Blood pressure measurement: algorithm, norm
Last reviewed: 23.04.2024
All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
Arterial pressure is the pressure that blood exerts on the walls of the vessels. This pressure is somewhat less in peripheral, smaller vessels. It fluctuates due to the contractile function of the heart. In the systole period, when the pulse wave is raised, a higher, maximal, or systolic pressure is determined; during diastole, when the pulse wave falls, the pressure decreases, it is diastolic, or minimal, pressure. The difference between the maximum and minimum pressure is called the pulse pressure. Arterial pressure can be roughly estimated by the pulse voltage: the higher the pulse voltage, the higher the blood pressure.
[How to measure blood pressure?
The blood pressure can most accurately be determined by a bloody method, by inserting a needle connected to the manometer directly into the vessel. In practice, blood pressure is usually determined with the help of the Riva-Rocchi apparatus with simultaneous listening in the ulnar fossa of Korotkov's tones. S. Riva-Rocchi in 1896 described the device used today to measure blood pressure, including a mercury manometer and a cuff. Russian physician Nikolai Sergeyevich Korotkov in St. Petersburg in 1905 proposed a method of measuring blood pressure with auscultation using the Riva-Rocchi apparatus.
This method was substantiated by NS Korotkov in experiments on dogs. Allocated iliac and femoral arteries and studied the blood flow in them when applying the cuff while listening to the vessels below the cuff at a different level of pressure in it. At the same time, the same sounds were heard and in the same order as the person in the same conditions. This method is used to measure blood pressure today.
A cuff of at least 12 cm wide is placed on the forearm, into which air is pumped. Gradually increase the air pressure in the cuff until the moment when it begins to exceed the pressure in the brachial artery. As a result, pulsation in the brachial artery ceases. By releasing air from the cuff and lowering the pressure to just below the systolic level, we restore blood circulation in the brachial artery, which can be recorded palpation on the radial artery. The cuff is connected to a Riva-Rocci mercury manometer or a specially calibrated spring manometer, by which we estimate the pressure in the cuff and, therefore, we can estimate the magnitude of the systolic pressure in determining the pulse.
An important achievement that provided not only the measurement of systolic pressure, but also diastolic blood pressure, was the auscultative method discovered by NS Korotkov. It consists in the fact that when the pressure in the cuff decreases, the doctor simultaneously listens for the tones appearing in the brachial artery. When the pressure in the cuff decreases slightly below the systolic pressure, tones begin to be heard on the brachial artery (phase I of sounds), the appearance of which is associated with the vibrations of the relaxed wall of an empty arterial vessel.
With further decrease in pressure in the cuff and listening to the brachial artery, the first phase is replaced by the second phase of noise, and then the tones (phase III) reappear. Further, these sonorous tones of the third phase suddenly become weaker and soon cease (phase IV).
The transition from loud tones to quiet ones, i.e. From III to IV phase, or a rapid weakening of the loudness of tones corresponds to diastolic pressure.
Arterial pressure is measured in millimeters of mercury. The normal systolic (maximum) pressure ranges from 100-140 mm Hg. Art. The diastolic (minimum) pressure is 60-80 mm Hg. Art. In addition, there is an idea of the average arterial pressure. This is the arterial pressure, which without pulsation could provide blood movement in the vascular system at the same rate. The value of the mean blood pressure is calculated by the formula: Р ср. = P diast. + 1/2 P pulse.
When measuring blood pressure, the Riva-Rocchi apparatus is set so that the zero division of the pressure gauge is at the level of the artery being examined.
Under normal conditions, in a healthy person, blood pressure is subject to significant fluctuations. Currently, there is the possibility of monitoring the monitoring of blood pressure (systolic and diastolic) for hours and even days. The lowest figures of blood pressure are observed at night. The increase in pressure is noted with physical exertion, mental stress, after eating, especially stimulating drinks, such as strong tea, coffee, and after drinking alcohol and excessive smoking. Therefore, it is important to measure blood pressure in the subject who is in a state of maximum rest. The lowest blood pressure is recorded in the morning, on an empty stomach, during a person's stay in bed, immediately after sleep. This pressure is called basic, or basal. Arterial pressure is also measured on the legs. For this, the cuff is placed on the thigh and the tones of Korotkov are heard in the popliteal fossa. Normally, the arterial pressure on the legs is 10 mm higher than on the arms. In patients with coarctation of the aorta with high pressure on the hands, the pressure on the legs is significantly lower, which is of diagnostic significance. Distorted indices of blood pressure can be obtained with an incorrectly selected (i.e., narrower) cuff of the sphygmomanometer. The cuff should be wider when measuring pressure in obese individuals.
It is advisable to measure arterial pressure both in a supine position and standing; with a tendency to orthostatic hypotension (a decrease in pressure in the standing position).
When you inhale, your blood pressure decreases slightly, usually within 10 mm Hg. Art. With such conditions as cardiac tamponade in patients with pericarditis, a decrease in inspiratory pressure exceeds 10 mm Hg. Art.
When measuring blood pressure, it is advisable to rapidly reduce the pressure in the cuff, as more accurate data can be obtained. It is advisable to measure the pressure on both hands. In this case, small differences are not normally related to the usual true difference in pressure, but to the time variations of these indices. It should also be borne in mind that in the period between the systole and the diastole a moment is possible when the tones completely disappear. In this regard, an incorrect estimate of the true systolic pressure is possible. It is usually enough to measure blood pressure with an accuracy of 5 mm Hg. Although some prefer to do this within 3 mm of Hg. Art. In some healthy individuals, barely audible tones of IV-V phases are determined until the pressure in the cuff decreases to zero, which should be taken into account when registering the moment of sharp decrease in the volume of tones corresponding to the level of diastolic pressure.
Indicators of normal blood pressure and in pathology
The amount of blood pressure depends on the cardiac output and the minute volume of the heart, with which it increases, and also on the state of the peripheral vessels, i.e., the total peripheral resistance. With a tendency to widespread spasm of peripheral vessels or insufficient expansion of arterioles with an increase in cardiac output, there is an increase in blood pressure. The tendency to increase cardiac output usually occurs when the amount of circulating blood increases.
Elevated blood pressure is noted in hypertension, kidney disease ( glomerulonephritis, pyelonephritis, etc.), diseases of the endocrine system. It is possible to increase only systolic pressure, for example, with a heart condition such as aortic valve failure, thyrotoxicosis.
An increase in diastolic pressure, which to a much greater extent reflects the state of the peripheral vascular bed, the overall peripheral resistance, has a much greater clinical significance.
Reduced blood pressure is observed with the so-called orthostatic hypotension (the transition from lying to standing), some endocrine diseases ( addison's disease ). An important manifestation of shock in myocardial infarction, severe trauma, anaphylaxis, infection, blood loss is pronounced hypotension. It is usually based on a significant reduction in the amount of circulating blood and a decrease in cardiac output. In this case, peripheral vascular resistance can be even increased, but not to the extent that it provides normal blood pressure.
