Basics SV

• SV:

  • normally SV correlates closely to force of contraction
  • at rest around 70 ml of blood is ejected per ventricle
  • SV = end diastole ventricular volume minus end systole ventricular volume
  • SV = (amount of blood in the ventricles just before contraction) minus (amount of blood left in the ventricles after contraction)
  • only around 60% of the blood in the ventricles get ejected
  • the blood left in the ventricles after ventricular contraction is called the reserve volume
• • CO is variable, depending on activity intensity and cardiorespiratory fitness
  • average person CO at rest = 5 L
  • average person CO during exercise = 25 L
  • athlete CO during exercise = 35 to 40 L
  • cardiac reserve = CO max - CO rest
• Differing contributions of HR & SV to CO:

  • someone whos unfit will have a higher HR, but lower SV, so CO will still be ~ 5 L/min
  • someone whos fit will have a lower HR, but higher SV, so CO will still be ~ 5 L/min
  • at rest, cardiac energy costs are greatest in those with the highest HR at rest
• • a change in SV can cause a change in CO
  • a change in HR ca cause a change in CO
• How to increase SV:

  • increase blood into heart
  • increase venous return
  • increase time available for filling
  • squeeze more blood out
  • contracting harder
• SV can be altered by:

  • pre-load
  • after-load
  • contractility
• Factors affecting SV:

  • pre-load - at rest and on exercise
  • contractility - on exercise
  • after-load