Journal of Biomedical Engineering and Medical Devices
Open Access

Blood Pressure Measurement: An Overview

Nathalie Johnson^{* *}Correspondence: Nathalie Johnson, Harvard University, Cambridge, MA, United States, Email:

Author info »

Short Communication

The most popular method of measuring arterial blood pressure is with a sphygmomanometer, which previously employed the height of a mercury column to indicate the circulating pressure. Although aneroid and electronic devices do not contain mercury, blood pressure readings are commonly reported in millimeters of mercury (mmHg). Blood pressure swings between systolic and diastolic values with each heartbeat. The peak pressure in the arteries comes near the conclusion of the cardiac cycle, when the ventricles are contracting, and is known as systolic pressure. Diastolic pressure is the lowest pressure in the arteries, which occurs when the ventricles are full of blood at the start of the cardiac cycle. 120 mmHg systolic and 80 mmHg diastolic (written as 120/80 mmHg and spoken as "one-twenty over eighty") are two examples of normal measured values for a resting, healthy adult human.

The systolic and diastolic arterial blood pressures do not remain constant from one heartbeat to the next and throughout the day (in a circadian rhythm). They also alter in response to stress, nutritional variables, medicines, sickness, exercise, and standing up for a brief period of time. The fluctuations might be quite considerable at times. When arterial pressure is too high, it is called hypertension; when it is abnormally low, it is called hypotension. Blood pressure is one of the four basic vital indicators commonly measured by medical experts and healthcare providers, along with body temperature, respiration rate, and pulse rate. Invasive pressure measurement, which involves entering the artery wall to obtain a reading, is far less prevalent and usually limited to a hospital setting. Non-invasive auscultatory and oscillometric measurements are less intrusive and time-consuming than invasive measurements, needless knowledge, have few consequences, and are less uncomfortable and painful for the patient.

Noninvasive approaches, on the other hand, may produce lesser accuracy and slight systematic deviations in numerical results. For routine checkups and monitoring, non-invasive measuring technologies are increasingly routinely used. Non-invasive measurement of blood pressure and other advanced hemodynamic parameters is becoming more applicable in general anesthesia and surgery, where periods of hypotension may be missed by intermittent measurements, thanks to new non-invasive and continuous technologies based on the CNAP vascular unloading technique. Palpation can be used to estimate a minimum systolic value, which is most commonly utilised in emergency situations but should be used with caution. Carotid, femoral, and radial pulses are present in patients with a systolic blood pressure of >70 mmHg, carotid and femoral pulses alone in patients with a systolic blood pressure of >50 mmHg, and only a carotid pulse in patients with a systolic blood pressure of >40 mmHg, according to 50% percentiles.

A more accurate value of systolic blood pressure can be obtained with a sphygmomanometer and palpating the radial pulse. Measurement of blood pressure from radial artery pulse has been proposed using constitutive models. This approach does not allow for the estimation of diastolic blood pressure. Before employing the auscultatory approach, the American Heart Association recommends using palpation to establish an estimate. A stethoscope and a sphygmomanometer are used in the auscultatory method (from the Latin word "listening"). An inflatable (Riva-Rocci) cuff is wrapped around the upper arm and attached to a mercury or aneroid manometer at nearly the same vertical height as the heart. The mercury manometer, regarded as the gold standard, measures the height of a column of mercury, providing an absolute result that does not require calibration and is hence immune to the mistakes and drift of other methods.

Mercury manometers are frequently used in clinical studies and for clinical hypertension measurement in high-risk patients, such as pregnant women. A smooth and snugly fitting cuff is used, which is then manually inflated by continuously squeezing a rubber bulb until the artery is totally occluded. It's critical that the cuff size is correct: smaller cuffs can result in excessively high pressure, while large cuffs can result in excessively low pressure. Three or four cuff sizes should typically be available to accommodate for measurements in arms of various sizes. The examiner progressively releases the pressure in the cuff while listening to the brachial artery at the antecubital area of the elbow with a stethoscope. The turbulent flow makes a "whooshing" or thumping sound when blood initially begins to flow in the artery (first Korotkoff sound). The systolic blood pressure is the pressure at which this sound is first heard. At the diastolic arterial pressure, the cuff pressure is further reduced until no sound can be heard (fifth Korotkoff sound). The auscultatory approach of clinical measurement is the most common. The oscillometric approach, which was first demonstrated in 1876, involves observing oscillations in the sphygmomanometer cuff pressure induced by oscillations in blood flow, i.e. the pulse. In long-term measurements and general practise, the electronic version of this procedure is sometimes utilised.

In 1976, the Dinamap 825, an acronym for "Device for Indirect Non-invasive Mean Arterial Pressure," became the first completely automated oscillometric blood pressure cuff. The Dinamap 845, which could also monitor systolic and diastolic blood pressure as well as heart rate, succeeded it in 1978. The oscillometric approach, like the auscultatory method, uses a sphygmomanometer cuff, but with an electronic pressure sensor (transducer) to observe cuff pressure oscillations, electronics to interpret them, and automatic inflation and deflation of the cuff. To maintain accuracy, the pressure sensor should be calibrated on a regular basis. Oscillometric measurement requires less skill than auscultatory measurement and may be appropriate for inexperienced personnel and automated patient home monitoring. When it comes to the auscultatory technique, the cuff size must be adequate for the arm. Although there are several single cuff systems that may be utilised for arms of various sizes, there is limited experience with these. Over the course of around 30 seconds, the cuff is inflated to a pressure above the systolic arterial pressure and subsequently deflated to below diastolic pressure. Cuff pressure will be virtually constant when blood flow is zero (cuff pressure surpassing systolic pressure) or unhindered (cuff pressure below diastolic pressure).

The recorded pressure waveform generates a signal known as the cuff deflation curve over the deflation time. The oscillometric pulses from the cuff deflation curve are extracted using a bandpass filter. The extracted oscillometric pulses produce a signal known as the Oscillometric Waveform during the deflation period (OMW). With additional deflation, the amplitude of the oscillometric pulses reaches a maximum and then drops. To calculate the systolic, diastolic, and mean arterial pressures, a variety of analysis procedures can be used.