Transcript Lecture 14 - CV Pump physiology

Cardiac Physiology
Pump Function
Jim Pierce
Bi 145a
Lecture 12, 2009-10
Cardiac Pump
• The Heart Pumps Blood
•
•
•
•
… by contraction and relaxation
Contraction is called systole
Relaxation is called diastole
The Cardiac Cycle is the cycle through
one systole and one diastole
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
Cardiac Pump
• We can measure pressures and
volumes during the cardiac cycle
• These will help us understand the heart
Echocardiography
Swan-Ganz Catheter
Swan-Ganz Catheter
Arterial Pressure
Swan-Ganz Catheter
Cardiopulmonary Function
• When we combine cardiac output with
oxygen carrying capacity of the blood,
we begin to evaluate …
• Delivery of Oxygen
Swan-Ganz Parameters
Volumes
• There are a variety of ways to measure
vascular 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 all
compartments)
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
Compliance
• Compliance is the change in pressure
caused by a change in absolute volume
• Compliance = P / V
• Point Compliance = dP / dV
Compliance (Computation)
Compliance (Real)
Contractility
• Contractility is the change in Volume
per Time caused by a change in
Pressure
• Contractility = (dV/dT) / dP
Contractility
Compliance and Contractility
Contractility
determines
EMPTYING
Compliance
determines
FILLING
Pressure Volume Loop
Contractility
Area = Work
Compliance
Cardiac Cycle
• Thus, each part of the cardiac cycle is
dominated by a relationship between
volume and pressure.
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)
Cardiac Cycle
• Diastole
– Muscle is Relaxing
– Veins return blood to the heart
– As the heart fills with blood, the absolute
volume and pressure change
– This relationship is measured by
COMPLIANCE
– This is affected by
• Connective Tissue
• Venous Pressure
• Venous Resistance
Cardiac Cycle
• Both systole and diastole can be divided
into early and late phase
Cardiac Cycle
• We begin at the end of diastole…
• Here, the ventricles are relaxed and
maximally filled with blood, including an
extra “fuel injection” fuel injection from
the atria
Cardiac Cycle
• Early Systole
– The Pressure in the Ventricle is the same
as 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.
Cardiac Cycle
• Early Systole …
• Is …
• ISOMETRIC CONTRACTION!
Pressure Volume Loop
Early
Systole
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 as
well and increase in volume causes only a
small increase in pressure)
Cardiac Cycle
• Late Systole …
• Is …
• ISOTONIC CONTRACTION!
Pressure Volume Loop
Late Systole
Cardiac Cycle
• Early Diastole
– The Ventricles begin to relax
– As the Ventricular pressure falls below the
great 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 the
ball falls at a fixed volume.
– ISOMETRIC RELAXATION
Pressure Volume Loop
Early
Diastole
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 AV
valves open
– The blood flows down its pressure gradient
and the ventricles fill passively at a fixed
pressure (because the ventricle has
compliance)
– ISTONIC RELAXATION
Pressure Volume Loop
Late
Diastole
Cardiac Cycle
• End Diastole
– Is unique because the atria contract
– This leads to an increase in pressure in
three places:
• The great veins
• The atria
• The ventricles
Pressure Volume Loop
End
Diastole
Cardiac Cycle
• End Diastole
– Atrial Contraction
• Early Systole
– Isometric Contraction
• Late Systole
– Isotonic Contraction
• Early Diastole
– Isometric Relaxation
• Late Diastole
– Isotonic Relaxation
• End Diastole
Cardiac Cycle
• Why does this work?
• The heart is like a sphere.
• The volume of the sphere is a function of the
radius.
• The surface diameter / area is a function of
the radius
• Thus the surface area can be expressed as a
function of the volume.
• Since the muscle fiber length is a function of
the surface area …
Cardiac Cycle
• The muscle fiber length is a function of
the Cardiac Volume
• Just like with a muscle or with a
sphincter, we can draw a “VOLUMEFORCE” graph and a “VOLUMESHORTENING” graph (for isometric and
isotonic contraction respectively)
Cardiac Cycle
• Similarly, PRESSURE and VOLUME
are related.
• So we can draw a “PRESSUREFORCE” and “PRESSURESHORTENING” graph, as well.
Cardiac Cycle
• Thus, if we know two things:
– Ventricular COMPLIANCE
(during diastole)
– Ventricular CONTRACTILITY
(during systole)
• We can use PRESSURE and VOLUME
interchangably. (very useful!)
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 CARDIAC
OUTPUT (Volume per time)
Pressure Volume Loop
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 an
AFTERLOAD?
Cardiac Output
• First:
– Systemic venous return must equal right
cardiac output
– Right cardiac output must equal pulmonary
venous return
– Pulmonary venous return must equal left
cardiac output
– Left cardiac output must equal systemic
venous return
Cardiac Output
• Thus COright = COleft
• Flux is constant,
even though pressure is not.
Cardiac Output
• Second:
– Blood comes in from Venous Return
– Despite lots of flow, there is little change in
pressure
– Thus, the Venous return is from a
capacitant system and provides preload to
the heart
Cardiac Output
• Third:
– Blood goes into the Arterial Tree
– With the same amount of flow, there are
much higher pressures
– Thus, the Arterial Tree is a resistance
system, and that resistance is the afterload
on the heart.
Cardiac Output
• Is any vessel just a
capacitor or resistor?
• Of course not.
Cardiac Output
• Capacitant Veins have venous
resistance 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 given
pressure, and is appropriately called
compliance. (V / P)
Beginning Diastole
End Diastole
Beginning Systole
End Systole
Ventricular Pressure
Central Venous Pulse
Cardiac Output
Guyton’s Model
Venous Return
Venous Return
Venous Resistance
Frank - Starling Curve
Contractility
Cardiac Output
Blood Flux (CO versus VR)
Pressure versus Afterload
Velocity versus Afterload
Ventricular Pressure
Blood Flux (CO versus VR)
Cardiac
Cycle
Economic Effects
Questions?