Deep inspiration avoidance and airway response to methacholine: Influence of body mass index

Allergic Diseases and Childhood Obesity: A Detrimental Link?

Several epidemiological studies have described childhood obesity as a risk factor for atopic disease, particularly asthma. At the same time, this association seems to be more conflicting for allergic rhinitis, atopic dermatitis, and chronic urticaria. This article aims to deepen the possibility of a relationship between childhood obesity and allergic diseases. As regards asthma, the mechanical and inflammatory effects of obesity can lead to its development. In addition, excess adiposity is associated with increased production of inflammatory cytokines and adipokines, leading to low-grade systemic inflammation and an increased risk of asthma exacerbations. Allergic rhinitis, atopic dermatitis, food allergies, and chronic urticaria also seem to be related to this state of chronic low-grade systemic inflammation typical of obese children. Vitamin D deficiency appears to play a role in allergic rhinitis, while dyslipidemia and skin barrier defects could explain the link between obesity and atopic dermatitis. Starting from this evidence, it becomes of fundamental importance to act on body weight control to achieve general and allergic health, disentangling the detrimental link between obesity allergic diseases and childhood obesity. Further studies on the association between adiposity and atopy are needed, confirming the biologically active role of fat tissue in the development of allergic diseases and exploring the possibility of new therapeutic strategies.

Role of small airway dysfunction in unexplained exertional dyspnoea

Background

Isolated small airway abnormalities may be demonstrable at rest in patients with normal spirometry; however, the relationship of these abnormalities to exertional symptoms remains uncertain. This study uses an augmented cardiopulmonary exercise test (CPET) to include evaluation of small airway function during and following exercise to unmask abnormalities not evident with standard testing in individuals with dyspnoea and normal spirometry.

Methods

Three groups of subjects were studied: 1) World Trade Center (WTC) dust exposure (n=20); 2) Clinical Referral (n=15); and Control (n=13). Baseline evaluation included respiratory oscillometry. Airway function during an incremental workload CPET was assessed by: 1) tidal flow versus volume curves during exercise to assess for dynamic hyperinflation and expiratory flow limitation; and 2) post-exercise spirometry and oscillometry to evaluate for airway hyperreactivity.

Results

All subjects demonstrated normal baseline forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC). Dyspnoea was reproduced during CPET in WTC and Clinical Referral groups versus Control without abnormality in respiratory pattern and minute ventilation. Tidal flow-volume curves uncovered expiratory flow limitation and/or dynamic hyperinflation with increased prevalence in WTC and Clinical Referral versus Control (55%, 87% versus 15%; p<0.001). Post-exercise oscillometry uncovered small airway hyperreactivity with increased prevalence in WTC and Clinical Referral versus Control (40%, 47% versus 0%, p<0.05).

Conclusions

We uncovered mechanisms for exertional dyspnoea in subject with normal spirometry that was attributable to either small airway dysfunction during exercise and/or small airway hyperreactivity following exercise. The similarity of findings in WTC environmentally exposed and clinically referred cohorts suggests broad relevance for these evaluations.

Obesity in women with asthma: Baseline disadvantage plus greater small-airway responsiveness

BACKGROUND

Obesity is known to diminish lung volumes and worsen asthma. However, mechanistic understanding is lacking, especially as concerns small-airway responsiveness. The objective of this study was therefore to compare small-airway responsiveness, as represented by the change in expiratory:inspiratory mean lung density ratios (MLD_e/i , as determined by computed tomography [CT]) throughout methacholine testing in obese versus non-obese women with asthma.

METHODS

Thoracic CT was performed during methacholine bronchoconstriction challenges to produce standardized response curves (SRC: response parameter versus ln[1 + % PD20], where PD20 is the cumulative methacholine dose) for 31 asthma patients (n = 18 non-obese and n = 13 obese patients). Mixed models evaluated obesity effects and interactions on SRCs while adjusting for age and bronchial morphology. Small airway responsiveness as represented by SRC slope was calculated for each third of the MLD_e/i response and compared between groups.

RESULTS

Obesity-associated effects observed during experimental bronchoconstriction included: (i) a significant baseline effect for forced expiratory volume in 1 second with lower values for the obese (73.11 ± 13.44) versus non-obese (82.19 ± 8.78; p = 0.002) groups prior to methacholine testing and (ii) significantly higher responsiveness in small airways as estimated via differences in MLD_e/i slopes (group×ln(1 + % PD20 interaction; p = 0.023). The latter were pinpointed to higher slopes in the obese group at the beginning 2/3 of SRCs (p = 0.004 and p = 0.021). Significant obesity effects (p = 0.035 and p = 0.008) indicating lower forced vital capacity and greater % change in MLD_e/I (respectively) throughout methacholine testing, were also observed.

CONCLUSION

In addition to baseline differences, small-airway responsiveness (as represented by the change in MLD_e/i ) during methacholine challenge is greater in obese women with asthma as compared to the non-obese.

Increased Abdominal Perimeter Differently Affects Respiratory Function in Men and Women

Obesity is a worldwide epidemic being the main cause of cardiovascular, metabolic disturbances and chronic pulmonary diseases. The increase in body weight may affect the respiratory system due to fat deposition and systemic inflammation. Herein, we evaluated the sex differences in the impact of obesity and high abdominal circumference on basal ventilation. Thirty-five subjects, 23 women and 12 men with a median age of 61 and 67, respectively, were studied and classified as overweight and obese according to body mass index (BMI) and were also divided by the abdominal circumference. Basal ventilation, namely, respiratory frequency, tidal volume, and minute ventilation, was evaluated. In normal and overweight women, basal ventilation did not change, but obese women exhibited a decrease in tidal volume. In men, overweight and obese subjects did not exhibit altered basal ventilation. In contrast, when subjects were subdivided based on the abdominal perimeter, a higher circumference did not change the respiratory frequency but induced a decrease in tidal volume and minute ventilation in women, while in men these two parameters increased. In conclusion, higher abdominal circumference rather than BMI is associated with alterations in basal ventilation in women and men.

Paucigranulocytic Asthma: Potential Pathogenetic Mechanisms, Clinical Features and Therapeutic Management

Asthma is a heterogeneous disease usually characterized by chronic airway inflammation, in which several phenotypes have been described, related to the age of onset, symptoms, inflammatory characteristics and treatment response. The identification of the inflammatory phenotype in asthma is very useful, since it allows for both the recognition of the asthmatic triggering factor as well as the optimization of treatment The paucigranulocytic phenotype of asthma (PGA) is characterized by sputum eosinophil levels <1−3% and sputum neutrophil levels < 60%. The precise characteristics and the pathobiology of PGA are not fully understood, and, in some cases, it seems to represent a previous eosinophilic phenotype with a good response to anti-inflammatory treatment. However, many patients with PGA remain uncontrolled and experience asthmatic symptoms and exacerbations, irrespective of the low grade of airway inflammation. This observation leads to the hypothesis that PGA might also be either a special phenotype driven by different kinds of cells, such as macrophages or mast cells, or a non-inflammatory phenotype with a low grade of eosinophilic inflammation. In this review, we aim to describe the special characteristics of PGA and the potential therapeutic interventions that could be offered to these patients.

Paediatric obesity-related asthma: Disease burden and effects on pulmonary physiology

The prevalence of asthma and obesity in children has been steadily increasing globally over the past several decades, with increased concern in low and middle income countries. In this review, we summarize the current literature on these two parallel epidemics and explore the relationship between paediatric obesity and asthma in the paediatric population. Finally, we focus on the current literature as it relates to underlying physiologic alterations and changes in pulmonary function for children with obesity and asthma.

Asthma and Lung Mechanics

This article will discuss in detail the pathophysiology of asthma from the point of view of lung mechanics. In particular, we will explain how asthma is more than just airflow limitation resulting from airway narrowing but in fact involves multiple consequences of airway narrowing, including ventilation heterogeneity, airway closure, and airway hyperresponsiveness. In addition, the relationship between the airway and surrounding lung parenchyma is thought to be critically important in asthma, especially as related to the response to deep inspiration. Furthermore, dynamic changes in lung mechanics over time may yield important information about asthma stability, as well as potentially provide a window into future disease control. All of these features of mechanical properties of the lung in asthma will be explained by providing evidence from multiple investigative methods, including not only traditional pulmonary function testing but also more sophisticated techniques such as forced oscillation, multiple breath nitrogen washout, and different imaging modalities. Throughout the article, we will link the lung mechanical features of asthma to clinical manifestations of asthma symptoms, severity, and control. © 2020 American Physiological Society. Compr Physiol 10:975-1007, 2020.

Mechanisms and therapeutic strategies for non-T2 asthma

Non-T2 asthma is traditionally defined as asthma without features of T2 asthma. The definition is arbitrary and is generally based on the presence of neutrophils in sputum, or the absence (or normal levels) of eosinophils or other T2 markers in sputum (paucigranulocytic), airway biopsies or in blood. This definition may be imprecise as we gain more knowledge from applying transcriptomics and proteomics to blood and airway samples. The prevalence of non-T2 asthma is also difficult to estimate as most studies are cross-sectional and influenced by concomitant treatment with glucocorticosteroids, and by the presence of recognized or unrecognized airway infections. No specific therapies have shown any clinical benefits in patients with asthma that is associated with a non-T2 inflammatory process. It remains to be seen if such an endotype truly exists and to identify treatments to target that endotype. Meanwhile, identifying intense airway neutrophilia as an indicator of airway infection and airway hyperresponsiveness as an indicator of smooth muscle dysfunction, and treating them appropriately, and not increasing glucocorticosteroids in patients who do not have obvious T2 inflammation, seem reasonable.

Shortening of airway smooth muscle is modulated by prolonging the time without simulated deep inspirations in ovine tracheal strips

The shortening of airway smooth muscle (ASM) is greatly affected by time. This is because stimuli affecting ASM shortening, such as bronchoactive molecules or the strain inflicted by breathing maneuvers, not only alter quick biochemical processes regulating contraction but also slower processes that allow ASM to adapt to an ever-changing length. Little attention has been given to the effect of time on ASM shortening. The present study investigates the effect of changing the time interval between simulated deep inspirations (DIs) on ASM shortening and its responsiveness to simulated DIs. Excised tracheal strips from sheep were mounted in organ baths and either activated with methacholine or relaxed with isoproterenol. They were then subjected to simulated DIs by imposing swings in distending stress, emulating a transmural pressure from 5 to 30 cmH₂O. The simulated DIs were intercalated by 2, 5, 10, or 30 min. In between simulated DIs, the distending stress was either fixed or oscillating to simulate tidal breathing. The results show that although shortening was increased by prolonging the interval between simulated DIs, the bronchodilator effect of simulated DIs (i.e., the elongation of the strip post- vs. pre-DI) was not affected, and the rate of re-shortening post-simulated DIs was decreased. As the frequency with which DIs are taken increases upon bronchoconstriction, our results may be relevant to typical alterations observed in asthma, such as an increased rate of re-narrowing post-DI.NEW & NOTEWORTHY The frequency with which patients with asthma take deep inspirations (DIs) increases during bronchoconstriction. This in vitro study investigated the effect of changing the time interval between simulated DIs on airway smooth muscle shortening. The results demonstrated that decreasing the interval between simulated DIs not only decreases shortening, which may be protective against excessive airway narrowing, but also increases the rate of re-shortening post-simulated DIs, which may contribute to the increased rate of re-narrowing post-DI observed in asthma.

[The impact of obesity on respiratory function]

The respiratory impact of obesity can be both symptomatic (resting and exertional breathlessness) and functional (pulmonary function at rest and on exercise). The prevalence of breathlessness is increased in adult obese individuals, ∼50% at rest and ∼75% on exertion (mMRC score>0). Pulmonary function abnormalities in obese adults include reduced functional residual capacity (FRC) and expiratory residual volume (ERV), and less frequently reduced total lung capacity (a restrictive defect, with TLC below the 5th percentile of predicted is present in around 15% in severe obese adults), with normal residual volume (RV). Airflows are barely affected by obesity, but bronchial hyperresponsiveness (BHR) is very prevalent, which may be due to the loss of bronchoprotective effect of deep inspiration in obesity (mechanical pathophysiology of BHR). In children, the modifications of lung volumes seen are quite different: TLC is normal while FRC and RV are reduced, explaining the increase in FVC. FEV1/FVC is therefore reduced by obesity, without true airflow obstruction (dysanaptic growth). Resting oxygen consumption (V'O₂) is increased due to obesity and normally increases with exercise. Maximum V'O₂ is normal or weakly reduced in obese patients; on the other hand, the increase in respiratory load increases the oxygen cost of ventilation, which tends to be rapid, both at rest and during exertion. Finally, it should be noted that there is only limited statistical correlation between exercise dyspnoea and respiratory function abnormalities in obesity.

Association of pediatric obesity and asthma, pulmonary physiology, metabolic dysregulation, and atopy; and the role of weight management

Introduction: Obesity affects about 40% of US adults and 18% of children. Its impact on the pulmonary system is best described for asthma. Areas covered: We reviewed the literature on PubMed and Google Scholar databases and summarize the effect of obesity, its associated metabolic dysregulation and altered systemic immune responses, and that of weight gain and loss on pulmonary mechanics, asthma inception, and disease burden. We include a distinct approach for diagnosing and managing the disease, including pulmonary function deficits inherent to obesity-related asthma, in light of its poor response to current asthma medications. Expert opinion: Given the projected increase in obesity, obesity-related asthma needs to be addressed now. Research on the contribution of metabolic abnormalities and systemic immune responses, intricately linked with truncal adiposity, and that of lack of atopy, to asthma disease burden, and pulmonary function deficits among obese children is fairly consistent. Since current asthma medications are more effective for atopic asthma, investigation for atopy will guide management by distinguishing asthma responsive to current medications from the non-responsive disease. Future research is needed to elucidate mechanisms by which obesity-mediated metabolic abnormalities and immune responses cause medication non-responsive asthma, which will inform repurposing of medications and drug discovery.

The Strain on Airway Smooth Muscle During a Deep Inspiration to Total Lung Capacity

The deep inspiration (DI) maneuver entices a great deal of interest because of its ability to temporarily ease the flow of air into the lungs. This salutary effect of a DI is proposed to be mediated, at least partially, by momentarily increasing the operating length of airway smooth muscle (ASM). Concerningly, this premise is largely derived from a growing body of in vitro studies investigating the effect of stretching ASM by different magnitudes on its contractility. The relevance of these in vitro findings remains uncertain, as the real range of strains ASM undergoes in vivo during a DI is somewhat elusive. In order to understand the regulation of ASM contractility by a DI and to infer on its putative contribution to the bronchodilator effect of a DI, it is imperative that in vitro studies incorporate levels of strains that are physiologically relevant. This review summarizes the methods that may be used in vivo in humans to estimate the strain experienced by ASM during a DI from functional residual capacity (FRC) to total lung capacity (TLC). The strengths and limitations of each method, as well as the potential confounders, are also discussed. A rough estimated range of ASM strains is provided for the purpose of guiding future in vitro studies that aim at quantifying the regulatory effect of DI on ASM contractility. However, it is emphasized that, owing to the many limitations and confounders, more studies will be needed to reach conclusive statements.

Interval between simulated deep inspirations on the dynamics of airway smooth muscle contraction in guinea pig bronchi

A certain amount of time is required to achieve a maximal contraction from airway smooth muscle (ASM) and stretches of substantial magnitude, such as the ones imparted by deep inspirations (DIs), interfere with contraction. The duration of ASM contraction without interference may thus affect its shortening, its mechanical response to DIs and the overall toll it exerts on the respiratory system. In this study, the effect of changing the interval between DIs on the dynamics of ASM was examined in vitro. Isolated bronchi derived from guinea pigs were held isotonically and stimulated to both contract and relax, in a randomized order, in response to 10^-5 M of methacholine and 10^-6 M of isoproterenol, respectively. Interference to ASM was inflicted after 2, 5, 10 and 30 min in a randomized order, by imposing a stretch that simulated a DI. The shortening before the stretch, the stiffness before and during the stretch, the post-stretch elongation of ASM and the ensuing re-shortening were measured. These experiments were also performed in the presence of simulated tidal breathing achieved through force fluctuations. The results demonstrate that, with or without force fluctuations, increasing the interval between simulated DIs increased shortening and post-stretch elongation, but not stiffness and re-shortening. These time-dependent effects were not observed when ASM was held in the relaxed state. These findings may help understand to which extent ASM shortening and the regulatory effect of DI are affected by changing the interval between DIs. The potential consequences of these findings on airway narrowing are also discussed.

[Guidelines for methacholine provocation testing]

Bronchial challenge with the direct bronchoconstrictor agent methacholine is commonly used for the diagnosis of asthma. The "Lung Function" thematic group of the French Pulmonology Society (SPLF) elaborated a series of guidelines for the performance and the interpretation of methacholine challenge testing, based on French clinical guideline methodology. Specifically, guidelines are provided with regard to the choice of judgment criteria, the management of deep inspirations, and the role of methacholine bronchial challenge in the care of asthma, exercise-induced asthma, and professional asthma.

Receptor for advanced glycation end-products and World Trade Center particulate induced lung function loss: A case-cohort study and murine model of acute particulate exposure

World Trade Center-particulate matter(WTC-PM) exposure and metabolic-risk are associated with WTC-Lung Injury(WTC-LI). The receptor for advanced glycation end-products (RAGE) is most highly expressed in the lung, mediates metabolic risk, and single-nucleotide polymorphisms at the AGER-locus predict forced expiratory volume(FEV). Our objectives were to test the hypotheses that RAGE is a biomarker of WTC-LI in the FDNY-cohort and that loss of RAGE in a murine model would protect against acute PM-induced lung disease. We know from previous work that early intense exposure at the time of the WTC collapse was most predictive of WTC-LI therefore we utilized a murine model of intense acute PM-exposure to determine if loss of RAGE is protective and to identify signaling/cytokine intermediates. This study builds on a continuing effort to identify serum biomarkers that predict the development of WTC-LI. A case-cohort design was used to analyze a focused cohort of male never-smokers with normal pre-9/11 lung function. Odds of developing WTC-LI increased by 1.2, 1.8 and 1.0 in firefighters with soluble RAGE (sRAGE)≥97pg/mL, CRP≥2.4mg/L, and MMP-9≤397ng/mL, respectively, assessed in a multivariate logistic regression model (ROCAUC of 0.72). Wild type(WT) and RAGE-deficient(Ager-/-) mice were exposed to PM or PBS-control by oropharyngeal aspiration. Lung function, airway hyperreactivity, bronchoalveolar lavage, histology, transcription factors and plasma/BAL cytokines were quantified. WT-PM mice had decreased FEV and compliance, and increased airway resistance and methacholine reactivity after 24-hours. Decreased IFN-γ and increased LPA were observed in WT-PM mice; similar findings have been reported for firefighters who eventually develop WTC-LI. In the murine model, lack of RAGE was protective from loss of lung function and airway hyperreactivity and was associated with modulation of MAP kinases. We conclude that in a multivariate adjusted model increased sRAGE is associated with WTC-LI. In our murine model, absence of RAGE mitigated acute deleterious effects of PM and may be a biologically plausible mediator of PM-related lung disease.

Asthma and obesity: mechanisms and clinical implications

Obesity is the most common asthma co-morbidity; it has been associated with increased risk for asthma exacerbations, worse respiratory symptoms and poor control. The exact mechanisms remain elusive and are probably multifactorial, stemming from mechanical alterations of the airways and lung parenchyma, to systemic and airway inflammatory and metabolic dysregulation that adversely influences lung function and or response to therapy. However, the fact that not every obese asthmatic is equally affected by weight gain highlights the many challenges and complexities in understanding this association. The factors that determine susceptibility may not depend on being obese alone, but rather the interactions with other phenotypical characteristics, such as age of asthma onset, gender and race to name a few. Inability to account for asthma phenotypes that are differentially affected by increasing body mass index (BMI) may contribute to the lack of consistent results across studies. This review will provide a succinct summary of obesity-related mechanisms and the clinical impact on asthma including highlights on recent progress.

Deep inspiration and the emergence of ventilation defects during bronchoconstriction: a computational study

Deep inspirations (DIs) have a dilatory effect on airway smooth muscle (ASM) that helps to prevent or reduce more severe bronchoconstriction in healthy individuals. However, this bronchodilation appears to fail in some asthmatic patients or under certain conditions, and the reason is unclear. Additionally, quantitative effects of the frequency and magnitude of DIs on bronchodilation are not well understood. In the present study, we used a computational model of bronchoconstriction to study the effects of DI volumes, time intervals between intermittent DIs, relative speed of ASM constriction, and ASM activation on bronchoconstriction and the emergence of ventilation defects (VDefs). Our results showed a synergistic effect between the volume of DIs and the time intervals between them on bronchoconstriction and VDefs. There was a domain of conditions with sufficiently large volumes of DIs and short time intervals between them to prevent VDefs. Among conditions without VDefs, larger volumes of DIs resulted in greater airway dilation. Similarly, the time interval between DIs, during which the activated ASM re-constricts, affected the amplitude of periodic changes in airway radii. Both the relative speed of ASM constriction and ASM activation affected what volume of DIs and what time interval between them could prevent the emergence of VDefs. In conclusion, quantitative characteristics of DIs, such as their volume and time interval between them, affect bronchoconstriction and may contribute to difficulties in asthma. Better understanding of the quantitative aspects of DIs may result in novel or improved therapeutic approaches.

Role of weight management in asthma symptoms and control

Obesity and asthma have increasingly been linked with an increased risk of developing asthma associated with increasing body mass index. Overweight/obese patients with asthma have more symptoms, poor asthma control, and decreased response to conventional asthma therapies. Weight loss may be associated with improvements in asthma control, response to medications, and overall asthma-related quality of life. This article discusses the effect of weight loss via dietary modifications and surgical interventions on asthma symptoms and control. Weight loss should be encouraged as a means of improving asthma control but there are insufficient data to recommend surgical interventions solely for this purpose.

Airway-parenchymal interdependence

In this article, we discuss the interaction of the lung parenchyma and the airways as well as the physiological and pathophysiological significance of this interaction. These two components of the respiratory organ can be thought of as two independent elastic structures but in fact the mechanical properties of one influence the behavior of the other. Traditionally, the interaction has focused on the effects of the lung on the airways but there is good evidence that the opposite is also true, that is, that the mechanical properties of the airways influence the elastic properties of the parenchyma. The interplay between components of the respiratory system including the airways, parenchyma, and vasculature is often referred to as "interdependence." This interdependence transmits the elastic recoil of the lung to create an effective pressure that dilates the airways as transpulmonary pressure and lung volume increase. By using a continuum mechanics analysis of the lung parenchyma, it is possible to predict the effective pressure between the airways and parenchyma, and these predictions can be empirically evaluated. Normal airway caliber is maintained by this pressure in the adventitial interstitium of the airway, and it attenuates the ability of airway smooth muscle to narrow airways. Interdependence has physiological and pathophysiological significance. Weakening of the forces of interdependence contributes to airway dysfunction and gas exchange impairment in acute and chronic airway diseases including asthma and emphysema.

Environmental perturbations: Obesity

Obesity currently affects about one-third of the U.S. population, while another one-third is overweight. The importance of obesity for certain conditions such as heart disease and type 2 diabetes is well appreciated. The effects of obesity on the respiratory system have received less attention and are the subject of this article. Obesity alters the static mechanical properties of the respiratory system leading to a reduction in the functional residual capacity (FRC) and the expiratory reserve volume (ERV). There is substantial variability in the effects of obesity on FRC and ERV, at least some of which is related to the location rather than the total mass of adipose tissue. Obesity also results in airflow obstruction, which is only partially attributable to breathing at low lung volume, and can also promote airway hyperresponsiveness and asthma. Hypoxemia is common is obesity and correlates well with FRC, as well as with measures of abdominal obesity. However, obese subjects are usually eucapnic, indicating that hypoventilation is not a common cause of their hypoxemia. Instead, hypoxemia results from ventilation-perfusion mismatch caused by closure of dependent airways at FRC. Many obese subjects complain of dyspnea either at rest or during exertion, and the dyspnea score also correlates with reductions in FRC and ERV. Weight reduction should be encouraged in any symptomatic obese individual, since virtually all of the respiratory complications of obesity improve with even moderate weight loss.

Asthma and obesity

The prevalence and incidence of asthma have increased among obese children and adults, particularly among women. Obesity seems to be a predisposing factor for the development of asthma, but the underlying mechanisms of its influence are still uncertain. Various hypotheses have been proposed to explain the link between obesity and asthma such as a common genetic predisposition, developmental changes, altered lung mechanics, the presence of a systemic inflammatory process, and an increased prevalence of associated comorbid conditions. Over-diagnosis of asthma does not seem to be more frequent in obese compared to non-obese subjects, but the added effects of obesity on respiratory symptoms can affect asthma control assessment. Obesity can make asthma more difficult to control and is associated with a reduced beneficial effect of asthma medications. This could be due to a change in asthma phenotype, particularly evidenced as a less eosinophilic type of airway inflammation combined to the added effects of changes in lung mechanics. Weight loss is associated with a universal improvement of asthma and should be part of asthma management in the obese patient. Additional research should be conducted to better determine how obesity influences the development and clinical expression of asthma, establish the optimal management of asthma in this population and determine how obesity affects long-term asthma outcomes in these patients.

Obesity and asthma: physiological perspective

Obesity induces some pertinent physiological changes which are conducive to either development of asthma or cause of poorly controlled asthma state. Obesity related mechanical stress forces induced by abdominal and thoracic fat generate stiffening of the lungs and diaphragmatic movements to result in reduction of resting lung volumes such as functional residual capacity (FRC). Reduced FRC is primarily an outcome of decreased expiratory reserve volume, which pushes the tidal breathing more towards smaller high resistance airways, and consequentially results in expiratory flow limitation during normal breathing in obesity. Reduced FRC also induces plastic alteration in the small collapsible airways, which may generate smooth muscle contraction resulting in increased small airway resistance, which, however, is not picked up by spirometric lung volumes. There is also a possibility that chronically reduced FRC may generate permanent adaptation in the very small airways; therefore, the airway calibres may not change despite weight reduction. Obesity may also induce bronchodilator reversibility and diurnal lung functional variability. Obesity is also associated with airway hyperresponsiveness; however, the mechanism of this is not clear. Thus, obesity has effects on lung function that can generate respiratory distress similar to asthma and may also exaggerate the effects of preexisting asthma.

Risk factors for airway hyperresponsiveness in severely obese women

Obesity affects airway diameter and tidal ventilation pattern, which could perturb smooth muscle function. The objective was to assess the pathophysiology of airway hyperresponsiveness in obesity while controlling for gastro-oesophageal reflux disease. Obese women (n=118, mean±SD BMI 46.1±6.8kg/m(-2)) underwent pulmonary function testing (including tidal ventilation monitoring and methacholine challenge) and oesogastro-duodenal fibroscopy. Fifty-seven women (48%, 95% CI: 39-57%) exhibited hyperresponsiveness (dose-response slope ≥2.39% decrease/μmol) that was independently and positively correlated with predicted % FRC, Raw0.5 and negatively correlated with sigh frequency during tidal ventilation. Obese women had an increased breathing frequency but a similar sigh frequency than healthy lean women (n=30). Twenty-two obese women (19%, 95% CI: 12-26%) were classified as asthmatics (hyperresponsiveness and suggestive symptoms) without confounding effect of gastro-oesophageal reflux disease. In conclusion, in women referred for bariatric surgery, unloading of bronchial smooth muscle (reduced airway calibre and sigh frequency) is associated with hyperresponsiveness.

Effect of bariatric surgery on airway response and lung function in obese subjects with asthma

BACKGROUND

Obesity is a risk factor for self-reported asthma and makes asthma management more difficult. The effects of bariatric surgery on asthma in severely obese subjects remain to be documented.

METHODS

In this prospective study, 12 asthmatic patients with severe obesity were evaluated before, 6 and 12 months after bariatric surgery. Each had methacholine inhalation tests, measures of expiratory flows and lung volumes, measurements of C-reactive protein and questionnaires on asthma medication, asthma symptoms and co-morbid conditions. Eleven severely obese patients with asthma (considered as controls) underwent the same evaluations. Primary endpoint was airway responsiveness to methacholine and secondary endpoints were lung volumes and markers of systemic inflammation.

RESULTS

Mean body mass index decreased from 51.2 to 34.4 kg/m(2) twelve months post-surgery. Mean PC(20) methacholine improved from 0.84 to 6.2 mg/ml (P < 0.001); FEV(1), FVC, FRC, FRC/TLC and ERV all improved (P ≤ 0.006). C-reactive protein decreased from 8.6 to 1.7 mg/L (P < 0.001) Asthma symptoms total score was significantly reduced (P = 0.03) and asthma medication needs decreased, ten patients being able to stop all asthma drugs. No significant changes of these parameters from baseline were observed in asthmatic controls. Improvements in airway responsiveness and lung volumes happened in parallel and correlated with reductions of body mass index (r = 0.58, P = 0.049), C-reactive protein levels (r = -0.74, P = 0.004).

CONCLUSION

Airway responsiveness, lung volumes and asthma severity/control markedly improved with weight loss following bariatric surgery in severely obese patients.

Obesity, metabolic dysregulation and oxidative stress in asthma

BACKGROUND

Epidemiological data demonstrate an increased risk of developing incident asthma with increasing adiposity. While the vast majority of studies support the interaction between obesity and asthma, the causality is unclear.

SCOPE OF REVIEW

This article will review the current literature supporting the presence of an obese asthma phenotype and the possible mechanisms mediating the effects of obesity on asthma.

MAJOR CONCLUSIONS

Obesity is associated with poor asthma control, altered responsiveness to medications and increased morbidity. Obesity is characterized by systemic inflammation that may result in increased airway inflammation. However, this assertion is not supported by current studies that demonstrate a lack of significant airway inflammation in obese asthmatics. In spite this observation one must consider limitations of these studies including the fact that most subjects were treated with inhaled corticosteroids that would likely alter inflammation in the lung. Thus, it remains unclear if obesity is associated with alterations in inflammation in the airways of subjects with asthma. Hormones such as leptin and adiponectin are affected by obesity and may play a role in mediating innate immune responses and allergic responses, respectively. The role of oxidative stress remains controversial and the current evidence suggests that while oxidative stress is important in asthma, it does not fully explain the characteristics associated with this unique phenotype.

GENERAL SIGNIFICANCE

Obesity related asthma is associated with increased morbidity and differential response to asthma therapies. Understanding the mechanisms mediating this phenotype would have significant implications for millions of people suffering with asthma. This article is part of a Special Issue entitled Biochemistry of Asthma.

Impaired response to deep inspiration in obesity

Deep inspirations modulate airway caliber and airway closure and their effects are impaired in asthma. The association between asthma and obesity raises the question whether the deep inspiration (DI) effect is also impaired in the latter condition. We assessed the DI effects in obese and nonobese nonasthmatics. Thirty-six subjects (17 obese, 19 nonobese) underwent routine methacholine (Mch) challenge and 30 of them also had a modified bronchoprovocation in the absence of DIs. Lung function was monitored with spirometry and forced oscillation (FO) [resistance (R) at 5 Hz (R5), at 20 Hz (R20), R5-R20 and the integrated area of low-frequency reactance (AX)]. The response to Mch, assessed with area under the dose-response curves (AUC), was consistently greater in the routine challenge in the obese (mean ± SE, obese vs. nonobese AUC: R5: 15.7 ± 2.3 vs. 2.4 ± 2.0, P < 0.0005; R20: 5.6 ± 1.4 vs. 1.4 ± 1.2, P = 0.027; R5-R20: 10.2 ± 1.6 vs. 0.9 ± 0.1.4, P < 0.0005; AX: 115.6 ± 22.0 vs. 1.5 ± 18.9, P < 0.0005), but differences between groups in the modified challenge were smaller, indicating reduced DI effects in obesity. Given that DI has bronchodilatory and bronchoprotective effects, we further assessed these components separately. In the obese subjects, DI prior to Mch enhanced Mch-induced bronchoconstriction, but DI after Mch resulted in bronchodilation that was of similar magnitude as in the nonobese. We conclude that obesity is characterized by increased Mch responsiveness, predominantly of the small airways, due to a DI effect that renders the airways more sensitive to the stimulus.

A deep breath bronchoconstricts obese asthmatics

BACKGROUND

Asthma is characterized by the loss of a deep breath (DB)-induced bronchodilation and bronchoprotection. Obesity causes lung restriction and increases airway resistance, which may further worsen the capacity of a DB to induce bronchodilation; however, whether increasing BMI impairs the bronchodilatory response to a DB in asthmatics is unknown.

METHODS

The population consisted of 99 subjects, 87 with moderate to severe persistent asthma and 12 obese control subjects. Using transfer impedance we derived airway resistance (Raw). Participants breathed for 1 minute and took a slow DB followed by passive exhalation to functional residual capacity (FRC) and tidal breathing for another minute.

RESULTS

After a DB, obese asthmatics had the largest percent increase in Raw (median 9.8% interquartile range [IQR] 3.1-15.1), compared with overweight (6.5% IQR -1.3, 12.1) and lean (0.7% IQR -3, 7.9) asthmatics and obese controls (2.5% IQR -.6, 11) (p for trend = 0.008). The association between the percent increase in Raw after a DB and BMI as a continuous variable was significant (p = 0.02).

CONCLUSIONS

In obese, moderate to severe and poorly controlled asthmatics, a DB results in increased Raw. This phenomenon was not observed in leaner asthmatics of similar severity or in obese control subjects.

Asthma and obesity in childhood: on the road ahead

Epidemiological data show a link between asthma and obesity, suggesting many different mechanisms that may underlie the association. However, diagnosis of asthma is often self-reported by patients or caregivers. Definition of asthma is crucial, particularly in childhood. Obesity can be associated with symptoms commonly attributed to asthma, such as wheezing, dyspnoea and sleep apnoea. Obese subjects are less fit and may have more frequent bouts of breathlessness on exertion accompanied by an exaggerated symptom perception. Therefore, the link between the two diseases should be analysed by focusing not only on reported diagnosis of asthma but also on objective markers that can better characterize the asthma phenotype. These markers should include lung function parameters, bronchial hyper-reactivity, atopic sensitization and indices of lung inflammation. As we look back and move forward, a multidisciplinary approach is increasingly necessary to understand the complexity of obesity and asthma, keeping in mind that diet and exercise could influence both diagnosis and treatment. In the meantime, in clinical settings, physicians should be cautious about diagnosing asthma in obese children on the basis of self-reported symptoms alone and should confirm the diagnosis by using objective measurements and marker evaluations that can better identify asthma phenotype and exclude overdiagnosis.

Effects of obesity on perceptual and mechanical responses to bronchoconstriction in asthma

RATIONALE

The influence of obesity on the perception of respiratory discomfort during acute bronchoconstriction in asthma is unknown.

OBJECTIVES

We hypothesized that the respiratory impairment associated with an increased body mass index (BMI) would predispose to greater perceived symptom intensity during acute airway narrowing. We therefore compared relationships between induced changes in dyspnea intensity and lung function during methacholine (MCh) bronchoprovocation in obese (OBA) and normal-weight (NWA) individuals with asthma of mild to moderate severity.

METHODS

High-dose MCh challenge tests to a maximum 50% decrease in FEV(1) were conducted in 51 NWA (BMI, 18.5-24.9 kg/m(2); 29% male) and 45 OBA (BMI, 30.1-51.4 kg/m(2); 33% male) between 20 and 60 years of age. Serial spirometry, inspiratory capacity (IC), plethysmographic end-expiratory lung volume (EELV) and dyspnea intensity using the Borg scale were measured throughout bronchoprovocation.

MEASUREMENTS AND MAIN RESULTS

Spirometry and airway sensitivity were similar in both groups; baseline EELV was lower (P < 0.0005) and IC was higher (P = 0.007) in OBA compared with NWA. From baseline to PC(20), EELV increased more in OBA (20% predicted) than NWA (13% predicted) (P = 0.008) with concomitant greater reductions in IC (P < 0.0005). Dyspnea ratings were not different for a given FEV(1) or IC across groups. By mixed effects regression analysis, relationships between induced dyspnea and changes in lung function parameters were not influenced by BMI, sex, or their interaction.

CONCLUSIONS

Perceptual responses to MCh-induced bronchoconstriction and lung hyperinflation were similar in obese and normal-weight individuals with asthma despite significant group differences in baseline lung volumes.

Physiology of obesity and effects on lung function

In obese people, the presence of adipose tissue around the rib cage and abdomen and in the visceral cavity loads the chest wall and reduces functional residual capacity (FRC). The reduction in FRC and in expiratory reserve volume is detectable, even at a modest increase in weight. However, obesity has little direct effect on airway caliber. Spirometric variables decrease in proportion to lung volumes, but are rarely below the normal range, even in the extremely obese, while reductions in expiratory flows and increases in airway resistance are largely normalized by adjusting for lung volumes. Nevertheless, the reduction in FRC has consequences for other aspects of lung function. A low FRC increases the risk of both expiratory flow limitation and airway closure. Marked reductions in expiratory reserve volume may lead to abnormalities in ventilation distribution, with closure of airways in the dependent zones of the lung and ventilation perfusion inequalities. Greater airway closure during tidal breathing is associated with lower arterial oxygen saturation in some subjects, even though lung CO-diffusing capacity is normal or increased in the obese. Bronchoconstriction has the potential to enhance the effects of obesity on airway closure and thus on ventilation distribution. Thus obesity has effects on lung function that can reduce respiratory well-being, even in the absence of specific respiratory disease, and may also exaggerate the effects of existing airway disease.

Mechanical effects of obesity on airway responsiveness in otherwise healthy humans

We investigated whether obesity is associated with airway hyperresponsiveness in otherwise healthy humans and, if so, whether this correlates with a restrictive lung function pattern or a decreased number of sighs at rest and/or during walking. Lung function was studied before and after inhaling methacholine (MCh) in 41 healthy subjects with body mass index ranging from 20 to 56. Breathing pattern was assessed during a 60-min rest period and a 30-min walk. The dose of MCh that produced a 50% decrease in the maximum expiratory flow measured in a body plethysmograph (PD50MCh) was inversely correlated with body mass index ( r2 = 0.32, P < 0.001) and waist circumference ( r2 = 0.25, P < 0.001). Significant correlations with body mass index were also found with the maximum changes in respiratory resistance ( r2 = 0.19, P < 0.001) and reactance ( r2 = 0.40, P < 0.001) measured at 5 Hz. PD50MCh was also positively correlated with functional residual capacity ( r2 = 0.56, P < 0.001) and total lung capacity ( r2 = 0.59, P < 0.001) in men, but not in women. Neither PD50MCh nor body mass index correlated with number of sighs, average tidal volume, ventilation, or breathing frequency. In this study, airway hyperresponsiveness was significantly associated with obesity in otherwise healthy subjects. In obese men, but not in women, airway hyperresponsiveness was associated with the decreases in lung volumes.

Obesity and asthma: a specific phenotype?

BACKGROUND

Obesity is associated with an increased prevalence of asthma, especially in women, and appears to be more severe in the obese. This study aimed to determine if obese subjects have a specific asthma phenotype.

METHODS

Forty-four consecutive obese subjects (body mass index [BMI] > or = 30 kg/m(2)) and 44 consecutive nonobese subjects (BMI < 25 kg/m(2)), all with asthma, completed an asthma control questionnaire, and underwent methacholine challenge with symptom perception scores, and sputum induction for differential cell count. BMI, waist circumference, and waist-to-hip ratio also were measured.

RESULTS

Despite similar expiratory flows, bronchodilator response, airway responsiveness to methacholine, and symptom perception scores, asthma control was poorer in obese subjects than in nonobese subjects (p = 0.005). Total lung capacity (p = 0.01), expiratory reserve volume (p < 0.0001), functional residual capacity (p < 0.0001), and residual volume (p = 0.006) were lower in obese subjects than in nonobese subjects. Induced-sputum eosinophil and neutrophil counts were similar in both groups, although there was an inverse correlation between sputum eosinophils and waist circumference and a trend for a similar relationship for BMI. Blood serum C-reactive protein (p = 0.009) and fibrinogen (p = 0.0004) levels were higher in obese subjects than in nonobese subjects.

CONCLUSION

Obese people with asthma had poorer asthma control than nonobese asthmatics despite similar symptoms perception. Bronchial and systemic inflammatory characteristics and the specific pattern of pulmonary function changes suggest a different phenotype of asthma in these subjects.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT00532363 and NCT00532831.

The effects of leptin on airway smooth muscle responses

Obesity is associated with asthma and airway hyperresponsiveness. Leptin modulates some of the proinflammatory effects observed in obesity. The objective of this study was to determine the effects of leptin on airway smooth muscle responses. The effect of leptin (0.1-100 ng/ml) on migration (toward platelet-derived growth factor [PDGF], 10 ng/ml, across collagen-coated membrane in Transwell culture plates), proliferation (by BrDU incorporation), and cytokine production (by Bioplex bead assay) of cultured human airway smooth muscle cells from nine nonasthmatic donors was assessed. Effects of leptin on the contractile responses were studied in bovine tracheal smooth muscle rings. Leptin receptor expression and activation of STAT-3, Src kinase, Suppressor of Cytokine Signaling-3 (SOCS-3), and COX were evaluated by Western blotting and PCR. PGE(2) levels in supernatant were assessed by enzyme immunoassay. Human airway smooth muscle cells express leptin receptor, which, when engaged, phosphorylated STAT-3. Leptin inhibited PDGF-induced human airway smooth muscle migration and proliferation and IL-13-induced eotaxin production. Leptin did not stimulate cytokine synthesis and did not evoke contractile responses or inhibit isoproterenol-induced relaxation of carbachol-induced contraction of bovine tracheal rings. The inhibitory effects on migration and eotaxin production are not due to activation of SOCS-3 but are partly due to increased production of PGE(2) because they were attenuated by indomethacin. In conclusion, leptin inhibited human airway smooth muscle proliferation, migration toward PDGF, and IL-13-induced eotaxin production. This is partly mediated by PGE(2) secretion from smooth muscle cells induced by leptin. The association between obesity and asthma is unlikely to be due to a direct effect of leptin on airway smooth muscle.

Obesity and asthma: possible mechanisms

Epidemiologic data indicate that obesity increases the prevalence and incidence of asthma and reduces asthma control. Obese mice exhibit innate airway hyperresponsiveness and augmented responses to certain asthma triggers, further supporting a relationship between obesity and asthma. Here I discuss several mechanisms that may explain this relationship. In obesity, lung volume and tidal volume are reduced, events that promote airway narrowing. Obesity also leads to a state of low-grade systemic inflammation that may act on the lung to exacerbate asthma. Obesity-related changes in adipose-derived hormones, including leptin and adiponectin, may participate in these events. Comorbidities of obesity, such as dyslipidemia, gastroesophageal reflux, sleep-disordered breathing, type 2 diabetes, or hypertension may provoke or worsen asthma. Finally, obesity and asthma may share a common etiology, such as common genetics, common in utero conditions, or common predisposing dietary factors. Novel therapeutic strategies for treatment of the obese patient with asthma may result from an increased understanding of the mechanisms underlying this relationship.

Clinical management of chronic obstructive pulmonary disease and asthma in an obese patient

The prevalence of obesity has noticeably increased worldwide. The clinician is now frequently facing the challenge of managing patients with concomitant chronic obstructive pulmonary disease (COPD) or asthma and obesity. Obesity is often associated with a poorer control of these chronic respiratory diseases and the optimal management of these conditions in the presence of obesity remains to be determined. Herein, the authors review the present understanding of the influence of obesity in the development, clinical manifestations and management of asthma and COPD. The influence of weight loss, response to present therapies as well as new targets for the treatment of COPD and asthma in obese subjects are also discussed, in addition to future directions for research.

The link between obesity and asthma: a Canadian perspective

Asthma is considered to be more prevalent in obese subjects, and a possible causal link between these two entities has been suggested. In the present study, various observations on this relationship were reviewed, and an analysis of data obtained from the 2000 to 2001 Canadian Community Health Survey on the prevalence of self-reported asthma, medication use and allergy, according to body weight, was reported. Asthma medication use and self-reported asthma were more prevalent in the obese population, particularly in women. Mean body mass index was higher in the asthmatic population compared with the nonasthmatic population. Self-reported nonfood-related allergies were higher in the more obese subjects in the general population, but the prevalence of allergy was not different in obese asthmatic subjects compared with nonobese asthmatic subjects. Smoking did not seem to influence the relationship between asthma and body mass index. Further research should investigate the mechanisms by which obesity may influence the prevalence of asthma or asthma-like symptoms.

Symposium on obesity and asthma - November 2, 2006

Asthma and obesity are frequently associated, and obesity has been considered a factor contributing to both an increase in severity of asthma and to its development. The present document summarizes the proceedings of a symposium held in Montreal, Quebec, on November 2, 2006, under the auspices of the Réseau en santé respiratoire du Fonds de la recherche en santé du Québec in collaboration with the McGill University - Strauss Severe Asthma Program, Université Laval (Quebec City) and Université de Montréal. It includes an overview of the various aspects of the relationships between asthma and obesity with regard to animal models; genetic, hormonal and physiological determinants; influence of comorbidities (eg, sleep apnea syndrome); epidemiology; clinical and psychological features; and management of asthma in the obese population.

Influence of obesity on response to fluticasone with or without salmeterol in moderate asthma

RATIONALE

Obesity may contribute to the development and clinical expression of asthma. However, how obesity can influence response to asthma medications is still uncertain.

OBJECTIVES

To examine the relationship between body mass index (BMI) and the response to an inhaled corticosteroid (ICS), fluticasone propionate, with or without the long-acting beta2-agonist salmeterol (LABA).

METHODS

Achievement of asthma control as defined by the global initiative on asthma guidelines (GINA) was examined in 1242 asthmatic patients not currently using ICS, enrolled in five clinical trials comparing fluticasone propionate and the combination of fluticasone and salmeterol.

RESULTS

In both obese and non-obese subjects, fluticasone propionate combined with salmeterol was more effective in controlling asthma than fluticasone alone. However, for both treatments the odds of achieving well-controlled asthma were significantly lower in obese subjects, particularly among those with a BMI of >or=40 kg/m2. Reported prevalence of atopy increased with BMI. Age did not influence the effect of obesity in response to asthma medications.

CONCLUSION

Obese patients are less likely than the non-obese to achieve asthma control with an ICS or an ICS combined with a LABA. The causes of such reduced response to asthma medication in obese subjects should be studied, and their implications for asthma therapy determined.

Effect of obesity on airway inflammation: a cross-sectional analysis of body mass index and sputum cell counts

BACKGROUND

Several observational studies have demonstrated an association between obesity and asthma. Studies evaluating exhaled nitric oxide levels and obesity have revealed that a higher body mass index (BMI) is associated with elevated exhaled nitric oxide levels. Airway inflammation using sputum cell counts has not been assessed in obese patients with airway diseases.

OBJECTIVE

The primary aim of this study was to determine whether obesity (based on BMI) is associated with eosinophilic or neutrophilic bronchitis.

METHODS

The results from a database of induced sputum cell counts were compared with BMI and analysed using correlation statistics, regression and parametric and non-parametric analysis.

RESULTS

Seven-hundred and twenty-seven adult participants with an equal number of sputum samples were included in the analysis. BMI varied from 14.5 to 55 kg/m(2). Sputum total cell count (mean+/-SD: 12.9 x 10(6) cell/g+/-21.5), eosinophil percent (median; min to max: 0.3%; 0-89.0), and neutrophil percent (mean+/-SD: 63.5+/-26.6%) were within normal limits. Participants with asthma had a higher percentage of sputum eosinophils than those without asthma (P=0.01). However, there was no difference in the total or differential cell counts among the obese and non-obese participants, when the data were analysed according to BMI category, gender, dose of inhaled corticosteroid, and presence or absence of asthma.

CONCLUSION

In this large sample of adult asthmatic and non-asthmatic participants, there was no association between BMI and airway inflammation measured by sputum cell counts. Other mechanisms to explain the relationship between obesity and asthma will need to be explored if this association is to be better understood.

Altered respiratory physiology in obesity

The major respiratory complications of obesity include a heightened demand for ventilation, elevated work of breathing, respiratory muscle inefficiency and diminished respiratory compliance. The decreased functional residual capacity and expiratory reserve volume, with a high closing volume to functional residual capacity ratio of obesity, are associated with the closure of peripheral lung units, ventilation to perfusion ratio abnormalities and hypoxemia, especially in the supine position. Conventional respiratory function tests are only mildly affected by obesity except in extreme cases. The major circulatory complications are increased total and pulmonary blood volume, high cardiac output and elevated left ventricular end-diastolic pressure. Patients with obesity commonly develop hypoventilation and sleep apnea syndromes with attenuated hypoxic and hypercapnic ventilatory responsiveness. The final result is hypoxemia, pulmonary hypertension and progressively worsening disability. Obese patients have increased dyspnea and decreased exercise capacity, which are vital to quality of life. Decreased muscle, increased joint pain and skin friction are important determinants of decreased exercise capacity, in addition to the cardiopulmonary effects of obesity. The effects of obesity on mortality in heart failure and chronic obstructive pulmonary disease have not been definitively resolved. Whether obesity contributes to asthma and airway hyper-responsiveness is uncertain. Weight reduction and physical activity are effective means of reversing the respiratory complications of obesity.

The effect of obesity on chronic respiratory diseases: pathophysiology and therapeutic strategies

Sedentary lifestyles and increased pollution brought about by industrialization pose major challenges to the prevention of both obesity and chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD), asthma, obstructive sleep apnea and obesity hypoventilation syndrome. Obesity has emerged as an important risk factor for these respiratory diseases, and in many instances weight loss is associated with important symptomatic improvement. Moreover, obesity may influence the development and presentation of these diseases. In this article, we review the current understanding of the influence of obesity on chronic respiratory diseases and the clinical management of obesity concurrent with asthma, COPD, obstructive sleep apnea or obesity hypoventilation syndrome.