Hypertension and Antihypertensive Drugs

Understanding Blood Pressure

• Definition: Blood pressure is the force exerted by circulating blood on the walls of blood vessels.
• Measurement: Taken using a cuff around the brachial artery (branch of the aorta).
• Phases:
  • Systolic: When heart contracts, highest pressure.
  • Diastolic: When heart relaxes, pressure due to artery recoil.
• Normal Blood Pressure: Systolic < 120 mmHg, Diastolic < 80 mmHg.
• Pre-hypertension: Systolic 120-129 mmHg, Diastolic 80-89 mmHg.
• Hypertension: Systolic ≥ 140 mmHg, Diastolic ≥ 90 mmHg.

Factors Influencing Blood Pressure

• Equation: Blood Pressure = Cardiac Output x Systemic Vascular Resistance (SVR).
• Cardiac Output:
  • Stroke Volume: Amount of blood pumped per contraction (~70 ml).
  • Heart Rate: Number of heartbeats per minute (~75 beats/min).
  • Cardiac Output ≈ 5 liters/minute.
• Systemic Vascular Resistance (SVR):
  • Affected by vessel diameter and length.
  • Narrow vessels = higher resistance.

Key Factors Affecting Hypertension

• Variables:
  • Blood Volume
  • Heart Rate
  • Stroke Volume
  • Systemic Vascular Resistance (SVR)

Antihypertensive Drugs

Types of Hypertension

• Primary (Essential) Hypertension: Unknown cause.
• Secondary Hypertension: Due to another disease.
• Malignant Hypertension: Rapid onset, organ damage.

Common Antihypertensive Medications

Beta Blockers

• Function: Inhibit sympathetic nervous system stimulation.
• Selective Beta-1 Blockers: Atenolol, Metoprolol
  • Decrease heart rate and contractility.
• Non-selective Beta Blockers: Propranolol
  • Affect lungs (risk for COPD/asthma patients).

ACE Inhibitors

• Function: Inhibit conversion of Angiotensin I to Angiotensin II.
• Effect: Reduce vasoconstriction, aldosterone release.
• Medication: Enalapril

Angiotensin II Receptor Antagonists

• Function: Block receptors for Angiotensin II.
• Medication: Candesartan

Calcium Channel Blockers

• Function: Block calcium entry, reducing heart muscle contraction.
• Types:
  • Nifedipine: Acts on vascular smooth muscle.
  • Verapamil: Acts on nodal tissues, reduces arrhythmias.
  • Diltiazem: Acts on coronary vasculature.

Diuretics

• Function: Increase sodium and water excretion, lower blood volume.
• Type: Thiazides (e.g., Hydrochlorothiazide)
  • Act on distal convoluted tubules.
  • Potential potassium loss (monitor levels).

Conclusion

• Antihypertensive medications target various factors influencing blood pressure.
• Understanding drug mechanisms aids in effective hypertension management.