: If diameter of alveoli is reduced to half, resistance becomes? this is an MCQ for my upcoming exam. I have searched the internet but found mixed answers so far.

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The resistance is defined as pressure difference per flow (basically just an application of Ohm's law).

With Hagen-Poiseulle:

So if the alveoli diameter is reduced to half (resulting in a halved radius), as the resistance changes by the fourth, it is increased by factor 16 (24).

Note: As the bronchioles terminales are connected parallel, they actually do only make up roughly 20% versus 40% for the other bronchioli and 40% for the upper airways.

Source: Pape H, Kurtz A, Silbernagl S, ed. 9., Physiologie 2019. doi:10.1055/b-006-163285