Bronchial responsiveness to methacholine and adenosine 5'-monophosphate in young children with asthma: their relationship with blood eosinophils and serum eosinophil cationic protein

Can bronchial challenge test with adenosine or methacholine at preschool age predict school-age asthma?

OBJECTIVE

Bronchial challenge test (BCT) measures current airways-hyperreactivity, however, its predictive role in pre-school children (<6 years) for the diagnosis of asthma at school age is still debatable. We aimed to find whether preschool children with a positive adenosine or methacholine BCT are more prone to asthma at school age.

METHODS

We included children aged 6-13 years with respiratory symptoms that were previously referred to our pulmonary function laboratory for BCT (methacholine or adenosine, depending on the question asked) at age 10 months to 6 years (baseline). BCT was considered positive based on spirometry results or wheezing, desaturation, and tachypnea reactions. The primary outcome measure was asthma diagnosis at school age using the well-validated International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. We used logistic regression analysis to explore whether positive BCT could predict school-age asthma while including age and collected modified asthma predictive index in the model.

RESULTS

One hundred and fifty-one of 189 children (53% males), completed the ISAAC questionnaire (response rate = 80%). Mean ages at BCT and at follow-up were 3.9 ± 1.28 and 9.4 ± 1.85 years, respectively. At baseline, 40 of 67 had a positive adenosine test and 73 of 84 had a positive methacholine BCT. Thirty-nine children were diagnosed with asthma at school age. Logistic regression analysis showed that a positive adenosine test at pre-school age was the best predictor, significantly increasing the odds of asthma at school age by 6.34 (95% CI: 1.23-32.81, p = .028), while methacholine did not show significance (p = .69).

CONCLUSION

Choosing the relevant BCT for the question asked, positive adenosine, but not methacholine test, at pre-school, may predict asthma at school age.

Airway hyperresponsiveness to inhaled mannitol identifies a cluster of non-eosinophilic asthma patients with high symptom burden

BACKGROUND

Patients with asthma are heterogeneous in clinical presentation and in response to treatment. Despite this, tools to guide treatment are limited and include mainly measures of eosinophilic inflammation and symptoms. Airway hyperresponsiveness (AHR) to mannitol is present in patients across inflammatory phenotypes and improve with inhaled cortico-steroids.

OBJECTIVE

To investigate whether measuring AHR to mannitol in addition to eosinophilic inflammation and symptoms add information to the phenotypic characterization of patients with asthma.

METHODS

A total of 317 patients with asthma from six different cohorts were included in the analysis. All patients had measures of AHR to mannitol, blood eosinophils and ACQ-5 available. A cluster analysis using Wards minimum variance method was performed. The distribution of FeNO, IgE, lung function, induced sputum inflammatory cell count, age of onset and severity of disease was compared between clusters.

RESULTS

Four clusters were identified. Three of the clusters had proportionate levels of AHR, eosinophilic inflammation and symptoms, but one cluster presented with low levels of eosinophilic inflammation and a significant symptom burden. Half of the subjects in this cluster presented with AHR to inhaled mannitol. Lung function, fractional exhaled nitric oxide, Body Mass Index and IgE were normal.

CONCLUSION

Information on AHR to mannitol in addition to blood eosinophils and symptoms identifies a subgroup of asthma patients with symptomatic, non-eosinophilic disease. AHR to mannitol may provide a treatable trait in a subgroup of patients with non-eosinophilic asthma.

Comparison of methacholine and mannitol challenges: importance of method of methacholine inhalation

Background

Direct inhalation challenges (e.g. methacholine) are stated to be more sensitive and less specific for a diagnosis of asthma than are indirect challenges (e.g. exercise, non-isotonic aerosols, mannitol, etc.). However, data surrounding comparative sensitivity and specificity for methacholine compared to mannitol challenges are conflicting. When methacholine is inhaled by deep total lung capacity (TLC) inhalations, deep inhalation inhibition of bronchoconstriction leads to a marked loss of diagnostic sensitivity when compared to tidal breathing (TB) inhalation methods. We hypothesized that deep inhalation methacholine methods with resulting bronchoprotection may be the explanation for conflicting sensitivity/specificity data.

Methods

We reviewed 27 studies in which methacholine and mannitol challenges were performed in largely the same individuals. Methacholine was inhaled by dosimeter TLC methods in 13 studies and by tidal breathing in 14 studies. We compared the rates of positive methacholine (stratified by inhalation method) and mannitol challenges in both asthmatics and non-asthmatics.

Results

When methacholine was inhaled by TLC inhalations the prevalence of positive tests in asthmatics, 60.2% (548/910), was similar to mannitol, 58.9% (537/912). By contrast, when methacholine was inhaled by tidal breathing the prevalence of positive tests in asthmatics 83.1% (343/413) was more than double that of mannitol, 41.5% (146/351). In non-asthmatics, the two methacholine methods resulted in positive tests in 18.8% (142/756) and 16.2% (27/166) by TLC and TB inhalations respectively. This compares to an overall 8.3% (n = 76) positive rate for mannitol in 913 non-asthmatics.

Conclusion

These data support the hypothesis that the conflicting data comparing methacholine and mannitol sensitivity and specificity are due to the method of methacholine inhalation. Tidal breathing methacholine methods have a substantially greater sensitivity for a diagnosis of asthma than either TLC dosimeter methacholine challenge methods or mannitol challenge. Methacholine challenges should be performed by tidal breathing as per recent guideline recommendations. Methacholine (more sensitive) and mannitol (more specific) will thus have complementary diagnostic features.

Factors Associated with Positive Adenosine Challenge Test in Young Children with Suspected Asthma

Background: To investigate the predictive factors associated with positive adenosine monophosphate challenge using the auscultation method (AMP-PCW) test results. Methods: This is a prospective study of young children with suspected asthma who underwent AMP-PCW test. Patients with a positive AMP-PCW test were compared with those with a negative AMP-PCW. A multivariate logistic regression model was performed to identify the independent determinants of positive AMP-PCW. Results: A total of 159 patients completed the AMP-PCW test. The median age was 53 months. In total, 54.0% of patients had a positive AMP-PCW. The prevalence of atopic dermatitis and family history of asthma and allergy were significantly higher among the positive AMP-PCW group (P = 0.04, P = 0.02, and P = 0.007, respectively), as were the prevalences of elevated immunoglobulin E (IgE), peripheral blood eosinophils percentage (P = 0.003, P < 0.001, respectively), and number of emergency department (ED) visits/hospitalizations before AMP-PCW test (P = 0.006). A significant inverse correlation exists between peripheral blood eosinophils percentage and serum IgE levels with the AMP end-point concentrations (r = -0.302, P = 0.001, and r = -0.312, P = 0.001, respectively). In multivariate logistic regression model, peripheral blood eosinophils percentage, IgE levels, and the number of ED visits/hospitalizations before the AMP-PCW test were found as independent predictors for positive AMP-PCW test result. Conclusions: Our results suggest that bronchial responsiveness to AMP-PCW is related to proxy markers of airway inflammation (elevated eosinophils and IgE levels) and clinical exacerbation of asthma before the test. This may support the role of AMP-PCW in detecting inflammatory changes and monitoring their trend among young children with suspected asthma.

ERS technical standard on bronchial challenge testing: pathophysiology and methodology of indirect airway challenge testing

Recently, this international task force reported the general considerations for bronchial challenge testing and the performance of the methacholine challenge test, a "direct" airway challenge test. Here, the task force provides an updated description of the pathophysiology and the methods to conduct indirect challenge tests. Because indirect challenge tests trigger airway narrowing through the activation of endogenous pathways that are involved in asthma, indirect challenge tests tend to be specific for asthma and reveal much about the biology of asthma, but may be less sensitive than direct tests for the detection of airway hyperresponsiveness. We provide recommendations for the conduct and interpretation of hyperpnoea challenge tests such as dry air exercise challenge and eucapnic voluntary hyperpnoea that provide a single strong stimulus for airway narrowing. This technical standard expands the recommendations to additional indirect tests such as hypertonic saline, mannitol and adenosine challenge that are incremental tests, but still retain characteristics of other indirect challenges. Assessment of airway hyperresponsiveness, with direct and indirect tests, are valuable tools to understand and to monitor airway function and to characterise the underlying asthma phenotype to guide therapy. The tests should be interpreted within the context of the clinical features of asthma.

Bronchial hyper-responsiveness after preterm birth

Being born preterm often adversely affects later lung function. Airway obstruction and bronchial hyperresponsiveness (BHR) are common findings. Respiratory symptoms in asthma and in lung disease after preterm birth might appear similar, but clinical experience and studies indicate that symptoms secondary to preterm birth reflect a separate disease entity. BHR is a defining feature of asthma, but can also be found in other lung disorders and in subjects without respiratory symptoms. We review different methods to assess BHR, and findings reported from studies that have investigated BHR after preterm birth. The area appeared understudied with relatively few and heterogeneous articles identified, and lack of a pervasive understanding. BHR seemed related to low gestational age at delivery and a neonatal history of bronchopulmonary dysplasia. No studies reported associations between BHR after preterm birth and the markers of eosinophilic inflammatory airway responses typically found in asthma. This should be borne in mind when treating preterm born individuals with BHR and airway symptoms.

Does airway hyperresponsiveness monitoring lead to improved asthma control?

The current guidelines recommend an approach to asthma management based on asthma control, rather than asthma severity. Although several specific questionnaires have been developed and control criteria have been established based on clinical guidelines, the evaluation of asthma control is still not optimal. In general, these indicators provide adequate assessment of current control, but they are more limited when estimating future risk. There is much evidence demonstrating the persistence of airway inflammation and airway hyperresponsiveness (AHR) in patients with total control. Therefore, the objective of this review was to analyse the possible role of AHR monitoring as an instrument for assessing asthma control. We will evaluate its capacity as an indicator for future risk, both for estimating the possibility of clinical deterioration and loss of lung function or exacerbations. Furthermore, its relationship with inhaled corticosteroid treatment will be analysed, while emphasizing its capacity for predicting response and adjusting dosage, as well as information about the capability of AHR for monitoring treatment. Last of all, we will discuss the main limitations and emerging opportunities of AHR as an assessment instrument for asthma control.

Genetic factors explain half of all variance in serum eosinophil cationic protein

BACKGROUND

Eosinophil cationic protein (ECP) is one of four basic proteins of the secretory granules of eosinophils. It has a variety of functions associated with inflammatory responses. Little is known about the causes for variation in serum ECP levels.

AIM

To identify factors associated with variation in serum ECP and to determine the relative proportion of the variation in ECP due to genetic and non-genetic factors, in an adult twin sample.

METHODS

A sample of 575 twins, selected through a proband with self-reported asthma, had serum ECP, lung function, airway responsiveness to methacholine, exhaled nitric oxide, and skin test reactivity, measured. Linear regression analysis and variance component models were used to study factors associated with variation in ECP and the relative genetic influence on ECP levels.

RESULTS

Sex (regression coefficient = -0.107, P < 0.001), body mass index (BMI) (0.007, P = 0.028), and airway responsiveness to methacholine (0.074, P = 0.001) were significantly associated with ECP. Adjusted for these factors, ECP correlated 0.53 (P < 0.001) and 0.27 (P = 0.001) in monozygotic and dizygotic twins, respectively (P-value for difference = 0.05). According to the most parsimonious variance component model, genetic factors accounted for 57% (CI: 42-72%, P < 0.001) of the variance in ECP levels, whereas the remainder (43%) was ascribable to non-shared environmental factors. The genetic correlation between ECP and airway responsiveness to methacholine was statistically non-significant (r = -0.11, P = 0.50).

CONCLUSION

Around half of all variance in serum ECP is explained by genetic factors. Serum ECP is influenced by sex, BMI, and airway responsiveness. Serum ECP and airway responsiveness seem not to share genetic variance.

Bronchodilator responses after methacholine and adenosine 5'-monophosphate (AMP) challenges in children with asthma: their relationships with eosinophil markers

BACKGROUND

Bronchodilator responsiveness (BDR) and eosinophilic inflammation are characteristic features of asthma. Objective. The aim of this study was to compare the relationships of BDR after methacholine challenge or adenosine 5'-monophosphate (AMP) challenge to blood eosinophil markers in children with asthma.

METHODS

Methacholine and AMP challenges were performed on 69 children with mild intermittent to moderate persistent asthma. BDR was calculated as the change in forced expiratory volume in 1 second, expressed as percentage change of the value immediately after the each challenge and the value after inhalation of salbutamol. Serum total IgE levels, blood eosinophil counts, and serum eosinophil cationic protein (ECP) levels were determined for each subject.

RESULTS

A positive relationship between serum total IgE levels and BDR was found only after the AMP challenge (R(2) = 0.345, p = .001) rather than after the methacholine challenge (R(2) = 0.007, p = .495). Peripheral blood eosinophil counts correlated more significantly with BDR after AMP challenge (R(2) = 0.212, p = .001) than BDR after methacholine challenge (R(2) = 0.002, p = .724). Both BDR after methacholine challenge (R(2) = 0.063, p = .038) and BDR after AMP challenge (R(2) = 0.192, p = .001) were significantly correlated with serum ECP levels.

CONCLUSION

BDR after AMP challenge may be more closely related to eosinophilic inflammation, compared with that after methacholine challenge.

Predictive value of adenosine 5'-monophosphate challenge in preschool children for the diagnosis of asthma 5 years later

We evaluated the predictive values of preschool bronchial challenge with nebulized adenosine 5'-monophosphate (AMP) using the auscultation method for having asthma 5 years later. Preschool AMP challenge had a high negative (90%) and a moderate positive (67%) predictive value for asthma 5 years later. Positive predictive value increased with the age at which the challenge was performed. The degree of preschool response to AMP was associated with the severity of asthma at school age.

AMP affects intracellular Ca2+ signaling, migration, cytokine secretion and T cell priming capacity of dendritic cells

The nucleotide adenosine-5'-monophosphate (AMP) can be released by various cell types and has been shown to elicit different cellular responses. In the extracellular space AMP is dephosphorylated to the nucleoside adenosine which can then bind to adenosine receptors. However, it has been shown that AMP can also activate A(1) and A(2a) receptors directly. Here we show that AMP is a potent modulator of mouse and human dendritic cell (DC) function. AMP increased intracellular Ca(2+) concentration in a time and dose dependent manner. Furthermore, AMP stimulated actin-polymerization in human DCs and induced migration of immature human and bone marrow derived mouse DCs, both via direct activation of A(1) receptors. AMP strongly inhibited secretion of TNF-α and IL-12p70, while it enhanced production of IL-10 both via activation of A(2a) receptors. Consequently, DCs matured in the presence of AMP and co-cultivated with naive CD4(+)CD45RA(+) T cells inhibited IFN-γ production whereas secretion of IL-5 and IL-13 was up-regulated. An enhancement of Th2-driven immune response could also be observed when OVA-pulsed murine DCs were pretreated with AMP prior to co-culture with OVA-transgenic naïve OTII T cells. An effect due to the enzymatic degradation of AMP to adenosine could be ruled out, as AMP still elicited migration and changes in cytokine secretion in bone-marrow derived DCs generated from CD73-deficient animals and in human DCs pretreated with the ecto-nucleotidase inhibitor 5'-(alpha,beta-methylene) diphosphate (APCP). Finally, the influence of contaminating adenosine could be excluded, as AMP admixed with adenosine desaminase (ADA) was still able to influence DC function. In summary our data show that AMP when present during maturation is a potent regulator of dendritic cell function and point out the role for AMP in the pathogenesis of inflammatory disorders.

Bronchial hyperresponsiveness in preschool children with allergic rhinitis

BACKGROUND

Nonasthmatic subjects with allergic rhinitis often have bronchial hyperresponsiveness (BHR), characteristic of asthma. The presence and degree of atopy is suggested to be important for BHR in patients with asthma. We aimed to assess BHR to methacholine (direct stimulus) and to adenosine 5'-monophosphate (AMP; indirect stimulus) in preschool children with allergic rhinitis and to investigate their relationship with the degree of atopy.

METHODS

Methacholine and AMP bronchial challenges were performed in preschool children with allergic rhinitis (n = 96), using a modified auscultation method. The end point concentration, resulting in audible wheezing and/or oxygen desaturation, was determined for each challenge. The degree of atopy was assessed using serum total IgE levels, the number of positive skin-prick tests, and atopic scores (sum of graded wheal size).

RESULTS

BHR to methacholine (end point concentration, ≤8 mg/mL) and to AMP (end point concentration, ≤200 mg/mL) was observed in 32 (33.3%) and 26 (27.1%) subjects, respectively. No significant relationship was observed between BHR to methacholine and any atopy parameter. In contrast, the atopic scores were higher in the AMP-BHR(+) group compared with the AMP-BHR(-) group, and a significant association was found between the degree of atopic scores and the frequency of BHR to AMP (score for trend, p = 0.006). Such a relationship was not observed for serum total IgE levels and the number of positive SPTs.

CONCLUSION

BHR to methacholine and BHR to AMP were detected in a significant proportion of preschool children with allergic rhinitis. The degree of atopy in terms of atopic scores seems to be an important factor for BHR to AMP but not for BHR to methacholine.

Bronchial Hyperresponsiveness to Methacholine and AMP in Children With Atopic Asthma

Purpose

Bronchial hyperresponsiveness (BHR) is typically measured by bronchial challenge tests that employ direct stimulation by methacholine or indirect stimulation by adenosine 5'-monophosphate (AMP). Some studies have shown that the AMP challenge test provides a better reflection of airway inflammation, but few studies have examined the relationship between the AMP and methacholine challenge tests in children with asthma. We investigated the relationship between AMP and methacholine testing in children and adolescents with atopic asthma.

Methods

The medical records of 130 children with atopic asthma (mean age, 10.63 years) were reviewed retrospectively. Methacholine and AMP test results, spirometry, skin prick test results, and blood tests for inflammatory markers (total IgE, eosinophils [total count, percent of white blood cells]) were analyzed.

Results

The concentration of AMP that induces a 20% decline in forced expiratory volume in 1 second [FEV1] (PC20) of methacholine correlated with the PC20 of AMP (r²=0.189, P<0.001). No significant differences were observed in the levels of inflammatory markers (total eosinophil count, eosinophil percentage, and total IgE) between groups that were positive and negative for BHR to methacholine. However, significant differences in inflammatory markers were observed in groups that were positive and negative for BHR to AMP (log total eosinophil count, P=0.023; log total IgE, P=0.020, eosinophil percentage, P<0.001). In contrast, body mass index (BMI) was significantly different in the methacholine positive and negative groups (P=0.027), but not in the AMP positive and negative groups (P=0.62). The PC20 of methacholine correlated with FEV1, FEV1/forced vital capacity (FVC), and maximum mid-expiratory flow (MMEF) (P=0.001, 0.011, 0.001, respectively), and the PC20 of AMP correlated with FEV1, FEV1/FVC, and MMEF (P=0.008, 0.046, 0.001, respectively).

Conclusions

Our results suggest that the AMP and methacholine challenge test results correlated well with respect to determining BHR. The BHR to AMP more likely implicated airway inflammation in children with atopic asthma. In contrast, the BHR to methacholine was related to BMI.

Comparison of bronchial hyperresponsiveness to methacholine and adenosine and airway inflammation markers in patients with suspected asthma

BACKGROUND

Bronchial hyperresponsiveness is usually measured by bronchial challenge test with direct (e.g., methacholine) and indirect (e.g., adenosine) agonists. There are few studies comparing both types of agents and they have had conflicting concordance.

OBJECTIVE

We sought to compare the results of both tests in a population with symptoms suggestive of asthma so as to determine their relationship with bronchial inflammatory markers.

METHODS

Seventy-nine patients whose age ranged from 14 to 81 years were recruited for this study. Challenge tests were performed using the tidal volume method. PC₂₀ methacholine and PC₁₅ and PC₂₀ adenosine were calculated. Induced sputum and fraction of exhaled nitric oxide measurements were also performed.

RESULTS

Atopy was found in 69% of the patients. Methacholine PC₂₀ and adenosine PC₁₅ were positive in 32 patients (40.5%), both having a sensitivity of 73%. Percentage of agreement was 45.45% and κ index was only 0.369. Adenosine PC₂₀ elicited lower sensitivity and agreement. No correlation between methacholine PC₂₀ and adenosine PC₁₅ was observed. Higher fraction of exhaled nitric oxide values and sputum eosinophil counts were seen in patients with positive adenosine challenge results. The use of adenosine PC₁₅ or PC₂₀ did not alter the association with inflammatory markers.

CONCLUSIONS

The concordance between both techniques was low. Methacholine is not a reliable predictor of hyperresponsiveness to adenosine, leading us to conclude that the two tests are complementary but not interchangeable in clinical practice. Additionally, responsiveness to the two bronchoconstrictor stimuli does not indicate presence of the same airway abnormality. Indirect stimuli provide a better reflection of bronchial inflammation.

Acute additive effect of montelukast and beclomethasone on AMP induced bronchoconstriction

Bronchial hyperresponsiveness to 5-adenosine mono-phosphate (AMP) is a marker of airway inflammation. Inhaled corticosteroids and antileukotrienes are used as anti-inflammatory drugs for the treatment of asthma. To find out if these two drugs exert their protection in an additive fashion, we compared the effects of acute treatment with inhaled beclomethasone (BDP) and montelukast (ML), alone or in combination, on methacholine and AMP induced bronchoconstriction. 15 asthmatic patients undertook methacholine and AMP challenges at baseline and after receiving ML or BDP, alone or in combination, in a randomized, double-blind, double-dummy placebo-controlled, crossover design. BDP pretreatment significantly increased the AMP PC(20) value (68.34+/-15.9mg/mL) as compared to placebo (22.87+/-5.7mg/mL). Combined treatment, BDP plus ML, afforded a further significant increase of AMP PC(20) (154.57+/-55.0mg/mL) as compared to each single treatment. The significant protection exerted by combined treatment as compared to each single active treatment was also demonstrated by the change of AMP PC(20) doubling dose as compared to placebo and each single active treatment. Our findings suggest that these two agents exert their acute additive protection against AMP induced bronchoconstriction acting on distinct inflammatory pathways and their combined use might provide greater protection against inflammatory response elicited by AMP than either drug alone.

Relationships of methacholine and adenosine monophosphate responsiveness with serum vascular endothelial growth factor in children with asthma

BACKGROUND

Airway hyperresponsiveness, which is a characteristic feature of asthma, is usually measured by means of bronchial challenge with direct or indirect stimuli. Vascular endothelial growth factor (VEGF) increases vascular permeability and angiogenesis, leads to mucosal edema, narrows the airway diameter, and reduces airway flow.

OBJECTIVE

To examine the relationships between serum VEGF level and airway responsiveness to methacholine and adenosine monophosphate (AMP) in children with asthma.

METHODS

Peripheral blood eosinophil counts, serum eosinophil cationic protein (ECP) concentrations, and serum VEGF concentrations were measured in 31 asthmatic children and 26 control subjects. Methacholine and AMP bronchial challenges were performed on children with asthma.

RESULTS

Children with asthma had a significantly higher mean (SD) level of VEGF than controls (361.2 [212.0] vs 102.7 [50.0] pg/mL; P < .001). Blood eosinophil counts and serum ECP levels significantly correlated inversely with AMP provocation concentration that caused a decrease in forced expiratory volume in 1 second of 20% (PC20) (r = -0.474, P =.01; r = -0.442, P =.03, respectively), but not with methacholine PC20 (r = -0.228, P = .26; r = -0.338, P =.10, respectively). Serum VEGF levels significantly correlated with airway responsiveness to AMP (r = -0.462; P = .009) but not to methacholine (r = -0.243; P = .19).

CONCLUSIONS

Serum VEGF levels were increased in children with asthma and were related to airway responsiveness to AMP but not to methacholine. Increased VEGF levels in asthmatic children may result in increased airway responsiveness by mechanisms related to airway inflammation or increased permeability of airway vasculature.

Direct and indirect challenges in the clinical assessment of asthma

OBJECTIVE

To compare direct and indirect bronchoprovocation challenges in the clinical assessment of asthma.

DATA SOURCES

PubMed search using the keywords adenosine monophosphate, eucapnic voluntary hyperpnea, exercise, hypertonic saline, mannitol, and methacholine challenges and asthma.

STUDY SELECTION

Articles were selected based on their relevance to the topic of this review.

RESULTS

Methacholine is the most widely used direct challenge. Methacholine is highly sensitive, provided symptoms are clinically current and deep inhalations are avoided during inhalation. There are many causes of a false-positive test result. Specificity is increased if the pretest probability of asthma is greater, if the methacholine responsiveness is moderate or greater, and if the methacholine-induced symptoms mimic the natural symptoms. Indirect challenges are more specific for asthma but are insensitive, particularly for mild and/or well-controlled asthma. The lower sensitivity may relate to the fact that many indirect challenges (eg, exercise, eucapnic voluntary hyperpnea, adenosine monophosphate) are dose limited (ie, the dose of stimulus cannot be increased above a level based on physiology or solubility). Indirect challenges also correlate better with airway inflammation and are more responsive to anti-inflammatory treatments.

CONCLUSIONS

Direct challenges (ie, methacholine), because of the high sensitivity, function best to exclude clinically current asthma; a positive test result is consistent with but not diagnostic of asthma. By contrast, indirect challenges are superior for confirming asthma and are the challenges of choice when exercise bronchospasm is the question (eg, certification for international athletic competition, armed forces, scuba diving). Indirect challenges would be preferred for monitoring of asthma control and used serially to help diagnose occupational asthma.

Diagnostic and therapeutic value of airway challenges in asthma

Airway challenges are of value in the assessment of asthma. Direct challenges (histamine and methacholine) are highly sensitive for clinically current symptomatic asthma and particularly useful to exclude current asthma when they are negative. Indirect challenges (exercise, eucapnic voluntary hyperventilation, adenosine monophosphate, hypertonic saline, mannitol) are more specific but very insensitive for clinical asthma. They are of particular value to confirm asthma and to differentiate asthma from other airway diseases, such as chronic airflow limitation. The indirect stimuli are the challenges of choice for evaluating exercise-induced bronchoconstriction.

Provocative challenges to help diagnose and monitor asthma: exercise, methacholine, adenosine, and mannitol

PURPOSE OF REVIEW

To review bronchial provocations tests used in the measurement of bronchial hyperresponsiveness to help in the diagnosis of asthma.

RECENT FINDINGS

The bronchial provocations tests reviewed include exercise, methacholine, AMP and mannitol, with reference to methodology and monitoring of treatment.

SUMMARY

Methacholine is used for identifying bronchial hyperresponsiveness and to guide treatment. Exercise is used as a bronchial provocation test because demonstrating prevention of exercise-induced asthma is an indication for use of a drug. Both of these tests are being used to study tolerance to beta2 agonists. There is increasing use of eucapnic voluntary hyperpnea as a surrogate bronchial provocation test for exercise to identify exercise-induced asthma, particularly in athletes. For methacholine and AMP there is concern about the different breathing patterns used to inhale these aerosols and the impact they have on the cutoff point for identifying bronchial hyperresponsiveness. A new test that uses a kit containing prepacked capsules of different doses of mannitol and a delivery device is discussed. There is increasing interest in using tests that act indirectly by release of mediators because the bronchial hyperresponsiveness itself is an indicator of the presence of inflammation. Since treatment of inflammation leads to loss of bronchial hyperresponsiveness to indirect stimuli, these tests are well suited to identify success of treatment.