perfusion

• perfusion refers to the flow of blood through arteries and capillaries delivering nutrients and oxygen to cells.

  normal physiological process that requires the heart to generate sufficient outputs to transport through patient blood vessels for distribution to tissues throughout the body
• Stroke volume is the difference between end-diastolic and end-systolic volumes; it is the volume ejected with each heartbeat. The normal range is 50 to 100 ml. In the ICU, stroke volume is usually measured by a pulmonary artery catheter and is reported as cardiac output
• Systole = the pressure when the heart contracts Diastole = pressure reading that refers to the amount of pressure in the arteries while the heart is resting (in between beats)
• The concept of perfusion and problems associated with impaired perfusion represent a wide range of physiological processes and conditions. The scope of perfusion ranges from optimal perfusion to no perfusion.
• Variations in perfusion are seen among individuals across the lifespan with multiple causative factors and a wide range of impact and duration. Changes in perfusion can be temporary, long-term, or permanent.
• disorders that lead to changes in perfusion include acute conditions (such as myocardial infarction, stroke, or shock) and chronic disorders (such as hypertension)
• Conditions that specifically involve perfusion include neurologic conditions (interfering with blood flow within the brain), pulmonary (impairing blood flow to and from the lungs), and cardiovascular (interfering with blood flow in heart, arteries and veins). Causes of these disorders include congenital defects, genetic disorders, injury, inflammation, and infections.
• Left Ventricle - Oxygenated blood is pumped from the left ventricle of the heart into the aorta, the largest artery in the body.
• Aorta and Arteries - The aorta branches into a network of arteries that carry oxygen-rich blood to all parts of the body.
• Arterioles and Capillaries - Arteries branch into smaller arterioles, which further divide into capillaries. Capillaries are the site of nutrient and gas exchange between blood and tissues. Oxygen and nutrients diffuse from the blood into the tissues, while carbon dioxide and waste products move from the tissues into the blood.
• Venules and Veins - Capillaries converge into venules, which in turn merge into veins. These veins carry deoxygenated blood back to the heart.
• Venae Cavae - The systemic veins converge into the superior and inferior venae cavae, the two large veins that return deoxygenated blood to the right atrium of the heart.
• Pulmonary Circulation: Right Atrium - Deoxygenated blood from the body enters the right atrium via the superior and inferior venae cavae.
• Right Ventricle - Blood flows from the right atrium into the right ventricle. Pulmonary Arteries - The right ventricle pumps the deoxygenated blood into the pulmonary trunk, which splits into the right and left pulmonary arteries. These arteries carry blood to the lungs.
• Lungs - In the lungs, pulmonary arteries branch into smaller arterioles and then into capillaries surrounding the alveoli (air sacs). Here, carbon dioxide is exchanged for oxygen through the process of respiration. Carbon dioxide is exhaled, and oxygen is absorbed into the blood.
• Pulmonary Veins - Oxygenated blood is collected from the capillaries into venules and then into pulmonary veins. There are typically four pulmonary veins, two from each lung.
• Left Atrium - Pulmonary veins return the oxygenated blood to the left atrium of the heart. Left Ventricle: Blood flows from the left atrium into the left ventricle, completing the circuit and readying it for another cycle through systemic circulation.
• Oxygenation: The primary function of pulmonary circulation is gas exchange – removing carbon dioxide and replenishing oxygen.
• Distribution: The systemic circulation distributes oxygenated blood to tissues and organs and returns deoxygenated blood to the heart.
• Pressure Differences: Systemic circulation operates under higher pressure compared to pulmonary circulation, as it needs to deliver blood throughout the entire body. Pulmonary circulation operates under lower pressure because it only needs to move blood through the lungs.
• Ischemia is a reversible cellular injury that occurs when the demand for oxygen exceeds the supply because of a reduction or cessation of blood flow. When ischemia is prolonged, it may result in a lack of oxygen to tissues followed by necrosis and irreversible cellular injury. Examples are myocardial ischemia causing angina or chest pain from reduced blood flow and myocardial infarction causing cardiac arrest and cardiogenic shock with permanent damage to affected areas of the myocardium
• Infarction specifically refers to an obstruction of the blood supply to an organ or region of tissue, typically by a thrombus or embolus (An embolus is a particle or mass that flows through the bloodstream. A thrombus is a blood clot in a blood vessel. If a thrombus breaks off, it can become an embolus), causing local death of the tissue
• Hypoxia and anoxia are examples of the interrelationship between the cardiovascular and respiratory systems because cells are deprived of oxygen from the lack of blood flow, from the lack of oxygen, or both
• Central perfusion is generated by cardiac output, which is the amount of blood the heart pumps each minute. Cardiac output results from the coordinated effects of electrical and mechanical factors that move blood through the heart into peripheral vessels. It propels blood to all organs and tissues through arteries and capillaries, then returns blood to the heart through veins.
• Systole - Electrical impulses from the sinoatrial (SA) node travel to the atrioventricular (AV) node, then through the bundle of His and Purkinje fibers, causing ventricles to contract. This closes the mitral and tricuspid valves to prevent backflow and opens the aortic and pulmonic valves, ejecting blood into the aorta and pulmonary arteries.
• Diastole - As ventricles relax, blood fills them from the atria once atrial pressure exceeds ventricular pressure, opening the mitral and tricuspid valves.
• Cardiac Output: Normal range is 4 to 6 L/min and it is influenced by: 1) Stroke Volume - blood ejected per contraction which is affected by Preload, Contractility (Frank-Starling Law) and Afterload. 2) Heart Rate - Controlled by the autonomic nervous system (sympathetic increases, parasympathetic decreases).
• Tissue perfusion is the blood flow through arteries and capillaries to target tissues
• Arterial Blood Pressure: Determined by cardiac output and systemic vascular resistance (SVR).
• Ventricular contraction generates pressure to push blood through arteries, into capillaries, and into interstitial spaces, delivering oxygen, fluids, and nutrients to cells. Arteries and arterioles maintain blood pressure by constricting or dilating in response to stimuli.
• Venous Return: Blood returns to the heart through veins and venules, which are less sturdy but more expansible, acting as reservoirs. Vein valves ensure forward blood flow towards the heart.
• Coagulation Process: Upon vascular injury, vasoconstriction reduces blood flow, initiating clotting. Platelets form a plug at the injury site. Clotting factors activate in a cascade, leading to thrombin-stimulated fibrinogen forming fibrin, stabilizing the clot.
• Impairment of tissue perfusion is associated with occlusion, constriction, or dilation of arteries or veins as well as blood loss
• Atherosclerosis or thrombi can occlude arteries (which reduce the blood flow to tissues) and thrombi can occlude veins (which interrupt the return of blood to the heart).
• Vasoconstriction can result in hypertension, which increases the risk for stroke or myocardial infarction. Examples of dilation are aneurysms in arteries and varicose veins. Blood loss occurs with bleeding or hemorrhage. Impaired tissue perfusion interferes with blood flow, resulting in ischemia to localized tissue and, if uncorrected, infarction and cellular death.
• Acute coronary syndromes (ACS) encompass a spectrum of conditions resulting from sudden, reduced blood flow to the heart, typically due to an acute obstruction in a coronary artery. This obstruction can significantly compromise heart function and lead to various clinical outcomes, depending on the severity and location of the blockage.
• Unstable Angina: A condition where the heart does not get enough blood flow and oxygen, potentially leading to a heart attack. Characteristics: Chest pain or discomfort that is unexpected, occurs at rest, or with minimal exertion, and is more severe or prolonged than typical angina. Diagnostic Indicators: No significant changes in the ST-segment on an electrocardiogram (ECG) and no elevation in cardiac biomarkers (such as troponins).
• Non–ST-Segment Elevation Myocardial Infarction (NSTEMI): A type of heart attack where blood flow to the heart muscle is reduced but not completely blocked. Characteristics: Similar symptoms to unstable angina but with evidence of myocardial necrosis (death of heart tissue) indicated by elevated cardiac biomarkers. Diagnostic Indicators: No ST-segment elevation on ECG but elevated cardiac enzymes.
• ST-Segment Elevation Myocardial Infarction (STEMI): A more severe type of heart attack where there is a complete blockage of a coronary artery. Characteristics: Intense and persistent chest pain, which can be more severe than in NSTEMI. Diagnostic Indicators: Elevated ST-segments on ECG and elevated cardiac biomarkers.
• Sudden Cardiac Death: An unexpected death due to cardiac causes, occurring shortly after symptom onset, typically within one hour. Characteristics: Often due to a severe arrhythmia (irregular heartbeat) or massive heart attack. Diagnostic Indicators: This condition may occur without prior warning symptoms and is confirmed post-mortem