Lung ventilation and lung volumes

The magnitude of pulmonary ventilation is determined by the depth of breathing and the frequency of respiratory movements.

A quantitative characteristic of pulmonary ventilation is the minute respiratory volume – the volume of air passing through the lungs in 1 minute. At rest, the frequency of human respiratory movements is approximately 16 to 1 minute, and the volume of exhaled air is about 500 ml. Multiplying the frequency of breathing in 1 minute by the value of the respiratory volume, we obtain the MOD, which in humans at rest is on average 8 l/min.

Maximum ventilation of the lungs – the volume of air that passes through the lungs for 1 minute during the maximum frequency and depth of respiratory movements. Maximum ventilation occurs during intensive work, with a lack of O2 content   (hypoxia) and an excess of CO2 (hypercapnia) in the inhaled air. In these conditions, Maximum ventilation of the lungs can reach 150 – 200 liters in 1 minute.

The volume of air in the lungs and airways depends on the constitutional anthropological and age characteristics of a person, the properties of lung tissue, the surface tension of the alveoli, as well as the strength developed by the respiratory muscles.

To assess the ventilation function of the lungs, the condition of the respiratory tract, the study of the breathing pattern (drawing), various research methods are used: pneumography, spirometry, spirography,pneumoscreen. With the help of a spirograph, it is possible to determine and record the values ​​of the pulmonary volumes of air passing through the airways of a person (Fig. 20).

With a quiet inhale and exhale, a relatively small amount of air passes through the lungs. This is the tidal volume (TO), which in an adult is about 500 ml. In this case, the act of inhalation is somewhat faster than the act of exhalation. Usually, 12-16 respiratory cycles occur in 1 minute. This type of breathing is usually called “ eipnea” or “good breathing.”

When forced (deep) inhale, a person can additionally inhale a certain amount of air. This reserve volume of inhalation (ROVD) is the maximum amount of air that a person is able to inhale after taking a quiet breath. The size of the reserve volume of inspiration in an adult is approximately 1.8 – 2.0 liters.

After a quiet exhalation, a person may, with a forced expiration, additionally exhale a certain amount of air. This is the expiratory reserve volume (POVL1D), the value of which is on average 1.2 – 1.4 l.

The volume of air that remains in the lungs after maximum expiration and in the lungs of a dead person is the residual volume of the lungs (OO). The value of the residual volume is 1.2-1.5 liters. The aborigines of the highlands because of the barrel chest maintain higher values ​​of this index, which makes it possible to preserve the necessary CO2 content in the body, sufficient to regulate respiration in these conditions.

The following lung capacities are distinguished:

1) total lung capacity (OEL) – the volume of air in the lungs after the maximum inhalation – all four volumes;

2) the vital capacity of the lungs (VC) includes respiratory volume, reserve volume of breath, reserve volume of exhalation. VC is the volume of air exhaled from the lungs after the maximum inhalation with maximum exhalation.  Maximum ventilation of the lungs is 3.5–5.0 l for men, 3.0–4.0 l for women;

3) the inhalation capacity (UHP) is equal to the sum of the respiratory volume and the reserve volume of inspiration, averaging 2.0 – 2.5 liters;

4) functional residual capacity – the volume of air in the lungs after a quiet exhalation. In the lungs with a quiet inhale and exhale constantly contains about 2500 ml of air filling the alveoli and lower respiratory tract. Due to this, the gas composition of the alveolar air is kept at a constant level.

The study of pulmonary volumes and capacities as the most important indicators of the functional state of the lungs is of great medical and physiological importance not only for diagnosing diseases (atelectasis, cicatricial lung changes, pleural lesions), but also for environmental monitoring of the area and assessing the state of respiratory function of the population in ecologically unfavorable areas.

For comparability of measurements of gas volumes and capacities, research materials should be brought to the standard state of BTPS, i.e. correlate with the conditions in the lungs, where the temperature of the alveolar air corresponds to the temperature of the body, in addition, the air is at a certain pressure and saturated with water vapor.

The air in the airways (oral cavity, nose, pharynx, trachea, bronchi and bronchioles) does not participate in gas exchange, and therefore the airway space is called harmful or dead respiratory space. During a quiet breath of 500 ml, only 350 ml of inhaled atmospheric air enters the alveoli. The remaining 150 ml linger in the anatomical dead space. Averaging a third of the respiratory volume, the dead space reduces the effectiveness of alveolar ventilation with this value during quiet breathing. In cases where, when performing physical work, the tidal volume is increased several times, the volume of the anatomical dead space has practically no effect on the effectiveness of alveolar ventilation.

In some pathological conditions – with anemia, pulmonary embolism or emphysema, foci may occur – zones of alveolar dead space. In such zones of the lungs does not occur gas exchange.

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