Heart Sounds: S1 and S2

Heart Sounds

• Two heart sounds are normally heard by a stethoscope during each cardiac cycle
• First heart sound (S1):
  • Caused by closure of mitral and tricuspid valves at the beginning of systole
  • Mitral valve closes before the tricuspid valve
• Second heart sound (S2):
  • Caused by closure of aortic and pulmonary valves at the end of systole and beginning of diastole
  • Delay is greater than in the first heart sound, making it usually audible

Listening to Heart Sounds

• Four main areas to listen to heart sounds:
  • Mitral valve: at the position of the apex beat
  • Tricuspid valve: over the xiphoid process
  • Aortic valve: in the 2nd right intercostal space, close to the sternum
  • Pulmonary valve: at the 2nd left intercostal space, close to the sternum

Arterial Pulse

• Arterial pulse: a pressure wave distending the arterial wall, starting from the aorta towards peripherally
• Reflects the number of heartbeats per minute
• Measured at different parts of the body
• Common parts to measure:
  • Radial artery in the wrist
  • Brachial artery in the elbow
  • Common carotid artery in the neck

Assessing Arterial Pulse

• Characteristics to examine:
  • Heart rate: number of beats per minute
  • Rhythm: regularity of intervals
  • Character of the pulse wave
• Radial pulse is usually used to assess rate, rhythm, character, and volume
• Compare pulse volume with the other side (not simultaneously in the case of the carotid pulse)

Measuring Pulse Rate

• Method to measure pulse rate:
  1. Place index and middle finger over the underside of the opposite wrist, below the base of the thumb
  2. Press firmly with flat fingers until the pulse is felt in the radial artery
  3. Count the pulse waves for 30 seconds and multiply by two to get the per-minute total
• Normal range: 60-100 beats per minute
• Average radial pulse: 73 beats per minute
• Abnormal rates:
  • Bradycardia (rate below 60)
  • Tachycardia (rate above 100)

Blood Pressure

• Blood pressure: the pressure exerted by circulating blood upon the walls of blood vessels
• Varies between a maximum (systolic) and a minimum (diastolic) pressure during each heartbeat
• Measured in millimeters of mercury (mmHg)
• Recorded as two numbers, written as a ratio (e.g., 117/76 mmHg)
• Systolic pressure: maximum pressure in an artery during ventricular contraction
• Diastolic pressure: lowest pressure in an artery during ventricular relaxation
• Factors influencing blood pressure:
  • Age, gender, and body type
  • Time of day
  • Body position
  • Activity and exercise
  • Emotional status
  • Medication
  • Medical and family history
  • Social habits (e.g., smoking and alcohol consumption)
  • Disease (e.g., kidney, metabolic, or congestive heart failure)
  • Pain
  • Blood volume
  • Blood thickness/viscosity
  • Vessel resistance and size

Measuring Blood Pressure

• Measured in the peripheral artery of the arm or leg (usually in the brachial artery)
• Normal range for adults: 120/80 mmHg
• Materials needed:
  • Mercuric sphygmomanometer (cuff, inflator, and pressure indicator)
  • Stethoscope
• Methods to measure blood pressure:
  • Palpatory method (measures systolic pressure)
  • Auscultatory method (measures both systolic and diastolic pressure)

Korotkoff Sounds

• Five phases of sounds heard during blood pressure measurement:
  1. Sudden appearance of sharp tapping sound (systolic)
  2. Swishing sound
  3. Crisp sound (loud knocking)
  4. Muffled sound
  5. Silence (sound disappeared)

Blood Pressure Tips

• Avoid errors in measurement:
  • Too-narrow cuff: causes a false high reading
  • Too-wide cuff: causes a false low reading
  • Cuff wrapped too loosely: causes a false high reading
  • Arm above heart level: causes a false low reading
  • Muscle contracted on arm: causes a false high reading
• Arm pressures should not differ more than 10 mm Hg
• Leg pressures should be the same or slightly higher than arm pressures

Which Arm to Use?

• Usually, either arm can be used for BP measurement, but avoid using an arm with:
  • Injury or cast
  • IV site
  • Mastectomy
  • Vascular access for dialysis