Patho Hemodynamic Disorders

Hemodynamic Disorders

• Disorders involving interruptions of normal blood flow often include thrombus or thromboembolus.

Thrombosis

• Thrombosis: Formation of a thrombus, which is a solid mass of blood components that occurs within a blood vessel. This can lead to complications such as ischemia, infarction, or even embolism if the thrombus dislodges and travels to other parts of the circulatory system.

  • A thrombus differs from a clot in several ways:

    • Is never formed outside a blood vessel.

    • Maintains attachment to the vascular wall.

    • Has a more organized structure (alternating layers of fibrin and platelets) compared to the random structure of clots.

Formation of a Thrombus

• Mechanism of thrombus formation:

  • Platelets adhere to the vascular wall due to irregularities and exposed subendothelial collagen following damage.

  • Platelet activation occurs without inflammation due to blood movement.

  • Thin layers of fibrin form as platelets bind to each other.

  • Turbulent blood flow allows platelets to adhere, leading to further fibrin buildup that traps RBCs and WBCs.

  • Alternating layers of fibrin and cells in the thrombus are termed "lines of Zahn."

  • In veins:

    • Slow blood flow and activated clotting factors generate large accumulations of fibrin, resulting in a prominent "red cap" downstream on the thrombus.

Types of Thrombus

• Post-mortem thrombus:

  • Characterized as a large gelatinous mass occluding the vessel.

• Ante-mortem thrombus:

  • Attached to the vessel wall and organized, generally does not fully occlude the vessel.

Factors Important for Thrombus Formation

• Endothelial Damage: Stripping of the endothelial layer exposes collagen, leading to platelet aggregation.

  • Can occur in various vessels due to bacterial infections or hemodynamic stress (e.g., hypertension).

  • Iatrogenic causes include long-term IV fluid administration or trauma.

  • Conditions like appendicitis, tumors, and aneurysms can also damage blood vessels.

• Flow Abnormalities:

  • Can lead to reduction or stasis of blood flow or turbulence at branch points.

  • Factors such as inactivity, varicose veins, and prolonged bed rest can lead to venous thrombi due to reduced venous return.

Deep Vein Thrombosis (DVT)

• Most venous thrombi occur in the superficial veins of the legs.

• The most dangerous thrombi are in deep veins.

• Mural thrombus: Occurs behind a cardiac valve; turbulence increases platelet contact.

• Common causes include deformities in the vessel due to tumors or aneurysms.

Blood Hypercoagulation

• Can occur due to extensive burns, kidney disease, heart failure, wide-spread tumor growth, and estrogen from contraceptive pills.

• Post-surgery inactivity can exacerbate thrombus development; therefore, compression cuffs and early walking are essential preventive measures.

• Elderly patients often have increased risks associated with heart and vascular disease, alongside potential undiagnosed tumors.

Sequelae of Thrombosis

• Resolution: Thrombus can resolve via the anticoagulation system.

• Organization: Involves phagocytic digestion leading to recanalization, potentially restoring blood flow.

• Propagation: Downstream growth of thrombus may occur where collateral vessels are present.

• Infarction: Complete occlusion of a vessel by thrombus or moving thrombus (thromboembolism) results in necrosis due to oxygen loss, with serious consequences often occurring in large arteries.

Types of Infarction

• Myocardial Infarction (heart attack): Affected coronary arteries.

• Cerebral Infarction (stroke): Affected brain arteries.

Factors Affecting Severity of Infarction

• Sensitivity of the organ to hypoxia, vascular supply patterns, and rate of blockage development all affect outcomes.

Embolism

• Thromboembolism: Sudden occlusion of a vessel by a moving thrombus, leading to ischemia or infarction. Arterial thromboemboli originate from arteries or heart surfaces and can affect various organs.

Venous Thromboembolism (TE)

• 90% originate in leg veins.

• Pulmonary TE primarily comes from leg veins; effects are mitigated by clot retraction and double blood supply to lungs.

Therapy for Thromboembolism (TE)

• Anticoagulants:

  • Heparin: Blocks thrombin formation, thereby inhibiting fibrin formation.

  • Aspirin: Inhibits platelet aggregation (antiplatelet therapy).

• Fibrinolytic agents:

  • t-PA, streptokinase, and urokinase promote plasmin formation to dissolve thrombi.

Other Types of Emboli

• Fat Emboli: Arise from yellow marrow after long bone fractures, may present with respiratory symptoms.

• Air Emboli: Occur due to gas bubbles in arteries, particularly critical in divers or post-surgery. Ex: The Bends: A condition caused by nitrogen bubbles forming in the bloodstream due to rapid decompression, leading to joint pain and other serious complications.

• Amniotic Fluid Emboli (AFE): Contains fetal cells that can cause disseminated intravascular coagulation (DIC) in the mother.

  • Amniotic fluid emobolism: occurs when amniotic fluid enters the maternal circulation, often during labor or shortly after delivery, leading to severe respiratory distress and cardiovascular collapse. The baby’s skin cells are foreign and causes massive inflammation.

• Foreign Body Emboli: Bullet fragments and glass shards can occlude vessels or cause trauma.