BP, CO, afterload question

[himicu]

hi,

i feel very confused now about the whole bp, co stuff now..

please help me!!

i will write my thread of thinking, please tell me where i am confused or where i'm mixing up..

so, i was studying about bp..

1) co=HR x SV.. and SV is related to afterload, preload, contractility..

my book says,

if afterload, or SVR increases, SV decreases because it's hard to pump the volume out, therefore CO decrease and BP decrease..

but then, my book also says,

2) BP=SVR x CO

if SVR increases, BP increases

i feel like, it contradicts itself..

it says 1) "afterload (SVR) goes up-->BP down" and 2)"afterload(SVR) goes up-->BP up"

for example, i know phenylephrine vasoconstrict and increase SVR.. therefore increase BP,,

but then if i think about the 1st formula, since it's hard to pump for the heart, SV will go down, and BP should go down..

where am i confused?

i'm very frustrated..

please clear my thoughts..

thank you!

[CRNA1982]

hi,

i feel very confused now about the whole bp, co stuff now..

please help me!!

i will write my thread of thinking, please tell me where i am confused or where i'm mixing up..

so, i was studying about bp..

1) co=HR x SV.. and SV is related to afterload, preload, contractility..

my book says,

if afterload, or SVR increases, SV decreases because it's hard to pump the volume out, therefore CO decrease and BP decrease..

but then, my book also says,

2) BP=SVR x CO

if SVR increases, BP increases

i feel like, it contradicts itself..

it says 1) "afterload (SVR) goes up-->BP down" and 2)"afterload(SVR) goes up-->BP up"

for example, i know phenylephrine vasoconstrict and increase SVR.. therefore increase BP,,

but then if i think about the 1st formula, since it's hard to pump for the heart, SV will go down, and BP should go down..

where am i confused?

i'm very frustrated..

please clear my thoughts..

thank you!

Both are correct....SV will always decrease with an overly increased SVR/afterload. The only way that BP would decrease with increased SVR/afterload is in an extreme situation of severe increased afterload/SVR AND poor contractility. When you give Neo, your SV will go down but BP will increase because the pts. SVR is typically VERY LOW. You need to look at each pt. specifically when you apply these concepts. Your second example is a more typical clinical picture seen with pts. experiencing hypotension.