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Hypertension: Definition, Classification and Treatment

Definition of Hypertension

Hypertension is the most common cardiovascular disease in humans. It can be defined as a sustained increase in arterial blood pressure (BP) to different age and sex, where systolic blood pressure is more than 130-140 mm Hg and diastolic pressure is more than 85-90 mm Hg.

Sustained increase in arterial blood pressure may decrease the blood vessels in kidney, brain and heart and increase the incidence of:
  • renal failure
  • coronary heart disease
  • cardiac failure
  • stroke

Classification of Hypertension

Based on the BP level, hypertension can be classified into four classes. They are:

1. Borderline Hypertension

Diastolic: 90-95 mm Hg
Systolic: 140 mm Hg

2. Mild Hypertension

Diastolic: 95-104 mm Hg
Systolic: 140-160 mm Hg

3. Moderate Hypertension

Diastolic: 105-120 mm Hg
Systolic: 140 mm Hg

4. Severe Hypertension

Diastolic: 120 mm Hg
Systolic: 140 mm Hg

Treatment of Hypertension

All anti-hypertensive agents act at anatomic BP control sites.

List of Frequently Used Anti-hypertensive Agents

1) Diuretics
• Decrease Na+ and leads to decrease in blood volume
• Thiazide, loop, K+ sparking

2) Peripherally acting agents
• Ganglion blocker, e.g. trimethophane
• Adrenargic neuron blocker, e.g. guanthidine

Alpha1 blocks acting vasodilators Hydrolezire, Na-nitropruside.

4) Beta2 Adrenoceptor blocker
• e.g. Metoprolol, Atenolol

5) Centrally acting agents
• alpha2-agonist e.g. Clomidire

6) Angiotensive converting enzyme inhibitor
• e.g. coptopril, Lisinopil

7) Angiotensive receptor blocker
• E.g. Lasortar,Valsartar.

8) Ca++ Channel blocker
• E.g. Diltagem,verapamil.

Pharmacology of Anti-hypertensive Agents

(1) Diuretics

Diuretics are the drugs that act on nephron. They lower the blood pressure by inhibiting reabsorption of electrolytes. They work by:
  • decreasing BP through depleting body Na+
  • enhancing efficacy of ACE inhibitors
🗉 For mild or moderate hypertension, diuretics alone are sufficient (e.g. thiazides).

🗉 For severe hypertension, more powerful diuretics are used along with vasodilators to prevent volume retention and edema.

(2)Peripherally acting agents

a) Ganglion blocker
They block the autonomic ganglion and reduce BP by vasodilation, decrease nervous return and decrease cardiac output. Hence, sympathetically mediated vasomotor reflexes are inhibited.

b) Adrenergic Neuron-blocking Agents
• Decrease BP by blocking release of norepinephrine (NE) from postganglionic sympathetic neurons.
• Uniquely target to peripheral adrenergic neurone and inhibit the sympathetic function.
• Depletes NE concentrations leading to decrease in NE release.
• Used for patients with severe refractory hypertension.
• Side-effect is orthostatic hypotension.

(3) Vasodilators

• All vasodilators used in hypertension, relax smooth muscle of arterioles and lead to decreased peripheral vascular resistance, which leads to decrease in BP.

• Compensatory responses from baroreceptors and renin angiotensin system oppose the antihypertensive effect. Therefore, vasodilators work best in combination with other antihypertensive drugs (e.g. beta blockers and diuretics) that oppose the compensatory responses.

For Example:
Hydralozine– direct acting vasodilators, they cause arterial smooth muscle relaxation.
Na-nitroprusside--- it causes arterial and various smooth muscle relaxations.

(4) Adrenoceptor Antagonists (alpha and beta-blockers)

They block adrenoceptor. They decrease myocardial contractility and cardiac output also decrease the level of renin.

a) Alpha blocker: e.g. Parazosine
b) Beta-blocker: e.g. Propranolol, Metoprolol

(5)Centrally Acting Sympatholytic Drugs

• Decrease sympathetic outflow from vasopressor centers in the brain. Stimulate alpha2 adrenergic receptor in the brain stem cells and results a reduction sympathetic outflow from the CNS.

Alpha2 agonist: Methyldopa and Clonidine

(6) Angiotensin-converting Enzyme (ACE) Inhibitors

They target renin angiotensive enzyme and inhibit the renin angiotensive enzyme followed by inhibition of angiotensive I and II. 

Studies have shown ACE inhibitors to be useful first line agents in all subsets of CHF patients i.e. a symptomatic to severe chronic failure.

(7) Calcium channel blockers (e.g. verapamil, nefidipine)

• Used in both long-term and emergency treatment.
• Target block Ca++ channel in the cardiac and vascular smooth muscles.
• Inhibition of Ca++ influx into arterial smooth muscle cells leading to dilation of peripheral arterioles.