Cardiovascular Physiology Lecture 1 PDF

Introduction ============ The learning objectives for this course are as follows: - to understand the fundamental science behind the cardiovascular system and - to apply this knowledge to basic clinical scenarios. There are two primary textbooks for this course: *Cunningham* and *Sjaasta...

Introduction ============ The learning objectives for this course are as follows: - to understand the fundamental science behind the cardiovascular system and - to apply this knowledge to basic clinical scenarios. There are two primary textbooks for this course: *Cunningham* and *Sjaastad*. Both texts are highly recommended. While I personally prefer *Cunningham*, many others favor *Sjaastad* due to its excellent diagrams. The cardiovascular system is vital to life What is cardiovascular physiology? It is the study of the heart, blood vessels, and blood. We will cover all these topics throughout the course. As mentioned, the cardiovascular system is essential for sustaining life. What happens if the heart stops? When the heart ceases to function, circulation halts, leading to unconsciousness within one minute. Irreversible damage to the brain and other tissues occurs within a few minutes, followed by death. This is due to insufficient blood flow to tissues and a lack of oxygen, a condition known as **ischemia**. Ischemia can result in irreversible tissue damage, known as an **infarct**. Anatomy of the heart ==================== The image above shows a section through the heart, revealing the inner surfaces. The left side of the heart has a significantly thicker wall than the right side because it must pump blood throughout the body, whereas the right side only pumps blood to the lungs. You can also observe the right side of the heart, with the tricuspid valve situated between the right atrium and ventricle. The tricuspid valve is so named because it has three cusps, while the mitral, or bicuspid valve, located on the left side, has two cusps. These are visible in the short-axis view of the valves. In this view, the tricuspid valve with its three cusps and the bicuspid (or mitral) valve with its two cusps are clearly distinguishable. Additionally, the aortic and pulmonary valves can also be observed. These short-axis views are critical in cardiology, especially when performing ultrasound imaging of the heart, as they allow us to identify potential issues. In the top image, the tricuspid and mitral valves are shown open together, while in the bottom image, the aortic and pulmonary valves are open simultaneously. Distribution of cardiac output ==============================  This graph illustrates the distribution of cardiac output, i.e., the amount of blood each organ receives with every heartbeat. You will notice that **the kidneys, skeletal muscles, brain, and digestive tract receive a significant proportion of cardiac output.** The pink bars represent the organ\'s weight as a percentage of body mass. For instance, although the **kidneys** account for a small percentage of body mass, they receive nearly 20% of cardiac output. Similarly, the **skeletal muscles** receive 20% of cardiac output but constitute approximately 40% of body mass. The **brain** also receives a large portion of cardiac output relative to its body weight. Functions of the cardiovascular system ====================================== The cardiovascular system performs numerous essential functions, acting as a transporter and communication route for various processes, including respiration, nutrition, excretion, and the maintenance of acid-base balance. It also regulates water balance, body temperature, hormones, and hemostasis. This table provides **examples of the substances transported by the cardiovascular system**, though you are not required to memorize it. For example, oxygen is transported from the lungs to all cells. Other examples include immune cells and antibodies, clotting proteins available in the blood at any site, hormones secreted by endocrine cells and delivered to target cells, and nutrients stored in the liver and distributed to cells when needed. Components of blood =================== Next, let's briefly discuss the components of blood. Below, you can see whole blood, which appears red. However, when a blood sample is taken from an animal on tubes added with anticoagulants such as heparin or EDTA, and subsequently centrifuged or left to settle for a day, the **red blood cells** will sink to the bottom. Above the red blood cells lies a layer of **white blood cells**, known as the **buffy coat**, and above that is the **plasma**, which contains primarily water, proteins, electrolytes, and other substances. The **packed cell volume** refers to the **percentage of red blood cells in a blood sample**. Numerous other blood parameters can be measured, such as protein levels, white blood cell subsets (which indicate inflammation), and platelet counts (which assess clotting issues). Various biochemical tests can also be conducted.  Blood and oxygen transport ========================== --------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ A picture containing person, person, comb, wooden Description automatically generated The majority of oxygen in the blood is carried by hemoglobin molecules within red blood cells. Oxygenated hemoglobin is bright red, but when oxygen is released, oxyhemoglobin becomes reduced or deoxygenated, turning a darker blue-red. The oxygenation status of an animal's blood can be assessed by observing the mucous membranes, such as the gums (on dogs) or the inside surfaces of the eyelids (on large animals). Cyanosis, which means blue, occurs when blood or tissue is poorly oxygenated. For example, in pigs with African Swine Fever, a viral infection in which the virus infects capillary endothelial cells, causing cyanosis in the extremities, such as the tips of the ears, because blood is not delivered. --------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Similarly, a dog's dark mucous membranes indicate poor oxygenation, which can be due to cardiovascular or other health issues.  A close up Description automatically generated ----------------------- ------------------------------------------------  Pressure, flow and resistance ============================= Let us now consider pressure, flow, and resistance within blood vessels. Blood flows from areas of higher pressure to areas of lower pressure. The pressure exerted is called hydrostatic pressure, a key concept not only for this course but also for your broader veterinary education. The parameters are: - Blood flow, measured in liters per minute, and - blood pressure, measured in millimeters of mercury.  The radius of blood vessels can change due to nerve activity and local factors, causing vasodilation or vasoconstriction. Even small changes in vessel diameter can significantly impact blood flow and can help compensate for various disease conditions. Blood pressure varies throughout the vascular system. For instance, major arteries like the aorta have much higher blood pressure than veins such as the vena cava. As blood moves through arteries, arterioles, capillaries, and veins, the pressure decreases because of the flow from high-pressure to low-pressure areas.  Oncotic pressure, hydrostatic pressure and Starling's forces ============================================================ +-----------------------------------+-----------------------------------+ | Now, I would like to introduce | http://upload.wikimedia.org/wikip | | the concept of oncotic pressure, | edia/commons/0/03/Illu\_capillary | | which is highly relevant to this | \_microcirculation.jpg | | course. As we discussed earlier, | | | plasma proteins have numerous | | | functions and one of them is to | | | exert osmotic pressure on blood | | | vessels, encouraging water to | | | move into the vessels. One the | | | most important ones is albumin. | | | This process prevents water from | | | leaking into surrounding tissues. | | | | | | Hydrostatic pressure is the | | | pressure of blood in the confined | | | space of the blood vessels. | | | | | | Oncotic pressure is the opposing | | | pressure due to the proteins in | | | the bloodstream. Oncotic pressure | | | retains fluid in the blood | | | vessels. | | +-----------------------------------+-----------------------------------+ Clinical case ============= To conclude, here is a clinical case study of a six-month-old female goat presenting with lethargy and difficulty breathing over the past month. The goat has access to pasture, but no treatments have been administered. On clinical examination, the goat appears slightly thin with pale mucous membranes, elevated pulse and respiratory rates, and fluid accumulation under the jaw (edema). What might be the cause of these symptoms? +-----------------------------------+-----------------------------------+ | **History:** |  | | | | | A 6-month-old female kid goat is | | | presented for lethargy and | | | difficulty breathing that | | | developed over the last month. It | | | has access to pasture. No | | | treatments have been given. | | | | | | **Clinical examination:** | | | | | | The goat is thin and has pale | | | mucous membranes. The pulse and | | | respiratory rates are increased. | | | There is a swelling (with fluid) | | | under the jaw. | | | | | | **What is the cause of the edema | | | and clinical signs in this | | | goat?** | | | | | | **What's important here?** | | | | | | - Pale mucous membranes | | | | | | - Increased pulse and | | | respiratory rates | | | | | | - Edema | | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | | The pale mucous membranes suggest | | | anemia. | | | | | | The image below (next page) shows | | | a sheep with similarly pale | | | mucous membranes, which can also | | | be seen in goats. | | | | | | Anemia is confirmed through a | | | blood sample revealing low plasma | | | protein levels and a low packed | | | cell volume, indicating a reduced | | | number of red blood cells. | | | | | | Fecal analysis reveals the | | | presence of *Haemonchus | | | contortus*, a blood-sucking | | | parasite found in the abomasum of | | | sheep and goats. | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ |  | To relate this case to our | | | lecture, the **anemia** limits | | | oxygen delivery to the organs, | | | **causing elevated respiratory | | | and heart rates** as the body | | | attempts to compensate for | | | reduced oxygen levels. | | | | | | The **edema** is due to | | | **hypoproteinemia**, which | | | results in water leaking from | | | capillaries into surrounding | | | tissues, causing dependent edema, | | | as seen in the soft swelling | | | under the sheep's jaw ("bottle | | | jaw", classic sign of | | | *Haemonchus*). | | | | | | *Haemonchus contortus* causes | | | anemia by consuming blood, | | | leading to a loss of red blood | | | cells and plasma proteins, | | | ultimately resulting in edema. | +-----------------------------------+-----------------------------------+