 |  CO, SV, bp, mean filling&pulse pressures..???
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| Author | 3 Posts |
namf
Forum Elite
Topics: 80
Posts: 312
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Hi everyone!
This has been my nemasis for a long time. I never could understand the inter-relationships between the vascular system elements, especially CO, SV, and blood pressure(bp). For example, as a kid in the park, if you "constrict" the water fountain, it seems that the "blood pressure" goes up..Do you see the analogy to the vascular system? BUT the bp does not go up with constriction.. :shock:
I just don't get it very well. IF anyone is so inclined, could you give me a brief explanation on the basics?? I know CO=HRxSV, but I don't seem to do well if you ask me which vessels must constrict for the CO to go up, or for the mean filling pressure to go up, or what the difference between stroke volume, pulse pressure, and blood pressure, etc are!!
Thanks in advance..
P.S. if you can't explain it yourself, but saw some really basic resource, I am all ears. Thanks again 
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| BumbleB
Forum Junior
Topics: 2
Posts: 83
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In the water fountain...
YOu do constrict the vessel (increasing the resistance), while the flow rate (Q) or CO is constant.
So if you you this formula - P=QR you can see that if Q is constant and R is increased, P will also increase.
But what happens in the body is that the baroreceptors are more concerned in keeping a proper P, so if R increases they are gonna compensate by decreasing Q. The body tries to keep a constant pressure and reduces the cardiac output when the peripheral resistance increases.
Blood presure: this is the pressure generated by your left ventricle when it squeezes the blood into your aorta. The diastolic pressure (the lower number) is the amount of force needed for the aortic valve to open and the systolic pressure is the maximum pressure that the LV creates .
The pulse pressure is just the difference between the systolic (120) and diastolic (80). It's significance is that its and indication of how hard your heart is working. It falls dramatically when you are in shock or bleeding to death.
THe stroke volume is just the difference in the volume of blood in your left ventricle between the time its full and the time it squeezes out the blood into the aorta. Generally, the LV squeezes only 50% of the blood it receives in each filling. So
1. Left ventricle has 40 ml of blood in it
2. the bicuspid valve opens and 50 more ml of blood go into the LV
3. now the LV has 90 ml of blood this is its end diastolic volume
4.the LV squeezes until the aortic valve opens, and it shoots out 50 ml of blood into the aorta
5.So now the LV again has only 40ml of blood - this is its end systolic volume
The stroke volume is EDV-ESV = 90-40 = 50ml
CO and vessel constriction.
CO is governed mostly by our sympathetic NS I believe - when BV constrict (increasing R) the baroreceptors compensate by reducing Q (CO).
Also, when the body needs more blood, as when you're running away from a dog and the BV's in your muscles are dilated -the CO greatly increases so that the P can stay close to normal.
Mean filling pressure - this is the pressure that the blood vessel walls exert on the blood itself when there's absolutely no circulation. This number has a significance in that it increases transiently after a transfusion.
I hope this helped a little bit. Check out this website:
http://www.missouri.edu/~huxleyv/bloodpressure200...
or this one http://www.missouri.edu/~huxleyv/Biophysics2000.h...
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| namf
Forum Elite
Topics: 80
Posts: 312
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BumbleB--
Thanks for all your sweet "honey" and teaching me the "PQR"s of cardiovascular physiology~ Wow, you're so kind and did a really good job of keeping things simple and clear for me..Thank you so much, sweet BumbleB!
Namf
P.S. I take the USMLE 8.3 and I am keeping a diary on this forum if you're curious about my emotional rollercoaster world these days. Thanks so much, once again! :icon_queen: :icon_queen: :icon_joker: :icon_joker: :icon_king: :icon_king: :icon_thumb: :icon_thumb: :icon_thumb:
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