L4.3.2: Cardiac Cycle and Heart Sounds

• CARDIAC CYCLE AND HEART SOUNDS

  ● Cardiac Cycle

  ○ One complete heartbeat in which both atria and ventricles contract and then relax

  ○ Systole = contraction

  ○ Diastole = relaxation

  ○ Normal length is 0.8 seconds

  ○ Average heart rate is 75 bpm
• CARDIAC CYCLE AND HEART SOUNDS

  ● Heart Sounds

  ○ Lub — longer, louder heart sound caused by the closing of the AV valves

  ○ Dup — short, sharp heart sound caused by the closing of the semilunar valves at the end of ventricular systole
• 5 PERIODS OF CARDIAC CYCLE

  1. Atrial Diastole — VENTRICULAR FILLING
  2. Atrial Systole
  3. Isovolumetric Contraction
  4. Ventricular Systole — EJECTION PHASE
  5. Isovolumetric Relaxation
• [1] Atrial Diastole — VENTRICULAR FILLING

  ○ Heart is relaxed

  ○ Pressure in heart is low

  ○ AV valves are open

  ○ Blood flows passively into the atria and into ventricles

  ○ Semilunar valves are closed
• [2] Atrial Systole

  ○ Ventricles remain in diastole

  ○ Atria contract

  ○ Blood is forced into the ventricles to complete ventricular filling
• [3] Isovolumetric Contraction

  ○ Atrial systole ends; ventricular systole begins

  ○ Intraventricular pressure rises

  ○ AV valves close

  ○ For a moment, the ventricles are completely closed chamber
• [4] Ventricular Systole — EJECTION PHASE

  ○ Ventricles continue to contract

  ○ Intraventricular pressure now surpasses the pressure in the major arteries leaving the heart

  ○ Semilunar valves open

  ○ Blood is ejected from the ventricles

  ○ Atria are relaxed and filling with blood
• [5] Isovolumetric Relaxation

  ○ Ventricular diastole begins

  ○ Pressure falls below than in the major arteries

  ○ Semilunar valves close

  ○ For another moment, the ventricles are completely closed chambers

  ○ When atrial pressure increases above intraventricular pressure, the AV valves open
• TYPE - AV VALVES - SEMILUNAR VALVES

  • OPEN - heart relaxation (diastole) - ventricular contraction (systole)
  • CLOSED - ventricular contraction (systole) - heart relaxation (diastole)