Simple concept that I don't understand

[Xbocker]

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Ok sorry if this is a dumb question but Im a bit confused. According to the equation Pressure = Flow x Resistance

But the largest decrease in pressure occurs in arteriole because they have the highest resistance. Wouldn't that then contradict the equation? Shouldn't a decrease in pressure be associated with a decrease in resistance?

 

[withrye]

This equation is actually a variant of Ohm's law, which claims that current (I) is directly proportional to the potential difference (V) across two points. I = V/R

In this case, I is blood flow, R is the resistance of the segment of blood vessel, and V is the pressure difference between your start and end points. So really, pressure in your above equation is delta-pressure between two points. Looking at I = V/R, you can see that the point with the highest resistance will require the highest delta-pressure (i.e. decrease in pressure). This is because blood flow has to remain constant (unless you're hemorrhaging), so if R is large, the pressure drop must also be large.

 

[Stellar Clouds]

That pressure is delta pressure (aka change in pressure), so an increase in resistance with the same flow equals a greater net change in pressure (decrease).

 

[bangarang]

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[withrye]

Restating what others said because I had trouble with this when learning it for the first time: rearrange your equation to flow = (delta)pressure/resistance. So now, if your resistance increases, your change in pressure has to decrease proportionally in order to keep the same flow.

I think you meant to write "increase proportionally."

 

[bangarang]

I think you meant to write "increase proportionally."

Haha I knew it didn't sound right and deleted it right before I saw your post. Thanks. *smh

 

[Sanzy]

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