Bronchodilator testing "confidence intervals" based on the level of bronchial responsiveness

Effect of ADRB2 (adrenergic receptor β2) gene polymorphisms on the occurrence of asthma and on the response to nebulized salbutamol in South Indian patients with bronchial asthma

INTRODUCTION

Genetic mutations in the β2 receptor could alter its functioning and the response to β2 agonists. The study was done to find out the effect of two commonly occurring polymorphisms-Arg16Gly and Gln27Glu, on cause of asthma and on response to nebulized salbutamol in South Indian subjects of asthma.

METHODS

After baseline measurements of Forced Expiratory Volume in 1st second (FEV1), Forced Vital Capacity (FVC) and Peak Expiratory Flow Rate (PEFR), five mg of nebulized salbutamol was administered and spirometry was repeated. The increase in these parameters was calculated and patients were included for genotyping if the percentage increase in FEV1 was ≥12%. The frequencies of these polymorphisms in patients were compared with those of healthy volunteers.

RESULTS

112 patients and 127 healthy volunteers were genotyped. The frequencies of the polymorphisms were found to be similar to previously published Dravidian population frequencies. The frequencies of genotypes in asthmatics were similar to healthy volunteers. The increase in FEV1, FVC and PEFR was similar across various genotypes and haplotypes in both the polymorphisms. The GG-CG haplotype was associated with 3.1 times increased occurrence of asthma (p value = 0.02). The G allele of the Arg16Gly polymorphism was associated with lower baseline FEV1, FVC and PEFR values, but these were not statistically significant.

CONCLUSION

The Arg16Gly and Gln27Glu polymorphisms do not determine the occurrence of asthma individually, but the GG-CG haplotype is associated with an increased risk of asthma. There is no effect of the genotypes on the response to nebulized salbutamol.

The bronchodilator test with increasing doses of terbutaline in chronic obstructive pulmonary disease patients

There is no uniform consensus on the dose of bronchodilator to be used in the bronchodilator test (BDT). The objective of the study was to determine the dose of inhaled terbutaline that can safely achieve a greater number of positive BDT in patients with chronic obstructive pulmonary disease (COPD). The study was prospective and single blinded. One-hundred and fifty patients with stable COPD were included. Their mean (+/-SD) age was 67.4 (8.8) years. Their mean forced expiratory volume in the first second (FEV1) was 1.14 (0.48) l (41% of the predicted value). A baseline spirometry was performed and a second 20 min after the inhalation of placebo. Three consecutive doses of 500 microg of inhaled terbutaline were administered and a new spirometry was performed after each one. A multivariate analysis based on the comparison of the repeated means was performed in order to analyse the spirometric changes achieved after the different doses of bronchodilator. The increase of FEV1 and forced vital capacity (FVC) with the two first doses of terbutaline was statistically significant; the increase of the peak expiratory flow (PEF) was significant after the three doses administered. The number of positive BDT were 40, 47 and 60 after each dose of terbutaline (P=0.004). The higher dose of terbutaline was more useful in identifying patients with significant bronchoreversibility and, moreover, was well tolerated. We suggest that this dose (1500 microg) should be routinely used in performing the BDT.