Why is it more difficult to breathe out because of Asthma while breathing in is less difficult?

Asthma is caused to decreased cross sectional area of the bronchi and bronchioles. If you know the mechanism of breathing in and out, you would know that during expiration the Lungs kind of get compressed so it is more difficult to breathe out for a person who is already suffering from reduced cross sectional area of the Bronchi and Bronchioles because of compression of the Bronchi and Bronchioles. Breathing in or Inspiration is kind of less difficult as the Lungs increase in Size so as to suck in air so Bronchi and Bronchioles are not really compressed.

So any disease that causes reduced cross sectional area of the Bronchi and Bronchioles makes it especially more difficult to Breathe out or Expire, such disease are called Obstructive Lung Disease, for eg: Asthma, Bronchiectasis, Bronchitis, Chronic Obstructive Pulmonary disease(COPD) etc.

Such diseases can be caused due to Increased mucus secretion, contraction of Smooth muscle and other causes.

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