Conditions that can Affect Stroke Volume

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Conditions that can Affect Stroke Volume

• By Andrew Simon, Kelly Kasner, Kelley Neumann,
  Michelle Nunez

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Definitions

• Stroke Volume The amount of blood pumped by one
  ventricle during a contraction
• End Diastolic volume - End Systolic volume
• Factors contributing to Stroke Volume
• Venous return
• Skeletal muscle pump
• Respiratory pump
• Sympathetic activity
• Length-Tension relationship of muscle fibers
• Contractility of the myocardium

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Venous Return

• Skeletal Muscle influence
• Contraction or compression of veins returning
  blood to the heart
• Respiratory influence
• The negative pressure (vacuum) created during
  inhalation serves to draw blood from abdominal
  organs and the lower extremities
• Sympathetic influence
• Can limit stroke volume with an increase in Heart
  Rate
• Affects blood vessel tone in the periphery

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Respiratory Influence

• Tidal Volume Volume of air that moves in a
  single expiration or inspiration
• Low pressure in the thorax increases venous
  return from abdominal veins during inspiration as
  diaphragm lowers
• High pressure in the Abdomen due to the diaphragm
  placing pressure on the veins in the abdomen

Exercise requires more oxygen leading to an
increase in Tidal Volume
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Skeletal Muscle

• Muscle Contraction forces blood against gravity
• One-way valve prevents backflow
• Plays a major role during exercise as more
  muscles are contracting

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Dehydration

• A loss of both body water and important
  electrolytes that regulate the amount of fluid in
  the cells
• Can cause hypovolemia
• Reduces blood flow to the muscles due to
  constriction and increases blood flow to the
  brain due to dilation
• During exercise
• Blood flow increases to the muscles
• Blood volume decreases to the rest of the body
• Dehydration decreases stroke volume resulting in
  decreased cardiac output despite elevated heart
  rate

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Effects on Stroke Volume
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Progressively Intense Exercise

• At the onset of exercise
• Increased skeletal muscle pump
• Increased respiratory pump
• Increased sympathetic activity
• increases pre-load and therefore stroke volume
• to a point

Then, high HR limits ventricular filling and SV
levels off
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Analogy

• The carburetor in a combustion engine regulates
  power output by controlling gas volume
• In the cardiac cycle, stroke volume is the amount
  of power