Cycle

• How does it start?

  Each cycle is initiated by spontaneous generation of an action potential in the sinus node
• Fluids flow according to pressure gradients, moving from regions higher in pressure to regions lower in pressure
• Events are the same in the right & left sides of the heart, but with lower pressures in the right side due to less muscle size and less distance to move the blood
• Pressure changes during cardiac cycle

  1. Rapid ejection

  2. Reduced (slow) ejection of deoxygenated blood and oxygenated blood during ventricular diastole
• A single cardiac cycle is a complete beat of the heart
• Pressure-volume loop


  Describing the phases of the cardiac cycle
• Ventricular pressures are important
• The cardiac cycle consists of the mechanical and electrical events that occur from the beginning of one heartbeat to the beginning of the next
• Pressures changes in the cardiac chambers/cycle
• Maximum pressure and minimal pressure in various parts of the heart and arteries
• Phases of the cardiac cycle

  1. A period of relaxation (filling) called Diastole during which the heart fills with blood (atrial and ventricular Diastole)

  2. Followed by a period of contraction called systole (atrial and ventricular Systole)
• Normal range of pressures in cardiac chambers (mm Hg)

  • Right atrium: Average = 2-8
  • Left atrium: Average = 2-10
  • Right ventricle: Systolic = 25-30, Diastolic = 2-8
  • Left ventricle: Systolic = 100-120, Diastolic = 3-12
  • Aorta: Maximum pressure (during systole) = 120, Minimal pressure (during diastole) = 80
  • Pulmonary arteries: Systolic = 25-30, Diastolic = 4-8 - 12
• Chambers
• Rapid ejection

  Happen in ventricular systole
• LVP increase (slightly above 0-2 mmHg)
• IVP < pressure of large arteries, so the semilunar valves also remain closed
• Rapid filling

  End of ejection phase and eject the blood out
• No change in volume in the end
• All valves are closed, No blood enters or leaves the ventricles
• Ventricle filling (20%)
• Pressure changes in the cardiac chambers/cycle
• During ventricular diastole

  Blood flows from the body, lungs
• Minimal pressure range

  • 0-2
• LV contracts with no significant shortening of fibers (increase tension)
• Which valve is open? AV valves (tricuspid+mitral)
• Atrial distole

  Reduced (slow) ejection of deoxygenated blood, oxygenated blood
• Heart sound: S4 is not audible in normal adults. If heard, it is caused by stiffness in ventricles (e.g., ventricular hypertrophy), atria needs to contract strongly to fill (Pathological sound)
• Maximum pressure = 25
• LVP > LAP
• Due to blood building up in the ventricles, the AV valves close down, and at this point the pressure in the atria
• Isovolumetric

  The same volume measurement
• Beginning of ventricular contraction

  • Increased tension in fibers
• At the end of the ST segment or the beginning of the T wave on the ECG, the right ventricle contracts with shortening of the fibers
• Ventricular contraction

  Shortening of the fibers
• During reduced ventricular ejection, the ventricles begin to repolarize marked by the T wave on the ECG
• At the end of rapid ventricular ejection, the atria have the least pressure
• Aortic valve opening

  70% of blood is ejected from the left ventricle to the aorta
• The blood does not enter the ventricles when ventricular pressure is higher than atrial pressure
• Pressure in the pulmonary artery and aorta is higher than in the ventricles

  Semilunar valves remain closed
• Ventricular pressure is higher than atrial pressure


  AV valves remain closed