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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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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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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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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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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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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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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?

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