The bronchial microcirculation in asthma.

Airway wall remodelling in asthma involves a number of changes including increased vascularity, vasodilation and microvascular leakage. Evidence suggests that the number and size of bronchial vessels is increased in patients with asthma compared with normal controls. In particular, there may be increased numbers of vessels in patients with fatal asthma. Treatment with inhaled corticosteroids is now known to reduce this vascularity. Bronchial vessels may undergo proliferation in response to inflammatory stimuli. Many factors can induce angiogenesis including a range of mediators and growth factors. Others can cause a vascular response by causing vasodilation and microvascular leakage. Airway wall oedema is likely to be important in asthma but has not yet been quantified. It is thought that mast cells play a key role in modulating these vascular remodelling changes by releasing cytokines and growth factors. Many key issues remain to be resolved before we fully understand the role of the bronchial microcirculation in asthma. In the future, novel therapies may be directed towards angiogenesis, vasodilation and microvascular leakage.