# if diameter of alveoli is reduced to half, resistance becomes? [closed]

this is an MCQ for my upcoming exam. I have searched the internet but found mixed answers so far.

• What makes you think alveolar disease alters airways resistance? – Graham Chiu May 11 '20 at 20:36

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

• Does alveolar disease cause obstructive or restrictive lung disease? – Graham Chiu May 12 '20 at 20:37
• @GrahamChiu I don’t quite understand what you are getting at. Alveoli only play a minor role in Resistance, most important are the intermediate bronchioli. An increase in resistance there results in an obstructive pulmonary disease (i.e. asthma bronchiale). // COPD is an obstructive lung disease characterised by increased resistance, but the pathophysiology is different; emphysema play an important role, not so much decrease of radius in functioning alveoli. – Narusan May 13 '20 at 6:20
• That's my point. Shrinking the alveoli doesn't affect pulmonary resistance. Pulmonary resistance is measured between the alveoli and mouth. – Graham Chiu May 13 '20 at 6:57
• @GrahamChiu Yeah, that's why I had my note there. Mathematically, the resistance within the alveoli will increase 16-fold if diameter is halved. It will not matter in the general picture but still, this is the increase. It's not important for clinical care, but important for multiple choice questions. – Narusan May 13 '20 at 7:06
• Maybe it's a trick question? – Graham Chiu May 13 '20 at 8:09