Control of Cardiac Output

• What is the formula for cardiac output?

  Heart rate x stroke volume
• What does heart rate measure?

  Number of heart beats per minute
• What is stroke volume?

  Volume of blood ejected by each ventricle per beat
• How is cardiac output defined?

  Volume of blood ejected by each ventricle per minute
• What is the average resting heart rate?

  70 bpm
• How does cardiac output change during exercise?

  Cardiac output increases
• What are the cardiac output values at rest and during exercise?

  • At rest: CO ~ 5 L/min
  • During exercise: CO ~ 20 L/min
• What are the heart rate values at rest and during exercise?

  • At rest: HR ~ 70 bpm
  • During exercise: HR ~ 190 bpm
• What are the stroke volume values at rest and during exercise?

  • At rest: SV ~ 70 ml
  • During exercise: SV ~ 105 ml
• What are chronotropic effects related to?

  Heart rate, autonomic innervation, hormones
• What is bradycardia?

  Pathologically low heart rate
• What is tachycardia?

  Pathologically fast heart rate
• What are the neurotransmitters and their effects on heart rate?

  • Parasympathetic: Acetylcholine (Negative effect)
  • Sympathetic: Noradrenaline (Positive effect)
• How do parasympathetic and sympathetic effects differ on heart rate and cardiac output?

  • Parasympathetic: Lowers HR and CO
  • Sympathetic: Increases HR and CO
• What is the role of repolarisation and depolarisation in heart rate control?

  Repolarisation is parasympathetic; depolarisation is sympathetic
• What factors affect heart rate?

  • Atrial reflex
  • Venous return
  • Autonomic innervation
  • Hormones
• What is preload in relation to stroke volume?

  Degree to which ventricular muscle cells are stretched at end diastole
• What is contractility?

  Force produced by ventricular muscle cells during systole
• What is afterload?

  Force the ventricle needs to overcome to eject blood
• What are the determinants of end diastolic volume (EDV) and end systolic volume (ESV)?

  • Preload
  • Venous return & filling time
  • EDV - ESV
  • Stroke volume (SV) affects cardiac output (CO)
• How is preload related to EDV?

  Preload is directly proportional to EDV
• What factors affect venous return?

  Posture, skeletal muscle pump, respiratory pump
• How does posture affect venous return?

  • Blood pools in leg veins while standing
  • Decreases venous return
• How does the skeletal muscle pump aid venous return?

  • Movement constricts veins
  • Valves prevent backflow
• How does the respiratory pump affect venous return?

  • Inspiration reduces intrathoracic pressure
  • Increases venous return
• How does sympathetic nervous system (SNS) activity affect venous capacitance?

  • Reduces compliance
  • Increases central venous pressure
• What is the relationship between force of contraction and stroke volume?

  More force leads to more blood ejected
• What are the effects of SNS on contractility?

  • Increases force of contraction
  • Increases velocity of conduction
  • Maximizes diastolic time
  • Increases filling