To determine the activity of the heart, vascular system and kidneys, it is necessary to measure blood pressure. The algorithm of action for its determination must be observed in order to obtain the most accurate figures.
It is known from medical practice that the timely determination of pressure helped a large number of patients not become disabled and saved the lives of many people.
History of measuring devices
For the first time, pressure was measured in animals by Hales in 1728. To do this, he inserted a glass tube directly into the horse’s artery. After this, Poiseuille added a manometer with a mercury scale to the glass tube, and subsequently Ludwig invented a kimograph with a float, which made it possible to continuously record blood pressure. These devices are equipped with sensors of mechanical stress and electronic systems. Direct methods for measuring blood pressure by catheterization of blood vessels are used for scientific purposes in diagnostic laboratories.
How is blood pressure formed?
The rhythmic contractions of the heart include two phases: systole and diastole. The first phase, systole, is a contraction of the heart muscle, during which the heart pushes blood into the aorta and pulmonary artery. Diastole is the period during which the cavity of the heart expands and fills with blood. Then again systole occurs and subsequent diastole. Blood from the largest vessels: the aorta and pulmonary artery, passes the path to the smallest - arterioles and capillaries, enriching all organs and tissues with oxygen and collecting carbon dioxide. Capillaries pass into venules, then into small veins and into larger vessels, and finally into veins that fit the heart.
Pressure in the vessels and heart
With the release of blood from the cavities of the heart, the pressure is 140-150 mm RT. Art. In the aorta, it decreases to 130-140 mm RT. Art. And the farther from the heart, the lower the pressure becomes: in the venules it is 10-20 mmHg. Art., and blood in large veins is lower than atmospheric.
When blood pours out of the heart, a pulse wave is recorded, which gradually fades away as it passes through all the vessels. The speed of its distribution depends on the value of blood pressure and the elasticity or elasticity of the vascular walls.
With age, blood pressure rises. In people from 16 to 50 years old, it is 110-130 mm RT. Art., and after 60 years - 140 mm RT. Art. and higher.
Methods for measuring blood pressure
There are direct (invasive) and indirect methods. In the first method, a catheter with a transducer is inserted into the vessel and blood pressure is measured. The action algorithm of this study is such that, using a computer, the process of signal control is automated.
Indirect method
The technique of measuring blood pressure in an indirect way is possible by several methods: palpation, auscultatory and oscillometric. The first method involves the gradual compression and relaxation of the limb in the arterial region and the digital determination of its pulse below the compression site. Rivva-Rocci at the end of the 19th century proposed the use of a 4-5 cm cuff and a mercury gauge scale. However, such a narrow cuff overestimated the true data, so it was proposed to increase it to 12 cm in width. And now the technique of measuring blood pressure involves the use of this particular cuff.
The pressure in it is pumped to the extent that the pulse stops, and then slowly decreases. Systolic pressure is the moment when the pulsation appears, diastolic pressure - when the pulse dies out or noticeably accelerates.
In 1905, N.S. Korotkov proposed a method for measuring blood pressure through auscultation. A typical device for measuring blood pressure by the Korotkov method is a tonometer. It consists of a cuff, a mercury scale. The air in the cuff is pumped with a pear, and then gradually released air through a special valve.
This auscultatory method has been the standard for measuring blood pressure for more than 50 years, but, according to examinations, doctors rarely follow the recommendations, and the technique for measuring blood pressure is impaired.
The oscillometric method is used in automatic and semi-automatic devices in intensive care units, since the use of these devices does not require constant injection of air into the cuff. Blood pressure is recorded at various stages of air volume reduction. Measurement of blood pressure is possible with auscultatory failures and weak tones of Korotkov. This method is the least dependent on the elasticity of the walls of the vessels and in cases of atherosclerosis. The oscillometric method made it possible to create devices for determining the upper and lower extremities on various arteries. It allows you to make the process more accurate, reducing the impact of the human factor.
Rules for measuring blood pressure
Step 1 - choose the right equipment.
What you need:
1. Quality stethoscope
2. The correct cuff size.
3. An aneroid barometer or an automated sphygmomanometer - a device with a manual boost mode.
Step 2 - prepare the patient: make sure that he is relaxed, give him 5 minutes of rest. For half an hour to determine blood pressure, smoking and drinking alcohol and caffeinated drinks is not recommended. The patient should sit upright, release the upper part of the arm, position it conveniently for the patient (can be placed on a table or other support), the feet should be on the floor. Remove excess clothing that could interfere with airflow into the cuff or blood flow to the arm. You and the patient should refrain from talking during the measurement. If the patient is in a supine position, it is necessary to position the upper part of the arm at heart level.
Step 3 - choose the correct cuff size depending on the arm volume: often errors arise due to improper selection of the cuff. Put the cuff on the patient’s arm.
Step 4 - place the phonendoscope on the same hand where you placed the cuff, feel your hand on the elbow, to find the place of the strongest pulsed sounds, and place the stethoscope over the brachial artery in this place.
Step 5 - inflate the cuff: start pumping up while listening to the pulse. When the pulse waves disappear, you should not hear any sounds through the phonendoscope. If no pulse is heard, then inflate so that the pressure gauge needle is higher than 20 to 40 mmHg on the numbers. Art. than with the expected pressure. If this value is unknown, inflate the cuff to 160 - 180 mmHg. Art.
Step 6 - slowly deflate the cuff: deflation begins. Cardiologists recommend slowly opening the valve so that the pressure in the cuff is reduced by 2 - 3 mm RT. Art. per second, otherwise a faster decrease may lead to inaccurate measurements.
Step 7 - listening to systolic pressure - the first sounds of the pulse. This blood begins to flow through the patient's arteries.
Step 8 - listen to the pulse. Over time, when the pressure in the cuff decreases, the sounds disappear. This will be diastolic, or lower pressure.
Verification of indicators
It is necessary to check the accuracy of the indicators. To do this, measure the pressure on both hands to average the data. To check the pressure again for accuracy, wait about five minutes between measurements. Typically, blood pressure is higher in the morning and lower in the evening. Sometimes the blood pressure figures are unreliable due to the patient's concern about people in white coats. In this case, use the daily measurement of blood pressure. The algorithm of action in this case is the determination of pressure during the day.
Disadvantages of the method
Currently, the blood pressure measurement is performed by an auscultatory method in any hospital or clinic. The action algorithm has disadvantages:
• lower numbers of SBP and higher numbers of DBP than those obtained with an invasive technique;
• susceptibility to noise in the room, various disturbances during movement;
• the need for the correct location of the stethoscope;
• poor listening tones of low intensity;
• determination error - 7-10 units.
This technique for measuring blood pressure is not suitable for a monitoring procedure during the day. To monitor the patient's condition in intensive care units, it is impossible to constantly inflate the cuff and create noise. This can adversely affect the general condition of the patient and cause him concern. Pressure figures will be unreliable. With the patient's unconscious state and increased motor activity, his hand cannot be laid at the level of the heart. An uncontrolled action of the patient can also create an intense interference signal, so the computer will fail, which will negate the measurement of blood pressure and heart rate.
Therefore, in resuscitation chambers, cuffless methods are used, which, although inferior in accuracy, are more reliable, efficient and convenient for constant monitoring of pressure.
How to measure blood pressure in pediatrics?
The measurement of blood pressure in children does not differ from the technique for determining it in adults. Only an adult cuff will not work. In this case, a cuff is required, the width of which should be three quarters of the distance from the elbow bend to the axillary fossa. Currently, there is a large selection of automatic and semi-automatic devices for measuring blood pressure in children.
Numbers of normal pressure depend on age. To calculate the numbers of systolic pressure, you need to multiply the figure of the child's age in years by 2 and increase by 80, the diastolic is 1/2 - 2/3 of the previous figure.
Blood Pressure Meters
Blood pressure meters are also called tonometers. There are mechanical and digital blood pressure monitors. Mechanical are mercury and aneroid. Digital - automatic and semi-automatic. The most accurate and long-term device is a mercury tonometer, or a sphygmomanometer. But digital ones are more convenient and easy to operate, which allows them to be used at home.