Aerosol-derived airway morphometry and aerosol bolus dispersion in patients with lung fibrosis and lung emphysema

Automated airway quantification associates with mortality in idiopathic pulmonary fibrosis

OBJECTIVES

The study examined whether quantified airway metrics associate with mortality in idiopathic pulmonary fibrosis (IPF).

METHODS

In an observational cohort study (n = 90) of IPF patients from Ege University Hospital, an airway analysis tool AirQuant calculated median airway intersegmental tapering and segmental tortuosity across the 2nd to 6th airway generations. Intersegmental tapering measures the difference in median diameter between adjacent airway segments. Tortuosity evaluates the ratio of measured segmental length against direct end-to-end segmental length. Univariable linear regression analyses examined relationships between AirQuant variables, clinical variables, and lung function tests. Univariable and multivariable Cox proportional hazards models estimated mortality risk with the latter adjusted for patient age, gender, smoking status, antifibrotic use, CT usual interstitial pneumonia (UIP) pattern, and either forced vital capacity (FVC) or diffusion capacity of carbon monoxide (DLco) if obtained within 3 months of the CT.

RESULTS

No significant collinearity existed between AirQuant variables and clinical or functional variables. On univariable Cox analyses, male gender, smoking history, no antifibrotic use, reduced DLco, reduced intersegmental tapering, and increased segmental tortuosity associated with increased risk of death. On multivariable Cox analyses (adjusted using FVC), intersegmental tapering (hazard ratio (HR) = 0.75, 95% CI = 0.66-0.85, p < 0.001) and segmental tortuosity (HR = 1.74, 95% CI = 1.22-2.47, p = 0.002) independently associated with mortality. Results were maintained with adjustment using DLco.

CONCLUSIONS

AirQuant generated measures of intersegmental tapering and segmental tortuosity independently associate with mortality in IPF patients. Abnormalities in proximal airway generations, which are not typically considered to be abnormal in IPF, have prognostic value.

CLINICAL RELEVANCE STATEMENT

Quantitative measurements of intersegmental tapering and segmental tortuosity, in proximal (second to sixth) generation airway segments, independently associate with mortality in IPF. Automated airway analysis can estimate disease severity, which in IPF is not restricted to the distal airway tree.

KEY POINTS

• AirQuant generates measures of intersegmental tapering and segmental tortuosity. • Automated airway quantification associates with mortality in IPF independent of established measures of disease severity. • Automated airway analysis could be used to refine patient selection for therapeutic trials in IPF.

Emerging Roles of Airway Epithelial Cells in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal disease with incompletely understood aetiology and limited treatment options. Traditionally, IPF was believed to be mainly caused by repetitive injuries to the alveolar epithelium. Several recent lines of evidence, however, suggest that IPF equally involves an aberrant airway epithelial response, which contributes significantly to disease development and progression. In this review, based on recent clinical, high-resolution imaging, genetic, and single-cell RNA sequencing data, we summarize alterations in airway structure, function, and cell type composition in IPF. We furthermore give a comprehensive overview on the genetic and mechanistic evidence pointing towards an essential role of airway epithelial cells in IPF pathogenesis and describe potentially implicated aberrant epithelial signalling pathways and regulation mechanisms in this context. The collected evidence argues for the investigation of possible therapeutic avenues targeting these processes, which thus represent important future directions of research.

Functional parameters of small airways can guide bronchodilator use in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) may present comorbid obstructive lung diseases with small airway dysfunction (SAD). Existing guidelines suggest that inhaled bronchodilators should be used if the ratio of forced expiratory volume in the 1st second and forced vital capacity (FEV₁/FVC) < 0.7 in IPF. However, most IPF patients have FEV₁/FVC > 0.7 even with coexisting emphysema. We retrospectively enrolled IPF patients who were registered at our outpatient clinic. At baseline, 63 patients completed computed tomography (CT) scans, lung function measurements, and symptom questionnaires. Among these patients, 54 (85.71%) underwent antifibrotic treatment and 38 (60.32%) underwent long-acting bronchodilator treatment. The median FEV₁/FVC was 0.86. Not all patients treated with bronchodilators showed significant changes in lung function. IPF patients with SAD, determined by IOS parameters, showed significant improvement in FEV₁, FEF_25–75%, and symptom scores after bronchodilator treatment. Bronchodilator efficacy was not observed in patients without SAD. CT-confirmed emphysema was seen in 34.92% of patients. There were no changes in lung function or symptom scores after bronchodilator treatment in patients with emphysema. In conclusion, FEV₁/FVC cannot reflect the airflow limitation in IPF. Emphysema in IPF is not a deciding factor in whether patients should receive bronchodilator treatment. IOS parameters may be useful to guide bronchodilator therapy in patients with IPF coexisting with SAD.

Charting the human respiratory tract with airborne nanoparticles: evaluation of the Airspace Dimension Assessment technique

Airspace Dimension Assessment (AiDA) is a technique to assess lung morphology by measuring lung deposition of inhaled nanoparticles. Nanoparticles deposit in the lungs predominately by diffusion, and average diffusion distances, corresponding to effective airspace radii ( rAiDA), can be inferred from measurements of particle recovery after varied breath holds. Also, particle recovery after a 0-s breath hold ( R0) may hold information about the small conducting airways. This study investigates rAiDA at different volumetric sample depths in the lungs of healthy subjects. Measurements were performed with 50-nm polystyrene nanospheres on 19 healthy subjects aged 17–67 yr. Volumetric sample depths ranged from 200 to 5,000 ml and breath-hold times from 5 to 20 s. At the examined volumetric sample depths, rAiDA values ranged from ~200–600 μm, which correspond to dimensions of the bronchiolar and the gas-exchanging regions of the lungs. R0 decreased with volumetric sample depth and showed more intersubject variation than rAiDA. Correlations were found between the AiDA parameters, anthropometry, and lung function tests, but not between rAiDA and R0. For repeated measurements on 3 subjects over an 18-mo period, rAiDA varied on average within ± 7 μm (± 2.4%). The results indicate that AiDA has potential as an efficient new in vivo technique to assess individual lung properties. The information obtained by such measurements may be of value for lung diagnostics, especially for the distal lungs, which are challenging to examine directly by other means.

NEW & NOTEWORTHY This is the first study to measure effective airspace radii ( rAiDA) at volumetric sample depths 200–5,000 ml in healthy subjects by Airspace Dimension Assessment (AiDA). Observed rAiDA were 200–600 μm, which corresponds to airspaces for the bronchiolar and the gas-exchanging regions around airway generation 14–17. rAiDA correlated with lung function tests and anthropometry. Measurements of rAiDA on 3 subjects over 11–18 mo were within ± 7 μm.

Altered deposition of inhaled nanoparticles in subjects with chronic obstructive pulmonary disease

Background

Respiratory tract deposition of airborne particles is a key link to understand their health impact. Experimental data are limited for vulnerable groups such as individuals with respiratory diseases. The aim of this study is to investigate the differences in lung deposition of nanoparticles in the distal lung for healthy subjects and subjects with respiratory disease.

Methods

Lung deposition of nanoparticles (50 and 100 nm) was measured after a 10 s breath-hold for three groups: healthy never-smoking subjects (n = 17), asymptomatic (active and former) smokers (n = 15) and subjects with chronic obstructive pulmonary disease (n = 16). Measurements were made at 1300 mL and 1800 mL volumetric lung depth. Each subject also underwent conventional lung function tests, including post bronchodilator FEV₁, VC, and diffusing capacity for carbon monoxide, D_L,CO. Patients with previously diagnosed respiratory disease underwent a CT-scan of the lungs. Particle lung deposition fraction, was compared between the groups and with conventional lung function tests.

Results

We found that the deposition fraction was significantly lower for subjects with emphysema compared to the other subjects (p = 0.001–0.01), but no significant differences were found between healthy never-smokers and smokers. Furthermore, the particle deposition correlated with pulmonary function tests, FEV_1%Pred (p < 0.05), FEV₁/VC_%Pred (p < 0.01) and D_L,CO (p < 0.0005) when all subjects were included. Furthermore, for subjects with emphysema, deposition fraction correlated strongly with D_L,CO (Pearson’s r = 0.80–0.85, p < 0.002) while this correlation was not found within the other groups.

Conclusions

Lower deposition fraction was observed for emphysematous subjects and this can be explained by enlarged distal airspaces in the lungs. As expected, deposition increases for smaller particles and deeper inhalation. The observed results have implications for exposure assessment of air pollution and dosimetry of aerosol-based drug delivery of nanoparticles.

Physiology of the lung in idiopathic pulmonary fibrosis

The clinical expression of idiopathic pulmonary fibrosis (IPF) is directly related to multiple alterations in lung function. These alterations derive from a complex disease process affecting all compartments of the lower respiratory system, from the conducting airways to the lung vasculature. In this article we review the profound alterations in lung mechanics (reduced lung compliance and lung volumes), pulmonary gas exchange (reduced diffusing capacity, increased dead space ventilation, chronic arterial hypoxaemia) and airway physiology (increased cough reflex and increased airway volume), as well as pulmonary haemodynamics related to IPF. The relative contribution of these alterations to exertional limitation and dyspnoea in IPF is discussed.

Physiological impairment in IPF is complex and involves all compartments of the respiratory systemhttp://ow.ly/gyao30hdHUb

Do nanoparticles provide a new opportunity for diagnosis of distal airspace disease?

There is a need for efficient techniques to assess abnormalities in the peripheral regions of the lungs, for example, for diagnosis of pulmonary emphysema. Considerable scientific efforts have been directed toward measuring lung morphology by studying recovery of inhaled micron-sized aerosol particles (0.4-1.5 µm). In contrast, it is suggested that the recovery of inhaled airborne nanoparticles may be more useful for diagnosis. The objective of this work is to provide a theoretical background for the use of nanoparticles in measuring lung morphology and to assess their applicability based on a review of the literature. Using nanoparticles for studying distal airspace dimensions is shown to have several advantages over other aerosol-based methods. 1) Nanoparticles deposit almost exclusively by diffusion, which allows a simpler breathing maneuver with minor artifacts from particle losses in the oropharyngeal and upper airways. 2) A higher breathing flow rate can be utilized, making it possible to rapidly inhale from residual volume to total lung capacity (TLC), thereby eliminating the need to determine the TLC before measurement. 3) Recent studies indicate better penetration of nanoparticles than micron-sized particles into poorly ventilated and diseased regions of the lungs; thus, a stronger signal from the abnormal parts is expected. 4) Changes in airspace dimensions have a larger impact on the recovery of nanoparticles. Compared to current diagnostic techniques with high specificity for morphometric changes of the lungs, computed tomography and magnetic resonance imaging with hyperpolarized gases, an aerosol-based method is likely to be less time consuming, considerably cheaper, simpler to use, and easier to interpret (providing a single value rather than an image that has to be analyzed). Compared to diagnosis by carbon monoxide (DL,CO), the uptake of nanoparticles in the lung is not affected by blood flow, hemoglobin concentration or alterations of the alveolar membranes, but relies only on lung morphology.

[Monte-Carlo-Model for the aerosol bolus dispersion in the human lung--part 1: theoretical model description and application]

Aerosol bolus dispersion, which has excited enormous interest in lung medicine due to its possible use as an efficient toolfor the non-invasive clinical diagnosis of lung function, was simulated by a Monte Carlo model based on the concept of effective diffusivities and a stochastic lung geometry. The mathematical approach enabled the computation of essential characteristics of the exhaled bolus (half width, standard deviation, skewness, and mode shift) as well as the estimation of their dependence upon the volumetric lung depth (VLD) of the inhaled bolus. Results of the dispersion model generally show a very good correspondence with preliminary published experimental data. Half width and standard deviation of the exhaled bolus increase with VLD according to specific functions, whereas skewness and mode shift are subject to a decrease. While no correlation between bolus dispersion and flow rate could be worked out with the model, dispersion linearly increased with total lung capacity (TLC).

Aerosol probes of emphysema progression in dogs treated with all trans retinoic acid--an exploratory study

This study used aerosol probes and lung function tests to investigate whether all trans retinoic acid (RA) can reverse experimental emphysema in dogs. Three dogs were evaluated with lung mechanics tests, including inspiratory capacity (IC), total lung capacity (TLC), and the ratio of forced expired volume in 0.5 sec to forced vital capacity (FEV0.5/FVC), an aerosol-derived measure of pulmonary airspace size (effective airspace diameter, EAD), and an aerosol-derived measure of nonuniform ventilation (aerosol dispersion, AD). Emphysema was induced by exposure to aerosolized papain. At 11 or 12 weeks post-papain exposure, dogs received oral RA (2 mg/kg/day) for 8 weeks, and were followed for an additional 4 weeks after stopping RA treatment. In all dogs, lung injury increased in the first 11-12 weeks following papain exposure, as evidenced by increasing trends of inspiratory capacity IC, TLC, EAD, and AD, and a decreasing trend of FEV0.5/FVC. These parameters of lung injury partially and transiently reversed their trends between 2 and 6 weeks following the initiation of RA treatment. A sham RA-treated group was not studied. However, similar reversals of lung injury were not seen in a previous study of dogs treated with papain but not RA, suggesting that RA altered emphysema progression in the current study. The limited reversal of lung injury in this study contrasts with more pronounced treatment effects seen in previous studies with rats. This paper discusses possible reasons for differences in these studies, as well as suggestions for improved experimental investigations of emphysema therapies.

Usefulness of 99mTc-Technegas and 133Xe dynamic SPECT in ventilatory impairment

AIM

To assess the usefulness of SPECT images using (99m)Tc-Technegas (Technegas) and (133)Xe dynamic single photon emission computed tomography (SPECT) (Xe gas) and high-resolution computed tomography (HRCT), as compared with pathological assessment in the detection of small-airway disease including pulmonary emphysema.

METHODS

Seventeen patients with lung cancer were studied. All patients who had undergone both Technegas and Xe gas and CT prior to surgery were examined. SPECT and HRCT results were compared with the results of pathological findings. Histopathological analysis was performed in an area distant from cancer in lobectomy specimens obtained at surgery. Pathological analysis was performed in relation to bronchitis, bronchiolitis, fibrosis of the alveoli and disruption in walls of the alveoli.

RESULTS

Pathological abnormality (mild-to-moderate abnormal change) was seen in all 17 cases. Three patients showed low attenuation areas on CT, and abnormal patterns in SPECT images. In 11 of 14 patients who showed normal findings on CT, SPECT imaging depicted abnormal findings. The remaining three patients had no abnormal findings on CT and both SPECT imaging.

CONCLUSION

Technegas and (133)Xe SPECT imaging is useful for evaluating small-airway disease including pulmonary emphysema. Furthermore, SPECT imaging is more useful than morphological HRCT imaging in the evaluation of small-airway disease including pulmonary emphysema.

Aerosol morphometry and aerosol bolus dispersion in patients with CT-determined combined pulmonary emphysema and lung fibrosis

The simultaneous occurrence of pulmonary fibrosis and emphysema may present considerable problems in clinical assessment. Recent studies have shown that Aerosol Derived Airway Morphometry (ADAM) and Aerosol Bolus Dispersion (ABD) are changed in patients with pulmonary emphysema. This study was performed to assess the effect of simultaneous lung fibrosis in patients with emphysema on ADAM and ABD. ADAM and ABD measurements were performed in 20 patients with lone high resolution CT scan (HRCT) confirmed emphysema (E), and compared to those in 15 emphysematics with HRCT-confirmed superimposed pulmonary fibrosis (FE). In both groups the peripheral effective airspace dimension (EAD) (E: 0.63 +/- 0.20 mm; FE: 0.60 +/- 0.27 mm, N.S.) was increased by more than a factor of two compared to that of healthy subjects (0.28 +/- 0.05 mm) (p < 0.001). Patients with E showed a significantly higher bolus dispersion than patients with FE (724 +/- 122 cm3 vs. 546 +/- 80 cm3; p < 0.001). However, in patients with FE, bolus dispersion was still significantly higher than in previously published control groups of healthy subjects (546 +/- 80 cm3 vs. 455 +/- 68 cm3; p < 0.001). The results of this study confirm that ADAM and ABD are powerful tools for identifying emphysema even in patients with superimposed pulmonary fibrosis.