How quickly pulmonary edema develops
• The most common causes of pulmonary edema:
- Heart failure (it can be the result of myocardial infarction, heart disease, exudative pericarditis, accompanied by compression of the heart, hypertensive crisis, arrhythmias.
-Toxic substances that increase the permeability of the walls of microvessels of the lungs (for example, some warfare agents such as phosgene, organophosphorus compounds, carbon monoxide, pure oxygen under high pressure).
• Mechanism of the development of pulmonary edema with heart failure (Figure 12-16).</ strong>
The initial and primary pathogenetic factor of pulmonary edema in heart failure - hemodynamic. It is the result of a decrease in the contractile function of the left ventricular myocardium and a reduction in cardiac output. This leads to :
-increase in residual systolic blood volume in the left ventricle of the heart;
- increase in the final diastolic volume and pressure in the left ventricle of the heart;
- increase in blood pressure in the vessels of the small circle of blood circulation above 25-30 mm Hg and an increase in the effective hydrodynamic pressure. When he has an effective oncotic suction force, the transudate enters the intercellular space of the lungs (develops interstitial edema ).
When accumulated in the interstitium of a large amount of edematous fluid, it penetrates between the cells of the endothelium and the epithelium of the alveoli, filling the cavities of the latter (develops alveolar edema ). In this connection, gas exchange in the lungs is disrupted, respiratory hypoxia (aggravating existing circulatory) and acidosis develop. This requires, even with the first signs of pulmonary edema, the carrying out of urgent medical measures
STILL Insert file "PF Figure 12 16 Pathogenesis of pulmonary edema in heart failure"
Rice .12-16 .Pathogenesis of pulmonary edema with heart failure .
• Mechanism of development of pulmonary edema under the influence of toxic substances (Figure 12-15).
The initial and the main pathogenetic factor is the membranogenic (leading to an increase in the permeability of microvessel walls). Causes this is: - toxic substances (for example, fighting poisonous types of phosgene) and / or - high concentration of oxygen, especially under increased pressure. In the experiment it was shown that for pO2 respiratory mixture above 350 mm Hg. develops edema of the lungs and hemorrhages in them. The use of 100% oxygen in the course of ventilation leads to the development of pronounced interstitial and alveolar edema, combined with signs of endothelial and alveolocyte destruction. In this regard, in the clinic for the treatment of hypoxic conditions, gas mixtures with 30-50% oxygen concentration are used. This is sufficient to maintain adequate gas exchange by intact lungs.
The greatest value in increasing the permeability of the walls of blood vessels under the action of toxic substances have:
- acidosis ( which potentiates non-enzymatic hydrolysis of the basic substance of the basement membrane of microvessels);
- increase (in conditions of acidosis)activity of hydrolytic enzymes;
- the formation of "channels" between the rounded damaged cells of the endothelium.