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

Characterization of Obesity in Severe Asthma in the German Asthma Net

BACKGROUND

Asthma is increasingly recognized as heterogeneous, characterized by different endotypes, with obesity not only a distinct phenotype but a risk factor for severe asthma.

OBJECTIVE

We sought to understand the associations of obesity with relevant parameters of severe asthma, including asthma control, disease burden, and lung function.

METHODS

The German Asthma Net registry is a multicenter international real-life registry capturing long-term follow-up data. This analysis included 2213 patients (52 ± 16 years, 58% female, 29% with obesity [body mass index ≥30 kg/m2], 4.2 ± 4.3 exacerbations/year). The primary analysis assessed relationships between BMI and variables through univariate tests, followed by a multiple regression model. Secondary outcomes regarded clinically relevant variables in relation to weight groups.

RESULTS

Patients with obesity were more frequently female, more likely to have depression and gastroesophageal reflux, and suffered from worse asthma control, lower quality of life, reduced static lung volumes, more pronounced hypoxemia, and higher blood neutrophil counts, all statistically significant. Blood eosinophils, exhaled nitric oxide, and total IgE were independent of obesity. In the multiple regression analysis, obesity was significantly associated with more frequent reflux and depression, reduced static lung function values, older age, poor asthma control, and long-acting muscarinic antagonist therapy, and inversely associated with bronchiectasis and nonsmoking status.

CONCLUSION

In this large, well-characterized cohort, we identified the association of obesity with a significantly higher disease burden and a similar portfolio of inflammation type 2 markers in patients with and without obesity; therefore, patients with obesity seem similarly eligible for the treatment with biologics targeting these disease endotypes.

The association of asthma duration with body mass index and Weight-Adjusted-Waist index in a nationwide study of the U.S. adults

BACKGROUNDS

The association between obesity and asthma has been of interest, but whether the duration of asthma has an effect on obesity is still limitedly studied.

AIM

The purpose of this study was to investigate the association between asthma duration and obesity-related indexes, where obesity-related indexes include Body mass index (BMI) and Weight-adjusted-waist index (WWI).

METHODS

Data from National Health and Nutrition Examination Survey (NHANES) 2009-2018 were obtained to conduct this cross-sectional study. Duration of asthma was used as the independent variable and obesity-related indexes as the response variables. Multiple linear regression was used to assess the association between the independent variable and the response variables, and subsequently smoothed curve fitting and threshold effect analysis were performed to clarify whether there was a nonlinear correlation between the independent variable and the response variables. Finally, subgroup analysis was conducted to find sensitive populations.

RESULTS

A total of 9170 participants were included in the analysis. Asthma duration was statistically different between the two groups when all participants were grouped by median WWI (Q1 < 11.65, Q2 ≥ 11.65) (P < 0.001), but not by median BMI (Q1 < 31.8, Q2 ≥ 31.8) (P = 0.130). There was a positive association between asthma duration and WWI [β = 0.016, 95% CI (0.016, 0.017)], but a negative one with BMI [β = - 0.098, 95% CI (- 0.112, - 0.085)], and the correlations between the independent and response variables became more pronounced with increasing asthma duration (P for trend < 0.01). In addition, there were nonlinear relationships between asthma duration with BMI and WWI (log likelihood ratio < 0.001), with the best valid inflection points for asthma duration being 2 years (with WWI as the response variable) and 3 years (with BMI as the response variable), respectively. In the subgroup analysis, the positive association between asthma duration and WWI was more pronounced in the participants who were male, aged less than 40 years, and had asthma onset before 12 years of age. In contrast, when BMI was used as the response variable, the negative association between it and asthma duration was more pronounced among participants of female, aged 60 years or older, and with asthma onset less than 12 years of age.

CONCLUSIONS

In US adults, asthma duration might cause changes in obesity-related indexes. Longer asthma duration might cause weight loss, but might increase the risk of abdominal obesity.

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.

Asthma medication use in obese and healthy weight asthma: systematic review/meta-analysis

BACKGROUND

Obesity is a common comorbidity in asthma and associated with poorer asthma control, more frequent/severe exacerbations, and reduced response to asthma pharmacotherapy.

OBJECTIVE

This review aims to compare use of all classes of asthma medications in obese (body mass index (BMI) ≤30 kg·m^-2) versus healthy-weight (BMI <25 kg·m^-2) subjects with asthma.

DESIGN

Databases including CINAHL (Cumulative Index to Nursing and Allied Health Literature), Cochrane, Embase and MEDLINE were searched up to July 2019 for English-language studies that recorded medication use or dose in obese and healthy-weight adults with asthma. A critical appraisal checklist was utilised for scrutinising methodological quality of eligible studies. Meta-analysis was performed and heterogeneity was examined with the use of the Chi-squared test. This review was conducted based on a published protocol (www.crd.york.ac.uk/PROSPERO CRD42020148671).

RESULTS

Meta-analysis showed that obese subjects are more likely to use asthma medications, including short-acting β₂-agonists (OR 1.75, 95% CI 1.17-2.60; p=0.006, I²=41%) and maintenance oral corticosteroids (OR 1.86, 95% CI 1.49-2.31; p<0.001, I²=0%) compared to healthy-weight subjects. Inhaled corticosteroid (ICS) dose (µg·day^-1) was significantly higher in obese subjects (mean difference 208.14, 95% CI 107.01-309.27; p<0.001, I²=74%). Forced expiratory volume in 1 s (FEV₁) % predicted was significantly lower in obese subjects (mean difference -5.32%, 95% CI -6.75--3.89; p<0.001, I²=42%); however, no significant differences were observed in FEV₁/forced vital capacity (FVC) ratio between groups.

CONCLUSIONS

We found that obese subjects with asthma have higher use of all included asthma medication classes and higher ICS doses than healthy-weight asthma subjects, despite lower FEV₁ and a similar FEV₁/FVC %. A better understanding of the factors driving increased medication use is required to improve outcomes in this subgroup of asthmatics.

Cardiopulmonary exercise testing in patients with asthma: What is its clinical value?

Asthma is one of the most common respiratory disorders, characterized by fully or largely reversible airflow limitation. Asthma symptoms can be triggered or magnified during exertion, while physical activity limitation is often present among asthmatic patients. Cardiopulmonary exercise testing (CPET) is a dynamic, non-invasive technique which provides a thorough assessment of exercise physiology, involving the integrative assessment of cardiopulmonary, neuromuscular and metabolic responses during exercise. This review summarizes current evidence regarding the utility of CPET in the diagnostic work-up, functional evaluation and therapeutic intervention among patients with asthma, highlighting its potential role for thorough patient assessment and physician clinical desicion-making.

Obesity Does Not Increase the Risk of Asthma Readmissions

The relationship between obesity and asthma exacerbations is still under debate. The aim of our work is to analyse the relationship between obesity and hospital re-admissions in asthmatics. A review was retrospectively performed on all hospital admissions of adult patients due to asthma exacerbation occurring in our hospital for 11 years. All those cases with asthma as the first diagnosis in the discharge report were included, or those with asthma as the second diagnosis provided when the first diagnosis was respiratory infection or respiratory failure. Only the first hospital admission of each patient was included in this study. The Odds Ratios of a higher incidence of early/late readmissions due to asthma exacerbation were calculated using a binary logistic regression, using the body mass index (BMI) as independent variable, adjusted for all the variables included in the study. The study included 809 patients with a mean age of 55.6 years, and 65.2% were female. The majority (71.4%) were obese or overweight. No significant relationship was observed in the univariate or multivariate analyses between overweight or obesity and the early or late hospital readmissions due to asthma. Therefore, obesity does not seem to be a determining factor in the risk of asthma exacerbations.

Symptoms and perception of airway obstruction in asthmatic patients: Clinical implications for use of reliever medications

BACKGROUND

Asthma causes the unpleasant sensation of breathlessness (dyspnea) caused by airway obstruction. Patients with poor perception of airway obstruction are at risk of delay in seeking medical attention and undertreatment, which can lead to avoidable deaths. Conversely, those with heightened perception are at risk of overtreatment and iatrogenic adverse effects with reliever medications, anxiety, and unnecessary use of health care resources.

OBJECTIVE

We sought to review evidence about symptom misperception in asthmatic patients and how to identify and manage affected patients, particularly with regard to reliever medications.

METHODS

We conducted a systematic literature search for studies of perception of airway function in asthmatic patients. We searched the OVID (Medline and Medline [R] in process [PubMed]), Embase, and Adisearch/Odyssey databases, restricting our search to human studies published in English from 1990-2018, with no restrictions on age, sex, or racial origin.

RESULTS

We found that both underperception and overperception assessed during induced bronchoconstriction or bronchodilation or during changes in airway resistance were common across all age groups and that aging, disease severity, smoking, sex, ethnicity, psychologic factors, and medication are all associated with differences in perception. Importantly, airway inflammation was associated with impaired perception and a history of severe or near-fatal asthma. We also identified knowledge gaps, such as whether an individual patient's perception varies over time and the influence perception has on patients' use of reliever medication.

CONCLUSION

We found that abnormal perception of airway obstruction has important clinical implications for the management of patients with asthma.

The asthma-obesity relationship: underlying mechanisms and treatment implications

PURPOSE OF REVIEW

Obesity is a worldwide epidemic with a prevalence that has tripled in the last two decades. Worldwide, more than 1.5 billion adults are overweight and more than 500 million obese. Obesity has been suggested to be a risk factor for the development of more difficult-to-control asthma. Although the mechanisms underlying the asthma-obesity relationship are not fully understood, several possible explanations have been put forward. These will be reviewed in this manuscript as well as the implications for the treatment of overweight and obese asthma patients.

RECENT FINDINGS

Insulin resistance is a possible factor contributing to the asthma-obesity relationship and the effect is independent of other components of the metabolic syndrome such as hypertriglyceridemia, hypertension, hyperglycemia, and systemic inflammation. Obesity has important effects on airway geometry, by especially reducing expiratory reserve volume causing obese asthmatics to breathe at low lung volumes. Furthermore, obesity affects the type of inflammation in asthma and is associated with reduced inhaled corticosteroids treatment responsiveness.

SUMMARY

Obesity induces the development of asthma with a difficult-to-control phenotype. Treatment targeting insulin resistance may be beneficial in obese asthma patients, especially when they have concomitant diabetes. Systemic corticosteroids should be avoided as much as possible as they are not very effective in obese asthma and associated with side-effects like diabetes, weight gain, and osteoporosis.

Overweight, Obesity, and Lung Function in Children and Adults-A Meta-analysis

BACKGROUND

There is conflicting evidence on the effect of obesity on lung function in adults and children with and without asthma. We aimed to evaluate the relation between overweight or obesity and lung function, and whether such relationship varies by age, sex, or asthma status.

METHODS

We searched PubMed, Scopus, CINAHL, Cochrane, and EMBASE for all studies (in English) reporting on obesity status (by body mass index) and lung function, from 2005 to 2017. Main outcomes were forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), FEV1/FVC, forced expiratory flow between 25th and 75th percentile of the forced vital capacity (FEF25-75), total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC). Random-effects models were used to calculate the pooled risk estimates; each study was weighed by the inverse effect size variance. For each outcome, we compared overweight or obese ("obese") subjects with those of normal weight.

RESULTS

All measures of lung function were decreased among obese subjects. Obese adults showed a pattern (lower FEV1, FVC, TLC, and RV) different from obese children (more pronounced FEV1/FVC deficit with unchanged FEV1 or FVC). There were also seemingly different patterns by asthma status, in that subjects without asthma had more marked decreases in FEV1, TLC, RV, and FRC than subjects with asthma. Subjects who were obese (as compared with overweight) had even further decreased FEV1, FVC, TLC, RV, and FRC.

CONCLUSIONS

Obesity is detrimental to lung function, but specific patterns differ between children and adults. Physicians should be aware of adverse effects of obesity on lung function, and weight control should be considered in the management of airway disease among the obese.

Dynamic hyperinflation and exercise limitations in obese asthmatic women

Obese individuals and patients with asthma can develop dynamic hyperinflation (DH) during exercise; however, no previous study has investigated DH as a factor associated with reduced exercise capacity in obese asthmatic women. The aim of the present study was to examine the occurrence of DH and exercise limitations in obese asthmatics. Obese grade II [obese group (Ob-G); BMI 35-39.9 kg/m²; n=36] and nonobese [nonobese group (NOb-G); BMI 18.5-29.9 kg/m²; n=18] asthmatic patients performed a cardiopulmonary test to quantify peak V̇o₂ and a submaximal exercise test to assess DH. Anthropometric measurements, quadriceps endurance, and lung function were also evaluated. A forward stepwise regression was used to evaluate the association between exercise tolerance (wattage) and limiting exercise factors. Fifty-four patients completed the protocol. The Ob-G (n = 36) presented higher peak V̇o₂ values but lower power-to-weight ratio values than the NOb-G (P <0 .05). DH was more common in the Ob-G (72.2%) than in the NOb-G (38.9%, P < 0.05). The Ob-G had a greater reduction in the inspiratory capacity (-18 vs. -4.6%, P < 0.05). Exercise tolerance was associated with quadriceps endurance (r = 0.65; p<0.001), oxygen pulse (r = 0.52; p=0.001), and DH (r = -0.46, P = 0.005). The multiple regression analysis showed that the exercise tolerance could be predicted from a linear association only for muscular endurance (r = 0.82 and r² = 0.67). This study shows that dynamic hyperinflation is a common condition in obese asthmatics; they have reduced fitness for activities of daily living compared to nonobese asthmatics. However, peripheral limitation was the main factor associated with reduced capacity of exercise in these patients.NEW & NOTEWORTHY This is the first study to investigate the occurrence of dynamic hyperinflation (DH) in obese asthmatics. Our results demonstrate that obese asthmatics present a higher frequency and intensity of DH than nonobese asthmatics. We also show that physical deconditioning in this population is linearly associated with cardiac (O₂ pulse), respiratory (DH), and peripheral muscle (resistance) limitation. However, multiple linear regression demonstrated that peripheral muscle limitation may explain the exercise limitation in this population.

Discrepancies between asthma control criteria in asthmatic patients with and without obesity

OBJECTIVE

To compare the prevalence of discrepancies between clinical, physiological, and inflammatory asthma control parameters between patients with asthma and obesity and patients with asthma but not obesity using the Asthma Control Scoring System (ACSS).

METHODS

A retrospective analysis of demographic data and ACSS scores was performed in two groups of patients with asthma (74 with obesity and 74 without obesity) paired for sex, age, and asthma severity. Scores from each asthma control parameter-clinical (respiratory symptoms), physiological (forced expiratory volume in 1 s), and inflammatory (sputum eosinophil percentage)-were compared. Discrepancy was defined as a >20% difference between two scores.

RESULTS

The prevalence of discrepancies between scores was similar between asthma patients with or without obesity. A sub-analysis on patients with uncontrolled asthma (ACSS global score <80%) showed a higher prevalence of discrepancies between the clinical and physiological scores in subjects with obesity, the clinical score being higher than the physiological one in most (87%) cases.

CONCLUSIONS

Subjects with obesity and uncontrolled asthma show higher clinical scores than physiological scores, suggesting an under-evaluation of asthma symptoms. Future studies are needed to evaluate the influence of obesity on each type of asthma symptom.

Combined effects of mild-to-moderate obesity and asthma on physiological and sensory responses to exercise

Despite the close link between asthma and obesity, there are no studies that have evaluated the sensory and physiological responses to exercise in obese asthmatics. We recently demonstrated that normal weight asthmatics with well controlled disease have preserved cardiorespiratory and sensory responses to exercise relative to non-asthmatic controls. However, these similarities may not hold true in patients with combined obesity and asthma. Accordingly, we sought to determine if combined asthma and obesity was associated with deleterious effects on cardiorespiratory fitness, exercise performance, dyspnoea, and physiological responses to exercise. Fourteen well-controlled obese asthmatics and fourteen age-matched normal weight asthmatics performed routine spirometry and underwent an incremental cardiopulmonary cycle test to assess the ventilatory, pulmonary gas exchange, cardiovascular, and sensory responses to exercise. Groups were well matched for age, height, spirometry, and asthma control. Obese asthmatics had a significantly greater body mass index (33 ± 3 vs. 23 ± 1 kg/m(2), p < 0.001) and lower self-reported activity levels by 47 % relative to normal weight asthmatics (p < 0.05). Obese asthmatics had a significantly lower maximal oxygen uptake (VO(2)) (82 ± 14 vs. 92 ± 10 %predicted) and work rate (75 ± 8 vs. 89 ± 13 %predicted) relative to normal weight asthmatics (p < 0.05). The anaerobic threshold occurred at a lower VO(2) in obese asthmatics vs. normal weight asthmatics (54 ± 15 vs. 66 ± 16 %predicted, p < 0.05). Ventilatory responses were superimposed throughout exercise with no evidence of a ventilatory limitation in either group. Cardiovascular responses were normal in both groups. Dyspnoea responses were similar but the obese asthmatics experienced greater leg fatigue ratings at submaximal work rates. In conclusion, obese individuals with well controlled asthma have reduced cardiorespiratory fitness and greater leg fatigue ratings relative to normal weight asthmatics. The relatively reduced cardiorespiratory fitness and exercise performance in obese compared to normal weight asthmatics is most likely driven by their more sedentary lifestyle and resultant deconditioning rather than due to respiratory factors.

Association of pulmonary function with adiposity and metabolic abnormalities in urban minority adolescents

RATIONALE

Childhood obesity is a known risk factor for pulmonary diseases, likely due to obesity-mediated alteration of pulmonary function. Inflammation and mechanical fat load are two proposed causative mechanisms for altered pulmonary function among obese children; however, the association of metabolic abnormalities with pulmonary function among children is poorly understood.

OBJECTIVES

We investigated the independent association of truncal and general adiposity and metabolic abnormalities with pulmonary function in a sample of urban minority adolescents.

METHODS

Spirometry and lung volume indices were compared between adolescents with general (body mass index [BMI] > 95th percentile) or truncal adiposity (waist circumference > 90th percentile) and normal-weight (BMI < 85th percentile or waist circumference ≤ 90th percentile) and between those with metabolic abnormalities (homeostatic model assessment of insulin resistance [HOMA-IR] in the top quartile or high-density lipoprotein [HDL] < 40 mg/dl) and those with a normal metabolic profile.

MEASUREMENTS AND MAIN RESULTS

Obese adolescents had lower lung volumes, including residual volume (RV), RV/TLC ratio, expiratory reserve volume (ERV), and FRC, and higher inspiratory capacity (IC) than normal-weight adolescents, but did not differ in measures of lower airway obstruction, FEV1/FVC ratio, and mid-expiratory flow rate. Adolescents with high HOMA-IR had lower FEV1/FVC ratio, RV, RV/TLC ratio, ERV, and FRC and higher IC, whereas those with low HDL had lower FEV1/FVC and RV/TLC ratios. After adjusting for adiposity, HOMA-IR remained a predictor of ERV (β = -1.4; P = 0.02) and FEV1/FVC ratio (β = -0.5; P = 0.03), and HDL remained a predictor of FEV1/FVC ratio (β = 0.1; P = 0.01). General adiposity was a predictor of FRC (β = -0.5; P < 0.001), IC (β = 0.3; P < 0.001), RV (β = -0.8; P < 0.0001), and RV/TLC ratio (β = -0.2; P < 0.0001), and truncal adiposity was a predictor of RV (β = -20.3; P = 0.03) and FRC (β = -13.8; P = 0.004). Thus, adiposity and metabolic abnormalities were independent predictors of ERV, but only metabolic abnormalities independently predicted FEV1/FVC ratio. Although general adiposity predicted RV and RV/TLC ratio, truncal adiposity was predictive of RV and FRC, conferring additional risk above general adiposity.

CONCLUSIONS

These results suggest that metabolic abnormalities and adiposity are independently associated with pulmonary function deficits among urban adolescents. Metabolic assessment of obese adolescents may identify those at risk of developing obesity-associated pulmonary morbidity.

Potential role of the airway wall in the asthma of obesity

The pathogenesis of late-onset TH2-low asthma in obesity is thought to be related to weight-related decreases in lung volume, but why only a subset of individuals with obesity develop this condition is unknown. We tested the hypothesis that natural variations in both airway wall stiffness and airway wall thickness could lead to a subpopulation of hyperresponsive individuals exhibiting the symptoms of asthma in the setting of obesity. Increases in airway resistance (Raw) after airway smooth muscle stimulation were simulated using a computational model of an elastic airway embedded in elastic parenchyma. Using a range of randomly chosen values for both airway wall stiffness and thickness, we determined the resulting probability distributions of Raw responsiveness for a variety of different levels of transpulmonary pressure (Ptp). As Ptp decreased from 5 to 1 cmH2O, the resulting distributions of Raw moved toward progressively higher levels of responsiveness. With appropriate choices for the mean and standard deviation of the parameter that controls either airway wall stiffness or thickness, the model predicts a relationship between airway hyperresponsiveness and body mass index that is similar to that which has been reported in populations with obesity. We conclude that natural variations in airway wall mechanics and geometry between different individuals can potentially explain why an increasing percentage of the population exhibits the symptoms of asthma as the obesity of the population increases.

Impact of obesity on the clinical profile of a population-based sample with chronic obstructive pulmonary disease

Aims

To characterize the distribution of BMI in a population-based sample of COPD patients and to evaluate the impact of obesity on their health status, exercise tolerance, systemic inflammation and comorbidity.

Methods

A population-based sample of 3,797 subjects aged 40–80 years from the EPI-SCAN study was selected. Subjects were categorized according their body mass index (BMI) as underweight (<18.5 kg/m²), normal weight (18.5–24.9 kg/m²), overweight (25.0–29.9 kg/m²) or obese (BMI≥30.0 kg/m²). Subjects were evaluated with post-bronchodilator spirometry and 6-minute walk tests. Smoking habits, respiratory symptoms, generic and specific quality of life, daily physical activities, comorbidities and systemic inflammatory biomarkers were recorded.

Results

The prevalence of obesity or being overweight was higher in the 382 COPD patients than in the subjects without airflow limitation (29.4%, 95%CI 24.8–33.9% vs. 24.3, 95%CI 22.9–25.8; and 44.7%, 95%CI 39.7–49.6% vs. 43.0%, 95%CI 41.3–44.6, respectively; p = 0.020). In the COPD subgroup, obese subjects presented more dyspnea and less chronic cough, chronic bronchitis or chronic phlegm than normal-weight patients, as well as a worse health status. Moreover, reduced exercise tolerance and higher plasmatic C-reactive protein levels were found in the obese patients, who also presented a greater prevalence of cardiovascular disease (adjusted odds ratio 4.796, 95%CI 1.806–12.736, p = 0.002).

Conclusions

In a population-based sample, obesity is more prevalent in COPD patients than in subjects without airflow limitation. Furthermore, obesity affects the clinical manifestations, quality of life and exercise tolerance of COPD patients, and it may contribute to a phenotype characterized by increased systemic inflammation and greater frequency of cardiovascular comorbidity.

Investigating the association between obesity and asthma in 6- to 8-year-old Saudi children: a matched case-control study

BACKGROUND

Previous studies have demonstrated an association between obesity and asthma, but there remains considerable uncertainty about whether this reflects an underlying causal relationship.

AIMS

To investigate the association between obesity and asthma in pre-pubertal children and to investigate the roles of airway obstruction and atopy as possible causal mechanisms.

METHODS

We conducted an age- and sex-matched case-control study of 1,264 6- to 8-year-old schoolchildren with and without asthma recruited from 37 randomly selected schools in Madinah, Saudi Arabia. The body mass index (BMI), waist circumference and skin fold thickness of the 632 children with asthma were compared with those of the 632 control children without asthma. Associations between obesity and asthma, adjusted for other potential risk factors, were assessed separately in boys and girls using conditional logistic regression analysis. The possible mediating roles of atopy and airway obstruction were studied by investigating the impact of incorporating data on sensitisation to common aeroallergens and measurements of lung function.

RESULTS

BMI was associated with asthma in boys (odds ratio (OR)=1.14, 95% confidence interval (CI), 1.08-1.20; adjusted OR=1.11, 95% CI, 1.03-1.19) and girls (OR=1.37, 95% CI, 1.26-1.50; adjusted OR=1.38, 95% CI, 1.23-1.56). Adjusting for forced expiratory volume in 1 s had a negligible impact on these associations, but these were attenuated following adjustment for allergic sensitisation, particularly in girls (girls: OR=1.25; 95% CI, 0.96-1.60; boys: OR=1.09, 95% CI, 0.99-1.19).

CONCLUSIONS

BMI is associated with asthma in pre-pubertal Saudi boys and girls; this effect does not appear to be mediated through respiratory obstruction, but in girls this may at least partially be mediated through increased risk of allergic sensitisation.

Effect of obesity on bronchial hyperreactivity among Latino children

BACKGROUND

The association between obesity and bronchial hyperreactivity (BHR) in children has not been fully demonstrated in cross-sectional or longitudinal studies, and no study has specifically addressed Latino children.

METHODS

A cross-sectional study of 450 children (10-18 years) from public schools was conducted in Mexico city. Among this group, 260 met the study criteria (no chronic respiratory illnesses, including asthma and rhinitis; no acute respiratory infections; and no tobacco-exposure or endocrine or body dysmorphic disorders), and 229 performed reproducible pulmonary function and methacholine challenge tests and were fully analyzed.

RESULTS

According to BMI percentiles, 40 were normal weight, 116 were obese, and 73 morbidly obese. Children in the morbidly obese group had significantly higher % FVC than those in the normal-weight group, and obese children had higher % PEF those in the morbidly obese and normal-weight groups. In the BHR methacholine challenge test, baseline FEV1 values among obese children were significantly lower than in the morbidly obese group. Using adjusted percentages for FEV1 , values were significantly lower among obese compared to morbidly obese children at metacholine concentrations of 0.25, 1, and 4 mg/ml. The proportion of positive BHR (PC20  ≤ 16 mg/ml) was higher in these two groups compared to normal-weight children (28.4%, 17.8%, and 12.5%, respectively), although differences were not significant.

CONCLUSION

Our findings show that obesity by itself is not a sufficient condition to alter airway responsiveness to methacholine in a group of adolescents.

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.

Distal airway impairment in obese normoreactive women

Background. Asthma-like symptoms are frequent in overweight and obesity, but the mechanism is unclear when airway hyperresponsiveness (AHR) is lacking. In this study, we focused on obese women with a clinical suspicion of asthma but negative methacholine challenge and tested distal airway hyperreactivity, explored by Forced Vital Capacity dose-response slope (FVC DRS). Objective. To question AHR at the distal airway level in obese women. Methods. A total of 293 symptomatic obese and nonobese women free of treatment were investigated. Methacholine challenge tests were undertaken, and patients were divided according to their results to the test. In hyperreactive and nonhyperreactive patients and in our total population, correlations, regression analyses, and analyses of covariance were performed to compare distal airway hyperreactivity in three groups of body mass index (BMI). Results. After adjusting for age and baseline respiratory values, the relationship between FVC and FEV1 (forced expiratory volume in one second) DRS was influenced by BMI, with a lower slope in obese than overweight and normal patients in our total population (P = 0.008) and in our nonhyperreactive one (P = 0.028). Conclusion. Distal airway hyperresponsiveness was observed in symptomatic wheezing obese women negative to methacholine challenge.

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.

BMI can influence adult males' and females' airway hyperresponsiveness differently

Background

Epidemiological data indicate that obesity is a risk factor for asthma, but scientific literature is still debating the association between changes in body mass index (BMI) and airway hyperresponsiveness (AHR).

Methods

This study aimed at evaluating the influence of BMI on AHR, in outpatients with symptoms suggestive of asthma.

4,217 consecutive adult subjects (2,439 M; mean age: 38.2±14.9 yrs; median FEV₁ % predicted: 100 [IQR:91.88-107.97] and FEV₁/FVC % predicted: 85.77% [IQR:81.1-90.05]), performed a methacholine challenge test for suspected asthma. Subjects with PD₂₀ < 200 or 200 < PD₂₀ < 800 or PD₂₀ > 800 were considered affected by severe, moderate or mild AHR, respectively.

Results

A total of 2,520 subjects (60% of all cases) had a PD₂₀ < 3,200 μg, with a median PD₂₀ of 366 μg [IQR:168–1010.5]; 759, 997 and 764 patients were affected by mild, moderate and severe AHR, respectively. BMI was not associated with increasing AHR in males. On the contrary, obese females were at risk for AHR only when those with moderate AHR were considered (OR: 1.772 [1.250-2.512], p = 0.001). A significant reduction of FEV₁/FVC for unit of BMI increase was found in moderate AHR, both in males (β = −0.255; p =0.023) and in females (β = −0.451; p =0.017).

Conclusions

Our findings indicate that obesity influences AHR only in females with a moderate AHR level. This influence may be mediated by obesity-associated changes in baseline lung function.

Influence of asthma definition on the asthma-obesity relationship

Background

Epidemiological studies suggest an association between obesity and asthma in adults and children. Asthma diagnosis criteria are different among studies. The aim of this study was to test the influence of asthma definition on the asthma-obesity relationship.

Methods

In a cross-sectional analysis of 1922 men and women, subjects completed a translated questionnaire from the European Community Respiratory Health Survey and underwent spirometry and a bronchial challenge test. Weight, height and waist circumference were measured. Multiple logistic regression analysis was carried out to assess the association of variables related to obesity and asthma. Asthma was defined either by the presence of symptoms with bronchial hyperresponsiveness (BHR) or by a self-report of a physician-made diagnosis. The following variables were separately tested for associations with asthma: socioeconomic characteristics, schooling, physical activity, smoking status, anthropometry and spirometry.

Results

No association was detected between asthma confirmed by BHR and obesity indicators, odds ratio (OR) = 1.08 (95% confidence interval: 0.69 - 1.68) for obesity assessed by body mass index ≥ 30 kg/m²; OR = 1.02 (0.74 - 1.40) for obesity assessed by abnormal waist-to-height ratio; and, OR = 0.96 (0.69 - 1.33) for abnormal waist circumference. On the contrary, a previous diagnosis of asthma was associated with obesity, OR = 1.48 (1.01 - 2.16) for body mass index ≥ 30 kg/m²; OR = 1.48 (1.13 - 1.93) for abnormal waist-to-height ratio; and, OR = 1.32 (1.00 – 1.75) for abnormal waist circumference. Female gender, schooling ≥ 12 years and smoking were associated with BHR-confirmed asthma. Physically inactive subjects were associated with a previous diagnosis of asthma.

Conclusions

Our findings indicate that the relationship between asthma and obesity in epidemiological studies depends on the definition adopted. Certain components of asthma, for instance, symptoms may be more prone to the obesity influence than other ones, like bronchial hyperresponsiveness.

Asthma and obesity: a known association but unknown mechanism

The obese asthma phenotype is an increasingly common encounter in our clinical practice. Epidemiological data indicate that obesity increases the prevalence and incidence of asthma, and evidence that obesity precedes the development of asthma raises the possibility of a causal association. Obese patients with asthma experience more symptoms and increased morbidity compared with non-obese asthma patients. Despite more than a decade of research into this association, the exact mechanisms that underlie the interaction of obesity with asthma remain unclear. It is unlikely that the asthma-obesity association is simply due to comorbidities such as obstructive sleep apnoea or gastroesophageal reflux disease. Although inflammatory pathways are purported to play a role, there is scant direct evidence in humans that systemic inflammation modulates the behaviour of the asthmatic airway or the expression of symptoms in the obese. The role of non-eosinophilic airway inflammation also requires further study. Obesity results in important changes to the mechanical properties of the respiratory system, and these obesity-related factors appear to exert an additive effect to the asthma-related changes seen in the airways. An understanding of the various physiological perturbations that might be contributing to symptoms in obese patients with asthma will allow for a more targeted and rational treatment approach for these patients.

Asthma and obesity: does weight loss improve asthma control? a systematic review

Aim and methods

Obesity is a major health problem, and obesity is associated with a high incidence of asthma and poor asthma control. The aim of the present paper is to systematically review the current knowledge of the effect on overall asthma control of weight reduction in overweight and obese adults with asthma.

Results

Weight loss in obese individuals with doctor-diagnosed asthma is associated with a 48%–100% remission of asthma symptoms and use of asthma medication. Published studies, furthermore, reveal that weight loss in obese asthmatics improves asthma control, and that especially surgically induced weight loss results in significant improvements in asthma severity, use of asthma medication, dyspnoea, exercise tolerance, and acute exacerbations, including hospitalizations due to asthma. Furthermore, weight loss in obese asthmatics is associated with improvements in level of lung function and airway responsiveness to inhaled methacholine, whereas no significant improvements have been observed in exhaled nitric oxide or other markers of eosinophilic airway inflammation.

Conclusion

Overweight and obese adults with asthma experience a high symptomatic remission rate and significant improvements in asthma control, including objective measures of disease activity, after weight loss. Although these positive effects of weight loss on asthma-related health outcomes seem not to be accompanied by remission or improvements in markers of eosinophilic airway inflammation, it has potentially important implications for the future burden of asthma.

Obesity, expiratory flow limitation and asthma symptoms

Obesity is associated with poor asthma control, but the reason for this is unclear. Reduction in operating lung volume, as occurs in obesity, and bronchoconstriction, as occurs in asthma, can increase expiratory flow limitation during tidal breathing (EFLt), which may in turn increase respiratory symptoms. The aim of this study was to determine the effect of obesity on EFLt at baseline and after bronchoconstriction in non-asthmatic and asthmatic subjects, and to determine the association between EFLt, and respiratory symptoms. Data from previously published studies in non-asthmatic and asthmatic subjects were reanalyzed using an index of EFLt derived from respiratory system reactance measured by the forced oscillation technique. The analysis showed that during bronchoconstriction both non-asthmatic and asthmatic obese individuals were more likely to develop EFLt than non-obese subjects, despite similar changes in FEV1. Furthermore the index of EFLt was a significant determinant of the severity of breathlessness during challenge in non-asthmatic subjects, and of asthma symptom control in asthmatic subjects following anti-inflammatory treatment. These studies suggest that the combination of bronchoconstriction and low resting lung volume increase the risk of EFLt, and that this altered response to bronchoconstriction may increase the severity of symptoms and lead to worse asthma control.

Risk of misdiagnosis, health-related quality of life, and BMI in patients who are overweight with doctor-diagnosed asthma

BACKGROUND

Obesity and asthma both cause breathlessness, and there is a risk of misdiagnosis of asthma in patients who are obese. Impaired health-related quality of life (HRQoL) and increased BMI increase physician attendance rates, increasing this risk. We explored the possibility of misdiagnosis and the relationship between BMI, HRQoL, and other traditional measures of asthma severity in subjects who were obese with a doctor's diagnosis of asthma.

METHODS

Data were obtained from subjects who were overweight with physician-diagnosed asthma screened as part of another study, including bronchial provocative concentration of methacholine to produce a 20% fall in FEV(1) (PC(20)) or reversibility to bronchodilators, HRQoL measured using generic (Short Form-36 [SF-36]) and disease-specific (St. George Respiratory Questionnaire and Impact of Weight on Quality of Life-Lite) questionnaires. The fraction of exhaled nitric oxide (Feno), height, weight, and atopic status were also recorded.

RESULTS

Of 91 subjects (mean BMI, 38 kg/m(2); mean FEV(1)%, 85.8%; mean FEV(1)/FVC, 70.0%; mean Feno, 25.1 parts per billion taking a mean chlorofluorocarbon-beclomethasone-equivalent dose of 1,273.5 μg/d), 36.3% had no bronchial hyperresponsiveness (possible misclassification of asthma diagnosis.) The BMI and HRQoL were significantly related: The St. George Respiratory Questionnaire total (r = 0.33, P < .001), SF-36 physical health subtotal (r = -0.42, P < .001), SF-36 mental health subtotal (r = -0.39, P < .001), and Impact of Weight on Quality of Life-Lite total (r = 0.51, P < .001) showed no relationship to airways inflammation and bronchial reactivity. There was no significant difference in quality-of-life scores in subjects with or without bronchial hyperreactivity.

CONCLUSIONS

We found evidence of misdiagnosis of asthma in subjects who were obese. The BMI in subjects who were obese and had asthma negatively correlates with the HRQoL, which may relate to the diagnostic uncertainty and requires further exploration.

TRIAL REGISTRY

ISRCTN Register; No.: 54432221; URL: www.controlled-trials.com/isrctn.

Impact of obesity on the severity and therapeutic responsiveness of acute episodes of asthma

BACKGROUND

It has been suggested that obesity adversely influences both the severity and the therapeutic responsiveness of chronic asthma. However, it is unclear if it also impacts acute situations.

METHODS

To determine whether adiposity worsens the clinical and physiological manifestations of acute asthma and limits therapeutic effectiveness of standard treatment, we contrasted signs, symptoms, medication use, arterial oxygen saturation, peak expiratory flow rate, and the bronchodilator response to standard doses of albuterol in 90 non-obese and 90 obese asthmatics as they presented for urgent care. Treatment and clinical decisions were systematized using published care paths and the peak flow was measured with standard techniques. Body mass index (BMI) was calculated according to consensus criteria.

RESULTS

Other than BMI (p < .001), there were no between-group differences in age, gender, race, signs, symptoms, pulse oximetry, or pre-presentation medication use. The pretreatment peak flow in the obese population was 22.4% higher on average (p = .007), but there were no differences in the distribution of severity (p = .38), the response to albuterol (p = .61), or admission-discharge ratios (p = .62).

CONCLUSIONS

Obesity does not adversely influence the severity or the resolution of acute episodes of asthma.

Obesity is a determinant of asthma control independent of inflammation and lung mechanics

BACKGROUND

It is unclear why obesity is associated with worse asthma control. We hypothesized that (1) obesity affects asthma control independent of spirometry, airway inflammation, and airway hyperresponsiveness (AHR) and (2) residual symptoms after resolution of inflammation are due to obesity-related changes in lung mechanics.

METHODS

Forty-nine subjects with asthma underwent the following tests, before and after 3 months of high-dose inhaled corticosteroid (ICS) treatment: five-item asthma control questionnaire (ACQ-5), spirometry, fraction of exhaled nitric oxide (Feno), methacholine challenge, and the forced oscillation technique, which allows for the calculation of respiratory system resistance (Rrs) and respiratory system reactance (Xrs) as indicators of airway caliber and elastic load, respectively. The effects of treatment were assessed by BMI group (18.5-24.9, 25-29.9, and ≥ 30 kg/m²) using analysis of variance. Multiple regression analyses determined the independent predictors of ACQ-5 results.

RESULTS

At baseline, the independent predictors of ACQ-5 results were FEV(1), Feno, and BMI (model r² = 0.38, P < .001). After treatment, asthma control, spirometry, airway inflammation, and AHR improved similarly across BMI groups. The independent predictors of ACQ-5 results after treatment were Rrs and BMI (model r² = 0.42, P < .001).

CONCLUSIONS

BMI is a determinant of asthma control independent of airway inflammation, lung function, and AHR. After ICS treatment, BMI again predicts ACQ-5 results, but independent of obesity-related changes in lung mechanics.

Effect of obesity on respiratory mechanics during rest and exercise in COPD

The presence of obesity in COPD appears not to be a disadvantage with respect to dyspnea and weight-supported cycle exercise performance. We hypothesized that one explanation for this might be that the volume-reducing effects of obesity convey mechanical and respiratory muscle function advantages. Twelve obese chronic obstructive pulmonary disease (COPD) (OB) [forced expiratory volume in 1 s (FEV(1)) = 60%predicted; body mass index (BMI) = 32 ± 1 kg/m(2); mean ± SD] and 12 age-matched, normal-weight COPD (NW) (FEV(1) = 59%predicted; BMI = 23 ± 2 kg/m(2)) subjects were compared at rest and during symptom-limited constant-work-rate exercise at 75% of their maximum. Measurements included pulmonary function tests, operating lung volumes, esophageal pressure, and gastric pressure. OB vs. NW had a reduced total lung capacity (109 vs. 124%predicted; P < 0.05) and resting end-expiratory lung volume (130 vs. 158%predicted; P < 0.05). At rest, there was no difference in respiratory muscle strength but OB had greater (P < 0.05) static recoil and intra-abdominal pressures than NW. Peak ventilation, oxygen consumption, and exercise endurance times were similar in OB and NW. Pulmonary resistance fell (P < 0.05) at the onset of exercise in OB but not in NW. Resting inspiratory capacity, dyspnea/ventilation plots, and the ratio of respiratory muscle effort to tidal volume displacement were similar, as was the dynamic performance of the respiratory muscles including the diaphragm. In conclusion, the lack of increase in dyspnea and exercise intolerance in OB vs. NW could not be attributed to improvement in respiratory muscle function. Potential contributory factors included alterations in the elastic properties of the lungs, raised intra-abdominal pressures, reduced lung hyperinflation, and preserved inspiratory capacity.

Effects of BMI on static lung volumes in patients with airway obstruction

BACKGROUND

Both chronic airway obstruction and obesity are increasing in prevalence but the effect of their combination on pulmonary function parameters across the range of airway obstruction is unknown.

METHODS

We studied the impact of increasing BMI on static lung volumes and airway function in a cohort of 2,265 subjects from a large pulmonary function laboratory database who were 40 to 80 years of age and met GOLD (Global Initiative for Chronic Obstructive Lung Disease) spirometric criteria for COPD (postbronchodilator FEV₁/FVC < 0.7). We also evaluated the influence of severity of airway obstruction (by GOLD criteria) on these relationships.

RESULTS

With increasing BMI in the group as a whole, functional residual capacity, residual volume, expiratory reserve volume, and specific airway resistance (sRaw) decreased exponentially (all P < .001); total lung capacity (TLC) decreased linearly (P < .001); and inspiratory capacity (IC) and IC/TLC increased linearly (P < .001). However, vital capacity was not influenced significantly. The effects of increasing BMI on FEV₁/FVC and sRaw were greatest in GOLD stage III/IV (P < .05), whereas increasing BMI had greater effects on IC in GOLD stage I (P < .001).

CONCLUSIONS

With increasing BMI, subjects with airway obstruction had consistent reductions in lung hyperinflation, with significant improvements in IC and the FEV₁/FVC ratio; this effect was greatest in patients with the most severe airway obstruction. These results have important implications for the clinical assessment of patients with combined obesity and airway obstruction.

Effect of body mass index on self-reported exercise-triggered asthma

INTRODUCTION

Exercise-induced asthma (EIA) is common in individuals diagnosed with asthma, with 80% to 90% experiencing asthma symptoms during moderate exercise. Asthma has been linked to obesity such that obesity may be a risk factor for adult-onset asthma. Adults with asthma disclose comorbid obesity as one of the most common barriers to exercise. Physical inactivity has been linked to increases in body mass index (BMI). Few studies have explicitly examined the relationship between BMI and reporting exercise as an asthma trigger. It was hypothesized that individuals with asthma who have an increased BMI will also have increased reports of exercise as an asthma trigger.

METHODS

In total, 673 adult outpatients with asthma at Hôpital du Sacré-Cœur de Montréal in Montréal, Quebec, Canada underwent a brief sociodemographic and medical history interview. Patients provided information on their height, weight (used to calculate BMI), and triggers that generally provoked an asthma exacerbation (though it should be noted that a formal EIA test was not performed).

RESULTS

When individuals were classified as normal, overweight, or obese, logistic regression analysis revealed that those who were overweight had a 95% increase in the likelihood of reporting exercise-triggered asthma (odds ratio [OR], 1.95; 95% confidence interval [CI], 1.30-2.94) compared with those of normal weight, and this likelihood was more than doubled if the individuals were obese (OR, 2.34; 95% CI, 1.44-3.82). Assessing BMI as a continuous variable revealed that every 1-point increase in BMI was associated with a 9% increase in patients reporting exercise as a trigger (OR, 1.09; 95% CI, 1.04-1.14). All analyses were conducted adjusting for age, sex, asthma severity, and asthma control.

CONCLUSION

Results suggest that BMI influences the likelihood of reporting exercise as an asthma trigger, such that individuals with higher BMIs report exercise as an asthma trigger more often than those with a lower BMI. Given that the current study is cross-sectional, further prospective research is needed to define the causal pathway of this relationship.

Effect of obesity on asthma phenotype is dependent upon asthma severity

BACKGROUND

We recently reported that obese and non-obese patients with asthma have similar airflow limitation and bronchodilator responsiveness, but obese patients have more symptoms overall. There is limited information on the effect of obesity on asthmatics of varying severity measured by objective physiological parameters. Understanding how obesity affects asthmatics of differing severity can provide insights into the pathogenesis of asthma in the obese and a rationale for the therapeutic approach to such patients.

METHODS

Participants with asthma from two American Lung Association--Asthma Clinical Research Center (ALA-ACRC) studies were grouped by tertiles of airflow obstruction (forced expiratory volume in one second (FEV(1)%) predicted, FEV(1)/forced vital capacity (FVC)) and methacholine reactivity (PC(20)FEV(1)). Within each tertile, we examined the independent effect of body mass index (BMI), divided into normal weight, overweight, and obese categories, on lung function, airway reactivity, and symptoms.

RESULTS

Overall, both FEV(1) and FVC decreased and symptoms worsened with increasing BMI; airway reactivity was unchanged. When stratified by the degree of airflow obstruction, higher BMI was not associated with greater airway reactivity to methacholine. Higher BMI was associated with more asthma symptoms only in the least obstructed FEV(1)/FVC tertile. When stratified by degree of airway reactivity, BMI was inversely associated with FVC in all PC(20)FEV(1) tertiles. BMI was directly associated with asthma symptoms only in those with the least airway reactivity.

CONCLUSIONS

Obesity does not influence airway reactivity in patients with asthma and it is associated with more symptoms only in those with less severe disease.

Respiratory function and the obesity paradox

PURPOSE OF REVIEW

Obese individuals have impaired respiratory function relative to their normal-weight counterparts. Despite these negative effects, obesity is paradoxically associated with better survival in individuals with chronic obstructive pulmonary disease (COPD). The purpose of this review is to describe this 'obesity paradox', to discuss the effects of obesity on respiratory function, and to speculate as to whether obesity-related alterations in respiratory mechanics can influence the natural history of COPD.

RECENT FINDINGS

Given the known negative effects of obesity on respiratory physiology, it is reasonable to predict that obese COPD patients would be more likely to experience greater dyspnea and exercise intolerance relative to COPD patients of normal weight. However, recent evidence suggests that obese COPD patients have similar or better dyspnea scores during exercise and do not have diminished exercise capacity. These observations may be attributable to the fact that obese COPD patients have reduced operating lung volumes and higher inspiratory capacity to total lung capacity ratios than their lean COPD counterparts.

SUMMARY

Obese patients with COPD do not appear to be at a disadvantage during exercise relative to lean COPD patients. Obesity may be associated with improved survival in COPD but specific mechanisms for this paradox remain to be elucidated.

Effect of increased body mass index on asthma risk, impairment and response to asthma controller therapy in African Americans

OBJECTIVE

To explore whether obesity alters the risk, impairment and response to treatment in African Americans with asthma.

METHODS

The data used for this secondary analysis are from a 1-year study in African American subjects comparing fluticasone propionate/salmeterol 100/50 microg combination (FSC) and fluticasone propionate 100 microg (FP). Subjects were retrospectively stratified by body mass index (BMI) <20 [underweight], 20-24.9 [normal weight], 25-29.9 [overweight], 30-34.9 [obese I], 35-39.9 [obese II], and >or=40 [obese III] kg/m(2). Outcomes studied included impairment domains: FEV(1), morning and evening peak expiratory flow (AM and PM PEF), daily albuterol use, daily symptom scores and future risk domain: exacerbations.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov; NCT00102765.

RESULTS

There were 475 subjects evenly distributed between FSC and FP by baseline parameters. There were 207 subjects with a BMI >or=30, including 70 subjects with a BMI >or=40. Baseline BMI >or=40 was associated with numerically lower baseline AM and PM PEF. There was an attenuation of response to both treatments for only PM PEF (p < 0.05). By contrast, subjects with lower degrees of obesity or overweight did not differ from those with normal weight. The total population exacerbation rate was 2-fold greater in obese III subjects (39%) compared with subjects in other BMI categories (16-21%) (p < 0.05). A potential study limitation is the retrospective analysis of existing data.

DISCUSSION

Response to treatment was attenuated for PM PEF for subjects with BMI >or=40 and was also associated with an increased rate of asthma exacerbations.