Question 7

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Look at the deposition pattern of inhaled particles of 5 µm diameter.

• Explain why such particles deposit preferentially from trachea to 4th generation, and then again from the 12th airway generation.copier
• Where do very small particles (<1 µm) deposit in the smallest airways?
  Why this preferential deposition? Estimate the percentage of <1 µm particles that is exhaled.

You should now appreciate that drugs or substances administered by aerosol and used to challenge airways (e.g. histamine, methacholine), to dilate airways, or to exert any other local effect, should have a specific size for maximizing deposition in the intrathoracic airways.

• What are the size limitations if the particles in an aerosol are to be deposited onto the lower airways?
• Where in the airways will the mucosal concentration of the pharmacological agent be highest?