Oscillometry and computed tomography findings in patients with idiopathic pulmonary fibrosis

The significance of periostin in the diagnosis of idiopathic pulmonary fibrosis and prediction of acute exacerbations

Background

This study aims to elucidate the capability of periostin (POSTN) as a serum biomarker in diagnosing idiopathic pulmonary fibrosis (IPF), assessing disease severity, and predicting acute exacerbations of IPF (AE-IPF), and to compare it with traditional IPF serum biomarkers Krebs von den Lungen-6 (KL-6), surfactant protein A (SP-A), and surfactant protein D (SP-D).

Methods

From October 2022 to October 2023, 55 patients who were diagnosed with IPF and treated at the Third Affiliated Hospital of Anhui Medical University were enrolled in the IPF group. Additionally, 30 patients with bacterial pneumonia (BP) and 30 healthy individuals were selected as the BP and healthy control (HC) groups, respectively. All participants underwent pulmonary function tests, and enzyme-linked immunosorbent assay (ELISA) was used to measure serum POSTN, KL-6, SP-A, and SP-D levels. IPF patients also underwent high-resolution computed tomography (HRCT) to quantify HRCT scores. Receiver operating characteristic (ROC) curves were plotted to obtain sensitivity and specificity. Binary logistic regression analysis was conducted to identify AE-IPF risk factors.

Results

Serum POSTN, KL-6, SP-A, and SP-D concentrations were significantly greater in the IPF group than in the BP and HC groups (P<0.001), whereas serum SP-A and SP-D levels were greater in the BP group than in the HC group (P=0.001, P=0.04). The sensitivity of POSTN for diagnosing IPF is 94.5%, and the specificity is 93.3%, both of which are higher than those of KL-6, SP-A, and SP-D. Within the IPF group, serum POSTN levels were negatively correlated with the percentage of predicted forced expiratory volume in one second (FEV1%pred) (P=0.01) and the percentage of the predicted diffusing capacity for carbon monoxide (DLCO%pred) (P=0.003). Additionally, in IPF patients, serum POSTN, KL-6, and SP-A levels were significantly positively associated with HRCT scores. Logistic regression analysis indicated that decreased DLCO%pred and increased baseline serum KL-6 levels were both independent risk factors for AE-IPF.

Conclusions

POSTN is a valuable serum biomarker for IPF and has the highest sensitivity and specificity among the four serum markers, with a diagnostic performance superior to that of KL-6, SP-A, and SP-D. DLCO%pred and KL-6 have high predictive value for AE-IPF.

Respiratory Oscillometry in Patients With Acute Hypoxemic Respiratory Failure

Background: Assessing respiratory mechanics in patients with acute hypoxemic respiratory failure who are not intubated could provide useful information about illness trajectory. Oscillometry is a respiratory function test used to measure total respiratory impedance during tidal breathing, which reveals resistive and elastic properties of the lung. This study assessed the feasibility of oscillometry in patients with acute hypoxemic respiratory failure and described their respiratory mechanics. Methods: Adult participants with acute hypoxemic respiratory failure who were receiving noninvasive respiratory support with F IO 2 ≥0.4 and flow ≥6 L/min underwent oscillometry at baseline and after resolution of acute hypoxemic respiratory failure. The primary end point was the number of participants who completed the baseline measurement. The feasibility criterion was in obtaining baseline oscillometry measurements in ≥80% of enrolled participants. Results: Of 183 patients screened between July 2022 and August 2023, 29% were unable to cooperate due to altered mental state, 20% with extreme hypoxemia were excluded because of clinical instability, and 12% declined participation. Of the 10 participants (5.4%) recruited, all tolerated oscillometry measurements. At baseline, the median (minimum, maximum) F IO 2 was 0.8 (0.4, 0.8), median oxygen saturation of 94% dropped to a nadir of 82% at the end of oscillometry and recovered within 2 min. Lung reactance was increased, with a reactance area of 25 (15-32) cm H2O/L. Hypoxemia resolved in 9 participants. After resolution of acute hypoxemic respiratory failure in 8 (6-16) d, the median reactance area dropped to 15 (14-19) cm H2O/L. Conclusions: Respiratory mechanics in the participants with acute hypoxemic respiratory failure who were not intubated could be assessed by oscillometry in carefully selected cases.

Pathophysiology of small airways in idiopathic pulmonary fibrosis (IPF): the silent zone

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disease characterized by distorted alveolar structure and reduced lung compliance, and impaired ventilation-perfusion. Small airway disease (SAD) is  often termed a 'quietzone' due to its asymptomatic nature. Around 30-40% of IPF patients exhibit SAD, which is associated with worse prognosis, higher fibrosis and emphysema scores, and elevated mortality risk. We used PubMed and Google Scholar for literature search.

AREAS COVERED

This review explores the pathophysiology of small airways in IPF, focusing on 1. Risk factors, including age, gender, smoking and occupational dust exposure, and ozone. 2. Diagnostic challenges: SAD is difficult to detect through traditional spirometry or high-resolution computed tomography  imaging due to resolution limitations.  3. Early physiological changes of small airways include airway wall thickening, lumen distortion, and reduced terminal bronchioles, preceding microscopic fibrosis, occurs in the early process of IPF. 4. Pathological mechanisms: The review examines the underlying mechanisms driving small airway disease in IPF.

EXPERT OPINION

A comprehensive approach is essential to improve the understanding and management of SAD in IPF. Priorities include identifying therapeutic targets, advanced imaging and functional assessments. Forced oscillation technique should be introduced for early detection for small airway abnormalities in IPF.

Oscillometry Assesses Small Airway Disease and Reveals Peripheral Lung Pathology in Early Pulmonary Fibrosis: A Cross-Sectional Study

Background/Objectives: Small airway disease/dysfunction (SAD) is crucial in obstructive airway diseases but is less investigated in interstitial lung disease (ILD). There are only a few physiological studies investigating SAD in the context of pulmonary fibrosis. Oscillometry is a simple technique that assesses SAD with minimal patient effort. In this study, we investigated the role of oscillometry in patients with mild pulmonary fibrosis without evident obstructive disorder, focusing on small airways. Methods: Oscillometry and pulmonary function test (PFT) data of consecutive patients newly diagnosed with pulmonary fibrosis of unknown etiology in a university hospital ILD clinic were collected and analyzed. Results: Data from 34 patients with mild pulmonary fibrosis were collected in 6 months. Disease severity, as evaluated by FVC, presented strong correlations with the oscillometry parameters: resistance (R5: r = -0.588, p < 0.001), reactance (X5: r = 0.671, p < 0.001), resonant frequency (Fres: r = -0.562, p = 0.001), and the area of reactance (AX: r = -0.515, p = 0.002). The oscillometry parameter R5-19-expressing was abnormal in 27% of patients, correlated with FEF25-75% (r = -0.370, p = 0.021) and was a predictor of a FEF25-75% < 60% pred. with AUC 0.738 (95%Cl 0.519-0.956). R5-19 correlated with FVC (r = -0.481, p = 0.004) and was the only SAD parameter that correlated with the composite physiologic index (CPI, r = 0.338, p = 0.04), while FEF 25-75% and RV/TLC% did not. Conclusions: Oscillometry is an easy to perform technique that may reveal early mechanical alterations caused by pulmonary fibrosis. Peripheral resistance, as expressed by R5-19, which identifies small airway dysfunction as a marker of peripheral lung pathology, may be complementary to pulmonary function testing and may also have prognostic implications for ILD patients.

A comparison of respiratory oscillometry and spirometry in idiopathic pulmonary fibrosis: performance time, symptom burden and test-retest reliability

Study question

In large multinational patient surveys, spirometry (which requires repeated, reproducible maximal efforts) can be associated with cough, breathlessness and tiredness, particularly in those with idiopathic pulmonary fibrosis (IPF). Oscillometry is an effort-independent test of airways resistance and reactance. We hypothesised that oscillometry would take less time to perform and would be associated with reduced symptom burden than spirometry.

Patients and methods

Spirometry and oscillometry were performed in 66 participants with IPF and repeated 2 weeks later. We compared time taken to perform tests, symptom burden and test-retest reliability with Bland-Altman plots and intraclass correlation coefficients (ICCs).

Results

Oscillometry took significantly less time to perform than spirometry (mean -4.5 (99% CI -6.0 to -3.0) min) and was associated with lower symptom burden scores for cough (-1.3, 99% CI -1.7 to -0.8), breathlessness (-1.0, 99% CI -1.4 to -0.5), and tiredness (-0.5, 99% CI -0.9 to -0.2). On Bland-Altman analysis, all measures showed good agreement, with narrow limits of agreement and the mean bias lying close to 0 in all cases. The ICCs for forced expiratory volume in 1 s and forced vital capacity were 0.94 and 0.89, respectively, and ranged between 0.70 and 0.90 for oscillometry measures.

Conclusion

Oscillometry is quicker to perform and provokes less symptoms than spirometry in patients with IPF.

Is Lung Function Measured by Oscillometry Useful in Interstitial Lung Diseases?

Introduction

The role of oscillometry in interstitial lung disease (ILD) is still unclear. The main objective of our study was to describe the parameters determined by oscillometry in these patients and compare them with those obtained in conventional respiratory function tests.

Methods

This was a cross-sectional observational study. Patients with no respiratory disease and patients being followed up for ILD in the specialist unit of Hospital Universitario de Getafe, Madrid were included.

Results

A total of 45 individuals were analyzed. Fifteen had no respiratory disease, 15 were ILD patients with mild functional impairment, and another 15 were ILD patients with severe impairment. None of the participants had an obstructive pattern on spirometry.Comparison between the three groups showed statistically significant differences in the values of R5-19, reactance at 5 Hz and reactance at 11 Hz. No differences were observed between the three groups in Delta Xrs. The study showed a strong correlation between total and inspiratory reactance at 5 Hz and forced vital capacity and diffusing capacity for carbon monoxide.

Conclusions

Our results suggest that the findings in ILD are characteristic of this disease and that they differ from those found in other diseases such as chronic obstructive pulmonary disease. It also seems that there are differences according to the degree of functional impairment of the patients. The results show a strong correlation with standard pulmonary function tests, so oscillometry could be a useful tool in patients with ILD who are unable to perform it, and could provide additional information.

Respiratory Impedance is Associated with Ventilation and Diffusing Capacity in Patients with Idiopathic Pulmonary Fibrosis Combined with Emphysema

Purpose

Pulmonary fibrosis and emphysema result in relatively maintained ventilation and reduced diffusing capacity. This pulmonary functional impairment complicates the evaluation of pulmonary function in patients with combined pulmonary fibrosis and emphysema (CPFE). Therefore, a single and easy-to-use pulmonary function index to evaluate patients with CPFE warrants further studies. Respiratory impedance can easily be provided by oscillometry and might be a candidate index to evaluate pulmonary function in patients with CPFE. As a preliminary study to assess the utility of respiratory impedance, we investigated the associations of physiological indices, including respiratory impedance, in patients with idiopathic pulmonary fibrosis (IPF) with and without emphysema.

Patients and Methods

This retrospective study evaluated patients with IPF who did and did not satisfy the diagnostic criteria of CPFE. All patients underwent oscillometry, spirometry, and diffusing capacity for carbon monoxide (D_LCO). Correlations of the obtained physiological indices were analyzed.

Results

In total, 47 patients were included (18 and 29 patients with CPFE and IPF, respectively). Respiratory reactance (Xrs) at 5 Hz (X5) in the inspiratory phase was associated with forced vital capacity (FVC) % predicted in patients with CPFE (r_S=0.576, P=0.012) and IPF (r_S=0.539, P=0.003). Inspiratory X5 positively correlated with D_LCO % predicted only in patients CPFE (r_S=0.637, P=0.004).

Conclusion

Emphysema might associate Xrs with ventilation and diffusing capacity in patients with IPF and emphysema. Given the multiple correlations of Xrs with FVC and D_LCO, this study warrants further studies to verify the utility of oscillometry in a large-scale study for patients with CPFE.

Correlation of respiratory oscillometry with CT image analysis in a prospective cohort of idiopathic pulmonary fibrosis

Background

Markers of idiopathic pulmonary fibrosis (IPF) severity are based on measurements of forced vital capacity (FVC), diffusing capacity (DLCO) and CT. The pulmonary vessel volume (PVV) is a novel quantitative and independent prognostic structural indicator derived from automated CT analysis. The current prospective cross-sectional study investigated whether respiratory oscillometry provides complementary data to pulmonary function tests (PFTs) and is correlated with PVV.

Methods

From September 2019 to March 2020, we enrolled 89 patients with IPF diagnosed according to international guidelines. We performed standard spectral (5–37 Hz) and novel intrabreath tracking (10 Hz) oscillometry followed by PFTs. Patients were characterised with the gender-age-physiology (GAP) score. CT images within 6 months of oscillometry were analysed in a subgroup (26 patients) using automated lung texture analysis. Correlations between PFTs, oscillometry and imaging variables were investigated using different regression models.

Findings

The cohort (29F/60M; age=71.7±7.8 years) had mild IPF (%FVC=70±17, %DLCO=62±17). Spectral oscillometry revealed normal respiratory resistance, low reactance, especially during inspiration at 5 Hz (X5in), elevated reactance area and resonance frequency. Intrabreath oscillometry identified markedly low reactance at end-inspiration (XeI). XeI and X5in strongly correlated with FVC (r²=0.499 and 0.435) while XeI was highly (p=0.004) and uniquely correlated with the GAP score. XeI and PVV exhibited the strongest structural-functional relationship (r²=0.690), which remained significant after adjusting for %FVC, %DLCO and GAP score.

Interpretation

XeI is an independent marker of IPF severity that offers additional information to standard PFTs. The data provide a cogent rationale for adding oscillometry in IPF assessment.

Machine learning associated with respiratory oscillometry: a computer-aided diagnosis system for the detection of respiratory abnormalities in systemic sclerosis

INTRODUCTION

The use of machine learning (ML) methods would improve the diagnosis of respiratory changes in systemic sclerosis (SSc). This paper evaluates the performance of several ML algorithms associated with the respiratory oscillometry analysis to aid in the diagnostic of respiratory changes in SSc. We also find out the best configuration for this task.

METHODS

Oscillometric and spirometric exams were performed in 82 individuals, including controls (n = 30) and patients with systemic sclerosis with normal (n = 22) and abnormal (n = 30) spirometry. Multiple instance classifiers and different supervised machine learning techniques were investigated, including k-Nearest Neighbors (KNN), Random Forests (RF), AdaBoost with decision trees (ADAB), and Extreme Gradient Boosting (XGB).

RESULTS AND DISCUSSION

The first experiment of this study showed that the best oscillometric parameter (BOP) was dynamic compliance, which provided moderate accuracy (AUC = 0.77) in the scenario control group versus patients with sclerosis and normal spirometry (CGvsPSNS). In the scenario control group versus patients with sclerosis and altered spirometry (CGvsPSAS), the BOP obtained high accuracy (AUC = 0.94). In the second experiment, the ML techniques were used. In CGvsPSNS, KNN achieved the best result (AUC = 0.90), significantly improving the accuracy in comparison with the BOP (p < 0.01), while in CGvsPSAS, RF obtained the best results (AUC = 0.97), also significantly improving the diagnostic accuracy (p < 0.05). In the third, fourth, fifth, and sixth experiments, different feature selection techniques allowed us to spot the best oscillometric parameters. They resulted in a small increase in diagnostic accuracy in CGvsPSNS (respectively, 0.87, 0.86, 0.82, and 0.84), while in the CGvsPSAS, the best classifier's performance remained the same (AUC = 0.97).

CONCLUSIONS

Oscillometric principles combined with machine learning algorithms provide a new method for diagnosing respiratory changes in patients with systemic sclerosis. The present study's findings provide evidence that this combination may help in the early diagnosis of respiratory changes in these patients.