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How to calculate minute breathing volume. Minute breathing volume

One of the main methods for assessing the ventilation function of the lungs used in the practice of medical labor examination is spirography, which allows you to determine statistical pulmonary volumes - vital capacity of the lungs (VC), functional residual capacity (FRC), residual lung volume, total lung capacity, dynamic pulmonary volumes - tidal volume, minute volume, maximum ventilation.

The ability to fully maintain the gas composition of arterial blood does not yet guarantee the absence of pulmonary failure in patients with bronchopulmonary pathology. Blood arterialization can be maintained at a level close to normal due to compensatory overstrain of the mechanisms that provide it, which is also a sign of pulmonary failure. Such mechanisms include, first of all, the function ventilation.

The adequacy of volumetric ventilation parameters is determined by “ dynamic lung volumes", which include tidal volume And minute volume of respiration (MOV).

Tidal volume at rest in a healthy person it is about 0.5 liters. Due MAUD obtained by multiplying the required basal metabolic rate by a factor of 4.73. The values obtained in this way lie in the range of 6-9 l. However, comparison of the actual value MAUD(determined under the conditions of basal metabolism or close to it) with due meaning only for a summary assessment of changes in value, which may include both changes in ventilation itself and disturbances in oxygen consumption.

To assess the actual ventilation deviations from the norm, it is necessary to take into account Oxygen utilization factor (KIO 2)- ratio of absorbed O 2 (in ml/min) to MAUD(in l/min).

Based on oxygen utilization factor the effectiveness of ventilation can be judged. In healthy people, the CI is on average 40.

At KIO 2 below 35 ml/l ventilation is excessive in relation to the oxygen consumed ( hyperventilation), with increasing KIO 2 above 45 ml/l we are talking about hypoventilation.

Another way of expressing the gas exchange efficiency of pulmonary ventilation is by defining respiratory equivalent, i.e. the volume of ventilated air per 100 ml of oxygen consumed: determine the ratio MAUD to the amount of oxygen consumed (or carbon dioxide - DE carbon dioxide).

In a healthy person, 100 ml of oxygen consumed or carbon dioxide released is provided by a volume of ventilated air close to 3 l/min.

In patients with lung pathology and functional disorders, gas exchange efficiency is reduced, and the consumption of 100 ml of oxygen requires a greater volume of ventilation than in healthy people.

When assessing the effectiveness of ventilation, an increase breathing rate(RR) is considered as a typical sign of respiratory failure, it is advisable to take this into account during a labor examination: with the I degree of respiratory failure, the RR does not exceed 24, with the II degree it reaches 28, with the III degree the RR is very large.

Medical rehabilitation / Ed. V. M. Bogolyubova. Book I. - M., 2010. pp. 39-40.

Ventilator! If you understand it, it is equivalent to the appearance, as in the films, of a superhero (doctor) super weapons(if the doctor understands the intricacies of mechanical ventilation) against the death of the patient.

To understand mechanical ventilation you need basic knowledge: physiology = pathophysiology (obstruction or restriction) of breathing; main parts, structure of the ventilator; provision of gases (oxygen, atmospheric air, compressed gas) and dosing of gases; adsorbers; elimination of gases; breathing valves; breathing hoses; breathing bag; humidification system; breathing circuit (semi-closed, closed, semi-open, open), etc.

All ventilators provide ventilation by volume or pressure (no matter what they are called; depending on what mode the doctor has set). Basically, the doctor sets the mechanical ventilation mode for obstructive pulmonary diseases (or during anesthesia) by volume, during restriction by pressure.

The main types of ventilation are designated as follows:

CMV (Continuous mandatory ventilation) - Controlled (artificial) ventilation

VCV (Volume controlled ventilation) - volume controlled ventilation

PCV (Pressure controlled ventilation) - pressure controlled ventilation

IPPV (Intermittent positive pressure ventilation) - mechanical ventilation with intermittent positive pressure during inspiration

ZEEP (Zero endexpiratory pressure) - ventilation with pressure at the end of expiration equal to atmospheric

PEEP (Positive endexpiratory pressure) - Positive end expiratory pressure (PEEP)

CPPV (Continuous positive pressure ventilation) - ventilation with PDKV

IRV (Inversed ratio ventilation) - mechanical ventilation with a reverse (inverted) inhalation:exhalation ratio (from 2:1 to 4:1)

SIMV (Synchronized intermittent mandatory ventilation) - Synchronized intermittent mandatory ventilation = A combination of spontaneous and mechanical breathing, when, when the frequency of spontaneous breathing decreases to a certain value, with continued attempts to inhale, overcoming the level of the established trigger, mechanical breathing is synchronously activated

You should always look at the letters ..P.. or ..V.. If P (Pressure) means by distance, if V (Volume) by volume.

Vt – tidal volume,
f – respiratory rate, MV – minute ventilation
PEEP – PEEP = positive end expiratory pressure
Tinsp – inspiratory time;
Pmax - inspiratory pressure or maximum airway pressure.
Gas flow of oxygen and air.

Tidal volume(Vt, DO) set from 5 ml to 10 ml/kg (depending on the pathology, normal 7-8 ml per kg) = how much volume the patient should inhale at a time. But to do this, you need to find out the ideal (proper, predicted) body weight of a given patient using the formula (NB! remember):

Men: BMI (kg)=50+0.91 (height, cm – 152.4)

Women: BMI (kg)=45.5+0.91·(height, cm – 152.4).

Example: a man weighs 150 kg. This does not mean that we should set the tidal volume to 150kg·10ml= 1500 ml. First, we calculate BMI=50+0.91·(165cm-152.4)=50+0.91·12.6=50+11.466= 61,466 kg our patient should weigh. Imagine, oh allai deseishi! For a man with a weight of 150 kg and a height of 165 cm, we must set the tidal volume (TI) from 5 ml/kg (61.466·5=307.33 ml) to 10 ml/kg (61.466·10=614.66 ml) depending on pathology and extensibility of the lungs.

2. The second parameter that the doctor must set is respiration rate(f). The normal respiratory rate is 12 to 18 per minute at rest. And we don't know what frequency to set: 12 or 15, 18 or 13? To do this we must calculate due MOD (MV). Synonyms for minute breathing volume (MVR) = minute ventilation (MVL), maybe something else... This means how much air the patient needs (ml, l) per minute.

MOD=BMI kg:10+1

according to the Darbinyan formula (outdated formula, often leads to hyperventilation).

Or modern calculation: MOD=BMIkg·100.

(100%, or 120%-150% depending on the patient’s body temperature..., from the basal metabolism in short).

Example: The patient is a woman, weighs 82 kg, height is 176 cm. BMI = 45.5 + 0.91 (height, cm - 152.4) = 45.5 + 0.91 (176 cm - 152.4) = 45.5+0.91 23.6=45.5+21.476= 66,976 kg should weigh. MOD = 67 (rounded up immediately) 100 = 6700 ml or 6,7 liters per minute. Now only after these calculations can we find out the breathing frequency. f=MOD:UP TO=6700 ml: 536 ml=12.5 times per minute, which means 12 or 13 once.

3. Install REER. Normally (previously) 3-5 mbar. Now you can 8-10 mbar in patients with normal lungs.

4. The inhalation time in seconds is determined by the ratio of inhalation to exhalation: I: E=1:1,5-2 . In this parameter, knowledge about the respiratory cycle, ventilation-perfusion ratio, etc. will be useful.

5. Pmax, Pinsp peak pressure is set so as not to cause barotrauma or rupture the lungs. Normally, I think 16-25 mbar, depending on the elasticity of the lungs, the weight of the patient, the extensibility of the chest, etc. In my knowledge, lungs can rupture when Pinsp is more than 35-45 mbar.

6. The fraction of inhaled oxygen (FiO 2) should be no more than 55% in the inhaled respiratory mixture.

All calculations and knowledge are needed so that the patient has the following indicators: PaO 2 = 80-100 mm Hg; PaCO 2 =35-40 mm Hg. Just, oh allai deseishi!

Ventilation- This is the exchange of gases between the alveolar air and the lungs. A quantitative characteristic of pulmonary ventilation is the minute volume of respiration (MVR) - the volume of air passing through the lungs in 1 minute. You can determine the MOD if you know the frequency of respiratory movements (at rest in an adult it is 16-20 per 1 minute) and tidal volume (DO = 350 - 800 ml).

MOD=RR´DO = 5000 -16000 ml/min

However, not all of the ventilated air participates in pulmonary gas exchange, but only that part of it that reaches the alveoli. The fact is that approximately 1/3 of the tidal volume at rest falls on the ventilation of the so-called anatomical dead space (MF), filled with air, which does not directly participate in gas exchange and only moves in the lumen of the airways during inhalation and exhalation. But sometimes some of the alveoli do not function or function partially due to the absence or reduction of blood flow in the nearby capillaries. From a functional point of view, these alveoli also represent dead space. When the alveolar dead space is included in the general dead space, the latter is called not anatomical, but physiological dead space. In a healthy person, the anatomical and physiological spaces are almost equal, but if part of the alveoli does not function or functions only partially, the volume of physiological dead space may be several times greater than the anatomical one.

Therefore, ventilation of the alveolar spaces is alveolar ventilation (AV) - represents pulmonary ventilation minus dead space ventilation.

AB= BH´(DO –MP)

The intensity of alveolar ventilation depends on the depth of breathing: the deeper the breathing (more DO), the more intense the ventilation of the alveoli.

Maximum ventilation (MVL)- the volume of air that passes through the lungs in 1 minute during the maximum frequency and depth of respiratory movements. Maximum ventilation occurs during intense work, with a lack of O 2 (hypoxia) and an excess of CO 2 (hypercapnia) in the inhaled air. Under these conditions, MOR can reach 150 - 200 liters per minute.

The indicators listed above are dynamic and reflect the efficiency of the respiratory system in time (usually within 1 minute).

In addition to dynamic indicators, external respiration is assessed by static indicators (Fig. 7):

§ tidal volume (TO) - this is the volume of air inhaled and exhaled during quiet breathing (in an adult it is 350 - 800 ml);

§ inspiratory reserve volume (IRV)– an additional volume of air that can be inhaled beyond a quiet inhalation during forced breathing (PO vd on average 1500-2500 ml);

§ expiratory reserve volume (ERV)– the maximum additional volume of air that can be exhaled after a quiet exhalation (PO exhalation on average 1000-1500 ml);

§ residual lung volume (00) - volume of air that remains in the lungs after maximum exhalation (OO = 1000 -1500 ml)

Fig.7. Spirogram for quiet and forced breathing

When the lungs collapse (pneumothorax), most of the residual air escapes ( collapse residual volume = 800-1000 ml), and remains in the lungs minimum residual volume(200-400 ml). This air is retained in so-called air traps, since part of the bronchioles collapses before the alveoli (the terminal and respiratory bronchioles do not contain cartilage). This knowledge is used in forensic medicine to test whether a child was born alive: the lung of a stillborn drowns in water because it contains no air.

The sums of lung volumes are called lung capacities.

The following lung capacities are distinguished:

1. total lung capacity (TLC)- the volume of air in the lungs after maximum inspiration - includes all four volumes

2. vital capacity of the lungs (VC) includes tidal volume, inspiratory reserve volume, expiratory reserve volume. Vital capacity is the volume of air exhaled from the lungs after maximum inhalation with maximum exhalation.

Vital = DO + ROvd + ROvyd

Vital vital capacity is 3.5 - 5.0 l in men, 3.0-4.0 l in women. The value of vital capacity depends on height, age, gender, and the degree of functional training.

With age, this figure decreases (especially after 40 years). This is due to a decrease in the elasticity of the lungs and the mobility of the chest. Women have vital capacity on average 25% less than men. Vital vital capacity depends on height, since the size of the chest is proportional to other body dimensions. Vital capacity depends on the degree of training: Vital capacity is especially high (up to 8 l) in swimmers and rowers, since these athletes have well-developed auxiliary muscles (pectoralis major and minor).

3. inspiratory capacity (Evd) equal to the sum of tidal volume and inspiratory reserve volume, averages 2.0 - 2.5 l;

4. functional residual capacity (FRC)- volume of air in the lungs after a quiet exhalation. During quiet inhalation and exhalation, the lungs constantly contain approximately 2500 ml of air, filling the alveoli and lower respiratory tract. Thanks to this, the gas composition of the alveolar air is maintained at a constant level.

In a routine study, TLC, OO and FRC are not available for measurement. They are determined using gas analyzers, studying changes in the composition of gas mixtures in a closed loop (helium, nitrogen content).

To assess the ventilation function of the lungs, the condition of the respiratory tract, and study the breathing pattern (pattern), various research methods are used: pneumography, spirometry, spirography.

Spirography (Latin spiro breathe + Greek graphо write, depict)- a method of graphically recording changes in lung volumes during natural respiratory movements and volitional forced respiratory maneuvers.

Spirography allows you to obtain a number of indicators that describe lung ventilation.

In technical terms, all spirographs are divided into open and closed type devices (Fig. 8).

Rice. 8. Schematic representation of a spirograph

In open-type devices, the patient inhales atmospheric air through a valve box, and the exhaled air enters a Douglas bag or a Tiso spirometer (capacity 100-200 l), sometimes to a gas meter, which continuously determines its volume. The air collected in this way is analyzed: the values of oxygen absorption and carbon dioxide release per unit of time are determined. Closed-type devices use the air from the bell of the device, circulating in a closed circuit without communication with the atmosphere. Exhaled carbon dioxide is absorbed by a special absorber.

Modern devices that record changes in lung volume during breathing (both open and closed types) have electronic computing devices for automatic processing of measurement results.

When analyzing a spirogram, speed indicators are also determined. Calculation of speed indicators is of great importance in identifying signs of bronchial obstruction.

§ Forced expiratory volume in 1 s(FEV1) - the volume of air expelled with maximum effort from the lungs during the first second of exhalation after a deep inhalation, i.e. part of the FVC exhaled in the first second. FEV1 primarily reflects the condition of the large airways and is often expressed as a percentage of VC (normal FEV1 = 75% VC).

§ Tiffno index – FEV1/FVC ratio, expressed in %:

IT= FEV1´ 100%

FVC

It is determined in the respiratory “push” test (Tiffno test) and consists of studying a single forced exhalation, allowing important diagnostic conclusions to be made about the functional state of the respiratory apparatus. At the end of exhalation, the intensity of the respiratory flow is limited due to compression of the small airways (Fig. 8).

Rice. 9. Schematic representation of the spirogram and its indicators

Forced expiratory volume in the first second (FEV1) is normally at least 70-75%. A decrease in the Tiffno index and FEV1 is a characteristic sign of diseases that are accompanied by a decrease in bronchial patency - bronchial asthma, chronic obstructive pulmonary disease, bronchiectasis, etc.

From the spirogram you can determine oxygen volume, consumed by the body. If there is an oxygen compensation system in the spirograph, this indicator is determined by the slope of the curve of oxygen entering it; in the absence of such a system, by the slope of the spirogram of quiet breathing. Dividing this volume by the number of minutes during which oxygen consumption was recorded gives the value VО 2(is 200-400 ml at rest).

All indicators of pulmonary ventilation are variable. They depend on gender, age, weight, height, body position, the state of the patient’s nervous system and other factors. Therefore, for a correct assessment of the functional state of pulmonary ventilation, the absolute value of one or another indicator is insufficient. It is necessary to compare the obtained absolute indicators with the corresponding values in a healthy person of the same age, height, weight and gender - the so-called proper indicators.

for men JEL = 5.2xP - 0.029xB - 3.2

for women JEL = 4.9xP - 0.019xB - 3.76

for girls from 4 to 17 years old with height from 1.0 to 1.75 m:

JEL = 3.75xP - 3.15

for boys of the same age with a height of up to 1.65 m:

JEL = 4.53xP - 3.9, and with the growth of St. 1.65 m - JEL = 10xP - 12.85

where P is height (m), B is age

This comparison is expressed as a percentage relative to the proper indicator. Deviations exceeding 15-20% of the expected value are considered pathological.

Security questions

1. What is pulmonary ventilation, what indicator characterizes it?

2. What is anatomical and physiological dead space?

3. How to determine alveolar ventilation?

4. What is MVL?

5. What static indicators are used to assess external respiration?

6. What types of lung capacities are there?

7. On what factors does the value of vital capacity depend?

8. For what purpose is spirography used?

10. What are proper indicators, how are they determined?

Total quantity new air entering the airways every minute is called the minute volume of respiration. It is equal to the product of tidal volume and respiratory rate per minute. At rest, the tidal volume is about 500 ml and the respiratory rate is about 12 times per minute, therefore, the minute volume of breathing averages about 6 l/min. A person can live for a short period of time with a minute breathing volume of about 1.5 l/min and a respiratory rate of 2-4 times per minute.

Sometimes breathing rate can increase to 40-50 times per minute, and the tidal volume in a young adult male can reach approximately 4600 ml. The minute volume may be more than 200 l/min, i.e. 30 times or more than at rest. Most people are not able to maintain these indicators even at the level of 1/2-2/3 of the given values for more than 1 minute.

Home the task of pulmonary ventilation is the constant renewal of air in the gas exchange zones of the lungs, where the air is located close to the pulmonary capillaries filled with blood. These areas include the alveoli, alveolar sacs, alveolar ducts and bronchioles. The amount of new air reaching these zones per minute is called alveolar ventilation.

A certain amount air inhaled by humans does not reach the gas exchange zones, but simply fills the respiratory tract - the nose, nasopharynx and trachea, where there is no gas exchange. This volume of air is called dead space air, because. it does not participate in gas exchange.

When you exhale, the air fills the dead space, is exhaled first - before air from the alveoli returns to the atmosphere, so dead space is an additional element when removing exhaled air from the lungs.

Dead space volume measurement. The figure shows a simple way to measure dead space volume. The subject takes a sharp, deep breath of pure oxygen, filling all the dead space with it. Oxygen mixes with alveolar air, but does not replace it completely. After this, the subject exhales through a nitrometer with a quick recording (the resulting recording is shown in the figure).

The first portion of exhaled air consists of air that was in the dead space of the respiratory tract, where it was completely replaced by oxygen, so in the first part of the recording there is only oxygen and the nitrogen concentration is zero. When alveolar air begins to reach the nitrometer, the nitrogen concentration increases sharply, because alveolar air containing a large amount of nitrogen begins to mix with air from the dead space.

With the release of more and more amount of exhaled air All the air that was in the dead space is washed out of the respiratory tract, and only alveolar air remains, so the nitrogen concentration on the right side of the record appears as a plateau at the level of its content in the alveolar air. The gray area in the figure represents air that does not contain nitrogen and is a measure of the volume of dead space air. For an accurate measurement, use the following equation: Vd = Gray area x Ve / Pink area + Gray area, where Vd is dead space air; Ve is the total volume of exhaled air.

For example: let the area gray area on the graph is 30 cm, the pink area is 70 cm, and the total exhaled volume is 500 ml. The dead space in this case is 30: (30 + 70) x 500 = 150 ml.

Normal dead space volume. The normal volume of air in the dead space in a young adult male is about 150 ml. With age, this figure increases slightly.

Anatomical dead space and physiological dead space. The previously described method of measuring dead space allows you to measure the entire volume of the respiratory system, except for the volume of the alveoli and the gas exchange zones located near them, which is called anatomical dead space. But sometimes some of the alveoli do not function or function partially due to the absence or reduction of blood flow in the nearby capillaries. From a functional point of view, these alveoli also represent dead space.

When turned on alveolar dead space into the general dead space, the latter is called not anatomical, but physiological dead space. In a healthy person, the anatomical and physiological spaces are almost equal, but if in a person in some parts of the lungs part of the alveoli does not function or functions only partially, the volume of physiological dead space may be 10 times greater than the anatomical one, i.e. 1-2 l. These issues will be discussed further in relation to gas exchange in the lungs and certain lung diseases.

Educational video - FVD (spirometry) indicators in health and disease

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Tidal volume and vital capacity are static characteristics measured during one respiratory cycle. But oxygen consumption and carbon dioxide formation occur continuously in the body.

Therefore, the constancy of the gas composition of arterial blood does not depend on the characteristics of one respiratory cycle, but on the rate of oxygen intake and carbon dioxide removal over a long period of time. A measure of this speed, to some extent, can be considered the minute volume of respiration (MVR), or pulmonary ventilation, i.e. the volume of air passing through the lungs in 1 minute. The minute volume of breathing with uniform automatic (without the participation of consciousness) breathing is equal to the product of the tidal volume by the number of respiratory cycles in 1 minute. At rest in a man, it is on average 8000 ml or 8 liters per minute)" (500 ml x 16 breaths per minute). It is believed that the minute volume of breathing provides information about ventilation of the lungs, but in no way determines the efficiency of breathing. With a tidal volume of 500 ml, during inhalation, the alveoli first receive 150 ml of air located in the respiratory tract, i.e., in the anatomical dead space, and which entered them at the end of the previous exhalation. This is already used air that entered the anatomical dead space from. alveoli. Thus, when you inhale 500 ml of “fresh” air from the atmosphere, 350 ml of inhaled “fresh” air enters the alveoli. The last 150 ml of inhaled “fresh” air fills the anatomical dead space and does not participate in gas exchange with the blood in 1 minute. with a tidal volume of 500 ml and 16 breaths in the first minute, not 8 liters of atmospheric air will pass through the alveoli, but 5.6 liters (350 x 16 = 5600), the so-called alveolar ventilation. When the tidal volume is reduced to 400 ml, in order to maintain the same value of the minute volume of breathing, the respiratory rate should increase to 20 breaths per 1 minute (8000: 400). In this case, alveolar ventilation will be 5000 ml (250 x 20) instead of 5600 ml, which are necessary to maintain a constant gas composition of arterial blood. To maintain arterial blood gas homeostasis, it is necessary to increase the respiratory rate to 22-23 breaths per minute (5600: 250-22.4). This implies an increase in minute respiratory volume to 8960 ml (400 x 22.4). With a tidal volume of 300 ml, to maintain alveolar ventilation and, accordingly, blood gas homeostasis, the respiratory rate should increase to 37 breaths per minute (5600: 150 = 37.3). In this case, the minute volume of breathing will be 11100 ml (300 x 37 = 11100), i.e. will increase almost 1.5 times. Thus, the minute volume of breathing in itself does not determine the effectiveness of breathing.
A person can take control of breathing upon himself and, at will, breathe with his stomach or chest, change the frequency and depth of breathing, the duration of inhalation and exhalation, etc. However, no matter how he changes his breathing, in a state of physical rest the amount of atmospheric air , entering the alveoli in 1 minute)", should remain approximately the same, namely, 5600 ml, to ensure normal blood gas composition,
the needs of cells and tissues for oxygen and for the removal of excess carbon dioxide. If you deviate from this value in any direction, the gas composition of arterial blood changes. The homeostatic mechanisms of its maintenance are immediately activated. They come into conflict with the deliberately formed overestimated or underestimated value of alveolar ventilation. In this case, the feeling of comfortable breathing disappears, and either a feeling of lack of air or a feeling of muscle tension arises. Thus, maintaining a normal blood gas composition while deepening breathing, i.e. with an increase in tidal volume, it is possible only by decreasing the frequency of respiratory cycles, and, conversely, with an increase in respiratory frequency, maintaining gas homeostasis is possible only with a simultaneous decrease in tidal volume.
In addition to the minute volume of breathing, there is also the concept of maximum pulmonary ventilation (MVL) - the volume of air that can pass through the lungs in 1 minute at maximum ventilation. In an untrained adult male, maximum ventilation during physical activity can exceed the minute volume of breathing at rest by 5 times. In trained people, maximum ventilation of the lungs can reach 120 liters, i.e. minute breathing volume can increase 15 times. With maximum ventilation of the lungs, the ratio of tidal volume and respiratory rate is also significant. With the same value of maximum ventilation of the lungs, alveolar ventilation will be higher at a lower respiratory rate and, accordingly, at a larger tidal volume. As a result, more oxygen can enter the arterial blood during the same time and more carbon dioxide can leave it.

How to calculate minute breathing volume. Minute breathing volume

Educational video - FVD (spirometry) indicators in health and disease

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