Chapter 26: Disorders of Blood Flow and Blood Pressure Regulation

Chapter 26: Disorders of Blood Flow and Blood Pressure Regulation

1. Objectives

  • Describe the functions of the endothelial cells and define the term endothelial dysfunction.

  • Describe the function of vascular smooth muscle and its role in vascular repair.

  • Define the terms:   - Systolic blood pressure (SBP)   - Diastolic blood pressure (DBP)   - Pulse pressure (PP)   - Mean arterial blood pressure (MAP)

  • Explain how cardiac output (CO) and peripheral vascular resistance (PVR) interact in determining SBP and DBP.

  • Describe the possible mechanisms involved in the development of atherosclerosis.

  • Describe the pathology associated with vasculitis and relate it to disease conditions associated with vasculitis.

  • Distinguish between the pathology and manifestations of aortic aneurysms and dissection of the aorta.

  • Explain venous return from lower extremities, including the function of muscle pumps and gravity effects related to varicose vein development.

  • Characterize the pathology of venous insufficiency and relate it to stasis dermatitis and venous ulcers.

  • List the four common causes of lower leg ulcers.

  • Define hypertension and identify clinical blood pressure limits for identifying hypertension.

  • Describe how hypertension contributes to target-organ damage, identifying the most affected organs and discussing pathophysiological changes.

  • Discuss the four types of hypertension that can occur during pregnancy.

  • Define orthostatic hypotension.

  • Describe cardiovascular, neurohumoral, and muscular responses that help maintain blood pressure when standing from a supine position.

  • Explain how various factors contribute to orthostatic hypotension.

2. Blood Vessel Review

  • Arteries:   - High-pressure system   - Elastic and maintain tone

  • Veins:   - Low-pressure system   - Have valves to prevent backflow

  • Capillaries:   - Sites of gas and nutrient exchange

3. Blood Pressure Concepts

3.1. Systolic Blood Pressure (SBP)

  • Reflects:   - Stroke volume
      - Heart rate and contractility
      - Arterial compliance

  • Increases with age due to decreased elasticity

3.2. Diastolic Blood Pressure (DBP)

  • Reflects:   - Peripheral vascular resistance
      - Arterial recoil

  • Important for coronary perfusion

3.3. Blood Pressure Equation

  • Blood Pressure = Cardiac Output × Systemic Vascular Resistance

  • Mean Arterial Pressure (MAP)   - Average driving pressure for perfusion
      - Calculation: extMAPext≈extDBP+rac13(extSBP−extDBP)ext{MAP} ext{≈ } ext{DBP} + rac{1}{3} ( ext{SBP} - ext{DBP})
      - Normal value for adults: > 60 ext{ mmHg}

3.4. Cardiac Output (CO) Equation

  • Cardiac Output = Stroke Volume × Heart Rate

  • Normal CO: 4ext−8extL/min4 ext{−} 8 ext{ L/min}

  • Blood Pressure is the force of blood against artery walls and is reported as Systolic/Diastolic pressure.

  • Pulse Pressure:   - extPulsePressure=extSBP−extDBPext{Pulse Pressure} = ext{SBP} - ext{DBP}   - Measures components of perfusion

4. Endothelial Function

4.1. Normal Endothelial Function

  • Endothelium:   - Composed of squamous epithelial cells   - Specialized to line blood vessels   - Functions:     - Continuous and semi-permeable
        - Regulates transport across the vessel wall, platelet adhesion, clotting, vascular resistance, immune/inflammatory reactions, and cell growth

4.2. Endothelial Dysfunction

  • Triggered by:   - Inflammation
      - Hemodynamic stress
      - Lipids
      - Hypoxia

  • Leads to conditions like:   - Atherosclerosis   - Hypertension   - Thrombosis

  • Endothelial injury is the initiating event in many vascular diseases.

5. Vascular Smooth Muscle (VSM)

5.1. Function and Role in Regulation

  • Located in the tunica media of arteries and arterioles

  • Responds to:   - Autonomic nervous system stimulation
      - Hormones (e.g., angiotensin II, epinephrine)

  • Controls vessel diameter (vasoconstriction & vasodilation), affecting peripheral vascular resistance and blood pressure.

5.2. Vascular Smooth Muscle in Disease

  • Chronic activation leads to:   - Vascular remodeling (thickening and stiffening of vessels)   - Sustained hypertension   - Migration into plaques contributing to plaque growth

  • Endothelium signals while vascular smooth muscle executes responses.

6. Disorders of Systemic Arterial Blood Flow

6.1. Normal Arterial Flow

  • Characteristics of a high-pressure system driven by cardiac output and elastic recoil, with flow directed away from the heart.

6.2. Dyslipidemia

  • Abnormal levels of circulating lipids, particularly increased low-density lipoprotein (LDL), a major risk factor for atherosclerosis.

6.3. HDL vs. LDL
6.3.1. LDL (Low-Density Lipoprotein)

  • Delivers cholesterol to tissues and easily enters injured endothelium

  • Major contributor to plaque formation

  • High levels indicate increased vascular risk

6.3.2. HDL (High-Density Lipoprotein)

  • Removes cholesterol from tissues and returns it to the liver

  • Provides protection against atherosclerosis

6.4. Atherosclerosis Etiology and Risk Factors

  • Etiology:   - Chronic inflammatory disease initiated by endothelial dysfunction
      - Major risk factors include:     - Dyslipidemia (↑ LDL)
        - Hypertension
        - Smoking
        - Diabetes
        - Age and genetics

6.5. Atherosclerosis Pathogenesis

  • Endothelial injury allows LDL to enter vessel walls.

  • Macrophages ingest LDL → foam cell formation leading to plaque formation, which narrows the lumen progressively.

6.6. Atherosclerosis Progression Timeline

  • Stages include:   - Fatty streak
      - Fibrotic plaque
      - Complicated lesion

  • Risk factors accelerate disease progression (e.g., hyperlipidemia, diabetes, smoking, hypertension).

6.7. Clinical Significance of Atherosclerosis

  • Results in:   - Narrowed lumen causing decreased perfusion
      - Plaque rupture leading to thrombosis and organ ischemia   

  • Clinical conditions depend on plaque location:   - Coronary arteries → Coronary Artery Disease (CAD)   - Peripheral arteries → Peripheral Artery Disease (PAD)   - Cerebral arteries → Stroke or Transient Ischemic Attack (TIA)

7. Acute Coronary Syndromes (ACS)

7.1. Myocardial Ischemia and Infarction

  • Ischemia:   - Reduced perfusion; tissue remains alive but dysfunctional (reversible)

  • Infarction:   - Prolonged ischemia leading to cell death (irreversible)

7.2. Clinical Priorities

  • Identify unstable angina and myocardial infarction, characterized by plaque rupture and thrombosis.

  • Clinical priority for ACS management is rapid restoration of blood flow.

7.3. Clinical Manifestations of Myocardial Infarction

  • Symptoms include severe chest pressure/pain, dyspnea, diaphoresis, nausea, and ECG changes (ST elevation or depression).

  • Complications may include dysrhythmias leading to sudden cardiac arrest and left ventricular failure.

8. Peripheral Artery Disease (PAD)

8.1. Overview

  • Defined as atherosclerosis affecting lower-extremity arteries, leading to reduced blood flow during activity.

  • Classic manifestations include claudication, cool/pale extremities, diminished pulses, and poor wound healing.

8.2. Acute Arterial Occlusion

  • Caused by thrombus or embolus, often due to plaque rupture.

  • Clinical manifestations include sudden pain, pallor, pulselessness, paresthesia, and paralysis, constituting a limb and life-threatening emergency.

9. Inflammatory/Functional Arterial Disease

9.1. Mechanisms

  • Not driven by lipid plaque; symptoms may occur without progressive plaque buildup.

  • Primary problems include:   - Vessel wall inflammation
      - Abnormal vasoconstriction

9.2. Key Exemplars

  • Vasculitis (e.g., giant cell temporal arteritis), thromboangiitis obliterans, and Raynaud disease/phenomenon.

10. Aortic Aneurysm

10.1. Definition and Etiology

  • Abnormal localized dilation of an artery, commonly the aorta.

  • Etiologies include:   - Atherosclerosis
      - Degeneration of the vessel wall

  • Risk Factors:   - Hypertension, smoking, male sex, age > 50.

10.2. Clinical Features

  • Often asymptomatic but may present with substernal, back, or abdominal pain.

  • Major complication is rupture, which can lead to life-threatening hemorrhage.

  • Diagnosis via ultrasound or CT.

11. Aortic Dissection

11.1. Definition and Key Features

  • Defined as a tear in the inner layer (intima) of the aortic wall.

  • Leads to blood entering the vessel wall and creating a false lumen.

  • Strongly associated with hypertension, can impair blood flow to organs or extremities.

11.2. Clinical Manifestations

  • Sudden onset of severe chest or back pain, often described as ripping or tearing.

  • May cause pulse deficits, neurologic symptoms, or signs of organ ischemia, necessitating emergent imaging and surgery.

12. Disorders of Systemic Venous Circulation

12.1. Normal Venous Return

  • A low-pressure system that relies on muscle pumps, venous valves, and is opposed by gravity.

12.2. Venous Insufficiency
12.2.1. Pathophysiology

  • Valve failure leads to blood pooling and increased venous pressure, resulting in chronic venous hypertension.

12.2.2. Clinical Manifestations

  • Varicose veins, edema, skin changes (stasis dermatitis), and venous ulcers typically around the medial ankle.

  • Nursing implications include elevation, compression, activity, and skin assessment; prevention through lifestyle changes is key.

13. Disorders of Blood Pressure Regulation

13.1. Hypertension

  • Defined as sustained SBP ≥ 130 or DBP ≥ 80 mmHg.

  • Types include:   - Primary hypertension: idiopathic.   - Secondary hypertension: due to an identifiable cause (renal, endocrine).

  • Effects include:   - Heart: Left ventricular hypertrophy and heart failure   - Brain: Increased stroke risk
      - Kidneys: Nephropathy
      - Eyes: Retinopathy

13.2. Orthostatic Hypotension

  • Characterized by a drop in blood pressure upon standing (≥20 mmHg SBP or ≥10 mmHg DBP).

  • Causes may include dehydration, medications, autonomic dysfunction.

  • Symptoms can include dizziness and fainting.

14. Summary of Disorders

14.1. Arterial Disorders (Ischemia - Delivery Problem)

  • Mechanisms include:   - Decreased lumen, flow, or vessel integrity.   - Conditions like CAD, PAD, stroke, and aortic diseases lead to acute ischemia.

14.2. Venous Disorders (Congestion - Return Problem)

  • Mechanism involves valve failure with gravity leading to chronic venous insufficiency, characterized by increased venous pressure and associated symptoms like edema and skin changes.

14.3. Blood Pressure Disorders (Regulation Failure)

  • Hypertension involves increased cardiac output and/or peripheral resistance with long-term target-organ damage.

  • Orthostatic hypotension results in failure of compensatory responses upon standing, leading to impaired perfusion despite measured blood pressure values.