Brad is 45 years old and has been working as a coal cutter in a mine for the last 25 years. He likes the job because it pays well and the same mine had employed his father. Like many of his colleagues, Brad has had problems with a chronic cough. He has avoided his annual checkups for fear that he will be told he has "black lung," or coal worker's pneumoconiosis. The disease causes fibrosis, decreased diffusing capacity, and permanent small airway dilation. In later stages, pulmonary capillaries, alveoli, and airways are destroyed.
1. How can the disease described above create a mismatch between ventilation and perfusion? Use your understanding of alveolar dead space and physiologic shunt to explain your answer.
2. Individuals with chronic obstructive pulmonary disease have more difficulty exhaling than inhaling. Why is this so?
3. In general terms, what mechanisms in lung disease can affect diffusing capacity across alveolar membranes? Use the Fick law to explain your answer.