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44 Cards in this Set

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  • Back
How much does intrapleural pressure fluctuate during normal breathing?
+/- 2
What happens to CO when you inhale? Why?
It increases - because you've decreased intrapleural pressure (made it more neg) and made it easier for the heart to pump.
What happens to CO when you exhale? Why?
It decreases - because you've increased intrapleural pressure (made it more pos) and now the right atrium needs more pressure to be able to fill.
What is cardiac tamponade?
Increased pericardial pressure
How does cardiac tamponade affect the CO curve?
It shifts it to the right - CO is decreased
How is the right shift in CO curve due to cardiac tamponade different from that in exhalation?
It is more exaggerated at the top - because the external tamponade pressure rises to higher values as the chambers of the heart fill during high CO.
What does opening the chest cavity do to cardiac output initially? Why?
Decreases CO from 5 to 2.5 - because of the increase in RAP needed to allow right atrial filling.
But max permissive ability is the same.
What happens to CO after opening the chest after time?
The baroreceptors detect falling MAP, respond by increasing TPR to get CO back up to normal (Psf goes up to about 9).
What changes are seen in the CO curve as a result of the baroreceptor response? (2)
1. Psf = 9 via vasoconstriction
2. CO curve is hypereffective (max perm ability ~18) and so CO is now 4
What is the price you pay for the increased CO as a result of compensation for opening the chest cavity?
Increased right atrial pressure - CO is almost normal (4) but RAP remains about 3.5
What is the most threatening type of cardiac tamponade?
Trauma induced hemorrhage
What effect does Cardiac Tamponade have on transmural pressure?
It decreases transmural pressure.
Why does transmural pressure decrease as you increase pressure outside the heart?
Because normally there is NEGATIVE pressure outside the heart. As that increases (ie pericardial fluid) the gradient decreases.
What is the initial compensation for cardiac tamponade?
Sympathetic stimulation
How does cardiac tamponade effect blood circulation?
Blood will be shifted to the peripheral circulation because of the loss (hemorrhage) into the pericardial cavity.
What does the blood shift to periphery do to the CO curve?
Shifts it to the right b/c of the increased Psf.
What does the symp stimulation do for the CO curve?
Not much; CO is not returned all the way to normal and remains depressed.
What does the cardiac tamponade curve look like in contrast to all the other curves?
CURVED - not squarish.
Does increasing sympathetic output to the heart ALONE have much of an effect on cardiac output?
why not?
Because if you don't have an increased venous return the CO curve is limited to the plateau of the VR curve - 6 L/min
What is the effect on cardiac output when you stimulate only the peripheral circulation with SNS output, not the heart?
Much more marked than the heart alone; CO goes up to almost 10 L/min as Psf increases.
So what are the 2 main effects of increasing sympathetic output?
1. Makes the heart a stronger pump
2. Increases Psf b/c of periphal vessel contraction.
How much does maximal sympathetic stimulation increase Psf? CO?
Psf = up to 17 mm Hg
CO = up to 11 L/min
What happens to the venous return curve as max sympathetic outflow increases Psf?
The curve becomes much more shallow - due to INCREASED RVR
What happens to the CO curve with maximal sympathetic stim?
Max permissive pumping ability is increased by 100% to about 25 L/min
What does total spinal anesthesia do to the CO/VR curve?
VR: decreased Psf to 4mmHg
CO: decreased max permissive pumping to about 10 (80% of normal)
Why does total spinal anesthesia make the heart such a poor pump?
Because it knocks out sympathetic output so there is no vasotone of the vessels.
In general what does AV fistula do?
What is the major change that occurs in AV fistula, curve-wise?
The VR becomes markedly steeper due to decreased RVR
What is the initial effect on MAP when the AV shut is opened?
MAP falls - due to decreased TPR
What happens as the baroreceptors respond and symp outflow restores MAP to normal?
The heart becomes more and more effective and CO increases.
Why does the heart pumping continue to increase in effectiveness?
Because Psf continues to increase and heart contractility continues to increase with SNS outflow.
What is the longterm effect of AV fistula, after a few weeks?
Kidneys kick in to increase blood volume in response to the decreased MAP and SNS stimulation. Prolonged workload on the heart hypertrophies.
What are the final results of the CO/VR curve for av fistula?
RAP = 6
CO = 20L/min
What does myocardial infarct do to the CO curve in general?
Shifts it to the right.
What is the initial effect of MI on the curve?
-Dramatically decreased max permissive ability
-RAP shifted to +4 mm Hg
What happens in response to the decreased CO from MI?
-Low MAP responded to by baroreceptors
-Cardiac function improves a little
-VR shows increased Psf
What is the most important compensation for MI in the longterm?
Renal-Blood volume regulation
What does Renal-blood volume regulation do for the curve?
Makes it more effective by increasing Psf.
What is the price you pay for the increased CO in compensated MI?
Increased RAP
What physiological changes occur in circulation during very strenuous exercise?
-Increased SNS outflow
What are the 2 reasons for increased VR during strenuous exercise?
1. Global vasoconstriction of splanchnic/renal bloodflow increases Psf
2. Vasodilation in active muscles reduces RVR
What are the 2 reasons for the hypereffective CO curve seen in strenuous exercise?
1. Increased contractility
2. Increased heartrate
How does strenuous exercise affect RAP?
Hardly at all - it often goes down in fact.