Homothety ratio of airway diameters and site of airway resistance in healthy and COPD subjects (original) (raw)
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Lumen areas and homothety factor influence airway resistance in COPD
Respiratory physiology & neurobiology, 2010
The remodelling process of COPD may affect both airway calibre and the homothety factor, which is a constant parameter describing the reduction of airway lumen (h(d): diameter of child/parent bronchus) that might be critical because its reduction would induce a frank increase in airway resistance. Airway dimensions were obtained from CT scan images of smokers with (n=22) and without COPD (n=9), and airway resistance from plethysmography. Inspiratory airway resistance correlated to lumen area of the sixth bronchial generation of right lung, while peak expiratory flow correlated to the area of the third right generation (p=0.0009, R=0.57). A significant relationship was observed between h(d) and resistance (p=0.036; R(2)=0.14). A modelling approach of central airways (5 generations) further described the latter relationship. In conclusion, a constant homothety factor can be described by CT scan analysis, which partially explains inspiratory resistance, as predicted by theoretical argu...
Airflow Limitation and Airway Dimensions in Chronic Obstructive Pulmonary Disease
American Journal of Respiratory and Critical Care Medicine, 2006
Rationale: Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation caused by emphysema and/or airway narrowing. Computed tomography has been widely used to assess emphysema severity, but less attention has been paid to the assessment of airway disease using computed tomography. Objectives: To obtain longitudinal images and accurately analyze short axis images of airways with an inner diameter у 2 mm located anywhere in the lung with new software for measuring airway dimensions using curved multiplanar reconstruction. Methods: In 52 patients with clinically stable COPD (stage I, 14; stage II, 22; stage III, 14; stage IV, 2), we used the software to analyze the relationship of the airflow limitation index (FEV 1 , % predicted) with the airway dimensions from the third to the sixth generations of the apical bronchus (B1) of the right upper lobe and the anterior basal bronchus (B8) of the right lower lobe. Measurements and Main Results: Airway luminal area (Ai) and wall area percent (WA%) were significantly correlated with FEV 1 (% predicted). More importantly, the correlation coefficients (r ) improved as the airways became smaller in size from the third (segmental) to sixth generations in both bronchi (Ai: r ϭ 0.26, 0.37, 0.58, and 0.64 for B1; r ϭ 0.60, 0.65, 0.63, and 0.73 for B8).
The effect of disease and respiration on airway shape in patients with moderate persistent asthma
PLOS ONE
Computational models of gas transport and aerosol deposition frequently utilize idealized models of bronchial tree structure, where airways are considered a network of bifurcating cylinders. However, changes in the shape of the lung during respiration affect the geometry of the airways, especially in disease conditions. In this study, the internal airway geometry was examined, concentrating on comparisons between mean lung volume (MLV) and total lung capacity (TLC). A set of High Resolution CT images were acquired during breath hold on a group of moderate persistent asthmatics at MLV and TLC after challenge with a broncho-constrictor (methacholine) and the airway trees were segmented and measured. The airway hydraulic diameter (Dh) was calculated through the use of average lumen area (Ai) and average internal perimeter (Pi) at both lung volumes and was found to be systematically higher at TLC by 13.5±9% on average, with the lower lobes displaying higher percent change in comparison to the lower lobes. The average internal diameter (Din) was evaluated to be 12.4±6.8% (MLV) and 10.8±6.3% (TLC) lower than the Dh, for all the examined bronchi, a result displaying statistical significance. Finally, the airway distensibility per bronchial segment and per generation was calculated to have an average value of 0.45±0.28, exhibiting high variability both between and within lung regions and generations. Mixed constriction/dilation patterns were recorded between the lung volumes, where a number of airways either failed to dilate or even constricted when observed at TLC. We conclude that the Dh is higher than Din, a fact that may have considerable effects on bronchial resistance or airway loss at proximal regions. Differences in caliber changes between lung regions are indicative of asthma-expression variability in the lung. However, airway distensibility at generation 3 seems to predict distensibility more distally.
The relation of airway size to lung function
Medical Imaging 2008: Physiology, Function, and Structure from Medical Images, 2008
Chronic obstructive pulmonary disease may cause airway remodeling, and small airways are the mostly likely site of associated airway flow obstruction. Detecting and quantifying airways depicted on a typical computed tomography (CT) images is limited by spatial resolution. In this study, we examined the association between lung function and airway size. CT examinations and spirometry measurement of forced expiratory volume in one second as a percent predicted (FEV 1 %) from 240 subjects were used in this study. Airway sections depicted in axial CT section were automatically detected and quantified. Pearson correlation coefficients (PCC) were computed to compare lung function across three size categories: (1) all detected airways, (2) the smallest 50% of detected airways, and (3) the largest 50% of detected airways using the CORANOVA test. The mean number of all airways detected per subject was 117.4 (r 40.1) with mean size ranging from 20.2 to 50.0 mm 2 . The correlation between lung function (i.e., FEV 1 ) and airway morphometry associated with airway remodeling and airflow obstruction (i.e., lumen perimeter and wall area as a percent of total airway area) was significantly stronger for smaller compared to larger airways (p < 0.05). The PCCs between FEV 1 and all airways, the smallest 50%, and the largest 50% were 0.583, 0.617, 0.523, respectively, for lumen perimeter and -0.560, -0.584, and -0.514, respectively, for wall area percent. In conclusion, analyzing a set of smaller airways compared to larger airways may improve detection of an association between lung function and airway morphology change.
2012
A defi ning characteristic of COPD is expiratory airfl ow limitation due to intrinsic remodeling of the small airways and their dynamic collapse during forced exhalation. 1 In a normal lung, infl ation results in a predictable increase in airway caliber because of the interdependence of parenchyma and airways (the relative change in airway diameter is linearly related with the cube root of lung volume). 2 Emphysema alters this relationship by disrupting airway-parenchymal interdependence. Early work in small animals demonstrated that methacholine-induced bronchoconstriction was increased in elastase models of emphysema, 3 suggesting that the bronchoconstrictive effect of airway smooth muscle activation is opposed by the Background: An increase in airway caliber (airway distensibility) with lung infl ation is attenuated in COPD. Furthermore, some subjects have a decrease in airway caliber with lung infl ation. We aimed to test the hypothesis that airway caliber increases are lower in subjects with emphysemapredominant (EP) compared with airway-predominant (AP) CT scan subtypes. Additionally, we compared clinical and CT scan features of subjects with (airway constrictors) and without a decrease in airway caliber. Methods: Based on GOLD (Global Initiative for Chronic Obstructive Lung Disease) stages and CT scan subtypes, we created a control group (n 5 46) and the following matched COPD groups (n 5 23 each): GOLD-2-AP, GOLD-2-EP, GOLD-4-AP, and GOLD-4-EP. From the CT scans of all 138 subjects, we measured emphysema, lung volumes, and caliber changes in the third and fourth airway generations of two bronchi. We expressed airway distensibility (ratio of airway lumen diameter change to lung volume change from end tidal breathing to full inspiration) as a global or lobar measure based on normalization by whole-lung or lobar volume changes. Results: Global distensibility in the third and fourth airway generations was signifi cantly lower in the GOLD-2-EP and GOLD-4-EP groups than in control subjects. In GOLD-2 subjects, lobar distensibility of the right-upper-lobe fourth airway generation was signifi cantly lower in those with EP than in those with AP. In multivariate analysis, emphysema was an independent determinant of global and lobar airway distensibility. Compared with nonconstrictors, airway constrictors experienced more dyspnea, were more hyperinfl ated, and had a higher percentage of emphysema. Conclusions: Distensibility of large-to medium-sized airways is reduced in subjects with an EP CT scan subtype. Emphysema seems to alter airway-parenchyma interdependence.
American Journal of Roentgenology, 2010
logic examination and their relation to spirometric measures of expiratory airflow [1-3, 6, 10]. Hasegawa and colleagues [1] refined such observations by finding that wall area percentage and luminal area from the distal airways, typically the fifth or sixth generations of the bronchial tree, have stronger correlations with airflow limitation than those from the proximal airways. Replication of such findings has led to the consensus that quantitative assessment of the wall area percentage and luminal area of the distal fifth and sixth airway generations results in the strongest correlation with lung function in persons with COPD .
Relationship between heterogeneous changes in airway morphometry and lung resistance and elastance
Journal of applied physiology (Bethesda, Md. : 1985), 1997
We present a dog lung model to predict the relation between inhomogeneous changes in airway morphometry and lung resistance (RL) and elastance (EL) for frequencies surrounding typical breathing rates. The RL and EL were sensitive in distinct ways to two forms of peripheral constriction. First, when there is a large and homogeneous constriction, the RL increases uniformly over the frequency range. The EL is rather unaffected below 1 Hz but then increases with frequencies up to 5 Hz. This increase is caused by central airway wall shunting. Second, the RL and EL are extremely sensitive to mild inhomogeneous constriction in which a few highly constricted or nearly closed airways occur randomly throughout the periphery. This results in extreme increases in the levels and frequency dependence of RL and EL but predominantly at typical breathing rates (<1 Hz). Conversely, the RL and EL are insensitive to highly inhomogeneous airway constriction that does not produce any nearly closed air...
Respiratory Research
Background: Decreased airway lumen size and increased lung volume are major structural changes in chronic obstructive pulmonary disease (COPD). However, even though the outer wall of the airways is connected with lung parenchyma and the mechanical properties of the parenchyma affect the behaviour of the airways, little is known about the interactions between airway and lung sizes on lung function and symptoms. The present study examined these effects by establishing a novel computed tomography (CT) index, namely, airway volume percent (AWV%), which was defined as a percentage ratio of the airway tree to lung volume. Methods: Inspiratory chest CT, pulmonary function, and COPD Assessment Tests (CAT) were analysed in 147 stable males with COPD. The whole airway tree was automatically segmented, and the percentage ratio of the airway tree volume in the right upper and middle-lower lobes to right lung volume was calculated as the AWV% for right lung. Low attenuation volume % (LAV%), total airway count (TAC), luminal area (Ai), and wall area percent (WA%) were also measured. Results: AWV% decreased as the Global Initiative for Chronic Obstructive Lung Disease (GOLD) spirometric grade increased (p < 0.0001). AWV% was lower in symptomatic (CAT score ≥ 10) subjects than in non-symptomatic subjects (p = 0.036). AWV% was more closely correlated with forced expiratory volume in 1 s (FEV 1) and ratio of residual volume to total lung capacity (RV/TLC) than Ai, Ai to lung volume ratio, and volume of either the lung or the airway tree. Multivariate analyses showed that lower AWV% was associated with lower FEV 1 and higher RV/TLC, independent of LAV%, WA%, and TAC. Conclusions: A disproportionally small airway tree with a relatively large lung could lead to airflow obstruction and gas trapping in COPD. AWV% is an easily measured CT biomarker that may elucidate the clinical impacts of the airway-lung interaction in COPD.
Scientific reports, 2017
The forced oscillation technique provides information concerning respiratory impedance, which comprises resistance and reactance of the respiratory system. However, its relationship with morphological changes of the lungs in chronic obstructive pulmonary disease (COPD) remains unclear. Respiratory impedance and spirometric data were evaluated in 98 patients with COPD and 49 reference subjects. Wall thickness (WT) and airway intraluminal area (Ai) of third- to sixth-generation bronchi, and percentage low-attenuation area with less than -950 HU (%LAA) of lungs were measured using three-dimensional computed tomography. COPD patients had higher respiratory impedance, decreased Ai, and increased %LAA compared with reference subjects. Indices of respiratory resistance and reactance and forced expiratory volume in 1 second (FEV1) were correlated with Ai, and the association between percent predicted FEV1 and Ai was predominant in distal bronchi. The difference in respiratory resistance bet...