Realising the potential of various inhaled airway challenge agents through improved delivery to the lungs

FEV1 recovery following methacholine challenge in asthma: Variability and comparison of methods

BACKGROUND

Methacholine challenges have been used in clinical trials to assess therapeutic effects and potential adverse reactions of interventions on pulmonary function in a sensitive population, such as in subjects with asthma. Here, we evaluate the variability of the methacholine challenge recovery model, and compare the results obtained for both incremental and bolus challenge methods.

METHODS

The extent, time course and variability of change in forced expiratory volume in 1 s (FEV₁) following repeated methacholine challenges in subjects with mild asthma were investigated in an open-label, four-period, fixed-sequence, two-method, replicate crossover study. At Visits 1 and 2, subjects underwent an incremental challenge using doubling doses of methacholine until a ≥20% decrease in FEV₁ was observed; at Visits 3 and 4, subjects underwent a bolus challenge, inhaling a single dose of methacholine calculated from the cumulative dose established during Visit 1.

RESULTS

A total of 19 subjects were included in the study. Both the mean FEV₁ area under the curve (FEV₁ AUC_0-tz) and mean maximum reductions in FEV₁ (absolute and relative) 120 min post-challenge values were higher for the incremental challenges than the bolus challenges, with no reported difference between repetitions of the same methodology. FEV₁ AUC_0-tz decrease 120 min post challenge demonstrated an intra-subject coefficient of variation (CV) of 47.2% (incremental) and 78.3% (bolus), suggesting considerable between-visit variability. The mean absolute, and similarly relative, maximum reductions in FEV₁ compared with post-diluent baseline values demonstrated lower intra-subject variability (incremental 21.16%, bolus 40.67%) than the FEV₁ AUC_0-tz-based endpoint. There was a trend towards faster recovery following the bolus challenge than with the incremental challenge. The provocative dose of methacholine inducing a ≥20% decrease in FEV₁ resulted in a between-group mean difference of 27.20% in the incremental challenge periods, with a high intra-subject CV of 80.64%, demonstrating considerable variability.

CONCLUSION

Maximum reduction in FEV₁ had the lowest variability. There was little difference between repetitions of the same methodology, as indicated by overlapping confidence intervals. There was a trend towards faster recovery following bolus challenge than with the incremental challenge. The results of this trial could be of value when designing future clinical trials using the methacholine challenge methodology.

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.

Approaches to Asthma Diagnosis in Children and Adults

Although the hallmark features of asthma include reversible airflow obstruction, airway eosinophilia, and symptoms of recurrent wheeze associated with breathlessness and cough, it is a heterogeneous disease. The extent of the pathophysiological abnormalities are variable between patients. Despite this, until recently, asthma diagnosis had been made very simplistically predominantly from a clinical history and examination, and often a trial of medication such as short acting bronchodilators. The limitations of this approach have become increasingly apparent with evidence of inappropriate over diagnosis, under diagnosis and misdiagnosis. Although there is no gold standard single test to make a diagnosis of asthma, there are several objective tests that can be used to support the diagnosis including physiological measures such as obstructive spirometry associated with bronchodilator reversibility and airway hyperresponsiveness. In addition, non-invasive tests of airway inflammation such as exhaled nitric oxide or peripheral blood eosinophils are important to identify those with an allergic or eosinophilic phenotype. Diagnostic guidelines reflect the importance of using objective tests to support a diagnosis of asthma, however practical application in the clinic may not be straightforward. The focus of this review is to discuss the need to undertake objective tests in all patients to support asthma diagnosis and not just rely on clinical features. The advantages, challenges and limitations of performing tests of lung function and airway inflammation in the clinic, the difficulties related to training and interpretation of results will be explored, and the utility and relevance of diagnostic tests will be compared in adults and children.