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#1
07-22-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 662 Threads: 72 Thanked 370 Times in 204 Posts Reputation: 380
Resistance, pressure... flow

Hello guys... quick Q here... suddenly, I got stucked with the concept of

"Resistance is directly proportional to viscosity and inversely proportional to the radius to the 4th power."

I've learned the definition.. I just forgot how to apply it... S.O.S. my exam is next week. Any help will be more than welcome
__________________
"Disease is very old, and nothing about it has changed. It is we who change as we learn to recognize what was formerly imperceptible." JMC

#2
07-22-2012
 USMLE Forums Veteran Steps History: Not yet Posts: 218 Threads: 4 Thanked 74 Times in 55 Posts Reputation: 84

[QUOTE=Dr. Mexito;134666]Hello guys... quick Q here... suddenly, I got stucked with the concept of

"Resistance is directly proportional to viscosity and inversely proportional to the radius to the 4th power."

I've learned the definition.. I just forgot how to apply it... S.O.S. my exam is next week. Any help will be more than welcome[/

Check FA 2011 pg 256
 The above post was thanked by: Dr. Mexito (07-23-2012)
#3
07-22-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 570 Times in 323 Posts Reputation: 580
.

Quote:
 Originally Posted by Dr. Mexito Hello guys... quick Q here... suddenly, I got stucked with the concept of "Resistance is directly proportional to viscosity and inversely proportional to the radius to the 4th power."
polycythemia - increased resistance
anemia - decreased resistance

vasoconstriction - incresed resistance
vasodilation - decreased resistance
 The above post was thanked by: Dr. Mexito (07-23-2012)

#4
07-23-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 662 Threads: 72 Thanked 370 Times in 204 Posts Reputation: 380

Quote:
 Originally Posted by Casandra polycythemia - increased resistance anemia - decreased resistance vasoconstriction - incresed resistance vasodilation - decreased resistance
I was thinking about that part were they mention... if you reduce the R by half... what next????

I get so confused... I've memorized the definition, but haven't been able to put it on practice.
__________________
"Disease is very old, and nothing about it has changed. It is we who change as we learn to recognize what was formerly imperceptible." JMC
#5
07-23-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 570 Times in 323 Posts Reputation: 580

Quote:
 Originally Posted by Dr. Mexito I was thinking about that part were they mention... if you reduce the R by half... what next???? I get so confused... I've memorized the definition, but haven't been able to put it on practice.

If you reduce the R by half - vasoconstriction (and all the other parameters, eg. viscocity, remain constant) the resistance increases 8 times (1/2xR to the 4th power + inverse relation).

#6
07-24-2012
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 205 Threads: 6 Thanked 151 Times in 80 Posts Reputation: 161

Quote:
 Originally Posted by Casandra If you reduce the R by half - vasoconstriction (and all the other parameters, eg. viscocity, remain constant) the resistance increases 8 times (1/2xR to the 4th power + inverse relation). Let me know if this is what you were asking about
If we reduce radius by half shouldn't the resistance increases by 16 folds i.e(1/2*1/2*1/2*1/2)=1/16 and as everyone has mentioned resistance and radius have inverse relation ship so resistance increases by 16 folds

please correct me if I am wrong???
 The above post was thanked by: Dr. Mexito (07-24-2012), riya_rai84 (08-24-2012)
#7
07-24-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 570 Times in 323 Posts Reputation: 580

Quote:
 Originally Posted by offpiste If we reduce radius by half shouldn't the resistance increases by 16 folds i.e(1/2*1/2*1/2*1/2)=1/16 and as everyone has mentioned resistance and radius have inverse relation ship so resistance increases by 16 folds please correct me if I am wrong???
yup, you are right - my mistake!
It should be 16 (2 to power 4)

Thanks for correcting me offpiste

And as I wrote before the resistance will increase
 The above post was thanked by: Dr. Mexito (07-24-2012)
#8
08-24-2012
 USMLE Forums Scout Steps History: Not yet Posts: 85 Threads: 13 Thanked 32 Times in 21 Posts Reputation: 42

Quote:
 Originally Posted by offpiste If we reduce radius by half shouldn't the resistance increases by 16 folds i.e(1/2*1/2*1/2*1/2)=1/16 and as everyone has mentioned resistance and radius have inverse relation ship so resistance increases by 16 folds please correct me if I am wrong???
1) 2* radius = 1/16 R ~16* FLOW (Q)
2) 1/2 radius + 16* R ~1/16* Q

acording to above given data:

1) when 2 times radius increases,resistance will decreases about 16 times, and flow will increases about 16 times
2)when 1/2 of radius decrease ,16times resistance will increases and flow will decreases about 16 times
am i right??

after completing physio subject when i move to next subject this chapter easily wash out from mine brain then again i put mine ful eforts here to undrstand this one chapter,from next month mine triad wil start, am so tense about few physio chapters they easily wash out from mine brain, what i do i have no time to again go through dvds

Last edited by riya_rai84; 08-24-2012 at 12:53 AM.
 The above post was thanked by: Dr. Mexito (09-17-2012)

 Tags Cardiovascular-, Physiology-

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