S1 COMPONENT

• S1 produced when ventricles contract causing closure of AV valves - mitral and tricuspid valves
• S1 is loudest at apex of heart
• The left ventricle is capable of generating higher pressures more quickly
• Mitral valve (left ventricle) closes slightly before the tricuspid (right ventricle) due pressure difference
• The two sounds slightly overlap and create one sound - S1
  • In reality, the first half of S1 is the mitral component
  • Second half of S1 is the tricuspid contribution
• With practice (much practice!) individual components of S1 and S2 can be appreciated
• S1-S2 are easier to distinguish at slower heart rates (e.g. 56 bpm);
• Discerning S1 and S2 is difficult at higher rates
• S1 is always after the longer pause
• As heart rate increases, systole time is constant; diastole time shortens
  • Distinction (S1 and S2) is challenging at faster heart rates
  • Keeping finger on pulse is useful aid to distinguish S1 from S2
  • Pulse felt between S1 and S2 at the neck

• S2 produced with closure of semilunar valves - aortic and pulmonic valve
• S2 is loudest at base of heart
• Aortic valve closes slightly ahead of pulmonic creating two component
  • A2 and P2 indicate aortic and pulmonic component respectively
  • A2 normally precedes P2 (aortic valve closes before pulmonic valve)
  • Inspiration lowers intrathoracic pressure thus draws more blood from both venae cavae
  • Increased blood volume (from inspiration) requires more time to eject all blood into PA
  • Pulmonic valve thus stays open longer thus P2 occurs later with inspiration vs expiration
  • Difference is called physiologic split (covered later under Spit