Hypertension

Definitions

  • Blood Pressure (BP): The pressure of blood pushing against the walls of arteries.

  • Cardiac Output (CO): The amount of blood the heart pumps in one minute.

  • Systemic Vascular Resistance (SVR): The amount of force exerted by blood vessels, influencing blood flow.

  • Mean Arterial Pressure (MAP): The average arterial pressure throughout one cardiac cycle.

  • Stroke Volume (SV): The volume of blood ejected from the left ventricle during each contraction.

Mathematical Representation of Blood Pressure

  • Basic Equation: BP = CO x SVR

  • Calculating Mean Arterial Blood Pressure: MAP = (SBP + 2 DBP) / 3

  • Further Components: SV x HR x blood viscosity / (vessel radius)^4

Factors Affecting Blood Pressure

  • Changes in stroke volume, heart rate, viscosity, or vessel length influence blood pressure.

    • Increased Stroke Volume, HR, viscosity, and vessel length → BP increases

    • Increased vessel radius (vasodilation) → BP decreases

Regulation of Blood Pressure

  • Arterial Blood Pressure: Influenced by cardiac output, peripheral vascular resistance, and various regulating mechanisms.

  • Neurohormonal Regulation:

    • Sympathetic Nervous System (SNS): Increases BP by enhancing CO and SVR through norepinephrine (NE).

      • Baroreceptors: Provide feedback to adjust BP via the SNS.

      • Vasomotor Center: Located in the medulla, maintains normal BP levels.

Effects of Norepinephrine (NE)

  • In the Heart:

    • Alpha-1: Increases contractile force (inotropic effect).

    • Beta-1: Increases heart rate (chronotropic effect) and contractility.

  • In Vascular Smooth Muscle:

    • Alpha-1 & Alpha-2: Causes vasoconstriction of peripheral vessels.

    • Beta-2: Causes vasodilation of skeletal muscle vessels and coronary arteries.

  • In the Kidneys:

    • Beta-1: Increases renin secretion from juxtaglomerular, leading to fluid retention and vasoconstriction.

Homeostasis Maintenance

  • Parasympathetic Nervous System: Activating the vagus nerve counteracts SNS effects, slowing heart rate and lowering BP.

Vascular Endothelium and Its Role

  • Nitric Oxide: Maintains low arterial tone during rest, inhibits smooth muscle growth and platelet aggregation.

  • Prostacyclin & Endothelium-Derived Factors: Promote vasodilation.

  • Endothelin: A potent vasoconstrictor, promotes smooth muscle growth and influences neutrophil activity.

Renal and Endocrine Regulation

  • Renal System: Regulates sodium excretion and extracellular fluid volume influencing cardiac output.

  • Renin-Angiotensin-Aldosterone System: Key in managing blood volume and pressure.

  • Aldosterone: Promotes sodium and water retention by kidneys to increase BP.

  • Antidiuretic Hormone (Vasopressin): Increases ECF volume via water reabsorption in the kidneys.

Hypertension Pathophysiology

  • Primary Hypertension: High BP due to unidentified causes, accounts for 90-95% of cases.

  • Risk Factors: Include age, alcohol use, obesity, dietary sodium intake, and more. Each factor contributes to the likelihood of developing hypertension.

Secondary Hypertension

  • Causes: Hypertension due to identifiable reasons, such as renal disease or endocrine disorders. Sudden onset or occurrence in children can suggest secondary hypertension.

Significance of Hypertension (HTN)

  • Prevalence increases with age; more prominent in specific demographics (e.g., Black adults). HTN is often asymptomatic, leading to potential target organ diseases (TOD).

  • Notable TODs include hypertensive heart disease, retinopathy, and nephrosclerosis.

  • Awareness is crucial as 1 in 4 adults may have or be taking medication for hypertension but only half achieve control.

Classification of Hypertension

  • Categories:

    • Normal: SBP < 120 and DBP < 80

    • Elevated: SBP 120-129 and DBP < 80

    • Stage 1 Hypertension: SBP 130-139 or DBP 80-89

    • Stage 2 Hypertension: SBP > 140 or DBP > 90

Management and Treatment Approaches

  • Interprofessional Care: Focus on accurate BP assessment, risk assignment, and periodic monitoring.

  • Drug Therapy: Begin with lifestyle changes, medications introduced if changes are inadequate. Thiazide diuretics often first choice for essential hypertension.

  • Nutritional Therapy: Manage sodium intake (<2 gm/day), reduce weight, restrict cholesterol/saturated fats, and adhere to the DASH diet.

  • Lifestyle Modifications: Include regular physical activity (30 mins most days), smoking cessation, moderate alcohol intake, and managing psychosocial stressors.