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Blood Pressure Measurement

What is blood pressure

Lateral pressure exerted on the vessel wall by the circulating blood; also referred to as systemic arterial pressure.

Calculation of blood pressure:


BP = blood pressure.

CO = cardiac output, volume of blood ejected from the ventricle in one minute.

TPR = total peripheral resistance, sum of the resistance of all peripheral vasculature in the systemic circulation.


Systolic pressure: Peak pressure that occurs in the artery following ventricular systole

Diastolic pressure: The level to which the arterial blood pressure falls during ventricular diastole.


Normal blood pressure is arbitrarily set at 120/80 mm Hg, although variations from this often occur in normal healthy people.

Factors affecting blood pressure

Cardiac output:

a) Increase cardiac output 

  1. Increase in blood volume
  2. Physical exercise
  3. Emotional excitement

b) Decrease cardiac output

  1. Change of posture
  2. Reduction in blood volume
  3. Cardiac compression
  4. Myocardial ischaemia and infarction


Peripheral resistance

a) Increase peripheral resistance

  1. Chemoreceptor reflex (React to blood O2, CO2 and pH level) *
  2. Baroreceptor reflex (React to vessel wall stretching)*
  3. Renin-angiotensin mechanism


*Chemoreceptor and baroreceptors are located in aortic and carotid bodies. They adjust blood pressure through autonomic nervous system.

    b) Decrease peripheral resistance

    1. Vasovagal attack
    2. Exercise



    Age, sleep, gravity, and any other underlying diseases.

      Equipment for blood pressure measurement

      Things to prepare for blood pressure measurement:

      1. Stethoscope

      2. Blood pressure set (Meter, pump, cuff of CORRECT SIZE in relation to the patient)

      Before starting:

      1. Wash your hand.
      2. Introduce yourself to the patient.
      3. Explain what you are doing, and possible, why you doing it, and obtain permission.
      4. 5 questions to be asked:
      • Smoking.
      • Caffeinated drink, such as coffee or tea.
      • Enough sleep?
      • Exercise.
      • Any Anti-hypertensive drugs.
      • ANY PAIN?



      Good morning, I'm XXX, 3rd year medical student. May I check on your full name and date of birth please?

      The doctor had instructed me to measure your blood pressure today (because of your history of hypertension / the symptoms you are having / previous high blood pressure / normal check up / etc...). Have you had your blood pressure measured before? Would you like me to explain how this is done?

      Basically, I will fit this cuff around your arm and inflate air into it, then slowly deflate to gain an estimate of your blood pressure from the meter reading. You may experience some temporary discomfort as the cuff may become quite tight. Please do let me know if it becomes too painful to continue.

      Before we start, there are several routine questions I would like to ask you...

        Locate pulses

        Radial pulse:

        Locate by following your thumb down to the wrist. lateral to the flexor carpi radialis tendon.

        Comment on: rate, rhythm, volume and characteristic.


        Brachial pulse:

        Located medial to biceps tendon.

        Taking the measurement

        Palpating method

        1. Patient's upper arm should be at the level of the heart.
        2. Wrap the cuff around upper arm with bladder centred over the brachial artery.
        3. Feel for radial pulse.
        4. Inflate cuff until radial pulse is impalpable.
        5. Increase pressure by 20mmHg then deflate until radial pulse is back.
        6. The measurement is the estimated systolic pressure.
        7. This should be follow by auscultating method as shown below to obtain a more accurate estimation of blood pressure

        Auscultating method

        Auscultating Method

        1. Place stethoscope over the brachial artery.
        2. Inflate the cuff until the measurement reaches the estimated systolic pressure + 20 mmHg.
        3. Deflate SLOWLY and listen to the first “click” sound => this is the systolic blood pressure.
        4. Continue deflate until the “clicking” sound disappear => final reading is the diastolic blood pressure.

        Importance of Palpating method

        It is important to perform palpating method before auscultatory method to:

        1. Prevent discomfort from unnecessary high cuff pressure.

        2. Avoid auscultatory gap (the sounds disappear just below the systolic pressure and reappear before diastolic pressure, can lead to underestimate of systolic blood pressure)

        Korotkoff Sound

        5 phases sounds will be heard as the cuff is slowy released, which are called the Korotkoff sounds:

        • Phase 1: 1st appearance of sound (systolic pressure)
        • Phase 2 and 3: increase volume
        • Phase 4: muffling of sound
        • Phase 5: disappear of sound (diastolic pressure)


        NJ Talley, SO Connor, Clinical Examination: A systematic guide to physical diagnosis, 6th Edition, 2010.


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