The total lung capacity of an adult male is on average 5-6 liters, but during normal breathing only a small part of this volume is used. When breathing calmly, a person completes about 12-16 respiratory cycles, inhaling and exhaling about 500 ml of air in each cycle. This volume of air is commonly called tidal volume. When you take a deep breath, you can inhale an additional 1.5-2 liters of air - this is the inhalation reserve volume. The volume of air that remains in the lungs after maximum exhalation is 1.2-1.5 liters - this is the residual volume of the lungs.
Lung volume measurement
Under the term measurement of lung volumes usually refers to the measurement of total lung capacity (TLC), residual lung volume (RLV), functional residual capacity (FRC) of the lungs and vital capacity of the lungs (VC). These indicators play a significant role in analyzing the ventilation capacity of the lungs; they are indispensable in the diagnosis of restrictive ventilation disorders and help assess the effectiveness of the therapeutic intervention. Measuring lung volumes can be divided into two main stages: measuring the FRC and conducting a spirometric study.
To determine FRC, one of the three most common methods is used:
- gas dilution method (gas dilution method);
- bodyplethysmographic;
- X-ray.
Lung volumes and capacities
Typically, four pulmonary volumes are distinguished - inspiratory reserve volume (IRV), tidal volume (TI), expiratory reserve volume (ERV) and residual lung volume (RLV) and the following capacities: vital capacity of the lungs (VC), inspiratory capacity (EIV), functional residual capacity (FRC) and total lung capacity (TLC).
The total lung capacity can be represented as the sum of several lung volumes and capacities. Lung capacity is the sum of two or more lung volumes.
Tidal volume (VT) is the volume of gas that is inhaled and exhaled during the respiratory cycle during quiet breathing. DO should be calculated as the average after recording at least six respiratory cycles. The end of the inhalation phase is called the end-inspiratory level, the end of the exhalation phase is called the end-expiratory level.
Inspiratory reserve volume (IRV) is the maximum volume of air that can be inhaled after a normal average quiet inspiration (end-inspiratory level).
Expiratory reserve volume (ERV) is the maximum volume of air that can be exhaled after a quiet exhalation (end-expiratory level).
Residual lung volume (RLV) is the volume of air that remains in the lungs after a full exhalation. TRL cannot be measured directly; it is calculated by subtracting ROvyd from FRC: OOL = FOE – ROvyd or OOL = OEL – Vital. Preference is given to the latter method.
Vital capacity of the lungs (VC) is the volume of air that can be exhaled during a full exhalation after a maximum inhalation. With forced exhalation, this volume is called the forced vital capacity of the lungs (FVC), with a quiet maximum (inhalation) exhalation - the vital capacity of the lungs of inhalation (exhalation) - VVC (VCL). VIC includes DO, ROvd and ROvyd. Vital capacity is normally approximately 70% of TLC.
Inspiratory capacity (EIC) is the maximum volume that can be inhaled after a quiet exhalation (from the end-expiratory level). EDV is equal to the sum of DO and RVD and normally is 60–70% of vital capacity.
Functional residual capacity (FRC) is the volume of air in the lungs and respiratory tract after a quiet exhalation. FRC is also called final expiratory volume. FRC includes ROvyd and OOL. Measuring FRC is a decisive step in assessing lung volumes.
Total lung capacity (TLC) is the volume of air in the lungs at the end of a full inhalation. TEL is calculated in two ways: OEL = OEL + vital capacity or OEL = FFU + Evd. The latter method is preferable.
Measurement of total lung capacity and its components is widely used in various diseases and provides significant assistance in the diagnostic process. For example, with pulmonary emphysema, there is usually a decrease in FVC and FEV1, and the FEV1/FVC ratio is also reduced. A decrease in FVC and FEV1 is also observed in patients with restrictive disorders, but the FEV1/FVC ratio is not reduced.
Despite this, the FEV1/FVC ratio is not a key parameter in the differential diagnosis of obstructive and restrictive disorders. For differential diagnosis of these ventilation disorders, mandatory measurement of TEL and its components is necessary. With restrictive disorders, there is a decrease in TLC and all its components. With obstructive and combined obstructive-restrictive disorders, some components of the TLC are reduced, some are increased.
Measuring FRC is one of two main steps in measuring TLC. FRC can be measured by gas dilution methods, body plethysmography or x-ray. In healthy individuals, all three methods provide similar results. The coefficient of variation of repeated measurements within the same subject is usually below 10%.
The gas dilution method is widely used due to the simplicity of the technique and the relative cheapness of the equipment. However, in patients with severe obstruction of bronchial conduction or emphysema, the true value of TLC when measured by this method is underestimated, since the inspired gas does not penetrate into hypoventilated and unventilated spaces.
The body plethysmographic method allows you to determine the intrathoracic volume (ITV) of gas. Thus, FRC measured body plethysmography includes both ventilated and non-ventilated parts of the lungs. In this regard, in patients with pulmonary cysts and air traps, this method gives higher results compared to the gas dilution method. Body plethysmography is a more expensive method, technically more complex and requires greater effort and cooperation from the patient compared to the gas dilution method. However, the body plethysmography method is preferable because it allows a more accurate assessment of FRC.
The difference between the values obtained using these two methods provides important information about the presence of unventilated air space in the chest. With severe bronchial obstruction, the general plethysmography method may overestimate FRC values.
Based on materials from A.G. Chuchalina
To assess the quality of lung function, it examines tidal volumes (using special devices - spirometers).
Tidal volume (TV) is the amount of air that a person inhales and exhales during quiet breathing in one cycle. Normal = 400-500 ml.
Minute respiration volume (MRV) is the volume of air passing through the lungs in 1 minute (MRV = DO x RR). Normal = 8-9 liters per minute; about 500 l per hour; 12000-13000 liters per day. With increasing physical activity, MOD increases.
Not all inhaled air participates in alveolar ventilation (gas exchange), because some of it does not reach the acini and remains in the respiratory tract, where there is no opportunity for diffusion. The volume of such airways is called “respiratory dead space”. Normally for an adult = 140-150 ml, i.e. 1/3 TO.
Inspiratory reserve volume (IRV) is the amount of air that a person can inhale during the strongest maximum inhalation after a quiet inhalation, i.e. over DO. Normal = 1500-3000 ml.
Expiratory reserve volume (ERV) is the amount of air that a person can additionally exhale after a quiet exhalation. Normal = 700-1000 ml.
Vital capacity of the lungs (VC) is the amount of air that a person can maximally exhale after the deepest inhalation (VC=DO+ROVd+ROVd = 3500-4500 ml).
Residual lung volume (RLV) is the amount of air remaining in the lungs after maximum exhalation. Normal = 100-1500 ml.
Total lung capacity (TLC) is the maximum amount of air that can be held in the lungs. TEL=VEL+TOL = 4500-6000 ml.
DIFFUSION OF GASES
Composition of inhaled air: oxygen - 21%, carbon dioxide - 0.03%.
Composition of exhaled air: oxygen - 17%, carbon dioxide - 4%.
The composition of the air contained in the alveoli: oxygen - 14%, carbon dioxide -5.6%.
As you exhale, the alveolar air is mixed with the air in the respiratory tract (in the “dead space”), which causes the indicated difference in air composition.
The transition of gases through the air-hematic barrier is due to the difference in concentrations on both sides of the membrane.
Partial pressure is that part of the pressure that falls on a given gas. At an atmospheric pressure of 760 mm Hg, the partial pressure of oxygen is 160 mm Hg. (i.e. 21% of 760), in the alveolar air the partial pressure of oxygen is 100 mm Hg, and carbon dioxide is 40 mm Hg.
Gas voltage is the partial pressure in a liquid. Oxygen tension in venous blood is 40 mm Hg. Due to the pressure gradient between alveolar air and blood - 60 mm Hg. (100 mm Hg and 40 mm Hg), oxygen diffuses into the blood, where it binds to hemoglobin, converting it into oxyhemoglobin. Blood containing a large amount of oxyhemoglobin is called arterial. 100 ml of arterial blood contains 20 ml of oxygen, 100 ml of venous blood contains 13-15 ml of oxygen. Also, along the pressure gradient, carbon dioxide enters the blood (since it is contained in large quantities in the tissues) and carbhemoglobin is formed. In addition, carbon dioxide reacts with water, forming carbonic acid (the reaction catalyst is the enzyme carbonic anhydrase, found in red blood cells), which breaks down into a hydrogen proton and bicarbonate ion. CO 2 tension in venous blood is 46 mm Hg; in alveolar air – 40 mm Hg. (pressure gradient = 6 mm Hg). Diffusion of CO 2 occurs from the blood into the external environment.
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Currently, these data are of more academic interest, but existing computer spirographs in a matter of seconds are able to provide information about them that largely objectifies the patient’s condition.
Tidal volume(DO) - the volume of air inhaled or exhaled during each respiratory cycle.
Norm: 300 - 900 ml.
Decrease TO possible with pneumosclerosis, pneumofibrosis, spastic bronchitis, severe pulmonary congestion, severe heart failure, obstructive emphysema.
Inspiratory reserve volume- the maximum volume of gas that can be inhaled after a quiet breath.
Norm: 1000 - 2000 ml.
A significant decrease in volume is observed with a decrease in the elasticity of the lung tissue.
Expiratory reserve volume- the volume of gas that a subject can exhale after a quiet exhalation.
Norm: 1000 - 1500 ml.
Vital capacity of the lungs (VC) Normally it is 3000 - 5000 ml. Considering the large variability in healthy individuals from the proper value by ± 15-20%, this indicator is rarely used to assess external respiration in intensive care patients.
Residual volume (Оо)- the volume of gas remaining in the lungs after maximum exhalation. To calculate the proper value (in milliliters), it is proposed to multiply the first four digits of the third degree of growth (in centimeters) by an empirical coefficient of 0.38.
In a number of situations, a phenomenon called “expiratory airway closure” (ECAC) occurs. Its essence lies in the fact that during exhalation, when the volume of the lungs is already approaching the residual volume, a certain amount of gas is retained in different zones of the lungs (gas traps). A.P. Zilber devoted more than 30 years to the study of this phenomenon. Today it has been proven that this phenomenon occurs quite often in seriously ill patients with lung diseases of any origin, as well as a number of critical conditions. Assessing the degree of ECDP allows for a multifaceted presentation of the clinical pathophysiology of systemic disorders and gives a prognosis and assessment of the effectiveness of the measures taken.
Unfortunately, the assessment of the ECDP phenomenon has so far been more academic in nature, although today dictates the need for widespread implementation of methods for assessing ECDP. We will give only a brief description of the methods used, and we will gladly refer those interested to the monograph by A. P. Zilber (Respiratory Medicine. Etudes of Critical Medicine. Vol. 2. - Petrozavodsk: PSU Publishing House, 1996 - 488 pp.).
The most accessible methods are based on the analysis of the expiratory test gas curve or the pneumotachographic curve when the flow is interrupted. The remaining methods - whole body plethysmography and the method of diluting test gas in a closed system - are used much less frequently.
The essence of the methods based on the analysis of the expiratory curve of the test gas is that the subject inhales a portion of the test gas at the beginning of inspiration, and then the exhalation curve of the gas is recorded, recorded synchronously with the spirogram or pneumotachogram. Xenon-133, nitrogen, and sulfur hexafluoride (SF6) are used as test gases.
To characterize the OADP, one of the indicators characterizing the OADP phenomenon is used - this is lung closure volume. The physiological meaning of this indicator can be understood from the characteristics of the value itself. The VLC is the portion of the vital capacity remaining in the lungs from the moment the airways close to the residual lung volume. VA is expressed as a percentage of vital lung capacity (VC).
Thus, the value of OZL measured by xenon-133 is 13.2 ± 2.7%, and by nitrogen - 13.7 ± 1.9%.
The respiratory flow interruption method, previously used to measure alveolar pressure, with a high degree of correlation (r = 0.81; p<0,001) совпадает с методами, основанными на тест-газах (И. Г. Хейфец, 1978). Определение ОЗЛ данным методом возможно с помощью пневмотахографа любой конструкции.
OZL can be determined by the formula proposed by I. G. Heifetz (1978).
For sitting position The regression equation is:
PV / vital capacity (%) = 0.4 +0.38. age (years) ± 3.7;
For lying position the equation is:
BC/VC (%) = -2.75 + 0.55 age (years).
Although the value of OCL is quite informative, however, to fully characterize the phenomenon of ECDP, it is desirable to measure a number of other indicators: lung closing capacity (LCC), functional residual capacity reserve (RFRC), retained lung gas (RLG).
FOE reserve(RFRC) is the difference between the functional residual capacity (FRC) and the lung closing capacity (LCC), it is the most important indicator characterizing the ECDP.
IN sitting position RFOE (l) can be determined by the regression equation:
RFOE (l) = 1.95 - 0.003 age (years) ± 0.5.
IN lying down position:
RFOE (l) = 1.33 - 0.33 age (years)
V sitting position -
RFRC/VC (%) = 49.1 - 0.8 age (years) + 7.5;
V lying down position -
RFEC/VC (%) = 32.8 - 0.77 age (years).
Determination of the metabolic rate of severe patients is carried out on the basis of O2 consumption and CO2 release. Considering that the metabolic rate changes during the day, it is necessary to repeatedly determine these parameters to calculate the respiratory coefficient. CO2 emissions are measured as total exhaled CO2 multiplied by exhaled minute ventilation.
It is necessary to pay attention to thorough mixing of the exhaled air. CO2 in exhaled air is determined using a capnograph. To simplify the method of determining energy consumption (PE), it is assumed that the respiratory (respiratory) coefficient is 0.8, and it is assumed that 70% of calories are provided by carbohydrates and 30% by fats. Then the energy consumed can be determined by the following formula:
PE (kcal / 24 h) = BCO2 24 60 4.8 / 0.8,
where BCO2 is the total emission of CO2 (it is determined by the product of the concentration of CO2 at the end of exhalation and the minute ventilation of the lungs);
0.8 - respiratory coefficient, at which the oxidation of 1 liter of O2 is accompanied by the formation of 4.83 kcal.
In a real situation, the respiratory coefficient can change hourly in seriously ill patients depending on the methods of parenteral nutrition, the adequacy of pain relief, the degree of anti-stress protection, etc. This circumstance requires monitor (repeated) determination of O2 consumption and CO2 release. To quickly estimate energy consumption, use the following formulas:
PE (kcal/min) = 3.94 (VO2) + (VCO2),
where VO2 is the absorption of O2 in milliliters per minute, and VCO2 is the release of CO2 in milliliters per minute.
To determine energy consumption over 24 hours, you can use the formula:
PE (kcal/day) = PE (kcal/min) 1440.
After transformation, the formula takes the form:
PE (kcal/day) = 1440.
In the absence of the possibility of determining energy consumption using calorimetry, you can use calculation methods, which, naturally, will be approximate to a certain extent. Such calculations are most often necessary for the management of seriously ill patients on long-term parenteral nutrition.
Lung volumes and capacities
During the process of pulmonary ventilation, the gas composition of the alveolar air is continuously updated. The amount of pulmonary ventilation is determined by the depth of breathing, or tidal volume, and the frequency of respiratory movements. During breathing movements, a person’s lungs are filled with inhaled air, the volume of which is part of the total volume of the lungs. To quantitatively describe pulmonary ventilation, total lung capacity was divided into several components or volumes. In this case, the pulmonary capacity is the sum of two or more volumes.
Lung volumes are divided into static and dynamic. Static pulmonary volumes are measured during completed respiratory movements without limiting their speed. Dynamic pulmonary volumes are measured during respiratory movements with a time limit for their implementation.
Lung volumes. The volume of air in the lungs and respiratory tract depends on the following indicators: 1) anthropometric individual characteristics of the person and the respiratory system; 2) properties of lung tissue; 3) surface tension of the alveoli; 4) the force developed by the respiratory muscles.
Tidal volume (VT) is the volume of air that a person inhales and exhales during quiet breathing. In an adult, DO is approximately 500 ml. The value of DO depends on the measurement conditions (rest, load, body position). DO is calculated as the average value after measuring approximately six quiet breathing movements.
Inspiratory reserve volume (IRV) is the maximum volume of air that a subject can inhale after a quiet inhalation. The size of the ROVD is 1.5-1.8 liters.
Expiratory reserve volume (ERV) is the maximum volume of air that a person can additionally exhale from the level of quiet exhalation. The value of ROvyd is lower in a horizontal position than in a vertical position, and decreases with obesity. It is equal to an average of 1.0-1.4 liters.
Residual volume (VR) is the volume of air that remains in the lungs after maximum exhalation. The residual volume is 1.0-1.5 liters.
Lung capacity. Vital capacity of the lungs (VC) includes tidal volume, inspiratory reserve volume, and expiratory reserve volume. In middle-aged men, vital capacity varies between 3.5-5.0 liters and more. For women, lower values are typical (3.0-4.0 l). Depending on the methodology for measuring vital capacity, a distinction is made between inhalation vital capacity, when after a complete exhalation a maximum deep breath is taken, and exhalation vital capacity, when after a full inhalation a maximum exhalation is made.
Inspiratory capacity (EIC) is equal to the sum of tidal volume and inspiratory reserve volume. In humans, EUD averages 2.0-2.3 liters.
Functional residual capacity (FRC) is the volume of air in the lungs after a quiet exhalation. FRC is the sum of expiratory reserve volume and residual volume. The value of FRC is significantly influenced by the level of physical activity of a person and body position: FRC is smaller in a horizontal position of the body than in a sitting or standing position. FRC decreases in obesity due to a decrease in the overall compliance of the chest.
Total lung capacity (TLC) is the volume of air in the lungs at the end of a full inhalation. TEL is calculated in two ways: TEL - OO + VC or TEL - FRC + Evd.
Static lung volumes may decrease under pathological conditions that lead to limited lung expansion. These include neuromuscular diseases, diseases of the chest, abdomen, pleural lesions that increase the rigidity of the lung tissue, and diseases that cause a decrease in the number of functioning alveoli (atelectasis, resection, scar changes in the lungs).
During inhalation, the lungs are filled with a certain amount of air. This value is not constant and may change under different circumstances. The volume of an adult's lungs depends on external and internal factors.
What affects lung capacity?
The level of filling of the lungs with air is influenced by certain circumstances. Men have a larger average organ volume than women. In tall people with a large body constitution, the lungs can hold more air when inhaling than in short and thin people. With age, the amount of air inhaled decreases, which is a physiological norm.
Systematic smoking reduces lung capacity. Low filling capacity is typical for hypersthenics (short people with a rounded body and short, wide-boned limbs). Asthenics (narrow-shouldered, thin) are able to inhale more oxygen.
All people living high relative to sea level (mountainous areas) have reduced lung capacity. This is due to the fact that they breathe thin, low-density air.
Temporary changes in the respiratory system occur in pregnant women. The volume of each lung is reduced by 5-10%. The rapidly growing uterus increases in size and puts pressure on the diaphragm. This does not affect the woman’s general condition, since compensatory mechanisms are activated. Due to accelerated ventilation, they prevent the development of hypoxia.
Average lung volumes
Lung volume is measured in liters. Average values are calculated during normal breathing at rest, without deep inhalations and full exhalations.
The average figure is 3-4 liters. In physically developed men, the volume during moderate breathing can reach up to 6 liters. The normal number of respiratory acts is 16-20. With active physical activity and nervous strain, these numbers increase.
Vital capacity, or vital capacity of the lungs
The vital capacity is the greatest capacity of the lung during maximum inhalation and exhalation. In young, healthy men, the figure is 3500-4800 cm 3, in women – 3000-3500 cm 3. For athletes, these figures increase by 30% and amount to 4000-5000 cm 3. Swimmers have the largest lungs - up to 6200 cm 3.
Taking into account the phases of lung ventilation, the following types of volume are divided:
- respiratory - air that circulates freely through the bronchopulmonary system at rest;
- reserve during inhalation - air filled with the organ during maximum inhalation after a quiet exhalation;
- exhalation reserve - the amount of air removed from the lungs during a sharp exhalation after a calm inhalation;
- residual - air remaining in the chest after maximum exhalation.
Airway ventilation refers to gas exchange for 1 minute.
The formula for determining it is:
tidal volume × number of breaths/minute = minute breathing volume.
Normally, an adult's ventilation is 6-8 l/min.
Table of indicators of the average lung volume:
The air that is located in such parts of the respiratory tract does not participate in gas exchange - the nasal passages, nasopharynx, larynx, trachea, central bronchi. They constantly contain a gas mixture called “dead space”, which is 150-200 cm 3 .
Vital capacity measurement method
External respiratory function is examined using a special test - spirometry (spirography). The method records not only the capacity, but also the speed of air flow circulation.
For diagnostics, digital spirometers are used, which replaced mechanical ones. The device consists of two devices. A sensor for recording air flow and an electronic device that converts measurement indicators into a digital formula.
Spirometry is prescribed to patients with respiratory dysfunction and chronic bronchopulmonary diseases. Calm and forced breathing are assessed, and functional tests are performed with bronchodilators.
Digital data of vital fluid during spirography are distinguished by age, gender, anthropometric data, and the absence or presence of chronic diseases.
Formulas for calculating individual vital capacity, where P is height, B is weight:
- for men – 5.2×P – 0.029×B – 3.2;
- for women – 4.9×P – 0.019×B – 3.76;
- for boys from 4 to 17 years old with a height of up to 165 cm – 4.53×P – 3.9; with height over 165 cm – 10×P – 12.85;
- for girls from 4 to 17 years old the swarm grows from 100 to 175 cm - 3.75×P - 3.15.
Measurement of vital capacity is not carried out for children under 4 years of age, patients with mental disorders, or with maxillofacial injuries. An absolute contraindication is acute contagious infection.
Diagnostics are not prescribed if it is physically impossible to carry out the test:
- neuromuscular disease with rapid fatigue of the striated muscles of the face (myasthenia gravis);
- postoperative period in maxillofacial surgery;
- paresis, paralysis of the respiratory muscles;
- severe pulmonary and heart failure.
Reasons for an increase or decrease in vital capacity indicators
Increased lung capacity is not a pathology. Individual values depend on the physical development of the person. In athletes, VC can exceed standard values by 30%.
Respiratory function is considered impaired if a person’s lung capacity is less than 80%. This is the first signal of insufficiency of the bronchopulmonary system.
External signs of pathology:
Initially, it is difficult to determine violations, since compensatory mechanisms redistribute air in the structure of the total volume of the lungs. Therefore, spirometry is not always of diagnostic value, for example, in cases of pulmonary emphysema and bronchial asthma. During the course of the disease, swelling of the lungs is formed. Therefore, for diagnostic purposes, percussion is performed (low position of the diaphragm, specific “boxy” sound), chest X-ray (more transparent lung fields, expansion of boundaries).
Factors reducing vital capacity:
- reduction in the volume of the pleural cavity due to the development of the cor pulmonale;
- rigidity of the organ parenchyma (hardening, limited mobility);
- high standing of the diaphragm with ascites (accumulation of fluid in the abdominal cavity), obesity;
- pleural hydrothorax (effusion in the pleural cavity), pneumothorax (air in the pleural layers);
- diseases of the pleura - tissue adhesions, mesothelioma (tumor of the inner lining);
- kyphoscoliosis – curvature of the spine;
- severe pathology of the respiratory system - sarcoidosis, fibrosis, pneumosclerosis, alveolitis;
- after resection (removal of part of an organ).
Systematic monitoring of VC helps to track the dynamics of pathological changes and take timely measures to prevent the development of diseases of the respiratory system.
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