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Chapter 3 Disorders of Vascular Flow Yiran Ni M.D
INTRODUCTION The health of cells and organs critically depends on an unbroken circulation to deliver oxygen and nutrients and to remove wastes. However, the well-being of tissues also requires normal fluid balance; abnormalities in vascular permeability or hemostasis can result in injury even in the setting of an intact blood supply.
This chapter will describe major disturbances involving hemodynamics and the maintenance of blood flow, including: 1. edema 2. hyperemia and congestion 3. hemorrhage 4. thrombosis 5. embolism 6. infarction 7. shock.
Normal fluid homeostasis encompasses maintenance of vessel wall integrity as well as intravascular pressure and osmolarity within certain physiologic ranges. Changes in vascular volume, pressure, or protein content, or alterations in endothelial function, all affect the net movement of water across the vascular wall.
Such water extravasation into the interstitial spaces is called edema and has different manifestations depending on its location. In the lower extremities, edema mainly causes swelling. in the lungs, edema causes water to fill alveoli, leading to difficulty in breathing. Defination:1.edema
Normal fluid homeostasis also means maintaining blood as a liquid until such time as injury necessitates clot formation. Clotting at inappropriate sites (thrombosis) or migration of clots (embolism) obstructs blood flow to tissues and leads to cell death (infarction). Defination:2. thrombosis 3. embolism 4. infarction
Conversely, inability to clot after vascular injury results in hemorrhage. local bleeding can compromise regional tissue perfusion, while more extensive hemorrhage can result in hypotension (shock) and death. Defination: 5. hemorrhage 6. shock
What do you find?
What do you find? Edema!
Defination Approximately 60% of lean body weight is water, two-thirds of which is intracellular and the remainder is in extracellular compartments, mostly as interstitial fluid; only 5% of total body water is in blood plasma. The term edema signifies increased fluid in the interstitial tissue spaces.
Defination Fluid collections in different body cavities are variously designated hydrothorax, hydropericardium, or hydroperitoneum (the last is more commonly called ascites). Anasarca is a severe and generalized edema with profound subcutaneous tissue swelling.
movement of fluid
There are several pathophysiologic categories of edema: 1.Increased Hydrostatic Pressure 2.Reduced Plasma Osmotic Pressure (Hypoproteinemia) 3.Lymphatic Obstruction 4.Sodium Retention 5.Inflammation
Increased Hydrostatic Pressure Localized increases in intravascular pressure can result from impaired venous return: deep venous thrombosis, pregancy Generalized increases in venous pressure, with resultant systemic edema, occur most commonly in congestive heart failure
Reduced Plasma Osmotic Pressure Reduced Plasma Osmotic Pressure (Hypoproteinemia) Protein-losing glomerulopathies (nephrotic syndrome) Liver cirrhosis (ascites) Malnutrition Protein-losing gastroenteropathy Reduced plasma osmotic pressure can result from excessive loss or reduced synthesis of albumin, the serum protein most responsible for maintaining colloid osmotic pressure
orange peel In breast carcinoma infiltration and obstruction of superficial lymphatics can also cause edema of the overlying skin, the so-called orange peel appearance. Such a finely pitted surface results from an accentuation of depressions in the skin at the site of hair follicles.
Sodium and Water Retention Sodium Retention Excessive salt intake with renal insufficiency Increased tubular reabsorption of sodium Renal hypoperfusion Increased renin-angiotensin-aldosterone secretion
Inflammation Acute inflammation Chronic inflammation Angiogenesis The edema fluid occurring with volume or pressure overload, or under conditions of reduced plasma protein, is typically a protein-poor transudate; it has a specific gravity less than Conversely, because of the increased vascular permeability, inflammatory edema is a protein-rich exudate with a specific gravity that is usually greater than
Morphology Edema is most easily recognized grossly; microscopically, edema fluid is reflected primarily as a clearing and separation of the extracellular matrix elements with subtle cell swelling. Although any organ or tissue in the body may be involved, edema is most commonly encountered in subcutaneous tissues, lungs, and brain.
Subcutaneous edema Subcutaneous edema may have different distributions depending on the cause. It can be diffuse, or it may be relatively more conspicuous at the sites of highest hydrostatic pressures. In the latter case, the edema distribution is typically influenced by gravity and is termed dependent. Edema of the dependent parts of the body (e.g., the legs when standing, the sacrum when recumbent) is a prominent feature of congestive heart failure, particularly of the right ventricle.
Morphology Edema as a result of renal dysfunction or nephrotic syndrome is generally more severe than cardiac edema and affects all parts of the body equally. It may, however, initially manifest itself in tissues with a loose connective tissue matrix, such as the eyelids; thus, periorbital edema is a characteristic finding in severe renal disease.
Morphology Finger pressure over substantially edematous subcutaneous tissue displaces the interstitial fluid and leaves a finger-shaped depression, so-called pitting edema.
Heart failure or renal hypofunction?
Pulmonary edema It is a common clinical problem most typically seen in the setting of left ventricular failure but also occurring in renal failure, acute respiratory distress syndrome, pulmonary infections, and hypersensitivity reactions. The lungs are two to three times their normal weight, and sectioning reveals frothy, blood-tinged fluid representing a mixture of air, edema fluid, and extravasated red blood cells.
Edema of the brain It may be localized (e.g., owing to abscess or neoplasm) or may be generalized, as in encephalitis, hypertensive crises, or obstruction to the brain's venous outflow. Trauma may result in local or generalized edema depending on the nature and extent of the injury. With generalized edema, the brain is grossly swollen, with narrowed sulci and distended gyri, showing signs of flattening against the unyielding skull.
Clinical Correlation Effects of edema may range from merely annoying to fatal. Subcutaneous tissue edema in cardiac or renal failure is important primarily because it signals underlying disease; however, when significant, it can also impair wound healing or the clearance of infection.
Clinical Correlation Pulmonary edema can cause death by interfering with normal ventilatory function. Not only does fluid collect in the alveolar septa around capillaries and impede oxygen diffusion, but edema fluid in the alveolar spaces also creates a favorable environment for bacterial infection.
Clinical Correlation Brain edema is serious and can be rapidly fatal; if severe, brain substance can herniate (extrude) through, for example, the foramen magnum, or the brain stem vascular supply can be compressed. Either condition can injure the medullary centers and cause death.
SUMMARY Edema is extravasation of fluid from vessels into interstitial spaces; the fluid may be protein poor (transudate) or may be protein rich (exudate).
SUMMARY Edema results from any of the following conditions: Increased hydrostatic pressure, caused by a reduction in venous return (as in heart failure) Decreased colloid osmotic pressure, caused by reduced concentration of plasma albumin (due to decreased synthesis, as in liver disease, or increased loss, as in kidney disease)
SUMMARY Lymphatic obstruction that impairs interstitial fluid clearance (as in scarring, tumors, or certain infections) Primary renal sodium retention (in renal failure) Increased vascular permeability (in inflammation)