Airway responsiveness and peak flow variability in the diagnosis of asthma for epidemiological studies

Role of circulating microRNA-132 in allergic bronchopulmonary aspergillosis: A case-control study

Allergic bronchopulmonary aspergillosis (ABPA) is an allergic respiratory disease. In the current study, we aimed to evaluate the roles of miRNA-21 and miRNA132 as biomarkers in the diagnosis of ABPA. A total of 30 controls, 30 allergic asthmatic patients, 30 severe asthma with fungal sensitization (SAFS) patients, and 30 ABPA patients were included. Real-time polymerase chain reaction was used to quantify the level of miRNAs expression. The expression level of miRNA-21 was significantly higher in allergic asthmatic, SAFS, and ABPA patients in comparison with controls (p < 0.001). However, no significant difference was detected in the expression level of miRNA-21 among the different patient groups (p > 0.05). The ABPA patients had significantly higher levels of miRNA-132 expression compared to controls, allergic asthmatic patients, and SAFS patients (p < 0.001), but there was a non-significant difference between controls and allergic asthmatic patients (p = 0.09). At a cut-off of 1.52, the sensitivity of miRNA-132 expression was 93.3% and the specificity was 100% different ABPA from healthy controls. At a cut-off of 6.5, miRNA-132 expression was found to reliably differentiate between ABPA and SAFS, with a sensitivity of 86.7% and a specificity of 80%. In ABPA patients, miRNA-132 expression positively correlation with the levels of serum IL-5 (r = 0.91, p < 0.001). miRNA-132 has a role in ABPA detection and distinguishing ABPA from allergic asthma and SAFS. These preliminary data from case-control study need further studies to confirm its finding.

Clinical predictors of frequent exacerbations in subjects with severe chronic obstructive pulmonary disease (COPD)

BACKGROUND

Acute exacerbations are a significant source of morbidity and mortality associated with chronic obstructive pulmonary disease. Among individuals with COPD, some patients suffer an inordinate number of exacerbations while others remain relatively protected. We undertook a study to determine the clinical factors associated with "frequent exacerbator" status within a population of subjects with severe COPD.

METHODS

Case-control cohort recruited from two Boston-area practices. All subjects had GOLD stage 3 or 4 (FEV(1) ≤ 50% predicted) COPD. "Frequent exacerbators" (n = 192) had an average of ≥2 moderate-to-severe exacerbations per year while "non-exacerbators" (n = 153) had no exacerbations in the preceding 12 months. Multivariate logistic regression was performed to determine the significant clinical predictors of "frequent exacerbator" status.

RESULTS

Physician-diagnosed asthma was a significant predictor of frequent exacerbations. Within a subset of our cohort, the modified Medical Research Council dyspnea score and FEF (25-75%) predicted were also significant clinical predictors of frequent exacerbator status (p < 0.05). Differences in exacerbation frequency were not found to be due to increased current tobacco use or decreased rates of maintenance medication use.

CONCLUSIONS

Within our severe COPD cohort, a history of physician-diagnosed asthma was found to be a significant clinical predictor of frequent exacerbations. Although traditional risk factors such as decreased FEV(1)% predicted were not significantly associated with frequent exacerbator status, lower mid-expiratory flow rates, as assessed by FEF (25-75%) predicted, were significantly associated with frequent exacerbations in a subset of our cohort.

Dietary sodium manipulation and asthma

BACKGROUND

There is a wide geographical variation in the prevalence of asthma and observational studies have suggested that dietary sodium may play a role.

OBJECTIVES

To assess the effect of dietary sodium manipulation on asthma control.

SEARCH STRATEGY

We carried out a search using the Cochrane Airways Group asthma register. We searched the bibliographies of included randomised controlled trials (RCTs) for additional studies. We carried out the most recent search in November 2010.

SELECTION CRITERIA

We considered only RCTs that involved dietary sodium reduction or increased sodium intake in patients with asthma.

DATA COLLECTION AND ANALYSIS

Both review authors assessed study and extracted data. We conducted data analyses in RevMan 5 using mean differences and random effects.

MAIN RESULTS

We identified a total of nine studies in relation to sodium manipulation and asthma, of which five were in people with asthma (318 participants), and four in people with exercise-induced asthma (63 participants). There were no significant benefits of salt restriction on the control of asthma. There was some evidence from the exercise-induced asthma studies that a low sodium diet may improve lung function after exercise and possibly baseline lung function, but this is based on findings from a very small numbers of participants.

AUTHORS' CONCLUSIONS

This review did not find any evidence that dietary sodium reduction significantly improves asthma control. Although dietary sodium reduction may result in improvements in lung function in exercise-induced asthma, the clinical significance of this effect is unclear.

Assessing the exacerbations risk of influenza-associated chronic occupational asthma

The purpose of this article was to conduct a risk-based study based on a linkage of experimental human influenza infections and fluctuation analysis of airway function to assess whether influenza viral infection was risk factor for exacerbations of chronic occupational asthma. Here we provided a comprehensive probabilistic analysis aimed at quantifying influenza-associated exacerbations risk for occupational asthmatics, based on a combination of published distributions of viral shedding and symptoms scores and lung respiratory system properties characterized by long-range peak expiratory flow (PEF) dynamics. Using a coupled detrended fluctuation analysis-experimental human influenza approach, we estimated the conditional probability of moderate or severe lung airway obstruction and hence the exacerbations risk of influenza-associated occupational asthma in individuals. The long-range correlation exponent (alpha) was used as a predictor of future exacerbations risk of influenza-associated asthma. For our illustrative distribution of PEF fluctuations and influenza-induced asthma exacerbations risk relations, we found that the probability of exacerbations risk can be limited to below 50% by keeping alpha to below 0.53. This study also found that limiting wheeze scores to 0.56 yields a 75% probability of influenza-associated asthma exacerbations risk and a limit of 0.34 yields a 50% probability that may give a representative estimate of the distribution of chronic respiratory system properties. This study implicates that influenza viral infection is an important risk factor for exacerbations of chronic occupational asthma.

Exhaled carbon monoxide in asthmatic adults with bronchial reactivity: a prospective study

HYPOTHESIS

We hypothesized that eCO may permit non-invasive assessment of disease activity in adults with asthma and bronchial reactivity.

METHODS

A total of 209 participants 18 to 65 years of age with a diagnosis of asthma and bronchial reactivity provided data for analysis. The association between eCO and bronchial reactivity, forced expiratory volume in one second (FEV(1)), forced vital capacity (FVC), peak expiratory flow rate measurements (PEFR), asthma symptoms score, and bronchodilator use cross-sectionally and within-subject change in eCO were analyzed in relation to change in these variables over 6 weeks.

RESULTS

There was no difference in eCO in those who were taking inhaled corticosteroids and those who were not (p = 0.33). There was also no cross-sectional or within-in subject association between eCO and bronchial reactivity, FEV(1), FVC, PEFR, symptoms score, or bronchodilator use.

CONCLUSIONS

In a population of adults with bronchial reactivity, eCO has no or very limited potential as a biomarker of asthma activity.

An evaluation of the use of bronchoconstriction induced by deep inspiration as a new epidemiological measure for asthma

RATIONALE

Bronchoconstriction after deep inhalation is associated with increased severity of asthma and is also a predictor of length of hospital stay in individuals admitted with asthma exacerbations. We hypothesized that this effect may represent a new non-invasive method to assess bronchial reactivity and other measures of asthma control.

METHODS

We used a cross-sectional study design recruiting participants 18 to 65 years of age with a physician diagnosis of asthma. All participants were asked to provide three serial peak expiratory flow rate (PEFR) measurements in the morning, and bronchial reactivity was measured up to a maximum inhaled dose of 24.5 micromoL methacholine on the same day. Participants also recorded their asthma symptoms score and bronchodilator use during the 7 days before measuring bronchial reactivity.

RESULTS

A total of 127 people provided data for analysis. There was no significant relationship between bronchoconstriction after deep inhalation (as measured by three serial PEFR measurements) and either bronchial reactivity to methacholine, asthma symptoms, or bronchodilator use.

CONCLUSIONS

Bronchoconstriction induced by deep inspiration does not appear to be a valid marker of airway hyperresponsiveness or asthma severity in adults with mild to moderate asthma.

NFAT1 transcription factor regulates pulmonary allergic inflammation and airway responsiveness

Allergic asthma is a chronic inflammatory disease of the lung whose incidence and morbidity continues to rise in developed nations. Despite being a hallmark of asthma, the molecular mechanisms that determine airway hyperresponsiveness (AHR) are not completely established. Transcription factors of the NFAT family are involved in the regulation of several asthma-related genes. It has been shown that the absence of NFAT1 leads to an increased pleural eosinophilic allergic response accompanied by an increased production of Th2 cytokines, suggesting a role for NFAT1 in the regulation of allergic diseases. Herein, we analyze NFAT1-/- mice to address the role of NFAT1 in a model of allergic airway inflammation and its influence in AHR. NFAT1-/- mice submitted to airway inflammation display a significant exacerbation of several features of the allergic disease, including lung inflammation, eosinophilia, and serum IgE levels, which were concomitant with elevated Th2 cytokine production. However, in spite of the increased allergic phenotype, NFAT1-/- mice failed to express AHR after methacholine aerosol. Refractoriness of NFAT1-/- mice to methacholine was confirmed in naïve mice, suggesting that this refractoriness occurs in an intrinsic way, independent of the lung inflammation. In addition, NFAT1-/- mice exhibit increased AHR in response to serotonin inhalation, suggesting a specific role for NFAT1 in the methacholine pathway of bronchoconstriction. Taken together, these data add support to the interpretation that NFAT1 acts as a counterregulatory mechanism to suppress allergic inflammation. Moreover, our findings suggest a novel role for NFAT1 protein in airway responsiveness mediated by the cholinergic pathway.

Does a low sodium diet improve asthma control? A randomized controlled trial

RATIONALE

Observational studies and initial randomized trials have indicated that a low sodium diet may improve asthma control.

OBJECTIVES

We tested the hypothesis that a low sodium diet would improve asthma control over a 6-week period.

METHODS

Participants with a physician diagnosis of asthma and measurable bronchial reactivity to methacholine entered a randomized double-blind placebo-controlled trial. All adopted a low sodium diet and were randomized to receive either 80 mmol/day of oral sodium supplements (normal sodium intake) or matched placebo (low sodium intake) for 6 weeks. The primary outcome was change in bronchial reactivity to methacholine; secondary outcomes were change in lung function, morning and evening peak expiratory flow, asthma symptoms score, daily bronchodilator use, Juniper Standardized Asthma Quality of Life Questionnaire score, and atopy.

MEASUREMENTS AND MAIN RESULTS

A total of 220 individuals entered the study, of whom 199 completed the protocol. In the low sodium-intake group, mean daily urinary sodium excretion decreased by 20 mmol (SD, 64 mmol) and in the normal-sodium-intake group increased by 28 mmol (SD, 74 mmol). There were no differences between the two groups in the primary or secondary outcome measures; the mean difference in bronchial reactivity between the low- and normal-intake groups was -0.03 doubling doses of methacholine (95% confidence interval, -0.60 to 0.53).

CONCLUSIONS

The use of a low sodium diet as an adjunctive therapy to normal treatment has no additional therapeutic benefit in adults with asthma and bronchial reactivity to methacholine.

The American Thoracic Society's spirometric criteria alone is inadequate in asthma diagnosis

BACKGROUND

The diagnosis of asthma is based on clinical symptoms, physical examination and pulmonary function tests, and can be very challenging. Most patients with asthma have a significant postbronchodilator response on spirometry indicating airway hyperresponsiveness. However, having a significant bronchodilator response by itself is not diagnostic of asthma. The definition of a 'significant' response has also been controversial. Many respirologists use the American Thoracic Society (ATS) postbronchodilator response criteria of 12% (provided it is 200 mL or greater) improvement in forced expiratory volume in 1 s (or forced vital capacity) from the baseline spirometry.

METHODS

In the present study, 644 patients who met the ATS criteria for a significant postbronchodilator spirometric response were retrospectively reviewed. The staff respirologist's diagnosis of asthma, based on all clinical and pulmonary function data, was used as the standard for the diagnosis of asthma.

RESULTS

Relying on spirometric criteria alone was inadequate in asthma diagnosis because only 54.7% of 310 patients who met the ATS bronchodilator response criteria were thought to have clinical asthma. Increasing the postbronchodilator percentage improvement from the ATS criteria only marginally improved diagnostic specificity and resulted in a decline in sensitivity.

CONCLUSIONS

The results of the present study further emphasize the need to use spirometric criteria as a guide but not as an unimpeachable gold standard with which to make a diagnosis of asthma. The diagnosis of asthma depends on expert physician correlation of patient history, physical examination and pulmonary function test results.

[The shuttle run test is not valid for the detection of asthma in school physical education programs]

OBJECTIVE

Certain sporting activities may trigger asthma exacerbations of varying intensity in children. Such exacerbations may lead to limitations in and rejection of such activities. During school hours, teachers are in a good position to observe these phenomena. The aim of the present study was to evaluate the shuttle run, a test of physical fitness used in school physical education programs, as a way of detecting asthma.

PATIENTS AND METHODS

We carried out a cross-sectional observational study of school children between the ages of 6 and 12 years using the asthma symptom questionnaire of the International Study of Asthma and Allergies in Childhood (ISAAC), a shuttle run test, and a free running test at maximum effort in order to study bronchial hyperresponsiveness. The principal measure of bronchial hyperresponsiveness used in both physical fitness tests was peak expiratory flow rate as measured with a peak flow meter. In comparing the results of the shuttle run test with those of the free running test and the ISAAC questionnaire we used the chi(2) test to measure association and the Cohen kappa coefficient to measure agreement.

RESULTS

We distributed the ISAAC questionnaire (n=919) to 460 (50.1%) boys and 459 (49.9%) girls between the ages of 6 and 12 years. All the tests were completed by 826 children. The level of agreement between the shuttle run test and free running test was positive but low for decreases in peak expiratory flow rate compared to baseline of 15% (chi(2)=5.6; P< .05; kappa=0.093; SE, 0.042) and of 20% (chi(2)=4.5; P< .05; kappa=0.08; SE, 0.046). For 10% decreases association was not significant and agreement was low (kappa=0.05; SE, 0.04). There was no agreement between the ISAAC questionnaire and the shuttle run test (kappa=0.095; SE, 0.63).

CONCLUSIONS

The shuttle run test using peak expiratory flow rate as the principal measure of bronchial hyperresponsiveness is not valid for the detection of asthma in schoolchildren.

Home exposures, parental atopy, and occurrence of asthma symptoms in adulthood in southern Taiwan

OBJECTIVE

Parental atopy and environmental exposures at home have been recognized risk factors for adulthood asthma. However, the relative contributions of specific risk factors and the overall contributions of heredity or home exposure remain unexplored. The purpose of this study was to identify predictors and estimate the population attributable risk (PAR) of each exposure for typical asthma symptoms among 26- to 50-year-old Taiwanese. We also investigated whether an interactive effect existed between parental atopy and home exposures on the occurrence of asthma symptoms in adulthood.

DESIGN

A cross-sectional study with retrospective components.

SETTING

Elementary and middle schools in Southern Taiwan.

SUBJECTS

Between March and October 2004, we conducted a cross-sectional survey among schoolchildren's parents from 94 elementary and middle schools in Southern Taiwan. The main outcome measure was typical asthma-like symptoms occurring within the preceding 5 years. Information on hereditary and home exposures was collected by using a self-administered questionnaire.

RESULTS

After excluding unqualified questionnaires, data from 24,784 subjects were left for analysis. New-onset asthma was reported for 0.83% of male (n = 80 of 9,662) and 1.36% of female subjects (n = 206 of 15,122). Besides parental atopic factors, environmental tobacco smoke or pet avoidance and visible mold on walls at home were independently associated with the occurrence of asthma symptoms. Mutually adjusted models produced statistically significant associations between any home exposure (odds ratio [OR], 1.80; 95% confidence interval [CI], 1.08 to 3.23; PAR, 28.04%), parental atopy (OR, 4.47; 95% CI, 3.47 to 5.75; PAR, 31.38%), and new-onset asthma. However, there was no interaction between parental atopy and home exposures.

CONCLUSIONS

Home exposures and parental atopy both increased the risks of new-onset asthma in adulthood but did not show an interactive effect. These two exposure categories approximately contributed equally to the adulthood asthma.

Overcoming gaps in the management of asthma in older patients: new insights

Asthma is under-recognised and undertreated in older populations. This is not surprising, given that one-third of older people experience significant breathlessness. The differential diagnosis commonly includes asthma, chronic obstructive pulmonary disease (COPD), heart failure, malignancy, aspiration and infections. Because symptoms and signs of several cardiorespiratory diseases are nonspecific in older people and diseases commonly co-exist, investigations are important. A simple strategy for the investigation of breathlessness in older people should include a full blood count, chest radiograph, ECG, peak flow diary and/or spirometry with reversibility as a minimum. If there are major abnormalities on the ECG, an echocardiogram should also be performed. Diurnal variability in peak flow readings >or=20% or >or=15% reversibility in forced expiratory volume in 1 second, spontaneously or with treatment, support a diagnosis of asthma. Distinguishing asthma from COPD is important to allow appropriate management of disease based on aetiology, accurate prediction of treatment response, correct prognosis and appropriate management of the chest condition and co-morbidities. The two conditions are usually readily differentiated by clinical features, particularly age at onset, variability of symptoms and nocturnal symptoms in asthma, supported by the results of reversibility testing. Full lung function tests may not necessarily help in differentiating the two entities, although gas transfer factor is characteristically reduced in COPD and usually normal or high in asthma. Methacholine challenge tests previously mainly used in research are now also used widely and safely to confirm asthma in clinical settings. Interest in exhaled nitric oxide as a biomarker of airways inflammation is increasing as a noninvasive tool in the diagnosis and monitoring of asthma. Regular inhaled corticosteroids (ICS) are the mainstay of treatment of asthma. Even in mild disease in older adults, regular preventive treatment should be considered, given the poor perception of bronchoconstriction by older asthmatic patients. If symptoms persist despite ICS, addition of long-acting beta(2)-adrenoceptor agonists (LABA) should be considered. Addition of LABA to ICS improves asthma control and allows reduction in ICS dose. However, older people have been grossly under-represented in trials of LABA, many trials having excluded those >or=65 years of age. On meta-analysis, beta(2)-adrenoceptor agonists (both short acting and long acting) are associated with increased cardiovascular mortality and morbidity in asthma and COPD. While the evidence for excess cardiovascular mortality is stronger for short-acting beta(2)-adrenoceptor agonists, it would be prudent to exercise particular care in using beta(2)-adrenoceptor agonists (long acting and short acting) in those at risk of adverse cardiovascular outcomes, including older people. Regular review of cardiovascular status (and monitoring of serum potassium concentration) in patients taking beta(2)-adrenoceptor agonists is crucial. The response to LABA should be carefully monitored and alternative 'add-on' therapy such as leukotriene receptor antagonists (LRA) should be considered. LRA have fewer adverse effects and in individual cases may be more effective and appropriate than LABA. Long-term trials evaluating beta(2)-adrenoceptor agonists and other bronchodilator strategies are needed particularly in the elderly and in patients with cardiovascular co-morbidities. There is no evidence that addition of anticholinergics improves control of asthma further, although the role of long-acting anticholinergics in the prevention of disease progression is currently being researched. Older patients need to be taught good inhaler technique to improve delivery of medications to lungs, minimise adverse effects and reduce the need for oral corticosteroids. Nurse-led education programmes that include a written asthma self-management plan have the potential to improve outcomes.

Spirometric criteria for asthma: adding further evidence to the debate

BACKGROUND

Objective assessments of pulmonary function are considered essential for the diagnosis of asthma. The degree of reversibility of FEV(1) considered supportive of asthma varies between international asthma guidelines.

OBJECTIVE

We sought to compare the relative performance of international guideline reversibility criteria for identifying impairment in persons with a significant bronchodilator response (SBR) without an asthma diagnosis.

METHODS

The North West Adelaide Health (Cohort) Study, a population biomedical study of 4060 subjects, conducted spirometry according to American Thoracic Society criteria. SBR was defined as postbronchodilator FEV(1) responses of at least 12% or 15% of baseline values, 9% of predicted values, or 400 mL. A self-completed questionnaire assessed current asthma (CA), respiratory symptoms, and participant demographics.

RESULTS

The prevalence of CA was 9.4% (n = 380), whereas 1.3% (>/=400 mL) to 4.5% (>/=9% of predicted value) of participants demonstrated an SBR in the absence of CA. With the exception of the 9% predicted criterion, prebronchodilator mean FEV(1) (percent predicted) in those demonstrating an SBR but no CA was significantly worse than that in the CA group. Significantly more respiratory symptoms were experienced by the SBR groups than the group without asthma. Logistic regression analyses identified different characteristics of those classified by the following criteria: 12% and 15%, age of 40 years or greater and household income of less than $40,000; 9% predicted, household income of less than $40,000; 400 mL, male sex (odds ratio, 4.5; 95% CI, 2.1-9.3).

CONCLUSIONS

Different criteria identify different persons, but SBR by any criteria was associated with significant respiratory impairment, some of which might be attributable to asthma. Postbronchodilator change as a percentage of predicted value was the least biased of the criteria.

Reference values for methacholine reactivity (SAPALDIA study)

BACKGROUND

The distribution of airway responsiveness in a general population of non-smokers without respiratory symptoms has not been established, limiting its use in clinical and epidemiological practice. We derived reference equations depending on individual characteristics (i.e., sex, age, baseline lung function) for relevant percentiles of the methacholine two-point dose-response slope.

METHODS

In a reference sample of 1567 adults of the SAPALDIA cross-sectional survey (1991), defined by excluding subjects with respiratory conditions, responsiveness during methacholine challenge was quantified by calculating the two-point dose-response slope (O'Connor). Weighted L1-regression was used to estimate reference equations for the 95th , 90th , 75th and 50th percentiles of the two-point slope.

RESULTS

Reference equations for the 95th , 90th , 75th and 50th percentiles of the two-point slope were estimated using a model of the form a + b* Age + c* FEV1 + d* (FEV1)2 , where FEV1 corresponds to the pre-test (or baseline) level of FEV1. For the central half of the FEV1 distribution, we used a quadratic model to describe the dependence of methacholine slope on baseline FEV1. For the first and last quartiles of FEV1, a linear relation with FEV1 was assumed (i.e., d was set to 0). Sex was not a predictor term in this model. A negative linear association with slope was found for age. We provide an Excel file allowing calculation of the percentile of methacholine slope of a subject after introducing age--pre-test FEV1--and results of methacholine challenge of the subject.

CONCLUSION

The present study provides equations for four relevant percentiles of methacholine two-point slope depending on age and baseline FEV1 as basic predictors in an adult reference population of non-obstructive and non-atopic persons. These equations may help clinicians and epidemiologists to better characterize individual or population airway responsiveness.

Underestimation of the peak flow variability in asthmatic children: evaluation of a new formula

Asthma guidelines suggest evaluation of peak expiratory flow (PEF) variability, but timing for the two PEF measurements is not mentioned. Usual formula calculates amplitude as percentage of mean day-night PEF values. Since PEF circadian changes follow a sinusoidal function, we reasoned that variability might be calculated by measuring PEF at 4 pm (PEF(1)) and either at 10 am or 10 pm (PEF(2)) with the formula %variability = 200 . |PEF(1)-PEF(2)|/PEF(2). Children with stable, mild intermittent asthma were recruited from an Asthma Clinic and asked to perform PEF measurements at even hours during a week, until 12 measurements covering a 24-h period were accomplished. From these measurements we calculated PEF variability through several methods. Accuracy of such methods to predict actual PEF variability was assessed through the concordance correlation coefficient (r(c)). Thirty five asthmatic children were recruited. Actual PEF variability, calculated with the usual formula using the highest and lowest PEF obtained at any time of the 24 h cycle had a median of 37.3% (range, 0-88.5%). Variability calculated through other methods was: usual formula with highest and lowest PEF obtained from the sinusoidal curve, 21.4% (r(c) = 0.79); usual formula with PEF measured at 4 pm and 4 am, 17.8% (r(c) = 0.67); proposed formula using PEF measured at 4 pm and either 10 pm, 15.9% (r(c) = 0.68), or 10 am, 17.4% (r(c) = 0.69). Some examples with PEF measured in the morning (8 am or 10 am) and at night (8 pm or 10 pm) yielded median PEF variability from 4.0% (r(c) = 0.18) to 8.7% (r(c) = 0.38). Current methods for calculating PEF variability seemed not to be accurate enough as to be confident, suggesting that an in-deep reevaluation of the usefulness of PEF variability or, conversely, of the methods to assess it, should be done.

Association between air pollution exposure and exhaled nitric oxide in an elderly population

BACKGROUND

Animal models suggest that the cardiovascular effects of air pollution result in part from inflammation caused by proinflammatory mediators originating in the lung. In a human study of the cardiovascular effects of air pollution, we aimed to evaluate the potential association between air pollution levels and the fraction of exhaled nitric oxide (FE(NO)), a non-invasive measure of airway inflammation.

METHODS

Breath samples were collected weekly between September and December 2000 in a community based group of elderly subjects (median age 70.7 years) in Steubenville, Ohio. The samples were analysed for NO. Air pollution levels were measured concurrently at a central site monitor.

RESULTS

An increase in the 24 hour average PM(2.5) concentration of 17.7 micro g/m(3) was associated with an increase in FE(NO) of 1.45 ppb (95% CI 0.33 to 2.57) in models adjusted for subject, week of study, day of the week, hour of the day, ambient barometric pressure, temperature, and relative humidity. This represents a change of approximately 15% compared with the mean FE(NO) in the cohort (9.9 ppb). A significant association was also observed for a 24 hour moving average of ambient NO (0.83 ppb increase, 95% CI 0.26 to 1.40). In two-pollutant models, the magnitude and precision of the PM(2.5) effect was not reduced and the ambient NO effect was no longer significant. The associations between FE(NO) and PM(2.5) were significantly higher in subjects with a doctor's diagnosis of COPD (p value for interaction = 0.03).

CONCLUSIONS

Ambient pollution may lead to airway inflammation as measured by FE(NO). These subclinical inflammatory changes may be an important step in the pathogenesis of the cardiopulmonary effects induced by exposure to air pollution.

Use of pulmonary function tests in the diagnosis of occupational asthma

OBJECTIVE

To discuss the different methods of assessing lung function measurements for the diagnosis of occupational asthma, focusing in particular on serial peak expiratory flow rate (PEFR) monitoring, including details on how PEFR records should be kept, plotted, and analyzed and limitations of the method.

DATA SOURCES

Published studies on the use of diagnostic methods in occupational asthma, expert opinion, and recently obtained data from studies performed at a large occupational lung disease clinic. STUDY SOURCES: The expert opinion of the author was used to select the relevant data for review.

RESULTS

Objective methods are necessary for the diagnosis of occupational asthma, since clinical history alone is not a satisfactory means of diagnosis. Serial PEFR monitoring has a high diagnostic sensitivity and specificity for occupational asthma and is more useful than evaluation of cross-shift change in forced expiratory volume in 1 second or change in nonspecific bronchial hyperresponsiveness. Interpretation is best performed by expert visual evaluation of plots of maximum, mean, and minimum daily PEFR readings.

CONCLUSIONS

Despite some limitations of the method, serial PEFR monitoring is usually the most appropriate first-line investigation in workers suspected of having occupational asthma.