Cardiac Physiology Pump Function

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Cardiac PhysiologyPump Function

• Jim Pierce
• Bi 145a
• Lecture 12 and 14, 2008-09

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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 through one
  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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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 with oxygen
  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 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)

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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 Volume per Time
  caused by a change in Pressure
• Contractility (dV/dT) / dP

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Contractility
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Compliance and Contractility
Contractility determines EMPTYING
Compliance determines FILLING
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Pressure Volume Loop
Contractility
Area Work
Compliance
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Cardiac Cycle

• Thus, each part of the cardiac cycle is dominated
  by a relationship between volume 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 absolute
  volume and pressure change
• This relationship is measured by COMPLIANCE
• This is affected by
• Connective Tissue
• Venous Pressure
• Venous Resistance

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Cardiac Cycle

• Both systole and diastole can be divided into
  early and late phase

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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

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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.

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Cardiac Cycle

• Early Systole
• Is
• ISOMETRIC CONTRACTION!

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Pressure Volume Loop
Early Systole
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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 as well
  and increase in volume causes only a small
  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 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

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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 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

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Pressure Volume Loop
Late Diastole
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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

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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 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

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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 VOLUME-FORCE graph and a
  VOLUME-SHORTENING graph (for isometric and
  isotonic contraction respectively)

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Cardiac Cycle

• Similarly, PRESSURE and VOLUME are 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 VOLUME interchangably.
  (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 (VIR),
  then can be related to CARDIAC OUTPUT (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 an AFTERLOAD?

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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

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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 in
  pressure
• Thus, the Venous return is from a capacitant
  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 are much
  higher pressures
• Thus, the Arterial Tree is a resistance system,
  and that resistance is the afterload on the heart.

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Cardiac Output

• Is any vessel just a capacitor or resistor?
• Of course not.

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Cardiac Output

• Capacitant Veins have venous resistance to
  control flow rates
• (just like VIR, ?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)

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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?