Why Prolonged Expiration in Asthma?

Respiratory muscles normally relax during exhalation, but during an asthma attack accessory muscles are needed to push air out. This causes a prolonged expiratory phase, and wheezing from turbulent airflow through constricted airways.

Why is expiration difficult in asthma?

During an asthma attack, it is harder and takes much longer to breathe out (expire or exhale) than to breathe in (inspire or inhale). Since it is so hard to breathe out during an asthma attack, more and more air gets trapped inside the lungs – making it feel like you can't breathe in or out!

What causes the wheezing on expiration in asthma?

In asthma, the wheezing is due to narrowing of the lower airways, whereas, with malignancies, the obstruction is usually in the upper, more proximal airways. In rare cases, wheezing may be heard both during inspiration and expiration.