Head of the Department, professor ___ F.A.Mindubaeva

Ф КГМУ 4/3-04/02

ИП №6 от 14 июня 2007 г.

KARAGANDA STATE MEDICAL UNIVERSITY

Department: PHYSIOLOGY

LECTURE

Topic: " Physiological methods of research respiration. Features at children "

Регуляция дыхания. Особенности дыхания в различных физиологических условиях. Особенности дыхания у детей.

Regulation of respiration. Features of the breath at various physiological conditions. Features breathing in children.

Discipline FIZ-2 3208 «Physiology-2»

Specialty «General medicine» 5В130100

Course: 3

Duration 1 hour

Compliers: professor F.A. Mindubaeva

Ass. Prof. N.M. Kharissova

Karaganda 2014

Confirmed at the methodical meeting of the Department of Physiology

Protocol № 2 of 03.09.2012.

Head of the Department, professor _______________ F.A.Mindubaeva

 Topic «Physiological methods of research respiration. Features at children»

 Purpose: to give the basic concepts about respiratory system, its role in an organism, breath stages. To state breath and exhalation mechanisms, to show a role of negative pressure in a pleural cavity for breath.

 Brief contents:

1. The characteristic of respiration

2. Stages of respiration.

3. Surfactant system of lungs.

4. An origin of negative pressure in a chest cavity and its value for breath and blood circulation.

1. Concept about pneumothorax.

6. External breath.

1. The breath mechanism (inspiration).

8. The exhalation mechanism (exspiration).

9. "Dead" air space.

10. The first breath of the newborn.

Pulmonary ventilation (exchange of air) occurs due to the periodic changes in the volume of the thoracic cavity, which increases on inspiration and decreases on expiration. Inspiratory and expiratory phases comprise the respiratory cycle. During inspiration atmospheric air enters the lungs through the airways and during expiration part of it escapes into the en­vironment.

The volume of the thoracic cavity is changed at the expense of respiratory muscle contractions. The inspiratory muscles on contraction in­crease the volume of the thoracic cavity; contraction of the expiratory muscles leads to its decrease.

Inspiration results from contraction of the inspiratory muscles. During quiet breathing expiration proceeds in a passive manner at the expense of elastic energy accumulated during the preceding inspiration. On deep ex­piration the expiratory muscles contract, which is known as active, expira­tion.

Respiratory muscles. The muscular part of the diaphragm is the main inspiratory muscle which consists of striated fibres. On contraction of its lateral parts, which constitute the costal-diaphragmatic sinuses, the upper portion.of the diaphragm, including the central tendon, is pulled downward (Fig. 145). The incompressible organs located in the abdominal cavity are pulled downward and to the sides to distend the abdominal walls. During quiet inspiration the dome of the diaphragm descends by approximately 1.5 cm to increase vertical dimension of the thoracic cavity. Besides, contraction of the diaphragm is attended by elevation and out­ward displacement of the six lower ribs, which increases the volume of the thoracic cavity.

The inspiratory muscles comprise the vexternal intercostals and intercar-tilaginous parts of the internal intercostal muscles. Owing to the oblique orientation of their fibres the distance from the point where the ribs are at­tached to the spine and cartilages to the sternum is larger at the lower than at the upper ribs. Consequently, the moment offeree that determines lever movement is greater for the lower rib or cartilage (Fig. 146). Only the inter-cartilaginous parts of the internal intercostals and the intercostals of the upper three-five intercostal spaces are excited during quiet breathing. As a result of elevation of the ribs, the sternum is shifted toward the front, and the rib sides move outward.

In very deep breathing inspiration is accomplished by a number of ac cesory respiratory muscles which elevate the ribs. These are the scalenus, the major and minor pectoralis and the serratus anterior muscles. The ac­cessory inspiratory muscles also comprise muscles that draw the thoracic spine and the shoulder girdle backward (the trapezius, rhomboidei and the| levatores scapulae muscles)

The abdominal muscles (the external and internal oblique, transverswif abdomtnts and recius abdominis) in active expiration. As a result, the volume of the abdominal cavity decreases, while pressure in it rises. This pressure is transmitted to the diaphragm through the abdominals organs due to which the diaphragm is elevated. On contraction, the internal intercostal muscles cause the ribs to descend, their sides come closer to each other since the moment of force is greater for the upper than for the lower rib. The. accessory expiratory muscles- include muscles that participate in bending of the spine.

Intrapleural Pressure

The lungs and walls of the thoracic cavity are lined with the serous membrane or pleura. A narrow space (5-10 /mm) between the layers of the I visceral and parietal pleura contains serous fluid which resembles lymph in composition. The lungs remain constantly expanded.

If a needly connected to a manometer is introduced into the pleural space, the readings of the manometer will show the pressure in it to be below atmospheric. Negative pressure in the pleura! space is conditioned by the, elastic recoil force of the lungs, i.e. a tendency to decrease their volume. At the end of a quiet expiration, when almost all the respiratory muscles are relaxed, the pleural pressure (P_pl) approximates —3 cm H₂O. The alveolar pressure (P_A) at the same time is equal to atmospheric. The difference P_A-P_pl = 3 cm H₂O is known as the transpulmonary pressure (P_L). Thus, pressure in the pleural space is less than that in the alveoli by the magnitude created by the elastic recoil force of the lungs.

During inspiration the volume of the thoracic cavity increases because, of contraction of inspiratory muscles. The pleural pressure becomes 'more negative'. By the end of quiet inspiration it reduces to - 6 cm H₂O. Owing to increase in transpulmonary pressure the lungs become expanded, their volume increases at the expense of atmospheric air.

When the inspiratory muscles are relaxed, the elastic forces of ex­panded lungs and abdominal walls reduce the transpulmonary pressure and lung volume decreases, thus giving rise to expiration.

The mechanism of lung volume changes during breathing as demon­strated by means of Donders model (Fig. 147).

In deep inspiration, the intrapleural pressure can be reduced to - 20 cm X H₂O. During forced expiration it can become positive but still it is below alveolar pressure by the magnitude created by the elastic recoil force of the lungs.

Normally, no gases are contained in the pleural space. If certain air: volume is introduced into it, air will gradually resolve. Suction of gases from the pleural space occurs because the tension of resolved gases in the blood of fine lung veins is below atmospheric. Accumulation of fluid in the pleural space is hindered by oncotic pressure: the protein content in pleural fluid is significantly less than that in blood plasma. Relatively low ^hydrostatic pressure in lung vessels is also of importance.

Elastic properties oithe lungs. The elastic recoil force of the lungs is conditioned by two factors: (1) surface tension in the alveolar fluid film lining the alveoli and (2) tissue elasticity of the alveolar walls due to the presence in them of elastic fibres. Removal of forces of surface tension (by introducing saline solution into the lungs) reduces the elastic recoil force of.the lungs by two-thirds.

Suppose there was an aqueous layer in the alveolar wall. Then thesurface tension would be 5-8-fold greater. It might seem that under such conditions some of the alveoli would collapse (a condition known as atelectasis) and other remain overstretched. This does not occur, however, because the fluid layer of the alveolar wall contains the so-called surfactants, i.e. surface active substances with low surface tension. The alveolar fluid film is 20-100 nm thick and contains lipids (mainly lecithin) and proteins. It is formed by special alveolar cells, the prieumocytes of type. The surfactant film has a remarkable property as the size of alveoli is decreased, the surface tension is lowered to contribute to a stable state of alveoli.

The elastic properties of the lungs are expressed quantitatively by the so-called.compliance

where DV_L are changes in lung volume; DP_L, transpulmonary pressure changes, In adults it is approximately 200 ml/cm H₂O, in infants—5-10 ml/cm H₂O. This parameter is determined in lung diseases for diagnostic purposes.

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