Pulmonary physiology in interstitial lung disease: recent developments in diagnostic and prognostic implications

Increased expiratory flows identify early interstitial lung disease

BACKGROUND

Most interstitial lung diseases (ILDs) manifest with a restrictive ventilatory defect as the common physiologic abnormality. Low carbon monoxide diffusing capacity (Dlco) is considered to be the earliest abnormality on pulmonary function tests (PFTs) in patients with ILD. However, its measurement requires complex and expensive equipment. Our study aimed to assess if high expiratory flows are the earliest PFT abnormality in patients with idiopathic pulmonary fibrosis (IPF) and ILD.

METHODS

In a real-world cohort of incident cases with ILD, we identified the initial PFTs on all patients newly diagnosed with ILD at Kingston Health Sciences Center (in Kingston, Ontario, Canada) between 2013 and 2017. The diagnosis of ILD, including IPF, was established as per current guidelines. Among patients with normal forced vital capacity (FVC), total lung capacity (TLC), and Dlco, we assessed the frequency of high expiratory flows defined as forced expiratory volume in 1 s (FEV1)/FVC, FEF25, FEF25-75, FEF75, and peak expiratory flow > 95% confidence limit of normal. We adjusted for emphysema, increased airway resistance, and obesity.

RESULTS

We assessed PFTs of 289 patients with ILD; 88 (30%) of them had normal FVC, TLC, and Dlco. Among these, high FEV1/FVC was the most common abnormality in 37% of patients, in 43% of nonobese patients, and in 58% of those with no emphysema and normal airway resistance. Results were similar in the 88 patients with IPF.

CONCLUSIONS

High FEV1/FVC could allow identifying patients with ILD/IPF in the earliest stages of their disease with simple spirometry, leading to earlier diagnosis and treatment.

Exercise-Based Pulmonary Rehabilitation for Interstitial Lung Diseases: A Review of Components, Prescription, Efficacy, and Safety

Interstitial lung diseases (ILDs) comprise a heterogeneous group of disorders (such as idiopathic pulmonary fibrosis, sarcoidosis, asbestosis, and pneumonitis) characterized by lung parenchymal impairment, inflammation, and fibrosis. The shortness of breath (i.e., dyspnea) is a hallmark and disabling symptom of ILDs. Patients with ILDs may also exhibit skeletal muscle dysfunction, oxygen desaturation, abnormal respiratory patterns, pulmonary hypertension, and decreased cardiac function, contributing to exercise intolerance and limitation of day-to-day activities. Pulmonary rehabilitation (PR) including physical exercise is an evidence-based approach to benefit functional capacity, dyspnea, and quality of life in ILD patients. However, despite recent advances and similarities with other lung diseases, the field of PR for patients with ILD requires further evidence. This mini-review aims to explore the exercise-based PR delivered around the world and evidence supporting prescription modes, considering type, intensity, and frequency components, as well as efficacy and safety of exercise training in ILDs. This review will be able to strengthen the rationale for exercise training recommendations as a core component of the PR for ILD patients.

Exercise Pathophysiology in Interstitial Lung Disease

Interstitial lung disease (ILD) is a heterogeneous group of disorders that primarily affect the lung parenchyma. Patients with ILD have reduced lung volumes, impaired pulmonary gas exchange, and decreased cardiovascular function. These pathologic features of ILD become exacerbated during physical exertion, leading to exercise intolerance and abnormally high levels of exertional dyspnea. In this review, the authors summarize the primary pathophysiologic features of patients with ILD and their effect on the integrative response to exercise.

A comparison trial of eight weeks versus twelve weeks of exercise program in interstitial lung diseases

Background: Exercise training have been shown to be the effective approach for functional outcomes in interstitial lung diseases (ILD). In many studies, the duration of exercise programs (EPs) varies between 8-12 weeks. However, the optimal duration of EPs is still unknown. Objective: In our prospective non-controlled study, we aimed to compare the results of the 8^th week with the results of the 12^th week of the PR programs applied to the patients with ILD. Methods: A total of 14 patients [Age; 63(53,70) years, body mass index: 28(25,32) kg/m², disease duration; 1.5 (1,4) years] with ILD [11 idiopathic pulmonary fibrosis, 2 sarcoidosis (stage 3 and 4) and 1 nonspecific interstitial pneumonia] were included in the study. 6-minute walk test, pulmonary function test, arterial blood gas analysis, mMRC dyspnea scale, quality of life questionnaires and hospital anxiety depression scale were performed at before and 8 and 12 weeks after the program. Results: 6-minute walk distance, dyspnea, anxiety, depression and quality of life improved both at 8^th and 12^th week after EP when compared the with the initial assessment(P<0.05). When compared with 8^th week; mMRC dyspnea score, 6-minute walk distance and quality of life scores significantly improved at 12^th weeks (P=0.046, P=0.016, P<0.05, respectively). Conclusions: Prolonging duration of the EPs results in more improvement in functional outcomes in patients with ILD. However, it has no effect on pulmonary functions and arterial blood gas results. (Sarcoidosis Vasc Diffuse Lung Dis 2018; 35: 299-307)

Imaging of lung function using hyperpolarized helium-3 magnetic resonance imaging: Review of current and emerging translational methods and applications

During the past several years there has been extensive development and application of hyperpolarized helium-3 (HP (3)He) magnetic resonance imaging (MRI) in clinical respiratory indications such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, radiation-induced lung injury, and transplantation. This review focuses on the state-of-the-art of HP (3)He MRI and its application to clinical pulmonary research. This is not an overview of the physics of the method, as this topic has been covered previously. We focus here on the potential of this imaging method and its challenges in demonstrating new types of information that has the potential to influence clinical research and decision making in pulmonary medicine. Particular attention is given to functional imaging approaches related to ventilation and diffusion-weighted imaging with applications in chronic obstructive pulmonary disease, cystic fibrosis, asthma, and radiation-induced lung injury. The strengths and challenges of the application of (3)He MRI in these indications are discussed along with a comparison to established and emerging imaging techniques.

A model of ventilation of the healthy human lung

This paper presents a model of the lung mechanics which simulates the pulmonary alveolar ventilation. The model includes aspects of: the alveolar geometry; pressure due to the chest wall; pressure due to surface tension determined by surfactant activity; pressure due to lung tissue elasticity; and pressure due to the hydrostatic effects of the lung tissue and blood. The cross-sectional area of the lungs in the supine position derived from computed tomography is used to construct a horizontally layered model, which simulates heterogeneous ventilation distribution from the non-dependent to the dependent layers of the lungs. The model is in agreement with experimentally measured hysteresis of the pressure-volume curve of the lungs, static lung compliance, changes in lung depth during breathing and density distributions at total lung capacity (TLC) and residual volume (RV). In the dependent layers of the lungs, alveolar collapse may occur at RV, depending on the assumptions concerning lung tissue elasticity at very low alveolar volumes. The model simulations showed that ventilation increased with depth in the lungs, although not as pronounced as observed experimentally. The model simulates alveolar ventilation including all of the mentioned components of the respiratory system and to be validated against all the above mentioned experimental data.

Lung tissue mechanics as an emergent phenomenon

The mechanical properties of lung parenchymal tissue are both elastic and dissipative, as well as being highly nonlinear. These properties cannot be fully understood, however, in terms of the individual constituents of the tissue. Rather, the mechanical behavior of lung tissue emerges as a macroscopic phenomenon from the interactions of its microscopic components in a way that is neither intuitive nor easily understood. In this review, we first consider the quasi-static mechanical behavior of lung tissue and discuss computational models that show how smooth nonlinear stress-strain behavior can arise through a percolation-like process in which the sequential recruitment of collagen fibers with increasing strain causes them to progressively take over the load-bearing role from elastin. We also show how the concept of percolation can be used to link the pathologic progression of parenchymal disease at the micro scale to physiological symptoms at the macro scale. We then examine the dynamic mechanical behavior of lung tissue, which invokes the notion of tissue resistance. Although usually modeled phenomenologically in terms of collections of springs and dashpots, lung tissue viscoelasticity again can be seen to reflect various types of complex dynamic interactions at the molecular level. Finally, we discuss the inevitability of why lung tissue mechanics need to be complex.

Expiratory flow limitation in patients with pleural effusion

BACKGROUND

Expiratory flow limitation (EFL) is one of the main mechanisms contributing to dyspnea in patients with chronic obstructive pulmonary disease but has not been explored in patients with pleural effusion.

OBJECTIVES

It was the aim of this study to determine whether patients with pleural effusion exhibit EFL and to investigate the effect of therapeutic thoracentesis on EFL.

PATIENTS AND METHODS

The study was performed on 21 patients with pleural effusion who were subjected to thoracentesis and measurement of pleural pressure (PP). Spirometry and estimation of flow limitation by the negative expiratory pressure technique were performed before and after thoracentesis.

RESULTS

Statistically significant differences were observed in all spirometric parameters. No correlation between the increase in lung volumes and flows and any of the aspirated fluid parameters was observed. Before thoracentesis, 14 out of 21 patients were flow limited, compared with 7 patients after thoracentesis (chi(2) = 6.151, p = 0.013). Mean values of flow limitation before and after thoracentesis differed significantly. The decrease in flow limitation did not correlate with the increase in the spirometric parameters, the aspirated fluid volume or PP decrease.

CONCLUSIONS

In the majority of patients with pleural effusion, flow limitation improves after thoracentesis. Flow limitation may be a contributing factor to the sensation of dyspnea in these patients.

Registration of interstitial lung diseases by 20 centres of respiratory medicine in Flanders

We report the results of a prospective registration of the prevalence of interstitial lung diseases by 20 centres of respiratory medicine in Flanders from January 1992 till July 1996. The 20 centres registered a total of 362 cases. Sarcoidosis (31% with inclusion of stage I, or 22% without stage I), idiopathic pulmonary fibrosis (20%), hypersensitivity pneumonitis (13%) and unclassified forms of interstitial lung diseases (9%) were the most often diagnosed diseases. The mean age of the patients was 52 +/- 17 (SD) years, but ranged from 32 +/- 10 years in histiocytosis X to 70 +/- 13 years in drug induced interstitial lung diseases. The male to female ratio was 1.3 but ranged from 2.3 in interstitial lung diseases due to inhalation of inorganic materials to 0.8 in interstitial lung diseases due to connective tissue disease. The diagnosis was considered certain in 60%, probable in 30% and possible in 10%. In 50% of the cases the diagnosis was proven by biopsy and the most often used biopsy technique was transbronchiolo-alveolar biopsy (40% of biopsies) followed by open lung biopsy (32%). At diagnosis vital capacity was 82 +/- 22% pred. (ranging from 92 +/- 19% in sarcoidosis to 71 +/- 24% in idiopathic pulmonary fibrosis) and CO-diffusing capacity was 77 +/- 19% pred. (ranging from 77 +/- 19% in sarcoidosis to 41 +/- 13% in drug induced pneumonitis). The regional frequency of interstitial lung diseases in Flanders varied widely and was not proportional to the regional distribution of the 20 contributing centres. In conclusion this registration provides interesting information on the occurrence and presentation of the different forms of interstitial lung diseases, although it may still underestimate the real prevalence and incidence of interstitial lung diseases.