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Ventilation heterogeneity is an important marker of small airway dysfunction in asthma. The frequency dependence of respiratory system resistance ([R.sub.rs]) from oscillometry is used as a measure of this heterogeneity. However, this has not been quantitatively assessed or compared with other outcomes from oscillometry, including respiratory system reactance ([X.sub.rs]) and the associated elastance ([E.sub.rs]). Here, we used a multibranch model of the human lung, including an upper airway shunt, to match previously reported respiratory mechanics in mild to severe asthma. We imposed heterogeneity by narrowing a proportion of the peripheral airways to account for patient [E.sub.rs] at 5 Hz, and then narrowed central airways to account for the remaining [R.sub.rs] at 18 Hz. The model required >75% of the small airways to be occluded to reproduce severe asthma. While the model produced frequency dependence in [R.sub.rs], it was upward-shifted below 5 Hz compared with in-vivo results, indicating that other factors, including more distributed airway narrowing or central airway wall compliance, are required. However, [E.sub.rs] quantitatively reflected the imposed heterogeneity better than the frequency dependence of [R.sub.rs], independent of the frequency range for the estimation, and thus was a more robust measure of small-airway function. Thus, [E.sub.rs] appears to have greater potential as a clinical measure of early small-airway disease in asthma. Key words: small airway heterogeneity, ventilation defects, elastance, frequency dependence of resistance, oscillometry. L'heterogeneite ventilatoire constitue un marqueur important de la dysfonction des petites voies respiratoires dans l'asthme. La dependance en fonction de la frequence de la resistance du systeme respiratoire ([R.sub.rs]) a partir de l'oscillometrie est utilisee pour mesurer cette heterogeneite. Cependant, elle n'a pas ete evaluee de maniere quantitative ou comparee a d'autres resultats de l'oscillometrie, incluant la reactance du systeme respiratoire ([X.sub.rs]) et l'elastance associee ([E.sub.rs]). Les auteurs ont utilize ici un modele ramifie de poumon humain incluant une obstruction des voies aeriennes superieures qui reproduit la mecanique respiratoire de l'asthme leger a severe rapportee precedemment. Les auteurs ont impose une heterogeneite en retrecissant une partie des voies respiratoires peripheriques pour representer l'[E.sub.rs] a 5 Hz d'un patient, et en retrecissant ensuite les voies respiratoires centrales pour representer la [R.sub.rs] residuelle a 18 Hz. Une occlusion de >75 % des petites voies respiratoires etait necessaire pour representer l'asthme severe. Alors que le modele produisait une dependance en fonction de la frequence de la [R.sub.rs], elle se deplacait sous les 5 Hz relativement a la situation in vivo, indiquant que d'autres facteurs sont requis, incluant une meilleure distribution du retrecissement des voies respiratoires ou une compliance des parois des voies respiratoires centrales. Cependant, la [E.sub.rs] refletait quantitativement l'heterogeneite imposee davantage que la dependance en fonction de la frequence de la [R.sub.rs], de maniere independante du spectre de frequence pour l'estimation, et constituait ainsi une mesure plus robuste de la fonction des petites voies respiratoires. La [E.sub.rs] semble alors avoir un meilleur potentiel comme mesure clinique de la maladie precoce des petites voies respiratoires dans l'asthme. [Traduit par la Redaction] Mots-cles: heterogeneite des petites voies respiratoires, defauts de ventilation, elastance, dependance en fonction de la frequence de la resistance, oscillometrie., Introduction Heterogeneous airway narrowing is a hallmark feature of asthma; a fact also supported by the occurrence of 'patchy ventilation,' characterized by ventilation defects in asthmatic subjects as seen in [...]

Chronic contractile activation, or tone, in asthma coupled with continuous stretching due to breathing may be involved in altering the contractile function of airway smooth muscle (ASM). Previously, we (11) showed that cytoskeletal remodeling and stiffening responses to acute (2 h) localized stresses were modulated by the level of contractile activation of ASM. Here, we investigated if altered contractility in response to chronic mechanical strain was dependent on repeated modulation of contractile tone. Cultured human ASM cells received 5% cyclic (0.3 Hz), predominantly uniaxial strain for 5 days, with once-daily dosing of either sham, forskolin, carbachol, or histamine to alter tone. Stiffness, contractility (KCl), and 'relaxability' (forskolin) were then measured as was cell alignment, myosin light-chain phosphorylation (pMLC), and myosin light-chain kinase (MLCK) content. Cells became aligned and baseline stiffness increased with strain, but repeated lowering of tone inhibited both effects (P < 0.05). Strain also reversed a negative tone-modulation dependence of MLCK, observed in static conditions in agreement with previous reports, with strain and tone together increasing both MLCK and pMLC. Furthermore, contractility increased 176% (SE 59) with repeated tone elevation. These findings indicate that with strain, and not without, repeated tone elevation promoted contractile function through changes in cytoskeletal organization and increased contractile protein. The ability of repeated contractile activation to increase contractility, but only with mechanical stretching, suggests a novel mechanism for increased ASM contractility in asthma and for the role of continuous bronchodilator and corticosteroid therapy in reversing airway hyperresponsiveness. asthma; mechanical stress; cytoskeletal remodeling; myosin light-chain kinase; optical magnetic twisting cytometry

Abstract: Extracellular matrix proteins (ECMs) play a significant role in the transfer of mechanical strain to monocyte derived macrophages (MDMs) affecting morphological changes in a foreign body reaction. This study [...]

Viscoelasticity of human alveolar epithelial cells subjected to stretch. Am J Physiol Lung Cell Mol Physiol 287: L1025-L1034, 2004. First published July 9, 2004; doi:10.1152/ajplung.00077.2004.--Alveolar epithelial cells undergo stretching during breathing and mechanical ventilation. Stretch can modify cell viscoelastic properties, which may compromise the balance of forces in the alveolar epithelium. We studied the viscoelasticity of alveolar epithelial cells (A549) subjected to equibiaxial distention with a novel experimental approach. Cells were cultured on flexible substrates and subjected to stepwise deformations of up to 17% with a device built on an inverted microscope. Simultaneously, cell storage (G') and loss (G') moduli were measured (0.1-100 Hz) with optical magnetic twisting cytometry. G' and G' increased with strain up to 64 and 30%, respectively, resulting in a decrease in G'/G' (15%). This stretch-induced response was inhibited by disruption of the actin cytoskeleton with latrunculin A. G' increased with frequency following a power law with exponent [alpha] = 0.197. G' increased proportionally to G' but exhibited a more marked frequency dependence at high frequencies. Stretching (14%) caused a fall in [alpha] (13%). At high stretching amplitudes, actual cell strain (14.4%) was lower than the applied substrate strain (17.3%), which could indicate a partial cell detachment. These data suggest that cytoskeletal prestress modulates the elastic and frictional properties of alveolar epithelial cells in a coupled manner, according to soft glassy rheology. Stretch-induced cell stiffening could compromise the balance of forces at the cell-cell and cell-matrix adhesions. cell mechanics; cell stretching; magnetic twisting cytometry; prestress; power law

Mechanical stress (MS) causes cytoskeletal (CSK) and phenotypic changes in ceils. Such changes in airway smooth muscle (ASM) cells might contribute to the pathophysiology of asthma. We have shown that periodic mechanical strain applied to cultured ASM cells alters the structure and expression of CSK proteins and increases cell stiffness and contractility (Smith PG, Moreno R, and Ikebe M. Am J Physiol Lung Cell Mol Physiol 272: L20-L27, 1997; and Smith PG, Deng L, Fredberg JJ, and Maksym GN. Am J Physiol Lung Cell Mol Physiol 285: L456-L463, 2003). However, the mechanically induced CSK changes, altered cell function, and their time courses are not well understood. Here we applied MS to the CSK by magnetically oscillating ferrimagnetic beads bound to the CSK. We quantified CSK remodeling by measuring actin accumulation at the sites of applied MS using fluorescence microscopy. We also measured CSK stiffness using optical magnetic twisting cytometry. We found that, during MS of up to 120 min, the percentage of beads associated with actin structures increased with time. At 60 min, 68.1 [+ or -] 1.6% of the beads were associated with actin structures compared with only 6.7 [+ or -] 2.8% before MS and 38.4 [+ or -] 5.5% in time-matched controls (P < 0.05). Similarly, CSK stiffness increased more than twofold in response to the MS compared with time-matched controls. These changes were more pronounced than observed with contractile stimulation by 80 mM KCl or [10.sup.-4] M acetylcholine. Together, these findings imply that MS is a potent stimulus to enhance stiffness and contractility of ASM cells through CSK remodeling, which may have important implications in airway narrowing and dilation in asthma. mechanical stress; actin cytoskeleton; stiffness; airway smooth muscle cell; optical magnetic twisting cytometry; airway constriction and dilation; asthma

We tested the hypothesis that cytoskeletal reorganization induced by cyclic strain increases cytoskeletal stiffness (G'). G' was measured by optical magnetic twisting cytometry in control cells and cells that had received mechanical strain for 10-12 days. G' was measured before and after both contractile and relaxant agonists, and in the strained cells both parallel (Para) and perpendicular (Perp) to the aligned cytoskeleton. Before activation, G' Para was 24 [+ or -] 5% ([+ or -] SE) greater compared with Perp (P < 0.05), and 35% [+ or -] 6 greater compared with control (Cont, P < 0.01). The difference between strained and control cells was enhanced by KCl, increasing G' 171 [+ or -] 7% Para compared with 125 [+ or -] 6% Perp and 129 [+ or -] 8% Cont (P < [10.sup.-5] both cases). The decrease in G' from baseline due to relaxant agonists isoproterenol and dibutyryl cAMP was similar in all groups. Long-term oscillatory loading of airway smooth muscle (ASM) cells caused stiffness to increase and become anisotropic. These findings are consistent with the hypothesis that cytoskeletal reorganization can enhance ASM stiffness and contractility. They imply, furthermore, that oscillatory loading of ASM may contribute to airway narrowing and failure of airway dilation in asthma. smooth muscle contraction; plasticity; optical magnetic twisting cytometry; anisotropy; airway smooth muscle cell

Recently, "Technical standards for respiratory oscillometry" was published, which reviewed the physiological basis of oscillometric measures and detailed the technical factors related to equipment and test performance, quality assurance and reporting of results. Here we present a review of the clinical significance and applications of oscillometry. We briefly review the physiological principles of oscillometry and the basics of oscillometry interpretation, and then describe what is currently known about oscillometry in its role as a sensitive measure of airway resistance, bronchodilator responsiveness and bronchial challenge testing, and response to medical therapy, particularly in asthma and COPD. The technique may have unique advantages in situations where spirometry and other lung function tests are not suitable, such as in infants, neuromuscular disease, sleep apnoea and critical care. Other potential applications include detection of bronchiolitis obliterans, vocal cord dysfunction and the effects of environmental exposures. However, despite great promise as a useful clinical tool, we identify a number of areas in which more evidence of clinical utility is needed before oscillometry becomes routinely used for diagnosing or monitoring respiratory disease. [ABSTRACT FROM AUTHOR]

Frequency dependence of respiratory mechanics is a well-established behavior of the respiratory system and is known to be an indicator of severity of obstructive disease, attributed to both tissue viscoelasticity and heterogeneity of airflow in the lung. Despite the fact that respiratory parameters are known to vary in time, often amplified in disease, all analysis methods assume stationarity or short-time stationarity in the parameters used to describe the respiratory system, and the effects of this assumption have not yet been examined in any detail. Here, using a generalized approach, we developed a theory for time-varying respiratory mechanics in time-frequency domain for analysis of linear time-varying systems, then, we analyzed the same respiratory system model with time-varying parameters in the time domain. Both time-frequency domain and time-domain derivations revealed a striking correlation between time-varying behavior of the respiratory system and frequency dependence of resistance. Remarkably, this phenomenon arose from the amplitude of time variations of the elastance. This links two mechanisms that are known to increase in obstructive disease: apparent low frequency increases in resistance and the time variations of reactance. [ABSTRACT FROM AUTHOR]

Rationale: Histologic stains have been used as the gold standard to visualize extracellular matrix (ECM) changes associated with airway remodeling in asthma, yet they provide no information on the biochemical and structural characteristics of the ECM, which are vital to understanding alterations in tissue function.Objectives: To demonstrate the use of nonlinear optical microscopy (NLOM) and texture analysis algorithms to image fibrillar collagen (second harmonic generation) and elastin (two-photon excited autofluorescence), to obtain biochemical and structural information on the remodeled ECM environment in asthma.Methods: Nontransplantable donor lungs from donors with asthma (n = 13) and control (n = 12) donors were used for the assessment of airway collagen and elastin fibers by NLOM, and extraction of lung fibroblasts for in vitro experiments.Measurements and Main Results: Fibrillar collagen is not only increased but also highly disorganized and fragmented within large and small asthmatic airways compared with control subjects, using NLOM imaging. Furthermore, such structural alterations are present in pediatric and adult donors with asthma, irrespective of fatal disease. In vitro studies demonstrated that asthmatic airway fibroblasts are deficient in their packaging of fibrillar collagen-I and express less decorin, important for collagen fibril packaging. Packaging of collagen fibrils was found to be more disorganized in asthmatic airways compared with control subjects, using transmission electron microscopy.Conclusions: NLOM imaging enabled the structural assessment of the ECM, and the data suggest that airway remodeling in asthma involves the progressive accumulation of disorganized fibrillar collagen by airway fibroblasts. This study highlights the future potential clinical application of NLOM to assess airway remodeling in vivo. [ABSTRACT FROM AUTHOR]

Oscillometry is a useful measure of lung function and recently has been used to estimate temporal variation in physiological mechanical properties of the lung, but to date, analysis methods assume stationarity or short-time stationarity despite substantial temporal variation, particularly in disease. The effect of time-varying parameters on the accuracy of estimates of impedance has not been previously analyzed. In this paper we analytically, computationally, and with added experimental data from seven children with asthma, assess the time-frequency transfer function of the time-varying respiratory system. We then evaluate the accuracy in determining the time-varying parameters of respiratory impedance. We introduce, for the first time, the error arising from respiratory time variation, termed the time-varying error (TVE) and demonstrate how TVE unexpectedly increases with increasing breathing rate independent of breathing noise amplitude. For breathing rates less than 0.4 Hz, we found that common analysis methods could be moderately accurate with less than 5% error. Since tracking time-varying impedance shows strong potential for assessing the severity of respiratory disease, it is import to recognize that errors should be avoided, or compensation circuits and systems developed based on the TVE, particularly important in patients with high variation or breathing rate such as children and infants. [ABSTRACT FROM AUTHOR]

Laporte, Johanne D., Paul E. Moore, Joseph H. Abraham, Geoffrey N. Maksym, Ben Fabry, Reynold A. Panettieri, Jr., and Stephanie A. Shore. Role of ERK MAP kinases in responses of cultured human airway smooth muscle cells to IL-1[Beta]. Am. J. Physiol. 277 (Lung Cell. Mol. Physiol. 21): L943-L951, 1999.--We have previously reported that interleukin (IL)-1[Beta] causes [Beta]-adrenergic hyporesponsiveness in cultured human airway smooth muscle cells by increasing cyclooxygenase-2 (COX-2) expression and prostanoid formation. The purpose of this study was to determine whether extracellular signal-regulated kinases (ERKs) are involved in these events. Levels of phosphorylated ERK (p42 and p44) increased 8.3- and 13-fold, respectively, 15 min after treatment with IL-1[Beta] (20 ng/ml) alone. Pretreating cells with the mitogen-activated protein kinase kinase inhibitor PD-98059 or U-126 (2 h before IL-1[Beta] treatment) decreased ERK phosphorylation. IL-1[Beta] (20 ng/ml for 22 h) alone caused a marked induction of COX-2 and increased basal [PGE.sub.2] release 28-fold (P [is less than] 0.001). PD-98059 (100 [micro]M) and U-126 (10 [micro]M) each decreased COX-2 expression when administered before IL-1[Beta] treatment. In control cells, PD-98059 and U-126 had no effect on basal or arachidonic acid (AA; 10 [micro]M)-stimulated [PGE.sub.2] release, but both inhibitors caused a significant decrease in bradykinin (BK; 1 [micro]M)-stimulated [PGE.sub.2] release, consistent with a role for ERK in the activation of phospholipase [A.sub.2] by BK. In IL-1[Beta]-treated cells, prior administration of PD-98059 caused 81, 92 and 40% decreases in basal and BK- and AA-stimulated [PGE.sub.2] release, respectively (P [is less than] 0.01), whereas administration of PD-98059 20 h after IL-1[Beta] resulted in only 38 and 43% decreases in basal and BK-stimulated [PGE.sub.2] release, respectively (P [is less than] 0.02) and had no effect on AA-stimulated [PGE.sub.2] release. IL-1[Beta] attenuated isoproterenol-induced decreases in human airway smooth muscle stiffness as measured by magnetic twisting cytometry, and PD-98059 or U-126 abolished this effect in a concentration-dependent manner. These results are consistent with the hypothesis that ERKs are involved early in the signal transduction pathway through which IL-1[Beta] induces [PGE.sub.2] synthesis and [Beta]-adrenergic hyporesponsiveness and that ERKs act by inducing COX-2 and activating phospholipase [A.sub.2]. extracellular signal-regulated kinase; mitogen-activated protein; interleukin-1[Beta]; prostaglandin [E.sub.2]; [Beta]-adrenergic responses; PD-98059; U-126; magnetic twisting cytometry; cyclooxygenase

In contrast to other environmental allergens, the association with atopic dermatitis was present for Fel d 1, which may suggest that the skin is an important route of sensitization for this allergen. GLO:1X5/01dec19:all13927-fig-0002.jpg PHOTO (COLOR): Hierarchical clustering performed on patient sensitization profiles and allergen components indicating clusters by allergen source and biochemical family (sensitized: N = 37; nonsensitized: N = 18). In conclusion, we provide data describing a potentially high-risk preschool asthma cohort in Canada using a comprehensive approach capturing sensitization to allergens of paramount importance. By applying both allergen extracts and components, we identified that peanut and animal allergens from cat and dog were major allergen sources in this North American cohort of preschool asthmatics. [Extracted from the article]

In patients with asthma, magnetic resonance imaging ( MRI) provides direct measurements of regional ventilation heterogeneity, the etiology of which is not well-understood, nor is the relationship of ventilation abnormalities with lung mechanics. In addition, respiratory resistance and reactance are often abnormal in asthmatics and the frequency dependence of respiratory resistance is thought to reflect ventilation heterogeneity. We acquired MRI ventilation defect maps, forced expiratory volume in one-second ( FEV1), and airways resistance (Raw) measurements, and used a computational airway model to explore the relationship of ventilation defect percent ( VDP) with simulated measurements of respiratory system resistance (Rrs) and reactance (Xrs). MRI ventilation defect maps were experimentally acquired in 25 asthmatics before, during, and after methacholine challenge and these were nonrigidly coregistered to the airway tree model. Using the model coregistered to ventilation defect maps, we narrowed proximal (9th) and distal (14th) generation airways that were spatially related to the MRI ventilation defects. The relationships for VDP with Raw measured using plethysmography ( r = 0.79), and model predictions of Rrs>14 ( r = 0.91, P < 0.0001) and Rrs>9 ( r = 0.88, P < 0.0001) were significantly stronger ( P = 0.005; P = 0.03, respectively) than with FEV1 ( r = −0.68, P = 0.0001). The slopes for the relationship of VDP with simulated lung mechanics measurements were different ( P < 0.0001); among these, the slope for the VDP-Xrs0.2 relationship was largest, suggesting that VDP was dominated by peripheral airway heterogeneity in these patients. In conclusion, as a first step toward understanding potential links between lung mechanics and ventilation defects, impedance predictions were made using a computational airway tree model with simulated constriction of airways related to ventilation defects measured in mild-moderate asthmatics. [ABSTRACT FROM AUTHOR]

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Purpose To compare hyperpolarized helium-3 (3He) and xenon-129 (129Xe) MRI in asthmatics before and after salbutamol inhalation. Materials and Methods Seven asthmatics provided written informed consent and underwent spirometry, plethysmography, and MRI before and after salbutamol inhalation. 3He and 129Xe ventilation defect percent (VDP) and ventilation coefficient of variation (COV) were measured. To characterize the airways spatially related to ventilation defects, wall area percent (WA%) and lumen area (LA) were evaluated for two subjects who had thoracic x-ray computed tomography (CT) acquired 1 year before MRI. Results Before salbutamol inhalation, 129Xe VDP (8 ± 5%) was significantly greater than 3He VDP (6 ± 5%, P = 0.003). Post-salbutamol, there was a significant improvement in both 129Xe (5 ± 4%, P < 0.0001) and 3He (4 ± 3%, P = 0.001) VDP, and the improvement in 129Xe VDP was significantly greater ( P = 0.008). 129Xe MRI COV (Pre: 0.309 ± 0.028, Post: 0.296 ± 0.036) was significantly greater than 3He MRI COV (Pre: 0.282 ± 0.018, Post: 0.269 ± 0.024), pre- ( P < 0.0001) and post-salbutamol ( P < 0.0001) and the decrease in COV post-salbutamol was significant (129Xe, P = 0.002; 3He, P < 0.0001). For a single asthmatic, a sub-segmental 129Xe MRI ventilation defect that was visible only before salbutamol inhalation but not visible using 3He MRI was spatially related to a remodeled fourth generation sub-segmental airway (WA% = 78%, LA = 2.9 mm2). Conclusion In asthma, hyperpolarized 129Xe MRI may help reveal ventilation abnormalities before bronchodilation that are not observed using hyperpolarized 3He MRI. J. Magn. Reson. Imaging 2013;38:1521-1530. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Airway smooth muscle (ASM) cellular and molecular biology is typically studied with single-cell cultures grown on flat 2D substrates. However, cells in vivo exist as part of complex 3D structures, and it is well established in other cell types that altering substrate geometry exerts potent effects on phenotype and function. These factors may be especially relevant to asthma, a disease characterized by structural remodeling of the airway wall, and highlights a need for more physiologically relevant models of ASM function. We utilized a tissue engineering platform known as microfabricated tissue gauges to develop a 3D culture model of ASM featuring arrays of ∼0.4 mm long, ∼350 cell "microtissues" capable of simultaneous contractile force measurement and cell-level microscopy. ASM-only microtissues generated baseline tension, exhibited strong cellular organization, and developed actin stress fibers, but lost structural integrity and dissociated from the cantilevers within 3 days. Addition of 3T3-fibroblasts dramatically improved survival times without affecting tension development or morphology. ASM-3T3 microtissues contracted similarly to ex vivo ASM, exhibiting reproducible responses to a range of contractile and relaxant agents. Compared with 2D cultures, microtissues demonstrated identical responses to acetylcholine and KCl, but not histamine, forskolin, or cytochalasin D, suggesting that contractility is regulated by substrate geometry. Microtissues represent a novel model for studying ASM, incorporating a physiological 3D structure, realistic mechanical environment, coculture of multiple cells types, and comparable contractile properties to existing models. This new model allows for rapid screening of biochemical and mechanical factors to provide insight into ASM dysfunction in asthma. [ABSTRACT FROM AUTHOR]

ABSTRACT Background and objective: Spirometry is insensitive to small airway abnormalities in asthma. Our objective was to evaluate regional lung structure and function using hyperpolarized 3He magnetic resonance imaging (MRI) before, during and after a methacholine challenge (MCh). Methods: Twenty-five asthmatics (mean age = 34 ± 11 years) and eight healthy volunteers (HV) (mean age = 33 ± 11 years) underwent spirometry, plethysmography and hyperpolarized 3He MRI prior to a MCh. MRI was repeated following the MCh and again 25 min after salbutamol administration. 3He MRI gas distribution was quantified using semiautomated segmentation of the ventilation defect percent (VDP). Tissue microstructure was measured using the 3He apparent diffusion coefficient (ADC). Analysis of variance with repeated measures was used to evaluate changes at each time point as well as to determine interactions between regions of interest (ROI) and subject group. Pearson's correlations were performed to evaluate associations between 3He MRI measurements and established clinical measures. Results: In asthmatics, but not HV, whole-lung ADC was increased post-MCh ( P < 0.01). In asthmatics only, ADC was increased post-MCh in posterior ROI ( P < 0.01) and all ROI in the superior-inferior direction ( P < 0.01). VDP was increased in posterior and inferior ROI ( P < 0.001). There was a correlation between VDP and specific airway resistance ( r = 0.74, P < 0.0001), dyspnoea score ( r = 0.66, P < 0.01) and fractional exhaled nitric oxide ( r = 0.45, P < 0.05). Conclusions: We evaluated the regional pulmonary response to methacholine and salbutamol using 3He MRI and showed heterogeneous VDP and ADC consistent with bronchoconstriction and gas trapping, respectively, post-MCh. These regional alterations resolved post-salbutamol. [ABSTRACT FROM AUTHOR]

A deep inspiration (DI) temporarily relaxes agonist-constricted airways in normal subjects, but in asthma airways are refractory and may rapidly renarrow, possibly due to changes in the structure and function of airway smooth muscle (ASM). Chronic largely uniaxial cyclic strain of ASM cells in culture causes several structural and functional changes in ASM similar to that in asthma, including increases in contractility, MLCK content, shortening velocity, and shortening capacity. However, changes in recovery from acute stretch similar to a DI have not been measured. We have therefore measured the response and recovery to large stretches of cells modified by chronic stretching and investigated the role of MLCK. Chronic, 10% uniaxial cyclic stretch, with or without a strain gradient, was administered for up to 11 days to cultured cells grown on Silastic membranes. Single cells were then removed from the membrane and subjected to 1 Hz oscillatory stretches up to 10% of the in situ cell length. These oscillations reduced stiffness by 66% in all groups (P < 0.05). Chronically strained cells recovered stiffness three times more rapidly than unstrained cells, while the strain gradient had no effect. The stiffness recovery in unstrained cells was completely inhibited by the MLCK inhibitor ML-7, but recovery in strained cells exhibiting increased MLCK was slightly inhibited. These data suggest that chronic strain leads to enhanced recovery from acute stretch, which may be attributable to the strain-induced increases in MLCK. This may also explain in part the more rapid renarrowing of activated airways following DI in asthma. [ABSTRACT FROM AUTHOR]

Airway smooth muscle (ASM) cells are constantly under mechanical strain as the lung cyclically expands and deflates, and this stretch is now known to modulate the contractile function of ASM. However, depending on the experimental conditions, stretch is either beneficial or harmful limiting or enhancing contractile force generation, respectively. Stretch caused by a deep inspiration is known to be beneficial in limiting or reversing airway constriction in healthy individuals, and oscillatory stretch lowers contractile force and stiffness or lengthens muscle in excised airway tissue strips. Stretch in ASM culture has generally been reported to cause increased contractile function through increases in proliferation, contractile protein content, and organization of the cell cytoskeleton. Recent evidence indicates the type of stretch is critically important. Growing cells on flexible membranes where stretch is non-uniform and anisotropic leads to pro-contractile changes, whereas uniform biaxial stretch causes the opposite effects. Furthermore, the role of contractile tone might be important in modulating the response to mechanical stretch in cultured cells. This report will review the contrasting evidence for modulation of contractile function of ASM, both in vivo and in vitro, and summarize the recent evidence that mechanical stress applied either acutely within 2 h or chronically over 11 d is a potent stimulus for cytoskeletal remodelling and stiffening. We will also point to new data suggesting that perhaps some of the difference in response to stretch might lie with one of the fundamental differences in the ASM environment in asthma and in culture — the presence of elevated contractile tone. [ABSTRACT FROM AUTHOR]

The application of mechanical stresses to the airway smooth muscle (ASM) cell causes time-dependent cytoskeletal stiffening and remodeling (Dang L, Fairbank NJ, Fabry B, Smith PG, and Maksym GN. Am J Physiol Cell Physiol 287: C440–C448, 2004). We investigated here the extent to winch these behaviors are modulated by the state of cell activation (tone). Localized mechanical stress was applied to the ASM cell in culture via oscillating beads (4.5 μm) that were tightly bound to the actin cytoskeleton (CSK). Tone was reduced from baseline level using a panel of relaxant agonists (10-3 M dibutyryl cAMP, 10-4 M forskolin, or 10-4 M formoterol). To assess functional changes, we measured cell stiffness (G′) using optical magnetic twisting cytometry, and to assess structural changes of the CSK we measured actin accumulation in the neighborhood of the bead. Applied mechanical stress caused a twofold increase in G′ at 120 rain. Afar cessation of applied stress, G′ diminished only 24 ± 6% (mean ± SE) at 1 h, leaving substantial residual effects that were largely irreversible. However, applied stress-induced stiffening could be prevented by ablation of tone. Ablation of tone also inhibited the amount of actin accumulation induced by applied mechanical stress (P < 0.05). Thus the greater the contractile tone, the greater was applied stress-induced CSK stiffening and remodeling. As regards pathobiology of asthma, this suggests a maladaptive positive feedback in winch tone potentiates ASM remodeling and stiffening that further increases stress and possibly leads to worsening airway function. [ABSTRACT FROM AUTHOR]

Mechanical stress (MS) causes cytoskeletal (CSK) and phenotypic changes in cells. Such changes in airway smooth muscle (ASM) cells might contribute to the pathophysiology of asthma. We have shown that periodic mechanical strain applied to cultured ASM cells alters the structure and expression of CSK proteins and increases cell stiffness and contractility (Smith PG, Moreno R, and Ikebe M. Am J Physiol Lung Cell Mol Physiol 272: L20-L27, 1997; and Smith PG, Deng L, Fredberg JJ, and Maksym GN. Am J Physiol Lung Cell Mol Physiol 285: L456-L463, 2003). However, the mechanically induced CSK changes, altered cell function, and their time courses are not well understood. Here we applied MS to the CSK by magnetically oscillating ferromagnetic beads bound to the CSK. We quantified CSK remodeling by measuring actin accumulation at the sites of applied MS using fluorescence microscopy. We also measured CSK stiffness using optical magnetic twisting cytometry. We found that, during MS of up to 120 min, the percentage of beads associated with actin structures increased with time. At 60 min, 68.1 ± 1.6% of the beads were associated with actin structures compared with only 6.7 ± 2.8% before MS and 38.4 ± 5.5% in time-matched controls (P < 0.05). Similarly, CSK stiffness increased more than twofold in response to the MS compared with time-matched controls. These changes were more pronounced than observed with contractile stimulation by 80 mM KC1 or 10-4 M acetylcholine. Together, these findings imply that MS is a potent stimulus to enhance stiffness and contractility of ASM cells through CSK remodeling, which may have important implications in airway narrowing and dilation in asthma. [ABSTRACT FROM AUTHOR]

Developed over six decades ago, pulmonary oscillometry has re‐emerged as a noninvasive and effort‐independent method for evaluating respiratory‐system impedance in patients with obstructive lung disease. Here, we evaluated the relationships between hyperpolarized 3He ventilation‐defect‐percent (VDP) and respiratory‐system resistance, reactance and reactance area (AX) measurements in 175 participants including 42 never‐smokers without respiratory disease, 56 ex‐smokers with chronic‐obstructive‐pulmonary‐disease (COPD), 28 ex‐smokers without COPD and 49 asthmatic never‐smokers. COPD participants were dichotomized based on x‐ray computed‐tomography (CT) evidence of emphysema (relative‐area CT‐density‐histogram ≤ 950HU (RA950) ≥ 6.8%). In asthma and COPD subgroups, MRI VDP was significantly related to the frequency‐dependence of resistance (R5‐19; asthma: ρ = 0.48, P = 0.0005; COPD: ρ = 0.45, P = 0.0004), reactance at 5 Hz (X5: asthma, ρ = −0.41, P = 0.004; COPD: ρ = −0.38, P = 0.004) and AX (asthma: ρ = 0.47, P = 0.0007; COPD: ρ = 0.43, P = 0.0009). MRI VDP was also significantly related to R5‐19 in COPD participants without emphysema (ρ = 0.54, P = 0.008), and to X5 in COPD participants with emphysema (ρ = −0.36, P = 0.04). AX was weakly related to VDP in asthma (ρ = 0.47, P = 0.0007) and COPD participants with (ρ = 0.39, P = 0.02) and without (ρ = 0.43, P = 0.04) emphysema. AX is sensitive to obstruction but not specific to the type of obstruction, whereas the different relationships for MRI VDP with R5‐19 and X5 may reflect the different airway and parenchymal disease‐specific biomechanical abnormalities that lead to ventilation defects. We evaluated the relationships between hyperpolarized 3He ventilation defect percent (VDP) and respiratory system resistance, reactance and AX oscillometry measurements in 175 participants. R5‐19 and X5 demonstrated different relationships with VDP in patients with different disease phenotypes, whereas AX was weakly related to VDP in all subgroups with airflow obstruction. Our results demonstrated that AX is sensitive to obstruction but not specific to the type of obstruction, and that the different relationships for MRI VDP with R5‐19 and X5 may reflect airway and parenchymal disease‐specific biomechanical abnormalities that lead to ventilation defects. [ABSTRACT FROM AUTHOR]

Ventilation heterogeneity is an important marker of small airway dysfunction in asthma. The frequency dependence of respiratory system resistance ( Rrs) from oscillometry is used as a measure of this heterogeneity. However, this has not been quantitatively assessed or compared with other outcomes from oscillometry, including respiratory system reactance ( Xrs) and the associated elastance ( Ers). Here, we used a multibranch model of the human lung, including an upper airway shunt, to match previously reported respiratory mechanics in mild to severe asthma. We imposed heterogeneity by narrowing a proportion of the peripheral airways to account for patient Ers at 5 Hz, and then narrowed central airways to account for the remaining Rrs at 18 Hz. The model required >75% of the small airways to be occluded to reproduce severe asthma. While the model produced frequency dependence in Rrs, it was upward-shifted below 5 Hz compared with in-vivo results, indicating that other factors, including more distributed airway narrowing or central airway wall compliance, are required. However, Ers quantitatively reflected the imposed heterogeneity better than the frequency dependence of Rrs, independent of the frequency range for the estimation, and thus was a more robust measure of small-airway function. Thus, Ers appears to have greater potential as a clinical measure of early small-airway disease in asthma. [ABSTRACT FROM AUTHOR]

Oscillometry (also known as the forced oscillation technique) measures the mechanical properties of the respiratory system (upper and intrathoracic airways, lung tissue and chest wall) during quiet tidal breathing, by the application of an oscillating pressure signal (input or forcing signal), most commonly at the mouth. With increased clinical and research use, it is critical that all technical details of the hardware design, signal processing and analyses, and testing protocols are transparent and clearly reported to allow standardisation, comparison and replication of clinical and research studies. Because of this need, an update of the 2003 European Respiratory Society (ERS) technical standards document was produced by an ERS task force of experts who are active in clinical oscillometry research.The aim of the task force was to provide technical recommendations regarding oscillometry measurement including hardware, software, testing protocols and quality control.The main changes in this update, compared with the 2003 ERS task force document are 1) new quality control procedures which reflect use of "within-breath" analysis, and methods of handling artefacts; 2) recommendation to disclose signal processing, quality control, artefact handling and breathing protocols ( e.g. number and duration of acquisitions) in reports and publications to allow comparability and replication between devices and laboratories; 3) a summary review of new data to support threshold values for bronchodilator and bronchial challenge tests; and 4) updated list of predicted impedance values in adults and children., Competing Interests: Conflict of interest: G.G. King reports grants from American Thoracic Society and European Respiratory Society, during the conduct of the study; a collaborative research agreement and IP agreement with Restech, grants and personal fees for lectures from AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Menarini, MundiPharma and Cyclomedica, grants from NH&MRC, Philanthropic Societies, Sydney University, outside the submitted work. Conflict of interest: J. Bates is a minor shareholder and received personal fees for advisory board work from Oscillavent, LLC, outside the submitted work; and has a patent (patent application US 20160007882 A1; proposes the use of oscillometry in ventilated patients) pending to none, and a patent PCT application WO2015127377 A1 (proposes variable tidal volume ventilation as a means of performing oscillometry in ventilated patients) pending to none. Conflict of interest: K.I. Berger has nothing to disclose. Conflict of interest: P. Calverley has advised Philips Respironics about the clinical application of FOT and spoken on this topic at meetings supported by this company. Conflict of interest: P.L. de Melo has a patent 28727 issued. Conflict of interest: R.L. Dellacà has a patent on the detection of EFL by FOT with royalties paid to Philips Respironics and Restech srl, a patent on monitoring lung volume recruitment by FOT with royalties paid to Vyaire, and a patent on early detection of exacerbations by home monitoring of FOT with royalties paid to Restech, and is co-founder and shareholder of Restech srl, a spin-off company of the Politecnico di Milano University producing medical devices for lung function testing based on FOT. Conflict of interest: R. Farré reports contracts for bench assessment of CPAP devices from Resmed and ANTADIR, outside the submitted work. Conflict of interest: G.L. Hall reports grants from American Thoracic Society and European Respiratory Society, during the conduct of the study. Conflict of interest: I. Ioan has nothing to disclose. Conflict of interest: C.G. Irvin reports other for advisory board work from Methapharm, personal fees and non-financial support for advisory board work from Medical Graphics Corp, grants from NIH and American Lung Association, outside the submitted work. Conflict of interest: D.W. Kaczka reports grants from US Department of Defense (W81XWH-16-1-0434) and National Institutes of Health (R01-HL112986, R01-HL126838 and R41-HL140640), and is co-founder and shareholder from OscillaVent, Inc., during the conduct of the study; grants from ZOLL Medical Corporation, and is shareholder and member of an advisory board for Monitor Mask, Inc., outside the submitted work; and has a patent Systems and methods for multi-frequency oscillator ventilation pending to OscillaVent, Inc. (US20160339191A1), a patent Treatment of respiratory condition using targeted delivery pending (US20150290418A1), a patent System and method for setting positive end expiratory pressure during mechanical ventilation based on dynamic lung function (US20070240717A1, abandoned), a patent Enhanced ventilation waveform device issued (US 6,435,182 B1), and a patent Servo-controlled pneumatic pressure oscillator for respiratory impedance measurements and high-frequency ventilation (US20070006924A1, abandoned). Conflict of interest: D.A. Kaminsky reports personal fees for lectures from MGC Diagnostics, Inc., outside the submitted work. Conflict of interest: H. Kurosawa reports grants and personal fees from Chest M.I. Inc., during the conduct of the study; personal fees from Nippon Boehringer Ingelheim Co. Ltd, outside the submitted work; and has a patent US2012101400 with royalties paid to Tohoku University. Conflict of interest: E. Lombardi reports personal fees from Angelini, Boehringer, GSK, Omron and Vifor, grants and personal fees from Chiesi, Lusofarmaco and Novartis, grants and non-financial support from ResTech, personal fees and non-financial support from Vertex, outside the submitted work. Conflict of interest: G.N. Maksym reports financial support from Thorasys, Thoracic Medical Systems Inc, prior to the submitted work and non-financial support from Thorasys during the submitted work; and has a patent Respiratory Device (design patent) issued to Thorasys, a patent Respiratory Device filter issued to Thorasys, a patent Piezoelectric beam bending actuated Device for measuring respiratory system impedance issued to Thorasys, and a patent Method of assessment of airway variability in airway hyperresponsiveness issued to Thorasys. Conflict of interest: F. Marchal has nothing to disclose. Conflict of interest: B.W. Oppenheimer has nothing to disclose. Conflict of interest: S.J. Simpson has nothing to disclose. Conflict of interest: C. Thamrin has a patent WO 2006130922 A1 issued which is broadly relevant to the work, and has intellectual property arrangements with Thorasys Medical Systems and Restech srl relating to research collaborations, but does not have any financial relationships with either company. Conflict of interest: M. van den Berge reports grants paid to the university from AstraZeneca, TEVA, GSK and Chiesi, outside the submitted work. Conflict of interest: E. Oostveen has nothing to disclose., (Copyright ©ERS 2020.)

In patients with asthma, magnetic resonance imaging (MRI) provides direct measurements of regional ventilation heterogeneity, the etiology of which is not well-understood, nor is the relationship of ventilation abnormalities with lung mechanics. In addition, respiratory resistance and reactance are often abnormal in asthmatics and the frequency dependence of respiratory resistance is thought to reflect ventilation heterogeneity. We acquiredMRIventilation defect maps, forced expiratory volume in one-second (FEV1), and airways resistance (Raw) measurements, and used a computational airway model to explore the relationship of ventilation defect percent (VDP) with simulated measurements of respiratory system resistance (Rrs) and reactance (Xrs).MRIventilation defect maps were experimentally acquired in 25 asthmatics before, during, and after methacholine challenge and these were nonrigidly coregistered to the airway tree model. Using the model coregistered to ventilation defect maps, we narrowed proximal (9th) and distal (14th) generation airways that were spatially related to theMRIventilation defects. The relationships forVDPwith Raw measured using plethysmography (r = 0.79), and model predictions of Rrs>14(r = 0.91,P < 0.0001) and Rrs>9(r = 0.88,P < 0.0001) were significantly stronger (P = 0.005;P = 0.03, respectively) than withFEV1(r = -0.68,P = 0.0001). The slopes for the relationship ofVDPwith simulated lung mechanics measurements were different (P < 0.0001); among these, the slope for theVDP-Xrs0.2relationship was largest, suggesting thatVDPwas dominated by peripheral airway heterogeneity in these patients. In conclusion, as a first step toward understanding potential links between lung mechanics and ventilation defects, impedance predictions were made using a computational airway tree model with simulated constriction of airways related to ventilation defects measured in mild-moderate asthmatics., (© 2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.)

Spirometry is one of the most widely used tests in the assessment and monitoring of asthma. However, spirometry cannot be performed in very young children and some adult patients, and is poorly sensitive to small airways, which are primarily involved in the pathophysiology of asthma. The forced oscillation technique (FOT) has emerged as a powerful alternative technique that instead characterizes respiratory mechanics during normal breathing with no forced maneuver. In this review we highlight the current state of the art of the FOT and its utility in the assessment of lung function in asthma. First we briefly discuss the clinical features and characteristics of asthma. This is followed by a discussion of the assessment of airway obstruction and airway hyperresponsiveness using spirometry. We then review the basics of FOT and its application in respiratory diseases. FOT data are particularly amenable to modeling as an aide to physiological interpretation, and we review several common approaches. This is followed by an in-depth discussion of the assessment of airway variability and heterogeneity using FOT in asthma. Finally, we speculate on the potential clinical utility of FOT in asthma.

Asthma is a variable disease with changes in symptoms and airway function over many time scales. Airway resistance (Raw) is variable and thought to reflect changes in airway smooth muscle activity, but just how variation throughout the airway tree and the influence of gas distribution abnormalities affect Raw is unclear. We used a multibranch airway lung model to evaluate variation in airway diameter size, the role of coherent regional variation, and the role of gas distribution abnormalities on mean Raw (Raw) and variation in Raw as described by the SD (SDRaw). We modified an anatomically correct airway tree, provided by Merryn Tawhai (The University of Auckland, New Zealand), consisting of nearly 4,000 airways, to produce temporal and spatial heterogeneity. As expected, we found that increasing the diameter variation by twofold, with no change in the mean diameter, increased SDRaw more than fourfold. Perhaps surprisingly, Raw was proportional to SDRaw under several conditions-when either mean diameter was fixed, and its SD varied or when mean diameter varied, and SD was fixed. Increasing the size of a regional absence in gas distribution (ventilation defect) also led to a proportionate increase in both Raw and SDRaw. However, introducing regional dependence of connected airways strongly increased SDRaw by as much as sixfold, with little change in Raw. The model was able to predict previously reported Raw distributions and correlation of SDRaw on Raw in healthy and asthmatic subjects. The ratio of SDRaw to Raw depended most strongly on interairway coherent variation and only had a slight dependence on ventilation defect size. These findings may explain the linear correlation between variation and mean values of Raw but also suggest that regional alterations in gas distribution and local coordination in ventilation amplify any underlying variation in airway diameters throughout the airway tree.

Asthmatic individuals typically experience exaggerated decrements in their ability to breathe after receiving standardized doses of smooth muscle agonist, a phenomenon known as airways hyperresponsiveness (AHR). Breathing difficulties are caused by excessive narrowing of the pulmonary airways, which is instigated by shortening of the airway smooth muscle (ASM). Exactly why many asthmatic individuals are hyperresponsive, however, remains controversial because of the many varied mechanisms that could possibly be involved. Nevertheless, much of the understanding of AHR comes down to a matter of considering the spatial configuration of the components that make up the airway, and the static and dynamic physical forces these components experience. In this review, we consider these mechanical factors, which are conveniently subdivided into three groups involving (i) the active forces construing to narrow the airways, (ii) the mechanical loads against which these forces must work, and (iii) the geometric transformation of a given degree of ASM shortening into airway narrowing. Each of these groups of factors has potent potential to influence AHR. It is likely, however, that they operate together to produce the AHR characteristic of severe asthma.

Tissue engineering concepts have expanded in the last decade to consider the importance of biochemical signaling from extracellular matrix (ECM) proteins adhered to substrates such as polymeric and ceramic scaffolds. This study investigated combined ECM/mechanical factors on the key signaling cells (macrophages) for wound healing, since previously, mechanical strain and ECM proteins have only been considered separately for their effects on macrophage morphology. Human U937 macrophage-like cells were cultured on a model elastomeric membrane, coated with either collagen type I or poly-RGD peptide (ProNectin). The cells were subjected to cyclic uniform uniaxial or nonuniform biaxial strain with the Flexercell Tension Plus system to simulate strains that various soft tissue implants may undergo during the critical tissue-implant integration period. The surface coatings affected total cellular protein, which was significantly higher in cells on collagen than ProNectin coated surfaces after biaxial, but not uniaxial strain, whereas ProNectin coated surfaces caused a decrease in DNA following uniaxial, but not biaxial strain. Adding the protein coatings that relate to the wound healing process during tissue regeneration, elicited effects specific to the strain type imposed. The combination of these parameters caused changes in U937 macrophage-like cells that should be considered in the outcome of the desired performance in the tissue-material constructs., ((c) 2007 Wiley Periodicals, Inc.)