Disorders of Blood Flow and Blood Pressure Regulation

Blood Vessel Structure & Function

• Tunica Intima (inner coat): Endothelial cells. Controls molecular transfer, platelet adhesion/clotting, blood flow/resistance, hormone metabolism, immune/inflammatory reactions, cell growth.

• Endothelial Dysfunction: Reversible changes from inflammation (cytokines, bacteria, viruses), hemodynamic stresses, lipid products, hypoxia.

• Tunica Media (middle coat): Smooth muscle cells, collagen, elastic fibers. Controls vasoconstriction (Sympathetic Nervous System, SNS) and dilation (Nitric Oxide, NO).

• Tunica Externa (outer coat): Connective tissue.

Blood Pressure Regulation

• Acute Control (seconds/minutes): Neural mechanisms (SNS for fast HR, Parasympathetic/Vagal for slow HR).

• Long-Term Control (slow): Kidneys regulate extracellular volume.

• Circadian Variations: Nocturnal B/P declines $10\%$ to $20\%$

• Renin-Angiotensin-Aldosterone System (RAAS): Kidneys release renin when B/P drops $\rightarrow$ Angiotensinogen $\rightarrow$ Angiotensin I (in lungs w/ ACE) $\rightarrow$ Angiotensin II (potent vasoconstrictor) $\rightarrow$ Aldosterone release $\rightarrow$ Na$^{++}$ and water retention $\rightarrow$ Increased volume & B/P.

Dyslipidemia

• Imbalance of lipids: Triglycerides, phospholipids, cholesterol.

• Types:

  • Triglycerides: Excess calories converted to fat; risk of arteriosclerosis, stroke, heart attack.

  • Phospholipids: Lipoproteins in cell membranes, barriers, clotting.

  • Cholesterol:

    • LDL (Low-Density Lipoprotein): "Lousy" - carries cholesterol to arteries (main carrier of cholesterol).

    • HDL (High-Density Lipoprotein): "Happy" - carries cholesterol to liver for excretion (50% protein).

• Hyperlipidemia: Elevated levels of one or all lipids.

• Primary Dyslipidemia: Genetic (Familial hypercholesterolemia - very high LDL).

• Secondary Dyslipidemia: Associated with other health problems/behaviors (e.g., fats, cholesterol, triglycerides).

• Hypercholesterolemia: Serum cholesterol $\geq 200$ mg/dL, contributes to stroke, heart attack, atherosclerosis.

Atherosclerosis

• Definition: Narrowing of arteries due to fibro-fatty lesions in the intimal lining of large/medium arteries.

• Most often caused by: Hypercholesterolemia with high LDL.

• Lesion Development:

  • Fatty streaks: Thin, flat yellow intimal discolorations.

  • Fibrous atheromatous plaque: Accumulation of lipids, smooth muscle proliferation, scar tissue.

  • Complicated lesion: Hemorrhage, ulceration, scar tissue deposits.

• Major Risk Factors: Hypercholesterolemia (#1), cigarette smoking, hypertension, family history of CHD, age (men $\geq 45$ years; women $\geq 55$ years), HDL < 40 mg/dL, high C-reactive protein (CRP), high homocysteine levels.

• Complications: Arteriosclerosis (stiffening), heart disease, stroke, PVD, ischemia from narrow vessels, vessel obstruction (plaque rupture/hemorrhage), thrombosis/emboli from endothelial damage, aneurysm formation.

Diseases of the Arterial System

• Vasculitis: Inflammation/injury/necrosis of blood vessel walls (arteries, capillaries, veins).

• Peripheral Artery Disease (PAD): Atherosclerotic occlusion in extremities.

  • Risk Factors: Smoking (#1), HTN, high cholesterol, DM.

  • Clinical Manifestations: Intermittent claudication (pain with walking), pain at rest in advanced stages. Leg atrophy, brittle toenails, hair loss, pallor, dependent redness.

• Thromboangiitis Obliterans (Berger's Disease): Inflammatory arterial disorder causing thrombus formation, linked to smoking. Pain, burning, tingling hands/feet; pale, cyanotic, cold limbs.

• Raynaud Disease/Phenomenon: Intense vasospasm of arteries/arterioles, primarily in fingers/toes. Triggered by cold, anxiety, stress, trauma. Cyanosis, cold, numbness, tingling.

• Acute Arterial Embolism ("Seven P"s): Pistol shot (acute onset), Pallor, Polar (cold), Pulselessness, Pain, Paresthesia, Paralysis.

Aneurysms

• Definition: Abnormal localized dilation of a blood vessel (artery or vein).

• Types:

  • Berry aneurysm: Small, spherical dilation, often in Circle of Willis (brain).

  • Fusiform/Saccular aneurysms: Gradual, progressive enlargement, often in thoracic/abdominal aorta (e.g., AAA).

• Aortic Dissection: Acute, life-threatening longitudinal tearing (hemorrhage) into aortic wall. Etiology: uncontrolled HTN, atherosclerosis, existing aneurysm. Excruciating back pain, high BP & HR.

Venous Circulation & Disorders

• Characteristics: Low pressure, one-way valves, limited contractility, skeletal muscle pump, thin-walled.

• Disorders cause: Congestion, predisposition to clot formation (stagnation).

• Varicose Veins: Distensible, palpable veins with pooled blood due to incompetent valves.

• Thrombophlebitis: Inflammation of a vein, usually due to a clot (superficial).

• Deep Vein Thrombosis (DVT): Clot formation in deep veins.

  • Virchow's Triad: Stasis of blood (immobility/bed rest), blood hypercoagulability (thrombotic disorders), vessel wall injury (trauma, IV insertion).

  • Other Risk Factors: Obesity, genetics, oral birth control, smoking, surgery.

• Venous Insufficiency: Deformity of valve leaflets, valvular incompetence, leading to stasis dermatitis, venous ulcers.

Hypertension (HTN)

• Sustained elevated blood pressure.

• Silent Killer: Often asymptomatic until severe.

• B/P Levels:

  • Normal: SBP <120 & DBP <80 mmHg

  • Elevated: SBP $120-129$ & DBP <80 mmHg

  • Stage 1 HTN: SBP $130-139$ or DBP $80-89$ mmHg

  • Stage 2 HTN: SBP $\geq 140$ or DBP $\geq 90$ mmHg

• Types:

  • Primary (Essential): Common, multiple causes.

  • Secondary: Due to underlying disease (esp. renal disease, Cushing's, hyperaldosteronism).

  • Gestational HTN: HTN without proteinuria during pregnancy.

  • Preeclampsia: HTN with proteinuria during pregnancy.

• Target Organ Damage: Heart (angina, MI, heart failure), Brain (stroke, TIA, dementia), Peripheral vascular (atherosclerosis), Kidney (renal disease), Retinal complications.

• Risk Factors:

  • Non-modifiable: Age (>65), gender (males higher), race (African American), family history/genetics.

  • Modifiable: Dietary (salt/fat), tobacco, alcohol, obesity, sedentary lifestyle, DM.

Orthostatic (Postural) Hypotension

• Definition: Abnormal drop in B/P upon standing ($\geq 20$ mmHg SBP or $\geq 10$ mmHg DBP within 3 minutes).

• Etiology: Neurogenic (Parkinson's, DM), non-neurogenic (hypovolemia, medications, CHF, alcohol).

• Factors: Fluid deficit, medications, aging, ANS disorders, immobility.