During normal respiration, air travels through the nose, down the trachea, and into smaller and smaller airways called bronchi. The bronchi divide into bronchioles and finally into tiny grape-like clusters of thin, fragile sacs called alveoli. In alveoli, oxygen is exchanged for carbon dioxide in the blood.

Inhaled toxic vapors, such as those found in cigarette smoke, can lead to the development of emphysema, an irreversible disease that jeopardizes the lungs' ability to function.

In the early stage of emphysema, the alveoli are destroyed, resulting in "holes" in the tissue of the lower lungs. These holes cause the collapse of the bronchioles, preventing airflow from reaching the remaining alveoli.

The exchange of carbon dioxide for oxygen is thereby reduced, causing shortness of breath that progressively worsens and results in damage to the lungs and the heart.

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