Hemodynamic Pathology

Hemodynamic Pathology: Edema, Transudates, and Exudates

Endothelium

Lines blood vessels, heart chambers and lymphatics. Cover ~400 m² and weighs about 1.5 kg.

Endocrine organ, important in permeability, inflammatory and non-inflammatory

Types: continuous, discontinuous, fenestrated

Edema, Transudates and Exudates

Two types of Edema:

(1) Inflammatory Edema – due to increased vascular permeability.
(2) Non-inflammatory Edema – due to alterations in hemodynamic forces across the capillary wall.

Effusions – edema in fluid cavities (pericardial effusions, pleural effusions)

Transudates – ultrafiltrate of plasma ("edema fluid")

Exudates – fluid inflammation, may contain cells (PMNs, bacteria), debris and extravasated protein

	Exudates	Transudates
Defined	Fluid of Inflammation	Ultrafiltrate of plasma
Etiology	Inflammation, infection	Hemodynamic
Protein Content	High (4%)	Low (<2%)
Specific Gravity	>1.020	<1.012
Inflammatory Cells	Often	Rare
Bacteria	Often	Rare
Example	pneumonia	congestive heart failure

Types of Exudates:

Serous – has some protein, usually without cells, strawlike color (e.g. blister)

Fibrinous – high content of fibrin

Purulent – pus, high cellular content (PMNs), creamy color, pimple

Suppurative – puslike, debris with liquefactive necrosis

Hemorrhagic – RBCs and WBCs, outpouring of blood

Combinations – serofibrinous, fibrinopurulent, etc.

Pathophysiology of Edema:

(1) Ý hydrostatic Pressure - ß venous return (CHF, constrictive pericarditis, cirrhosis of liver, obstruction of veins) or Ý arterial pressure (vasodilation, heat, neurohumoral excess or deficit)

(2) ß Oncotic Pressure – (hypoproteinemia, e.g. nephrotic syndrome, cirrhosis, malnutrition)

(3) Na⁺ retention – (Ý Na⁺ intake with reduced renal function, Ý tubular reabsorption)

(4) Lymphatic Obstruction – inflammatory, neoplastic, postsurgical, postirradiation

Clinical Correlates of edema:

(1) Orthostatic – soft pitting on pressure, foot involvement, bilateral

(2) Lymphedema – soft pitting early, but becomes hard with skin thickening

(3) Lipedema – not a true edema, fatty deposits in legs

(4) Chronic Venous Insufficiency – chronic obstruction or valvular incompetence of deep veins, soft pitting but hardens

Hyperemia and Congestion – both mean an increased volume of blood in an affected tissue

Active Hyperemia

arterial or arteriolar dilation produces an increased flow of blood into capillary beds due to opening of inactive capillaries
imparts a "redness" to the affected part
occurs as a result of physiologic responses (exercise, blushing, etc.), or as a result of inflammatory response mediated by vasoactive substances acting on endothelial cells

Passive (congestion) Hyperemia

impaired venous return imparts a blue-red color to affected area (cyanosis)

Engorgement of an organ or tissue with venous blood, may be acute or chronic

Systemic congestion may occur as a consequence of ß cardiac output (CHF)

The pulmonary system is affected by left ventricular failure and organs such as the liver and spleen may be affected by decompensation of the right ventricle

Localized congestion may occur when venous return is diminished due to obstruction, or in the portal circulation due to portal hypertension secondary to cirrhosis

Hemorrhage – rupture of a blood vessel with extravasation of cells and fluid.

Types of Hemorrhage:

(1) Hematoma – blood is trapped and accumulates in tissues forming a mass ("oma"). e.g., bruises, hemopericardium, hemoperitoneum, hemothorax

(2) Petechia(e) – minute (1-2 mm) hemorrhages into skin, mucous membranes or serosal surfaces are associated with locally increased intravascular pressure and low platelet counts.

(3) Purpura- larger (>3 mm) than petechiae, vasculitis.

(4) Ecchymosis- large hemorrhages commonly found subcutaneously, often referred to as a bruise; follow trauma, RBCs degrade and are phagocytosized by macrophages. Hemoglobin is converted to bilirubin (blue-green) and eventually to hemosiderin (gold brown).

Significance: Large loss leads to hemorrhagic/hypovolemic shock. Can also lead to loss of iron.