Flashcards in Heart 9: Interactions between Heart and Peripheral Vasculature Deck (46):
State the main importance of arterial vs venous systems.
venous circulation- brings blood back to heart (holding most of blood, 60 percent in venous system) ..preload
arterial- important for bp and regulating bp
central venous pool
What is true in normal steady-state conditions regarding venous return?
Central venous pool- corresponds approximately to the volume enclosed by the right atrium and the great veins in the thorax
venous return- rate at which blood returns to the thorax from peripheral vascular beds; i.e. blood entering the central venous
cardiac output- rate at which blood leaves the central venous pool and is pumped out of the heart
under normal steady-state conditions, venous return= cardiac output
How do you increase venous return?
constrict volume in central venous pool
Describe the pressures in the R atrium and IVC.
Where does blood go?
both are in thorax. no valve between so pressures in the 2 vessels are similar.
central venous pool area right outside R atrium, considered great vein and the right atrium then blood goes to R ventricle and is pumped out as CO
How do you pull more blood back to central venous pool?
Describe venous return.
when take a deep breath you do pull more blood back to central venous pool … important mech. in exercise.
venous return- rel. between periphery and central venous pool, theres a gradient pressure in periphery is higher than central venous pool and thats driving blood back to heart.
How does CO influence central venous pressure? Why is this important?
-CO is taking blood from central venous pool so it influences central venous pressure-inflow into central venous pool and outflow through heart influence central venous pressure. important bc central venous pressure is indicator about whats going on in vascular system and heart.
-called central line or central catheter- central venous line in them after surgery sitting right outside R atrium in IVC. know meaning behind these pressures…pressure influenced by blood returning to central venous pool and blood taken out of pool to heart.
Describe the relationship between venous return and cardiac output over a minute.
What are exceptions?
venous return must equal cardiac output. its a closed system... whatever blood pumped out must come back to heart.
if vasodilated- may be delayed, or could change beat to beat. but whatever blood pumped out must come back to heart. only way this changes is if have hole in system. if stabbed or shot in arterial venous system they may not equal each other. in normal conditions must be equal to e/o.
Draw the vascular function curve (venous return curve).
What would happen in heart failure?
how central venous pressure changes with CO. as CO increase, central venous pressure falls off (more blood being accepted from central venous pool)
heart failure- pressure in central venous pool will tend to increase, in heart failure CO dropped a lot and pressure in central venous pool increased a lot. heart failing bc when look at central venous pressure its building up, means starting to retain fluid and have back up bc of low CO. diagnostic value
this graph now is normal where read indep. variable on abscissa (x axis) and read dependent variable on y axis (changes in venous pressure dep. on cardiac output.) …will flip that around.
What is mean circulatory pressure? (PMC)
What does it represent?
What is it influenced by?
What does it measure?
What is its value normally?
mean pressure that exists in the circulatory system when cardiac output stops and pressures within the vascular system redistribute
It represents the relationship between the volume of blood in the circulation compared to the functional capacity of the system.
It is influenced by the volume of circulating blood and the smooth muscle venous tone of the system (which determines the capacity of the system).
It is a measure of the fullness of the circulatory system. Pmc is normally about 7 mm Hg
PMC-mean circulatory pressure- theoretical value. helps conceptually understand. not monitored clinically bc PMC is pressure when heart stops. no one cares about that clinically… tells about system. when heart stops less blood taken out but pressure goes to 7mm Hg which is same as peripheral venous pressure. when CVP same as peripheral venous pressure no gradient for blood to flow anymore and will stand still. if heart stops goes to 7mmHg (not 0) bc system always pressurized bc volume of blood in closed container.
If you pressed on someone's skin and it left a dent what could be causing this?
more net secretion of fluid out of vasculature and not as much reabsorption so fluid build up in lower extremities- press on skin and leaves dent
On the venous return curve/vascular function why does the curve drop down at the y axis?
pressure is 0 there. collapse. heart going so fast that sucked all blood out of veins and they’ve collapsed down flat. can’t pump more blood than is coming into heart.
How will severe hemorrhage affect the vascular function curve?
severe hemorrhage will shift curve.. extrapolate down all way back on x -axis to 0 CO… central venous pressure goes up to PMC.
If you stopped the pump and let everything equilibrate what would happen?
bp doesn't drop to 0 ...
there is pressure inside bc of elasticity of vasculature. pressure on venous side will be same as arterial side.
What is the heart's job in regards to vascular function?
hearts job is to reduce pressure on central venous side and improve pressure on arterial side. this is why pressure drops in central veins and CO increases…
What is normal cardiac ouput/central venous pressure?
What does the graph show if you lower CO to 1L/min?
normal CO- 5L, drawing blood out of central venous pool and that pressure will be about 2mmHg.
if you lower CO to 1 L/min …blood backs up and not drawing as much blood out of venous pool so backs into venous pool and get higher central venous pressure,
What happens when central venous pressure is the same as peripheral venous pressure?
when heart stops less blood taken out but pressure goes to 7mm Hg which is same as peripheral venous pressure.
when central venous pressure same as peripheral venous pressure no gradient for blood to flow anymore and will stand still. if heart stops goes to 7mmHg (not 0) bc system always pressurized bc volume of blood in closed container.
If the heart stopped, blood would equilibrate between arterial and venous system and most would wind up where?
in venous system bc can stretch and hold a lot of volume compared to arterial system which has a small volume bc its a v low compliant system, v stiff.
PMC represents the relationship between blood volume in circulation compared to functional capacity of the system (size of container) ... what are the implications for this?
if you make container smaller that volume would go up, and if you make container larger than level of volume would come down and therefore fullness of system is lower. venous system can change size by venoconstriction or veno-dilation.
What influences venous fullness?
How can this change? Give a clinical and physiological example for both increase/decrease in venous fullness.
absolute volume … if you give transfusion most of that will go into the venous system and that will increase fullness of system. same thing can be accomplished if venous system veno-constricts. also increase fullness of system (more blood back to heart, more venous return)
if hemorrhage fullness of system comes down or if you veno-dilate then the fullness of system comes down. see both things will reduce venous return. venous system is dynamic system, not just container…can increase and decrease its functional capacity.
If you see an increase or decrease in central venous pressure what does this indicate about cardiac output and venous return?
a raise central venous pressure- means decrease in CO, reduced venous return bc reduce gradient for blood flowing back to heart.
a reduction in central venous pressure- means increase in CO, pulling blood out of central venous pool and this will decrease central venous pressure and increase the pressure gradient for venous return so you get a greater venous return
What happens when central venous pressure equals mean circulatory pressure?
no pressure gradient for venous return, blood flow ceases
How will an increase in cardiac output affect the pressure gradient for venous return?
increase pressure gradient for venous return, increase venous return
At negative central venous pressure, what happens? What situation could cause this
transmural pressure collapses the large veins resulting in zero venous return
How do you influence venous return?
altering pressure gradient between peripheral and central venous pressure/(pool)
-increase peripheral venous pressure (maximize venous return)
-decrease central venous pressure (right atrial pressure)
How do you maximize venous return?
increase peripheral venous pressure by:
-increased sympathetic venoconstriction
-increased blood volume
-increased skeletal leg muscle pumping activity (will also increase peripheral pressure and push more blood back to central venous pool)
How do you decrease central venous pressure (right atrial pressure)?
respiratory pump activity
How do venous valves influence venous return?
maintain pressure gradient between peripheral and central venous pools in the face of gravitation forces
when standing up, if didn’t have valves breaking up columns of fluid would have large pressure… if one column IVC to feet then gravity when stood up would cause large pressure in periphery which you don't want so valves are frequent and they break up the column of fluid and prevent gravitational effects of altering pressure gradients.
How does cardiac contraction influence venous return?
generates peripheral venous pressure bc thats pressure generated on arterial system over to venous side through capillary network.
What 2 things can you do to increase the pressure gradient between peripheral and central venous pressure?
decreasing central venous pressure
increase peripheral venous pressure (-decrease compliance of venous system and that increases peripheral pressure, increases gradient. )
What factors influence venous return?
-increase EDV...increase SV...Increase CO
-increase respirtory pump (decrease intrathoracic pressure)
-increase blood volume
-pressure on blood due to cardiac contraction
-increase sympathetic venoconstriction
-skeletal leg muscle pump
-venous valves (unidirectional flow)
all of these things contribute to EDV (preload) … whole idea of venous function talks about preload. det. EDV…through L/tension relationship- will det. SV. 60 percent of EDV ejected and thats SV. that in turn times HR is CO. these all compensate for decrease in filling time when HR goes up.
What happens if you increase HR alone?
then CO goes down bc SV goes down bc less time for filling (CO=SV x HR)
Describe the mechanism of the respiratory pump.
when take deep breath and reduce inter-thoracic pressure and pull more blood back to R side of heart. great vein expands, R atrium expands bc they’re v thin wall structures. expansion in volume creates negative pressure and pulls more blood back to heart. v important in heavy exercise.
What would happen if you didn't breathe during exercise? (HR up but no respiratory pump)
if HR goes up and didn’t breathe during exercise then you'd just have decrease in CO- this is VT (HR up, filling time down, cycle length down, nothing compensating for reduced filling time)
Describe the mechanism of the skeletal muscle pump and venous valves.
skeletal muscle pump-goes along w exercise ..every time take a step you're pushing more blood back to heart through venous valves - deep veins in skeletal muscle in legs squeezed when you activate skeletal muscles and this squeezes veins size and pushes blood back to heart… see veins if you have superficial you can see blood back if push finger against veins see nodules, those nodules are the valves preventing blood flow from going backwards. blood only goes forward to heart. see these nodules mostly in peripheral veins. all over body. these valves allow blood to only go in one direction… have in legs also.. if they don't close normally and you start accumulating blood in your superficial veins- those are varicose veins. venous valves along w skeletal muscle pump activity pushes blood back to heart. v important during exercise as well.
How does sympathetic nerve activity affect venous return? (when is this important?)
(imp during exercise)
important physiologically during exercise (increase symp. nerve) this increase in symp. nerve activity affects arterial and venous side -get sympathetic VENO-constriction… veno-constriction or changes in venous tone. vaso- means constriction or dilation is arterial tone. veno- constriction what does it do? … rather weak compared to arterial constriction (which can cut off blood to an organ) kidneys… non metabolically active tissues. but veno- decreases compliance of venous system. prevents from expanding w increase in volume. makes it a little stiffer. so when blood enters venous system its shunted back to heart through those valves. not reducing diameter significantly…mostly reducing compliance.
Describe the driving force for venous return.
What happens if you increase CO?
pressure generated by pushing blood around the system. have 120mmHg on L side and 0 in R atrium- drives blood around system. if you increase CO you increase venous return bc increased contraction strength
Describe cardiac suction.
more minor component- cardiac suction- heart changes its shape, floor of heart during systole moves up and walls out and becomes rounder. normally oblong. relaxes during diastole and floor down, apex moves down and walls move back in so heart sucks blood into ventricle during diastole. but not major… its important. wall motion contributes to end diastolic volume.
What is deep vein thrombosis. When might this occur?
not moving limbs around (long distance traveling) people get off air planes and have heart attacks. reason is deep vein thrombosis. DVP… get that from not moving legs or being dehydrated. at 800 feet cabins pressurized. evaporate fluid more rapidly. losing fluid if not drinking water… long distance flight. to europe/hawaii. need to hydrate… need to move around. older people sit and don't move and get stasis, get slow blood flow which causes blood clots..along w dehydration. clots move through venous system to pulmonary side of system then have a pulmonary embolism as a result.
How will transfusion or hemorrhage shift the vascular function curve? Draw.
1) Blood Volume (transfusion, hemorrhage):
a) increases in blood volume increase venous return.
b) decreases in blood volume decrease venous return.
2) Venous Tone (sympathetic nerve activity; drugs):
a) increases in venous tone (venoconstriction) increase venous return.
b) decreases in venous tone (venodilation) decrease venous return.
when you give someone transfusion, fullness of system changes, shift curve in parallel wall, not contractility... PMC goes up bc increased volume) you increase preload, venous return, and cardiac output. didnt change after load or contractility. just changed volume in venous system which translates into increase in preload. higher central venous pressure- we did force more blood into heart.
if hemorrhaging…venous function curve and PMC would shift down, CO down bc less blood returning to heart and less fullness of venous system means less preload.
if hemorrhage everything comes down and less blood in the venous system so mean circulatory pressure dropped and fullness of system reduced. transfusion the PMC increased and more blood in system.
How can you increase fullness of system (2 main ways)?
What are the only things that affect venous function?
How will these things shift the venous function graph?
increase volume or tone
if change venous tone. could put venoconstriction in place of transfusion… same shift on vascular function curve. in hemorrhage would have veno-dilation that would cause same shift. decrease venous tone= venodilation… less venous return. volume reduced.
blood volume and venous tone are only things that affect venous function
venoconstriction (increase in blood) shifts curve up and to the right.. veno-dilation or loss of blood volume shift curve down. increase contractility shift cardiac function curve up and to L. decrease in contractility down and to R. intersection point is cardiac function and venous return- venous return is preload.
Switch the axes on the cardiac function curve so central venous pressure is on y axis. Draw the normal cardiac output curve, increased cardiac sympathetic nerve activity (in response to hemorrhage) and severe heart failure.
Moderate or severe heart failure shifts the cardiac function curves downward and to the right.
Cardiac output decreases and CVP increases.
What happens in severe heart failure in regards to CO, central venous pressure. What are some physical indications? How do you treat? (discuss L-tension relationship too)
in severe heart failure CO even lower and central venous pressure even higher and the amount of heart failure translates into higher venous pressure- can see in neck vein. jugular connected to SVC. all those pressures elevated if heart not pumping blood out. in heart failure you also become hyper-volemic. you increase blood volume (PMC increased, fullness of system greater) what causes blood volume to increase in pt with heart failure (reason they give pt. diarhetics to bring fluid down) volume in vascular spaces…blood volume increasing… getting larger bc kidneys sense decrease in CO as hemorrhage… and there are long term mechanisms which help reabsorb more Na and therefore more water into cardio-vascular system and increase blood volume. not good bc already heart is congested w blood and now venous system is engorged with blood and last thing you want to do is increase blood volume… give Ace inhibitors or diahretics to bring volume down. heart can’t deal… L-tension rel. its depressed in heart failure. they cant respond to increase in preload. normally you get greater contraction w increase in preload but failing heart doesn't do that.
so central venous pressure elevated- hallmark of heart failure.
Describe the cardiovascular adjustments to hemorrhage. (Describe changes to the graphs).
during hemorrhage, baroreceptors extremely sensitive to changes in pressure. blood volume way down. mean circulatory pressure quite low. fullness of system reduced.
compensated baroreceptor reflex-sense decrease in bp and they increase sympathetic nerve activity and reduce parasympathetic activity. symp. increases HR, increases contractility and increases venoconstriction and vasoconstriction. increase in contractility shift curve up to left. cause venoconstriction- will decrease compliance and increase fullness of system. (making container smaller) shifts mean circulatory pressure.
(symp. NS affects cardiac function, contractility, venous function through venoconstriction by changing size of system)
(NS back down as bp goes up… this cardiac function curve returns to control and you are at same CO but with higher central venous pressure.)
1) Venoconstriction – improves venous return to the heart and shunts blood from the reserve side of the circulation
2) Arterial vasoconstriction occurs, increasing total peripheral resistance and improving BP, but with less perfusion of other tissues. Organs can become damaged by ischemia.
3) Cardiac contractility is increased by increased sympathetic activity and circulating catecholamines (e.g. adrenaline).
4) The low blood pressure results in dialysis of fluid from the tissues, partially restoring lost blood volume. This may make the patient feel very thirsty.
The maximum survivable blood loss is about 40% of total blood volume, around 2 L.
How does heart failure shift the vascular function curve and the cardiac function curve?
How do kidneys respond in heart failure? How does this affect the vascular function curve.
Moderate or severe heart failure shifts the cardiac function curves downward and to the right.
Cardiac output decreases and CVP increases.
The kidneys respond by increasing blood volume. This fluid retention shifts the vascular function curve upward and to the right (hypervolemia), further increasing CVP.
How does elevated CVP affect moderate and severe heart failure?
With moderate heart failure, the elevated CVP improves preload so that there is little reduction in cardiac output. However, in severe heart failure the heart’s contractility is reduced so much that cardiac output cannot be maintained even with a very elevated CVP.
The increased CVP also causes pulmonary congestion and pitting edema in the extremities.