One of the characteristic features of asthma is bronchial hyperresponsiveness (BHR) a poorly understood phenomenon used to describe the increase in airway responsiveness to their external environment resulting in airway obstruction in response to allergens, pollutants, virus, bronchoconstrictor agents, beta-blockers and physiological stimuli at significantly lower concentrations than otherwise observed in healthy subjects. Moreover, other respiratory diseases of the lung may show a similar heightened response but to a much limited range of stimuli and hence
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