Soda, volcano, Venus, refrigerator - what do they have in common? Carbon dioxide. We have collected for you the most interesting information about one of the most important chemical compounds on Earth.

What is carbon dioxide

Carbon dioxide is known mainly in its gaseous state, i.e. as carbon dioxide with the simple chemical formula CO2. In this form, it exists under normal conditions - at atmospheric pressure and “ordinary” temperatures. But at increased pressure, above 5,850 kPa (such as, for example, the pressure at a sea depth of about 600 m), this gas turns into liquid. And when strongly cooled (minus 78.5°C), it crystallizes and becomes so-called dry ice, which is widely used in trade for storing frozen foods in refrigerators.

Liquid carbon dioxide and dry ice are produced and used in human activities, but these forms are unstable and easily disintegrate.

But carbon dioxide gas is ubiquitous: it is released during the respiration of animals and plants and is an important part of the chemical composition of the atmosphere and ocean.

Properties of carbon dioxide

Carbon dioxide CO2 is colorless and odorless. Under normal conditions it has no taste. However, when you inhale high concentrations of carbon dioxide, you may experience a sour taste in your mouth, caused by the carbon dioxide dissolving on mucous membranes and in saliva, forming a weak solution of carbonic acid.

By the way, it is the ability of carbon dioxide to dissolve in water that is used to make carbonated water. Lemonade bubbles are the same carbon dioxide. The first apparatus for saturating water with CO2 was invented back in 1770, and already in 1783, the enterprising Swiss Jacob Schweppes began industrial production of soda (the Schweppes brand still exists).

Carbon dioxide is 1.5 times heavier than air, so it tends to “settle” in its lower layers if the room is poorly ventilated. The “dog cave” effect is known, where CO2 is released directly from the ground and accumulates at a height of about half a meter. An adult, entering such a cave, at the height of his growth does not feel the excess of carbon dioxide, but dogs find themselves directly in a thick layer of carbon dioxide and are poisoned.

CO2 does not support combustion, which is why it is used in fire extinguishers and fire suppression systems. The trick of extinguishing a burning candle with the contents of a supposedly empty glass (but in fact carbon dioxide) is based precisely on this property of carbon dioxide.

Carbon dioxide in nature: natural sources

Carbon dioxide is formed in nature from various sources:

• Respiration of animals and plants.
  Every schoolchild knows that plants absorb carbon dioxide CO2 from the air and use it in the processes of photosynthesis. Some housewives try to make up for shortcomings with an abundance of indoor plants. However, plants not only absorb, but also release carbon dioxide in the absence of light - this is part of the respiration process. Therefore, a jungle in a poorly ventilated bedroom is not a good idea: CO2 levels will rise even more at night.
• Volcanic activity.
  Carbon dioxide is part of volcanic gases. In areas with high volcanic activity, CO2 can be released directly from the ground - from cracks and fissures called mofets. The concentration of carbon dioxide in valleys with mofets is so high that many small animals die when they get there.
• Decomposition of organic matter.
  Carbon dioxide is formed during the combustion and decay of organic matter. Large natural emissions of carbon dioxide accompany forest fires.

Carbon dioxide is “stored” in nature in the form of carbon compounds in minerals: coal, oil, peat, limestone. Huge reserves of CO2 are found in dissolved form in the world's oceans.

The release of carbon dioxide from an open reservoir can lead to a limnological catastrophe, as happened, for example, in 1984 and 1986. in lakes Manoun and Nyos in Cameroon. Both lakes were formed on the site of volcanic craters - now they are extinct, but in the depths the volcanic magma still releases carbon dioxide, which rises to the waters of the lakes and dissolves in them. As a result of a number of climatic and geological processes, the concentration of carbon dioxide in waters exceeded a critical value. A huge amount of carbon dioxide was released into the atmosphere, which went down the mountain slopes like an avalanche. About 1,800 people became victims of limnological disasters on Cameroonian lakes.

Artificial sources of carbon dioxide

The main anthropogenic sources of carbon dioxide are:

• industrial emissions associated with combustion processes;
• automobile transport.

Despite the fact that the share of environmentally friendly transport in the world is growing, the vast majority of the world's population will not soon have the opportunity (or desire) to switch to new cars.

Active deforestation for industrial purposes also leads to an increase in the concentration of carbon dioxide CO2 in the air.

CO2 is one of the end products of metabolism (the breakdown of glucose and fats). It is secreted in the tissues and transported by hemoglobin to the lungs, through which it is exhaled. The air exhaled by humans contains about 4.5% carbon dioxide (45,000 ppm) - 60-110 times more than in the air inhaled.

Carbon dioxide plays a large role in regulating blood flow and respiration. An increase in CO2 levels in the blood causes the capillaries to dilate, allowing more blood to pass through, which delivers oxygen to the tissues and removes carbon dioxide.

The respiratory system is also stimulated by an increase in carbon dioxide, and not by a lack of oxygen, as it might seem. In reality, the lack of oxygen is not felt by the body for a long time and it is quite possible that in rarefied air a person will lose consciousness before he feels the lack of air. The stimulating property of CO2 is used in artificial respiration machines: where carbon dioxide is mixed with oxygen to “start” the respiratory system.

Carbon dioxide and us: why CO2 is dangerous

Carbon dioxide is necessary for the human body just like oxygen. But just like with oxygen, an excess of carbon dioxide harms our well-being.

A high concentration of CO2 in the air leads to intoxication of the body and causes a state of hypercapnia. With hypercapnia, a person experiences difficulty breathing, nausea, headaches, and may even lose consciousness. If the carbon dioxide content does not decrease, then oxygen starvation occurs. The fact is that both carbon dioxide and oxygen move throughout the body on the same “transport” - hemoglobin. Normally, they “travel” together, attaching to different places on the hemoglobin molecule. However, increased concentrations of carbon dioxide in the blood reduce the ability of oxygen to bind to hemoglobin. The amount of oxygen in the blood decreases and hypoxia occurs.

Such unhealthy consequences for the body occur when inhaling air with a CO2 content of more than 5,000 ppm (this can be the air in mines, for example). To be fair, in ordinary life we ​​practically never encounter such air. However, a much lower concentration of carbon dioxide does not have the best effect on health.

According to some findings, even 1,000 ppm CO2 causes fatigue and headaches in half of the subjects. Many people begin to feel stuffiness and discomfort even earlier. With a further increase in carbon dioxide concentration to 1,500 – 2,500 ppm critically, the brain is “lazy” to take the initiative, process information and make decisions.

And if a level of 5,000 ppm is almost impossible in everyday life, then 1,000 and even 2,500 ppm can easily be part of the reality of modern man. Ours showed that in rarely ventilated school classrooms, CO2 levels remain above 1,500 ppm much of the time, and sometimes jump above 2,000 ppm. There is every reason to believe that the situation is similar in many offices and even apartments.

Physiologists consider 800 ppm to be a safe level of carbon dioxide for human well-being.

Another study found a link between CO2 levels and oxidative stress: the higher the carbon dioxide level, the more we suffer from oxidative stress, which damages our body's cells.

Carbon dioxide in the Earth's atmosphere

There is only about 0.04% CO2 in the atmosphere of our planet (this is approximately 400 ppm), and more recently it was even less: carbon dioxide crossed the 400 ppm mark only in the fall of 2016. Scientists attribute the rise in CO2 levels in the atmosphere to industrialization: in the mid-18th century, on the eve of the Industrial Revolution, it was only about 270 ppm.

Colorless and odorless. The most important regulator of blood circulation and respiration. Non-toxic. Without it, there would be no rich buns and pleasantly tart carbonated drinks. From this article you will learn what carbon dioxide is and how it affects the human body...

Most of us do not remember well the school course in physics and chemistry, but we know: gases are invisible and, as a rule, intangible, and therefore insidious. Therefore, before answering the question of whether carbon dioxide is harmful to the body, let's remember what it is.

Earth Blanket

CO2 is carbon dioxide. It is also carbon dioxide, carbon monoxide (IV) or carbonic anhydride. Under normal conditions, it is a colorless, odorless gas with a sour taste.

Under atmospheric pressure, carbon dioxide has two states of aggregation: gaseous (carbon dioxide is heavier than air and poorly soluble in water) and solid (at –78 °C it turns into dry ice).

Carbon dioxide is one of the main components of the environment. It is found in the air and underground mineral waters, is released during the respiration of humans and animals, and is involved in plant photosynthesis.

Carbon dioxide actively influences the climate. It regulates the heat exchange of the planet: it transmits ultraviolet radiation and blocks infrared radiation. In this regard, carbon dioxide is sometimes called the Earth's blanket.

O2 - energy. CO2 - spark

Carbon dioxide accompanies a person throughout his life. Being a natural regulator of respiration and blood circulation, carbon dioxide is an integral component of metabolism.

Inhaling about 30 liters of oxygen per hour, a person emits 20–25 liters of carbon dioxide.

By inhaling, a person fills the lungs with oxygen. At the same time, a two-way exchange occurs in the alveoli (special “bubbles” of the lungs): oxygen passes into the blood, and carbon dioxide is released from it. The man exhales. CO2 is one of the end products of metabolism. Figuratively speaking, oxygen is energy, and carbon dioxide is the spark that ignites it.

Carbon dioxide is no less important for the body than oxygen. It is a physiological stimulant of respiration: it affects the cerebral cortex and stimulates the respiratory center. The signal for the next breath is not a lack of oxygen, but an excess of carbon dioxide. After all, metabolism in cells and tissues is continuous, and its end products must be constantly removed.

In addition, carbon dioxide affects the secretion of hormones, enzyme activity and the speed of biochemical processes.

Gas exchange equilibrium

Carbon dioxide is non-toxic, non-explosive and absolutely harmless to people. However, the balance of carbon dioxide and oxygen is extremely important for normal life. Lack and excess of carbon dioxide in the body leads to hypocapnia and hypercapnia, respectively.

Hypocapnia - lack of CO2 in the blood. It occurs as a result of deep, rapid breathing, when more oxygen enters the body than needed. For example, during too intense physical activity. The consequences can vary: from mild dizziness to loss of consciousness.

Hypercapnia - excess CO2 in the blood. A person inhales (together with oxygen, nitrogen, water vapor and inert gases) 0.04% carbon dioxide, and exhales 4.4%. If you are in a small room with poor ventilation, the concentration of carbon dioxide may exceed the norm. As a result, headache, nausea, and drowsiness may occur. But most often, hypercapnia accompanies extreme situations: a malfunction of the breathing apparatus, holding one’s breath under water, and others.

Thus, contrary to the opinion of most people, carbon dioxide in the quantities provided by nature is necessary for human life and health. In addition, it has found wide industrial application and brings many practical benefits to people.

Sparkling bubbles at the service of chefs

CO2 is used in many fields. But, perhaps, carbon dioxide is most in demand in the food industry and cooking.

Carbon dioxide is formed in yeast dough under the influence of fermentation. It is its bubbles that loosen the dough, making it airy and increasing its volume.

With the help of carbon dioxide, various refreshing drinks are made: kvass, mineral water and other sodas loved by children and adults. These drinks are popular with millions of consumers around the world, largely because of the sparkling bubbles that burst so funny in the glass and “prick” the nose so pleasantly.

Can the carbon dioxide contained in carbonated drinks contribute to hypercapnia or cause any other harm to a healthy body? Of course not!

Firstly, the carbon dioxide used in the preparation of carbonated drinks is specially prepared for use in the food industry. In the quantities in which it is contained in soda, it is absolutely harmless to the body of healthy people.

Secondly, most of the carbon dioxide evaporates immediately after opening the bottle. The remaining bubbles “evaporate” during the drinking process, leaving behind only a characteristic hiss. As a result, a negligible amount of carbon dioxide enters the body.

“Then why do doctors sometimes prohibit drinking carbonated drinks?” - you ask. According to the candidate of medical sciences, gastroenterologist Alena Aleksandrovna Tyazheva, this is due to the fact that there are a number of diseases of the gastrointestinal tract for which a special strict diet is prescribed. The list of contraindications includes not only drinks containing gas, but also many food products. A healthy person can easily include a moderate amount of carbonated drinks in his diet and allow himself a glass of cola from time to time.

Conclusion

Carbon dioxide is necessary to support the life of both the planet and an individual organism. CO2 affects the climate, acting as a kind of blanket. Without it, metabolism is impossible: metabolic products leave the body with carbon dioxide. It is also an indispensable component of everyone’s favorite carbonated drinks. It is carbon dioxide that creates playful bubbles that tickle your nose. At the same time, it is absolutely safe for a healthy person.

Scientists have long suspected that carbon dioxide has a direct connection to global warming, but as it turns out, carbon dioxide may have a lot to do with our health. Humans are the main source of carbon dioxide indoors as we exhale between 18 and 25 liters of the gas per hour. Elevated levels of carbon dioxide can be observed in all rooms where people are: in school classrooms and college auditoriums, in meeting rooms and office spaces, in bedrooms and children's rooms.

It is a myth that we lack oxygen in a stuffy room. Calculations show that, contrary to the existing stereotype, headaches, weakness, and other symptoms occur in a person indoors not from a lack of oxygen, but from an excess of carbon dioxide.

Until recently, in European countries and the USA, the level of carbon dioxide in a room was measured only to check the quality of ventilation, and it was believed that CO2 was dangerous for humans only in high concentrations. Research on the effect of carbon dioxide on the human body at a concentration of approximately 0.1% has appeared quite recently.

Few people know that clean air outside the city contains about 0.04% carbon dioxide, and the closer the CO2 content in the room is to this figure, the better a person feels.

According to recent research conducted in the UK by the major auditing firm KPMG, high levels of CO2 in office air can cause employee illness and reduce their attention span by a third. Elevated levels of carbon dioxide can cause headaches, inflammation of the eyes and nasopharynx, and also cause fatigue among staff. As a result of all this, companies are losing a lot of money, and carbon dioxide is to blame. Julia Bennett, who led the research, says high levels of carbon dioxide in office spaces are very common.

As a result of recent studies conducted by Indian scientists among residents of the city of Kolkata, it was found that even in low concentrations, carbon dioxide is a potentially toxic gas. Scientists concluded that carbon dioxide is similar in toxicity to nitrogen dioxide, taking into account its effects on the cell membrane and biochemical changes that occur in human blood, such as acidosis. Prolonged acidosis, in turn, leads to diseases of the cardiovascular system, hypertension, fatigue and other adverse consequences for the human body.

Residents of a large metropolis are negatively affected by elevated levels of carbon dioxide from morning to evening. First, in crowded public transport and in their own cars, which sit in traffic jams for a long time. Then at work, where it is often stuffy and you can’t breathe.

It is very important to maintain good air quality in the bedroom because... people spend a third of their lives there. In order to get a good night's sleep, the quality of air in the bedroom is much more important than the duration of sleep, and the level of carbon dioxide in bedrooms and children's rooms should be below 0.08%. High levels of CO2 in these areas can cause symptoms such as nasal congestion, throat and eye irritation, headaches and insomnia.

Finnish scientists have found a way to solve this problem based on the axiom that if in nature the level of carbon dioxide is 0.035-0.04%, then in rooms it should be close to this level. The device they invented removes excess carbon dioxide from indoor air. The principle is based on the absorption (absorption) of carbon dioxide by a special substance.

Carbon dioxide in water

From the village 149. Carbon dioxide slightly changes the acid-base environment. This has a bad effect on the human body. The fact is that any process in our body occurs at a certain acidity, which corresponds to almost pure water. The presence of carbon dioxide changes it greatly, which somewhat changes our biochemical processes. This also affects the taste properties (sourish taste), which leads to unpleasant sensations.

Thus, medicine around the world has been dealing with this issue for many years, which has led to the emergence of some contraindications to the consumption of carbonated water in any form.

Firstly, any chronic diseases of the gastrointestinal tract completely prohibit the consumption of carbonated water. The fact is that when drinking such water, irritation of the mucous membrane occurs, which leads to an exacerbation of many inflammatory processes. Most often, doctors prescribe mineral water for treatment, but do not forget that it is imperative to drink it only after carbon dioxide has been removed.

Secondly, children who are under three years old should not be given such drinks, because their body has not yet developed enough, which means there may be a metabolic disorder in their body.

Thirdly, individual allergic reactions to carbon dioxide are quite common among people, which means that the amount of carbonated water needs to be significantly reduced.

Fourthly, being overweight also obliges you to exclude carbonated drinks from your diet, because most often it is caused by improper metabolism, which can be worsened by carbon dioxide.

According to the legislation of European countries, the presence of carbon dioxide should not exceed four tenths of a percent. This will give an excellent preservative effect,

but at the same time it will not affect the human body, which will give better quality to the water. An exception is given only to natural mineral water, which may contain a slightly larger amount of gas.

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Studying the influence of the toxic effects of CO 2 on the human body is of significant practical interest for biology and medicine.

The source of CO 2 in the gaseous environment of a hermetic cabin is, first of all, the person himself, since CO 2 is one of the main end products of metabolism formed during the metabolic process in the body of humans and animals. At rest, a person emits about 400 liters of CO 2 per day; during physical work, the formation of CO 2 and, accordingly, its release from the body increase significantly. In addition, it must be borne in mind that CO 2 is continuously formed during the process of rotting and fermentation. Carbon dioxide is colorless, has a weak odor and a sour taste. Despite these qualities, when CO 2 accumulates in IGA up to several percent, its presence is invisible to humans, since the properties mentioned above (smell and taste) can apparently be detected only at very high concentrations of CO 2.

Breslav's studies, in which subjects made a “free choice” of the gas environment, showed that people begin to avoid IGA only in cases where P CO 2 in it exceeds 23 mm Hg. Art. At the same time, the detection reaction of CO 2 is associated not with smell and taste, but with the manifestation of its effect on the body, primarily with an increase in pulmonary ventilation and a decrease in physical performance.

The earth's atmosphere contains a small amount of CO 2 (0.03%), which is due to its participation in the circulation of substances. A tenfold increase in CO 2 in the inhaled air (up to 0.3%) does not yet have a noticeable effect on human life and performance. A person can stay in such a gas environment for a very long time, maintaining normal health and a high level of performance. This is probably due to the fact that during life, the formation of CO 2 in tissues is subject to significant fluctuations exceeding tenfold changes in the content of this substance in the inhaled air. A significant increase in P CO 2 in the IGA causes natural changes in the physiological state. These changes are caused primarily by functional changes that occur in the central nervous system, respiration, blood circulation, as well as changes in acid-base balance and disorders of mineral metabolism. The nature of functional changes during hypercapnia is determined by the value of PCO 2 in the inhaled gas mixture and the time of exposure of this factor to the body.

Even Claude Bernard showed in the last century that the main reason causing the development of a severe pathological condition in animals during a long stay in hermetically sealed, unventilated rooms is associated with an increase in the CO 2 content in the inhaled air. In animal studies, the mechanism of physiological and pathological effects of CO 2 was studied.

The physiological mechanism of the influence of hypercapnia can be judged in general terms based on the diagram shown in Fig. 19.

It should be borne in mind that in cases of long-term stay in an IGA, in which P CO 2 is increased to 60-70 mm Hg. Art. and moreover, the nature of physiological reactions and, above all, reactions of the central nervous system changes significantly. In the latter case, instead of a stimulating effect, as indicated in Fig. 19, hypercapnia has a depressing effect and already leads to the development of a narcotic state. It quickly occurs in cases where P CO 2 increases to 100 mm Hg. Art. and higher.

Increased pulmonary ventilation with an increase in P CO 2 in the IHA to 10-15 mm Hg. Art. and higher is determined by at least two mechanisms: reflex stimulation of the respiratory center from the chemoreceptors of the vascular zones, and primarily sinocorotid, and stimulation of the respiratory center from the central chemoreceptors. An increase in pulmonary ventilation during hypercapnia is the main adaptive reaction of the body aimed at maintaining Pa CO 2 at a normal level. The effectiveness of this reaction decreases as P CO 2 in the IHA increases, since despite the increasing increase in pulmonary ventilation, Pa CO 2 also increases steadily.

The increase in Pa CO 2 has an antagonistic effect on the central and peripheral mechanisms that regulate vascular tone. The stimulating effect of CO 2 on the vasomotor center and the sympathetic nervous system determines the vasoconstrictor effect and leads to an increase in peripheral resistance, an increase in heart rate and an increase in cardiac output. At the same time, CO 2 has a direct effect on the muscular wall of blood vessels, promoting their expansion.

Rice. 19. Mechanisms of physiological and pathophysiological action of CO 2 on the body of animals and humans (according to Malkin)

The interaction of these antagonistic influences ultimately determines the reactions of the cardiovascular system during hypercapnia. From the above, we can conclude that in the case of a sharp decrease in the central vasoconstrictor effect, hypercapnia can lead to the development of collaptoid reactions, which were noted in an experiment on animals under conditions of a significant increase in CO2 content in the IGA.

With a large increase in P CO 2 in tissues, which inevitably occurs under conditions of a significant increase in P CO 2 in the IGA, the development of a narcotic state is noted, which is accompanied by a clearly expressed decrease in the level of metabolism. This reaction can be assessed as adaptive, since it leads to a sharp decrease in the formation of CO 2 in tissues during a period when transport systems, including blood buffer systems, are no longer able to maintain Pa CO 2 - the most important constant of the internal environment at a level close to normal.

It is important that the threshold for reactions of various functional systems during the development of acute hypercapnia is not the same.

Thus, the development of hyperventilation manifests itself already with an increase in P CO 2 in the IGA to 10-15 mm Hg. Art., and at 23 mm Hg. Art. this reaction becomes quite pronounced - ventilation increases almost 2 times. The development of tachycardia and increased blood pressure appear when P CO 2 increases in the IHA to 35-40 mm Hg. Art. The narcotic effect was noted at even higher values ​​of P CO 2 in the IGA, about 100-150 mm Hg. Art., while the stimulating effect of CO 2 on the neurons of the cerebral cortex was noted at P CO 2 of the order of 10-25 mm Hg. Art.

Now we will briefly consider the effects of various values ​​of P CO 2 in IGA on the body of a healthy person.

Of great importance for judging a person’s resistance to hypercapnia and for CO 2 normalization are studies in which subjects, practically healthy people, were in conditions of IHA with excessive P CO 2 values. These studies established the nature and dynamics of the reactions of the central nervous system, respiration and blood circulation, as well as changes in performance at various values ​​of P CO 2 in the IHA.

During a relatively short-term stay of a person in conditions of IHA with P CO 2 up to 15 mm Hg. Art., despite the development of mild respiratory acidosis, no significant changes in the physiological state were detected. People who were in such an environment for several days maintained normal intellectual performance and did not present any complaints indicating a deterioration in their health; only at P CO 2 equal to 15 mm Hg. Art., some subjects noted a decrease in physical performance, especially when performing heavy work.

With an increase in P CO 2 in the IGA to 20-30 mm Hg. Art. The subjects had clearly expressed respiratory acidosis and an increase in pulmonary ventilation. After a relatively short-term increase in the speed of performing psychological tests, a decrease in the level of intellectual performance was observed. The ability to perform heavy physical work was also noticeably reduced. Nocturnal sleep disturbance was noted. Many subjects complained of headaches, dizziness, shortness of breath and a feeling of lack of air when performing physical work.

Rice. 20. Classification of various effects of the toxic action of CO 2 depending on the value of P CO 2 in IGA (compiled by Roth and Billings based on data from Schaeffer, King, Nevison)

I - indifferent zone;

L - zone of minor physiological changes;

III - zone of severe discomfort;

IV - zone of deep functional disorders, loss

consciousness A - indifferent zone;

B - zone of initial functional disorders;

In - an eon of deep violations

With an increase in P CO 2 in the IGA to 35-40 mm Hg. Art. In the subjects, pulmonary ventilation increased by 3 times or more. Functional changes appeared in the circulatory system: heart rate increased, blood pressure increased. After a short stay in such an IHA, the subjects complained of headache, dizziness, visual impairment, and loss of spatial orientation. Performing even light physical activity was associated with significant difficulties and led to the development of severe shortness of breath. Performing psychological tests was also difficult, and intellectual performance was noticeably reduced. With an increase in P CO 2 in the IGA more than 45-50 mm Hg. Art. acute hypercapnic disorders occurred very quickly - within 10-15 minutes.

Generalizing the data published in the literature regarding human resistance to the toxic effects of CO 2, as well as establishing the maximum permissible time for a person to stay in an IGA with a high CO 2 content, encounters certain difficulties. They are primarily due to the fact that a person’s resistance to hypercapnia largely depends on the physiological state and, first of all, on the amount of physical work performed. In most known works, studies were carried out with subjects who were in conditions of relative rest and only periodically performed various psychological tests.

Based on a generalization of the results obtained in these works, it was proposed to conditionally identify four different zones of the toxic effect of hypercapnia depending on the value of P CO 2 in the IHA (Fig. 20).

Of significant importance for the formation of physiological reactions and human resistance to hypercapnia is the growth rate of the P CO 2 value in the inhaled gas mixture. When a person is placed in an IGA with high PCO 2 , as well as when he is switched to breathing a gas mixture enriched with CO 2 , a rapid increase in RA CO 2 is accompanied by a more acute course of hypercapnic disorders than with a slow increase in P CO 2 in the IHA. Fortunately, the latter is more typical for the toxic effects of CO 2 under space flight conditions, since the ever-increasing volume of spacecraft cabins determines the relatively slow increase in P CO 2 in the IGA in cases of failure of the air regeneration system. A more acute course of hypercapnia can occur when the spacesuit regeneration system fails. In acute hypercapnia, the difficulty of accurately delineating zones that determine qualitatively different manifestations of the toxic effect of CO 2, depending on the value of P CO 2, is associated with the presence of a “primary adaptation” phase, the duration of which is longer, the higher the CO 2 concentration. The point is that after a person quickly enters an IHA containing a high concentration of CO 2, pronounced changes occur in the body, which, as a rule, are accompanied by complaints of headache, dizziness, loss of spatial orientation, visual disturbances, nausea, lack of air , chest pain. All this led to the fact that the study often stopped after 5-10 minutes. after the subject transitions to hypercapnic IHA.

Published studies show that with an increase in P CO 2 in the IGA to 76 mm Hg. Art. such an unstable state gradually passes and a partial adaptation to the changed gas environment occurs. The subjects show some normalization of intellectual performance, and at the same time complaints of headache, dizziness, visual disturbances, etc. become more moderate. The duration of the unstable state is determined by the time during which RA CO 2 increases and a continuous increase in pulmonary ventilation is noted. Soon after stabilization at a new level of RA CO 2 and pulmonary ventilation, the development of partial adaptation is noted, accompanied by an improvement in the well-being and general condition of the subjects. Such dynamics of the development of acute hypercapnia at large values ​​of P CO 2 in the IHA was the reason for significant discrepancies in the assessment by different researchers of the possible time of a person’s stay in these conditions.

In Fig. 20, when assessing the influence of different values ​​of P CO 2, although “primary adaptation” is taken into account in time, it is not indicated that the physiological state of a person is different during different periods of stay in an IGA with a high CO 2 content. Once again, it is advisable to note that the results presented in Fig. 20 were obtained in studies during which the subjects were at rest. In this regard, the data obtained without appropriate correlation cannot be used to predict changes in the physiological state of cosmonauts in cases of CO 2 accumulation in the IGA, since during the flight there may be a need to perform physical work of varying intensity.

It has been established that a person’s resistance to the toxic effects of CO 2 decreases as the physical activity he performs increases. In this regard, studies in which the toxic effect of CO 2 would be studied in practically healthy people performing physical work of varying severity are of great practical importance. Unfortunately, such information is scarce in the literature, and therefore this issue needs further study. Nevertheless, based on the available data, we considered it appropriate, with a certain approximation, to indicate the possibility of staying and performing various physical activities in the IGA, depending on the value of P CO 2 in it.

As can be seen from the data given in table. 6, with an increase in P CO 2 to 15 mm Hg. Art. long-term performance of heavy physical work is difficult; when P CO 2 increases to 25 mm Hg. Art. The ability to perform moderately heavy work is already limited and performing heavy work is noticeably more difficult. With an increase in P CO 2 to 35-40 mm Hg. Art. the ability to perform even light work is limited. When P CO 2 increases to 60 mm Hg. Art. and more, despite the fact that a person at rest may still be in such an IHA for some time, he already turns out to be practically unable to perform any work. To relieve the negative impact of acute hypercapnia, the best remedy is to transfer the victims to a “normal” atmosphere.

The results of studies by many authors show that a quick switch of people who have been in IHA for a long time with increased PCO 2 to breathing pure oxygen or air often causes a deterioration in their well-being and general condition. This phenomenon, expressed in a sharp form, was first discovered in experiments on animals and described by P. M. Albitsky, who gave it the name of the reverse effect of CO 2. In connection with the above, in cases where people develop hypercapnic syndrome, they should be gradually removed from IGA enriched with CO 2, relatively slowly reducing P CO 2 in it. Attempts to stop hypercapnic syndrome by introducing alkalis - Tris buffer, soda, etc. - did not give lasting positive results, despite the partial normalization of blood pH.

Of certain practical importance is the study of the physiological state and performance of a person in cases where, as a result of the failure of the regeneration unit in the IGA, P O 2 will simultaneously decrease and P CO 2 increase.

With a significant rate of increase in CO 2 and a corresponding rate of decrease in O 2, which occurs when breathing in a closed, small volume, as studies by Holden and Smith have shown, a sharp deterioration in the physiological state and well-being of the subjects is noted with an increase in CO 2 in the inhaled gas mixture up to 5-6% (P CO 2 -38-45 mm Hg), despite the fact that the decrease in O 2 content during this period of time was still relatively small. With a slower development of hypercapnia and hypoxia, as many authors indicate, noticeable impairments in performance and deterioration in physiological condition are observed when P CO 2 increases to 25-30 mm Hg. Art. and a corresponding decrease in P O 2 to 110-120 mm Hg. Art. According to Karlin et al., with 3-day exposure to IGA containing 3% CO 2 (22.8 mm Hg) and 17% O 2, the performance of the subjects was noticeably reduced. These data are in some contradiction with the results of studies that noted relatively small changes in performance even with a more significant (up to 12%) decrease in O 2 in the IGA and an increase in CO 2 in it to 3%.

With the simultaneous development of hypercapnia and hypoxia, the main symptom of toxicity is shortness of breath. The amount of ventilation of the lungs in this case turns out to be more significant than with hypercapnia of equal magnitude. According to many researchers, such a significant increase in pulmonary ventilation is determined by the fact that hypoxia increases the sensitivity of the respiratory center to CO 2, resulting in the combined effect of excess CO 2 and lack of O 2

in IHA does not lead to the additive influence of these factors, but to their potentiation. This can be judged because the amount of pulmonary ventilation turns out to be greater than the amount of ventilation that should have been if the effect of a decrease in RA O 2 and an increase in RA CO 2 were simply added up.

Based on these data and the nature of the observed disturbances in the physiological state, we can conclude that the leading role in the initial period of development of pathological conditions in situations where there is a complete failure of the regeneration system belongs to hypercapnia.

CHRONIC EFFECTS OF HYPERCAPNIA

Study of the long-term effects of elevated levels on the human body and animals; P CO 2 values ​​in IGA made it possible to establish that the appearance of clinical symptoms of the chronic toxic effect of CO 2 is preceded by natural changes in the acid-base balance - the development of respiratory acidosis, leading to metabolic disorders. In this case, shifts occur in mineral metabolism, which, apparently, are adaptive in nature, since they contribute to the preservation of acid-base balance. These changes can be judged by periodic increases in calcium levels in the blood and changes in calcium and phosphorus levels in bone tissue. Due to the fact that calcium enters into compounds with CO 2, with an increase in Pa CO 2, the amount of CO 2 associated with calcium in the bones increases. As a result of shifts in mineral metabolism, a situation arises that promotes the formation of calcium salts in the excretory system, which may result in the development of kidney stones. The validity of this conclusion is indicated by the results of a study on rodents, in which, after long-term keeping in an IGA with P CO 2 equal to 21 mm Hg. Art. and above, kidney stones were found.

In studies involving humans, it was also found that in cases of long-term stay in an IHA with P CO 2 exceeding 7.5-10 mm Hg. Art., despite the apparent preservation of the normal physiological state and performance, the subjects experienced metabolic changes caused by the development of moderate gas acidosis.

Thus, during Operation Hideout, the subjects spent 42 days in a submarine under IGA conditions containing 1.5% CO 2 (P CO 2 - 11.4 mm Hg). Basic physiological parameters, such as body weight and temperature, blood pressure and pulse rate, remained without significant changes. However, when studying respiration, acid-base balance and calcium-phosphorus metabolism, shifts were discovered that were adaptive in nature. Based on changes in the pH of urine and blood, it was found that from approximately the 24th day of stay in an IGA containing 1.5% CO 2, the subjects developed uncompensated gas acidosis. When young healthy men spent a month in an IHA containing 1% CO 2, according to data from S. G. Zharov et al., no changes in blood pH were found in the subjects, despite a slight increase in RA CO 2 and an 8-12% increase in pulmonary ventilation, indicating a slight compensated gas acidosis.

A long stay (30 days) of subjects in an IHA with a CO 2 content increased to 2% led to a decrease in blood pH, an increase in PA CO 2 and an increase in pulmonary ventilation by 20-25%. Under resting conditions, the subjects felt well, but when performing intense physical activity, some of them complained of headaches and rapid fatigue.

When staying in an IGA with 3% CO 2 (P CO 2 - 22.8 mm Hg), the majority of subjects noted a deterioration in their health. In this case, changes in blood pH indicate the rapid development of uncompensated gas acidosis. Staying in such an environment, although possible for many days, is always associated with the development of discomfort and a progressive decrease in performance.

As a result of these studies, it was concluded that a long-term (many months) stay of a person in an IGA with P CO 2 exceeding 7.5 mm Hg. Art., is undesirable, as it can lead to the manifestation of chronic toxic effects of CO 2. Some researchers indicate that when a person stays for 3-4 months in an IGA, the P CO 2 value should not exceed 3-6 mm Hg. Art..

Thus, when assessing the overall effect of the chronic influence of hypercapnia, one can agree with the opinion of K. Schaefer about the advisability of identifying three main levels of increase in P CO 2 in the IGA, which determine the different tolerance of hypercapnia to a person. The first level corresponds to an increase in P CO 2 in the IGA to 4-6 mm Hg. Art.; it is characterized by the absence of any significant effect on the body. The second level corresponds to an increase in P CO 2 in the IGA to 11 mm Hg. Art. In this case, the basic physiological functions and performance do not undergo significant changes, however, there is a slow development of changes in breathing, regulation

acid-base balance and electrolyte metabolism, which may result in pathological changes.

The third level is an increase in P CO 2 to 22 mm Hg. Art. and higher - leads to a decrease in performance, pronounced changes in physiological functions and the development of pathological conditions over different periods of time.

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The atmosphere around us contains many gases. The main percentage is nitrogen (78.08%). This is followed by oxygen (20.95%), argon (0.93%), water vapor (0.5-4%) and carbon dioxide (0.034%). The air also contains hydrogen, helium and other noble gases in small quantities. The concentration of the majority of gases in the atmosphere remains virtually constant. The exceptions are water and carbon dioxide (CO 2), the percentage of which can vary greatly depending on environmental conditions.

The main source of carbon dioxide indoors is humans. In any place where people are - school classrooms and kindergartens, offices and meeting rooms, fitness centers and swimming pools - there is always the possibility of excess carbon dioxide due to people's breathing.

Far from cities, in nature, CO 2 level in air is about 0.035%. In this case, the person feels comfortable. But within the city, especially in crowded transport or enclosed spaces, carbon dioxide can significantly exceed the norm. Scientists have proven that in a percentage of 0.1-0.2% carbon dioxide becomes toxic to humans. Symptoms such as headache or weakness occur from excess carbon dioxide.

Studies of the effect of CO 2 on people's well-being have shown that at high concentrations of this gas in the air, a significant decrease in attention is manifested and chronic fatigue occurs. Moreover, carbon dioxide causes increased morbidity in people. The nasopharynx and respiratory tract are primarily affected, and the number of asthmatic attacks increases. With prolonged exposure to carbon dioxide on the human body, biochemical changes begin to occur in the blood, which leads to hypertension, weakening of the cardiovascular system, etc.

Carbon dioxide needs to be controlled not only in schools, kindergartens and offices, but also in apartments, and especially in bedrooms. Increased levels of carbon dioxide in the apartment can lead to headaches and insomnia.

To normalize carbon dioxide in the air, premises must be equipped with ventilation systems and regularly ventilated. If its concentration often exceeds the norm, air purifiers are additionally installed in the premises.

For plants, the situation is exactly the opposite. First of all, for them, carbon dioxide is a source of carbon for the process of photosynthesis. Numerous experiments have shown that when the air is enriched with carbon dioxide, not only does plant productivity increase and their growth accelerates, but also resistance to various diseases increases. The concentration of carbon dioxide in the air that enters greenhouses from the street turns out to be too low for plants, especially on sunny days, when the process of photosynthesis occurs with greater intensity. Therefore, in greenhouses, people organize special fertilizing with carbon dioxide to improve plant growth and increase yields.

Mushrooms are very sensitive to carbon dioxide. For example, to obtain honey mushrooms with very small caps and long legs, increase the level of carbon dioxide. This unusual shape of these mushrooms simplifies the process of collecting them. Champignon treats carbon dioxide differently at different stages of growth. During the vegetative growth phase, this fungus normally tolerates high concentrations of CO2. But during the period of fruit formation and fruiting, it is necessary to lower the level of carbon dioxide in the room through intensive ventilation and regular supply of fresh air. High carbon dioxide content during this period deteriorates the quality of fruiting bodies and negatively affects their growth.

Not all cases are listed above when CO 2 level measurement is necessary. This led to the appearance of a device called. Depending on the application, gas analyzers have different shapes (portable or stationary), functions (determining the amount of carbon dioxide in the air, leak detection, etc.) and operating principles (mass spectrometry, photoacoustic analysis, and many others).

The operating principle of most stationary carbon dioxide analyzers installed in air control rooms is based on infrared (IR) optical analysis. This method became widely used after the invention of miniature sensors. Carbon dioxide molecules tend to absorb radiation with a wavelength of 4.255 microns (which corresponds to the infrared range). The higher the concentration of carbon dioxide in the air, the lower the amplitude of the transmitted infrared radiation. Carbon dioxide sensor inside the gas analyzer converts the radiation intensity into electric current and the result is displayed on the screen. The radiation source is located inside the device itself. Typically this is an LED or solid state laser.

Often CO 2 gas analyzers are equipped with an audible alarm that notifies about changes in the level of carbon dioxide in the air and allows you to take the necessary measures in time.

The versatility of carbon dioxide analyzers allows them to be easily used in various areas of human activity - at work and at home, in classrooms and gyms, in greenhouses or mushroom farms, at gas stations, in industry and production. They are easy to use and provide constant control of carbon dioxide where you need it.

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