Response to bronchodilators after exercise challenge predicts bronchial hyperreactivity

Seasonal variability of the methacholine challenge test

BACKGROUND

Since the intensity of some variables that influence bronchial hyper-responsiveness (BHR) varies across different seasons of the year, the percentage of positive metacholine challenge test (MCT) is theoretically subjected to seasonal variation. This study has looked at the seasonal variability of MCT among young adults with suspected asthma.

METHODS

The number of MCT performed and its corresponding proportion of positive results were retrospectively evaluated and compared for different seasons over a 5-year period.

RESULTS

Overall 645 subjects (mean age 21.4 +/- 2.3 yr) underwent MCT during the study period. Two-hundred nine MCTs (34.2%) were performed in the winter, significantly higher when compared to any other season of the year. Positive MCT (defined as PC(20) < 16 mg/mL) was noted in 163 patients (25.2%). The proportion of positive MCTs has shown significant seasonal trend, (p < 0.0001, chi-square test for trend), it was significantly higher in the winter and in the spring (32.2% and 32.4%, respectively) when compared with the summer (13.4%).

CONCLUSIONS

This study showed a significant seasonal variability for both pattern of referral to MCT and the seasonal prevalence of BHR young adults. These findings probably reflect seasonal variation in the intensity of external stimuli that involve in the pathogenesis of BHR, such as allergens burden and respiratory tract infections across the year. We suggest that interpretation of a positive MCT as predictive of BHR and of asthma should take into account the observed seasonal variability of the test.

Bronchodilator response after negative methacholine challenge test predicts future diagnosis of asthma

BACKGROUND

Currently there are no reliable means to predict the likelihood of a subject with negative results from a methacholine challenge test (MCT) to be diagnosed with asthma in the future. We sought to determine whether the magnitude of the response to bronchodilator (BD) administered after a negative MCT has a predictive value for future asthma.

METHODS

Over a 5 -year period, starting from January 2004, the change in the forced expiratory volume in 1 second (FEV(1)) after inhaling BD (salbutamol) was recorded among subjects with negative MCT despite symptoms suggestive of asthma such as wheezing and dyspnea. Subjects with a significant response to BD (defined as improvement in FEV(1) of more than 200 ml and 12%) were questioned for the presence of asthma on January 2009.

RESULTS

Overall 645 subjects (mean age 21.4 +/- 2.3 years) underwent MCT. Negative MCT (defined as PC(20) > 16 mg/mL) was noted in 482 (74.7%) patients of whom significant response to BD was identified in 35. Over a median observation time of 2.1 years, 11 of them (31.4% of the study population and 1.7% of the entire cohort) were subsequently diagnosed with asthma. Improvement of FEV(1) by 20% predicted asthma with sensitivity, specificity, and positive predictive values of 86.9%, 66.6%, 83.3%, respectively, p = 0.0022.

CONCLUSIONS

Our findings suggest that administration of BD after a negative MCT enhances the diagnostic accuracy of the challenge test as it identifies subjects who are likely to develop clinical asthma in the future.

The response to bronchodilators in adults is not predictive of bronchial-hyperreactivity

BACKGROUND

In some subjects with suspected asthma who have normal spirometry, administration of bronchodilators (BD) improves expiratory flow rates. The predictive value of this phenomenon in adults is not known.

OBJECTIVES

To evaluate the predictive value of the response to BD for bronchial hyper-responsiveness (BHR) using the metacholine challenge test (MCT). Patients and methods. The study population included 62 non-smoking adult patients (41.9% women) 29.5 +/- 15.5 years of age (range 18-64 years) with suspected asthma with normal spirometry that underwent MCT within 1 week. The response to BD (200 mu g inhaled salbutamol) was compared between subjects with positive and negative MCT using cutoff levels of provocative concentrations of metacholine causing a 20% decrease in forced expiratory volume in 1 second (FEV(1)) (PC(20)) of 4 and 8 mg/mL.

RESULTS

Mean (+/- SD) baseline FEV(1) was 87.8 +/- 12% of predicted. After BD administration the mean FEV(1) increased by 4.3 +/- 3.9%. The prevalence of BHR was 17.7% and 25.8% for PC(20) for PC(20) of 4 mg/mL and 8 mg/mL, respectively. The post-BD FEV(1) increment for subjects with positive and negative MCT tests was 3.9% +/- 3.3% versus 4.4% +/- 4.1%, respectively; p = 0.89, using cutoff of 4 mg/mL. The corresponding figures for cutoff of 8 mg/ml were 4.3% +/- 3.1% vs. 4.3% +/- 4.2%, respectively; p = 0.8465. There was no correlation between post-BD FEV(1) increment and PC(20) values in patients with positive MCT test for the above-mentioned cutoff levels (correlation coefficient r = 0.1645, p = 0.6289; and r = 0.2417, p = 0.4051, respectively).

CONCLUSIONS

In adults with suspected asthma who have normal spirometry, the response to BD cannot be used to predict BHR.