Week 2 - Chapter 15: Alterations in Blood Flow

Chapter 15: Alterations in Blood Flow

• Learning Objectives
  • Explain the development of arterial and venous obstructions.
  • Identify the consequences of acute and chronic arterial obstruction.
  • Identify the consequences of superficial and deep venous obstructions.

General Mechanisms Causing Altered Blood Flow

• Reduction in blood flow impairs the transport of gases and nutrients, resulting in:

  • Hypoxia
  • Ischemia
  • Venous engorgement
  • Venous obstruction

• Blood Vessel Obstructions:

  • Obstruction reduces flow downstream and increases pressure upstream.
  • Arterial obstructions lead to distal ischemia.
  • Venous obstructions lead to edema.

Thrombosis

• Thrombus: A stationary blood clot formed within a blood vessel or heart chamber.
• Causes: Slowing or turbulence of blood flow; damage to vessel walls; medications.
• Arterial thrombosis: Results in ischemia.
• Venous thrombosis: Results in edema.
• Inflammation in a vein: Phlebitis
• Inflammation with a clot in a vein: Thrombophlebitis

Clinical Manifestations of Thrombosis

• Arterial: Intermittent claudication, cool, cyanotic skin, painful ulcer around one toe.
• Venous: None to life-threatening (pulmonary embolism); calf/groin tenderness, swelling, and Homan's sign.

Treatment of Thrombosis

• Anticoagulant therapy to prevent clot enlargement.
• Thrombolytic drugs may be required.
• Additional interventions include antiembolic stockings or sequential compression devices. Ambulation is encouraged.
• Surgery may be an option to remove the thrombus.

Embolus

• Thromboembolus: A clot that travels within the bloodstream.
• Embolus leaving the left ventricle: Ischemic stroke (symptoms vary based on the impacted brain area).
• Embolus leaving the right ventricle: Pulmonary embolism (sudden onset of shortness of breath, increased respiratory rate, chest pain, and sudden death). Treatment involves embolectomy or a filter in the inferior vena cava (Greenfield filter).

Vasospasm

• Sudden constriction of arterial smooth muscles obstructing blood flow.
• Potential causes include hormonal changes, food additives, and environmental factors.
• Associated manifestations include Prinzmetal angina, hemorrhagic stroke, and migraine headaches.

Inflammation

• Can increase the risk of thrombotic processes.
• Vasculitis: Inflammation of the artery's intima.
• Phlebitis: Inflammation of the vein's lining.
• Arteritis: Inflammatory process of autoimmune origin in arteries.

Mechanical Compression

• External forces on the vascular system can cause partial or complete obstruction.
• Causes include trauma, tight casts, dressings, or stockings.
• Compartment syndrome is a possible consequence.

Blood Vessel Structural Alterations

• Types of structural alterations: Valvular incompetence, arteriosclerosis/atherosclerosis, aneurysms, and arteriovenous fistulas.

Lymphatic Vessels

• Changes in capillary or interstitial oncotic pressure increase filtration into tissues.
• This results in edema, and impairment in lymph circulation.

Alterations in Arterial Flow

• Obstruction: Artherosclerosis/atherosclerosis, inflammation, vasospasm, thrombi/emboli, acute occlusion, mechanical alterations, and arteriovenous fistulas/aneurysms.

Arteriosclerosis/Atherosclerosis

• Three pathologic processes include Mönckeberg sclerosis, arteriolar sclerosis, and atherosclerosis.
• Atherosclerosis underlies hypertension, cardiac disease, renal disease, peripheral disease, and stroke. The goal is modifiable risk reduction.

Atherosclerosis Details

• Low-density lipoproteins breach the intimal layer.
• Oxidization of lipids causes further damage to the vessel.
• Platelets aggregate, releasing growth factors, stimulating smooth muscle cell growth.
• Smooth muscle cells proliferate within the damaged endothelium.
• Resulting plaque is composed of smooth muscle cells, lipoproteins, and inflammatory debris, decreasing the lumen and affecting blood flow.
• Complications can include hypertension, cardiac disease, renal disease, peripheral arterial disease, stroke, and myocardial infarction.
• Modifiable risk reduction focuses on smoking cessation, physical activity, managing blood pressure and cholesterol levels, managing stress levels, reducing glucose intolerance and obesity.
• Diagnosis uses Doppler flow, plethysmography, ankle-brachial index, exercise/stress test, and angiography.

Treatment

• First line treatment is non-pharmacological: weight reduction, smoking cessation, exercise, low-fat diet. If unsuccessful, medications are added. Surgical options include balloon/laser angioplasty, stents, and CABG.
• Thromboangiitis Obliterans (Buerger Disease): Rare inflammatory condition causing obstruction in small and medium arteries/veins, requiring smoking cessation and prostaglandins.
• Raynaud Syndrome: Extreme vasoconstriction of digits in response to cold or stress, requiring biofeedback, relaxation techniques, calcium-channel blockers, sympatholytics, and prostaglandins for treatment.

Alterations in Venous Flow

• Incompetent valves: Obesity, pregnancy, and right heart failure can lead to varicose veins, chronic venous insufficiency, and deep vein thrombosis with edema, ulcers, and pain.
• Valvular incompetence: Excessive venous pressures cause valve overstretching, resulting in backflow and venous insufficiency. Treatment focuses on smoking cessation and regular exercise.
• Varicose veins: Impaired venous return causes increased capillary pressure, edema, and darkened, raised, and tortuous veins. Often affect the greater saphenous vein. Treatment is directed toward increasing venous flow and reducing venous pressure, sometimes with sclerotherapy or surgery.
• Chronic venous insufficiency: Valvular incompetence leads to deep vein problems, with venous stasis ulcers being common. Treatment involves compression therapy and controlling infection.
• Deep vein thrombosis: Most often caused by thrombi in deep veins, often in the lower extremities. Symptoms may be absent. Aggressive anticoagulation therapy is used. Previous occurrences of DVT are a risk factor for future problems.

Alterations in Lymphatic Flow

• Lymphedema: Obstruction/alterations in lymphatic flow cause swelling, particularly in extremities. Primary lymphedema has a congenital or lymphatic system dysfunction root cause. Secondary lymphedema stems from diseases or surgical procedures. Treatment often includes external compression therapy, exercise, and surgical resection (if applicable).

Acute Arterial Occlusion

• Absence of arterial circulation needing immediate intervention. May be caused by thrombi/emboli or compression. Classic indicators (6 P's) include pallor, paresthesia, paralysis, pain, polar, and pulselessness.
• Treatment options include loosening tight dressings, cutting casts, anticoagulant/thrombolytic therapy, bypass surgery, and embolectomy or amputation in severe cases.

Aneurysms

• Localized arterial dilations; categorized as true (involving all layers of the vessel) or false aneurysms (weakened vessel wall). Often found in cerebral circulation, thoracic, or abdominal aorta. Dissecting aortic aneurysms require urgent medical/surgical treatment.
• Symptoms include increasing intracranial pressure, hemorrhagic stroke, sudden tearing pain radiating to the back or abdomen, and shock. Diagnosis can use CT, MRI, or angiography.