Hypertension: Definition, Classification and Treatment
Hypertension or high blood pressure, is a common condition that affects millions of people globally. It is a primary risk factor for various cardiovascular diseases. If left untreated, it can even lead to death or disability. This article describes its definition, classification, and treatment options.
Definition of Hypertension
Hypertension is a condition in which the blood vessels have sustained increase in pressure. It happens when both blood pressure readings go beyond the normal range (diastolic BP ≥ 90 mm Hg; systolic BP ≥ 140 mm Hg). These values can vary depending on age and sex. In essence, hypertension means that the force of blood against the artery walls is higher than normal.
High blood pressure can decrease blood flow to the kidneys, brain, and heart and increase the incidence of following conditions:
- Renal failure
- Coronary heart disease
- Cardiac failure
- Stroke
Classification of Hypertension
Based on the BP level, hypertension can be classified into four classes.
| Classification | Systolic (mm Hg) | Diastolic (mm Hg) |
|---|---|---|
| Normal | Less than 120 | Less than 80 |
| Elevated | 120-129 | Less than 80 |
| Stage 1 Hypertension | 130-139 | 80-89 |
| Stage 2 Hypertension | ≥140 | ≥90 |
| Stage 3 Hypertension (consult your doctor immediately) | Higher than 180 | Higher than 120 |
Treatment of Hypertension
List of Frequently Used Anti-hypertensive Agents.
| Category | Example |
|---|---|
| 1) Diuretics | Thiazide, loop, and potassium-sparing diuretics |
| 2) Peripherally acting agents | Ganglion blocker, e.g. trimethophane; Adrenergic neuron blocker, e.g. guanthidine |
| 3) Vasodilators | Alpha-1 blockers (e.g. doxazosin and prazosin), hydralazine, sodium nitroprusside |
| 4) Adrenoceptor Antagonists (alpha and beta-blockers) | Metoprolol, atenolol |
| 5) Centrally acting agents | Alpha-2-agonist (e.g. clonidine) |
| 6) Angiotensive converting enzyme inhibitor | Captopril, lisinopril |
| 7) Angiotensive receptor blocker | Losartan, valsartan |
| 8) Ca++ Channel blocker | Diltiazem, verapamil |
Pharmacology of Anti-hypertensive Agents
(1) Diuretics
Diuretics act on the nephron. They lower blood pressure by inhibiting the reabsorption of electrolytes, mainly sodium (Na+). They work by:
- Decreasing BP through depleting body Na+
- Enhancing the efficacy of ACE inhibitors
For stage 1 hypertension, diuretics alone may be sufficient to lower blood pressure. For severe hypertension, more powerful diuretics are used along with vasodilators to prevent volume retention and edema.
(2) Peripherally acting agents
a) Ganglion blockers
Ganglion blockers reduce BP by inhibiting the autonomic ganglion, which results in vasodilation, decreased venous return, and decreased cardiac output. Sympathetically mediated vasomotor reflexes are also inhibited.
b) Adrenergic Neuron-blocking Agents
These agents decrease BP by blocking the release of norepinephrine (NE) from postganglionic sympathetic neurons. They uniquely target peripheral adrenergic neurons and inhibit sympathetic function, leading to decreased NE concentrations and release. They are used for patients with severe refractory hypertension, but a side effect is orthostatic hypotension.
(3) Vasodilators
All vasodilators used in hypertension relax the smooth muscle of arterioles, leading to decreased peripheral vascular resistance and a decrease in BP. Compensatory responses from baroreceptors and the 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:
- Hydralazine – a direct-acting vasodilator that causes arterial smooth muscle relaxation
- Sodium nitroprusside – causes relaxation of both arterial and venous smooth muscle
(4) Adrenoceptor Antagonists (alpha and beta-blockers)
Adrenoceptor antagonists block adrenoceptors, decreasing myocardial contractility, cardiac output, and renin release.
a) Alpha-blockers: e.g., prazosin
b) Beta-blockers: e.g., propranolol, metoprolol
(5) Centrally Acting Sympatholytic Drugs
These drugs decrease sympathetic outflow from vasopressor centers in the brain. They stimulate alpha2-adrenergic receptors in brainstem cells, resulting in a reduction of sympathetic outflow from the central nervous system (CNS).
Alpha2 agonists: e.g., methyldopa and clonidine
(6) Angiotensin-converting Enzyme (ACE) Inhibitors
ACE inhibitors target the renin-angiotensin system and inhibit the conversion of angiotensin I to angiotensin II. Studies have shown ACE inhibitors to be useful first-line agents in all subsets of CHF patients, from asymptomatic to severe chronic failure.
(7) Angiotensin receptor blockers (ARBs)
- They block the action of angiotensin II at its receptor, leading to vasodilation and reduced aldosterone release
- Examples: Losartan and valsartan
(8) Calcium Channel Blockers
Calcium channel blockers, such as verapamil and nifedipine, are used in both long-term and emergency treatment. They block calcium (Ca++) channels in cardiac and vascular smooth muscles. Inhibition of Ca++ influx into arterial smooth muscle cells leads to dilation of peripheral arterioles.
