australian Sleep Disorders Research Institute, Sir Charles Gairdner Hospital, Nedlands
| | - L.J. Janssen
- Dept of Medicine, McMaster University, Hamilton, Canada
| | - G.G. King
- Woolcock Institute of Medical Research, Camperdown
| | - D.A. Knight
- James Hogg iCAPTURE Centre, University of British Columbia, Vancouver
| | - A.M. Lauzon
- Meakins-Christie Laboratories, Dept of Medicine, McGill University, Montreal
| | - O.J. Lakser
- Section of Paediatric Pulmonary Medicine, University of Chicago, Chicago, IL
| | - M.S. Ludwig
- Meakins-Christie Laboratories, Dept of Medicine, McGill University, Montreal
| | - K.R. Lutchen
- Dept of Biomedical Engineering, Boston University, Boston
| | - G.N. Maksym
- School of Biomedical Engineering, Dalhousie University, Halifax
| | - J.G. Martin
- Meakins-Christie Laboratories, Dept of Medicine, McGill University, Montreal
| | - T. Mauad
- Dept of Pathology, Sao Paulo University Medical School, Sao Paulo, Brazil
| | | | - S.M. Mijailovich
- Program in Molecular and Integrative Physiological Sciences, Dept of Environmental Health, Harvard School of Public Health
| | - H.W. Mitchell
- Discipline of Physiology, School of Biomedical, Biomolecular and Chemical Sciences, University of Western Australia, Perth
| | | | - W. Mitzner
- Division of Physiology, Dept of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health
| | - T.M. Murphy
- Dept of Paediatrics, Duke University Medical Center, Durham, NC
| | - P.D. Paré
- James Hogg iCAPTURE Centre, University of British Columbia, Vancouver
| | - R. Pellegrino
- Dept of Respiratory Physiopathology, S. Croce e Carle Hospital, Cuneo, Italy
| | - M.J. Sanderson
- Dept of Physiology, University of Massachusetts Medical School, Worcester, MA
| | - R.R. Schellenberg
- James Hogg iCAPTURE Centre, University of British Columbia, Vancouver
| | - C.Y. Seow
- James Hogg iCAPTURE Centre, University of British Columbia, Vancouver
| | - P.S.P. Silveira
- Dept of Pathology, Sao Paulo University Medical School, Sao Paulo, Brazil
| | - P.G. Smith
- Dept of Paediatrics, School of Medicine, Case Western Reserve University, Cleveland, OH
| | - J. Solway
- Section of Pulmonary and Critical Care Medicine
| | - N.L. Stephens
- Dept of Physiology, University of Manitoba, Winnipeg
| | - P.J. Sterk
- Dept of Pulmonology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - A.G. Stewart
- Dept of Pharmacology, University of Melbourne, Parkville, Australia
| | - D.D. Tang
- Center for Cardiovascular Sciences, Albany Medical College, Albany, NY, USA
| | - R.S. Tepper
- Dept of Paediatrics, Indiana University School of Medicine, Indianapolis, IN
| | - T. Tran
- Dept of Physiology, University of Manitoba, Winnipeg
| | - L. Wang
- Dept of Paediatrics, Duke University Medical Center, Durham, NC
| |
Collapse
|
9
|
Lambert RK, Beck KC. Airway area distribution from the forced expiration maneuver. J Appl Physiol (1985) 2005; 97:570-8. [PMID: 15247198 DOI: 10.1152/japplphysiol.00912.2003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The maximal expiratory flow-volume (MEFV) maneuver is a commonly used test of lung function. More detailed interpretation than is currently available might be useful to understand disease better. We propose that a previously published computational model (Lambert RK, Wilson TA, Hyatt RE, and Rodarte JR. J Appl Physiol 52: 44-56, 1982) can be used to deduce, from the MEFV curve, the serial distribution of airway areas in the larger airways. An automated procedure based on the simulated annealing technique was developed. It was tested with model-generated flow data in which airway areas were reduced one generation at a time. The procedure accurately located the constriction and predicted its size within narrow bounds when the constriction was in the six most central generations of airways. More peripheral constrictions were detected but were not precisely located, nor were their sizes accurately evaluated. Airway areas of generations upstream of the constriction were usually overestimated. The procedure was applied to spirometric data obtained from eight volunteers (4 asthmatic and 4 normal subjects) at baseline and after methacholine challenge. The predicted areas show individual differences both in absolute values, and in relative distribution of areas. This result shows that detailed information can be obtained from the MEFV curve through the use of a model. However, this initial model, which lacks airway smooth muscle, needs further refinement.
Collapse
Affiliation(s)
- Rodney K Lambert
- Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
| | | |
Collapse
|
10
|
Abstract
The report will focus on studies that illustrate how high resolution computed tomography can be used to provide new insights into airway and lung function, that cannot be obtained with any other methodology in humans or animal models. In one series of experiments, we have clearly demonstrated that even large cartilaginous airways are capable of complete closure in vivo. These unequivocal in vivo results invalidate the ubiquitous concept that there is a limit to airway narrowing in normal subjects. In another series of experiments, we have investigated potential reasons why asthmatic subjects might show airway constriction following deep inspiration instead of the normal dilation. Experimental results show that a constrictor response to deep inspiration can be generated in normal airways simply by minimizing tidal stresses. The absence of these normal rhythmic stresses alters the smooth muscle throughout the airway tree, such that subsequent large stresses lead to a further constriction. These results also offer a possible mechanism by which the response to deep inspiration is altered in asthmatic subjects. By allowing accurate measurement of the size of individual airways, computed tomography with modern commercially available scanners thus provides a unique opportunity to evaluate specific hypotheses regarding mechanisms underlying lung disease.
Collapse
Affiliation(s)
- Robert H Brown
- Department of Anesthesiology and Critical Care Medicine, School of Medicine, The Johns Hopkins University, 620 North Wolfe Street, Baltimore, MD 21205, USA.
| | | |
Collapse
|
11
|
Abstract
Tidal stresses are thought to be involved in maintaining airway patency in vivo. The present study examined the effects of normal stresses exerted by the lung parenchyma during tidal ventilation on recovery from agonist-induced airway constriction. In seven anesthetized dogs, one lung was selectively ventilated with a Univent endotracheal tube (Vitaid, Lewiston, NY). Airway tone was increased either transiently (intravenous bolus) or continuously (intravenous infusion) with methacholine (MCh). During one-lung ventilation, changes in the airway size of both lungs were measured for up to 40 min during recovery from constriction by using high-resolution computed tomography. After recovery to baseline, the alternate lung was ventilated, and the protocol was repeated. The absence of tidal stresses led to an attenuated recovery from either transient or steady-state airway constriction. The effectiveness or lack thereof of normal tidal stress in stabilizing airway size may be one factor that contributes to the lack of reversal with tidal breathing and deep inspiration seen in asthmatic subjects.
Collapse
Affiliation(s)
- R Brown
- The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205, USA.
| | | |
Collapse
|
12
|
Mijailovich SM, Butler JP, Fredberg JJ. Perturbed equilibria of myosin binding in airway smooth muscle: bond-length distributions, mechanics, and ATP metabolism. Biophys J 2000; 79:2667-81. [PMID: 11053139 PMCID: PMC1301147 DOI: 10.1016/s0006-3495(00)76505-2] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
We carried out a detailed mathematical analysis of the effects of length fluctuations on the dynamically evolving cross-bridge distributions, simulating those that occur in airway smooth muscle during breathing. We used the latch regulation scheme of Hai and Murphy (Am. J. Physiol. Cell Physiol. 255:C86-C94, 1988) integrated with Huxley's sliding filament theory of muscle contraction. This analysis showed that imposed length fluctuations decrease the mean number of attached bridges, depress muscle force and stiffness, and increase force-length hysteresis. At frequencies >0.1 Hz, the bond-length distribution of slowly cycling latch bridges changed little over the stretch cycle and contributed almost elastically to muscle force, but the rapidly cycling cross-bridge distribution changed substantially and dominated the hysteresis. By contrast, at frequencies <0.033 Hz this behavior was reversed: the rapid cycling cross-bridge distribution changed little, effectively functioning as a constant force generator, while the latch bridge bond distribution changed substantially and dominated the stiffness and hysteresis. The analysis showed the dissociation of force/length hysteresis and cross-bridge cycling rates when strain amplitude exceeds 3%; that is, there is only a weak coupling between net external mechanical work and the ATP consumption required for cycling cross-bridges during the oscillatory steady state. Although these results are specific to airway smooth muscle, the approach generalizes to other smooth muscles subjected to cyclic length fluctuations.
Collapse
Affiliation(s)
- S M Mijailovich
- Harvard School of Public Health, Boston, Massachusetts 02115, USA.
| | | | | |
Collapse
|
13
|
Dolhnikoff M, Morin J, Ludwig MS. Human lung parenchyma responds to contractile stimulation. Am J Respir Crit Care Med 1998; 158:1607-12. [PMID: 9817715 DOI: 10.1164/ajrccm.158.5.9801068] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Tissue resistance increases after agonist challenge. Parenchymal contractile cells may be the responsible element. We investigated the viscoelastic properties of human parenchymal strips before and after challenge with acetylcholine (ACh) (10(-)3 M). Thirteen subpleural strips were oscillated in the organ bath, and measurements of resistance (R), elastance (E), and hysteresivity (eta) were obtained. After physiologic measurements, tissues were fixed for morphometric and immunohistochemical analysis. We quantitated the volume proportion of alveolar, airway, and blood vessel wall in individual strips. Smooth-muscle-specific actin was identified using a monoclonal antibody and the volume proportion of actin quantitated by point counting. After ACh, there was a significant increase in tension (2.6 +/- 0.6%), R (11.0 +/- 1.8%), E (4.3 +/- 0.7%), and eta (8.2 +/- 2.4%) (p < 0.002). Four strips contained no identifiable airways, yet in strips with and without airways there was no difference in the magnitude of the mechanical response or in the volume proportion of smooth-muscle-specific actin in the alveolar walls. We conclude that human lung parenchymal strips respond to ACh challenge with changes in dynamic mechanical behavior. Furthermore, small airways are not required for such a response to occur. This implicates a direct contractile response at the level of the alveolar wall and/or the alveolar duct.
Collapse
Affiliation(s)
- M Dolhnikoff
- Meakins-Christie Laboratories, Department of Medicine, Royal Victoria Hospital, Department of Surgery, Royal Victoria Hospital, McGill University, Montreal, Canada
| | | | | |
Collapse
|
14
|
Shen X, Wu MF, Tepper RS, Gunst SJ. Mechanisms for the mechanical response of airway smooth muscle to length oscillation. J Appl Physiol (1985) 1997; 83:731-8. [PMID: 9292457 DOI: 10.1152/jappl.1997.83.3.731] [Citation(s) in RCA: 131] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Airway smooth muscle tone in vitro is profoundly affected by oscillations in muscle length, suggesting that the effects of lung volume changes on airway tone result from direct effects of stretch on the airway smooth muscle. We analyzed the effect of length oscillation on active force and length-force hysteresis in canine tracheal smooth muscle at different oscillation rates and amplitudes during contraction with acetylcholine. During the shortening phase of the length oscillation cycle, the active force generated by the smooth muscle decreased markedly below the isometric force but returned to isometric force as the muscle was lengthened. Results indicate that at rates comparable to those during tidal breathing, active shortening and yielding of contractile elements contributes to the modulation of force during length oscillation; however, the depression of force during shortening cannot be accounted for by cross-bridge properties, shortening-induced cross-bridge deactivation, or active relaxation. We conclude that the depression of contractility may be a function of the plasticity of the cellular organization of contractile filaments, which enables contractile element length to be reset in relation to smooth muscle cell length as a result of smooth muscle stretch.
Collapse
Affiliation(s)
- X Shen
- Department of Physiology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
| | | | | | | |
Collapse
|