Positive end-expiratory pressure (peep). Where does hypertension come from? Check the kidneys and treat snoring Modern research on the Casimir effect

LAB #2

Topic: "BLOOD PRESSURE MEASUREMENT"

TARGET. To study the biophysical mechanism of creating blood pressure, as well as the biophysical properties of blood vessels. Learn the theoretical foundations of the method of indirect measurement of blood pressure. Master the method of N.S. Korotkov for measuring blood pressure.

INSTRUMENTS AND ACCESSORIES. Sphygmomanometer,

phonendoscope.

TOPIC STUDY PLAN

1. Pressure (definition, units of its measurement).

2. Bernoulli's equation, its use in relation to the movement of blood.

3. Basic biophysical properties of blood vessels.

4. Change in blood pressure along the vascular bed.

5. Hydraulic resistance of vessels.

6. Method for determining blood pressure according to the Korotkov method.

BRIEF THEORY

Pressure P is a value numerically equal to the ratio of the force F acting perpendicular to the surface to the area S of this surface:

P S F

The SI unit of pressure is pascal (Pa), non-systemic units: millimeter of mercury (1 mm Hg = 133 Pa), centimeter of water column, atmosphere, bar, etc.

The action of blood on the walls of the vessel (the ratio of the force acting perpendicular to the unit area of ​​the vessel) is called arterial pressure. There are two main cycles in the work of the heart: systole (contraction of the heart muscle) and diastole (its relaxation), therefore, systolic and diastolic pressures are noted.

When the heart muscle contracts, a volume of blood equal to 6570 ml, called the stroke volume, is pushed into the aorta, already filled with blood under the appropriate pressure. The additional volume of blood entering the aorta acts on the walls of the vessel, creating systolic pressure.

The wave of increased pressure is transmitted to the periphery of the vascular walls of the arteries and arterioles in the form of an elastic wave. This pressure wave

called a pulse wave. The speed of its propagation depends on the elasticity of the vascular walls and is equal to 6-8 m/s.

The amount of blood flowing through the cross section of a section of the vascular system per unit time is called the volumetric blood flow rate (l/min).

This value depends on the pressure difference at the beginning and end of the section and its resistance to blood flow.

The hydraulic resistance of the vessels is determined by the formula

R 8 , r 4

where is the viscosity of the liquid; is the length of the vessel;

r is the radius of the vessel.

If the cross-sectional area changes in the vessel, then the total hydraulic resistance is found by analogy with the series connection of resistors:

R=R1 +R2 +…Rn ,

where Rn is the hydraulic resistance of a section of the vessel with radius r and length.

If the vessel branches into n vessels with hydraulic resistance Rn, then the total resistance is found by analogy with the parallel connection of resistors:

The resistance R of the branched vascular system will be less than the smallest of the vascular resistances.

On fig. 1 shows a graph of changes in blood pressure in the main sections of the vascular system of the systemic circulation.

Rice. 1. where P0 is atmospheric pressure.

Pressure above atmospheric pressure is considered positive. Pressure less than atmospheric pressure is negative.

According to the chart in Fig. 1, we can conclude that the maximum pressure drop is observed in the arterioles, and in the vein, the pressure is negative.

Measurement of blood pressure plays an important role in the diagnosis of many diseases. Systolic and diastolic arterial pressure can be measured directly with a needle connected to a pressure gauge (direct or blood method). However, in medicine, the indirect (bloodless) method proposed by N.S. Korotkov. It consists of the following.

An air-fillable cuff is placed around the arm between the shoulder and the elbow. Initially, the excess air pressure in the cuff above atmospheric pressure is 0, the cuff does not compress the soft tissues and the artery. As air is pumped into the cuff, the latter compresses the brachial artery and stops blood flow.

The air pressure inside the cuff, consisting of elastic walls, is approximately equal to the pressure in the soft tissues and arteries. This is the basic physical idea of ​​the bloodless pressure measurement method. Releasing air, reduce the pressure in the cuff and soft tissues.

When the pressure becomes equal to systolic, the blood will be able to break through a very small section of the artery at high speed - while the flow will be turbulent.

The characteristic tones and noises that accompany this process are listened to by the doctor. At the time of listening to the first tones, pressure (systolic) is recorded. By continuing to reduce the pressure in the cuff, laminar blood flow can be restored. Noises stop, at the moment of their termination, diastolic pressure is recorded. To measure blood pressure, a device is used - a sphygmomanometer, consisting of a pear, cuff, manometer and phonendoscope.

QUESTIONS FOR SELF-CHECKING

1. What is called pressure?

2. In what units is pressure measured?

3. What pressure is considered positive, what is negative?

4. Formulate Bernoulli's rule.

5. Under what conditions is a laminar fluid flow observed?

6. What is the difference between turbulent flow and laminar flow? Under what conditions is turbulent fluid flow observed?

7. Write down the formula for the hydraulic resistance of vessels.

9. What is systolic blood pressure? What is it equal to in a healthy person at rest?

10. What is called diastolic blood pressure? What does it equal in vessels?

11. What is a pulse wave?

12. In which part of the cardiovascular system does the greatest pressure drop occur? What is it due to?

13. What is the pressure in the venous vessels, large veins?

14. What device is used to measure blood pressure?

15. What are the components of this device?

16. What causes the appearance of sounds when determining blood pressure?

17. At what point in time does the reading of the device correspond to systolic blood pressure? At what point is the diastolic blood pressure?

WORK PLAN

Subsequence			How to complete the task.
action
1. Check			The created pressure should not change within 3
tightness.
	Define		1. Take measurements 3 times, enter the readings in
systolic			table (see below).
diastolic	pressure		2. Apply a cuff to the bare shoulder, find
right and left hands			on the elbow bend a pulsating artery and
method N.S. Korotkov			set over it (without pressing hard)
			phonendoscope. Pressurize the cuff and then
			by slightly opening the screw valve, air is released, which
			leads to a gradual decrease in cuff pressure.
			At a certain pressure, the first weak sounds are heard
			short tones. At this moment fixed
			systolic blood pressure. With further
			as the cuff pressure decreases, the tones become louder,
			finally, abruptly muffled or disappear. Pressure
			air in the cuff at this moment is taken as
			diastolic.
			3. Time during which the measurement is made
			pressure according to N.S. Korotkov, should not last more than 1
	Definition		1. Do 10 squats.

systolic							2. Take a blood pressure measurement on your left arm.
diastolic			pressure				3. Record the readings in the table.
blood according to the Korotkov method
after exercise.
			Definition				Repeat measurements after 1, 2 and 3 minutes. after
systolic						physical activity.
diastolic			pressure				1. Take a blood pressure measurement on your left arm.
blood at rest.							2. Record the readings in the table.
	Norm (mm Hg)							After load		After rest
	Sist. pressure				diast. pressure
			Decor				1. Compare your results with normal
laboratory work.						blood pressure.
							2. Make a conclusion about the state of the cardiovascular

Analogy

A phenomenon similar to the Casimir effect was observed back in the 18th century by French sailors. When two ships, swaying from side to side in conditions of strong seas, but light winds, were at a distance of about 40 meters or less, as a result of wave interference in the space between the ships, the waves stopped. The calm sea between the ships created less pressure than the waves from the outer sides of the ships. As a result, a force arose that sought to push the ships sideways. As a countermeasure, the shipping manual of the early 1800s recommended that both ships send a lifeboat with 10-20 sailors to push the ships apart. Due to this effect (among others), garbage islands are formed in the ocean today.

Discovery history

Hendrik Casimir worked for Philips Research Laboratories in the Netherlands, studying colloidal solutions - viscous substances that have micron-sized particles in their composition. One of his colleagues, Theo Overbeck ( Theo Overbeek), found that the behavior of colloidal solutions did not quite agree with the existing theory, and asked Casimir to investigate this problem. Casimir soon came to the conclusion that deviations from the behavior predicted by the theory could be explained by taking into account the influence of vacuum fluctuations on intermolecular interactions. This led him to the question of what effect vacuum fluctuations can have on two parallel mirror surfaces, and led to the famous prediction about the existence of an attractive force between the latter.

Experimental discovery

Modern research on the Casimir effect

• Casimir effect for dielectrics
• Casimir effect at non-zero temperature
• connection of the Casimir effect and other effects or sections of physics (connection with geometric optics, decoherence, polymer physics)
• dynamic Casimir effect
• taking into account the Casimir effect in the development of highly sensitive MEMS devices.

Application

By 2018, a Russian-German group of physicists (V. M. Mostepanenko, G. L. Klimchitskaya, V. M. Petrov and a group led by Theo Tschudi from Darmstadt) developed a theoretical and experimental scheme for a miniature quantum optical interrupter for laser beams based on the Casimir effect, in which the Casimir force is balanced by light pressure.

In culture

The Casimir effect is described in some detail in Arthur Clarke's science fiction book The Light of Other Days, where it is used to create two paired wormholes in space-time, and transmit information through them.

Notes

1. Barash Yu. S., Ginzburg V. L. Electromagnetic fluctuations in matter and molecular (van der Waals) forces between bodies // UFN, vol. 116, p. 5-40 (1975)
2. Casimir H.B.G. On the attraction between two perfectly conducting plates (English) // Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen: journal. - 1948. - Vol. 51 . - P. 793-795.
3. Sparnaay, M.J. Attractive Forces between Flat Plates // Nature. - 1957. - Vol. 180, no. 4581 . - P. 334-335. - DOI:10.1038/180334b0. - Bibcode : 1957Natur.180..334S.
4. Sparnaay, M. Measurements of attractive forces between flat plates (English) // Physica: journal. - 1958. - Vol. 24, no. 6-10 . - P. 751-764. -

Positive end expiratory pressure (PEEP, PEEP) and continuous positive airway pressure (CPAP, CPAP).
The methods of PEEP (PEEP) and CPAP (CPAP) have long and firmly entered the practice of mechanical ventilation. Without them, it is impossible to imagine effective respiratory support in seriously ill patients (13, 15, 54, 109, 151).

Most doctors, without even thinking, automatically turn on the PEEP regulator on the breathing apparatus from the very beginning of mechanical ventilation. However, we must remember that PEEP is not only a powerful weapon of a doctor in the fight against severe pulmonary pathology. Thoughtless, chaotic, on the "eye" application (or abrupt cancellation) of PEEP can lead to serious complications and worsening of the patient's condition. A specialist conducting mechanical ventilation is simply obliged to know the essence of PEEP, its positive and negative effects, indications and contraindications for its use. According to modern international terminology, English abbreviations are generally accepted: for PEEP - PEEP (positive end-expiratory pressure), for CPAP - CPAP (continuous positive airway pressure). The essence of PEEP is that at the end of expiration (after a forced or assisted breath), the airway pressure does not decrease to zero, but
remains above atmospheric by a certain amount set by the doctor.
PEEP is achieved by electronically controlled expiratory valve mechanisms. Without interfering with the beginning of exhalation, at a certain stage of exhalation, these mechanisms subsequently close the valve to a certain extent and thereby create additional pressure at the end of exhalation. It is important that the PEEP valve mechanism does not create.1 additional expiratory resistance in the main phase of expiration, otherwise Pmean increases with corresponding undesirable effects.
The CPAP function is primarily designed to maintain a constant positive airway pressure during spontaneous patient breathing from the circuit. The CPAP mechanism is more complex and is provided not only by closing the expiratory valve, but also by automatically adjusting the level of a constant flow of the respiratory mixture in the respiratory circuit. During exhalation, this flow is very small (equal to the base expiratory flow), the CPAP value is equal to PEEP and is maintained mainly by the expiratory valve. On the other hand, to maintain a given level of a certain positive pressure during spontaneous inspiration (especially at the beginning). the device delivers a sufficiently powerful inspiratory flow to the circuit, corresponding to the inspiratory needs of the patient. Modern fans automatically regulate the flow level, maintaining the set CPAP - the principle of "flow on demand" ("Demand Flow"). With spontaneous attempts to inhale the patient, the pressure in the circuit decreases moderately, but remains positive due to the supply of inspiratory flow from the apparatus. During exhalation, the airway pressure initially rises moderately (after all, it is necessary to overcome the resistance of the breathing circuit and the expiratory valve), then it becomes equal to PEEP. Therefore, the pressure curve for CPAP is sinusoidal. A significant increase in airway pressure does not occur in any phase of the respiratory cycle, since the expiratory valve remains at least partially open during inhalation and exhalation.

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