Gas diffusion disorder

Introduction The process of gas exchange between alveoli and blood through the alveolar-capillary membrane (hereinafter referred to as alveolar membrane) is a physical diffusion process. The amount of gas per unit time depends on the difference in partial pressure of the gas on both sides of the alveolar membrane, the area and thickness of the alveoli, and the diffusion constant of the gas. The diffusion constant is in turn related to the molecular weight and solubility of the gas. In addition, the total amount of gas diffusion is also determined by the time the blood is in contact with the alveoli. Dissemination refers to the process of gas exchange between the alveoli and capillaries, oxygen and carbon dioxide, through the alveolar-capillary membrane. The diffusion function is when the gas partial pressure difference between the alveolar capillary membranes is 0.1333 kPa (1 mmHg); the amount of gas that can pass per minute is an indicator, and the diffusion capacity is expressed. The diffusion capacity of carbon dioxide is strong, larger than oxygen. 21 times, there is no clinical disorder of carbon dioxide diffusion, so the diffusion disorder mainly refers to oxygen. The measurement method is carbon monoxide as a measurement gas. The advantages are: (1) Except for a large number of smokers, the CO of the common person entering the capillary mixed venous blood is almost zero, and no calculation is needed. (2) The affinity of CO and hemoglobin is 210 times that of oxygen. After inhaling a small amount of CO through the capillary membrane to the plasma, it quickly enters into red blood cells and binds to hemoglobin. The partial pressure of CO in plasma is equal to zero, which can be ignored. DLco normal value: 206.2ml / kPa / m Pulmonary oxygen diffusion (Dlo2) = 1.23 × DLco. The amount of dispersion depends on the partial pressure difference of the gas on the membrane, the area of dispersion, the distance, the time, the molecular weight of the gas and its solubility in the dispersion medium. Emphysema and other lung tissue lesions, diffuse pulmonary interstitial fibrosis and other diseases can cause a decrease in diffuse function. Clinically, when the pulmonary lesions produce diffuse dysfunction, there is often a significant ventilatory/blood flow imbalance, which results in hypoxia.

Cause

(1) Reduction of alveolar membrane area: The total alveolar area of normal adults is about 80 m ² , and the alveolar surface area involved in ventilation during resting breathing is only about 35-40 m ² , which increases during exercise. Due to the large reserve, the ventilatory dysfunction will only occur when the alveolar membrane dysfunction is reduced. The reduction of the alveolar membrane area can be seen in the consolidation of the lungs, lung insufflation, and lobectomy.

(2) Increase in alveolar membrane thickness: The thin part of the alveolar membrane is a gas exchange site, which is composed of alveolar epithelium, capillary endothelium and a basement membrane shared by both, and its thickness is less than 1 m. Although the gas from the alveolar cavity to the red blood cells needs to pass through the liquid layer on the surface of the alveoli, the plasma layer in the tube, and the erythrocyte membrane, the total thickness is also less than 5 m. Therefore, normal gas exchange is very fast. When pulmonary edema, alveolar hyaline membrane formation, pulmonary fibrosis, alveolar telangiectasia, or thinning leads to thickening of the plasma layer, the diffusion of the alveolar membrane or the widening of the diffusion distance may affect the gas dispersion.

(3) The contact time between blood and alveoli is too short: when resting normally, the blood flows through the alveolar capillaries for about 0.75 sec. Since the alveolar membrane is very thin and has a wide contact with the blood, only 0.25 sec hemoglobin is needed. Can be fully oxygenated. When the blood flows through the alveolar capillaries for too short a time, the amount of gas diffusion will decrease. In patients with reduced alveolar membrane area and increased thickness, although the oxygen partial pressure in the blood of the pulmonary capillaries rises slowly, the gas exchange in the lungs can still reach equilibrium at rest, so that hypoxemia is not caused, often only in When the physical load is increased, the blood flow will be accelerated, the blood and alveolar contact time will be shortened, and a significant diffusion disorder will occur, thereby causing hypoxemia. It is currently believed that respiratory failure occurs in alveolar lesions, mainly due to the imbalance of blood flow in alveolar ventilation.

an examination

Related inspection

Lung ventilation imaging lung diffusion function test (DL) lung biopsy

Dissemination refers to the process of gas exchange between the alveoli and capillaries, oxygen and carbon dioxide, through the alveolar-capillary membrane. The diffusion function is when the gas partial pressure difference between the alveolar capillary membranes is 0.1333 kPa (1 mmHg); the amount of gas that can pass per minute is an indicator, and the diffusion capacity is expressed. The diffusion capacity of carbon dioxide is strong, larger than oxygen. 21 times, there is no clinical disorder of carbon dioxide diffusion, so the diffusion disorder mainly refers to oxygen. The measurement method is carbon monoxide as a measurement gas. The advantages are: (1) Except for a large number of smokers, the CO of the common person entering the capillary mixed venous blood is almost zero, and no calculation is needed.

The affinity of CO and hemoglobin is 210 times that of oxygen. After inhaling a small amount of CO through the capillary membrane to the plasma, it quickly enters into red blood cells and binds to hemoglobin. The partial pressure of CO in plasma is equal to zero, which can be ignored.

DLco normal value: 206.2ml / kPa / m

Pulmonary oxygen diffusion (Dlo2) = 1.23 × DLco.

The amount of dispersion depends on the partial pressure difference of the gas on the membrane, the area of dispersion, the distance, the time, the molecular weight of the gas and its solubility in the dispersion medium. Emphysema and other lung tissue lesions, diffuse pulmonary interstitial fibrosis and other diseases can cause a decrease in diffuse function. Clinically, when the pulmonary lesions produce diffuse dysfunction, there is often a significant ventilatory/blood flow imbalance, which results in hypoxia.

Differential diagnosis

The gas diffusion function is reduced : the diffusion function is a measure of the ventilation function. It is used to evaluate the efficiency of gas exchange of alveolar capillary membranes. A diagnosis can be made by a clinical examination of vital capacity.

Males were (28.84±4.84) ml/(mmHg.min) and females were (22.13±3.09) ml/(mmHg.min). Below this value, the gas diffusion function decreases.

Pulmonary hyperinflation : what is commonly referred to as emphysema. Emphysema refers to the airway elasticity of the distal bronchioles (breathing bronchioles, alveolar ducts, alveolar sacs, and alveoli), excessive expansion, inflation, and increased lung volume or pathological conditions associated with airway wall destruction. . According to the cause of the disease, emphysema has the following types: senile emphysema, compensatory emphysema, interstitial emphysema, focal emphysema, paraventricular emphysema, obstructive pulmonary qi swollen.

Hyperventilation syndrome: It is a body and heart disease. Excessive fatigue and mental stress irritate the nerves of the plant and cause an increase in respiratory rate. This causes both inhaled oxygen and exhaled carbon dioxide to increase, but the oxygen in the blood is saturated, so too much oxygen cannot be exchanged into the blood, which is equivalent to excessive CO ² emission. While CO ² is the raw material of H ₂ CO ³ in the blood, the blood H ₂ CO ^{3 is} reduced, disrupting the blood acid-base balance and causing respiratory alkalosis. If not improved, it may cause organ failure.

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