How does asthma affect my lungs?

It narrows the... ...Airways by the process of inflammation in the airway walls and so increases their resistance to air movement.
Various ways. Asthma is an inflammatory disease. Inflammation takes place that leads to swelling of the airways and narrowing. Additionally, asthma is characterized by airway muscle constriction that leads to further narrowing of the airways. Finally, proper control of asthma is crucial and may help avoid what is called "airway remodeling", a more permanent structural change of the airway.