Irreversible acinar airway abnormality in well controlled asthma

Small airways in asthma: from bench-to-bedside

INTRODUCTION

Historically, asthma was considered a disease predominantly of the large airways, but gradually small airways have been recognized as the major site of airflow obstruction. Small airway dysfunction (SAD) significantly contributes to the pathophysiology of asthma and it is present across all asthma severities. Promising pre-clinical findings documented enhanced beneficial effects of combination therapies on small airways compared to monocomponents, thus it was questioned whether this could translate into further clinical implications from bench-to-bedside. The aim of this review was to systematically assess the state of the art of small airway involvement in asthma, especially in response to different pharmacological treatments acting on the respiratory system.

EVIDENCE ACQUISITION

A comprehensive literature search was performed in MEDLINE for randomized controlled trials (RCTs) characterizing the impact on small airways of different pharmacological treatments acting on the respiratory system. The results were extracted and reported via qualitative synthesis.

EVIDENCE SYNTHESIS

Overall, 63 studies were identified from the literature search, whereas 23 RCTs met the inclusion criteria. Evidence confirms that both drug particle size and the type of inhalation devices represent two of the most important variables for an effective peripheral lung distribution.

CONCLUSIONS

Despite the numerous methodological tools to detect SAD, there is still no gold standard diagnostic method to assess small airways, especially in severe asthma. Further research should be directed to improve primary and secondary prevention strategies by supporting the combined approach of different non-invasive techniques for an early detection of peripheral abnormalities and optimization of asthma therapy.

Ventilation heterogeneity and oscillometry predict asthma control improvement following step-up inhaled therapy in uncontrolled asthma

BACKGROUND AND OBJECTIVE

Abnormal peripheral airway function is an important feature of asthma and relates to asthma symptoms and poor asthma control. We aimed to determine whether peripheral airway function, as measured by forced oscillatory impedance and multiple-breath nitrogen washout (MBNW), relates to symptom improvement in asthmatic participants with uncontrolled asthma, after stepping up to high-dose ICS/LABA treatment.

METHODS

A total of 19 subjects (14 females, mean age: 29.9 ± 13.6 years) with uncontrolled asthma, as defined by an ACQ5 > 1.5, taking 500 μg/day fluticasone equivalent or less, underwent spirometry, plethysmography, fractional exhaled FeNO, forced oscillatory resistance (Rrs_5Hz ) and reactance (Xrs_5Hz ), and indices of MBNW ventilation heterogeneity (lung clearance index (LCI), diffusion-convection-dependent (Sacin) and convection-dependent (Scond)). Measurements were made before and after 8 weeks of treatment with fluticasone/formoterol combination inhaler 250/10 μg, 2 puffs twice daily.

RESULTS

Treatment improved ACQ5 (P = 0.0002), FEV₁ (P = 0.02), FVC (P = 0.04), FeNO (P = 0.0008), Xrs_5Hz (P = 0.01), LCI (P = 0.0002), Sacin (P = 0.006) and Scond (P = 0.01). At baseline, ACQ5 correlated with Xrs_5Hz (r_s = 0.52, P = 0.03) and Rrs_5Hz (r_s = 0.55, P = 0.02). The improvement in ACQ5 was predicted by more abnormal baseline LCI (P = 0.03), Scond (P = 0.02) and Rrs_5Hz (P = 0.006). Baseline Scond was the best predictor of a clinically meaningful improvement in asthma control (ΔACQ > 0.5, ROC-AUC = 0.91, P = 0.007).

CONCLUSION

Step-up to high-dose combination treatment in uncontrolled asthma is associated with improved peripheral airway function as measured by Xrs_5Hz and MBNW. Baseline MBNW and FOT parameters correlated with the improvement in symptoms and may predict a positive response to up-titration in uncontrolled asthmatic patients.

Τhe Co-Existence of Obstructive Sleep Apnea and Bronchial Asthma: Revelation of a New Asthma Phenotype?

Bronchial asthma (BA) and obstructive sleep apnea (OSA) are common respiratory obstructive diseases that may coexist. It would be interesting to study the possible influence of that coexistence on both diseases. Until now, reviews focused mainly on epidemiology. The aim of this study was to review the literature in relation to epidemiology, pathophysiology, consequences, screening of patients, and treatment of the coexistence of OSA and BA. We pooled studies from the PubMed database from 1986 to 2019. OSA prevalence in asthmatics was found to be high, ranging from19% to 60% in non-severe BA, reaching up to 95% in severe asthma. Prevalence was correlated with the duration and severity of BA, and increased dosage of steroids taken orally or by inhalation. This high prevalence of the coexistence of OSA and BA diseases could not be a result of just chance. It seems that this coexistence is based on the pathophysiology of the diseases. In most studies, OSA seems to deteriorate asthma outcomes, and mainly exacerbates them. CPAP (continuous positive airway pressure) treatment is likely to improve symptoms, the control of the disease, and the quality of life in asthmatics with OSA. However, almost all studies are observational, involving a small number of patients with a short period of follow up. Although treatment guidelines cannot be released, we could recommend periodic screening of asthmatics for OSA for the optimal treatment of both the diseases.

The Role of Airway Myofibroblasts in Asthma

Airway remodeling is a characteristic feature of asthma and is thought to play an important role in the pathogenesis of airway hyperresponsiveness. Myofibroblasts are key structural cells involved in injury and repair, and there is evidence that dysregulation of their normal function contributes to airway remodeling. Despite the importance of myofibroblasts, a lack of specific cellular markers and inconsistent nomenclature have limited recognition of their key role in airway remodeling. Myofibroblasts are increased several-fold in the airways in asthma, in proportion to the severity of the disease. Myofibroblasts are postulated to be derived from both tissue-resident and bone marrow-derived cells, depending on the stage of injury and the tissue. A small number of studies have demonstrated attenuation of myofibroblast numbers and also reversal of established myofibroblast populations in asthma and other inflammatory processes. In this article, we review what is currently known about the biology of myofibroblasts in the airways in asthma and identify potential targets to reduce or reverse the remodeling process. However, further translational research is required to better understand the mechanistic role of the myofibroblast in asthma.

Myofibroblasts are increased in the lung parenchyma in asthma

Background

Increased airway smooth muscle is observed in large and small airways in asthma. Semi-quantitative estimates suggest that cells containing alpha smooth muscle actin (α-SMA) are also increased in the lung parenchyma. This study quantified and characterized α-SMA positive cells (α-SMA+) in the lung parenchyma of non-asthmatic and asthmatic individuals.

Methods

Post-mortem sections of peripheral lung from cases of fatal asthma (FA), persons with asthma dying of non-respiratory causes (NFA) and non-asthma control subjects (NAC) were stained for α-SMA, quantified using point-counting and normalised to alveolar basement membrane length and interstitial area.

Results

α-SMA+ fractional area was increased in alveolar parenchyma in both FA (14.7 ± 2.8% of tissue area) and NFA (13.0 ± 1.2%), compared with NAC (7.4 ± 2.4%), p < 0.05 The difference was greater in upper lobes compared with lower lobes (p < 0.01) in both asthma groups. Similar changes were observed in alveolar ducts and alveolar walls. The electron microscopic features of the α-SMA+ cells were characteristic of myofibroblasts.

Conclusions

We conclude that in asthma there is a marked increase in α-SMA+ myofibroblasts in the lung parenchyma. The physiologic consequences of this increase are unknown.

The prevalence of small airways disease in adult asthma: A systematic literature review

BACKGROUND

Small airways dysfunction and inflammation contribute significantly to the clinical impact of asthma, yet conventional methods of assessing airways function in the clinic cannot reliably evaluate its presence. However, most recently, promising methods of assessment are being utilised.

METHODS

We conducted a systematic literature review, using PubMed, with the aim of determining the prevalence of small airways disease in adult patients with asthma. We ascertained how small airways disease prevalence compared between different studies when measured using distinct techniques of small airways assessment.

RESULTS

Fifteen publications were identified determining the prevalence of small airways disease in asthma. Methods of assessments included impulse oscillometry, spirometry, body plethysmography, multiple-breath nitrogen washout, and high-resolution computed tomography. These studies used differing inclusion characteristics and recruited patients with a broad range of asthma severity, yet collectively they reported an overall prevalence of small airways disease of 50-60%. Small airways disease was present across all asthma severities, with evidence of distal airway disease even in the absence of proximal airway obstruction.

CONCLUSIONS

Small airways disease is highly prevalent in asthma, even in patients with milder disease. Given the clinical impact of small airways disease, its presence should not be underestimated or overlooked as part of the daily management of patients with asthma.

Long-term CPAP treatment improves asthma control in patients with asthma and obstructive sleep apnoea

PURPOSE

Both asthma and obstructive sleep apnoea cause sleep disturbance, daytime sleepiness and diminished quality of life. Continuous positive airway pressure (CPAP) is efficient in reducing symptoms related to sleep apnoea. Here we report the impact of long-term use of CPAP on asthma symptoms.

METHODS

A survey questionnaire was distributed to all of our obstructive sleep apnoea patients with CPAP therapy in 2013. We used the Finnish version of the Asthma Control Test™ (ACT) and a visual analogue scale (0 = no symptoms, 100 = severe asthma symptoms). Asthma was defined as self-reported physician-diagnosed disease and a special reimbursement for asthma medication by the Social Insurance Institution.

RESULTS

We sent 2577 questionnaires and received 1586 answers (61 %). One hundred ninety-seven patients were asthmatics with a prevalence of asthma among CPAP users of 13 %. We studied 152 patients (58 females) whose CPAP therapy was initiated after starting asthma medication. Their mean (SD) age was 62 (10) years, duration of CPAP 5.7 (4.7) years and their CPAP daily use was 6.3 (2.4) h. Self-reported asthma severity decreased significantly from 48.3 (29.6) to 33.1 (27.4) (p < 0.001), and ACT score increased significantly from 15.35 (5.3) to 19.8 (4.6) (p < 0.001) without a significant change in the body mass index (BMI). The percentage of patients using rescue medication daily reduced from 36 to 8 % with CPAP (P < 0.001).

CONCLUSIONS

We noticed a significant decrease in asthma symptoms with long-term use of CPAP in patients with both asthma and obstructive sleep apnoea.

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

BACKGROUND

The multiple-breath inert gas washout parameter acinar ventilation heterogeneity (Sacin) is thought to be a marker of acinar airway involvement but has not been validated by using quantitative imaging techniques in asthmatic patients.

OBJECTIVE

We aimed to use hyperpolarized (3)He diffusion magnetic resonance at multiple diffusion timescales and quantitative computed tomographic (CT) densitometry to determine the nature of acinar airway involvement in asthmatic patients.

METHODS

Thirty-seven patients with asthma and 17 age-matched healthy control subjects underwent spirometry, body plethysmography, multiple-breath inert gas washout (with the tracer gas sulfur hexafluoride), and hyperpolarized (3)He diffusion magnetic resonance. A subset of asthmatic patients (n = 27) underwent quantitative CT densitometry.

RESULTS

Ninety-four percent (16/17) of patients with an increased Sacin had Global Initiative for Asthma treatment step 4 to 5 asthma, and 13 of 17 had refractory disease. The apparent diffusion coefficient (ADC) of (3)He at 1 second was significantly higher in patients with Sacin-high asthma compared with that in healthy control subjects (0.024 vs 0.017, P < .05). Sacin correlated strongly with ADCs at 1 second (R = 0.65, P < .001) but weakly with ADCs at 13 ms (R = 0.38, P < .05). ADCs at both 13 ms and 1 second correlated strongly with the mean lung density expiratory/inspiratory ratio, a CT marker of expiratory air trapping (R = 0.77, P < .0001 for ADCs at 13 ms; R = 0.72, P < .001 for ADCs at 1 second).

CONCLUSION

Sacin is associated with alterations in long-range diffusion within the acinar airways and gas trapping. The precise anatomic nature and mechanistic role in patients with severe asthma requires further evaluation.

What long-term changes in lung function can tell us about asthma control

Asthma severity is typically classified according to lung function, but asthma control in relation to lung function is often harder to define. In this paper, we will review how lung function measured at rest, as well as over time, relates to asthma control. We will explore not only conventional lung function as measured by spirometry, such as peak expiratory flow and forced expiratory volume in 1 s, but also more sophisticated measurements of peripheral airway function related to respiratory system impedance and ventilation heterogeneity. In particular, we will review the emerging area of assessing the fluctuation of lung function over time and how it may correlate to both past and future asthma control.