Great job with the video! Many thanks. One anomaly that I find is that during a compensated heart failure, the renal compensatory mechanisms cause retention of fluid causing venous return to actually increase. Therefore, the VR curve also shifts up and to the right so as to maintain the steady state cardiac output to near normal.
100lurics I know it’s been many moons but we still need u buddy, to make these easy grasping concepts tutorials please. You are one of the few who are good at the game!
Thank you . Please make another video on anti hypertensive drugs with more details . Your explanation is more simple and interesting . Very informative too.Best regards Dr.Joe , India
does anyone know where i can find the video when she about cardiogenic/hypovolemic/etc shock???!!! I saw it but now i cannot find it anymore...she describes how to use a specific formula including pulmonary wedge pressure, SV, etc
Great video!! Just note that during exercise the venous return curve s`X intercept or mean systemic pressure (10 mmHg) should stay in the same place. Because the total circulating volume was not altered. Greetings!
shobs iyer For those nerds wondering why?There are some flaws in your thinking, let me correct them for you. Follow along. flow characteristics of the systemic venous circulation are dependent on Vo (unstressed[reservoir] volume in veins), Vs(stressed volume in veins), Vt(total volume in veins), C(compliance), and Rv (Resistance to venous flow) recall that venous return; VR= ( Pms-Pra ) / Rv Pms is mean systemic pressure, Pms=Vs/C which can be written as Pms=(Vt-Vo)/C This new equation suggests that Pms can be altered through two basic mechanisms: (1) a change in the total volume in the reservoir(Vt); or (2) a change in the proportion of Vo and Vs. An alteration of autonomic tone, catecholamine stress responses, or infusion of exogenous vasoactive substances will alter the ratio of Vs to Vo without a change in C, thus changing Pms. Your partially right, but you should be thinking>exercise>SNS>increase in HR, venoconstriction in non vital organs and vasodilation in vital organs(heart, brain, muscle)>increased preload>increase in CO-->a change in proportion of Vs and Vo (volume of stressed venous blood vs Volume of unstressed venous blood) >increase in PMS A lot of books will says venoconstriction leads to a decrease venous compliance b/c of inverse relationship between resistance and compliance. They try to generalize it and make it simple, but compliance is way more complicated and depends on so many other factors The way I see it is that compliance in this model should be considered a static, passive mechanical property of veins. why? recall that venous system has two compartments; 1)venules and small veins, which lack smooth muscle layer and cannot constrict and account for 70-80% of bodies total blood reservoir, they have a very large crosssectional area contribute little to Rv and systemic compliance 2)Large veins and Medium sized veins, which can constrict, and contribute to compliance and they have small cross-sectional area and act as a valves. These two compartments work against each other under autonomic stress i.e increased stressed volume and Pms in the reservoir compartment (which increases VR) but decreased mean radius in the vena cava and large veins (which decreases VR). In conclusion its not the compliance/restriction of the vein, that increases Pms, but the change in proportion of Vs ans Vo. Yeah this shit is confusing, and a lot of books don't explain it properly.
Guru Jolly thanks for this explanation. Made me realize I had one misunderstanding about why nitro is used in angina. I always thought that venodialation decreased venous return but I realize it's because nitro causes pooling of blood in the periphery hence causing decreased preload not just because of the venodialation which actually makes alot more sense.
yes there will be release of catacholamines but there will also be vasodilatation of arterioles causing drop in TPR arterioles are the main determinant of TPR and the local adenosine rise due to exercise causes vasodilation and opening of these capillaries ie arterioles also increases perfusion to sk.muscle viz required to the energy requirments of body
in case of hemorrhage, the cardiac function curve should remain unchanged (because the contractility of heart is not affected by hemorrhage), please take a look at first aid 2014 page 269. practically the contractility is increased if you consider the increased sympathetic tone after hemorrhage, so the cardiac function curve should go up. Anyhow, the cardiac function curve should not go down as showed in this video
So yes I think that the curve in question (the cardiac function curve) can be called the contractility curve, as it is the curve that demonstrates the Frank-Starling mechanism that can be shifted by changes in contractility. You can do a quick check of wiki for "cardiac function curve" or I can dig through to my costanzo book if necessary.
@4:35 I am told by my professors that hemorrhage does not in fact affect the cardiac output and so we only see a drop in VR but CO and SV remain the same. Please clarify that point?
Correct, but during sympathetic nerve activation (during exercise) you will also get an increase in venous tone (reduced capacitance) - increasing MSFP.
Good video, however i have one remark: The curve that you mark as Cardiac output is actually the Cardiac Function curve. The whole point of the graph is to determine the Cardiac Output which lies at the point where the Cardiac function curve and the venous function curve cross.
GREAT explanation. Professors didn't attempt to teach this, and Boards and Beyond was BEYOND confusing. This was perfect. Now I actually understand the variables and can predict how they will change in different situations as well as interpret graphs to know what underlying disease process would give such changes! THANK YOU!!
Can you increase sympathetic only in veins? I doubt that is possible. But if you increase sympathetic stimulation the TPR increases. TPR is both for arteries and veins. Changing TPR will have effect on both and not only in veins. When you use this graph, think of situations only exclusive to CO and Venous return.
since u put the value as ~10mmHg. But this is MSFP we are talking about. A deeper concept involved. Even many comments in the journal said that Guyton's VRC has to be carefully interpreted, as it is not universally correct. If u r interested, u may google it. Happy learning...
Hi I use screen-o-matic which is a free screen recording website. I also use bamboo, which is like a tablet to draw my diagrams. If look onto youtube, you will find plenty of examples of what the are. Good Luck.
you are right... mean systemic pressure only changes with blood volume and/or venous compliance. The specific examples used of hemorrhage and exercise do influence one or the other. Exercise leads to increased sympathetics, hence venoconstriction. Hemorrhage leads to blood loss, loss of volume. TPR has no influence because mean systemic filling pressure is measured when the heart has stopped or the organism is dead.
that is perfect nice job explaining it. in Anesthesia school and professor does bad in explaining. the other thing that is important is that if you have a increase in central venous pressure (RAP or LVEDV) you will have a decreased CO like in Failure. You have high pressures with poor CO because your SNS is increasing in venous tone (SNS activation) in order for response of failing CO. This is marvelous. Bottom line increased CVP = decreased contractility
The venous return will actually increase Because of RAAS in kidney will cause fluid retention which increases venous return This usually confuses people because its said that CO=VR but if that was the case in heart failure there wouldn’t have been increased work load on the heart and diuretics would have been useful Thats how i like to think about it, hope i was able to help clear things up
I am not so sure. I think you might want to check the venous return curve again. When you change the TPR, the mean systemic pressure shouldn't be affected. The mean systemic pressure only change when you change the blood volume and the venous compliance. correct me if i am wrong. thanks
+sam s (ss) This is what I was thinking too... I even thought the curve would go up because of arterial vasodilatation, (causing the afterload to decrease), and a compensatory higher heart frequency and contractility because of sympathetic nervous system activation.. Edit: www.ncbi.nlm.nih.gov/books/NBK54474/
+Rosalie Poldervaart In hemorrhage the TPR increases (body's compensatory mechanism during blood loss is to vasoconstrict to prevent further blood loss) The Cardiac output drops because there isn't enough blood to pump forward (remember CO = SV x HR you may be thinking of increased HR to make up for the decrease in SV but ultimately SV drops so much that the racing heart just can't keep up and CO drops), and the Venous Return also drops, because of the same reason, loss of volume.
"mean systemic pressure" you/she are talking is called systemic function pressure which is a measure of venous return ( means at what pressure is VR=0 [check graph]) and is = BV/Complaince and below , what she is trying to explain is called "mean arterial pressure" which is = CO x TPR or HR x SV x TPR
In theory RAP is very low because right atrium has thin walls and the compliance is very high. The pressure is really the pressure of central venous pressure. So, RAP technically is not zero but very low. Think about it, how can the pressure be zero, then it will collapse.
Mean systemic filling pressure increases due to sympathetic activation--> contraction of the peripheral vessels. This means that the venous curve shifts to the right up to +17mmHg. However, due to increased venous resistance, the curve also rotates to the left (little bit). The net effect is around a maximum 100% increase in cardiac output before other regulatory measures will decrease it. At the same time the cardiac curve will rotate upwards due to a stronger heart pump.
well, initially i tried to explain, but i guess it would be difficult if ur basic concepts about cardiac and vascular functions are not profound enough. Please refer to the website (google-->venous return curve-->click "CVphysiology: cardiac and systemic..." link, the 'systemic vascular function curve' aka venous function curve part. Ur explanation is actually right for mean arterial pressure as MAP=COxTPR. But i am assuming ur mean systemic pressure refers to mean systemic filling pressure...
This explanation is completely wrong. The y axis represents both CO and VR, which are always the same in this steady state graph (the heart cannot put out more than its input!). CO and VR are not separate values. The curves do not represent CO and VR. They represent the positive influence of RAP on CO (the cardiac function curve) and the simultaneous negative influence of CO on RAP (the vascular function curve). e.g. in heart failure the CO is lower for any value of RAP, so the cardiac curve will be shifted down. If there is a compensatory increase in blood volume, the vascular curve will be shifted up, because there is a higher RAP for any value of CO. The intersection of the new curves will show a similar level of CO/ VR but a higher RAP (try drawing it). TPR declines in exercise to deliver higher flow through the tissues, not to the heart. The heart's job is always to match the changing flow from arteries to veins with an equal flow from veins to arteries. The vessels set the pace, the heart keeps up!
these curves are just evil, 8 years after your video was posted and people are still confused
thank you! i was literally almost in tears because of this, and you explained it so simply
Great job with the video! Many thanks.
One anomaly that I find is that during a compensated heart failure, the renal compensatory mechanisms cause retention of fluid causing venous return to actually increase. Therefore, the VR curve also shifts up and to the right so as to maintain the steady state cardiac output to near normal.
I could never understand this EVER! Your video really helped clarify many concepts for me. Thank you.
You have a simple God sent explanation to me this morning. Thank you
Really good explanation, Uworld managed to confuse me somehow, this clears it up. Cheers
100lurics I know it’s been many moons but we still need u buddy, to make these easy grasping concepts tutorials please. You are one of the few who are good at the game!
Thank you for making this video. It was made in 2012, but it's helping me out in 2014!
even BRS physio did not explain this as well as you did. well done! :)
Exactly I was about to say
excellent job. you're a great teacher. very basic way to understand something that seems overwhelming at first. thanks!
I take Step1 a week from tomorrow, thank you so much!
Thank you....I did my best.....
This topic is so high yield not only for the boards but in everyday practice....
Glad you like it
Wow thanks a lot, i was in confusion about whats up RAP in different scenerios, very few videos on youtube touch on RAP. Thanks again
absolutely amazing, tks maddam
Thank you so much for your great explanation!!!! i am glad!
Thank you . Please make another video on anti hypertensive drugs with more details . Your explanation is more simple and interesting . Very informative too.Best regards Dr.Joe , India
Hey you ROCK ,,, Thanks a lot :) you have a beautiful voice also ,,, Upload more videos plz
Awesome explanation! Thank you!
does anyone know where i can find the video when she about cardiogenic/hypovolemic/etc shock???!!! I saw it but now i cannot find it anymore...she describes how to use a specific formula including pulmonary wedge pressure, SV, etc
Great vid... Thanks a lot for the effort.
Thank you......This was a sore topic for me......
Glad I could make it a little easier for oyu as well..
Thank you so very much! I have an exam in a couple hours and you rescued me!
Great video!! Just note that during exercise the venous return curve s`X intercept or mean systemic pressure (10 mmHg) should stay in the same place. Because the total circulating volume was not altered. Greetings!
But then the catecholamines released during exercise do cause venous constriction which does increase the mean systemic pressure.
shobs iyer
For those nerds wondering why?There are some flaws in your thinking, let me correct them for you. Follow along.
flow characteristics of the systemic venous circulation are dependent on Vo (unstressed[reservoir] volume in veins), Vs(stressed volume in veins), Vt(total volume in veins), C(compliance), and Rv (Resistance to venous flow)
recall that venous return; VR= ( Pms-Pra ) / Rv
Pms is mean systemic pressure, Pms=Vs/C which can be written as Pms=(Vt-Vo)/C
This new equation suggests that Pms can be altered through two basic mechanisms: (1) a change in the total volume in the reservoir(Vt); or (2) a change in the proportion of Vo and Vs.
An alteration of autonomic tone, catecholamine stress responses, or infusion of exogenous vasoactive substances will alter the ratio of Vs to Vo without a change in C, thus changing Pms.
Your partially right, but you should be thinking>exercise>SNS>increase in HR, venoconstriction in non vital organs and vasodilation in vital organs(heart, brain, muscle)>increased preload>increase in CO-->a change in proportion of Vs and Vo (volume of stressed venous blood vs Volume of unstressed venous blood) >increase in PMS
A lot of books will says venoconstriction leads to a decrease venous compliance b/c of inverse relationship between resistance and compliance. They try to generalize it and make it simple, but compliance is way more complicated and depends on so many other factors
The way I see it is that compliance in this model should be considered a static, passive mechanical property of veins. why?
recall that venous system has two compartments; 1)venules and small veins, which lack smooth muscle layer and cannot constrict and account for 70-80% of bodies total blood reservoir, they have a very large crosssectional area contribute little to Rv and systemic compliance 2)Large veins and Medium sized veins, which can constrict, and contribute to compliance and they have small cross-sectional area and act as a valves. These two compartments work against each other under autonomic stress i.e increased stressed volume and Pms in the reservoir compartment (which increases VR) but decreased mean radius in the vena cava and large veins (which decreases VR). In conclusion its not the compliance/restriction of the vein, that increases Pms, but the change in proportion of Vs ans Vo.
Yeah this shit is confusing, and a lot of books don't explain it properly.
Guru Jolly thanks for this explanation. Made me realize I had one misunderstanding about why nitro is used in angina. I always thought that venodialation decreased venous return but I realize it's because nitro causes pooling of blood in the periphery hence causing decreased preload not just because of the venodialation which actually makes alot more sense.
Guru Jolly Thanks for taking the time to explain this. Greetings :)
yes there will be release of catacholamines but there will also be vasodilatation of arterioles causing drop in TPR arterioles are the main determinant of TPR and the local adenosine rise due to exercise causes vasodilation and opening of these capillaries ie arterioles also increases perfusion to sk.muscle viz required to the energy requirments of body
Hey! you are such an excellent teacher. really impressed...
I have exams in a few days. And not even the textbooks brought clarity on this aspect for me. Thank you 🙏
Hey greetings from India.. love ur videos..! Keep up the good work
Your video has given me hope ♥️
Thank you so much. Made it very easy to follow. God bless.
Quick and easy. Thank you!!!!
thank you so much..I was having trouble understanding it..
Thank You.....Glad you liked the video.
Excellent! 100 % recomended
in case of hemorrhage, the cardiac function curve should remain unchanged (because the contractility of heart is not affected by hemorrhage), please take a look at first aid 2014 page 269. practically the contractility is increased if you consider the increased sympathetic tone after hemorrhage, so the cardiac function curve should go up. Anyhow, the cardiac function curve should not go down as showed in this video
+yelzins yelzin
www.ncbi.nlm.nih.gov/books/NBK54474/
You are doing really well, Thanks a lot for explaining this.. And Please keep going whit your videos
Thank u very much...Great explaination!!!
Amazing explanation.. thank you!
So yes I think that the curve in question (the cardiac function curve) can be called the contractility curve, as it is the curve that demonstrates the Frank-Starling mechanism that can be shifted by changes in contractility. You can do a quick check of wiki for "cardiac function curve" or I can dig through to my costanzo book if necessary.
Thanx your really great a simplifying things.
Amazing video
great thank you you are amazing
Thank you!!
Great explanation! Thank you so much!!!!
really good efforts
thank you very much.. u made this concept very easy for me now..
thank you for this simple explanation, after 9 years
Thank you so much!!
wow! so excellent! thank you
Great job
@4:35 I am told by my professors that hemorrhage does not in fact affect the cardiac output and so we only see a drop in VR but CO and SV remain the same. Please clarify that point?
Hmm, First Aid also says CO should drop
But in TPR changes, the mean systemic filling pressure remains the same.
Correct, but during sympathetic nerve activation (during exercise) you will also get an increase in venous tone (reduced capacitance) - increasing MSFP.
Thank you so much!
Good video, however i have one remark: The curve that you mark as Cardiac output is actually the Cardiac Function curve. The whole point of the graph is to determine the Cardiac Output which lies at the point where the Cardiac function curve and the venous function curve cross.
Neat explanation!
What about myocardial infarction and Cardiac output curve vs Right Atrial pressure ? Where they will cross
THANK YOU !😃
GREAT explanation. Professors didn't attempt to teach this, and Boards and Beyond was BEYOND confusing. This was perfect. Now I actually understand the variables and can predict how they will change in different situations as well as interpret graphs to know what underlying disease process would give such changes! THANK YOU!!
Is it? Can you give me a reference?
Excellent! unbelievable . You made it so easy .Thanks
Would you please tell me what kind of software you have used to write and draw the charts?
Can you increase sympathetic only in veins? I doubt that is possible. But if you increase sympathetic stimulation the TPR increases. TPR is both for arteries and veins. Changing TPR will have effect on both and not only in veins. When you use this graph, think of situations only exclusive to CO and Venous return.
Thank you very much u really made it easy :)
Excellent!
since u put the value as ~10mmHg. But this is MSFP we are talking about. A deeper concept involved. Even many comments in the journal said that Guyton's VRC has to be carefully interpreted, as it is not universally correct. If u r interested, u may google it. Happy learning...
in 1st case during exercise..how come mean arterial pressure will increase on the graph while TPR decreases due to arterial vasodilatation ???
yes . increased RA pressure --> More Vent. filling ---> Increased SV and CO.
Hi I use screen-o-matic which is a free screen recording website. I also use bamboo, which is like a tablet to draw my diagrams. If look onto youtube, you will find plenty of examples of what the are. Good Luck.
Thank you so much
thanks for your help..
Thank u sooo much :)
so what happens when you increase sympathic only to the veins? does TRP and slope in the venous return decrease? Please help
you are right... mean systemic pressure only changes with blood volume and/or venous compliance. The specific examples used of hemorrhage and exercise do influence one or the other.
Exercise leads to increased sympathetics, hence venoconstriction.
Hemorrhage leads to blood loss, loss of volume.
TPR has no influence because mean systemic filling pressure is measured when the heart has stopped or the organism is dead.
how is right atrial pressure 5 in the normal situation? i thought it should be 0. please explain.
Thank you❤.
that is perfect nice job explaining it. in Anesthesia school and professor does bad in explaining. the other thing that is important is that if you have a increase in central venous pressure (RAP or LVEDV) you will have a decreased CO like in Failure. You have high pressures with poor CO because your SNS is increasing in venous tone (SNS activation) in order for response of failing CO. This is marvelous. Bottom line increased CVP = decreased contractility
ohhh thank you!!!
6:14 why VR stay normal? Now the volume of blood that pumped is less so how it’s will not be affected?
The venous return will actually increase Because of RAAS in kidney will cause fluid retention which increases venous return
This usually confuses people because its said that CO=VR but if that was the case in heart failure there wouldn’t have been increased work load on the heart and diuretics would have been useful
Thats how i like to think about it, hope i was able to help clear things up
Thanks a lot
thank yoU!
contractility affects SV and subsequently cardiac output. Hence, the curve can be interpreted as cardiac output or contractility curve
Thankyou so much
My hero 😍
does both MSP and TPR mean the same if yes then the changes seen with hemorrhage and exercise in this explanation is not shown properly .....
you. rock. seriously. you rock.
Thank you
I am not so sure. I think you might want to check the venous return curve again. When you change the TPR, the mean systemic pressure shouldn't be affected. The mean systemic pressure only change when you change the blood volume and the venous compliance. correct me if i am wrong. thanks
hemorrhage only decreases the venous return but the CO slope doesn't change
+sam s (ss) i think in mild hemorrahege , but in loss of high volume of blood could cause both decrease, cardiac out put as well as vr,
+sam s (ss)
This is what I was thinking too... I even thought the curve would go up because of arterial vasodilatation, (causing the afterload to decrease), and a compensatory higher heart frequency and contractility because of sympathetic nervous system activation..
Edit: www.ncbi.nlm.nih.gov/books/NBK54474/
+Rosalie Poldervaart In hemorrhage the TPR increases (body's compensatory mechanism during blood loss is to vasoconstrict to prevent further blood loss) The Cardiac output drops because there isn't enough blood to pump forward (remember CO = SV x HR you may be thinking of increased HR to make up for the decrease in SV but ultimately SV drops so much that the racing heart just can't keep up and CO drops), and the Venous Return also drops, because of the same reason, loss of volume.
thanks
"mean systemic pressure" you/she are talking is called systemic function pressure which is a measure of venous return ( means at what pressure is VR=0 [check graph]) and is = BV/Complaince
and below , what she is trying to explain is called "mean arterial pressure" which is = CO x TPR or HR x SV x TPR
I love ur voice ! 😍 , thanks a lot nice explanation:))
Thanks
In theory RAP is very low because right atrium has thin walls and the compliance is very high. The pressure is really the pressure of central venous pressure. So, RAP technically is not zero but very low. Think about it, how can the pressure be zero, then it will collapse.
Its awfuly gooooood
I believe you are confusing mean systemic filling pressure with mean arterial pressure.
During excercise RAP is same but MSP doesnt change.please verify .....)
Mean systemic filling pressure increases due to sympathetic activation--> contraction of the peripheral vessels. This means that the venous curve shifts to the right up to +17mmHg. However, due to increased venous resistance, the curve also rotates to the left (little bit). The net effect is around a maximum 100% increase in cardiac output before other regulatory measures will decrease it. At the same time the cardiac curve will rotate upwards due to a stronger heart pump.
she is correct
same thing remember that an increase in CO is an increase in contractility
some different explanations in FA21
I think what you are talking about is not CO but the operating point of heart.
well, initially i tried to explain, but i guess it would be difficult if ur basic concepts about cardiac and vascular functions are not profound enough. Please refer to the website (google-->venous return curve-->click "CVphysiology: cardiac and systemic..." link, the 'systemic vascular function curve' aka venous function curve part.
Ur explanation is actually right for mean arterial pressure as MAP=COxTPR. But i am assuming ur mean systemic pressure refers to mean systemic filling pressure...
2 mistakes
No change in MSP with change in TPR
No change in CO with acute hemorrhage
but thank you madam
This explanation is completely wrong.
The y axis represents both CO and VR, which are always the same in this steady state graph (the heart cannot put out more than its input!). CO and VR are not separate values.
The curves do not represent CO and VR. They represent the positive influence of RAP on CO (the cardiac function curve) and the simultaneous negative influence of CO on RAP (the vascular function curve). e.g. in heart failure the CO is lower for any value of RAP, so the cardiac curve will be shifted down. If there is a compensatory increase in blood volume, the vascular curve will be shifted up, because there is a higher RAP for any value of CO. The intersection of the new curves will show a similar level of CO/ VR but a higher RAP (try drawing it).
TPR declines in exercise to deliver higher flow through the tissues, not to the heart. The heart's job is always to match the changing flow from arteries to veins with an equal flow from veins to arteries. The vessels set the pace, the heart keeps up!