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Blood pressure describes the lateral pressures produced by blood upon vessel walls. It is a vital sign obtained routinely in hospital and outpatient settings and is one of the most common medical assessments performed worldwide. Blood pressure measurement helps clinicians evaluate cardiovascular function and detect potential health issues.

Blood pressure can be determined directly using an intra-arterial catheter or indirectly through non-invasive methods. Indirect measurement is most commonly used because it is safe, easily reproducible, and can be performed automatically by oscillometry or manually by auscultation utilizing a sphygmomanometer with an inflatable cuff and manometer.

The examiner places a stethoscope over the brachial artery, inflates the cuff above expected systolic pressure, then auscultates while deflating. Korotkoff sounds—audible turbulent blood flow in the partially squeezed artery—indicate systolic pressure at first sound and diastolic pressure when sounds cease. The auscultatory method relies on listening for these characteristic sounds to determine both pressure values.

Korotkoff sounds are audible turbulent blood flows produced when the cuff pressure falls below arterial pressure, partially squeezing the artery. The first audible sound signifies maximum arterial pressure during systole, while the point where sounds cease indicates minimal arterial pressure during diastole, representing systolic and diastolic blood pressure respectively.

Determination of the pulse-obliterating pressure by palpation is performed prior to auscultation to give a rough estimate of the target systolic pressure. This preliminary step helps the examiner know approximately how high to inflate the cuff, ensuring accurate measurement and efficient technique during the subsequent auscultatory phase.

Blood pressure is measured in millimeters of mercury (mmHg) and recorded as a fraction with systolic pressure over diastolic pressure. Repeated measurement is especially important given potential measurement errors and blood pressure variations. The physician may repeat vital signs after the patient interview to ensure accuracy and account for natural fluctuations.

In most instances, vital signs including blood pressure are initially measured by a health care assistant or registered nurse (RN). The physician may choose to repeat the vital signs and blood pressure measurement after completion of the patient interview to verify findings and ensure clinical accuracy.