The child's first breath is the factors that determine it. Physiology of breathing in the perinatal period

The fact that the irritant of chemoreceptors is a decrease in oxygen tension in the blood plasma, and not a decrease in its total content in the blood, is proven by the following observations of L. L. Shik. When the amount of hemoglobin decreases or when it binds carbon monoxide the oxygen content in the blood is sharply reduced, but the dissolution of O2 in the blood plasma is not impaired and its tension in the plasma remains normal. In this case, the chemoreceptors are not excited and breathing does not change, although oxygen transport is sharply impaired and the tissues experience a condition oxygen starvation, since not enough oxygen is delivered to them by hemoglobin. When atmospheric pressure decreases, when the oxygen tension in the blood decreases, chemoreceptors are excited and breathing increases.

The nature of changes in breathing with an excess of carbon dioxide and a decrease in oxygen tension in the blood is different. With a slight decrease in oxygen tension in the blood, a reflex increase in the breathing rhythm is observed, and with a slight increase in carbon dioxide tension in the blood, a reflex deepening of respiratory movements occurs.

Thus, the activity of the respiratory center is regulated by the influence increased concentration H+ ions and increased CO2 voltage on chemoreceptors medulla oblongata and on the chemoreceptors of the carotid and aortic bodies, as well as the effect on the chemoreceptors of these vascular reflexogenic zones decrease in oxygen tension arterial blood.

Causes of a newborn's first breath are explained by the fact that in the womb, gas exchange of the fetus occurs through the umbilical vessels, which are in close contact with the maternal blood in the placenta. The cessation of this connection with the mother at birth leads to a decrease in oxygen tension and the accumulation of carbon dioxide in the blood of the fetus. This, according to Barcroft, irritates the respiratory center and leads to inhalation.

For the first breath to occur, it is important that the cessation of embryonic respiration occurs suddenly: with slow clamping of the umbilical cord respiratory center is not excited and the fetus dies without taking a single breath.

It should also be taken into account that the transition to new conditions causes irritation of a number of receptors in the newborn and the flow of impulses through the afferent nerves, increasing the excitability of the central nervous system, including the respiratory center (I. A. Arshavsky).

The importance of mechanoreceptors in the regulation of breathing. The respiratory center receives afferent impulses not only from chemoreceptors, but also from pressoreceptors of vascular reflexogenic zones, as well as from mechanoreceptors of the lungs, respiratory tract And respiratory muscles.

The influence of pressoreceptors of vascular reflexogenic zones is found in the fact that an increase in pressure in the isolated carotid sinus, associated with the body only nerve fibers, leads to depression of respiratory movements. This also happens in the body when blood pressure. On the contrary, when blood pressure decreases, breathing becomes faster and deeper.

Impulses coming to the respiratory center via the vagus nerves from the lung receptors are important in the regulation of breathing. The depth of inhalation and exhalation largely depends on them. The presence of reflex influences from the lungs was described in 1868 by Hering and Breuer and formed the basis for the idea of ​​reflex self-regulation of breathing. It manifests itself in the fact that when you inhale, impulses arise in the receptors located in the walls of the alveoli, reflexively inhibiting inhalation and stimulating exhalation, and with a very sharp exhalation, when extreme As lung volume decreases, impulses arise that arrive at the respiratory center and reflexively stimulate inhalation. The presence of such reflex regulation is evidenced by the following facts:

IN lung tissue in the walls of the alveoli, i.e. in the most extensible part of the lung, there are interoreceptors, which are the perceiving irritations of the endings of the afferent fibers of the vagus nerve;

After cutting vagus nerves breathing becomes sharply slow and deep;

When the lung is inflated with an indifferent gas, for example nitrogen, with mandatory condition the integrity of the vagus nerves, the muscles of the diaphragm and intercostal spaces suddenly stop contracting, inhalation stops before reaching the usual depth; on the contrary, when air is artificially suctioned from the lung, the diaphragm contracts.

Based on all these facts, the authors came to the conclusion that stretching of the pulmonary alveoli during inspiration causes irritation of the lung receptors, as a result of which the impulses coming to the respiratory center through the pulmonary branches of the vagus nerves become more frequent, and this reflexively excites the expiratory neurons of the respiratory center, and, consequently, entails the occurrence of exhalation. Thus, as Hering and Breuer wrote, “every breath, as it stretches the lungs, itself prepares its end.”

If you connect the peripheral ends of the cut vagus nerves to an oscilloscope, you can record action potentials arising in the receptors of the lungs and traveling along the vagus nerves to the central nervous system not only when inflating the lungs, but also during artificial suction of air from them. During natural breathing, frequent currents of action in the vagus nerve are detected only during inhalation; during natural exhalation they are not observed (Figure 4).

Figure 4 - Currents of action in the vagus nerve during stretching of the lung tissue during inhalation (according to Adrian) From top to bottom: 1 - afferent impulses in the vagus nerve: 2 - recording of breathing (inhalation - up, exhalation - down); 3 – time stamp

Consequently, the collapse of the lungs causes reflex irritation of the respiratory center only with such strong compression of them, which does not happen during normal, ordinary exhalation. This is observed only when very deep exhalation or sudden bilateral pneumothorax, to which the diaphragm reflexively reacts with contraction. During natural breathing, the receptors of the vagus nerves are stimulated only when the lungs are stretched and reflexively stimulate exhalation.

In addition to the mechanoreceptors of the lungs, mechanoreceptors of the intercostal muscles and the diaphragm take part in the regulation of breathing. They are excited by stretching during exhalation and reflexively stimulate inhalation (S.I. Frankstein).

Relationships between inspiratory and expiratory neurons of the respiratory center. There are complex reciprocal (conjugate) relationships between inspiratory and expiratory neurons. This means that excitation of inspiratory neurons inhibits expiratory ones, and excitation of expiratory neurons inhibits inspiratory ones. Such phenomena are partly due to the presence of direct connections that exist between the neurons of the respiratory center, but mainly they depend on reflex influences and on the functioning of the pneumotaxis center.

The interaction between neurons of the respiratory center is currently represented as follows. Due to the reflex (through chemoreceptors) action of carbon dioxide on the respiratory center, excitation of inspiratory neurons occurs, which is transmitted to the motor neurons innervating the respiratory muscles, causing the act of inhalation. At the same time, impulses from the inspiratory neurons arrive at the pneumotaxis center located in the pons, and from it, through the processes of its neurons, impulses arrive at the expiratory neurons of the respiratory center of the medulla oblongata, causing excitation of these neurons, cessation of inhalation and stimulation of exhalation. In addition, excitation of expiratory neurons during inspiration is also carried out reflexively through the Hering-Breuer reflex. After transection of the vagus nerves, the flow of impulses from the mechanoreceptors of the lungs stops and expiratory neurons can be excited only by impulses coming from the pneumotaxis center. The impulse stimulating the exhalation center is significantly reduced and its stimulation is somewhat delayed. Therefore, after cutting the vagus nerves, inhalation lasts much longer and is replaced by exhalation later than before cutting the nerves. Breathing becomes rare and deep.

Respiratory center called a set of neurons that ensure the activity of the respiratory apparatus and its adaptation to changing conditions of external and internal environment. These neurons are located in the spinal cord, medulla oblongata, pons, hypothalamus and cerebral cortex. The main structure that sets the rhythm and depth of Breathing is the medulla oblongata, which sends impulses to motor neurons spinal cord, innervating the respiratory muscles. The pons, hypothalamus and cortex control and correct the automatic activity of the inspiratory and expiratory neurons of the medulla oblongata.

The respiratory center of the medulla oblongata is a paired formation symmetrically located at the bottom of the rhomboid fossa. It consists of two groups of neurons: inspiratory, which provide inhalation, and expiratory, which provide exhalation. There are reciprocal (conjugate) relationships between these neurons. This means that the excitation of inhalation neurons is accompanied by inhibition of exhalation neurons and, conversely, the excitation of exhalation neurons is combined with inhibition of inhalation neurons. Motor neurons innervating the diaphragm are located in the III-IV cervical segments, innervating the intercostal respiratory muscles - in the III-CN thoracic segments spinal cord.

The respiratory center is very sensitive to excess carbon dioxide, which is its main natural causative agent. In this case, excess CO 2 acts on respiratory neurons directly (through blood and cerebrospinal fluid), and reflexively (through chemoreceptors vascular bed and medulla oblongata).

The role of CO 2 in the regulation of respiration is revealed when inhaling gas mixtures containing 5-7% CO 2. At the same time there is an increase pulmonary ventilation 6-8 times. That is why, when the function of the respiratory center is depressed and breathing stops, the most effective is to inhale not pure O 2, but carbogen, i.e. mixtures of 5-7% CO 2 and 95-93% O 2. Increased content and oxygen tension in the environment, blood and tissues of the body (hyperoxia) can lead to depression of the respiratory center.

After preliminary hyperventilation, i.e. voluntary increase in the depth and frequency of breathing, the usual 40-second breath hold can increase to 3-3.5 minutes, which indicates not only an increase in the amount of oxygen in the lungs, but also a decrease in CO 2 in the blood and a decrease in excitation of the respiratory center until it stops breathing. During muscular work, the amount of lactic acid and CO2 increases in tissues and blood, which are powerful stimulants respiratory center. A decrease in CO 2 tension in arterial blood (hypoxemia) is accompanied by an increase in pulmonary ventilation (when ascending to a height, with pulmonary pathology).

Mechanism of the newborn's first breath

In a newborn child, after ligation of the umbilical cord, gas exchange through the umbilical vessels, which come into contact with the mother's blood in the placenta, stops. Carbon dioxide accumulates in the blood of a newborn, which, like the lack of oxygen, humorally stimulates his respiratory center and causes the first breath.

Reflex regulation of breathing carried out by constant and unstable reflex influences on the function of the respiratory center.

Constant reflex influences arise as a result of irritation of the following receptors:

1) mechanoreceptors of the alveoli - E. Hering - I. Breuer reflex;

2) mechanoreceptors lung root and pleura - pleuropulmonary reflex;

3) chemoreceptors of the carotid sinuses - K. Heymans reflex;

4) proprioceptors of the respiratory muscles.

Reflex E. Hering - I. Breuer called the inhalation inhibition reflex when the lungs stretch. Its essence: when you inhale, impulses arise in the lungs that reflexively inhibit inhalation and stimulate exhalation, and when you exhale, impulses arise that reflexively stimulate inhalation. It is an example of regulation according to the principle feedback. Cutting the vagus nerves turns off this reflex, breathing becomes rare and deep. In a spinal animal in which the spinal cord has been transected at the border with the medulla oblongata, after the disappearance spinal shock breathing and body temperature are not restored at all.

Pleuropulmonary reflex occurs when the mechanoreceptors of the lungs and pleura are stimulated when the latter are stretched. Ultimately, it changes the tone of the respiratory muscles, increasing or decreasing the tidal volume of the lungs.

K. Gaymans reflex consists in a reflex increase in respiratory movements with an increase in CO 2 tension in the blood washing

carotid sinuses.

The respiratory center constantly receives nerve impulses from the proprioceptors of the respiratory muscles, which, when inhaling, inhibit the activity of inspiratory neurons and promote the onset of exhalation.

Fickle reflex influences on the activity of the respiratory center are associated with excitation of extero- and interoreceptors:

mucous membrane of the upper respiratory tract;

temperature and pain receptors skin;

proprioceptors skeletal muscles.

For example, when inhaling ammonia, chlorine, smoke, etc. There is a reflex spasm of the glottis and breath holding; if the nasal mucosa is irritated by dust - sneezing; larynx, trachea, bronchial cough.

The cerebral cortex, sending impulses to the respiratory center, takes an active part in the regulation normal breathing. It is thanks to the cortex that adaptation of breathing occurs during conversation, singing, sports, labor activity person. It participates in the development of conditioned respiratory reflexes, in changing breathing upon suggestion, etc. So, for example, if a person in a state of hypnotic sleep is suggested that he is performing a difficult physical work, breathing intensifies, despite the fact that he continues to remain in a state of complete physical rest.

ILLUSTRATIONS

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Control questions

1. Review respiratory system. The meaning of breathing.

2. Nasal cavity.

3. Larynx.

4. Trachea and bronchi.

5. Structure of the lungs and pleura.

6. Respiratory cycle. Mechanisms of inhalation and exhalation.

7. Pulmonary volumes. Pulmonary ventilation.

8. Gas exchange in the lungs and oxygen transport and carbon dioxide blood.

9. Respiratory center and mechanisms of breathing regulation.

The mechanism of the first breath of a newborn.

RESPIRATORY CENTER.

The rhythmic sequence of inhalation and exhalation, as well as changes in the nature of respiratory movements depending on the state of the body, are regulated respiratory center located in the medulla oblongata.

There are two groups of neurons in the respiratory center: inspiratory And expiratory. When the inspiratory neurons that provide inspiration are excited, the activity of the expiratory nerve cells is inhibited, and vice versa.

At the top of the pons ( pons) located pneumotaxic center, which controls the activity of the lower inhalation and exhalation centers and ensures the correct alternation of cycles of respiratory movements.

The respiratory center, located in the medulla oblongata, sends impulses to motor neurons of the spinal cord, innervating the respiratory muscles. The diaphragm is innervated by axons of motor neurons located at the level III-IV cervical segments spinal cord. Motor neurons, the processes of which form the intercostal nerves that innervate the intercostal muscles, are located in the anterior horns (III-XII) of the thoracic segments spinal cord.

Regulation of the activity of the respiratory center.

Regulation of the activity of the respiratory center is carried out using humoral, reflex mechanisms and nerve impulses, coming from the overlying parts of the brain.

Humoral mechanisms. A specific regulator of the activity of neurons in the respiratory center is carbon dioxide, which acts on respiratory neurons directly and indirectly. In the reticular formation of the medulla oblongata, near the respiratory center, as well as in the area of ​​the carotid sinuses and aortic arch, chemoreceptors, sensitive to carbon dioxide. With an increase in carbon dioxide tension in the blood, chemoreceptors are excited, and nerve impulses are sent to inspiratory neurons, which leads to an increase in their activity.

Carbon dioxide increases the excitability of neurons in the cerebral cortex. In turn, KGM cells stimulate the activity of neurons in the respiratory center.

At optimal levels of carbon dioxide and oxygen in the blood, breathing movements, reflecting moderate degree excitation of neurons of the respiratory center. These breathing movements of the chest are called eipnea.

Excessive carbon dioxide and lack of oxygen in the blood increase the activity of the respiratory center, which causes frequent and deep breathing movements - hyperpnea. An even greater increase in the amount of carbon dioxide in the blood leads to disruption of the breathing rhythm and the appearance of shortness of breath - dyspnea. A decrease in the concentration of carbon dioxide and excess oxygen in the blood inhibit the activity of the respiratory center. In this case, breathing becomes shallow, rare and may stop - apnea.

The mechanism of the first breath of a newborn.

In the mother's body, gas exchange in the fetus occurs through the umbilical vessels. After the birth of the child and separation of the placenta, this connection is broken. Metabolic processes in the body of a newborn lead to the formation and accumulation of carbon dioxide, which, like the lack of oxygen, humorally stimulates the respiratory center. In addition, a change in the child’s living conditions leads to excitation of extero- and proprioceptors, which is also one of the mechanisms involved in the taking of the newborn’s first breath.

Reflex mechanisms.

Distinguish constant and intermittent (episodic) reflex influences on the functional state of the respiratory center.

Constant reflex influences arise as a result of irritation of alveolar receptors ( Hering-Breuer reflex ), root of the lung and pleura ( pulmothoracic reflex ), chemoreceptors of the aortic arch and carotid sinuses ( Heymans reflex ), proprioceptors of the respiratory muscles.

The most important reflex is Hering-Breuer reflex. The alveoli of the lungs contain stretch and collapse mechanoreceptors, which are sensitive nerve endings of the vagus nerve. Any increase in the volume of the pulmonary alveoli excites these receptors.

The Hering-Breuer reflex is one of the mechanisms of self-regulation of the respiratory process, ensuring a change in the acts of inhalation and exhalation. When the alveoli are stretched during inhalation, nerve impulses from stretch receptors travel along the vagus nerve to expiratory neurons, which, when excited, inhibit the activity of inspiratory neurons, which leads to passive exhalation. The pulmonary alveoli collapse, and nerve impulses from the stretch receptors no longer reach the expiratory neurons. Their activity decreases, which creates conditions for increasing the excitability of the inspiratory part of the respiratory center and the implementation of active inhalation.

In addition, the activity of inspiratory neurons increases with increasing concentration of carbon dioxide in the blood, which also contributes to the manifestation of inhalation.

Pulmothoracic reflex occurs when the receptors located in the lung tissue and pleura are excited. This reflex appears when the lungs and pleura are stretched. The reflex arc closes at the level of the cervical and thoracic segments of the spinal cord.

The respiratory center is constantly supplied nerve impulses from proprioceptors of the respiratory muscles. During inhalation, the proprioceptors of the respiratory muscles are excited and nerve impulses from them enter the inspiratory part of the respiratory center. Under the influence of nerve impulses, the activity of inspiratory neurons is inhibited, which promotes the onset of exhalation.

Fickle reflex influences on the activity of respiratory neurons associated with arousal various extero- and interoreceptors . These include reflexes that arise from irritation of receptors in the mucous membrane of the upper respiratory tract, nasal mucosa, nasopharynx, temperature and pain receptors in the skin, and proprioceptors in skeletal muscles. For example, when suddenly inhaling vapors of ammonia, chlorine, sulfur dioxide, tobacco smoke and some other substances, irritation of the receptors in the mucous membrane of the nose, pharynx, and larynx occurs, which leads to a reflex spasm of the glottis, and sometimes even the muscles of the bronchi and a reflex holding of breath.

When the epithelium of the respiratory tract is irritated by accumulated dust, mucus, as well as ingested chemical irritants and foreign bodies, sneezing and coughing are observed. Sneezing occurs when receptors in the nasal mucosa are irritated, while coughing occurs when receptors in the larynx, trachea, and bronchi are stimulated.

The influence of cerebral cortex cells on the activity of the respiratory center.

According to M.V. Sergievsky, regulation of the activity of the respiratory center is represented by three levels.

First level of regulation- spinal cord. The centers of the phrenic and intercostal nerves are located here, causing contraction of the respiratory muscles.

Second level of regulation- medulla. The respiratory center is located here. This level of regulation ensures a rhythmic change in the phases of breathing and the activity of spinal motor neurons, the axons of which innervate the respiratory muscles.

Third level of regulation- upper parts of the brain, including cortical neurons. Only with the participation of the cerebral cortex is it possible to adequately adapt the reactions of the respiratory system to changing environmental conditions.

BREATHING DURING PHYSICAL ACTIVITY.

In trained people, during intense muscular work, the volume of pulmonary ventilation increases to 50-100 l/min compared to 5-8 l in a state of relative physiological rest. Increased minute volume of breathing with physical activity associated with an increase in the depth and frequency of respiratory movements. At the same time, in trained people, the depth of breathing mainly changes, in untrained people, the frequency of respiratory movements changes.

During physical activity, the concentration of carbon dioxide and lactic acid in the blood and tissues increases, which stimulate the neurons of the respiratory center both humorally and through nerve impulses coming from vascular reflexogenic zones. Finally, the activity of the neurons of the respiratory center is ensured by the flow of nerve impulses coming from cells of the cerebral cortex, which are highly sensitive to a lack of oxygen and to an excess of carbon dioxide.

At the same time, adaptive reactions occur in the cardiovascular system. The frequency and strength of heart contractions increase, blood pressure rises, the vessels of working muscles dilate and the vessels of other areas narrow.

Thus, the respiratory system provides the body with increasing oxygen needs. The circulatory and blood systems, being reconstructed to a new functional level, promote the transport of oxygen to the tissues and carbon dioxide to the lungs.

In the prenatal period of development, the lungs are not an organ external respiration fetus, this function is performed by the placenta. But long before birth, breathing movements appear that are necessary for normal development lungs. The lungs are filled with liquid (about 100 ml) before ventilation begins.

Birth causes sudden changes in the state of the respiratory center, leading to the onset of ventilation. The first breath occurs 15-70 seconds after birth, usually after clamping the umbilical cord, sometimes before it, i.e. immediately after birth. Factors stimulating the first breath:

1) The presence of humoral respiratory irritants in the blood: CO 2, H + and lack of O 2. During childbirth, especially after ligation of the umbilical cord, CO 2 tension and H + concentration increase, and hypoxia intensifies. But hypercapnia, acidosis and hypoxia themselves do not explain the onset of the first breath. It is possible that in newborns, low levels of hypoxia can excite the respiratory center, acting directly on brain tissue.

2) An equally important factor stimulating the first breath is a sharp increase in the flow of afferent impulses from skin receptors (cold, tactile), proprioceptors, vestibuloreceptors, which occurs during childbirth and immediately after birth. These impulses activate the reticular formation of the brain stem, which increases the excitability of the neurons of the respiratory center.

3) The stimulating factor is the elimination of sources of inhibition of the respiratory center. Irritation of the receptors located in the nostril area by the liquid greatly inhibits breathing (the “diver’s” reflex). Therefore, immediately at the birth of the fetal head from birth canal, obstetricians remove mucus and amniotic fluid from the airways.

Thus, the occurrence of the first breath is the result simultaneous action a number of factors.

The newborn's first breath is characterized by strong excitement inspiratory muscles, especially the diaphragm. In 85% of cases, the first breath is deeper than subsequent ones, and the first respiratory cycle is longer. Happening strong decline intrapleural pressure. This is necessary to overcome the frictional force between the liquid in the airways and their wall, as well as to overcome the surface tension of the alveoli at the liquid-air interface after air enters them. The duration of the first inhalation is 0.1–0.4 seconds, and the exhalation is on average 3.8 seconds. Exhalation occurs against the background of a narrowed glottis and is accompanied by a cry. The volume of exhaled air is less than that of inhaled air, which ensures the beginning of the formation of FRC. FRC increases from inspiration to inspiration. Aeration of the lungs usually ends by 2-4 days after birth. FRC at this age is about 100 ml. With the beginning of aeration, the pulmonary circulation begins to function. The fluid remaining in the alveoli is absorbed into the bloodstream and lymph.

In newborns, the ribs are positioned at a lesser angle than in adults, so contractions of the intercostal muscles are less effective in changing volume chest cavity. Calm breathing in newborns it is diaphragmatic, the inspiratory muscles work only when crying and shortness of breath.

Newborns always breathe through their nose. The respiratory rate shortly after birth averages about 40 per minute. Airways in newborns they are narrow, their aerodynamic resistance is 8 times higher than in adults. The lungs have little extensibility, but the compliance of the walls of the chest cavity is high, which results in low elastic traction values ​​of the lungs. Newborns are characterized by a relatively small inspiratory reserve volume and a relatively large expiratory reserve volume. Newborn breathing is irregular, series rapid breathing alternate with more rare ones, deep sighs occur 1-2 times per minute. Breathing may be held during exhalation (apnea) for up to 3 seconds or more. Premature infants may experience Cheyne-Stokes breathing. The activity of the respiratory center is coordinated with the activity of the centers of sucking and swallowing. When feeding, the breathing rate usually corresponds to the frequency of sucking movements.

Age-related changes breathing:

After birth, until 7-8 years of age, differentiation processes take place bronchial tree and an increase in the number of alveoli (especially in the first three years). IN adolescence there is an increase in the volume of the alveoli.

Minute breathing volume increases with age by almost 10 times. But for children in general it is typical high level ventilation of the lungs per unit of body weight (relative MOD). Respiratory rate decreases with age, especially strongly during the first year after birth. With age, the breathing rhythm becomes more stable. In children, the duration of inhalation and exhalation is almost equal. An increase in the duration of exhalation in most people occurs during adolescence.

With age, the activity of the respiratory center improves, mechanisms develop that ensure a clear change respiratory phases. Children's ability to voluntarily regulate breathing gradually develops. From the end of the first year of life, breathing is involved in speech function.

During the prenatal period, the lungs are not the organ of external respiration of the fetus; this function is performed by the placenta. But long before birth, breathing movements appear, which are necessary for the normal development of the lungs. The lungs are filled with liquid (about 100 ml) before ventilation begins.

Birth causes sudden changes in the state of the respiratory center, leading to the onset of ventilation. The first breath occurs 15-70 seconds after birth, usually after clamping the umbilical cord, sometimes before it, i.e. immediately after birth.

Factors stimulating the first breath:

The presence of humoral respiratory irritants in the blood: CO 2, H + and lack of O 2. During childbirth, especially after ligation of the umbilical cord, CO 2 tension and H + concentration increase, and hypoxia intensifies. But hypercapnia, acidosis and hypoxia themselves do not explain the onset of the first breath. It is possible that in newborns, low levels of hypoxia can excite the respiratory center, acting directly on brain tissue.

An equally important factor stimulating the first breath is a sharp increase in the flow of afferent impulses from skin receptors (cold, tactile), proprioceptors, vestibuloreceptors, which occurs during childbirth and immediately after birth. These impulses activate the reticular formation of the brain stem, which increases the excitability of the neurons of the respiratory center.

The stimulating factor is the elimination of sources of inhibition of the respiratory center. Irritation of the receptors located in the nostril area by the liquid greatly inhibits breathing (the “diver’s” reflex). Therefore, immediately at the birth of the fetal head from the birth canal, obstetricians remove mucus and amniotic fluid from the airways.

Thus, the occurrence of the first breath is the result of the simultaneous action of a number of factors.

The first breath of a newborn is characterized by strong excitation of the inspiratory muscles, especially the diaphragm. In 85% of cases, the first breath is deeper, and the first respiratory cycle is longer than subsequent respiratory cycles. There is a strong decrease in intrapleural pressure. This is necessary to overcome the frictional force between the liquid in the airways and their wall, as well as to overcome the surface tension of the alveoli at the liquid-air interface after air enters them. The duration of the first inhalation is 0.1–0.4 seconds, and the exhalation is on average 3.8 seconds. Exhalation occurs against the background of a narrowed glottis and is accompanied by a cry. The volume of exhaled air is less than that of inhaled air, which ensures the beginning of the formation of FRC. FRC increases from inspiration to inspiration. Aeration of the lungs usually ends by 2-4 days after birth. FRC at this age is about 100 ml. With the beginning of aeration, the pulmonary circulation begins to function. The fluid remaining in the alveoli is absorbed into the bloodstream and lymph.

In newborns, the ribs are positioned at a lesser angle than in adults, so contractions of the intercostal muscles are less effective in changing the volume of the thoracic cavity. Quiet breathing in newborns is diaphragmatic; inspiratory muscles work only when crying and shortness of breath.

Newborns always breathe through their nose. The respiratory rate shortly after birth averages about 40 per minute. The airways in newborns are narrow, their aerodynamic resistance is 8 times higher than in adults. The lungs have little extensibility, but the compliance of the walls of the chest cavity is high, which results in low elastic traction values ​​of the lungs. Newborns are characterized by a relatively small inspiratory reserve volume and a relatively large expiratory reserve volume. The breathing of newborns is irregular, a series of rapid breathing alternates with more rare breathing, deep sighs occur 1-2 times per minute. Breathing may be held during exhalation (apnea) for up to 3 seconds or more. Premature newborns may experience Cheyne-Stokes breathing. The activity of the respiratory center is coordinated with the activity of the centers of sucking and swallowing. When feeding, the breathing rate usually corresponds to the frequency of sucking movements.

Age-related changes in breathing:

After birth, until the age of 7-8 years, the processes of differentiation of the bronchial tree and an increase in the number of alveoli occur (especially in the first three years). During adolescence, the volume of the alveoli increases.

Minute breathing volume increases with age by almost 10 times. But children in general are characterized by a high level of pulmonary ventilation per unit of body weight (relative MVR). Respiratory rate decreases with age, especially strongly during the first year after birth. With age, the breathing rhythm becomes more stable. In children, the duration of inhalation and exhalation is almost equal. An increase in the duration of exhalation in most people occurs during adolescence.

With age, the activity of the respiratory center improves, and mechanisms develop that ensure a clear change in respiratory phases. Children's ability to voluntarily regulate breathing gradually develops. From the end of the first year of life, breathing is involved in speech function.

8.7. RESEARCH OF METABOLISM AND ENERGY CONVERSION IN THE BODY

Metabolism in the body is interconnected with the transformation of energy. The potential energy of complex organic compounds supplied with food is converted into thermal, mechanical and electrical energy. Energy is spent not only on maintaining body temperature and performing work, but also on recreating the structural elements of cells, ensuring their vital activity, growth and development of the body.

Heat generation in the body is of a 2-phase nature. During the oxidation of proteins, fats and carbohydrates, most of the energy is converted into heat (primary heat), and less is used for the synthesis of ATP, i.e. for accumulation in high-energy connections. During the oxidation of carbohydrates, 77.3% of the energy of the chemical bond of glucose is dissipated in the form of heat, and 22.7% goes to the synthesis of ATP. The energy accumulated in ATP is further used for mechanical work, electrical processes, and ultimately also turns into heat (secondary heat). Thus, the amount of heat generated in the body is a measure of the total energy of chemical bonds that have undergone biological oxidation. The energy produced in the body can be expressed in heat units - calories or joules.

To study the processes of energy formation in the body, the following are used: direct calorimetry, indirect calorimetry and the study of gross metabolism.

Direct calorimetry is based on direct accounting of the heat generated by the body. A biocalorimeter is a sealed and well-insulated external environment a chamber where O 2 is supplied and excess CO 2 and vapors are absorbed. Water circulates through tubes. The heat generated by a person or animal in the chamber heats the circulating water, which makes it possible to calculate the amount of heat generated by the organism under study based on the amount of flowing water and the change in its temperature.

Because heat generation in the body is ensured by oxidative processes, it is possible indirect calorimetry, i.e. indirect, indirect determination of heat generation by gas exchange - accounting for consumed O 2 and released CO 2 with subsequent calculation of heat production.

For long-term studies of gas exchange, special respiratory chambers are used ( closed methods indirect calorimetry) - for example, the Shaternikov respiratory apparatus. Short-term determination of gas exchange is carried out using non-chamber methods (open methods of indirect calorimetry).

The most common is the Douglas-Haldane method. Within a few minutes, the exhaled air is collected in a bag made of airtight fabric (Douglas bag). Then the volume of exhaled air is measured and the amount of O 2 and CO 2 in it is determined.

The respiratory coefficient (RC) is the ratio of the volume of CO 2 released to the volume of O 2 absorbed.

DC during the oxidation of carbohydrates, proteins and fats is different. The oxidation of 1 g of each of these substances requires a different amount of O 2 and is accompanied by the release of different amounts of heat.

During the oxidation of carbohydrates DC = 1. For example, the result of glucose oxidation: C 6 H 12 O 6 + 6O 2 = 6CO 2 + 6H 2 O. The number of molecules of CO 2 formed is equal to the number of molecules of O 2 expended. And an equal number of gas molecules, at the same temperature and the same pressure, occupy the same volume (Avogadro-Gerard law).

For protein oxidation DC = 0.8; fat DC = 0.7. When a person is on a mixed diet under standard conditions, DC = 0.85 - 0.86.

Caloric equivalent of oxygen(CEC) or caloric cost of oxygen is the amount of heat released by the body after consuming 1 liter of oxygen.

This indicator depends on the DC and is determined using special tables, where each DC value corresponds to a certain value of the caloric cost of oxygen. For example: DC=0.8; KS=4.801 kcal. DC=0.9; KS=4.924.

Thus, gas analysis data are converted into thermal units.

After determining the volume of oxygen consumed per unit of time (day, hour, minute), it becomes possible to determine the amount of heat released by the body during this time (EK, multiplied by the volume of oxygen consumed).

During work, DC increases and in most cases approaches 1. This is explained by the fact that during intense muscular work the main source of energy is the oxidation of carbohydrates. After completion of the work, the DC first increases, then sharply decreases, and only after 30-50 minutes does it return to normal. These changes in DC after work do not reflect the true relationship between the oxygen currently used and the CO 2 released.

At the beginning of the recovery period, DC increases due to the fact that during work lactic acid accumulates in the muscles, for the oxidation of which there was not enough oxygen (oxygen debt). Lactic acid enters the blood and displaces CO 2 from bicarbonates, attaching bases. Due to this, the amount of CO 2 released becomes more quantity CO 2 formed in this moment in tissues.

The opposite picture is observed later, when lactic acid gradually disappears from the blood. One part of it is oxidized, the other is resynthesized into glycogen, and the third is excreted in sweat and urine. As the amount of lactic acid decreases, bases are released. Bases bind CO 2 and form bicarbonates. Therefore, DC falls due to retention of CO 2 in the blood coming from the tissues.

Study gross exchange- this is a long-term (over the course of a day) determination of gas exchange, which makes it possible not only to find the heat production of the body, but also to resolve the question of which substances were generated due to the oxidation. To do this, in addition to the oxygen used and CO 2 released, nitrogen (1 g of nitrogen is contained in 6.25 g of protein) and carbon (proteins contain approximately 53% carbon) excreted in the urine are determined.

BX(OO) is an indicator that reflects the level of energy processes under standard conditions, which are as close as possible to the state of functional rest of the body.

Energy expenditure under OO conditions is associated with maintaining the minimum level of oxidative processes necessary for cell life and with the activity of constantly working organs and systems - respiratory muscles, heart, kidneys, liver, and maintaining muscle tone. The release of thermal energy during these processes provides the heat production necessary to maintain body temperature.

5 conditions for defining an OO.

Time. The study is carried out in the morning before 9 hours after sleep.

On an empty stomach (12-16 hours after eating), since the intake and action of food causes an intensification of energy processes (specific dynamic action of food). SDDP persists for several hours. With protein foods, metabolism increases by 30%, with fats and carbohydrates by 14-15%.

Comfort temperature in the room: 18-20 degrees C. (temperature, barometric pressure, air humidity, etc. can affect the intensity of oxidative processes).

The study is carried out lying down, i.e. in a state of muscle rest.

The use of pharmacological drugs that affect energy processes, as well as narcotic substances, is preliminarily excluded.

Under these conditions, in a healthy person, OO ranges from 1600 to 1800 kcal per day, depending on: 1. Age, 2. Gender, 3 Body mass (weight), 4. Height.

OO formulas and tables – average data from a large number of studies healthy people different gender, age, body weight and height. Allowable fluctuations are 10%.

Disproportionately high values ​​of OO are observed with excessive thyroid function. A decrease in OO occurs with insufficiency of the thyroid gland (myxedema), pituitary gland, and gonads.

The intensity of OO, calculated per 1 kg of body weight, is significantly higher in children than in adults. The value of OO of a person aged 20-40 years remains at a fairly constant level. In old age, OO decreases.

Surface rule– energy expenditure by warm-blooded animals is proportional to the surface of the body.

If we recalculate the intensity of OO per 1 kg of body weight, it turns out that in different species of animals and even in people with different body weights and heights, this indicator varies greatly. If we recalculate the intensity of RO per 1 m 2 of body surface, then the results obtained do not differ so sharply.

This rule is relative. In two individuals with the same body surface area, metabolism can differ significantly. The level of oxidative processes is determined not so much by heat transfer from the surface of the body, but by heat production, depending on the biological characteristics of the animal species and the state of the body, which is determined by the activity of the nervous, endocrine and other systems.

Energy exchange during physical labor.

Muscular work significantly increases energy consumption, so daily energy consumption significantly exceeds the OO value. This increase constitutes a work increase. The more intense the muscle work, the greater it is.

The degree of energy expenditure during various physical activities is determined by the physical activity coefficient (PFA). CFA is the ratio of total energy consumption per day to the value of OO. According to this principle, 5 groups are distinguished:

Mental work causes an insignificant (2-3%) increase in energy expenditure compared to complete rest, if not accompanied by movement. However, physical activity and emotional arousal increase energy expenditure (experienced emotional arousal can cause an increase in metabolism by 11-19% over several days).

Daily energy expenditure in children and adolescents depends on age:

6 months - 1 g - 800 kcal

1 – 1.5 g - 1300

1,5 – 2 - 1500

14 – 17 (boys) – 3150

13 - 17 (girls) – 2750.

By the age of 80, energy expenditure decreases (2000-2200 kcal).