Transcription
Now we will move on to another very important topic, hemodynamic disorders. This section may be particularly interesting as it focuses on blood and circulation. Hemodynamics describes how blood circulates in the body, how it flows through vessels, how fluid is distributed between the bloodstream and tissues, and how organ perfusion is maintained. Hemodynamic disorders occur when blood does not flow in the correct direction or volume, when pressure in the vessel changes, or when coagulation is either excessively activated or impaired. These disturbances are extremely important in clinical practice because they can directly threaten life. Their consequences may include conditions such as shock, thromboembolism, or massive bleeding, and many of these conditions can be life-threatening.
Now, let's go through the main types of hemodynamic disorders. We'll start with one of the most common, edema, which is the accumulation of fluid in the interstitial space or body cavities. Edema itself is not a disease, but rather a manifestation of an underlying pathological process, and it most often develops when there's a disturbance in balance of pressures within the blood vessels. This can involve hydrostatic pressure, which is the pressure exerted by the blood itself, or colloid osmotic pressure, also called oncotic pressure as you know, which is generated by plasma proteins. Additionally, increased capillary permeability or impaired lymphatic drainage can also contribute to edema formation. We will We'll look at specific examples for each of these mechanisms.
So, for example, if hydrostatic pressure is increased, this can occur in conditions such as heart failure. In this case, venous return is impaired, meaning blood accumulates in the capillaries because the heart cannot pump it effectively. As a result, hydrostatic pressure rises, and eventually fluid is forced out of the capillaries into the surrounding tissues, so leading to edema. Another mechanism is reduced oncotic pressure. The main responsible protein for this, as you know already, is albumin. If albumin levels decrease, oncotic pressure also decreases, and fluid is no longer retained within the blood vessels. It begins to leak into the tissues. This can occur, for example, in liver cirrhosis, where the liver is unable to produce sufficient plasma proteins. But, of course, also it's possible in case of other conditions and liver diseases. Then, increased capillary permeability is another cause, which we have already discussed in the context of inflammation and allergic reactions. And finally, edema can also result from impaired lymphatic drainage. Normally, lymphatic vessels remove excess fluid from tissues, but this process can be disrupted. For example, after lymph node removal due to tumors, or also in certain parasitic infections, such as filariasis, where parasitic worms block lymphatic vessels. Clinically, edema can be either localized, for example, in an area of inflammation, or generalized, affecting the whole body. Particularly dangerous forms are pulmonary edema and brain edema as they can be life-threatening.
The next disorder is thrombosis, which is the formation of a blood clot within a blood vessel. These clots can partially or completely block the vessel leading to ischemia, which we will discuss in the next lecture. Thrombi can also become a source of embolism, which we'll cover in the following slide. Classically, thrombosis develops due to several key factors. One of them is endothelial damage, for example, caused by atherosclerosis, inflammation, or trauma. Changes in the vessel wall promote clot formation. Another factor is altered blood flow, particularly turbulent flow, which we have already discussed in hematology. And finally, there may be increased blood coagulability, which can be due to inherited or acquired conditions. When these factors occur together, the risk of thrombus formation increases significantly, of course. And clinically, arterial thrombi often lead to infarction, while venous thrombi are more commonly associated with embolism.
Now, and what is embolism? Most commonly, this term refers to a detached thrombus, a clot that has broken away from the vessel wall and now is traveling through the bloodstream. Once it is moving in the circulation, it is no longer called a thrombus, but an embolus. Technically, however, an embolus can be any material that travels through the bloodstream and blocks a vessel. The most common type, though, is thromboembolism, particularly pulmonary embolism, which is highly significant in clinical practice. Pulmonary embolism can lead to acute right-sided heart strain, severe hypoxia, and in some cases sudden death. Other types of embolism listed here are less common. For example, fat embolism can occur after fractures of long bones such as the femur. This happens when fat from bone marrow enters the bloodstream. Another rare type is air embolism, which can occur if air enters the blood stream. For example, due to improper medical procedures, which is of course not very likely to happen, but also another example could be decompression sickness during diving. In decompression sickness, rapid changes in pressure cause dissolved gases in the bloodstream, mainly nitrogen, to form bubbles, which then block blood vessels. But on the other hand, again, everyone who has tried some kind of diving in their life knows that before the actual happening, there's a diving instructor which gives careful instructions how to not encounter this decompression sickness, and of course other safety measurements are taking place. And finally, a very rare but serious condition is the amniotic fluid embolism, where amniotic fluid enters the maternal circulation during complications such as childbirth or surgical procedures. So, but as I said, it's very rare. But although all these forms are kind of rare, all of them can have severe and potentially life-threatening consequences.
Now, we move on to the next disorder, shock. In everyday language, the word shock is often used to describe an emotional reaction similar to what is visible in my picture here, but medically it has a very different meaning. In physiology, shock refers to a critical generalized decrease in blood flow. As a result, tissues do not receive enough oxygen, and this is known as then inadequate perfusion. Regardless of the cause of shock, the outcome is essentially the same. Cells become deprived of oxygen leading to metabolic acidosis, meaning the tissue environment becomes more acidic. If this condition persists, it ultimately leads, of course, to organ failure. There are several main types of shock, and here we will have four of them.
The first one is hypovolemic shock. Hypo means reduced, of course, and volemic is related to the total volume of blood in circulation, so from the word volume. And why would the circulation lose a large amount of blood? Of course, the first thing that comes to mind is bleeding, but it can also be fluid loss. So, the most common reasons for hypovolemic shock are severe trauma, for example, traffic accidents, major falls, stab or gunshot wounds, but there can also be internal bleeding or massive bleeding during or after surgery. And also severe and prolonged diarrhea, especially if combined with vomiting. So, but these are not just like everyday diarrhea and vomiting, but serious infectious diseases we are talking about here. So, not just food poisoning, but for example, such diseases as typhoid. Also, severe dehydration may occur, for example, if a person is left without water for a long time and burns because in burns fluid shifts into tissues and is lost from circulation. In any case, when blood volume decreases, blood pressure falls, tissue perfusion worsens, and the already mentioned organ failure can develop. And of course, also death if emergency help is not provided.
Next is cardiogenic shock. As the name suggests, it is related to the heart. The most common cause is an acute myocardial infarction, where the heart muscle can no longer contract effectively. It can also be caused by severe arrhythmias, such as ventricular tachycardia or fibrillation, or severe bradycardia. In these cases, the heart works inefficiently, and cardiac output is significantly reduced. Heart failure may also develop after myocardial infarction. There can also be mechanical complications, such as papillary muscle rupture, interventricular septum rupture, or even rupture of the heart wall. In all cases, cardiac output decreases, blood pressure falls, and the result is the same. Tissues and organs do not receive enough oxygen, leading to acute organ failure.
Next is septic shock. This is usually caused by a very severe infection, where the [clears throat] infectious agent enters the bloodstream. Most often, these are bacterial infections, and the common source is pneumonia. It can also come from bacterial infections in urinary tract or abdominal infections. So, if bacteria take the first place regarding these septic infections, then fungi, especially candida, can be involved and are placed in the second place, let's say, particularly in immunosuppressed or hospitalized patients. And the third place is taken up by viruses. Viruses are a less common cause, although severe viral infections can sometimes lead to septic shock. In any case, the presence of pathogens leads to a massive release of inflammatory mediators, which cause vasodilation and increased capillary permeability. As a result, blood pressure drops and tissues are not adequately [clears throat] perfused.
And finally, we have anaphylactic shock. We already discussed this earlier. It is an IgE-mediated allergic reaction. The main mediator is histamine, which causes rapid vasodilation and increased vascular permeability, and so we won't talk about this anymore. In any case, shock is always a life-threatening condition, and early recognition is critically important.
And finally, the last group of hemodynamic disorders is bleeding and disorders of hemostasis. Normally, hemostasis is a precisely regulated system that quickly stops bleeding, but at the same time does not cause thrombosis. We have already discussed this balance in the hematology course, but if this balance is disturbed, pathology develops. Here are a few examples. The first two are mostly inherited conditions. Hemophilia is an X-chromosome-linked recessive disease, where there is a deficiency of clotting factors, and therefore the blood clotting process does not function properly. The second is also mainly inherited, von Willebrand disease. In this case, I think you can also already imagine what's happening here. Von Willebrand factor is not produced properly. That means platelets cannot attach to the vessel wall during primary hemostasis. And this results in impaired platelet adhesion. And finally, a condition we have not discussed before, the disseminated intravascular coagulation syndrome. The result here is that clotting and bleeding occur at the same time because coagulation becomes uncontrollably activated throughout the circulation. And that means that microthrombi form while at the same time clotting factors and platelets become depleted. So, as a result, a paradoxical combination develops from thrombosis together with bleeding. And this is the only disease that is not inherited. It is always secondary to another condition. It can be caused by sepsis, severe trauma, burns, malignancy, severe intoxication, massive hemolysis, or major surgery, among others. Unfortunately, when the syndrome develops, it is associated with a high mortality rate. On the other hand, it is not very often though encountered.
Overall, hemodynamic disorders are a group of conditions that directly affect blood circulation, fluid balance, and organ perfusion. So, to summarize, edema reflects disturbances in fluid balance, thrombosis and embolism threaten organ viability, shock represents a general failure of circulation, and bleeding with hemostatic disorders reflects defects in coagulation. And that is everything I wanted to cover about hemodynamic disorders.