What causes bronchoconstriction during an asthma event?

Bronchoconstriction during an asthma event is primarily caused by stimuli such as dust, cold air, allergens, and irritants. When a person with asthma is exposed to these triggers, the immune system responds by causing inflammation and tightening the smooth muscles around the airways. This response leads to narrowing of the airways, known as bronchoconstriction, making it difficult to breathe. The presence of dust and cold air can trigger a significant reaction in sensitive airways, resulting in acute symptoms like wheezing, coughing, and shortness of breath.

The other options present concepts that do not directly lead to bronchoconstriction. For instance, temperature regulation of the air does not inherently cause bronchoconstriction, and relaxation of muscles around the airway would typically facilitate easier airflow, contrary to the state seen during an asthma event. Additionally, a reduction in airway resistance would actually ease breathing, rather than cause the constricted state observed during an asthma attack. Thus, the primary causes of bronchoconstriction are indeed external stimuli that provoke the reactive airway response characteristic of asthma.