Blood Pressure

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Systolic blood pressure is the pressure that the heart exerts when it contracts and pumps blood out.

Diastolic pressure is the “vacuum” pressure when the heart expands and pulls blood from veins (from other end).

Measurement Technique

Measuring systolic pressure makes intuitive sense: increase pressure until the heart can no longer overcome that pressure. This is measured by absence of a pulse at a high enough pressure.

Diastolic pressure has long been much trickier for me to nail down and understand. To measure, we are taking advantage of Korotkoff sounds. At at high pressure, there is turbulence in the blood flow and this produces a loud whoosh with every pulse. As the pressure drops, so does the turbulence and eventually the pressure is lower than diastolic pressure. When this happens, there is no longer a restriction/turbulence and the Korotkoff sounds will stop being heard.

Measurement Procedure

To measure:

  1. Tighten arm-cuff until the pressure is above systolic pressure. This effectively cuts off blood flow to the arm.
  2. Slowly release the pressure (2-3 mg per pulse).
  3. When the pressure drops to systolic pressure, blood will flow once more. This produces Korotkoff sounds, which is turbulence in fluid flow due to restriction.
  4. As the pressure continues to drop, the turbulence will decrease in magnitude.
  5. When Korotkoff sounds can no longer be heard, this is the diastolic pressure.