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Cardiac PhysiologyPump Function
Jim Pierce
Bi 145a
Lecture 12, 2009-10
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Cardiac Pump
The Heart Pumps Blood
by contraction and relaxation Contraction is called systole
Relaxation is called diastole
The Cardiac Cycle is the cycle throughone systole and one diastole
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Cardiac Pump
When the heart pumps, it generates:
Pressure Changes Volume Changes
We talk about both Blood Pressure, Arterial/Venous Pressure Cardiac Output, Venous Return
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Cardiac Pump
We can measure pressures and
volumes during the cardiac cycle
These will help us understand the heart
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Echocardiography
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Swan-Ganz Catheter
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Swan-Ganz Catheter
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Arterial Pressure
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Swan-Ganz Catheter
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Cardiopulmonary Function
When we combine cardiac output withoxygen carrying capacity of the blood,we begin to evaluate
Delivery of Oxygen
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Swan-Ganz Parameters
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Volumes
There are a variety of ways to measurevascular volumes.
Volume per Time, or Flux Thermodilution across compartments
Oxygen Extraction across compartments
Absolute Volume Echocardiogram (imaging study)
Thermodilution in a compartment
Actual Dilution (distribution across allcompartments)
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Pressure Versus Volume
Pressure and Volume are related
Increasing Pressure will Increase Volume
Decreasing Pressure will Decrease Volume
Increasing Volume will Decrease Pressure
Decreasing Volume will Increase Pressure
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Compliance
Compliance is the change in pressure
caused by a change in absolute volume
Compliance = P /V
Point Compliance = dP / dV
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Compliance (Computation)
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Compliance (Real)
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Contractility
Contractility is the change in Volumeper Time caused by a change inPressure
Contractility = (dV/dT) / dP
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Contractility
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Compliance and Contractility
Compliance
determines
FILLING
Contractility
determines
EMPTYING
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Pressure Volume Loop
Area = Work
Contractility
Compliance
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Cardiac Cycle
Thus, each part of the cardiac cycle isdominated by a relationship betweenvolume and pressure.
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Cardiac Cycle
Systole Muscle is Contracting
A contracting sphere generates Pressure
Pressure causes a change in Volume
This is measured by CONTRACTILITY
This is affected by
Function of Muscle Initial Volume (PRELOAD)
Initial Pressure (AFTERLOAD)
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Cardiac Cycle
Diastole Muscle is Relaxing
Veins return blood to the heart
As the heart fills with blood, the absolutevolume and pressure change
This relationship is measured byCOMPLIANCE
This is affected by Connective Tissue
Venous Pressure
Venous Resistance
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Cardiac Cycle
Both systole and diastole can be dividedinto early and late phase
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Cardiac Cycle
We begin at the end of diastole
Here, the ventricles are relaxed andmaximally filled with blood, including anextra fuel injection fuel injection from
the atria
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Cardiac Cycle
Early Systole
The Pressure in the Ventricle is the sameas in the great veins
The Ventricle contracts
The AV valves close
Since the Aortic and Pulmonic valves were
already closed, the heart is a closed ball As the heart contracts, the pressure in the
ball rises at a fixed volume.
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Cardiac Cycle
Early Systole
Is
ISOMETRIC CONTRACTION!
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Pressure Volume Loop
EarlySystole
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Cardiac Cycle
Late Systole The Pressure in the Ventricles is the same
as in the great arteries
The A/P valves open Further contraction of the ventricles causes
blood flow at a relatively constant pressure
(this is because the aorta is compliant aswell and increase in volume causes only asmall increase in pressure)
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Cardiac Cycle
Late Systole
Is
ISOTONIC CONTRACTION!
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Pressure Volume Loop
Late Systole
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Cardiac Cycle
Early Diastole
The Ventricles begin to relax
As the Ventricular pressure falls below thegreat artery pressure, the A/P valves close
Since the AV valves were already closed,the heart is a closed ball
As the heart relaxes, the pressure in theball falls at a fixed volume.
ISOMETRIC RELAXATION
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Pressure Volume Loop
Early
Diastole
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Cardiac Cycle
Late Diastole When the pressure inside the heart falls
below the pressure of the great veins AND
the papillary muscles have relaxed, the AVvalves open
The blood flows down its pressure gradientand the ventricles fill passively at a fixed
pressure (because the ventricle hascompliance)
ISTONIC RELAXATION
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Pressure Volume Loop
LateDiastole
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Cardiac Cycle
End Diastole
Is unique because the atria contract
This leads to an increase in pressure inthree places:
The great veins
The atria
The ventricles
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Pressure Volume Loop
End
Diastole
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Cardiac Cycle
End Diastole Atrial Contraction
Early Systole
Isometric Contraction Late Systole
Isotonic Contraction
Early Diastole
Isometric Relaxation
Late Diastole Isotonic Relaxation
End Diastole
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Cardiac Cycle
Why does this work?
The heart is like a sphere.
The volume of the sphere is a function of theradius.
The surface diameter / area is a function ofthe radius
Thus the surface area can be expressed as afunction of the volume.
Since the muscle fiber length is a function ofthe surface area
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Cardiac Cycle
The muscle fiber length is a function ofthe Cardiac Volume
Just like with a muscle or with asphincter, we can draw a VOLUME-FORCE graph and a VOLUME-SHORTENING graph (for isometric and
isotonic contraction respectively)
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Cardiac Cycle
Similarly, PRESSURE and VOLUMEare related.
So we can draw a PRESSURE-FORCE and PRESSURE-SHORTENING graph, as well.
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Cardiac Cycle
Thus, if we know two things:
Ventricular COMPLIANCE
(during diastole)
Ventricular CONTRACTILITY
(during systole)
We can use PRESSURE and VOLUMEinterchangably. (very useful!)
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Cardiac Cycle
We discover that: 1) Initial Volume is PRELOAD
Also called END DIASTOLIC VOLUME
Is related to END DIASTOLIC PRESSURE
2) AFTERLOAD is the outflow pressure Also called BLOOD PRESSURE
If we know the compliance and resistance(V=IR), then can be related to CARDIACOUTPUT (Volume per time)
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Pressure Volume Loop
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Cardiac Pump
So now we ask:
1) What determines PRELOAD? 2) What determines AFTERLOAD?
3) How does the heart turn PRELOAD
into CARDIAC OUTPUT against anAFTERLOAD?
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Cardiac Output
First:
Systemic venous return must equal rightcardiac output
Right cardiac output must equal pulmonaryvenous return
Pulmonary venous return must equal left
cardiac output Left cardiac output must equal systemic
venous return
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Cardiac Output
Thus COright = COleft
Flux is constant,
even though pressure is not.
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Cardiac Output
Second:
Blood comes in from Venous Return
Despite lots of flow, there is little change inpressure
Thus, the Venous return is from acapacitant system and provides preload to
the heart
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Cardiac Output
Third:
Blood goes into the Arterial Tree
With the same amount of flow, there aremuch higher pressures
Thus, the Arterial Tree is a resistancesystem, and that resistance is the afterload
on the heart.
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Cardiac Output
Is any vessel just acapacitor or resistor?
Of course not.
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Cardiac Output
Capacitant Veins have venousresistance to control flow rates (just like V=IR, P = JR, so J = P / R)
Resistant Arteries have capacitance This capacitance allows them to dilate
slightly to receive more volume at a givenpressure, and is appropriately calledcompliance. (V /P)
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Beginning Diastole
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End Diastole
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Beginning Systole
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End Systole
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Ventricular Pressure
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Central Venous Pulse
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Cardiac Output
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Guytons Model
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Venous Return
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Venous Return
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Venous Resistance
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Frank - Starling Curve
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Contractility
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Cardiac Output
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Blood Flux (CO versus VR)
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Pressure versus Afterload
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Velocity versus Afterload
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Ventricular Pressure
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Blood Flux (CO versus VR)
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CardiacCycle
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Economic Effects
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Questions?