Cigarette smoke causes the buildup of mucus within bronchi, paralyzes the cilia

Question

Cigarette smoke causes the buildup of mucus within bronchi, paralyzes the cilia and thickens the lining of the respiratory tract. How might these structural changes to the lower respiratory tract affect pulmonary function tests (ie. pulse oximeter reading, inspiratory capacity and expiratory capacity) and why would these be affected? If chronic smoking has leads to emphysema, how would the pulmonary function tests change and why would they change? Hint: Your answer should address alveolar and systemic gas exchange.

Explanation / Answer

Usually, when there is mucus in the respiratory tract , it is thrown out by the rhythmic beating of the cilia and cough reflex. In cigarette smoking , there is the paralysis of these cilia , the excess mucus will not be thrown out ,which will lead its accumulation.

The gaseous exchange between the air and the blood occurs at the terminal bronchioles and alveoli . There is very thin layer between the air and the blood which contains following layers -

The barrier between the air and blood is very thin ,which allows easy perfusion . But when there is an mucus accumulation in the smoker, the thickness of the exchange membrane also increases , which leads to abnormal reading in the pulmonary function test. The inspiratory and expiratory capacities will decrease and pulse oximeter reading will also decrease.

Emphysema is the condition where alveoli are damaged and enlarged , which leads to trapping of air inside it. Thus , it cannot retract and make space of new air. Hence , the effective alveoli that are working for the gaseous exchange decreases. This will again lead to abnormal pulmonary function test readings . The capacities will decrease, and the pulse oximeter will be low .

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