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Types of Hypoventilation Disorders
Depending on the prevailing disturbances in the biomechanics of respiration, obstructive and restrictive types of hypoventilation disorders are distinguished.
The obstructive type is characterized by a decrease in airway patency. The pathogenetic basis of this type of pathology is the increase in resistive, inelastic resistance to air flow. Obstructive ventilation disorders are characterized by a decrease in maximum lung ventilation (MVL) and other dynamic parameters (forced expiratory volume - FEV for 1 second, Tiffno index, FVC / FEV1%, forced expiratory flow - FEP 25-75%, peak volume velocity - Pic, volumetric flow rate throughout the expiration). Static volumes were preserved (residual lung volume - OO, functional residual lung capacity - FOE, total lung capacity - OEL, vital lung capacity - VC). With moderate obstruction, characteristic for moderate asthma, the forced vital capacity of the lungs - FVC does not change. With more significant obstruction, characteristic of severe emphysema, a significant loss of elastic recoil of the lungs causes an increase in OO and FOE. FVC is reduced against this background.
In case of impaired patency of the upper respiratory tract (URV) due to the ingress of foreign bodies into the lumen of the airways, thickening of the walls of the airways due to inflammatory swelling of the mucosa or tumor process, spasm of the muscles of the larynx, compression of the walls of the airways from the outside (tumor growth in the tissues surrounding the airways, pharyngeal abscess, an increase in the volume of neighboring organs - the thyroid gland) develops stenotic respiration. It is characterized by a slower filling of the lungs with air. Such a rare, deep breathing is explained by a weakening inhibitory effect of the Goering-Breyer reflex and an increased influx of impulses from the intercostal muscles. A study of the volumetric air velocity helps to identify the functional types of obstruction of the upper respiratory tract. With a fixed obstruction of the airway trauma (stenosis of the trachea), the air flow rate decreases both in the inspiratory phase and in the exhalation phase. With variable extrathoracic obstruction (paralysis or swelling of the vocal cords), a selective limitation of the volumetric rate of air flow during inspiration is observed. With variable intrathoracic obstruction (tracheal tumor above the bifurcation), the compression of the airways is selectively enhanced during exhalation. Therefore, the speed of the expiratory flow is reduced, and the inspiratory volumetric flow rate remains normal.
Violation of patency of the lower respiratory tract
due to? bronchial or bronchial spasm; the decline of small bronchi with the loss of light elastic properties; narrowing of the lumen of the airways due to the development of edematous-inflammatory changes in the wall of the bronchi; obstruction of bronchioles with pathological contents (blood, exudate); compression of the small bronchi under conditions of increased transmural pressure, for example, when coughing; loss of light elastic properties (emphysema). With obstruction of the lower respiratory tract or loss of light elastic properties, the expiratory phase is difficult. The force of elastic traction of the lungs and walls of the chest is insufficient to expel air from the alveolar spaces. Respiratory muscles become necessary to ensure exhalation. As a result of such active exhalation, intrapleural pressure becomes positive, which leads to an increase in intrapulmonary pressure and expiratory closure of the respiratory tract, causing additional difficulty in exhaling. Obstructive breathing disorders are characterized by expiratory dyspnea. A pneumogram for this type of disorder is characterized by an extension of the expiratory phase.
The restrictive type of hypoventilation disorder occurs due to the restriction of lung expansion in the inspiratory phase.
By origin, intra- and extrapulmonary forms of restrictive disorders are distinguished.
At the heart of the pulmonary form of these disorders is an increase in the elastic resistance of the lungs. For example, with extensive pneumonia, pneumofibrosis, atelectasis, tumors and cysts of the lungs, diffuse proliferation of connective tissue, surfactant deficiency.
Extrapulmonary forms of restrictive disorders arise due to the limitation of chest excursions in case of large pleural effusions, hemo- and pneumothorax, decreased mobility of the ligamentous-articular apparatus of the chest, and mechanical compression of the chest.
A decrease in the ability of the lungs to stretch during inspiration is accompanied by a decrease in the depth of inspiration and an increase in the frequency of respiration, mainly due to the shortening of exhalation. A superficial, rapid type of breathing is formed - tachypnea. In the mechanism of development of the surface type of respiration, reflexes from juxtacapillary receptors of the lungs, chest receptors, and pleura are of some importance.
For hypoventilation disorders of a restrictive type, a decrease in static volumes (VC, FOE, OO, OEL) and a decrease in the driving force of the expiratory flow are characteristic. The function of the airways remains normal, therefore, the speed of the air flow does not undergo changes. Although FVC and FEV1 decrease, the ratio FEV1 / FVC% within normal values or increased. In restrictive pulmonary disorders, a reduced lung volume reduces elastic recoil. Therefore, the forced expiratory flow - FEP between 25% and 75% FVC is reduced in the absence of airway obstruction. Due to the decrease in lung volume, the absolute volumetric air velocity and PIC are also reduced. But the volumetric velocities of the expiratory flow are increased in comparison with the volumetric flow rates in a healthy person with the same lung volume.
Hypoventilation respiratory disorders occur in disorders of regulation of SVD. They are accompanied by gross disturbances in rhythmogenesis, the formation of pathological types of respiration, and the development of apnea.
A change in the gas composition of arterial blood during alveolar hypoventilation is characterized by an increase in Raso2 tension - hypercapnia and a decrease in Rao2 tension - hypoxemia.
Alveolar hyperventilation is accompanied by an increase in MOD, VC, MVL. Can alveolar ventilation result? excessive stimulation of the respiratory center by the excess of exciting afferentation entering it; intoxication; fever; development of exogenous hypoxia; hardware ventilation of the lungs during operations, in the postoperative period, with paralysis and convulsive state of the respiratory muscles.
Alveolar hyperventilation is accompanied by the formation of frequent, deep breathing - hyperpnea. During alveolar hyperventilation, carbon dioxide is released, which leads to a decrease in Pso2 voltage in the alveolar air and in the arterial blood - hypocapnia.
Hyperventilation can cause serious disabilities, due to electrolyte imbalance and acid-base balance. A condition accompanied by hypocapnia contributes to impaired circulation of the heart, brain and inhibition of DC.
Uneven alveolar ventilation accompanies lung pathology, in which obstructive and restrictive ventilation disorders are observed. Violations of the gas composition of arterial blood are characterized by hypoxemia, but do not always lead to hypercapnia.
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Types of Hypoventilation Disorders
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