Source: Meghan Fashjian, ACNP-BC, Beth Israel Deaconess Medical Center, Boston MA

The term blood pressure (BP) describes lateral pressures produced by blood upon the vessel walls. BP is a vital sign obtained routinely in hospital and outpatient settings, and is one of the most common medical assessments performed around the world. It can be determined directly with the intra-arterial catheter or by indirect method, which is a non-invasive, safe, easily reproducible, and thus most used technique. One of the most important applications of BP measurements is the screening, diagnosis, and monitoring of hypertension, a condition that affects almost one third of the U.S. adult population and is one of the leading causes of the cardiovascular disease.

BP can be measured automatically by oscillometry or manually by auscultation utilizing a sphygmomanometer, a device with an inflatable cuff to collapse the artery and a manometer to measure the pressure. Determination of the pulse-obliterating pressure by palpation is done prior to auscultation to give a rough estimate of the target systolic pressure. Next, the examiner places a stethoscope over the brachial artery of the patient, inflates the cuff above the expected systolic pressure, and then auscultates while deflating the cuff and observing the manometer readings. When the pressure in the cuff falls below the pressure in the brachial artery, the turbulent blood flow in a partially squeezed artery produces the Korotkoff audible sounds. The first audible Korotkoff sound signifies the maximum arterial pressure during systole. When the pressure in the cuff is reduced further and falls below the minimal arterial pressure (during diastole), the Korotkoff sounds become no longer audible. The reading at this point signifies the diastolic blood pressure. The blood pressure is measured in mmHg and recorded as a fraction (systolic BP/ diastolic BP).

In most instances, the vital signs 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. Repeated measurement of blood pressure is especially important given the potential measurement errors and blood pressure variations.