CT-Based Evaluation of the Shape of the Diaphragm Using 3D Slicer

The diaphragm is the main inspiratory muscle and separates the thorax and the abdomen. In COPD, the evaluation of the diaphragm shape is clinically important, especially in the case of hyperinflation. However, delineating the diaphragm remains a challenge as it cannot be seen entirely on CT scans. Therefore, the lungs, ribs, sternum, and lumbar vertebrae are used as surrogate landmarks to delineate the diaphragm. We herein describe a CT-based method for evaluating the shape of the diaphragm using 3D Slicer-a free software that allows delineation of the diaphragm landmarks-in ten COPD patients. Using the segmentation performed with 3D Slicer, the diaphragm shape was reconstructed with open-source Free Pascal Compiler. From this graduated model, the length of the muscle fibers, the radius of curvature, and the area of the diaphragm-the main determinants of its function-can be measured. Inter- and intra-user variabilities were evaluated with Bland and Altman plots and linear mixed models. Except for the coronal length (p = 0.049), there were not statistically significant inter- or intra-user differences (p values ranging from 0.326 to 0.910) suggesting that this method is reproducible and repeatable. In conclusion, 3D Slicer can be applied to CT scans for determining the shape of the diaphragm in COPD patients.

The Impact of Airway Obstruction on Feno Values in Asthma Patients

BACKGROUND

Exhaled nitric oxide (Feno) is used as a marker of type-2 airway inflammation in asthma management. Studies with airway challenges demonstrated that a reduction in airway caliber decreases Feno levels.

OBJECTIVE

To evaluate the impact of airway caliber reduction occurring spontaneously in patients with asthma on Feno values in daily clinical practice.

METHODS

In this post hoc analysis, Feno, FEV1, and asthma control questionnaire scores were recorded on each visit for 120 (1073 visits) adult patients with asthma. Blood eosinophils were measured intermittently. The intraindividual relationship between Feno and FEV1 was evaluated via a linear mixed model. The determinants of the individual mean Feno were measured by a stepwise multivariate linear model including individual mean FEV1, inhaled corticosteroid dose, asthma control questionnaire score, and blood eosinophils.

RESULTS

Variations in the negative Feno-FEV1 relationship within individuals at different times were significantly determined by the individual's mean FEV1. This relationship did not hold for individuals above the 75th and below the 25th quartiles. The best explanatory variables for individual mean Feno were FEV1 (+4.3 parts per billion/10%pred) and blood eosinophil count (+1 part per billion per 100 cells/mm3).

DISCUSSION

In the presence of variable degrees of heterogeneous patterns of airway inflammation, airway caliber is shown to be an independent and significant determinant of Feno when measured in patients with asthma. We would propose a +4-parts-per-billion correction factor to the measured Feno value for each 10% reduction below 100% predicted FEV1. Doing this should improve the rigor of interpretation of Feno as an indicator of type-2 inflammation in patients with low FEV1.

Lung diffusing capacity for nitric oxide in space: microgravity gas density interactions

Introduction: During manned space exploration lung health is threatened by toxic planetary dust and radiation. Thus, tests such as lung diffusing capacity (DL) are likely be used in planetary habitats to monitor lung health. During a DL maneuver the rate of uptake of an inspired blood-soluble gas such as nitric oxide (NO) is determined (DL_NO). The aim of this study was to investigate the influence of altered gravity and reduced atmospheric pressure on the test results, since the atmospheric pressure in a habitat on the moon or on Mars is planned to be lower than on Earth. Changes of gravity are known to alter the blood filling of the lungs which in turn may modify the rate of gas uptake into the blood, and changes of atmospheric pressure may alter the speed of gas transport in the gas phase. Methods: DL_NO was determined in 11 subjects on the ground and in microgravity on the International Space Station. Experiments were performed at both normal (1.0 atm absolute, ata) and reduced (0.7 ata) atmospheric pressures. Results: On the ground, DL_NO did not differ between pressures, but in microgravity DL_NO was increased by 9.8% (9.5) (mean [SD]) and 18.3% (15.8) at 1.0 and 0.7 ata respectively, compared to normal gravity, 1.0 ata. There was a significant interaction between pressure and gravity (p = 0.0135). Discussion: Estimates of the membrane (Dm_NO) and gas phase (Dg_NO) components of DL_NO suggested that at normal gravity a reduced pressure led to opposing effects in convective and diffusive transport in the gas phase, with no net effect of pressure. In contrast, a DL_NO increase with reduced pressure at microgravity is compatible with a substantial increase of Dm_NO partially offset by reduced Dg_NO, the latter being compatible with interstitial edema. In microgravity therefore, Dm_NO would be proportionally underestimated from DL_NO. We also conclude that normal values for DL in anticipation of planetary exploration should be determined not only on the ground but also at the gravity and pressure conditions of a future planetary habitat.

The use of time-of-flight camera to assess respiratory rates and thoracoabdominal depths in patients with chronic respiratory disease

INTRODUCTION

Over the last 5 years, the analysis of respiratory patterns presents a growing usage in clinical and research purposes, but there is still currently a lack of easy-to-use and affordable devices to perform such kind of evaluation.

OBJECTIVES

The aim of this study is to validate a new specifically developed method, based on Kinect sensor, to assess respiratory patterns against spirometry under various conditions.

METHODS

One hundred and one participants took parts in one of the three validations studies. Twenty-five chronic respiratory disease patients (14 with chronic obstructive pulmonary disease (COPD) [65 ± 10 years old, FEV₁  = 37 (15% predicted value), VC = 62 (20% predicted value)], and 11 with lung fibrosis (LF) [64 ± 14 years old, FEV₁  = 55 (19% predicted value), VC = 62 (20% predicted value)]) and 76 healthy controls (HC) were recruited. The correlations between the signal of the Kinect (depth and respiratory rate) and the spirometer (tidal volume and respiratory rate) were computed in part 1. We then included 66 HC to test the ability of the system to detect modifications of respiratory patterns induced by various conditions known to modify respiratory pattern (cognitive load, inspiratory load and combination) in parts 2 and 3.

RESULTS

There is a strong correlation between the depth recorded by the Kinect and the tidal volume recorded by the spirometer: r = 0.973 for COPD patients, r = 0.989 for LF patients and r = 0.984 for HC. The Kinect is able to detect changes in breathing patterns induced by different respiratory disturbance conditions, gender and oral task.

CONCLUSIONS

Measurements performed with the Kinect sensors are highly correlated with the spirometer in HC and patients with COPD and LF. Kinect is also able to assess respiratory patterns under various loads and disturbances. This method is affordable, easy to use, fully automated and could be used in the current clinical context. Respiratory patterns are important to assess in daily clinics. However, there is currently no affordable and easy-to-use tool to evaluate these parameters in clinics. We validated a new system to assess respiratory patterns using the Kinect sensor in patients with chronic respiratory diseases.

SP-D and CC-16 Pneumoproteins' Kinetics and Their Predictive Role During SARS-CoV-2 Infection

Background

Surfactant protein D (SP-D) and pulmonary club cell protein 16 (CC-16) are called “pneumoproteins” and are involved in host defense against oxidative stress, inflammation, and viral outbreak. This study aimed to determine the predictive value of these pneumoproteins on the incidence of acute respiratory distress syndrome (ARDS) or death in patients with coronavirus disease-2019 (COVID-19).

Methods

This retrospective study included 87 patients admitted to an emergency department. Blood samples were collected on three time points (days 1, 5, and 14 from hospital admission). SP-D and CC-16 serum levels were determined, and univariate and multivariate analyses considering confounding variables (age, body mass index, tobacco use, dyspnea, hypertension, diabetes mellitus, neutrophil-to-lymphocyte ratio) were performed.

Results

Based on the multivariate analysis, SP-D level on D1 was positively and slightly correlated with subsequent development of ARDS, independent of body mass index, dyspnea, and diabetes mellitus. CC-16 level on D1 was modestly and positively correlated with fatal outcome. A rise in SP-D between D1 and D5 and D1 and D14 had a strong negative association with incidence of ARDS. These associations were independent of tobacco use and neutrophil-to-lymphocyte ratio.

Conclusions

Overall, our data reveal that increase in SP-D levels is a good prognostic factor for patients with COVID-19, and that initial CC-16 levels correlated with slightly higher risk of death. SP-D and CC-16 may prove useful to predict outcomes in patients with COVID-19.

Closing volume detection by single-breath gas washout and forced oscillation technique

Closing volume (CV) is commonly measured by single-breath nitrogen washout (CV_SBW). A method based on the forced oscillation technique was recently introduced to detect a surrogate CV (CV_FOT). As the two approaches are based on different physiological mechanisms, we aim to investigate CV_FOT and CV_SBW relationship at different degrees and patterns of airway obstruction. A mathematical model was developed to evaluate the CV_SBW and CV_FOT sensitivity to different patterns of airway obstruction, either located in a specific lung region or equally distributed throughout the lung. The two CVs were also assessed during slow vital capacity (VC) maneuvers in triplicate in 13 healthy subjects and pre- and postmethacholine challenge (Mch) in 12 subjects with mild-moderate asthma. Model simulations suggest that CV_SBW is more sensitive than CV_FOT to the presence of few flow-limited or closed airways that modify the contribution of tracer-poor and tracer-rich lung regions to the overall exhaled gas. Conversely, CV_FOT occurs only when at least ∼65% of lung units are flow limited or closed, regardless of their regional distribution. CV_SBW did not differ between healthy subjects and those with asthma (17 ± 9% VC vs. 22 ± 10% VC), whereas CV_FOT did (16 ± 5% VC vs. 23 ± 6% VC, P < 0.01). In patients with asthma, both CV_SBW and CV_FOT increased post-Mch (33 ± 7% VC P < 0.001 and 43 ± 12% VC P < 0.001, respectively). CV_SBW weakly correlated with CV_FOT (r = 0.45, P < 0.01). The closing capacities (CV + residual volume) were correlated (r = 0.74, P < 0.001), but the changes with Mch in both CVs and closing capacities did not correlate. CV_FOT is easy to measure and provides a reproducible parameter useful for describing airway impairment in obstructive respiratory diseases.NEW & NOTEWORTHY The forced oscillation technique can identify a surrogate of closing volume (CV_FOT). We investigated its relationship with the one measured by single-breath washout (CV_SBW). CV_FOT weakly correlates with CV_SBW. The respective closing capacities were correlated, but their increases after methacholine challenge in asthmatics did not. Our results suggest that CV_FOT is less sensitive than CV_SBW to few flow-limited/closed airways but more specific in detecting increases in flow-limited/closed airways involving the majority of the lung.

Exploring the sites and kinetics of bronchodilator response to -2 agonists in asthma

We previously documented, in patients with asthma, three different profiles of bronchodilation induced by short-acting β-2 mimetics (SABA), characterized by dilation up to central, preacinar, and intra-acinar airways assessed by ventilation distribution tests and associated with no change, increase, and decrease of fractional exhaled nitric oxide concentration (FENO), respectively. To investigate the dynamics of these profiles over the entire SABA action period, assuming that bronchodilation of proximal and peripheral airways could exhibit varying kinetics due to differences in the distribution of β-2 receptors in both the central and peripheral human airways. FENO, forced expired volume in one second (FEV₁), and the slope (S) of He and SF₆ phase III (single-breath test) were measured in asthma patients before, and up to 6 h after SABA inhalation (salbutamol 400 µg). S_He and S_SF6 decrease reflects pre- and intra-acinar obstruction relief, respectively. Thirty patients with asthma (12F/18M, aged 45 ± 18 yr) were divided into groups with positive (NO+, n = 9), negative (NO-, n = 11), and no (NO=, n = 10) FENO acute change. In the NO- group, FEV₁ increased for up to 4 h, whereas FENO, S_He, and S_F6 decreased in the early phase only. In stark contrast, in the NO+ group, FEV₁ increased in the early phase only whereas the FENO increase and the S_He decrease lasted for up to 4 h. This study documents various profiles of SABA-induced bronchodilation in patients with asthma, differing both by sites and dynamics of the bronchodilator process. So, detailed understanding of the bronchodilator effect of β2-agonists in asthma should not solely be limited to studying their impact on FEV₁.NEW & NOTEWORTHY FEV₁ increase usually observed after the inhalation of short-acting β2-agonists in asthma patients tends to involve peripheral airways. This study shows that the heterogeneity of responses to short-acting β2-agonists in asthma not only involves distinct sites of bronchodilation, but also distinct sequences between these sites. This indicates that a detailed understanding of the bronchodilator effect of β2-agonists in asthma should not be limited to studying its early impact on FEV₁.

Modeling of the Transport and Exchange of a Gas Species in Lungs With an Asymmetric Branching Pattern. Application to Nitric Oxide

Over the years, various studies have been dedicated to the mathematical modeling of gas transport and exchange in the lungs. Indeed, the access to the distal region of the lungs with direct measurements is limited and, therefore, models are valuable tools to interpret clinical data and to give more insights into the phenomena taking place in the deepest part of the lungs. In this work, a new computational model of the transport and exchange of a gas species in the human lungs is proposed. It includes (i) a method to generate a lung geometry characterized by an asymmetric branching pattern, based on the values of several parameters that have to be given by the model user, and a method to possibly alter this geometry to mimic lung diseases, (ii) the calculation of the gas flow distribution in this geometry during inspiration or expiration (taking into account the increased resistance to the flow in airways where the flow is non-established), (iii) the evaluation of the exchange fluxes of the gaseous species of interest between the tissues composing the lungs and the lumen, and (iv) the computation of the concentration profile of the exchanged species in the lumen of the tracheobronchial tree. Even if the model is developed in a general framework, a particular attention is given to nitric oxide, as it is not only a gas species of clinical interest, but also a gas species that is both produced in the walls of the airways and consumed within the alveolar region of the lungs. First, the model is presented. Then, several features of the model, applied to lung geometry, gas flow and NO exchange and transport, are discussed, compared to existing works and notably used to give new insights into experimental data available in the literature, regarding diseases, such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease.

Prevalence and frequency of subchondral bone marrow edema in the lumbar facet joints of asymptomatic and symptomatic individuals

OBJECTIVE

To prospectively compare the prevalence and frequency of subchondral bone marrow edema (BME) in the lumbar facet joints of low back pain patients and healthy subjects.

MATERIALS AND METHODS

Lumbar magnetic resonance imaging (MRI) examinations were performed on 55 asymptomatic participants (18 men; age range 21-63; mean 36 ± 12 years; body mass index (BMI) range 16-31; mean 22.6 ± 3.2 kg/m²) and 79 low back pain patients (36 men; age range 18-77; mean 47 ± 14 years; BMI range 18-40; mean 27.8 ± 4.4 kg/m²). In both groups, facet joint subchondral BME signal was evaluated using T2-weighted STIR imaging, and facet joint osteoarthritis was characterized as mild, moderate, and severe.

RESULTS

The BME signal was found in seven asymptomatic participants (12.7%) and 28 low back pain patients (35.4%) (P = 0.003). A significant portion of the patients (15.2%) presented more than one BME signal (P = 0.011). By pooling the ten facet joints of all subjects in each group, a significant difference in osteoarthritis grade distribution was observed between the two groups (P < 0.001). When adjusted for low back pain status, age, BMI, Modic type 1, disk herniation, and facet joint osteoarthritis maximal grade, only the latter was significantly associated with the facet joint BME signal (P < 0.001).

CONCLUSION

Despite the higher prevalence and frequency of the BME signal in facet joints of low back pain patients compared to that in healthy subjects, the signal was found to be associated with the severity of the patients' osteoarthritis and not with their low back pain status.

Variabilities in X-ray diagnostic reference levels

OBJECTIVES

To estimate the variability of X-ray diagnostic reference levels (DRLs) depending on the number of X-ray devices and data per device.

METHODS

Dose-area products (DAP) were collected by the national nuclear control agency from the 590 devices installed in 345 medical centers in the country. From 2015 to 2017, the number of chest (postero-anterior (PA) view alone, and both postero-anterior and lateral views (PA/LAT)), abdomen, pelvis, and lumbar spine examinations collected in these centers ranged from 23,000 to 77,000. The impact of the number of devices and DAP data per device on DRLs' variabilities (95th confidence intervals divided by medians) is estimated using a bootstrapping method as a function of the number of devices and DAP per device.

RESULTS

The DRLs' variabilities ranged from 30 to 200% depending on the number of devices and DAP data per device but stabilized at 30% when the number of devices was higher than 200 for chest PA and abdomen examinations, 300 for lumbar spine and pelvis examinations, and 400 for chest PA/LAT examinations, regardless of the number of DAP data per device. Extrapolations of our results suggest that thousands of devices are necessary to reduce DRLs' variabilities to 10%.

CONCLUSION

DAP-related DRL variabilities are high but only moderately influenced by the number of DAP data per device and of devices provided this number is higher than 200 to 400 devices according to the type of examination. Harmonization of methods of data collection between the authorities of the EU states should be recommended.

KEY POINTS

• DAP-related DRLs are not fixed values but ranges of values with at least 30% variability. • DAP-related DRLs strongly depend on the number of devices included when lower than 100. • If the number of devices included exceeds 200 to 400, the DRLs' variabilities do not depend on the number of DAP per device and should not exceed 30%.

The use of cognitive mobile games to assess the interaction of cognitive function and breath-hold

The relationship between cognitive function and breath-holding time is in need of further investigation. We aim to determine whether cognitive mobile games (CMG) are sensitive enough to assess the link between cognition and breath-holding time in non-trained subjects. Thirty-one healthy subjects participated in this study. A set of 3 short CMG: Must Sort (response control), Rush Back (attention, working memory) and True Color (mental flexibility, inhibition) was used. Apneic time was recorded in three different conditions: Total Lung Capacity (TLC): 88 ± 35 s, Functional Residual Capacity (FRC): 49 ± 17 s, and Residual Volume (RV): 32 ± 14 s. In males, breath-holding time at RV was correlated with True Color (r = 0.48) and Rush Back (r = 0.65) and at TLC with True Color (r = 0.45). In women, breath-holding time at TLC and FRC was inversely correlated with Must Sort (r = -0.59 and r = -0.49 respectively). Males and females appeared to differ in their use of cognitive resources during different breath-holding conditions.

Short halt in vaping modifies cardiorespiratory parameters and urine metabolome: a randomized trial

Propylene glycol and glycerol are e-cigarette constituents that facilitate liquid vaporization and nicotine transport. As these small hydrophilic molecules quickly cross the lung epithelium, we hypothesized that short-term cessation of vaping in regular users would completely clear aerosol deposit from the lungs and reverse vaping-induced cardiorespiratory toxicity. We aimed to assess the acute effects of vaping and their reversibility on biological/clinical cardiorespiratory parameters [serum/urine pneumoproteins, hemodynamic parameters, lung-function test and diffusing capacities, transcutaneous gas tensions (primary outcome), and skin microcirculatory blood flow]. Regular e-cigarette users were enrolled in this randomized, investigator-blinded, three-period crossover study. The periods consisted of nicotine-vaping (nicotine-session), nicotine-free vaping (nicotine-free-session), and complete cessation of vaping (stop-session), all maintained for 5 days before the session began. Multiparametric metabolomic analyses were used to verify subjects' protocol compliance. Biological/clinical cardiorespiratory parameters were assessed at the beginning of each session (baseline) and after acute vaping exposure. Compared with the nicotine- and nicotine-free-sessions, a specific metabolomic signature characterized the stop-session. Baseline serum club cell protein-16 was higher during the stop-session than the other sessions (P < 0.01), and heart rate was higher in the nicotine-session (P < 0.001). Compared with acute sham-vaping in the stop-session, acute nicotine-vaping (nicotine-session) and acute nicotine-free vaping (nicotine-free-session) slightly decreased skin oxygen tension (P < 0.05). In regular e-cigarette-users, short-term vaping cessation seemed to shift baseline urine metabolome and increased serum club cell protein-16 concentration, suggesting a decrease in lung inflammation. Additionally, acute vaping with and without nicotine decreased slightly transcutaneous oxygen tension, likely as a result of lung gas exchanges disturbances.

COPD patients with peripheral airway obstruction reversibility identified by exhaled nitric oxide

RATIONALE

Besides its role as an inflammatory marker in asthma, fractional exhaled nitric oxide (F_ENO) provides information on the extent of the airway obstruction process through evaluating its change after bronchodilation.

OBJECTIVE

To investigate whether F_ENO change after bronchodilation can identify different sites of airway obstruction in COPD patients.

METHODS

F_ENO, FEV₁ and the slopes (S) of the alveolar plateau of the single breath washout test (SBWT) were measured in 61 stable COPD patients (FEV₁ 34.5% predicted) before and after the inhalation of 400 μg salbutamol. SBWT used Helium (He), and sulfur-hexafluoride (SF₆). Obstruction relief occurring in pre-acinar and intra-acinar small airways is expected to decrease S_He and S_SF6, respectively. Indices changes (Δ) after bronchodilation were expressed as a percentage of pre-bronchodilation values.

RESULTS

F_ENO stability (∣ΔF_ENO∣ ≤ 11%) was observed in 19 patients [-2.7(6.7)%] [mean (SD)] (NO = group); ΔF_ENO > 11% [+37.4(27.7)%] in 20 patients (NO+ group) and ΔF_ENO < -11% in 22 patients [-31.2(9.8)%] (NO- group). A similar ΔFEV₁ (p = 0.583; [+9.4(9.6)%]) was found in the three groups. In NO = and NO+ groups, neither S_He nor S_SF6 changed; in NO- both S_He [-12.4(27.5)%, p = 0.007] and S_SF6 [-20.2(20.4)%, p < 0.001] significantly decreased.

CONCLUSION

Different patterns of F_ENO response to β ₂-agonists were observed in COPD most likely depending on the extent of the dilation process. A profile of airway obstruction with an extensive β ₂-agonist response down to lung periphery is identified by F_ENO reduction after acute bronchodilation in 30% of COPD patients. The clinical relevance of this profile requires further investigation.

X-ray examination dose surveys: how accurate are my results?

OBJECTIVES

To determine the variabilities of dose-area-products (DAP) of frequent X-ray examinations collected for comparison with diagnostic reference levels (DRLs).

METHODS

DAP values of chest, abdomen, and lumbar spine examinations obtained on devices from two manufacturers were collected in three centers over 1 to 2 years. The variability of the average DAP results defined as the 95% confidence interval in percentage of their median value was calculated for increasing sample sizes, each examination and center. We computed the sample sizes yielding variabilities lower or equal to 25% and 10%. The effect of narrowing patient selection based on body weight was also investigated (ranges of 67-73 Kg, or 60-80 Kg).

RESULTS

DAP variabilities ranged from 75 to 170% of the median value when collecting small samples (10 to 20 DAP). To reduce this variability, larger samples are needed, collected over up to 2 years, regardless of the examination and center. A variability ≤ 10% could only be reached for chest X-rays, requiring up to 800 data. For the abdomen and lumbar spine, the lowest achievable variability was 25%, regardless of the body weight selection, requiring up to 400 data.

CONCLUSION

Variabilities in DAP collected through small samples of ten data as recommended by authorities are very high, but can be reduced down to 25% (abdomen and lumbar spine) or even 10% (chest) through a substantial increase in sample sizes. Our findings could assist radiologists and regulatory authorities in estimating the reliability of the data obtained when performing X-ray dose surveys.

KEY POINTS

• Low but reasonable variabilities cannot be reached with samples sized as recommended by regulatory authorities. Higher numbers of DAP values are required to reduce the variability. • Variabilities of 10% for the chest and 25% for abdomen and lumbar spine examinations are achievable, provided large samples of data are collected over 1 year. • Our results could help radiologists and authorities interpret X-rays dose surveys.

Fourth generation e-cigarette vaping induces transient lung inflammation and gas exchange disturbances: results from two randomized clinical trials

When heated by an electronic cigarette, propylene glycol and glycerol produce a nicotine-carrying-aerosol. This hygroscopic/hyperosmolar aerosol can deposit deep within the lung. Whether these deposits trigger local inflammation and disturb pulmonary gas exchanges is not known. The aim of this study was to assess the acute effects of high-wattage electronic cigarette vaping with or without nicotine on lung inflammation biomarkers, transcutaneous gas tensions, and pulmonary function tests in young and healthy tobacco smokers. Acute effects of vaping without nicotine on arterial blood gas tensions were also assessed in heavy smokers suspected of coronary artery disease. Using a single-blind within-subjects study design, 25 young tobacco smokers underwent three experimental sessions in random order: sham-vaping and vaping with and without nicotine at 60 W. Twenty heavy smokers were also exposed to sham-vaping (n = 10) or vaping without nicotine (n = 10) in an open-label, randomized parallel study. In the young tobacco smokers, compared with sham-vaping: 1) serum club cell protein-16 increased after vaping without nicotine (mean ± SE, −0.5 ± 0.2 vs. +1.1 ± 0.3 µg/l, P = 0.013) and vaping with nicotine (+1.2 ± 0.3 µg/l, P = 0.009); 2) transcutaneous oxygen tension decreased for 60 min after vaping without nicotine (nadir, −0.3 ± 1 vs. −15.3 ± 2.3 mmHg, P < 0.001) and for 80-min after vaping with nicotine (nadir, −19.6 ± 2.8 mmHg, P < 0.001). Compared with sham vaping, vaping without nicotine decreased arterial oxygen tension for 5 min in heavy-smoking patients (+5.4 ± 3.3 vs. −5.4 ± 1.9 mmHg, P = 0.012). Acute vaping of propylene glycol/glycerol aerosol at high wattage with or without nicotine induces airway epithelial injury and sustained decrement in transcutaneous oxygen tension in young tobacco smokers. Intense vaping conditions also transiently impair arterial oxygen tension in heavy smokers.

Variability of CT Airways Measurements in COPD Patients Between Morning and Afternoon: Comparisons to Variability of Spirometric Measurements

RATIONALE AND OBJECTIVES

Computed tomography (CT) airways measurements can be used as surrogates to spirometric measurements for assessing bronchodilation in a particular patient with chronic obstructive pulmonary disease. Although spirometric measurements show variations within the opening hours of a hospital department, we aimed to compare the variability of CT airways measurements between morning and afternoon in patients with chronic obstructive pulmonary disease to that of spirometric measurements.

MATERIALS AND METHODS

Twenty patients had pulmonary function tests and CT around 8 am and 4 pm. Luminal area (LA) and wall thickness (WT) of third and fourth generation airways were measured twice by three readers. The percentage of airway area occupied by the wall (WA%) and the square root of wall area at an internal perimeter of 10 mm (√WAPi10) were calculated. The effects of examination time, reader, and measurement session on CT airways measurements were assessed, and the variability of these measurements was compared to that of spirometric measurements.

RESULTS

Variability of LA^3rd and LA^4th was greater than that of spirometric measurements (P values ranging from <.001 to .033). There was no examination time effect on √WAPi10, WT^3rd, LA^4th, or WA%^4th (P values ranging from .102 to .712). There was a reader effect on all CT airways measurements (P values ranging from <.001 to .028), except in WT^3rd (P> .999). There was no effect of measurement session on any CT airway measurement (P values ranging from .535 to >.999).

CONCLUSION

As the variability of LA^3rd and LA^4th is greater than that of spirometric measurements, clinical studies should include cohorts with larger numbers of patients when considering LA than when considering spirometric measurements as end points.

Short and long-term effects of pulmonary rehabilitation in interstitial lung diseases: a randomised controlled trial

BACKGROUND

Few data are available on the long-term effect of pulmonary rehabilitation (PR) and on long PR programs in interstitial lung diseases (ILD). We aimed to evaluate the effects of PR on exercise capacity (6-Minute Walking Distance, 6MWD; Peak Work Rate, W_max), quality of life (St George's Respiratory Questionnaire, SGRQ), quadriceps force (QF) and objectively measured physical activity in ILD after the 6-month PR-program and after 1 year.

METHODS

60 patients (64 ± 11 years; 62% males; 23% with IPF) were randomly assigned to receive a 6 month-PR program or usual medical care.

RESULTS

Exercise capacity, quality of life and muscle force increased significantly after the program as compared to control (mean,95%CI[ll to ul]; 6MWD + 72,[36 to 108] m; W_max 19, [8 to 29]%pred; SGRQ - 12,[- 19 to - 6] points; QF 10, [1 to 18] %pred). The gain was sustained after 1 year (6MWD 73,[28 to 118] m; Wmax 23, [10 to 35]%pred; SGRQ - 11,[- 18 to - 4] points; QF 9.5, [1 to 18] %pred). Physical activity did not change.

CONCLUSIONS

PR improves exercise tolerance, health status and muscle force in ILD. The benefits are maintained at 1-year follow-up. The intervention did not change physical activity.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00882817 .

New insights into the mechanisms controlling the bronchial mucus balance

In this work, we aim to analyze and compare the mechanisms controlling the volume of mucus in the bronchial region of the lungs of a healthy human adult, at rest and in usual atmospheric conditions. This analysis is based on a balance equation for the mucus in an airway, completed by a computational tool aiming at characterizing the evaporation, during respiration, of the water contained in the bronchial mucus. An idealized representation of the lungs, based on Weibel’s morphometric model, is used. The results indicate that the mechanisms controlling the volume of mucus in an airway depend on the localization of the airway in the bronchial region of the lungs. In the proximal generations, the volume of mucus in an airway is mainly controlled by the evaporation of the water it contains and the replenishment, with water, of the mucus layer by epithelial cells or the submucosal glands. Nevertheless, cilia beating in this part of the bronchial region remains of fundamental importance to transport the mucus and hence to eliminate dust and pathogens trapped in it. On the other hand, in the distal generations of the bronchial region, the volume of mucus in an airway is mainly controlled by the mucociliary transport and by the absorption of liquid by the epithelium. This absorption is a consequence of the mucus displacement by the cilia along generations with an interface between the epithelium and the airway surface layer of decreasing area. The numerical results obtained are in good agreement with previously published experimental data, thus validating our approach. We also briefly discuss how our results can improve the understanding and, possibly, the treatment of pulmonary diseases.

A new role for the exhaled nitric oxide as a functional marker of peripheral airway caliber changes: a theoretical study

Although considered as an inflammation marker, exhaled nitric oxide (FENO) was shown to be sensitive to airway caliber changes to such an extent that it might be considered as a marker of them. It is thus important to understand how these changes and their localization mechanically affect the total NO flux penetrating the airway lumen ( JawNO), and hence FENO, independently from any inflammatory status change. In this work, a new model was used. It simulates NO production, consumption, and diffusion inside the airway epithelium, NO excretion from the epithelial wall into the airway lumen and, finally, its axial transport by diffusion and convection in the airway lumen. This model may also consider the possible presence of a fluid layer coating the epithelial wall. Simulations were performed. They show the great sensitivity of JawNO to peripheral airway caliber changes. Moreover, FENO shows distinct behaviors, depending on the location of the caliber change. Considering a bronchodilation, absence of FENO change was associated with dilation of central airways, FENO increase with dilation down to pre-acinar small airways, and FENO decrease with intra-acinar dilation due to the amplification of the back diffusion flux. The presence of a fluid layer was also shown to play a significant role in FENO changes. Altogether, the present work theoretically supports that specific FENO changes in acute situations are linked to specifically located airway caliber changes in the lung periphery. This opens the way for a new role for FENO as a functional marker of peripheral airway caliber change.

NEW & NOTEWORTHY Using a new model of nitric oxide production and transport, allowing realistic simulation of airway caliber change, the present work theoretically supports that specific changes of the molar fraction of nitric oxide in the exhaled air, occurring without any change in the inflammatory status, are linked to specifically located airway caliber changes in the lung periphery. This opens the way for a new role for FENO as a functional marker of peripheral airway caliber change.

Small airways dysfunction: the link between allergic rhinitis and allergic asthma

Abnormal airway reactivity and overproduction of nitric oxide (NO) occurring in small airways have been found in asthma. If the "one airway, one disease" concept is consistent, such dysfunctions should also be detected in the peripheral airways of patients suffering from allergic rhinitis.We investigated whether peripheral airway reactivity and NO overproduction could be documented in distal airways in patients with allergic rhinitis. Exhaled NO fraction (F_eNO) and the slope (S) of phase III of the single-breath washout test (SBWT) of helium (He) and sulfur hexafluoride (SF₆) were measured in 31 patients with allergic asthma, 23 allergic rhinitis patients and 24 controls, before and after sputum induction. SBWT is sensitive to airway calibre change occurring in the lung periphery.The F_eNO decrease was more significant in asthma and rhinitis than in controls (-55.1% and -50.0%, respectively, versus -40.8%) (p=0.007 and p=0.029, respectively). S_SF6 and S_He increased in all groups. Change in S_He (ΔS_He) > ΔS_SF6 was observed in rhinitis (p=0.004) and asthma (p<0.001), whereas ΔS_SF6 = ΔS_He in controls (p=0.431).This study provides evidence of peripheral airway dysfunction in patients with allergic rhinitis quite similar to that described in asthma. Furthermore, a large proportion of the increased NO production reported in allergic rhinitis appears to originate in the peripheral airways.

Airway calibre variation is a major determinant of exhaled nitric oxide's ability to capture asthma control

Changes in airway calibre have the potential to modify exhaled nitric oxide fraction (F_ENO) values and could hamper how F_ENO captures changes in asthma control. Here, our objective was to assess whether forced expiratory volume in 1 s (FEV₁) variations alter the ability of F_ENO to reflect asthma control.F_ENO, asthma control (Asthma Control Questionnaire (ACQ)) and FEV₁ were measured at least two times in 527 patients during 1819 pairs of visits. Determinants of F_ENO-ACQ discordance probability were evaluated through a logistic regression analysis. The effectiveness of F_ENO at capturing either asthma control worsening or improvement between two visits was then assessed by undertaking a stratified receiver operating characteristic curves analysis.When FEV₁ and F_ENO change in the same direction, the odds of F_ENO-ACQ being discordant are multiplied by 3 (p<0.001). The area under the curve values were 0.765 (95% CI 0.713-0.805) (improvement; p<0.001) and 0.769 (95% 0.706-0.810) (worsening; p<0.001) or 0.590 (95% 0.531-0.653) (improvement; p=0.001) and 0.498 (95% 0.416-0.567) (worsening; p=0.482) when FEV₁ and F_ENO changed in the opposite or same direction, respectively.The manner in which F_ENO and FEV₁ vary concomitantly when asthma control changes determines the ability of F_ENO to capture this change: parallel or opposite changes in FEV₁ and F_ENO either decrease or increase this ability to capture asthma control changes.

Effect of total lung capacity, gender and height on CT airway measurements

OBJECTIVE

Testing the hypothesis that CT airway measurements could be influenced by total lung capacity (TLC), gender and height in normal individuals.

METHODS

In this ethics committee-approved prospective trial, 87 healthy never-smoking volunteers who provided written informed consent were included. From a helical CT scan of the chest, the wall thickness (WT) and the lumen area were twice measured in the third- and fourth-generation airways by three readers using a dedicated software. In addition, the TLC was also measured using CT (TLC_CT). The percentage of airway area occupied by the wall (WA%) and the square root of wall area at an internal perimeter of 10 mm (√WAPi10) were calculated. CT airway measurements were compared between genders by using a mixed linear model. The correlations between height, TLC_CT and CT airway measurements were tested by using a Pearson correlation analysis. These correlations were arbitrarily considered as significant if there was a significant correlation observed for each of the six measurement sessions.

RESULTS

√WAPi10, WT^3rd and WT^4th were significantly different between genders. For both genders, there was no significant correlation between any airway measurements and TLC_CT. In females only, WT^3rd and WT^4th were significantly and negatively correlated with height.

CONCLUSION

√WAPi10, WT^3rd and WT^4th are different in males and females. WT^3rd and WT^4th are correlated with height in females only but not with TLC or in males. Advances in knowledge: CT airway measurements are influenced by gender and by height in females only but not by TLC. They should be adjusted according to gender and height in females.

A European Respiratory Society technical standard: exhaled biomarkers in lung disease

Breath tests cover the fraction of nitric oxide in expired gas (F_eNO), volatile organic compounds (VOCs), variables in exhaled breath condensate (EBC) and other measurements. For EBC and for F_eNO, official recommendations for standardised procedures are more than 10 years old and there is none for exhaled VOCs and particles. The aim of this document is to provide technical standards and recommendations for sample collection and analytic approaches and to highlight future research priorities in the field. For EBC and F_eNO, new developments and advances in technology have been evaluated in the current document. This report is not intended to provide clinical guidance on disease diagnosis and management.Clinicians and researchers with expertise in exhaled biomarkers were invited to participate. Published studies regarding methodology of breath tests were selected, discussed and evaluated in a consensus-based manner by the Task Force members.Recommendations for standardisation of sampling, analysing and reporting of data and suggestions for research to cover gaps in the evidence have been created and summarised.Application of breath biomarker measurement in a standardised manner will provide comparable results, thereby facilitating the potential use of these biomarkers in clinical practice.

Modeling of the Nitric Oxide Transport in the Human Lungs

In the human lungs, nitric oxide (NO) acts as a bronchodilatator, by relaxing the bronchial smooth muscles and is closely linked to the inflammatory status of the lungs, owing to its antimicrobial activity. Furthermore, the molar fraction of NO in the exhaled air has been shown to be higher for asthmatic patients than for healthy patients. Multiple models have been developed in order to characterize the NO dynamics in the lungs, owing to their complex structure. Indeed, direct measurements in the lungs are difficult and, therefore, these models are valuable tools to interpret experimental data. In this work, a new model of the NO transport in the human lungs is proposed. It belongs to the family of the morphological models and is based on the morphometric model of Weibel (1963). When compared to models published previously, its main new features are the layered representation of the wall of the airways and the possibility to simulate the influence of bronchoconstriction (BC) and of the presence of mucus on the NO transport in lungs. The model is based on a geometrical description of the lungs, at rest and during a respiratory cycle, coupled with transport equations, written in the layers composing an airway wall and in the lumen of the airways. First, it is checked that the model is able to reproduce experimental information available in the literature. Second, the model is used to discuss some features of the NO transport in healthy and unhealthy lungs. The simulation results are analyzed, especially when BC has occurred in the lungs. For instance, it is shown that BC can have a significant influence on the NO transport in the tissues composing an airway wall. It is also shown that the relation between BC and the molar fraction of NO in the exhaled air is complex. Indeed, BC might lead to an increase or to a decrease of this molar fraction, depending on the extent of the BC and on the possible presence of mucus. This should be confirmed experimentally and might provide an interesting way to characterize the extent of BC in unhealthy patients.

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.

Effect of total lung capacity and gender on CT densitometry indexes

OBJECTIVE

Testing the hypothesis that CT densitometry indexes could be influenced by total lung capacity (TLC), gender and height in normal individuals.

METHODS

In this ethics committee-approved prospective study, 100 healthy non-smoking volunteers who provided written informed consent were included. From a helical scan of the chest, the relative area (RA) of the lung with attenuation coefficients lower than -960 HU and the 1st and 15th percentiles of the distribution of attenuation coefficients were calculated. Regression lines were drawn between each CT index and volunteers' height and total TLC at CT.

RESULTS

In males, there was no statistically significant correlation between any CT index and height. In females, there was a statistically significant correlation between the RA of the lung with attenuation coefficients lower than -960 HU and the 1st percentile and height but not with the 15th percentile. For both genders, there were significant correlations between all CT indexes and TLC. The relationships between CT indexes and TLC were different in males and females.

CONCLUSION

CT indexes are correlated with TLC and height but more closely with TLC than with height, and differently in males and females.

ADVANCES IN KNOWLEDGE

CT indexes are influenced by TLC, gender and height in normal individuals and are more closely correlated with TLC than with height. The relationships between CT indexes and TLC or height are different in males and females. CT indexes used to quantify emphysema should thus be adjusted according to TLC and gender.

Chronic Obstructive Pulmonary Disease: CT Quantification of Airway Dimensions, Numbers of Airways to Measure, and Effect of Bronchodilation

PURPOSE

To determine the effect of bronchodilation on airway indexes reflecting airway disease in patients with chronic obstructive pulmonary disease (COPD) and to determine the minimum number of segmental and subsegmental airways required.

MATERIALS AND METHODS

This study was approved by the local ethical committee, and written informed consent was obtained from all subjects. Twenty patients with COPD who had undergone pre- and postbronchodilator pulmonary function tests and computed tomographic (CT) examinations were prospectively included. Eight healthy volunteers underwent two CT examinations. Luminal area and wall thickness (WT) of third- and fourth-generation airways were measured twice by three readers. The percentage of total airway area occupied by the wall and the square root of wall area at an internal perimeter of 10 mm (√WAPi10) were calculated. The effects of pathologic status, session, reader, bronchodilation, and CT examination were assessed by using mixed linear model analyses. The number of airways to measure for a definite percentage error of √WAPi10 was computed by using a bootstrap method.

RESULTS

There were no significant session, reader, or bronchodilation effects on WT in third-generation airways and √WAPi10 in patients with COPD (P values ranging from .187 to >.999). WT in third-generation airways and √WAPi10 were significantly different in patients with COPD and control subjects (P = .018 and <.001, respectively). Measuring 12 third- or fourth-generation airways ensured a maximal 10% error of √WAPi10.

CONCLUSION

WT in third-generation airways and √WAPi10 are not significantly different before and after bronchodilation and are different in patients with COPD and control subjects. Twelve is the minimum number of third- or fourth-generation airways required to ensure a maximal 10% error of √WAPi10. (©) RSNA, 2015 Clinical trial registration no. NCT01142531 Online supplemental material is available for this article.

FeNO as a predictor of asthma control improvement after starting inhaled steroid treatment

INTRODUCTION

The fraction of NO in exhaled air (FeNO) is a marker of inflammation in asthma. The aim of the present study was to assess, in a real-world setting, whether only high (⩾50 ppb) FeNO levels predict improvement in asthma control when being treated with inhaled corticosteroids (ICS), as suggested by current guidelines on the clinical use of FeNO.

METHODS

FeNO and asthma control were assessed in a retrospective observational study in 153 non-smoking, steroid-naïve, adult subjects with asthma with a mean age of 40 years both before and after 6 weeks (median follow-up time) of treatment with 500 μg beclomethasone (median).

RESULTS

Having at the initial visit intermediate FeNO (⩾25 and <50 ppb) and high FeNO (⩾50 ppb), compared to normal FeNO (<25 ppb), were associated with a larger proportion of subjects achieving an improvement of Asthma Control Questionnaire (ACQ) score with ⩾1 (78% and 67% vs 43%, p<0.05) or both ⩾1 improvement and asthma control at follow-up (31% and 37% vs 4%, p<0.05). These associations were consistent in multiple logistic regression models after adjustments for confounders.

CONCLUSIONS

It is not only high but also intermediate FeNO levels that are associated with a significant improvement in asthma control after starting ICS treatment. This challenges current clinical guidelines stating that only high FeNO levels predict response to ICS treatment.

Exhaled nitric oxide: a biomarker integrating both lung function and airway inflammation changes

BACKGROUND

The increased fraction of exhaled nitric oxide (Feno) values observed in asthmatic patients are thought to reflect increased airway inflammation. However, Feno values can be affected by airway caliber reduction, representing a bias when using Feno values to assess asthma control.

OBJECTIVE

We sought to determine the effect of changes in both airway caliber and inflammation on Feno values using the allergen challenge model.

METHODS

FEV1 and Feno values were measured during early airway responses (EARs) and late airway responses after challenge with house dust mite allergens in 15 patients with mild allergic asthma. Helium and sulfur hexafluoride (SF6) phase III expired concentration slopes (SHe and SSF6, respectively) from single-breath washout tests were measured to identify sites of airway constriction.

RESULTS

In EARs, FEV1 and Feno value decreases reached 36.8% and 22%, respectively (P < .001). ΔSHe was greater than ΔSSF6 (+189.4% vs +82.2%, P = .001). In late airway responses FEV1 and Feno value decreases reached 31.7% and 28.7%, respectively (P < .001), with the same ΔSHe and ΔSSF6 pattern (+155.8% vs +76%, P = .001). Eight hours after the EAR, FEV1 was still decreased (P < .001), whereas Feno values had returned to baseline. At 24 hours, FEV1 had returned to baseline, with Feno values increased by 38.7% (P = .04).

CONCLUSION

In patients with mild allergic asthma, airway caliber changes modulate changes in Feno values resulting from airway inflammation. Therefore Feno should no longer be considered solely an inflammation biomarker but rather a biomarker that integrates both airway inflammation and lung function changes. Furthermore, early and late phases resulting from allergen exposure were shown to involve similar lung regions.

Physiological response to the 6-minute walk test in chronic heart failure patients versus healthy control subjects

BACKGROUND

The distance walked in 6 minutes (6MWD) has been reported to be linearly related to peak oxygen uptake (VO2) in cardiac diseases and in lung diseases. In these patients, the VO2 during a 6-min walk test (walkVO2) has been found to be nearly equivalent to peakVO2, but with a lower respiratory exchange ratio (RER). Whether these observations translate to the less functionally impaired patients or healthy control subjects is not exactly known.

METHODS

Thirty-two healthy control subjects and 15 chronic heart failure (CHF) patients performed a 6-min walk test and a maximal cardiopulmonary exercise test (CPET) both with measurements of gas exchange.

RESULTS

The 6MWD and peakVO2 were linearly correlated, but with an increased slope appearing above 532 m. In CHF patients, walkVO2 was similar to peakVO2, but with lower heart rate and ventilation than measured at peak exercise. In healthy control subjects, VO2, ventilation and heart rate were lower during the 6-min walk than at maximal exercise but higher than at the anaerobic threshold. The RER during the 6-min walk remained <1 in both groups.

CONCLUSIONS

Above 500 m, 6MWD becomes less sensitive to any increase in peakVO2. Furthermore, CHF patients and healthy control subjects exercise respectively at maximal and high VO2, but below the anaerobic threshold (as assessed by a CPET) during the 6-min walk test.

Ventilation heterogeneity in the acinar and conductive zones of the normal ageing lung

RATIONALE

Small airways function studies in lung disease have used three promising multiple breath washout (MBW) derived indices: indices of ventilation heterogeneity in the acinar (S(acin)) and conductive (S(cond)) lung zones, and the lung clearance index (LCI). Since peripheral lung structure is known to change with age, ventilation heterogeneity is expected to be affected too. However, the age dependence of the MBW indices of ventilation heterogeneity in the normal lung is unknown.

OBJECTIVES

The authors systematically investigated S(acin), S(cond) or LCI as a function of age, testing also the robustness of these relationships across two laboratories.

METHODS

MBW tests were performed by never-smokers (50% men) in the age range 25-65 years, with data gathered across two laboratories (n=120 and n=60). For comparison with the literature, the phase III slopes from classical single breath washout tests were also acquired in one group (n=120).

MEASUREMENTS AND MAIN RESULTS

All three MBW indices consistently increased with age, representing a steady worsening of ventilation heterogeneity in the age range 25-65. Age explained 7-16% of the variability in S(acin) and S(cond) and 36% of the variability in LCI. There was a small but significant gender difference only for S(acin). Classical single breath washout phase III slopes also showed age dependencies, with gender effects depending on the normalisation method used.

CONCLUSIONS

With respect to the clinical response, age is a small but consistent effect that needs to be factored in when using the MBW indices for the detection of small airways abnormality in disease.

Effects of ambient pressure on pulmonary nitric oxide

Airway nitric oxide (NO) has been proposed to play a role in the development of high-altitude pulmonary edema. We undertook a study of the effects of acute changes of ambient pressure on exhaled and alveolar NO in the range 0.5-4 atmospheres absolute (ATA, 379-3,040 mmHg) in eight healthy subjects breathing normoxic nitrogen-oxygen mixtures. On the basis of previous work with inhalation of low-density helium-oxygen gas, we expected facilitated backdiffusion and lowered exhaled NO at 0.5 ATA and the opposite at 4 ATA. Instead, the exhaled NO partial pressure (Pe(NO)) did not differ between pressures and averaged 1.21 ± 0.16 (SE) mPa across pressures. As a consequence, exhaled NO fractions varied inversely with pressure. Alveolar estimates of the NO partial pressure differed between pressures and averaged 88 (P = 0.04) and 176 (P = 0.009) percent of control (1 ATA) at 0.5 and 4 ATA, respectively. The airway contribution to exhaled NO was reduced to 79% of control (P = 0.009) at 4 ATA. Our finding of the same Pe(NO) at 0.5 and 1 ATA is at variance with previous findings of a reduced Pe(NO) with inhalation of low-density gas at normal pressure, and this discrepancy may be due to the much longer durations of low-density gas breathing in the present study compared with previous studies with helium-oxygen breathing. The present data are compatible with the notion of an enhanced convective backtransport of NO, compensating for attenuated backdiffusion of NO with increasing pressure. An alternative interpretation is a pressure-induced suppression of NO formation in the airways.

Relationships between the lung clearance index and conductive and acinar ventilation heterogeneity

The lung clearance index (LCI) derived from a multiple breath washout test has regained considerable popularity in recent years, alternatively being promoted as an early detection tool or a marker of small airways function. In this study, we systematically investigated the link between LCI and indexes of acinar and conductive airways ventilation heterogeneity (Sacin, Scond) to assess potential contributions from both lung zones. Relationships were examined in 55 normal subjects after provocation, where only Scond is known to be markedly increased, and in 55 asthma patients after bronchodilation, in whom both Scond and Sacin ranged between normal and abnormal. LCI was correlated to Scond in both groups (R = 0.37-0.43; P < 0.01 for both); in the asthma group, LCI was also tightly correlated to Sacin (R = 0.70; P < 0.001). Potential mechanisms operational at various levels of the bronchial tree were identified by considering washout curvilinearity in addition to LCI to distinguish specific ventilation and dead space effects (also illustrated by simple 2-compartment model simulations). Although the asthma data clearly demonstrate that LCI can reflect very peripheral ventilation heterogeneities, the normal provocation data also convincingly show that LCI increases may be the exclusive result of far more proximal ventilation heterogeneities. Because LCI potentially includes heterogeneities at all length scales, it is suggested that ventilation imaging in combination with LCI measurement at the mouth could identify the scale of relevant ventilation heterogeneities. In the meantime, interpretations of LCI results in the clinic based on washout curves collected at the mouth should be handled with caution.

Adenosine 5'-monophosphate challenge elicits a more peripheral airway response than methacholine challenge

Adenosine 5'-monophosphate (AMP) and methacholine are commonly used to assess airway hyperreactivity. However, it is not fully known whether the site of airway constriction primarily involved during challenges with either agent is similar. Using a ventilation distribution test, we investigated whether the constriction induced by each agent involves the lung periphery in a similar fashion. Ventilation distribution was evaluated by the phase III slope (S) of the single-breath washout, using gases with different diffusivities like helium (He) and hexafluorosulfur (SF(6)). A greater postchallenge increase in S(He) reflects alterations at the level of terminal and respiratory bronchioles, while a greater increase in S(SF6) reflects alterations in alveolar ducts, increases to an equal extent reflecting alterations in more proximal airways where gas transport is still convective for both gases. S(SF6) and S(He) were measured in 15 asthma patients before and after airway challenges (20% forced expired volume in 1-s fall) with AMP and methacholine. S(He) increased to a greater extent than S(SF6) after AMP challenge (5.7 vs. 3.7%/l; P = 0.002), with both slopes increasing to an equal extent after methacholine challenge (3.1%/l; P = 0.959). The larger increase in S(He) following AMP challenge suggests distal ventilation impairment up to the level of terminal and respiratory bronchioles. With methacholine, the similar increases in S(He) and S(SF6) suggest a less distal impairment. AMP, therefore, seems to affect more extensively the very peripheral airways, whereas methacholine seems to have an effect on less distal airways.

Gravitational gradients in expiratory computed tomography examinations of patients with small airways disease: effect of body position on extent of air trapping

PURPOSE

First, to test the hypothesis that air trapping in diseased patients follows a gravitational gradient and is more extensive in dependent than in nondependent lung regions. Second, to test the hypothesis that the dependent lung regions on combined supine and prone expiratory computed tomography (CT) examinations will show more air trapping than would a supine expiratory CT examination alone.

MATERIALS AND METHODS

For this ethics committee-approved study, supine and prone multidetector-row CT (4×1 mm collimation, 0.5 s rotation time, 140 kVp, and effective 80 mAs) was performed at full end-expiration on 47 lung transplant recipients (mean age 41±12 y; 18 without bronchiolitis, 18 with potential bronchiolitis, and 11 with bronchiolitis). The extent of air trapping was visually quantified in the supine and prone positions, and in dependent and nondependent lung regions. Individual air trapping scores from these regions were thus available and could be combined for later analysis. Differences in the extent of air trapping between the positions and regions were tested with a Wilcoxon signed-rank test.

RESULTS

Air trapping was significantly more extensive in the combined dependent lung regions than in the combined nondependent lung regions (15.00% vs. 5.77%; P<0.001). Air trapping was also significantly more extensive in the combined dependent regions than in the supine body position (15.00% vs. 7.50%; P<0.001). No statistically significant difference in the extent of air trapping was found between the supine and the prone positions (7.50% vs. 12.14%; P=0.735).

CONCLUSIONS

In patients with suspected or overt small airways disease, air trapping follows a gravitational gradient. A change from the supine to the prone position can make air trapping visible in formerly nondependent lung regions. The combined readings from supine and prone CT examinations in dependent lung regions show more air trapping than a standard supine CT examination alone.

Acinar effect of inhaled steroids evidenced by exhaled nitric oxide

BACKGROUND

The effects of inhaled corticosteroids (ICSs) on distal lung inflammation, as assessed by alveolar nitric oxide concentration (C(A)NO), are a matter of debate. Recently, a theoretic study suggested that acinar airway obstruction that is relieved by ICS treatment and associated with a decrease in fraction of exhaled nitric oxide (FeNO) concentration might, paradoxically, increase C(A)NO. This increase could be a hallmark effect of ICSs at the acinar level.

OBJECTIVE

In the light of this new hypothesis, we studied changes in C(A)NO and FeNO after administration of ICSs.

METHODS

C(A)NO and FeNO were measured before and after ICS treatment of 38 steroid-naive patients with uncontrolled asthma who showed clinical improvement after ICS therapy.

RESULTS

The average FeNO decreased from 78.3 to 28.9 ppb (P < .001); C(A)NO decreased from 7.7 to 4.3 ppb (P = .009). In 14 subjects (low-slope group), slope (= ΔC(A)NO/ΔFeNO) values (Δ = post-ICS - pre-ICS value) were less than the 95% normal CI (average ΔFeNO = -32.7 ppb and average ΔC(A)NO= +2.9 ppb). In this group, baseline C(A)NO was abnormally low when FeNO was taken into account. In 11 subjects (the high-slope group), the slope was above the normal interval (average ΔFeNO = -42.5 ppb and average ΔC(A)NO = -14.7 ppb).

CONCLUSION

Opposite patterns (one that was predicted) can indicate peripheral actions of ICSs; this difference might account for conflicting data reported from studies using C(A)NO to determine the peripheral action of ICSs. We show that a low C(A)NO does not preclude distal inflammation.

The effect of posture-induced changes in peripheral nitric oxide uptake on exhaled nitric oxide

Airway and alveolar NO contributions to exhaled NO are being extracted from exhaled NO measurements performed at different flow rates. To test the robustness of this method and the validity of the underlying model, we deliberately induced a change in NO uptake in the peripheral lung compartment by changing body posture between supine and prone. In 10 normal subjects, we measured exhaled NO at target flows ranging from 50 to 350 ml/s in supine and prone postures. Using two common methods, bronchial NO production [Jaw(NO)] and alveolar NO concentration (FANO) were extracted from exhaled NO concentration vs. flow or flow−1 curves. There was no significant Jaw(NO) difference between prone and supine but a significant FANO decrease from prone to supine ranging from 23 to 33% depending on the method used. Total lung capacity was 7% smaller supine than prone ( P = 0.03). Besides this purely volumetric effect, which would tend to increase FANO from prone to supine, the observed degree of FANO decrease from prone to supine suggests a greater opposing effect that could be explained by the increased lung capillary blood volume (Vc) supine vs. prone ( P = 0.002) observed in another set of 11 normal subjects. Taken together with the relative changes of NO and CO transfer factors, this Vc change can be attributed mainly to pulmonary capillary recruitment from prone to supine. Realistic models for exhaled NO simulation should include the possibility that a portion of the pulmonary capillary bed is unavailable for NO uptake, with a maximum capacity of the pulmonary capillary bed in the supine posture.

Axial distribution heterogeneity of nitric oxide airway production in healthy adults

Model simulations of nitric oxide (NO) transport considering molecular diffusion showed that the total bronchial NO production needed to reproduce a given exhaled value is deeply influenced by its axial distribution. Experimental data obtained by fibroscopy were available about proximal airway contribution (Silkoff PE, McClean PA, Caramori M, Slutsky AS. Zamel N. Respir Physiol 113: 33-38, 1998), and recent experiments using heliox instead of air gave insight on the peripheral airway production (Shin HW, Condorelli P, Rose-Gottron CM, Cooper DM, George SC. J Appl Physiol 97: 874-882, 2004; Kerckx Y, Michils A, Van Muylem A. J Appl Physiol 104: 918-924, 2008). This theoretical work aimed at obtaining a realistic distribution of NO production in healthy adults by meeting both proximal and peripheral experimental constraints. To achieve this, a model considering axial diffusion with geometrical boundaries derived from Weibel's morphometrical data was divided into serial compartments, each characterized by its axial boundaries and its part of bronchial NO production. A four-compartment model was able to meet both criteria. Two compartments were found to share all the NO production: one proximal (generations 0 and 1; 15-25% of the NO production) and one inside the acinus (proximal limit, generations 14-16; distal limit, generations 16 and 17; 75-85% of the NO production). Remarkably, this finding implies a quasi nil production in the main part of the conducting airways and in the acinar airways distal to generation 17. Given the chosen experimental outcomes and reliant on their accuracy, this very inhomogeneous distribution is likely the more realistic one that may be achieved with a "one-trumpet"-shaped model. Refinement should come from a more realistic description of the acinus structure.