Hemodynamic disorders

The health of cells and tissue depend on: Intact circulation ( to deliver oxygen and remove wastes). Normal fluid hemostasis-maintaining blood as liquid until when we have injury that necessitates formation of a clot. Normal fluid hemostasis require; normal vessel wall integrity and maintain of normal intravascular pressure and osmolality within certain physiological ranges. Any disturbance in these points will result in pathological conditions such as edema, hyperemia, congestion, hemorrhage, thrombosis, embolism, infarction and shock.

Edema 60% of lean body weight is water, 2/3 intracellular& 1/3 is a n extracellular, the latter is mostly interstitial fluid; only 5 % of total body water is blood plasma. Edema refer to increase fluid in the interstitial tissue spaces. Hydrothorax, hydropericardium, or hydroperitoneum (ascites) refer to fluid collection in respective body cavity. Anasarca is sever and generalized edema with profound subcutaneous tissue swelling.

Mechanism of edema Water extravasation (outward movement) across the vascular wall into the interstitial spaces. This movement controlled mainly by opposing effect of vascular hydrostatic pressure and plasma colloid osmotic pressure. Normally, the exit of fluid from the arteriole end of the microcirculation into the interstitium is balanced by inflow at venule end; the lymphatic drain a small residual amount of excess interstitial fluid, so any disturbance will lead to edema.

Types of edema Inflammatory edema-is a protein rich exudate with a specific gravity that is usually greater than 1.020 occurs due to increase vascular permeability. Non inflammatory edema-protein poor transudate with specific gravity less than 1.020 occur due to other reasons other than inflammation.

Causes of non inflammatory edema Increased hydrostatic pressure. Reduced plasma osmotic pressure. Lymphatic obstruction. Sodium and water retension.

1. Increased hydrostatic pressure Localized- increase in intravascular pressure can result from impaired venous return, for example; deep venous thrombosis in lower extremities can cause edema to distal portion of affected limb. Generalized- increase in venous pressure, with resultant systemic edema, occur most commonly in congestive heart failure in which reduced cardiac output results in reduced renal perfusion, inducing sodium and water retension by the kidney and eventually edema.

2. Reduced plasma osmotic pressure Albumin in serum protein synthesized by the liver, most responsible for maintaining intravascular colloid pressure, reduced osmotic pressure occurs when: Albumin is lost from circulation- as in nephrotic syndrome, in which glomerular capillary wall of kidney become leaky causing generalized edema. Reduce Albumin synthesis- in diffuse liver disease (e.g; liver cirrhosis). In each case, reduced plasma osmotic pressure lead to net movement of fluid into interstitial tissue resulting in edema.

3.Lymphatic obstruction Obstruction of lymphatic drainage and consequent lymphedema is usually localized; it can result from inflammatory or neoplastic lesion. Cancer of breast can be treated by resection/ and or irradiation of the associated axillary lymph nodes; the resultant scarring and loss of lymphatic drainage can cause severe upper extremity edema. In breast cancer infiltration and obstruction of superficial lymphatics can also cause edema of overlying skin called peau d orange appearance

4. Sodium and water retention Increase salt and water cause both increase hydrostatic pressure ( due to expansion of the intravascular volume) and reduce vascular osmotic pressure. Salt retention can occur in poststreptococcal glomerulonephritis and acute renal failure.

Morphology of edema Macroscopically- swelling. Microscopically- edema fluid appear as clearing and separation of the extracellular matrix elements with individual cell swelling. Finger pressure on significantly edematous subcutaneous tissue displace the interstitial fluid and leave a finger-shape depression, so called pitting edema.

Clinical significance of edema. Depending on its location, edema may have; Minimal effects as in lower extremities subcutaneous tissue edema fluid cause primarily swelling. Subcutaneous tissue edema in cardiac or renal failure is important primarily because it indicates underlying disease. In the lungs, edema fluid will fill alveoli and can cause life threatening breathing difficulties.

Hyperemia and congestion Both indicates a local increased volume of blood in particular tissue. Hyperemia: is active process resulting from increase blood flow due to vasodilatation (e.g; at site of inflammation or at skeletal muscles at time of exercise), the affected tissue are redder than normal because of engorgement with oxygenated blood. Congestion: passive process result from impaired venous return out of tissue, it may occur systemically as in cardiac failure, or it may be local, resulted from isolated obstruction of venous drainage, tissue has blue-red color (cyanosis) especially as worsening congestion lead to accumulation of deoxygenated hemoglobin in the affected tissue.

Congestion of capillary beds is closely related to the development of edema, so that the congestion and edema commonly occur together. Chronic passive congestion: it is long standing congestion, in which the stasis of poorly oxygenated blood cause chronic hypoxia ( decrease oxygen supply), result in degeneration or death of cells and subsequent tissue fibrosis. Capillary rupture at such site of chronic congestion can cause also small foci of hemorrhage; phagocytosis and catabolism of the erythrocytes debris can result in accumulation of hemosedrin laden macrophages.

Morphology Macroscopically; cut surface of hyperemic or congested tyissue are hemorrhagic and wet. Microscopically; Acute pulmonary congestion: alveolar capillaries engorged with blood; alveolar septal edema and/or focal minute intra-alveolar hemorrhage. Chronic pulmonary congestion: septa become thickened and fibrotic, and the alveolar spaces may contain numerous hemosiderin laden macrophage which are called heart failure cells.

Hemorrhage It is extravasation of blood from vessels into extravascular spaces. Causes: Condition of chronic congestion will result in capillary rupture. Coagulation disorders which are a wide variety of clinical disorders cause an increase tendency to hemorrhage usually within insignificant injury. Vascular injury, including trauma, atherosclerosis, inflammatory or neoplastic erosion of the vessel wall will end with the rupture of a large artery or vein results in sever hemorrhage.

Types of hemorrhage Hematoma: accumulated hemorrhage that can be external or can be confined within tissue. It could be insignificant (e.g; bruise) or can involve so much bleeding as to cause death (e.g; rupture aortic artery). Petechiae: Minute (1-2 mm) hemorrhages into skin, mucous membrane or serosal surfaces, typically associated with locally increase intravascular pressure, low platelet count (thrombocytopenia), defective platelet function or clotting factor deficiency.

Oral hematoma

3. Purpura : slightly larger 3-5 mm, hemorrhage can be associated with many of the same disorders than can cause petechaie, in addition; can occur with trauma, vascular inflammation (vasculitis) or increase vascular fragility. 4. Ecchymosis: larger 1-2 cm, subcutaneous hematoma, the erythrocytes in local hemorrhages are phagocytosed and degraded by nacrophages, the hemoglobin (red-blue color) is enzymatically converted into bilirubin (blue-green color) and eventually into hemosidren (golden-brown) accounting for the characteristic color change in hematoma. 5. Large accumulation of blood in one or another body cavities are called hemothorax, hemopericardium, hemoperitoneum or hemoarthrosis ( in joints)

Ecchymosis

Clinical significance of hemorrhage Rapid removal of as much 20% of the blood volume or slow looses of large amount may have little effect in healthy adults. Greater looses, however can cause hemorrhagic shock. Site of hemorrhage important, subcutaneous hemorrhage are harmless, while brain can be fatal. Chronic or recurrent external blood loss (e.g; peptic ulcer) cause net loss of iron resulting in iron deficiency anemia.