Blood pressure or blood pressure is an important indicator of the state and functioning of the human body. What does he mean physically? This is the force of the vertical pressure of blood on the walls of blood vessels. The measurement of this indicator is the first procedure at the doctor’s appointment. Its level is expressed in numbers in a fraction: the top line is systolic, the bottom is diastolic pressure.
How arises?
With contractions of the heart, systoles (contraction of the ventricles) and diastoles (relaxation) arise rhythmically. Let's consider in more detail. When the heart contracts, it pushes blood from the left ventricle to the aorta, this force and creates pressure on the walls of the vessels. What affects the values of this indicator?
Changes in arterial blood pressure are affected by:
- the amount and viscosity of blood that is released into the blood circulation per unit time;
- the capacity of the vascular bed itself;
- heart rate (HR);
- vascular wall resistance;
- Times of Day;
- arterial wall tension;
- physical exercise;
- external environment, etc.
The methods for measuring variable pressure are discussed in this article. We continue the study.
When blood is ejected from the heart into the aorta, systolic pressure (DM) occurs. The aortic valves then slam shut. The ventricles relax. The pressure drops. Now it is diastolic (DD). The difference between them is the pulse pressure.
The unit of measurement of blood pressure is considered to be 1 mmHg. Norm SD - 110-129 mm RT. Art., DD - 70-99 mm RT. Art. Figures other than these should be considered as pathology.
A differential is a process of changing pressure (drop or jump). It occurs over a period of time, such as morning and evening. Methods for measuring pressure drops are no different from conventional blood pressure measurements. Next, we consider devices designed for these purposes.
Characteristics
The anatomical and physiological structure of the cardiovascular system suggests the following types of pressure:
- in the cavity of the heart;
- in vessels - arterial, venous and capillary.
Let's consider in more detail. The peculiarity of the circulatory system is that the pressure in it increases from the center to the periphery. This was established by measuring by the method of variable differential pressure. That is, with a decrease in the radius of the vessel, the indicator drops, because the hydraulic resistance of the blood increases.
Only the aorta can boast the highest pressure. Further, it decreases immediately by 15%, and in capillaries - already by 85%. It turns out that the heart spends most of its energy on overcoming precisely this pressure in small vessels. The lowest value of the indicator is obtained in the vena cava system. The movement of blood through the vessels occurs due to the pressure gradient, i.e., its difference in different areas.
Why know your blood pressure
Owning this information is necessary because even small deviations of pressure from the norm create the prerequisites for serious diseases and pathological conditions - heart attacks, strokes, heart and kidney failure.
It is blood pressure that needs to be measured primarily for complaints of dizziness, headaches and weakness. The increase always begins with vascular damage. It has long been known that it is the measurement of pressure repeatedly in the practice of doctors that saved the lives of patients. Doctors in ancient times knew about the value of this indicator. Therefore, many diseases of bloodletting were treated and, at the same time, improvement was noted in many patients.
How did the measuring apparatus
The history of tonometers began 300 years ago. For the first time, pressure was measured in animals by Stefan Hels in 1733. To do this, he introduced a glass tube directly into the horse’s artery and determined the indicator by the height of the blood column in it.
Poiseuille improved this primitive apparatus by adding a manometer with a mercury scale to the existing device. Subsequently, Ludwig invented a kimograph with a float, which made it possible to continuously record the desired values.
At the end of the 19th century, the Italian Riva-Rocci created a bloodless method of measuring blood pressure by palpation. He suggested using a special rubber cuff for pinching the artery on his arm.
In 1905, the Russian doctor N. S. Korotkov improved the method. Its peculiarity consisted in listening with a stethoscope to the arterial tones in the elbow. Today, this principle of vascular compression to measure blood pressure is still in use.
Types of blood pressure monitors
All devices are divided into mechanical and electronic. Their action is a method of measuring a variable pressure drop. You can do this at any time of the day. Electronic devices exist automatic and semi-automatic, the principle of operation is the same for everyone. They are used for measurement at home. Automatic blood pressure monitors are divided into shoulder and wrist devices.
Mechanical devices
They, for the most part, consist of such parts:
- compression cuff;
- mercury or spring manometers;
- pear blower (cylinder);
- crane to bleed air.
All these parts are connected by rubber tubes. A phonendoscope is attached to this system. Such devices are used mainly in medical institutions.
Semi-automatic devices
The difference from a mechanical tonometer is the presence of a pear that pumps air into the cuff. The readings are due to the built-in electronics, they are shown on the display screen. These devices are used in hospitals and at home.
Automatic electronic shoulder devices
They work very simply. The patient needs to put cuffs on his shoulder and press the start button. Everything else is for the automation of the device: inflation of the cuff, analysis and result. Such meters are convenient for use at home.
Automatic blood pressure monitors
They differ from other devices only in their location on the body during the manipulation. They are convenient to take on the road due to their compactness. But such a measurement of blood pressure is not recommended for those who have changes in the vessels (with atherosclerosis, diabetes mellitus).
There are such models that record the time and date of timing, errors during operation. Data is stored in the memory of the device and can be transferred to a computer monitor. This is used for daily monitoring of blood pressure in a certain category of patients.
Next, we consider methods for measuring blood pressure.
Non-invasive (indirect) methods
Most of these methods are compression and are based on the alignment of blood pressure with external (atmospheric) when air is released from the cuff.
They are divided into:
- Palpation is the simplest. Suggested by Riva-Rocci. The pressure in the cuff is raised by pumping air into it. And obviously high, to squeeze the artery. Then the cuff is slowly blown off, releasing air from it. At the same time, the appearance of a pulse on the wrist in the radial artery is monitored. The pressure value will be systolic.
- Auscultatory - used since 1905. The Korotkov method for measuring pressure is currently recognized by WHO as the standard for non-invasive determination of blood pressure. Although data on its use are obtained somewhat lower for diabetes and higher for DD than when measuring invasive. The pressure gauge can be mercury, gauge or electronic. The cuff is always placed in the area of the brachial artery located at the level of the heart, and its pressure coincides with the pressure in the aorta.
- Oscillometric - will be discussed in detail later in the article.
Features of the auscultatory method
The patient's hands should be located at the level of the heart, on the table, and he should sit. Auscultation is performed by a phonendoscope over the projection of the brachial artery in the ulnar fossa. The physical basis of the clinical method for measuring blood pressure lies in the fact that there is a phenomenon of "sounding" of the artery. Let’s explain.
The passage of blood through the squeezed area creates noise due to the turbulent flow of blood. Their appearance is an indicator of diabetes. These are the first tones. Air continues to be released and the bloodstream gradually becomes completely laminar. Vortex noises disappear. This means that external pressure is equal to arterial pressure. The cessation of noise will be shown on the DD pressure gauge.
These are the physical foundations of the method of measuring blood pressure. Classical blood pressure in adults: diabetes - 128-132, DD - 83-85 mm RT. Art. on the right and left hand, respectively.
Although the measurement of blood pressure by the Korotkov method is officially considered the standard, it has its pros and cons. Plus - it is highly resistant to hand movement.
Cons more:
- noise in the room changes performance;
- the phonendoscope head should be located correctly - in the ulnar fossa;
- you need to have measurement skills.
In addition, errors may occur when the size of the cuff and shoulder volume do not match, the position of the arm is incorrect, and air is quickly released from the cuff.
Direct method
An invasive (direct) method of measuring blood pressure is used by catheterization of blood vessels. It is used for scientific purposes in diagnostic laboratories, cardiology and cardiac surgery centers.
Today, this method is the only method for measuring pressure in the aorta and the heart itself. A needle is connected to the pressure gauge in an artery or cannula through a tube. Or the sensor itself is introduced into the bloodstream. Its signals in the form of a curve are recorded by the magnetic tape of the manometer.
The method is applicable only in a hospital, in complete sterility, when there is a need for daily monitoring. Pressure and measurement time are drawn in a curve.
Although these methods of measuring blood pressure are highly accurate, they are quite traumatic because the needle is inserted directly into the vessel or cavity of the heart.
The disadvantage of the method is that such patients need the constant presence of a doctor because of the risk of disconnecting the probe, followed by bleeding, thrombosis at the puncture site, and secondary infection.
An invasive method of measuring pressure is a direct way to measure performance. He needs adequate blood flow in the artery.
The disadvantage of direct methods for measuring blood pressure is the need to penetrate into the cavity of the vessel, which is always fraught with complications.
Oscillometric method (electronic)
The method is based on the registration of pressure pulsations that occur in the device when blood passes through the compressed section of the artery. Devices of this type are most suitable for home use. Plus method - no need for an assistant.
Skills for taking measurements are also not needed, the device is resistant to noise in the room. There is a possibility not to expose your hand - accuracy will not be affected with a thin jacket. But practitioners believe the mechanical method is more accurate, since the performance of electronics depends on its quality, which is not always due to the high price.
Using an oscilloscope, the frequency of pulse blood oscillations is recorded and displayed on the tonometer display. The principle of operation is the same - compression, just the sensors are located in the cuff itself. Inflation and deflation - automatic.
Minuses:
- High price.
- Dependence of devices on batteries. If they started to discharge, there will be no accuracy.
- The immobility of the hand is required when measuring.
Why the blood pressure on the left and right hands does not match
This is due to the difference in the structure of blood vessels. The left subclavian artery departs independently from the aorta and immediately flows into the left brachial blood flow, where blood pressure is measured.
On the right, the course of the vessels is different. First, the brachiocephalic trunk leaves the aorta, which is then divided into the carotid and subclavian arteries. Therefore, blood pressure on the right hand, usually 5-10 mm RT. Art. lower than on the left limb (measurements are preferably carried out on it).
Pressure and age
With age in men, blood pressure rises evenly. But in women, before menopause, this process occurs weakly, since the body is protected by estrogens. But after that (with the extinction of the ovaries), the weaker sex not only catches up, but also surpasses men to increase the level of blood pressure.
What can affect the pressure when measuring
Fat people and smokers always have higher rates. Blood pressure rises with stress and physical exertion, with constipation and after eating, after drinking alcohol, tea and coffee, before urinating, when in a cold room, if there is a mobile phone nearby, in athletes before starting, after taking a bath or shower.
The basic rules of the procedure - how to measure:
- at rest;
- after eating an hour later;
- after urination.
Five deep breaths can be taken to stabilize the pressure.
Measurement procedure in the elderly and pregnant
In elderly people, blood pressure instability is more often observed due to changes in blood vessels. Measurements are carried out three times and take the arithmetic mean value. In addition, in older people, a change in posture can affect pressure, so indicators are taken while standing and sitting.
By blood pressure, you can judge the course of pregnancy. When measuring pressure, a woman in position should recline.