Acinar Ventilation Heterogeneity Research Articles

Respiratory function after 30+ years following sulfur mustard exposure in survivors in Sweden.

Sulfur mustard (SM) exposure causes acute and chronic respiratory diseases. The extent of small airway dysfunction (SAD) in individuals exposed to SM is unclear. This study evaluated and compared SAD in SM-exposed and SM-unexposed participants using noninvasive lung function tests assessing small airway function. This retrospective cohort study involved SM-exposed (n = 15, mean age: 53 ± 8 years) and SM-unexposed (n = 15, mean age: 53 ± 7 years) Kurdish-Swedish individuals in Sweden. Small airway resistance and reactance were assessed using impulse oscillometry (IOS). Nitrogen (N2) multiple breath washout (MBW) was employed to assess lung ventilation heterogeneity. The gas-exchanging capacity of the lungs was assessed using the diffusing capacity of the lungs for the carbon monoxide (DLCO) test. Lung function outcomes were reported as absolute values and z-scores. Group comparisons were performed using the Mann-Whitney U test. No statistically significant differences in age, height, or body mass index were observed between the two groups. IOS showed significantly increased small airway resistance, while N2MBW exhibited significantly increased global and acinar ventilation heterogeneity in SM-exposed individuals compared to that in unexposed individuals. SAD was identified in 14 of 15 SM-exposed individuals, defined as at least one abnormal IOS difference between resistance at 5 and 20 Hz (R5-R20) and/or area of reactance (AX) or N2MBW lung's acinar zone (Sacin), and DLCO adjusted to the alveolar volume (DLCO/VA) outcome. Of these 14 individuals, only 5 demonstrated concordant findings across the IOS and N2MBW tests. Exposure to SM was positively associated with long-term impairment of respiratory tract function in the small airways in the majority of the previously SM-exposed individuals in the present study. Furthermore, both IOS and N2MBW should be employed to detect SAD in SM-exposed survivors as they provide complementary information. Identifying and characterizing the remaining pathology of the small airways in survivors of SM exposure is a first step toward improved treatment and follow-up.

Relationship between concavity of the flow-volume loop and small airway measures in smokers with normal spirometry

BackgroundThere is increasing evidence of small airway abnormalities in smokers despite normal spirometry. The concavity in the descending limb of the maximum expiratory flow curve (MEFV) is a recognised feature of obstruction and can provide information beyond FEV1, and potentially early smoking-related damage. We aimed to evaluate concavity measures compared to known small airway measurements.MethodsEighty smokers with normal spirometry had small airway function assessed: multiple breath nitrogen washout (MBNW) from which ventilation heterogeneity in the diffusion-dependent acinar (Sacin) and convection-dependent conductive (Scond) airways were assessed, and impulse oscillometry system (IOS) from which respiratory resistance and reactance at 5 Hz (R5 and X5) were measured. Concavity measures were calculated from the MEFV, partitioned into global and peripheral concavity.ResultsWe found abnormal peripheral and global concavity as well as acinar ventilation heterogeneity are common in “normal” smokers. Concavity measures were not related to either MBNW or IOS measurements.ConclusionAbnormalities in concavity indices and MBNW or oscillometry parameters are common in smokers despite normal spirometry. However, these measures likely reflect different mechanisms of peripheral airway dysfunction.

The effect of oxygen and carbon dioxide cross-sensitivity sensor error in the Eco Medics Exhalyzer D device on measures of conductive and acinar airway function

IntroductionThe multiple breath nitrogen washout (MBNW) test provides important clinical information in obstructive airways diseases. Recently, a significant cross-sensitivity error in the O2 and CO2 sensors of a widely used commercial MBNW device (Exhalyzer D, Eco Medics AG, Duernten, Switzerland) was detected, which leads to overestimation of N2 concentrations. Significant errors in functional residual capacity (FRC) and lung clearance index (LCI) have been reported in infants and children. This study investigated the impact in adults, and on additional important indices reflecting conductive (Scond) and acinar (Sacin) ventilation heterogeneity, in health and disease.MethodsExisting MBNW measurements of 27 healthy volunteers, 20 participants with asthma and 16 smokers were reanalysed using SPIROWARE V 3.3.1, which incorporates an error correction algorithm. Uncorrected and corrected indices were compared using paired t-tests and Bland–Altman plots.ResultsCorrection of the sensor error significantly lowered FRC (mean difference 9%) and LCI (8–10%) across all three groups. Scond was higher following correction (11%, 14% and 36% in health, asthma and smokers, respectively) with significant proportional bias. Sacin was significantly lower following correction in the asthma and smoker groups, but the effect was small (2–5%) and with no proportional bias.DiscussionThe O2 and CO2 cross-sensitivity sensor error significantly overestimated FRC and LCI in adults, consistent with data in infants and children. There was a high degree of underestimation of Scond but minimal impact on Sacin. The presence of significant proportional bias indicates that previous studies will require reanalysis to confirm previous findings and to allow comparability with future studies.

Ventilation Heterogeneity in Asthma and COPD: The Value of the Poorly Communicating Fraction as the Ratio of Total Lung Capacity to Alveolar Volume

Background: The ventilation heterogeneity (VH) is reliably assessed by the multiple-breath nitrogen washout (MBNW), which provides indices of conductive (S_cond) and acinar (S_acin) VH as well as the lung clearance index (LCI), an index of global VH. VH can be alternatively measured by the poorly communicating fraction (PCF), that is, the ratio of total lung capacity by body plethysmography to alveolar volume from the single-breath lung diffusing capacity measurement. Objectives: Our objective was to assess VH by PCF and MBNW in patients with asthma and with COPD and to compare PCF and MBNW parameters in both patient groups. Method: We studied 35 asthmatic patients and 45 patients with COPD. Each patient performed spirometry, body plethysmography, diffusing capacity, and MBNW test. Results: Compared to COPD patients, asthmatics showed a significantly lesser degree of airflow obstruction and lung hyperinflation. In asthmatic patients, both PCF and LCI and S_acin values were significantly lower than the corresponding ones of COPD patients. In addition, in both patient groups, PCF showed a positive correlation with LCI (p < 0.05) and S_acin (p < 0.05), but not with S_cond. Lastly, COPD patients with PCF >30% were highly likely to have a value ≥2 of the mMRC dyspnea scale. Conclusions: These results showed that PCF, a readily measure derived from routine pulmonary function testing, can provide a comprehensive measure of both global and acinar VH in asthma and in COPD patients and can be considered as a comparable tool to the well-established MBNW technique.

Multiple breath washout (MBW) testing using sulfur hexafluoride: reference values and influence of anthropometric parameters

BackgroundMultiple breath washout (MBW) using sulfur hexafluoride (SF6) has the potential to reveal ventilation heterogeneity which is frequent in patients with obstructive lung disease and associated small airway dysfunction. However,...

Interrelationships Among Small Airways Dysfunction, Neutrophilic Inflammation, and Exacerbation Frequency in COPD

Small airways disease (SAD) is a key component of COPD and is a main contributing factor to lung function decline. Is SAD a key feature of frequent COPD exacerbators and is this related to airway inflammation? Thirty-nine COPD patients defined as either frequent exacerbator (FE) group (≥ 2 exacerbations/y; n= 17) and infrequent exacerbator (IFE) group (≤ 1 exacerbation/y; n= 22) underwent the forced oscillation technique (resistance at 5Hz minus 19Hz [R5-R19], area of reactance [AX]), multiple breath nitrogen washout (conducting airways ventilation heterogeneity, acinar ventilation heterogeneity [Sacin]), plethysmography (ratio of residual volume to total lung capacity), single-breath transfer factor of the lung for carbon monoxide, spirometry (FEV1, FEV1/FVC), and paired inspiratory-expiratory CT scans to ascertain SAD. A subpopulation underwent bronchoscopy to enable enumeration of BAL cell proportions. Sacin was significantly higher in the COPD FE group compared with the IFE group (P= .027). In the FE group, markers of SAD were associated strongly with BAL neutrophil proportions, R5-R19 (P= .001, r= 0.795), AX (P= .049, ρ= 0.560), residual volume to total lung capacity ratio (P= .004, r= 0.730), and the mean lung density of the paired CT scans (P= .018, r= 0.639). Increased Sacin may be a consequence of previous exacerbations or may highlight a group of patients prone to exacerbations. Measures of SAD were associated strongly with neutrophilic inflammation in the small airways of FE patients, supporting the hypothesis that frequent exacerbations are associated with SAD related to increased cellular inflammation.

Small airway dysfunction predicts excess ventilation and dynamic hyperinflation during exercise in patients with COPD

IntroductionSmall airway dysfunction (SAD) is a pathophysiological characteristic of chronic obstructive pulmonary disease (COPD). Excess ventilation and dynamic hyperinflation (DH) are two main pathophysiological traits and limiting factors of COPD patients while exercising. We aimed to ascertain whether or not SAD, assessed by the multiple breath nitrogen washout (MBNW), may predict exercise ventilatory inefficiency and DH. MethodsFifty stable COPD patients were prospectively studied and underwent MBNW and incremental cardio-pulmonary exercise test (CPET). Indices of conductive (Scond) and acinar (Sacin) ventilation heterogeneity as well as minute ventilation/CO2 production (VE/VCO2) linear relationship and the change in inspiratory capacity (IC) were analyzed. ResultsSacin was significantly and directly related to VE/VCO2 slope and inversely related to IC change and to peak O2 uptake (p < 0.01 for all correlations). No significant correlation was found between Scond and CPET parameters. The regression equation generated by stepwise multiple regression analysis for the VE/VCO2 slope and IC change, as dependent variables, included only Sacin, as independent variable. This model accounted for 31% and 36% of the total variance for the VE/VCO2 slope and IC change, respectively. ConclusionOur study shows the value of the SAD as determinant of the excess ventilation and DH during exercise in patients with stable COPD.

Feasibility and clinical applications of multiple breath wash-out (MBW) testing using sulphur hexafluoride in adults with bronchial asthma

Ventilation heterogeneity is frequent in bronchial asthma and can be assessed using multiple breath wash-out testing (MBW). Most data is available in paediatric patients and using nitrogen as a tracer gas. We aimed to evaluate sulphur hexafluoride (SF6) MBW in adult asthmatics. Spirometry, whole-body plethysmography, impulse oscillometry and SF6-MBW were prospectively performed. MBW parameters reflecting global (lung clearance index, LCI), acinar (Sacin) and conductive (Scond) ventilation heterogeneity were derived from three consecutive wash-outs. LCI was calculated for the traditional 2.5% and an earlier 5% stopping point that has the potential to reduce wash-out times. 91 asthmatics (66%) and 47 non-asthmatic controls (34%) were included in final analysis. LCI2.5 and LCI5 were higher in asthmatics (p < 0.001). Likewise, Sacin and Scond were elevated (p < 0.001 and p < 0.01). Coefficient of variation was 3.4% for LCI2.5 and 3.5% for LCI5 in asthmatics. Forty-one asthmatic patients had normal spirometry. ROC analysis revealed an AUC of 0.906 for the differentiation from non-asthmatic controls exceeding diagnostic performance of individual and conventional parameters (AUC = 0.819, p < 0.05). SF6-MBW is feasible and reproducible in adult asthmatics. Ventilation heterogeneity is increased as compared to non-asthmatic controls persisting in asthmatic patients with normal spirometry. Diagnostic performance is not affected using an earlier LCI stopping point while reducing wash-out duration considerably.

Exploring the relevance and extent of small airways dysfunction in asthma (ATLANTIS): baseline data from a prospective cohort study

Small airways dysfunction (SAD) is well recognised in asthma, yet its role in the severity and control of asthma is unclear. This study aimed to assess which combination of biomarkers, physiological tests, and imaging markers best measure the presence and extent of SAD in patients with asthma. In this baseline assessment of a multinational prospective cohort study (the Assessment of Small Airways Involvement in Asthma [ATLANTIS] study), we recruited participants with and without asthma (defined as Global Initiative for Asthma severity stages 1-5) from general practices, the databases of chest physicians, and advertisements at 29 centres across nine countries (Brazil, China, Germany, Italy, Spain, the Netherlands, the UK, the USA, and Canada). All participants were aged 18-65 years, and participants with asthma had received a clinical diagnosis of asthma more than 6 months ago that had been confirmed by a chest physician. This diagnosis required support by objective evidence at baseline or during the past 5 years, which could be: positive airway hyperresponsiveness to methacholine, positive reversibility (a change in FEV1 ≥12% and ≥200 mL within 30 min) after treatment with 400 μg of salbutamol in a metered-dose inhaler with or without a spacer, variability in peak expiratory flow of more than 20% (measured over 7 days), or documented reversibility after a cycle (eg, 4 weeks) of maintenance anti-asthma treatment. The inclusion criteria also required that patients had stable asthma on any previous regular asthma treatment (including so-called rescue β2-agonists alone) at a stable dose for more than 8 weeks before baseline and had smoked for a maximum of 10 pack-years in their lifetime. Control group participants were recruited by advertisements; these participants were aged 18-65 years, had no respiratory symptoms compatible with asthma or chronic obstructive pulmonary disease, normal spirometry, and normal airways responsiveness, and had smoked for a maximum of 10 pack-years. We assessed all participants with spirometry, body plethysmography, impulse oscillometry, multiple breath nitrogen washout, CT (in selected participants), and questionnaires about asthma control, asthma-related quality of life (both in participants with asthma only), and health status. We applied structural equation modelling in participants with asthma to assess the contribution of all physiological and CT variables to SAD, from which we defined clinical SAD and CT SAD scores. We then classified patients with asthma into SAD groups with model-based clustering, and we compared asthma severity, control, and health-care use during the past year by SAD score and by SAD group. This trial is registered with ClinicalTrials.gov, number NCT02123667. Between June 30, 2014, and March 3, 2017, we recruited and evaluated 773 participants with asthma and 99 control participants. All physiological measures contributed to the clinical SAD model with the structural equation modelling analysis. The prevalence of SAD in asthma was dependent on the measure used; we found the lowest prevalence of SAD associated with acinar airway ventilation heterogeneity (Sacin), an outcome determined by multiple breath nitrogen washout that reflects ventilation heterogeneity in the most peripheral, pre-acinar or acinar airways. Impulse oscillometry and spirometry results, which were used to assess dysfunction of small-sized to mid-sized airways, contributed most to the clinical SAD score and differed between the two SAD groups. Participants in clinical SAD group 1 (n=452) had milder SAD than group 2 and comparable multiple breath nitrogen washout Sacin to control participants. Participants in clinical SAD group 2 (n=312) had abnormal physiological SAD results relative to group 1, particularly their impulse oscillometry and spirometry measurements, and group 2 participants also had more severe asthma (with regard to asthma control, treatments, exacerbations, and quality of life) than group 1. Clinical SAD scores were higher (indicating more severe SAD) in group 2 than group 1, and we found that these scores were related to asthma control, severity, and exacerbations. We found no correlation between clinical SAD and CT SAD scores. SAD is a complex and silent signature of asthma that is likely to be directly or indirectly captured by combinations of physiological tests, such as spirometry, body plethysmography, impulse oscillometry, and multiple breath nitrogen washout. SAD is present across patients with all severities of asthma, but it is particularly prevalent in severe disease. The clinical classification of SAD into two groups (a milder and a more severe group) by use of impulse oscillometry and spirometry, which are easy to use, is meaningful given its association with GINA severity stages, asthma control, quality of life, and exacerbations. Chiesi Farmaceutici SpA.

Functional CT imaging for identification of the spatial determinants of small-airways disease in adults with asthma

Asthma is a disease characterized by ventilation heterogeneity (VH). Anumber of studies have demonstrated that VH markers derived by using impulse oscillometry (IOS) or multiple-breath washout (MBW) are associated with key asthmatic patient-related outcome measures and airways hyperresponsiveness. However, the topographical mechanisms of VH in the lung remain poorly understood. We hypothesized that specific regionalization of topographical small-airway disease would best account for IOS- and MBW-measured indices in patients. We evaluated the results of paired expiratory/inspiratory computed tomography in a cohort of asthmatic (n=41) and healthy (n=11) volunteers to understand the determinants of clinical VH indices commonly reported by using IOS and MBW. Parametric response mapping (PRM) was used to calculate the functional small-airways disease marker PRMfSAD and Hounsfield unit (HU)-based density changes from total lung capacity to functional residual capacity (ΔHU); gradients of ΔHU in gravitationally perpendicular (parallel) inferior-superior (anterior-posterior) axes were quantified. The ΔHU gradient in the inferior-superior axis provided the highest level of discrimination of both acinar VH (measured by using phase 3 slope analysis of multiple-breath washout data) and resistance at 5Hz minus resistance at 20Hz measured by using impulse oscillometry (R5-R20) values. Patients with a high inferior-superior ΔHU gradient demonstrated evidence of reduced specific ventilation in the lower lobes of the lungs and high levels of PRMfSAD. Acomputational small-airway tree model confirmed that constriction of gravitationally dependent, lower-zone, small-airway branches would promote the largest increases in R5-R20 values. Ventilation gradients correlated with asthma control and quality of life but not with exacerbation frequency. Lower lobe-predominant small-airways disease is a major driver of clinically measured VH in adults with asthma.

Small Airway Disease in Pulmonary Hypertension-Additional Diagnostic Value of Multiple Breath Washout and Impulse Oscillometry.

Airways obstruction is frequent in patients with pulmonary hypertension (PH). Small airway disease (SAD) was identified as a major contributor to resistance and symptoms. However, it is easily missed using current diagnostic approaches. We aimed to evaluate more elaborate diagnostic tests such as impulse oscillometry (IOS) and SF6-multiple-breath-washout (MBW) for the assessment of SAD in PH. Twenty-five PH patients undergoing body-plethysmography, IOS and MBW testing were prospectively included and equally matched to pulmonary healthy and non-healthy controls. Lung clearance index (LCI) and acinar ventilation heterogeneity (Sacin) differed significantly between PH, healthy and non-healthy controls. Likewise, differences were found for all IOS parameters between PH and healthy, but not non-healthy controls. Transfer factor corrected for ventilated alveolar volume (TLCO/VA), frequency dependency of resistance (D5-20), resonance frequency (Fres) and Sacin allowed complete differentiation between PH and healthy controls (AUC (area under the curve) = 1.0). Likewise, PH patients were separated from non-healthy controls (AUC 0.762) by D5-20, LCI and conductive ventilation heterogeneity (Scond). Maximal expiratory flow (MEF) values were not associated with additional diagnostic values. MBW and IOS are feasible in PH patients both providing additional information. This can be used to discriminate PH from healthy and non-healthy controls. Therefore, further research targeting SAD in PH and evaluation of therapeutic implications is justified.

A simulation study of diffusion-convection interaction and its effect on multiple breath washout indices

Experimental studies of acinar ventilation heterogeneity (Sacin) derived from the multiple breath washout have shown the potential of Sacin to pick up structural change in lung disease. Recent Sacin data suggest that even when intra-acinar structure is unaltered, the combination of convection, diffusion and number of acini fed by patent terminal bronchioles can modify Sacin. We show here how Sacin is affected by structural features such as the secondary alveolar septa, intra-acinar ramification and number of ventilated acini. The simulations also predict relationships between respective alterations in Sacin and washout indices such as lung clearance index (LCI) and alveolar mixing efficiency (AME). This was verified experimentally, with highly significant correlations between Sacin and LCI (r = +0.85;p < 0.001) and between Sacin and AME (r = − 0.92; p < 0.001). We have shown how acinar ventilation heterogeneity can be affected by a reduction of number of ventilated acini, a change in overall alveolization or in intra-acinar alveolization pattern, via their impact on the balance between convection and diffusion at acinar level.

Peripheral ventilation heterogeneity determines the extent of bronchoconstriction in asthma.

In asthma, bronchoconstriction causes topographically heterogeneous airway narrowing, as measured by three-dimensional ventilation imaging. Computation modeling suggests that peripheral airway dysfunction is a potential determinant of acute airway narrowing measured by imaging. We hypothesized that the development of low-ventilation regions measured topographically by three-dimensional imaging after bronchoconstriction is predicted by peripheral airway function. Fourteen asthmatic subjects underwent ventilation single-photon-emission computed tomography/computed tomography scan imaging before and after methacholine challenge. One-liter breaths of Technegas were inhaled from functional residual capacity in upright posture before supine scanning. The lung regions with the lowest ventilation (Ventlow) were calculated using a thresholding method and expressed as a percentage of total ventilation (Venttotal). Multiple-breath nitrogen washout was used to measure diffusion-dependent and convection-dependent ventilation heterogeneity (Sacin and Scond, respectively) and lung clearance index (LCI), before and after challenge. Forced expiratory volume in 1 s (FEV1) was 87.6 ± 15.8% predicted, and seven subjects had airway hyperresponsiveness. Ventlow at baseline was unrelated to spirometry or multiple-breath nitrogen washout indices. Methacholine challenge decreased FEV1 by 23 ± 5% of baseline while Ventlow increased from 21.5 ± 2.3%Venttotal to 26.3 ± 6.7%Venttotal (P = 0.03). The change in Ventlow was predicted by baseline Sacin (rs = 0.60, P = 0.03) and by LCI (rs = 0.70, P = 0.006) but not by Scond (rs = 0.30, P = 0.30). The development of low-ventilation lung units in three-dimensional ventilation imaging is predicted by ventilation heterogeneity in diffusion-dependent airways. This relationship suggests that acinar ventilation heterogeneity in asthma may be of mechanistic importance in terms of bronchoconstriction and airway narrowing.NEW & NOTEWORTHY Using ventilation SPECT/CT imaging in asthmatics, we show induced bronchoconstriction leads to the development of areas of low ventilation. Furthermore, the relative volume of the low-ventilation regions was predicted by ventilation heterogeneity in diffusion-dependent acinar airways. This suggests that the pattern of regional airway narrowing in asthma is determined by acinar airway function.

Physiological phenotyping of pediatric chronic obstructive airway diseases.

Inert tracer gas washout (IGW) measurements detect increased ventilation inhomogeneity (VI) in chronic lung diseases. Their suitability for different diseases, such as cystic fibrosis (CF) and primary ciliary dyskinesia (PCD), has already been shown. However, it is still unclear if physiological phenotypes based on different IGW variables can be defined independently of underlying disease. Eighty school-age children, 20 with CF, 20 with PCD, 20 former preterm children, and 20 healthy children, performed nitrogen multiple-breath washout, double-tracer gas (DTG) single-breath washout, and spirometry. Our primary outcome was the definition of physiological phenotypes based on IGW variables. We applied principal component analysis, hierarchical Ward's clustering, and enrichment analysis to compare clinical characteristics between the clusters. IGW variables used for clustering were lung clearance index (LCI) and convection-dependent [conductive ventilation heterogeneity index (Scond)] and diffusion-convection-dependent variables [acinar ventilation heterogeneity index (Sacin) and carbon dioxide and DTG phase III slopes]. Three main phenotypes were identified. Phenotype I (n = 38) showed normal values in all IGW outcome variables. Phenotype II (n = 21) was characterized by pronounced global and convection-dependent VI while diffusion-dependent VI was normal. Phenotype III (n = 21) was characterized by increased global and diffusion- and convection-dependent VI. Enrichment analysis revealed an overrepresentation of healthy children and former preterm children in phenotype I and of CF and PCD in phenotypes II and III. Patients in phenotype III showed the highest proportion and frequency of exacerbations and hospitalization in the year prior to the measurement. IGW techniques allow identification of clinically meaningful, disease-independent physiological clusters. Their predictive value of future disease outcomes remains to be determined.

Transfer factor, lung volumes, resistance and ventilation distribution in healthy adults.

Monitoring of chronic lung disease requires reference values of lung function indices, including putative markers of small airway function, spanning a wide age range.We measured spirometry, transfer factor of the lung for carbon monoxide (TLCO), static lung volume, resistance and ventilation distribution in a healthy population, studying at least 20 subjects per sex and per decade between the ages of 20 and 80 years.With respect to the Global Lung Function Initiative reference data, our subjects had average z-scores for forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and FEV1/FVC of -0.12, 0.04 and -0.32, respectively. Reference equations were obtained which could account for a potential dependence of index variability on age and height. This was done for (but not limited to) indices that are pertinent to asthma and chronic obstructive pulmonary disease studies: forced expired volume in 6 s, forced expiratory flow, TLCO, specific airway conductance, residual volume (RV)/total lung capacity (TLC), and ventilation heterogeneity in acinar and conductive lung zones.Deterioration in acinar ventilation heterogeneity and lung clearance index with age were more marked beyond 60 years, and conductive ventilation heterogeneity showed the greatest increase in variability with age. The most clinically relevant deviation from published reference values concerned RV/TLC values, which were considerably smaller than American Thoracic Society/European Respiratory Society-endorsed reference values.

Acinar ventilation heterogeneity in COPD relates to diffusion capacity, resistance and reactance

The aim of this study was to investigate heterogenic ventilation in the acinar (Sacin) and conductive (Scond) airways of patients with varying chronic obstructive pulmonary disease (COPD) severity and how these relates to advanced lung function parameters, primarily measured by impulse oscillometry (IOS). A secondary aim was to investigate the effects of a short acting beta2-agonist and a muscarinic antagonist on the heterogenic ventilation.Eleven never smoking controls, 12 smoking controls, and 57 COPD patients (7 GOLD 1, 25 GOLD 2, 14 GOLD 3 and 11 GOLD 4) performed flow-volume spirometry, IOS, body plethysmography, single breath carbon monoxide diffusion, and N2-multiple breath washout. Six smoking controls and 13 of the COPD patients also performed double reversibility test by using salbutamol and its combination with ipratropium.Sacin was significantly higher in GOLD 2–4 compared to never smoking controls and smoking controls, but showed similar levels in GOLD 3 and 4. A factor analysis identified 4 components consisting of; 1) IOS parameters, 2) volume parameters, 3) diffusion parameters, Sacin and some IOS parameters and 4) Scond with central obstruction/air trapping. Salbutamol and its combination with ipratropium had no effect on Sacin and Scond.Increased Sacin in COPD was strongly related to diffusion capacity and lung volumes, but also weakly to resistance and reactance, showing a link between ventilation heterogeneity in the acinar airways and parameters measured by IOS.

Characterization of acinar airspace involvement in asthmatic patients by using inert gas washout and hyperpolarized 3helium magnetic resonance

The multiple-breath inert gas washout parameter acinar ventilation heterogeneity (Sacin) is thought to be a marker of acinar airway involvement but has not been validated by using quantitative imaging techniques in asthmatic patients. We aimed to use hyperpolarized (3)He diffusion magnetic resonance at multiple diffusion timescales and quantitative computed tomographic (CT) densitometry to determine the nature of acinar airway involvement in asthmatic patients. Thirty-seven patients with asthma and 17 age-matched healthy control subjects underwent spirometry, body plethysmography, multiple-breath inert gas washout (with the tracer gas sulfur hexafluoride), and hyperpolarized (3)He diffusion magnetic resonance. Asubset of asthmatic patients (n= 27) underwent quantitative CT densitometry. Ninety-four percent (16/17) of patients with an increased Sacin had Global Initiative for Asthma treatment step 4 to 5 asthma, and 13 of 17 had refractory disease. The apparent diffusion coefficient (ADC) of (3)He at 1 second was significantly higher in patients with Sacin-high asthma compared with that in healthy control subjects (0.024 vs 0.017, P< .05). Sacin correlated strongly with ADCs at 1 second (R= 0.65, P< .001) but weakly with ADCs at 13 ms (R= 0.38, P< .05). ADCs at both 13 ms and 1 second correlated strongly with the mean lung density expiratory/inspiratory ratio, a CT marker of expiratory air trapping (R= 0.77, P< .0001 for ADCs at 13 ms; R=0.72,P<.001 for ADCs at 1 second). Sacin is associated with alterations in long-range diffusion within the acinar airways and gas trapping. The precise anatomic nature and mechanistic role in patients with severe asthma requires further evaluation.

Early bronchiolitis obliterans syndrome shows an abnormality of perfusion not ventilation in lung transplant recipients

Long-term survival of lung transplant patients is limited, principally because of Bronchiolitis Obliterans Syndrome (BOS). BOS is primarily classified based on airflow obstruction however there is recent data to suggest that the rejection process can lead to a restrictive ventilatory defect with involvement of the pulmonary vasculature. This study evaluates perfusion heterogeneity in different BOS stages by measuring the relative dispersion (RD) of an arterial spin labelling MRI blood flow image. Acinar ventilation heterogeneity (Sacin) was determined using the Multiple Breath Nitrogen Washout technique. In 24 post transplant patients with a range of severity in BOS status, Sacin increased as BOS level rose from stage 0 to stage 3. In contrast, RD-perfusion was not elevated at BOS 1 and 2 combined compared to BOS 0 and becoming elevated only at BOS-3. However, RD-perfusion in BOS-0p was elevated compared to BOS-0, without an increase in Sacin. These results suggest that BOS-0p is different in nature from other BOS stages.

Irreversible acinar airway abnormality in well controlled asthma

Even in stable asthma patients, acinar ventilation distribution can be abnormal, and we aimed to specifically maximize its reversibility by switching patients from a standard inhaled corticosteroid (iCS) to a fine particle iCS formulation. For this prospective double-blind double-dummy randomized study, 66 stable asthma patients under maintenance iCS (equivalent budesonide ≤ 800 μg/day) were screened for abnormal baseline acinar ventilation heterogeneity (Sacin). After a 3-week run-in period, 35 eligible patients were randomized to fine particle beclomethasone (HFA-BDP; Qvar Autohaler) or to budesonide (DPI-BUD; Pulmicort Turbohaler). Asthma Control Test (ACT) score and various lung function indices reflecting the small airways were obtained at baseline, after 6 and 12 weeks. Thirty one patients [age:52 ± 17(SD) years; FEV1:76 ± 19(SD)%pred] completed the study (DPI-BUD:n = 16; HFA-BDP:n = 15). After 6 and 12 weeks, there were no significant changes in acinar or conductive ventilation heterogeneity, nor in mid-expiratory flow, RV/TLC, closing capacity, impulse oscillometry indices (resistance, reactance), bronchial NO production or alveolar NO, in either treatment arm. Asthma control was maintained in both arms. In stable asthma patients with small airways dysfunction under maintenance therapy, there is a residual functional abnormality in the lung periphery which is probably not eosinophilic in origin and cannot be normalized with the iCS formulations under study. ISRCTN17195095.

Evidence of an Acinar Response following Treatment for Exacerbation in Adult Patients with Cystic Fibrosis

Background: Treating acute infectious exacerbations in cystic fibrosis (CF) patients with intravenous antibiotic therapy leads to variability in lung function and the ventilation distribution response. Part of the variable lung clearance index (LCI) response could be associated with the variable peripheral effects of intravenous antibiotic administration. Objectives: We explored to what extent the peripheral lung zones of CF patients could contribute to lung function improvements following treatment for infectious exacerbations. Methods: Over a 1-year period, 15 adult CF patients admitted for acute exacerbations were recruited. Lung function and multiple breath washout (MBW) tests were performed on the day of admission and at discharge. From the MBW test, we obtained acinar and conductive indices of ventilation heterogeneity and LCI. Results: The mean age (±SD) was 26 ± 5 years. Upon admission, the FEV₁ was 54 ± 16% predicted and the LCI was 181 ± 26% predicted. After treatment, the average FEV₁ increased to 61 ± 20% predicted (p < 0.001) and the LCI decreased to 173 ± 28% predicted (p = 0.042). The change in LCI was associated with a change in acinar (ρ = +0.54; p = 0.039) but not in conductive ventilation heterogeneity (p > 0.1). Conclusions: In CF patients in whom an improvement in LCI was obtained after treatment for an acute infectious exacerbation, this was paralleled by a decrease in acinar ventilation heterogeneity.