Airway remodeling in asthma amplifies heterogeneities in smooth muscle shortening causing hyperresponsiveness.

Although airway remodeling and inflammation in asthma can amplify the constriction response of a single airway, their influence on the structural changes in the whole airway network is unknown. We present a morphometric model of the human lung that incorporates cross-sectional wall areas corresponding to the adventitia, airway smooth muscle (ASM), and mucosa for healthy and mildly and severely asthmatic airways and the influence of parenchymal tethering. A heterogeneous ASM percent shortening stimulus is imposed, causing distinct constriction patterns for healthy and asthmatic airways. We calculate lung resistance and elastance from 0.1 to 5 Hz. We show that, for a given ASM stimulus, the distribution of wall area in asthmatic subjects will amplify not only the mean but the heterogeneity of constriction in the lung periphery. Moreover, heterogeneous ASM shortening that would produce only mild changes in the healthy lung can cause hyperresponsive changes in lung resistance and elastance at typical breathing rates in the asthmatic lung, even with relatively small increases in airway resistance. This condition arises when airway closures occur randomly in the lung periphery. We suggest that heterogeneity is a crucial determinant of hyperresponsiveness in asthma and that acute asthma is more a consequence of extensive airway wall inflammation and remodeling, predisposing the lung to produce an acute pattern of heterogeneous constriction.     

Effects of chronic L-NAME treatment lung tissue mechanics, eosinophilic and extracellular matrix responses induced by chronic pulmonary inflammation

The importance of lung tissue in asthma pathophysiology has been recently recognized. Although nitric oxide mediates smooth muscle tonus control in airways, its effects on lung tissue responsiveness have not been investigated previously. We hypothesized that chronic nitric oxide synthase (NOS) inhibition by N(omega)-nitro-L-arginine methyl ester (L-NAME) may modulate lung tissue mechanics and eosinophil and extracellular matrix remodeling in guinea pigs with chronic pulmonary inflammation. Animals were submitted to seven saline or ovalbumin exposures with increasing doses (1 approximately 5 mg/ml for 4 wk) and treated or not with L-NAME in drinking water. After the seventh inhalation (72 h), animals were anesthetized and exsanguinated, and oscillatory mechanics of lung tissue strips were performed in baseline condition and after ovalbumin challenge (0.1%). Using morphometry, we assessed the density of eosinophils, neuronal NOS (nNOS)- and inducible NOS (iNOS)-positive distal lung cells, smooth muscle cells, as well as collagen and elastic fibers in lung tissue. Ovalbumin-exposed animals had an increase in baseline and maximal tissue resistance and elastance, eosinophil density, nNOS- and iNOS-positive cells, the amount of collagen and elastic fibers, and isoprostane-8-PGF(2alpha) expression in the alveolar septa compared with controls (P<0.05). L-NAME treatment in ovalbumin-exposed animals attenuated lung tissue mechanical responses (P<0.01), nNOS- and iNOS-positive cells, elastic fiber content (P<0.001), and isoprostane-8-PGF(2alpha) in the alveolar septa (P<0.001). However, this treatment did not affect the total number of eosinophils and collagen deposition. These data suggest that NO contributes to distal lung parenchyma constriction and to elastic fiber deposition in this model. One possibility may be related to the effects of NO activating the oxidative stress pathway.     

Neurokinins and inflammatory cell iNOS expression in guinea pigs with chronic allergic airway inflammation

In the present study we evaluated the role of neurokinins in the modulation of inducible nitric oxide synthase (iNOS) inflammatory cell expression in guinea pigs with chronic allergic airway inflammation. In addition, we studied the acute effects of nitric oxide inhibition on this response. Animals were anesthetized and pretreated with capsaicin (50 mg/kg sc) or vehicle 10 days before receiving aerosolized ovalbumin or normal saline twice weekly for 4 wk. Animals were then anesthetized, mechanically ventilated, given normal saline or N(G)-nitro-l-arginine methyl ester (l-NAME, 50 mg/kg ic), and challenged with ovalbumin. Prechallenge exhaled NO increased in ovalbumin-exposed guinea pigs (P < 0.05 compared with controls), and capsaicin reduced this response (P < 0.001). Compared with animals inhaled with normal saline, ovalbumin-exposed animals presented increases in respiratory system resistance and elastance and numbers of total mononuclear cells and eosinophils, including those expressing iNOS (P < 0.001). Capsaicin reduced all these responses (P < 0.05) except for iNOS expression in eosinophils. Treatment with l-NAME increased postantigen challenge elastance and restored both resistance and elastance previously attenuated by capsaicin treatment. Isolated l-NAME administration also reduced total eosinophils and mononuclear cells, as well as those cells expressing iNOS (P < 0.05 compared with ovalbumin alone). Because l-NAME treatment restored lung mechanical alterations previously attenuated by capsaicin, NO and neurokinins may interact in controlling airway tone. In this experimental model, NO and neurokinins modulate eosinophil and lymphocyte infiltration in the airways.     

Oral tolerance attenuates changes in in vitro lung tissue mechanics and extracellular matrix remodeling induced by chronic allergic inflammation in guinea pigs

Recent studies emphasize the presence of alveolar tissue inflammation in asthma. Immunotherapy has been considered a possible therapeutic strategy for asthma, and its effect on lung tissue had not been previously investigated. Measurements of lung tissue resistance and elastance were obtained before and after both ovalbumin and acetylcholine challenges. Using morphometry, we assessed eosinophil and smooth muscle cell density, as well as collagen and elastic fiber content, in lung tissue from guinea pigs with chronic pulmonary allergic inflammation. Animals received seven inhalations of ovalbumin (1-5 mg/ml; OVA group) or saline (SAL group) during 4 wk. Oral tolerance (OT) was induced by offering ad libitum ovalbumin 2% in sterile drinking water starting with the 1st inhalation (OT1 group) or after the 4th (OT2 group). The ovalbumin-exposed animals presented an increase in baseline and in postchallenge resistance and elastance related to baseline, eosinophil density, and collagen and elastic fiber content in lung tissue compared with controls. Baseline and post-ovalbumin and acetylcholine elastance and resistance, eosinophil density, and collagen and elastic fiber content were attenuated in OT1 and OT2 groups compared with the OVA group. Our results show that inducing oral tolerance attenuates lung tissue mechanics, as well as eosinophilic inflammation and extracellular matrix remodeling induced by chronic inflammation.     

Effect of glycosaminoglycan degradation on lung tissue viscoelasticity

We tested the hypothesis that matrix glycosaminoglycans contribute to lung tissue viscoelasticity. We exposed lung parenchymal strips to specific degradative enzymes (chondroitinase ABC, heparitinase I, and hyaluronidase) and determined whether the mechanical properties of the tissue were affected. Subpleural parenchymal strips were obtained from Sprague-Dawley rats and suspended in a Krebs-filled organ bath. One end of the strip was attached to a force transducer and the other to a servo-controlled lever arm that effected sinusoidal oscillations. Recordings of tension and length at different amplitudes and frequencies of oscillation were recorded before and after enzyme exposure. Resistance, dynamic elastance, and hysteresivity were estimated by fitting the equation of motion to changes in tension and length. Quasi-static stress-strain curves were also obtained. Exposure to chondroitinase and heparitinase I caused significant increases in hysteresivity, no decrement in resistance, and similar decreases in dynamic elastance relative to control strips exposed to Krebs solution only. Conversely, measures of static elastance were different in treated versus control strips. Hyaluronidase treatment did not alter any of the mechanical measures. These data demonstrate that digestion of chondroitin sulfate and heparan sulfate alters the mechanical behavior of lung parenchymal tissues.     

Effects of salbutamol and Ro-20-1724 on airway and parenchymal mechanics in rats.

We investigated the effects of a selective beta(2)-agonist, salbutamol, and of phosphodiesterase type 4 inhibition with 4-(3-butoxy-4-methoxy benzyl)-2-imidazolidinone (Ro-20-1724) on the airway and parenchymal mechanics during steady-state constriction induced by MCh administered as an aerosol or intravenously (iv). The wave-tube technique was used to measure the lung input impedance (ZL) between 0.5 and 20 Hz in 31 anesthetized, paralyzed, open-chest adult Brown Norway rats. To separate the airway and parenchymal responses, a model containing an airway resistance (Raw) and inertance (Iaw), and a parenchymal damping (G) and elastance (H), was fitted to ZL spectra under control conditions, during steady-state constriction, and after either salbutamol or Ro-20-1724 delivery. In the Brown Norway rat, the response to iv MCh infusion was seen in Raw and G, whereas continuous aerosolized MCh challenge produced increases in G and H only. Both salbutamol, administered either as an aerosol or iv, and Ro-20-1724 significantly reversed the increases in Raw and G when MCh was administered iv. During the MCh aerosol challenge, Ro-20-1724 significantly reversed the increases in G and H, whereas salbutamol had no effect. These results suggest that, after MCh-induced changes in lung function, salbutamol increases the airway caliber. Ro-20-1724 is effective in reversing the airway narrowings, and it may also decrease the parenchymal constriction.     

Airway and tissue mechanics in a murine model of asthma: alveolar capsule vs. forced oscillations.

To better address the functional consequences of inflammation on bronchial responsiveness, we studied two groups of BALB/c mice: a nonimmunized control group (n = 8) and a group immunized and challenged with inhaled ovalbumin (n = 8). An alveolar capsule (AC) measured airway resistance (Raw(AC)) and lung elastance (EL). A forced oscillation (FO) technique independently estimated airway resistance (Raw(FO)) and a parameter H(ti) related to tissue elastance. Ovalbumin-immunized and -challenged mice had increased numbers of eosinophils in bronchoalveolar lavage and increased responsiveness to methacholine (MCh). Corresponding parameters from the AC and FO techniques were correlated: Raw(AC) vs. Raw(FO) (r = 0.76) and EL vs. H(ti) (r = 0.88, P < 0.0001 in all cases). AC and FO techniques showed significant increases in tissue elastance in response to MCh but no significant increases in airway resistance. These results demonstrated that the AC and FO techniques yield essentially equivalent results in mice, even when the lung is inhomogeneous, and that the bronchoconstrictive responses to MCh and inflammation in mice are predominantly located in the lung periphery.     

Mechanics, nonlinearity, and failure strength of lung tissue in a mouse model of emphysema: possible role of collagen remodeling.

Enlargement of the respiratory air spaces is associated with the breakdown and reorganization of the connective tissue fiber network during the development of pulmonary emphysema. In this study, a mouse (C57BL/6) model of emphysema was developed by direct instillation of 1.2 IU of porcine pancreatic elastase (PPE) and compared with control mice treated with saline. The PPE treatment caused 95% alveolar enlargement (P = 0.001) associated with a 29% lower elastance along the quasi-static pressure-volume curves (P < 0.001). Respiratory mechanics were measured at several positive end-expiratory pressures in the closed-chest condition. The dynamic tissue elastance was 19% lower (P < 0.001), hysteresivity was 9% higher (P < 0.05), and harmonic distortion, a measure of collagen-related dynamic nonlinearity, was 33% higher in the PPE-treated group (P < 0.001). Whole lung hydroxyproline content, which represents the total collagen content, was 48% higher (P < 0.01), and alpha-elastin content was 13% lower (P = 0.16) in the PPE-treated group. There was no significant difference in airway resistance (P = 0.7). The failure stress at which isolated parenchymal tissues break during stretching was 40% lower in the PPE-treated mice (P = 0.002). These findings suggest that, after elastolytic injury, abnormal collagen remodeling may play a significant role in all aspects of lung functional changes and mechanical forces, leading to progressive emphysema.     

Effect of Desmodium adscendens fractions on antigen- and arachidonic acid-induced contractions of guinea pig airways

Three fractions (n-butanol, F2, and L5), isolated from an aqueous extract of Desmodium adscendens, a plant used in Ghana for the management of asthma, were evaluated for their pharmacological activity using ovalbumin and arachidonic acid-induced contractions of guinea pig airways. All three fractions inhibited the ovalbumin-induced contractions of indomethacin-pretreated tracheal spirals from sensitized animals dose dependently, but only L5 and n-butanol inhibited such contractions in the absence of indomethacin. The concentrations required to inhibit ovalbumin-induced contractions of lung parenchymal strips were threefold higher than with trachea. The contractile response over a 60-min period was divided into three phases. F2 and n-butanol inhibited all phases, whereas L5 inhibited only the late phase. n-Butanol and L5 inhibited arachidonic acid-induced contractions on indomethacin-pretreated tracheal spirals, a leukotriene-dependent reaction. There was no inhibition of arachidonic acid-induced contractions of lung parenchymal strips, which is largely a thromboxane-dependent reaction. The results suggest that D. adscendens contains several pharmacologically active substances that can inhibit allergic airway smooth muscle contraction at multiple sites, including the synthesis and (or) activity of the bronchoconstrictor leukotrienes.     

How does airway inflammation modulate asthmatic airway constriction? An antigen challenge study.

During the late-phase (LP) response to inhaled allergen, mediators from neutrophils and eosinophils are released within the airways, resembling what occurs during an asthma attack. We compared the distribution of obstruction and degree of reversibility that follows a deep inspiration (DI) during early-phase (EP) and LP responses in nine asthmatic subjects challenged with allergen. Heterogeneity of constriction was assayed by determining frequency dependence of dynamic lung resistance and elastance, airway caliber by tracking airway resistance during a DI, and airway inflammation by measuring inflammatory cells in induced sputum postchallenge. Despite a paucity of eosinophils in the sputum at baseline (<1% of nonsquamous cells), asthmatic subjects showed a substantial EP response with highly heterogeneous constriction and reduced capacity to maximally dilate airways. The LP was associated with substantial airway inflammation in all subjects. However, five subjects showed only mild LP constriction, whereas four showed more marked LP constriction characterized by heterogeneous constriction similar to EP. Bronchoconstriction during LP was fully alleviated by administration of a bronchodilator. These findings, together with the impaired bronchodilatory response during a DI, indicate a physiological abnormality in asthma at the smooth muscle level and indicate that airway inflammation in asthma is associated with a highly nonuniform pattern of constriction. These data support the hypothesis that variability in responsiveness among asthmatic subjects derives from intrinsic differences in smooth muscle response to inflammation.     

卡介苗对哮喘小鼠肺组织中PPAR-γ表达的影响及意义

目的：探讨卡介苗对哮喘小鼠肺组织中PPAR-γ表达的影响及其意义。方法：30只健康雄性昆明种小鼠随机化原则分成正常对照组（A组）、哮喘模型组（B组）和卡介苗干预组（C组）,每组10只。卵蛋白致敏法复制哮喘模型,B组小鼠于实验的第1、8、15天分别给予卵蛋白与氢氧化铝混合腹腔注射。第22天开始给予卵蛋白溶液以压缩雾化器为动力雾化吸入激发哮喘,每日一次,每次30min。连续激发7天;C组小鼠每周一次皮内注射0.025mgBCG,连续3次,距首次皮内注射4周后按B组方法致敏和激发;A组予以等量生理盐水代替致敏液及雾化液进行腹腔注射与雾化吸入。检测细支气管炎症细胞浸润及肺组织病理,RT-PCR和western blotting方法检测肺组织PPAR-γ的表达情况。结果：哮喘组出现了明显气道炎症细胞浸润,上皮脱落、炎性细胞渗出、结构紊乱、PPAR-γ表达下降。卡介苗干预组炎症细胞数下降,炎症反应减轻,PPAR-γ表达明显增加,差异具有统计学意义（P〈0.01）。结论：卡介苗可通过上调表达PPAR-γ,减少炎症细胞的浸润,抑制炎症反应,从而可能防止气道重塑,该研究为卡介苗提供新的临床应用领域。     

Effect of lung volume on plateau response of airways and tissue to methacholine in dogs.

We have recently shown in dogs that much of the increase in lung resistance (RL) after induced constriction can be attributed to increases in tissue resistance, the pressure drop in phase with flow across the lung tissues (Rti). Rti is dependent on lung volume (VL) even after induced constriction. As maximal responses in RL to constrictor agonists can also be affected by changes in VL, we questioned whether changes in the plateau response with VL could be attributed in part to changes in the resistive properties of lung tissues. We studied the effect of changes in VL on RL, Rti, airway resistance (Raw), and lung elastance (EL) during maximal methacholine (MCh)-induced constriction in 8 anesthetized, paralyzed, open-chest mongrel dogs. We measured tracheal flow and pressure (Ptr) and alveolar pressure (PA), the latter using alveolar capsules, during tidal ventilation [positive end-expiratory pressure (PEEP) = 5.0 cmH2O, tidal volume = 15 ml/kg, frequency = 0.3 Hz]. Measurements were recorded at baseline and after the aerosolization of increasing concentrations of MCh until a clear plateau response had been achieved. VL was then altered by changing PEEP to 2.5, 7.5, and 10 cmH2O. RL changed only when PEEP was altered from 5 to 10 cmH2O (P < 0.01). EL changed when PEEP was changed from 5 to 7.5 and 5 to 10 cmH2O (P < 0.05). Rti and Raw varied significantly with all three maneuvers (P < 0.05). Our data demonstrate that the effects of VL on the plateau response reflect a complex combination of changes in tissue resistance, airway caliber, and lung recoil.     

A role for decorin in a murine model of allergen-induced asthma

Decorin (Dcn) is an extracellular matrix proteoglycan, which affects airway mechanics, airway-parenchymal interdependence, airway smooth muscle proliferation and apoptosis, and transforming growth factor-β bioavailability. As Dcn deposition is differentially altered in asthma, we questioned whether Dcn deficiency would impact the development of allergen-induced asthma in a mouse model. Dcn(-/-) and Dcn(+/+) mice (C57Bl/6) were sensitized with ovalbumin (OA) and challenged intranasally 3 days/wk × 3 wk. After OA challenge, mice were anesthetized, and respiratory mechanics measured under baseline conditions and after delivery of increasing concentrations of methacholine aerosol. Complex impedance was partitioned into airway resistance and tissue elastance and damping. Bronchoalveolar lavage was performed. Lungs were excised, and tissue sections evaluated for inflammatory cell influx, α-smooth muscle actin, collagen, biglycan, and Dcn deposition. Changes in TH-2 cytokine mRNA and protein were also measured. Airway resistance was increased in OA-challenged Dcn(+/+) mice only (P < 0.05), whereas tissue elastance and damping were increased in both OA-challenged Dcn(+/+) and Dcn(-/-), but more so in Dcn(+/+) mice (P < 0.001). Inflammation and collagen staining within the airway wall were increased with OA in Dcn(+/+) only (P < 0.001 and P < 0.01, respectively, vs. saline). IL-5 and IL-13 mRNA were increased in lung tissue of OA-challenged Dcn(+/+) mice. Dcn deficiency resulted in more modest OA-induced hyperresponsiveness, evident at the level of the central airways and distal lung. Differences in physiology were accompanied by differences in inflammation and remodeling. These findings may be, in part, due to the well-described ability of Dcn to bind transforming growth factor-β and render it less bioavailable.     

Maximal methacholine-induced constriction in rabbit lung: interactions between airways and tissue?

Six anesthetized paralyzed open-chest New Zealand White male rabbits were studied to obtain the maximal or plateau response to the inhalation of methacholine. Tracheal flow, tracheal pressure, and, by use of alveolar capsules, alveolar pressure were measured during tidal mechanical ventilation. We calculated total lung resistance (RL), tissue viscance (Vti), and lung elastance by digital fitting of the equation of motion to changes in tracheal and alveolar pressure. Airways resistance (Raw) was calculated as RL-Vti. Measurements were made under control conditions and after delivery of increasing concentrations of methacholine aerosol (0.5-128 mg/ml). We found that Vti accounted for the major proportion of RL both under control conditions (64.5 +/- 15.9%) and after methacholine-induced constriction (83.6 +/- 11.8%). There was a significant negative correlation between logarithmic percent change in Raw and Vti at the onset of the plateau response (r = 0.973). Furthermore, the slope of the relationship between log change in Vti and log change in Raw during the plateau response was strongly correlated with the degree of tissue response at the onset of the plateau (r = 0.957). Vti was positively correlated with lung elastance both before and during the plateau response (r = 0.946). We propose that the negative correlation between tissue resistance and Raw at the level of the plateau is consistent with a model of a mechanically interdependent lung, where decreases in airway caliber are limited by the constriction of the surrounding parenchyma.     

Relating maximum airway dilation and subsequent reconstriction to reactivity in human lungs.

Measures of airway resistance (Raw) during deep inspiration (DI) suggest that asthmatic subjects possess stiffer, more reactive airway smooth muscle. There is evidence that one can enhance airway reactivity in healthy lungs by prohibiting DI for an extended period. The present study had two goals. First, we determined whether the maximum dilation capacity of asthmatic subjects depended on the rate of the DI. Second, we investigated whether the enhanced reactivity in healthy humans might derive from additional mechanisms not present in asthmatic subjects. For the first goal, we tracked Raw in seven healthy and seven asthmatic subjects during a noncoached DI, a DI with a 5- to 10-s breath hold at total lung capacity, and a rapid DI. We found that the minimum resistance achieved at total lung capacity was independent of the manner in which the DI was performed. For the second goal, we tracked the rate of return of Raw after a DI as well as dynamic lung elastance before and after the DI, at baseline and after bronchial challenge. A drop in lung elastance post-DI would indicate reopening of lung regions and/or reduced heterogeneities. The data show that constricted healthy but not asthmatic subjects produce longer lasting residual dilation. Hence, a portion of the enhanced reactivity in a healthy subject's response to prohibition of DIs is likely due to airway closure and/or atelectasis that can be ablated with a DI. We conclude that preventing DIs does not ensure that healthy subjects will transition entirely to an asthmatic-like hyperreactive lung state.     

Identifying airways responsible for heterogeneous ventilation and mechanical dysfunction in asthma: an image functional modeling approach.

We present an image functional modeling approach, which synthesizes imaging and mechanical data with anatomically explicit computational models. This approach is utilized to identify the relative importance of small and large airways in the simultaneous deterioration of mechanical function and ventilation in asthma. Positron emission tomographic (PET) images provide the spatial distribution and relative extent of ventilation defects in asthmatic subjects postbronchoconstriction. We also measured lung resistance and elastance from 0.15 to 8 Hz. The first step in image functional modeling involves mapping ventilation three-dimensional images to the computational model and identifying the largest sized airways of the model that, if selectively constricted, could precisely match the size and anatomic location of ventilation defects imaged by PET. In data from six asthmatic subjects, these airways had diameters <2.39 mm and mostly <0.44 mm. After isolating and effectively closing airways in the model associated with these ventilation defects, we imposed constriction with various means and standard deviations to the remaining airways to match the measured lung resistance and elastance from the same subject. Our results show that matching both the degree of mechanical impairment and the size and location of the PET ventilation defects requires either constriction of airways <2.4 mm alone, or a simultaneous constriction of small and large airways, but not just large airways alone. Also, whereas larger airway constriction may contribute to mechanical dysfunction during asthma, degradation in ventilation function requires heterogeneous distribution of near closures confined to small airways.     

Tissue viscance during induced constriction in rabbit lungs: morphological-physiological correlations.

Tissue viscance (Vti), the pressure drop across the lung tissues in phase with flow, increases after induced constriction. To gain information about the possible site of response, we induced increases in Vti with methacholine (MCh) and attempted to correlate these changes with alterations in lung morphology. We measured tracheal (Ptr) and alveolar pressure (PA) in open-chest rabbits during mechanical ventilation [frequency = 1 Hz, tidal volume = 5 ml/kg, positive end-expiratory pressure (PEEP) = 5 cmH2O] under control conditions and after administration of saline or MCh (32 or 128 mg/ml) aerosols. We calculated lung elastance (EL), lung resistance (RL), Vti, and airway resistance (Raw) by fitting the equation of motion to changes in Ptr and PA. The lungs were then frozen in situ with liquid nitrogen (PEEP = 5 cmH2O), excised, and processed using freeze substitution techniques. Airway constriction was assessed by measuring the ratio of the airway lumen (A) to the ideally relaxed area (Ar). Tissue distortion was assessed by measuring the mean linear intercept between alveolar walls (Lm), the standard deviation of Lm (SDLm), and an atelectasis index (ATI) derived by calculating the ratio of tissue to air space using computer image analysis. RL, Vti, and EL were significantly increased after MCh, and Raw was unchanged. A/Ar, Lm, SDLm, and ATI all changed significantly with MCh. Log-normalized change (% of baseline) in Vti significantly correlated with A/Ar (r = -0.693), Lm (r = 0.691), SDLm (r = 0.648), and ATI (r = 0.656). Hence, changes in lung tissue mechanics correlated with changes in morphometric indexes of parenchymal distortion and airway constriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Linking Ventilation Heterogeneity Quantified via Hyperpolarized 3He MRI to Dynamic Lung Mechanics and Airway Hyperresponsiveness

Advancements in hyperpolarized helium-3 MRI (HP ³He-MRI) have introduced the ability to render and quantify ventilation patterns throughout the anatomic regions of the lung. The goal of this study was to establish how ventilation heterogeneity relates to the dynamic changes in mechanical lung function and airway hyperresponsiveness in asthmatic subjects. In four healthy and nine mild-to-moderate asthmatic subjects, we measured dynamic lung resistance and lung elastance from 0.1 to 8 Hz via a broadband ventilation waveform technique. We quantified ventilation heterogeneity using a recently developed coefficient of variation method from HP ³He-MRI imaging. Dynamic lung mechanics and imaging were performed at baseline, post-challenge, and after a series of five deep inspirations. AHR was measured via the concentration of agonist that elicits a 20% decrease in the subject’s forced expiratory volume in one second compared to baseline (PC₂₀) dose. The ventilation coefficient of variation was correlated to low-frequency lung resistance (R = 0.647, P < 0.0001), the difference between high and low frequency lung resistance (R = 0.668, P < 0.0001), and low-frequency lung elastance (R = 0.547, P = 0.0003). In asthmatic subjects with PC₂₀ values <25 mg/mL, the coefficient of variation at baseline exhibited a strong negative trend (R = -0.798, P = 0.02) to PC₂₀ dose. Our findings were consistent with the notion of peripheral rather than central involvement of ventilation heterogeneity. Also, the degree of AHR appears to be dependent on the degree to which baseline airway constriction creates baseline ventilation heterogeneity. HP ³He-MRI imaging may be a powerful predictor of the degree of AHR and in tracking the efficacy of therapy.     

支气管哮喘豚鼠肺组织中KLF2的表达及意义

目的：探讨锌指Krüppel样转录因2（KLF2）在豚鼠支气管哮喘肺组织中的表达及意义。方法：30只健康雄性豚鼠,按随机数字表法分为对照组（A组）、哮喘组（B组）及地塞米松治疗组（C组）,每组10只。卵清蛋白致敏法复制哮喘模型。观察豚鼠肺组织病理学改变,BALF细胞总数及分类计数;采用原位杂交和RT-PCR检测肺组织中KLF2的mRNA表达情况,免疫组化和Westernblot检测肺组织中KLF2的蛋白表达水平。结果：（1）哮喘组豚鼠BALF中细胞总数、嗜酸性粒细胞百分比（EOS%）、中性粒细胞百分比（NEU%）显著高于对照组（P〈0.01）,哮喘组肺组织可见大量炎症细胞浸润,及明显气道重塑改变,而地塞米松治疗组BALF炎细胞浸润及肺组织病理改变较哮喘组明显减轻;（2）KLF2mRNA和蛋白在哮喘组表达显著低于对照组,在地塞米松治疗组中的表达明显高于哮喘组,3组差异均有统计学意义（P均〈0.01）;（3）KLF2蛋白以及mRNA与肺泡灌洗液炎细胞总数及EOS%,NEU%呈负相关。结论：KLF2在支气管哮喘急性发作期模型中表达明显下降,而地塞米松治疗后KLF2的表达上调,提示KLF2可能在支气管哮喘的发病机制与防治中起重要作用。     

Oscillation mechanics of the human lung periphery in asthma.

To more precisely measure the mechanical properties of the lung periphery in asthma, we have developed a forced oscillation technique that applies a broad-band flow signal through a wedged bronchoscope. We interpreted the data from four healthy and eight mildly asthmatic subjects in terms of an anatomically accurate computer model of the wedged segment. There was substantial overlap in impedance between the two groups, with resistance (R) showing minimal frequency dependence and elastance (E) showing positive and negative frequency dependence across subjects. After direct instillation of methacholine, R rose in both groups, but compared with healthy subjects, the asthmatic subjects displayed upward, parallel shifts in their dose-response curves. The baseline frequency-response patterns of E were enhanced after methacholine. Frequency dependencies of R and E were well reproduced in two normal subjects by a computational model that employed rigid airways connected to constant-phase tissue units but were better reproduced in the other two normal and three asthmatic subjects when the model employed heterogeneous, peripheral airway narrowing and compliant airways. To capture the frequency dependencies of R and E in the remaining five asthmatic subjects, the model was modified by increasing airway wall stiffness. These results indicate that the lung periphery of mildly asthmatic subjects is not well distinguished from that of healthy subjects by measurement of mechanical impedance at baseline, but group differences are seen after challenge with methacholine. Modeling of the response suggests that variable contributions of airway narrowing and wall compliance are operative in determining overall mechanical impedance of the lung periphery in humans with asthma, likely reflecting the functional consequences of airway inflammation and remodeling.