Risk of severe asthma episodes predicted from fluctuation analysis of airway function

Late-onset asthma: current perspectives

Because the pathophysiology of asthma has diverse characteristics, to manage the disease effectively, it is important for clinicians to distinguish among the clinical phenotypes. Among them, adult-onset asthma, that is, late-onset asthma (LOA), is increasing because of the aging of the population. The phenotype of LOA is largely divided into two types according to the presence or absence of eosinophilic inflammation, T-helper (Th)2- and non-Th2-associated LOA. Especially in Th2 LOA related to rhinosinusitis, as pulmonary function at onset is poor and asthma exacerbations occur frequently, it is important to detect this phenotype in the early phase by using a biomarker of Th2-type inflammation such as fractional exhaled nitric oxide (FENO). As non-Th2-LOA is often resistant to corticosteroids, this phenotype often requires another treatment strategy such as macrolide, diet, or smoking cessation. We often struggle with the management of LOA patients due to a lack of evidence; therefore, the elucidation of the mechanism of LOA contributes to increased efficiency of diagnosis and treatment of LOA. Age-related immune system and structural changes are thought to be associated with the pathophysiology of LOA. In the former case, changes in inflammatory cell function such as variations in the innate immune response and acquisition of autoimmunity or upregulation of oxidative stress are thought to be involved in the mechanism. Meanwhile, the latter can also become triggers or exacerbating factors of LOA via enhancement of airway hyperresponsiveness, decline in lung function, increased air trapping, and reduction in chest wall compliance. Therefore, appropriate individualized management in LOA may be possible through precisely assessing the pathophysiology based on age-related functional changes, including the immune and structural system.

Effect of Rho-kinase inhibition on complexity of breathing pattern in a guinea pig model of asthma

Asthma represents an episodic and fluctuating behavior characterized with decreased complexity of respiratory dynamics. Several evidence indicate that asthma severity or control is associated with alteration in variability of lung function. The pathophysiological basis of alteration in complexity of breathing pattern in asthma has remained poorly understood. Regarding the point that Rho-kinase is involved in pathophysiology of asthma, in present study we investigated the effect of Rho-kinase inhibition on complexity of respiratory dynamics in a guinea pig model of asthma. Male Dunkin Hartley guinea pigs were exposed to 12 series of inhalations with ovalbumin or saline. Animals were treated by the Rho-kinase inhibitor Y-27632 (1mM aerosols) prior to each allergen challenge. We recorded respiration of conscious animals using whole-body plethysmography. Exposure to ovalbumin induced lung inflammation, airway hyperresponsiveness and remodeling including goblet cell hyperplasia, increase in the thickness of airways smooth muscles and subepithelial collagen deposition. Complexity analysis of respiratory dynamics revealed a dramatic decrease in irregularity of respiratory rhythm representing less complexity in asthmatic guinea pigs. Inhibition of Rho-kinase reduced the airway remodeling and hyperreponsiveness, but had no significant effect on lung inflammation and complexity of respiratory dynamics in asthmatic animals. It seems that airway hyperresponsiveness and remodeling do not significantly affect the complexity of respiratory dynamics. Our results suggest that inflammation might be the probable cause of shift in the respiratory dynamics away from the normal fluctuation in asthma.

How should treatment approaches differ depending on the severity of asthma?

INTRODUCTION

Asthma is nowadays regarded as a syndrome of various overlapping phenotypes with defined clinical characteristics, different underlying inflammatory mechanisms, identifiable genetic background, environmental risk factors and possible biomarkers. There are no doubts that due to the diversity of asthma, a 'one size fits all' management of the disease is no longer valid. Areas covered: Nowadays asthma management is based on the control of the disease, and the goals of asthma treatment are defined as good symptom control, decreased future risk of exacerbations, fixed airflow limitation, and side-effects of treatment. Alternative strategies for adjusting asthma treatment such as sputum or exhaled nitric oxide guided protocols have been evaluated and despite some effectiveness, are regarded as impractical in every-day clinical conditions. Further studies in the field of asthma phenotypes/endotypes and biomarkers are warranted with the main goal to define which of those possible subgroups will be useful in clinical practice in regards to the potential allocation of successful treatment. Expert commentary: Despite the availability of guidelines on the diagnosis and management of asthma, it seems that the disease is still not optimally controlled. Addressing unmet needs in every day care, improving education, adherence/compliance and inhalation technique may significantly improve asthma control across all severities of the disease.

Asthma Medication Ratio Phenotypes in Elderly Women

BACKGROUND

With population aging, further asthma research is needed in the elderly.

OBJECTIVE

We assessed the relevance of the controller-to-total asthma medication ratio and its fluctuations over time to identify participants with a subsequent risk of poor asthma-related outcomes among well-characterized elderly women.

METHODS

We studied 4,328 women with ever asthma (69.6 ± 6.1 years) from the Asthma-E3N study (Etude Epidémiologique auprès des femmes de la Mutuelle Générale de l'Education Nationale), which combined drug claims data since 2004 with prospective individual characteristics. The levels of the yearly controller-to-total asthma medication ratio from 2004 to 2011 were included in latent class analysis to identify groups of women characterized by specific long-term fluctuations of the ratio. Multiple regression models estimated the subsequent risk of uncontrolled asthma, asthma attacks, asthma exacerbations, and poor asthma-related quality of life associated with the level and the fluctuations of the ratio.

RESULTS

A short-term (12 months) ratio below 0.5 was associated with a higher risk of subsequent uncontrolled asthma, asthma attacks, asthma exacerbations (odds ratio [95% confidence interval (CI)] = 2.13 [1.41; 3.23], 1.51 [1.01; 2.26], and 2.18 [1.37; 3.44], respectively), and a lower total asthma quality of life questionnaire score (β [95% CI] = -0.49 [-0.68; -0.29]). The analysis of the long-term fluctuations of the ratio identified 5 profiles ("Never regular treatment," 53.2%; "Persistent high ratio," 21.8%; "Increasing ratio," 4.4%; "Initiating treatment," 8.8%; "Treatment discontinuation," 11.8%). The subsequent risk of poor asthma-related outcomes was significantly higher in profiles characterized by no or interrupted asthma maintenance therapy over time, compared with the "Persistent high ratio" group.

CONCLUSIONS

The level and the long-term fluctuations of the controller-to-total asthma medication ratio predict poor asthma-related outcomes in elderly women.

Effect of airway remodeling and hyperresponsiveness on complexity of breathing pattern in rat

The complexity of respiratory dynamics is decreased, in association with disease severity, in patients with asthma. However, the pathophysiological basis of decreased complexity of breathing pattern in asthma is not clear. In the present study, we investigated the effect of airway remodeling and hyperresponsiveness induced by repeated bronchoconstriction (using methacholine) on breathing pattern in rats with or without allergen-induced sensitization. Entropy analysis of respiratory variability showed decreased irregularity (less complexity) of respiratory rhythm in this rat model of asthma. Airway remodeling and hyperresponsiveness induced by repeated bronchoconstriction also led to increased regularity of respiratory dynamics in sensitized rats. However, these airway alterations had no significant effect on the complexity of breathing pattern in non-sensitized rats. Our results indicate that mechanical respiratory alterations cannot per se attenuate the complexity of respiratory dynamics, unless there is an underlying inflammation. We suggest further studies on underlying mechanisms of breathing variability with focus on respiratory control alterations due to airway inflammation.

Functional phenotypes determined by fluctuation-based clustering of lung function measurements in healthy and asthmatic cohort participants

RATIONALE

Asthma is characterised by inflammation and reversible airway obstruction. However, these features are not always closely related. Fluctuations of daily lung function contain information on asthma phenotypes, exacerbation risk and response to long-acting β-agonists.

OBJECTIVES

In search of subgroups of asthmatic participants with specific lung functional features, we developed and validated a novel clustering approach to asthma phenotyping, which exploits the information contained within the fluctuating behaviour of twice-daily lung function measurements.

METHODS

Forced expiratory volume during the first second (FEV₁) and peak expiratory flow (PEF) were prospectively measured over 4 weeks in 696 healthy and asthmatic school children (Protection Against Allergy - Study in Rural Environments (PASTURE)/EFRAIM cohort), and over 1 year in 138 asthmatic adults with mild-to-moderate or severe asthma (Pan-European Longitudinal Assessment of Clinical Course and BIOmarkers in Severe Chronic AIRway Disease (BIOAIR) cohort). Using enrichment analysis, we explored whether the method identifies clinically meaningful, distinct clusters of participants with different lung functional fluctuation patterns.

MEASUREMENTS AND MAIN RESULTS

In the PASTURE/EFRAIM dataset, we found four distinct clusters. Two clusters were enriched in children with well-known clinical characteristics of asthma. In cluster 3, children from a farming environment predominated, whereas cluster 4 mainly consisted of healthy controls. About 79% of cluster 3 carried the asthma-risk allele rs7216389 of the 17q21 locus. In the BIOAIR dataset, we found two distinct clusters clearly discriminating between individuals with mild-to-moderate and severe asthma.

CONCLUSIONS

Our method identified dynamic functional asthma and healthy phenotypes, partly independent of atopy and inflammation but related to genetic markers on the 17q21 locus. The method can be used for disease phenotyping and possibly endotyping. It may identify participants with specific functional abnormalities, potentially needing a different therapeutic approach.

Systems Biology and Clinical Practice in Respiratory Medicine. The Twain Shall Meet

Respiratory diseases are highly complex, being driven by host-environment interactions and manifested by inflammatory, structural, and functional abnormalities that vary over time. Traditional reductionist approaches have contributed vastly to our knowledge of biological systems in health and disease to date; however, they are insufficient to provide an understanding of the behavior of the system as a whole. In this Pulmonary Perspective, we discuss systems biology approaches, especially but not limited to the study of the lung as a complex system. Such integrative approaches take into account the large number of dynamic subunits and their interactions found in biological systems. Borrowing methods from physics and mathematics, it is possible to study the collective behavior of these systems over time and in a multidimensional manner. We first examine the physiological basis for complexity in the respiratory system and its implications for disease. We then expand on the potential applications of systems biology methods to study complex systems, within the context of diagnosis and monitoring of respiratory diseases including asthma, chronic obstructive pulmonary disease (COPD), and critical illness. We summarize the significant advances made in recent years using systems approaches for disease phenotyping, applied to data ranging from the molecular to clinical level, obtained from large-scale asthma and COPD networks. We describe new studies using temporal complexity patterns to characterize asthma and COPD and predict exacerbations as well as predict adverse outcomes in critical care. We highlight new methods that are emerging with this approach and discuss remaining questions that merit greater attention in the field.

Dynamics and complexity of body temperature in preterm infants nursed in incubators

BACKGROUND

Poor control of body temperature is associated with mortality and major morbidity in preterm infants. We aimed to quantify its dynamics and complexity to evaluate whether indices from fluctuation analyses of temperature time series obtained within the first five days of life are associated with gestational age (GA) and body size at birth, and presence and severity of typical comorbidities of preterm birth.

METHODS

We recorded 3h-time series of body temperature using a skin electrode in incubator-nursed preterm infants. We calculated mean and coefficient of variation of body temperature, scaling exponent alpha (Talpha) derived from detrended fluctuation analysis, and sample entropy (TSampEn) of temperature fluctuations. Data were analysed by multilevel multivariable linear regression.

RESULTS

Data of satisfactory technical quality were obtained from 285/357 measurements (80%) in 73/90 infants (81%) with a mean (range) GA of 30.1 (24.0-34.0) weeks. We found a positive association of Talpha with increasing levels of respiratory support after adjusting for GA and birth weight z-score (p<0.001; R2 = 0.38).

CONCLUSION

Dynamics and complexity of body temperature in incubator-nursed preterm infants show considerable associations with GA and respiratory morbidity. Talpha may be a useful marker of autonomic maturity and severity of disease in preterm infants.

Fluctuation Analysis of Peak Expiratory Flow and Its Association with Treatment Failure in Asthma

RATIONALE

Temporal fluctuations have been demonstrated in lung function and asthma control, but the effect of controller therapy on these fluctuations is unknown.

OBJECTIVES

To determine if fluctuations in peak expiratory flow (PEF) are predictive of subsequent treatment failure and may be modified by controller therapy.

METHODS

We applied detrended fluctuation analysis to once-daily PEF data from 493 participants in the LOCCS (Leukotriene Modifier Corticosteroid or Corticosteroid-Salmeterol) trial of the American Lung Association Airways Clinical Research Centers. We evaluated the coefficient of variation of PEF (CVpef) and the scaling exponent α, reflecting self-similarity of PEF, in relation to treatment failure from the run-in period of open-label inhaled fluticasone, and the treatment periods for subjects randomized to (1) continued twice daily fluticasone (F), (2) once daily fluticasone plus salmeterol (F + S), or (3) once daily oral montelukast (M).

MEASUREMENTS AND MAIN RESULTS

The CVpef was higher in those with treatment failure in the F and F + S groups in the run-in phase, and all three groups in the treatment phase. α was similar between those with and without treatment failure in all three groups during the run-in phase but was higher among those with treatment failure in the F and F + S groups during the treatment phase. Participants in all three groups showed variable patterns of change in α leading up to treatment failure.

CONCLUSIONS

We conclude that increased temporal self-similarity (α) of more variable lung function (CVpef) is associated with treatment failure, but the pattern of change in self-similarity leading up to treatment failure is variable across individuals.

Predicting and reducing risk of exacerbations in children with asthma in the primary care setting: current perspectives

Childhood asthma is a very common condition in western countries and is becoming more prevalent worldwide. Asthma attacks (or exacerbations) affect the quality of life for child and parent, can rarely result in death, and also come at a cost for health care providers and the economy. The aims of this review were to 1) describe the burden of asthma exacerbations, 2) describe factors that might predict a child at increased risk of having an asthma attack, and 3) explore what interventions might be delivered in primary care to reduce the risk of a child having an asthma attack. Asthma attacks are more common in younger children and those with more severe asthma, although prevalence varies between countries. Many factors are associated with asthma attacks including environmental exposures, patient–clinician relationship, and patient factors. Currently, the best predictor of an asthma attack is a history of an attack in the previous 12 months, and the more attacks, the greater the risk. Looking ahead, it is likely that surveillance of routinely collected primary care data can be used to identify an individual at increased risk. Stratified (or personalized) treatment, which might involve physiological monitoring and genetic analysis, offers the potential to reduce an individual’s risk of asthma attack. Whatever the future holds, the relationship between patient and clinician will remain central to asthma management.

Bronchodilator response following methacholine-induced bronchoconstriction predicts acute asthma exacerbations

Methacholine bronchial provocation test provides the concentration of methacholine causing a 20% decrease in forced expiratory volume in 1 s (FEV1) from baseline (PC20). The dose-response slope (DRS), and other continuous indices of responsiveness (CIR; the percentage decline from the post-diluent baseline FEV1 after the last dose of methacholine), and per cent recovery index (PRI; the percentage increase from the maximally reduced FEV1 after bronchodilator inhalation) are alternative measures. The clinical relevance of these indices in predicting acute asthma exacerbations has not been fully evaluated.In two prospective cohorts of childhood and elderly asthmatics, baseline PC20, DRS, CIR and PRI were measured and evaluated as predictors of acute asthma exacerbations.We found that PRI was significantly related to the presence of asthma exacerbations during the first year of follow-up in both cohorts of childhood (p=0.025) and elderly asthmatics (p=0.003). In addition, PRI showed a significant association with the total number of steroid bursts during 4.3 years of follow-up in the cohort of childhood asthmatics (p=0.04).We demonstrated that PRI, an index of reversibility following methacholine-induced bronchoconstriction, was a good clinical predictor of acute exacerbations of asthma in both childhood and elderly asthmatics.

Tidal flow variability measured by impedance pneumography relates to childhood asthma risk

Lung function variability is a fundamental feature of asthma but has been difficult to quantify in children due to methodological limitations. We assessed the feasibility and clinical implications of overnight flow variability measurement at home using impedance pneumography in young children.44 children aged 3-7 years with recurrent or persistent lower airway symptoms were recruited. Patients were divided into high- or lower-risk groups (HR and LR groups) based on their risk of asthma (modified Asthma Predictive Index), and a third group was formed of children who had a history of wheeze and who were treated with inhaled corticosteroids (ICS group). Tidal volume and the derived flow were recorded through skin electrodes using impedance pneumography at home during sleep. Quantities describing overnight change in expiratory flow-volume minimum curve shape correlation (CSRmin) and respiratory chaoticity (minimum noise limit (NLmin)) were derived.Recordings were successful in 34 children. CSRmin differed between the HR and LR groups (p=0.002) and between the HR and ICS groups (p=0.003), indicating a stronger change in flow profile shape in the HR group. NLmin differed between the HR and LR groups (p=0.014), indicating momentarily lowered chaoticity in the HR group.Impedance pneumography was found feasible for quantifying nocturnal lung function variability and the measured variability was associated with risk of asthma in young children.

Classification of Asthma Based on Nonlinear Analysis of Breathing Pattern

Normal human breathing exhibits complex variability in both respiratory rhythm and volume. Analyzing such nonlinear fluctuations may provide clinically relevant information in patients with complex illnesses such as asthma. We compared the cycle-by-cycle fluctuations of inter-breath interval (IBI) and lung volume (LV) among healthy volunteers and patients with various types of asthma. Continuous respiratory datasets were collected from forty age-matched men including 10 healthy volunteers, 10 patients with controlled atopic asthma, 10 patients with uncontrolled atopic asthma, and 10 patients with uncontrolled non-atopic asthma during 60 min spontaneous breathing. Complexity of breathing pattern was quantified by calculating detrended fluctuation analysis, largest Lyapunov exponents, sample entropy, and cross-sample entropy. The IBI as well as LV fluctuations showed decreased long-range correlation, increased regularity and reduced sensitivity to initial conditions in patients with asthma, particularly in uncontrolled state. Our results also showed a strong synchronization between the IBI and LV in patients with uncontrolled asthma. Receiver operating characteristic (ROC) curve analysis showed that nonlinear analysis of breathing pattern has a diagnostic value in asthma and can be used in differentiating uncontrolled from controlled and non-atopic from atopic asthma. We suggest that complexity analysis of breathing dynamics may represent a novel physiologic marker to facilitate diagnosis and management of patients with asthma. However, future studies are needed to increase the validity of the study and to improve these novel methods for better patient management.

Tidal breathing flow-volume curves with impedance pneumography during expiratory loading

Diagnosis of asthma in the preschoold children is difficult due to lack of objective lung function tests suitable for this age group. Impedance pneumography (IP) is a mode of measurement that may potentially enable ambulatory 24h recording of tidal breathing indices and respiratory dynamics that are known to relate to small airway obstruction. The aim of this research was to induce changes in breathing control and mechanics and study the ability of IP to reproduce TBFVC and track its changes under potentially difficult conditions. This was achieved by a comparison of direct mouth pneumotachograph (PNT) and IP tidal breathing flow-volume curves (TBFVC) during free breathing and expiratory loading obtained from 17 young lung-healthy subjects. The expiratory loading produced strong and significant changes in the respiratory pattern and mouth pressure. The agreement of PNT and IP normalized TBFVCs was found excellent having the highest distance between the normalized TBFVCs of (mean ± SD) 7.4 % ± 3.6 % and 6.2 % ± 3.0 % during free and loaded breathing, respectively. The agreement was not affected by the presence of the expiratory load despite it poses multiple potential hazards for the IP measurements. We conclude that by using correct electrode placement and cardiac filtering, IP was able to accurately reproduce and track changes in normalized TBFVCs under normal and abnormal respiratory conditions in healthy adult subjects.

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.

Risk of current asthma among adult smokers with respiratory syncytial virus illnesses in early life

RATIONALE

Risk of subsequent asthma-like symptoms after early-life lower respiratory illness (LRI) caused by respiratory syncytial virus (RSV) is increased during the first decade of childhood and diminished thereafter by adolescence.

OBJECTIVES

To determine the relation of early-life RSV-LRI on adult asthma-like symptoms and its interactive role with adult smoking.

METHODS

A total of 1,246 nonselected infants were enrolled at birth and prospectively followed. Virologically confirmed RSV-LRIs were assessed during the first 3 years of life. At age 22, 24, 26, and 29 years, current asthma and smoking behavior were evaluated by questionnaire. Peak flow variability was assessed at age 26 and expressed as amplitude % mean. A longitudinal analysis was used to investigate the relation of RSV-LRI and active smoking to adult outcomes.

MEASUREMENTS AND MAIN RESULTS

Neither RSV-LRI nor active smoking were directly associated with increased current adult asthma or peak flow variability. However, there was a significant interaction between RSV-LRI and active smoking in relation to current asthma (P for interaction = 0.004) and peak flow variability (P for interaction = 0.04). Among subjects with early RSV-LRI, those who actively smoked were 1.7 times more likely to have current asthma (95% confidence interval, 1.2-2.3; P = 0.003) and had greater amplitude % mean (10.0% vs. 6.4%; P = 0.02) than nonsmokers. Among subjects without early RSV-LRI, there was no difference in asthma risk or peak flow variability between active smokers and nonsmokers.

CONCLUSIONS

Smoking is associated with increased risk of having asthma in young adults who had RSV-LRI in early life but not among subjects without these illnesses.

Systems biology approach for subtyping asthma; where do we stand now?

PURPOSE OF REVIEW

The purpose of this review is to discuss the present systems biology approach to asthma and how it is helping to define asthma subtypes. Although the general concept of systems biology will be discussed, the article will focus on recent developments in the field related to asthma.

RECENT FINDINGS

The most recent work in systems biology and asthma has occurred in the area of genomics (e.g., pharmacogenomics and gene-environment interactions), protein interaction networks [e.g., interleukin (IL)-33/IL-1 receptor-like 1 signaling], cluster analysis of asthma patients (e.g., application of severe asthma research program clusters to a general urban asthma population), and multiscale approaches to asthma encompassing data from the molecule to whole organ (e.g., modeling of airways hyperresponsiveness).

SUMMARY

The results of recent work in this area have led to new insight into gene-cytokine and protein-protein networks involved in asthma, a better determination of key clinical factors associated with asthma subtypes, and the beginning of sophisticated multiscale approaches to modeling, understanding and predicting the behavior of the asthmatic lung.

Asthma and respiratory physiology: putting lung function into perspective

Bronchial asthma is a chronic disease characterized by airway hyperresponsiveness, airway inflammation and remodelling. The hypothesis that the illness is inflammatory in nature has recently been challenged by studies showing that airway smooth muscle (ASM) plays a more important role than previously thought. For example, it is now known that in asthma patients, ASM proliferates more and faster than in healthy subjects, carries intrinsic defects and exhibits impaired relaxation, increased velocity of shortening, plastic adaptation to short length and perturbed equilibrium of actin-to-myosin during cycling. Similar conclusions can be drawn from studies on airway mechanics. For instance, in asthma, abnormal ASM contributes to limiting the response to deep lung stretching and accelerates the return of bronchial tone to baseline conditions, and contributes to increased airway stiffness. Upon stimulation, ASM causes airway narrowing that is heterogeneous across the lung and variable over time. This heterogeneity leads to patchy ventilation. Experimental studies have shown that patchy ventilation may precipitate an asthma attack, and inability to maintain bronchial tone control over time can predict the occurrence of bronchospastic attacks over a matter of a few days. To improve our knowledge on the pathogenesis of asthma, we believe that it is necessary to explore the disease within the framework of the topographical, volume and time domains of the lung that play an important role in setting the severity and progression of the disease. Application of the forced oscillation technique and multiple breath nitrogen washout may, alone or in combination, help address questions unsolvable until now.

Effects of airway tree asymmetry on the emergence and spatial persistence of ventilation defects

Asymmetry and heterogeneity in the branching of the human bronchial tree are well documented, but their effects on bronchoconstriction and ventilation distribution in asthma are unclear. In a series of seminal studies, Venegas et al. have shown that bronchoconstriction may lead to self-organized patterns of patchy ventilation in a computational model that could explain areas of poor ventilation [ventilation defects (VDefs)] observed in positron emission tomography images during induced bronchoconstriction. To investigate effects of anatomic asymmetry on the emergence of VDefs we used the symmetric tree computational model that Venegas and Winkler developed using different trees, including an anatomic human airway tree provided by M. Tawhai (University of Auckland), a symmetric tree, and three trees with intermediate asymmetry (Venegas JG, Winkler T, Musch G, Vidal Melo MF, Layfield D, Tgavalekos N, Fischman AJ, Callahan RJ, Bellani G, Harris RS. Nature 434: 777-782, 2005 and Winkler T, Venegas JG. J Appl Physiol 103: 655-663, 2007). Ventilation patterns, lung resistance (RL), lung elastance (EL), and the entropy of the ventilation distribution were compared at different levels of airway smooth muscle activation. We found VDefs emerging in both symmetric and asymmetric trees, but VDef locations were largely persistent in asymmetric trees, and bronchoconstriction reached steady state sooner than in a symmetric tree. Interestingly, bronchoconstriction in the asymmetric tree resulted in lower RL (∼%50) and greater EL (∼%25). We found that VDefs were universally caused by airway instability, but asymmetry in airway branching led to local triggers for the self-organized patchiness in ventilation and resulted in persistent locations of VDefs. These findings help to explain the emergence and the persistence in location of VDefs found in imaging studies.

Ventilation heterogeneity in obesity

Obesity is associated with important decrements in lung volumes. Despite this, ventilation remains normally or near normally distributed at least for moderate decrements in functional residual capacity (FRC). We tested the hypothesis that this is because maximum flow increases presumably as a result of an increased lung elastic recoil. Forced expiratory flows corrected for thoracic gas compression volume, lung volumes, and forced oscillation technique at 5-11-19 Hz were measured in 133 healthy subjects with a body mass index (BMI) ranging from 18 to 50 kg/m(2). Short-term temporal variability of ventilation heterogeneity was estimated from the interquartile range of the frequency distribution of the difference in inspiratory resistance between 5 and 19 Hz (R5-19_IQR). FRC % predicted negatively correlated with BMI (r = -0.72, P < 0.001) and with an increase in slope of either maximal (r = -0.34, P < 0.01) or partial flow-volume curves (r = -0.30, P < 0.01). Together with a slight decrease in residual volume, this suggests an increased lung elastic recoil. Regression analysis of R5-19_IQR against FRC % predicted and expiratory reserve volume (ERV) yielded significantly higher correlation coefficients by nonlinear than linear fitting models (r(2) = 0.40 vs. 0.30 for FRC % predicted and r(2) = 0.28 vs. 0.19 for ERV). In conclusion, temporal variability of ventilation heterogeneities increases in obesity only when FRC falls approximately below 65% of predicted or ERV below 0.6 liters. Above these thresholds distribution is quite well preserved presumably as a result of an increase in lung recoil.

Asthma exacerbations: predisposing factors and prediction rules

PURPOSE OF REVIEW

Asthma is a multifaceted disease that is associated with decreased lung function, multiple symptoms, varying levels of asthma control, and risk of acute exacerbations. The ability to predict the risk of developing acute exacerbations may improve the management of asthmatics and facilitate identification of these patients for interventional studies.

RECENT FINDINGS

Factors that are associated with different manifestations of asthma differ. Biomarkers that are correlated with airways hyper-responsiveness do not necessarily correlate with risk of future exacerbations. Genetic factors that segregate with exacerbation risk are beginning to emerge. Outcome measures that demonstrate predictive validity have been developed and may facilitate patient management and provide novel clinically meaningful endpoints in clinical trials.

SUMMARY

This review will emphasize underlying factors associated with asthma exacerbations and clinical prediction rules that correlate with the risk of developing severe exacerbations of asthma.

A Review of Theoretical Perspectives in Cognitive Science on the Presence of 1/f Scaling in Coordinated Physiological and Cognitive Processes

Time series of human performances present fluctuations around a mean value. These fluctuations are typically considered as insignificant, and attributable to random noise. Over recent decades, it became clear that temporal fluctuations possess interesting properties, however, one of which the property of fractal 1/f scaling. 1/f scaling indicates that a measured process extends over a wide range of timescales, suggesting an assembly over multiple scales simultaneously. This paper reviews neurological, physiological, and cognitive studies that corroborate the claim that 1/f scaling is most clearly present in healthy, well-coordinated activities. Prominent hypotheses about the origins of 1/f scaling are confronted with these reviewed studies. It is concluded that 1/f scaling in living systems appears to reflect their genuine complex nature, rather than constituting a coincidental side-effect. The consequences of fractal dynamics extending from the small spatial and temporal scales (e.g., neurons) to the larger scales of human behavior and cognition, are vast, and impact the way in which relevant research questions may be approached. Rather than focusing on specialized isolable subsystems, using additive linear methodologies, nonlinear dynamics, more elegantly so, imply a complex systems methodology, thereby exploiting, rather than rejecting, mathematical concepts that enable describing large sets of natural phenomena.

Mechanical correlates of dyspnea in bronchial asthma

We hypothesized that dyspnea and its descriptors, that is, chest tightness, inspiratory effort, unrewarded inspiration, and expiratory difficulty in asthma reflect different mechanisms of airflow obstruction and their perception varies with the severity of bronchoconstriction. Eighty-three asthmatics were studied before and after inhalation of methacholine doses decreasing the 1-sec forced expiratory volume by ~15% (mild bronchoconstriction) and ~25% (moderate bronchoconstriction). Symptoms were examined as a function of changes in lung mechanics. Dyspnea increased with the severity of obstruction, mostly because of inspiratory effort and chest tightness. At mild bronchoconstriction, multivariate analysis showed that dyspnea was related to the increase in inspiratory resistance at 5 Hz (R 5) (r (2) = 0.10, P = 0.004), chest tightness to the decrease in maximal flow at 40% of control forced vital capacity, and the increase in R 5 at full lung inflation (r (2) = 0.15, P = 0.006), inspiratory effort to the temporal variability in R 5-19 (r (2) = 0.13, P = 0.003), and unrewarded inspiration to the recovery of R 5 after deep breath (r (2) = 0.07, P = 0.01). At moderate bronchoconstriction, multivariate analysis showed that dyspnea and inspiratory effort were related to the increase in temporal variability in inspiratory reactance at 5 Hz (X 5) (r (2) = 0.12, P = 0.04 and r (2) = 0.18, P < 0.001, respectively), and unrewarded inspiration to the decrease in X 5 at maximum lung inflation (r (2) = 0.07, P = 0.04). We conclude that symptom perception is partly explained by indexes of airway narrowing and loss of bronchodilatation with deep breath at low levels of bronchoconstriction, but by markers of ventilation heterogeneity and lung volume recruitment when bronchoconstriction becomes more severe.

Complexity and emergent phenomena

Complex biological systems operate under non-equilibrium conditions and exhibit emergent properties associated with correlated spatial and temporal structures. These properties may be individually unpredictable, but tend to be governed by power-law probability distributions and/or correlation. This article reviews the concepts that are invoked in the treatment of complex systems through a wide range of respiratory-related examples. Following a brief historical overview, some of the tools to characterize structural variabilities and temporal fluctuations associated with complex systems are introduced. By invoking the concept of percolation, the notion of multiscale behavior and related modeling issues are discussed. Spatial complexity is then examined in the airway and parenchymal structures with implications for gas exchange followed by a short glimpse of complexity at the cellular and subcellular network levels. Variability and complexity in the time domain are then reviewed in relation to temporal fluctuations in airway function. Next, an attempt is given to link spatial and temporal complexities through examples of airway opening and lung tissue viscoelasticity. Specific examples of possible and more direct clinical implications are also offered through examples of optimal future treatment of fibrosis, exacerbation risk prediction in asthma, and a novel method in mechanical ventilation. Finally, the potential role of the science of complexity in the future of physiology, biology, and medicine is discussed.

Quantitative computed tomography-derived clusters: redefining airway remodeling in asthmatic patients

BACKGROUND

Asthma heterogeneity is multidimensional and requires additional tools to unravel its complexity. Computed tomography (CT)-assessed proximal airway remodeling and air trapping in asthmatic patients might provide new insights into underlying disease mechanisms.

OBJECTIVES

The aim of this study was to explore novel, quantitative, CT-determined asthma phenotypes.

METHODS

Sixty-five asthmatic patients and 30 healthy subjects underwent detailed clinical, physiologic characterization and quantitative CT analysis. Factor and cluster analysis techniques were used to determine 3 novel, quantitative, CT-based asthma phenotypes.

RESULTS

Patients with severe and mild-to-moderate asthma demonstrated smaller mean right upper lobe apical segmental bronchus (RB1) lumen volume (LV) in comparison with healthy control subjects (272.3 mm(3) [SD, 112.6 mm(3)], 259.0 mm(3) [SD, 53.3 mm(3)], 366.4 mm(3) [SD, 195.3 mm(3)], respectively; P = .007) but no difference in RB1 wall volume (WV). Air trapping measured based on mean lung density expiratory/inspiratory ratio was greater in patients with severe and mild-to-moderate asthma compared with that seen in healthy control subjects (0.861 [SD, 0.05)], 0.866 [SD, 0.07], and 0.830 [SD, 0.06], respectively; P = .04). The fractal dimension of the segmented airway tree was less in asthmatic patients compared with that seen in control subjects (P = .007). Three novel, quantitative, CT-based asthma clusters were identified, all of which demonstrated air trapping. Cluster 1 demonstrates increased RB1 WV and RB1 LV but decreased RB1 percentage WV. On the contrary, cluster 3 subjects have the smallest RB1 WV and LV values but the highest RB1 percentage WV values. There is a lack of proximal airway remodeling in cluster 2 subjects.

CONCLUSIONS

Quantitative CT analysis provides a new perspective in asthma phenotyping, which might prove useful in patient selection for novel therapies.

Asthma

Asthma is a heterogeneous group of conditions that result in recurrent, reversible bronchial obstruction. Although the disease can start at any age, the first symptoms occur during childhood in most cases. Asthma has a strong genetic component, and genome-wide association studies have identified variations in several genes that slightly increase the risk of disease. Asthma is often associated with increased susceptibility to infection with rhinoviruses and with changes in the composition of microbial communities colonising the airways, but whether these changes are a cause or consequence of the disease is unknown. There is currently no proven prevention strategy; however, the finding that exposure to microbial products in early life, particularly in farming environments, seems to be protective against asthma offers hope that surrogates of such exposure could be used to prevent the disease. Genetic and immunological studies point to defective responses of lung resident cells, especially those associated with the mucosal epithelium, as crucial elements in the pathogenesis of asthma. Inhaled corticosteroids continue to be the mainstay for the treatment of mild and moderate asthma, but limited adherence to daily inhaled medication is a major obstacle to the success of such therapy. Severe asthma that is refractory to usual treatment continues to be a challenge, but new biological therapies, such as humanised antibodies against IgE, interleukin 5, and interleukin 13, offer hope to improve the quality of life and long-term prognosis of severe asthmatics with specific molecular phenotypes.

Quantifying memory in complex physiological time-series

In a time-series, memory is a statistical feature that lasts for a period of time and distinguishes the time-series from a random, or memory-less, process. In the present study, the concept of “memory length” was used to define the time period, or scale over which rare events within a physiological time-series do not appear randomly. The method is based on inverse statistical analysis and provides empiric evidence that rare fluctuations in cardio-respiratory time-series are ‘forgotten’ quickly in healthy subjects while the memory for such events is significantly prolonged in pathological conditions such as asthma (respiratory time-series) and liver cirrhosis (heart-beat time-series). The memory length was significantly higher in patients with uncontrolled asthma compared to healthy volunteers. Likewise, it was significantly higher in patients with decompensated cirrhosis compared to those with compensated cirrhosis and healthy volunteers. We also observed that the cardio-respiratory system has simple low order dynamics and short memory around its average, and high order dynamics around rare fluctuations.

Stratifying a risk for an increased variation of airway caliber among the clinically stable asthma

BACKGROUND

Recently, correlations of peak expiratory flow (PEF) variation have been shown to facilitate the prediction of later asthma symptoms and exacerbations. However, it has not been fully examined whether or not any patient characteristics are associated with the residual airway lability in treated asthmatics. The objective of this study is to examine a predictive marker for increased variation of PEF in patients with clinically stable asthma.

METHODS

We studied 297 asthmatic patients who were monitored for PEF twice a day. Asthma Control Questionnaire (ACQ), spirometry, and exhaled nitric oxide fraction (FENO) were measured. After the assessment of baseline values, PEF measuring was continued and associations between these clinical markers and later variation of PEF over a week (Min%Max) were investigated.

RESULTS

17.5% of the subjects showed increased PEF variability (Min%Max < 80%). ACQ, forced expiratory volume in 1 s % of predicted (%FEV1), and FENO were identified as independent predictors of Min%Max < 80%. An ACQ ≥ 0.4 yielded 96% sensitivity and 59% specificity, a %FEV1 ≤ 85% yielded 62% sensitivity and 89% specificity, and a FENO ≥ 40 ppb yielded 75% sensitivity and 90% specificity for identifying the subjects with high variability in PEF. When we combine %FEV1 ≤ 85% and FENO ≥ 40 ppb, this index showed the highest specificity (98%) for increased PEF variability.

CONCLUSIONS

These results indicate that ACQ, %FEV1 and FENO can stratify the risk for increased variation in airway caliber among patients with stable asthma. This may help identify subjects in whom further monitoring of lung function fluctuations is indicated.

Bronchodilator reversibility in chronic obstructive pulmonary disease: use and limitations

The change in forced expiratory volume in 1 s (FEV1) after administration of a short-acting bronchodilator has been widely used to identify patients with chronic obstructive pulmonary disease (COPD) who have a potentially different disease course and response to treatment. Despite the apparent simplicity of the test, it is difficult to interpret or rely on. Test performance is affected by the day of testing, the severity of baseline lung-function impairment, and the number of drugs given to test. Recent data suggest that the response to bronchodilators is not enhanced in patients with COPD and does not predict clinical outcomes. In this Review we will discuss the insight that studies of bronchodilator reversibility have provided into the nature of the COPD, and how the abnormal physiology seen in patients with this disorder can be interpreted.

Forecasting respiratory collapse: theory and practice for averting life-threatening infant apneas

Apnea of prematurity is a common disorder of respiratory control among preterm infants, with potentially serious adverse consequences on infant development. We review the capability for automatically assessing apnea risk and predicting apnea episodes from multimodal physiological measurements, and for using this knowledge to provide timely therapeutic intervention. We also review other, similar clinical domains of respiratory distress assessment and prediction in the hope of gaining useful insights. We propose an algorithmic framework for constructing discriminative feature vectors from physiological measurements, and for building robust and effective statistical models for apnea assessment and prediction.

Temporal asthma patterns using repeated questionnaires over 13 years in a large French cohort of women

Variable expression is one aspect of the heterogeneity of asthma. We aimed to define a variable pattern, which is relevant in general health epidemiological cohorts. Our objectives were to assess whether: 1) asthma patterns defined using simple asthma questions through repeated measurements could reflect disease variability 2) these patterns may further be classified according to asthma severity/control. Among 70,428 French women, we used seven questionnaires (1992–2005) and a comprehensive reimbursement database (2004–2009) to define three reliable asthma patterns based on repeated positive answers to the ever asthma attack question: “never asthma” (n = 64,061); “inconsistent” (“yes” followed by “no”, n = 3,514); “consistent” (fully consistent positive answers, n = 2,853). The “Inconsistent” pattern was related to both long-term (childhood-onset asthma with remission in adulthood) and short-term (reported asthma attack in the last 12 months, associated with asthma medication) asthma variability, showing that repeated questions are relevant markers of the variable expression of asthma. Furthermore, in this pattern, the number of positive responses (1992–2005) predicted asthma drug consumption in subsequent years, a marker of disease severity. The “Inconsistent” pattern is a phenotype that may capture the variable expression of asthma. Repeated answers, even to a simple question, are too often neglected.

Continuous multiorgan variability analysis to track severity of organ failure in critically ill patients

PURPOSE

The purpose of this study is to evaluate the utility of using continuous heart rate variability (HRV) and respiratory rate variability (RRV) monitoring for (a) tracking daily organ dysfunction in critically ill patients and (b) identifying patterns of variability changes during onset of shock and resolution of respiratory failure.

MATERIALS AND METHODS

Thirty-three critically ill patients experiencing respiratory and/or cardiac failure underwent continuous recording of their electrocardiogram and capnogram (CO2) waveforms from admission or intubation until discharge (maximum 14 days). HRV and RRV were computed in 5-minute overlapping windows, using Continuous Individualized Multi-organ Variability Analysis software. Multiple organ dysfunction scores were recorded daily. HRV and RRV trajectories were characterized during onset of shock and resolution of respiratory failure.

RESULTS

Both HRV and RRV decreased with increasing severity of multiple organ dysfunction scores for a variety of variability metrics. A decline in several measures of HRV and no decline in RRV were observed before onset of shock (n=6). In contrast, during resolution of respiratory failure, an increase in RRV was observed in patients who successfully passed extubation (n=12), with no change in RRV in those who subsequently failed extubation (n=2).

CONCLUSIONS

There is an association between reduced HRV and RRV and increasing organ dysfunction in critically ill patients. The significance of observing trends of decreasing HRV (with onset of shock) and increasing RRV (with resolution of respiratory failure) merits further investigation.

InSpire to Promote Lung Assessment in Youth: Evolving the Self-Management Paradigms of Young People With Asthma

Background

Asthma is the most common chronic disease in childhood, disproportionately affecting urban, minority, and disadvantaged children. Individualized care plans supported by daily lung-function monitoring can reduce morbidity and mortality. However, despite 20 years of interventions to increase adherence, only 50% of US youth accurately follow their care plans, which leads to millions of preventable hospitalizations, emergency room visits, and sick days every year. We present a feasibility study of a novel, user-centered approach to increasing young people’s lung-function monitoring and asthma self-care. Promoting Lung Assessment in Youth (PLAY) helps young people become active managers of their asthma through the Web 2.0 principles of participation, cocreation, and information sharing. Specifically, PLAY combines an inexpensive, portable spirometer with the motivational power and convenience of mobile phones and virtual-community gaming.

Objective

The objective of this study was to develop and pilot test InSpire, a fully functional interface between a handheld spirometer and an interactive game and individualized asthma-care instant-messaging system housed on a mobile phone.

Methods

InSpire is an application for mobile smartphones that creates a compelling world in which youth collaborate with their physicians on managing their asthma. Drawing from design-theory on global timer mechanics and role playing, we incentivized completing spirometry maneuvers by making them an engaging part of a game young people would want to play. The data can be sent wirelessly to health specialists and return care recommendations to patients in real-time. By making it portable and similar to applications normally desired by the target demographic, InSpire is able to seamlessly incorporate asthma management into their lifestyle.

Results

We describe the development process of building and testing the InSpire prototype. To our knowledge, the prototype is a first-of-its kind mobile one-stop shop for asthma management. Feasibility testing in children aged 7 to 14 with asthma assessed likability of the graphical user interface as well as young people’s interest in our incentivizing system. Nearly 100% of children surveyed said they would play games like those in PLAY if they involved breathing into a spirometer. Two-thirds said they would prefer PLAY over the spirometer alone, whereas 1/3 would prefer having both. No children said they would prefer the spirometer over PLAY.

Conclusions

Previous efforts at home-monitoring of asthma in children have experienced rapid decline in adherence. An inexpensive monitoring technology combined with the computation, interactive communication, and display ability of a mobile phone is a promising approach to sustainable adherence to lung-function monitoring and care plans. An exciting game that redefines the way youth conduct health management by inviting them to collaborate in their health better can be an incentive and a catalyst for more far-reaching goals.

The role of the circadian system in fractal neurophysiological control

Many neurophysiological variables such as heart rate, motor activity, and neural activity are known to exhibit intrinsic fractal fluctuations - similar temporal fluctuation patterns at different time scales. These fractal patterns contain information about health, as many pathological conditions are accompanied by their alteration or absence. In physical systems, such fluctuations are characteristic of critical states on the border between randomness and order, frequently arising from nonlinear feedback interactions between mechanisms operating on multiple scales. Thus, the existence of fractal fluctuations in physiology challenges traditional conceptions of health and disease, suggesting that high levels of integrity and adaptability are marked by complex variability, not constancy, and are properties of a neurophysiological network, not individual components. Despite the subject's theoretical and clinical interest, the neurophysiological mechanisms underlying fractal regulation remain largely unknown. The recent discovery that the circadian pacemaker (suprachiasmatic nucleus) plays a crucial role in generating fractal patterns in motor activity and heart rate sheds an entirely new light on both fractal control networks and the function of this master circadian clock, and builds a bridge between the fields of circadian biology and fractal physiology. In this review, we sketch the emerging picture of the developing interdisciplinary field of fractal neurophysiology by examining the circadian system's role in fractal regulation.

Detection of exacerbations in asthma based on electronic diary data: results from the 1-year prospective BIOAIR study

BACKGROUND

Objective measures are required that may be used as a proxy for exacerbations in asthma. The aim was to determine the sensitivity and specificity of electronic diary data to detect severe exacerbations (SEs) of asthma. A secondary aim was to identify phenotypic variables associated with a higher risk of exacerbation.

METHODS

In the BIOAIR study, 169 patients with asthma (93 severe (SA); 76 mild to moderate (MA)) recorded lung function, symptoms and medication use in electronic diaries for 1 year. Data were analysed using receiver-operator characteristics curves and related to physician-diagnosed exacerbations. Medical history and baseline clinical data were used to assess risk of exacerbation.

RESULTS

Of 122 physician-diagnosed exacerbations, 104 occurred in the SA group (1.1 per patient/year), 18 in the MA group (0.2 per patient/year) and 63 were severe using American Thoracic Society/European Respiratory Society criteria. During exacerbations, peak expiratory flow (PEF) and forced expiratory volume in 1 s significantly decreased, whereas day and night symptoms significantly increased. An algorithm combining a 20% decrease in PEF or a 20% increase in day symptoms on 2 consecutive days was able to detect SEs with 65% sensitivity and 95% specificity. The strongest risk factors for SEs were low Asthma Control Questionnaire score, sputum eosinophils ≥ 3%, body mass index >25 and low quality of life (St George's Respiratory Questionnaire), with ORs between 3.61 and 2.22 (p<0.05).

CONCLUSIONS

Regular electronic monitoring of PEF and asthma symptoms provides an acceptable sensitivity and specificity for the detection of SEs and may be suitable for personal internet-based monitoring of asthma control.

Asthma phenotyping, therapy, and prevention: what can we learn from systems biology?

Asthma has a high prevalence worldwide, and contributes significantly to the socioeconomic burden. According to a classical paradigm, asthma symptoms are attributable to an allergic, Th2-driven airway inflammation that causes airway hyperresponsiveness and results in reversible airway obstruction. Diagnosis and therapy are based mainly on these pathophysiologic concepts. However, these have increasingly been challenged by findings of recent studies, and the frequently observed failure in controlling asthma symptoms. Important recent findings are the protective "farm effect" in children, the possible prenatal mechanisms of this protection, the recognition of many different asthma phenotypes in children and adults, and the partly disappointing clinical effects of new targeted therapeutic approaches. Systems biology approaches may lead to a more comprehensive view of asthma pathophysiology and a higher success rate of new therapies. Systems biology integrates clinical and experimental data by means of bioinformatics and mathematical modeling. In general, the "-omics" approach, and the "mathematical modeling" approach can be described. Recently, several consortia have been attempting to bring together clinical and molecular data from large asthma cohorts, using novel experimental setups, biostatistics, bioinformatics, and mathematical modeling. This "systems medicine" approach to asthma will help address the different asthma phenotypes with adequate therapy and possibly preventive strategies.

Variability of respiratory mechanics during sleep in overweight and obese subjects with and without asthma

Variability of respiration may provide information regarding disease states. We sought to characterize variability of ventilation and resistance in healthy and asthma, to determine how respiratory control may be altered in sleep and with bi-level positive airway pressure (BPAP). Overweight and obese subjects with and without asthma were studied during sleep at baseline and with BPAP, while measuring respiratory system resistance (Rrs) continuously. Stable periods (>20min) of wake, NREM, and REM sleep were identified and correlation metrics of respiratory parameters were calculated, including coefficient of variation (CV). Variability of Rrs was also characterized over short time scales (20 breaths) during sleep and defined as either "leading to arousal" or "not leading to arousal". Data from 10 control and 10 subjects with asthma were analyzed. CV of Rrs was decreased in asthma at baseline (p<0.001) and decreased on BPAP as compared to baseline (p<0.001). Long time scale correlations were found in respiratory parameters, but the degree of correlations was decreased from wake to sleep (p<0.05). The variance and CV of Rrs was increased preceding an arousal from sleep at baseline; however, during BPAP, the CV was decreased and was not increased preceding arousals. At baseline, resistance was greater in those with asthma, but variability was smaller. BPAP reduced both resistance and overall variability. We conclude that the BPAP-induced decrease in variability may indicate that those with asthma are more likely to remain in a low resistance state, and that low resistance variability may reduce arousals from sleep.

A study of artifacts and their removal during forced oscillation of the respiratory system

Respiratory impedance measured by the forced oscillation technique (FOT) can be contaminated by artifacts such as coughing, vocalization, swallowing or leaks at the mouthpiece. We present a novel technique to detect these artifacts using multilevel discrete wavelet transforms. FOT was performed with artifacts introduced during separate 60 s recordings at known times in 10 healthy subjects. Brief glottal closures were generated phonetically and confirmed by nasopharyngoscopic imaging of the glottis. Artifacts were detected using Daubechies wavelets by applying a threshold to squared detail coefficients from the wavelet transforms of both pressure and flow signals. Sensitivity and specificity were compared over a range of thresholds for different level squared detail coefficients. Coughs could be identified using 1st level detail (cd1) coefficients of pressure achieving 96% sensitivity and 100% specificity while swallowing could be identified using cd2 thresholds of pressure with 95% sensitivity and 97% specificity. Male vocalizations could be identified using cd1 coefficients with 88% sensitivity and 100% specificity. For leaks at the mouthpiece, cd3 thresholds of flow could identify these events with 98% sensitivity and 99% specificity. Thus, this method provided an accurate, easy, and automated technique for detecting and removing artifacts from measurements of respiratory impedance using FOT.

Fluctuation analysis of respiratory impedance waveform in asthmatic patients: effect of airway obstruction

Fluctuation analysis has great potential to contribute to pulmonary clinical science and practice. We evaluated the relationship between asthma and the respiratory impedance recurrence period density entropy (RPDEnZrs) and the variability (SDZrs). A non-invasive and simple protocol for assessing respiratory mechanics during spontaneous breathing was used in a group of 74 subjects with various levels of airway obstruction. Airway obstruction resulted in a reduction in the RPDEnZrs that was significantly correlated with both spirometric indices of airway obstruction (R = 0.48, p < 0.0001) and mean respiratory impedance (R = -0.83, p < 0.0001). These results suggest that the impedance pattern becomes less complex in asthmatic patients, which may explain the reduction in respiratory systems' adaptability to daily life activities. Preliminary evaluations indicate that RPDEnZrs may contribute to the asthma diagnosis, presenting accuracies of 82 and 87 % in patients with moderate and severe airway obstruction, respectively. On the other hand, SDZrs increased with obstruction (p < 0.0001) and was inversely correlated with spirometric indices of obstruction (R = -0.42, p = 0.0003) and directly associated with mean impedance (R = 0.88, p < 0.0001). This analysis contributes to elucidate previous studies and identified respiratory changes in patients with moderate and severe obstruction with an adequate accuracy (85 and 87 %, respectively).

Day-to-day variability of oscillatory impedance and spirometry in asthma and COPD

Variability in airway function may be a marker of disease activity in COPD and asthma. The aim was to determine the effects of repeatability and airway obstruction on day-to-day variability in respiratory system resistance (Rrs) and reactance (Xrs) measured by forced oscillation technique (FOT). Three groups of 10 subjects; normals, stable asthmatic and stable COPD subjects underwent daily FOT recordings for 7 days. Mean total and inspiratory Rrs and Xrs, and expiratory flow limitation (EFL) Index (inspiratory - expiratory Xrs), were calculated. The ICC's were high for all parameters in all groups. Repeatability, in terms of absolute units, correlated with airway obstruction and was therefore lowest in COPD. Day-to-day variability was due mostly to repeatability, with a small contribution from the mean value for some parameters. FOT measures are highly repeatable in health, stable asthma and COPD in relation to the wide range of measures between subjects. For home monitoring in asthma and COPD, either the coefficient of variation or individualized SDs could be used to define day-to-day variability.

U.S. and European severe asthma cohorts: what can they teach us about severe asthma?

Asthma is a global health problem affecting around 300 million patients of all ages and ethnic groups in all countries around the world. In the majority of subjects with persistent, mild-to-moderate asthma (MA), the disease can be relatively well controlled by the use of currently available medications; however, five to ten per cent of patients suffer from a particularly severe disease that is poorly controlled clinically and often refractory to usual treatment. Improved care of severe asthma (SA) is a major unmet medical need and several international consortia aim at improving our understanding of mechanisms in SA. To manage SA better, standardized definitions and concepts of asthma severity, risk and level of control are critical. In the following sections, we present several guidelines approaches and definitions followed by an overview of U.S. (SARP) and European (ENFUMOSA, BIOAIR, U-BIOPRED) SA networks. Key findings regarding SA phenotypes, risk factors and pathophysiology are discussed. International cooperation in the area of respiratory diseases, including SA, across the Atlantic Ocean, will lead to a better understanding of asthma pathology, especially of those severe, not well controlled or difficult-to-treat cases.