Hypertension or high blood pressure is a condition in which the arteries have persistently elevated blood pressure. Blood pressure is the force of blood pushing up against the blood vessel walls. Higher blood pressure means that heart is pumping harder.
Untreated, hypertension can lead to damage of various organs such as retina and kidney, can cause renal failure (kidney failure), aneurysm, heart failure, stroke, heart attack or cognitive decline later in life.
Blood pressure has two components, systolic which represents peak pressure in arteries and is higher value, and diastolic which represents minimum pressure in arteries which is lower value. The normal level for blood pressure is below 120/80, where 120 represents the systolic measurement and 80 represents the diastolic measurement.
Blood pressure between 120/80 and 139/89 is called prehypertension and a blood pressure of 140/90 or above is considered hypertension. Prehypertension denotes increased risk of hypertension.
Types of Hypertension
Hypertension can be essential or secondary.
Essential hypertension is the high blood pressure with unknown cause. It accounts for about 95% of cases. Secondary hypertension is the term for high blood pressure with a known cause, such as renal disease, tumors, or oral contraceptives.
Labile hypertension is said to be present when patient is hypertensive at one time and normotensive at another time.
Malignant hypertension is the high blood pressures associated with complications like papilledema, retinal exudates, hemorrhage. No absolute BP level can be assigned for this condition. However, these patients usually have BP around 200/140 mmHg.
Risk Factors Associated with Hypertension
Exact causes of hypertension are unknown but several factors have been found associated. These are
- Obesity or being overweight
- Being obese/overweight as a child
- Sedentary lifestyle
- Lack of physical activity
- High levels of salt intake
- Insufficient calcium, potassium, and magnesium consumption
- Vitamin D deficiency
- High levels of alcohol consumption
- Medications – oral contraceptives
- Family history of hypertension
- Chronic renal disease
- Adrenal and thyroid tumors.
Known Causes of Hypertension
- Acute nephritis,
- Interstitial nephritis and pyelonephritis
- Polycystic kidneys
- Renal artery stenosis
- Coaractation of aorta
- Cushing’s syndrome
- Thyrotoxicosis, myxedema.
- Raised intracranial tension
- Lead encephalopathy
- Aortic incompetence
- Toxemia of pregnancy
- Periarteritis nodosa.
Effects of Hypertension
The common organs damaged by long-standing hypertension are heart, kidneys, blood vessels, retina and central nervous system.
Increased myocardial work leads to concentric hypertrophy of left ventricle, angina pectoris and accelerated coronary artery disease. There is systolic as well as diastolic dysfunction.
Progressive arteriosclerosis involves both the efferent and afferent renal arterioles and capillaries of glomerular tuft. This leads to compromise in renal function, shrinkage of kidney, proteinuria.
Hypertension may cause microaneurysms which may rupture and cause cerebral hemorrhage. Accelerated atherosclerosis may cause cerebral thrombosis, embolism and infarction. Cerebral arteriolar spasm may cause hypertensive encephalopathy.
In eye, the following changes may occur in the fundud
- Grade I: Arteriolar narrowing leading to copper wire and silver wire appearance.
- Grade II: Arteriovenous nipping where arteries cross the vein.
- Grade III: In addition to Grade II changes, superficial flame shaped and deep dot like hemorrhages and cotton wool exudates.
- Grade IV: Grade III changes with papilledema.
Symptoms of Hypertension
Hypertension is silent disease and there are no specific symptoms associated. In fact, many persons with high blood pressure are not even aware of that they have this condition.
However, extremely high blood pressure may lead to some symptoms like headaches, dizziness, nausea, vision problems, breathing troubles, irregular heartbeat, epistaxis and blood in urine.
The clinical features may be due to the elevated BP itself, target organ involvement or due to underlying disease, as in secondary hypertension.
Diagnosis of Hypertension
Hypertension can be diagnosed simply by measuring the blood pressure with a device called a sphygmomanometer which consists of arm cuff, dial, pump, and valve. Digital devices fro measuring blood pressure are available. The measurement of blood pressure involves recording systolic and diastolic values.
A recent activity or stress may result in erroneous reading and regular monitoring may be required before labeling someone as hypertensive. Smoking, high cholesterol, or diabetes and other risk factors are taken into assessment.
When required, tests such as electrocardiograms (EKG) and echocardiograms can be done to check the heart condition.
Blood investigations to identify possible causes of secondary hypertension and to measure renal function, electrolyte levels, sugar levels, and cholesterol levels are done.
Treatment of Hypertension
The treatment of hypertension aims to lower the blood pressure to less than 140/90 – or even lower.
The treatment involves lifestyle changes and drugs.
These help to control hypertension in some, but are useful as adjuvants to drug treatment in almost all patients. They include the following measures:
Modest salt restriction is effective in controlling hypertension in mild to moderate hypertension because sodium and water retention is involved in large proportion of hypertensives.
Loosing weight decreases blood pressure and modifies other CVS risk factors like diabetes and hyslipidemias.
Smoking acutely raises BP. In addition, it is an independent and most important reversible coronary risk factor. Since tolerance develops to nicotine-induced hemodynamic effects, chronic smoking may not be associated with high BP. All hypertensives must be advised to stop smoking.
Lactovegetarian diet [Milk and vegetables] and high intake of polyunsaturated fish oils lower BP due to high content of potassium and in vegetable diet high content of fiber. Natural vegetables contain high levels of potassium which lowers the BP by:
- Increased sodium excretion
- Decreased sympathetic activity
- Decreased rennin-angiotensin sectetion and direct dilatation of renal arteries
Potassium lowers BP in 3 weeks with a peak in 15 weeks.
Concept of DASH Diet
DASH stands for dietary approach to stop hypertension [Hypertension is high blood pressure]. It is an eating plan that is low in fat but rich in low-fat dairy foods, fruits, and vegetables. Apart from providing benefit in high blood pressure it is also claimed to reduce the stroke and cardiac disease risk.
Whole grains, fish, poultry, nuts, seeds, and dried beans are recommended as a part of a balanced diet.
Here are the major key points recommended for DASH
- Minimize processed foods, snack items, canned soups. This would decease the intake of sodium.
- Take diet rich in calcium, potassium, and magnesium. Pottassium is available in good amounts in fruits and vegetables. Dairy products are high in calcium and magnesium.
DASH recommends eat 8 to 10 servings of fruits and vegetables and 3 servings of low-fat dairy products everyday.
- Reduce your fat intake both saturated fat and total. Only 30% of your total calories should be from fat. Out of this only 7% to 10% of calories should come from saturated fat.
Saturated fat is found in meats, cheeses, butter, poultry, snack foods, and other processed foods.
- Control your weight and increase your physical activity
Generally speaking DASH diet is a kind of vegetarian diet low in sodium, fat and rich in potassium, calcium and magnesium.
Various forms of relaxation like yoga, biofeedback and psychotherapy lowers BP, especially in those with sympathetic activity.
Drugs for Hypertension
Diuretics increase production of urine and decrease fluid volume. Oral diuretics are the most widely used anti-hypertensive agents. They are effective alone in 50% of mild hypertensives. Thiazides are very effective. They are well tolerated and need to be given only once a day. They enhance the potency of other anti-hypertensives. They act by reducing extra-cellular fluid volume and cardiac output. They help to counteract the hypertensive effect of high salt intake. However they can aggravate diabetes by suppressing release of insulin due to hypokalemia. Moreover, hyperlipidemia, hyperuricemia, hypokalemia, hyponatremia, hypomagnesemia may occur.
Reduce cardiac output and lower BP but raise the peripheral resistance on acute administration (which increases BP). However, on chronic administration, BP falls to pretreatment levels. In mild to moderate hypertension, it lowers the BP to less than 90 mmHg in more than 50% patients. Drug withdrawl, if needed, should be done slowly, otherwise rebound hypertension may occur. They can be combined with diuretics, calcium blockers, ace inhibitors and vasodilators. They may precipitate bronchospasm, cardiac failure, peripheral vascular disease, impotence and depression.
Calcium Channel Blockers
Nifedipine Amlodipine, felodipine nicardipine and nitrendipine are all other useful calcium blocker. These drugs are especially useful in elderly hypertensive.
Flushing, headache, palpitations, edema and hypotension may occur.
Renin released from the kidney acts on circulating angiotensinogen to produce angiotensin I which is converted to angiotensin II by converting enzyme. Angiotensin II is a potent vasoconstrictor as well as it stimulated aldosterone which retains sodium and causes hypertension. ACE inhibitors act by inhibiting the converting enzyme preventing the formation of angiotensin II and lowering of BP. They also act by reducing the degradation of bradykinin a potent vasodilator, which lowers the BP.
ACE Inhibitors cause regression of ventricular hypertrophy, attenuation of reperfusion injury-induced ventricular arrhythmias, preload and afterload reduction and coronary vasodilatation. These drugs have no adverse effects of lipids, uric acid or glucose metabolism. They lower the BP by 15-25%. Diastolic pressure is lowered more than systolic pressure. Concommitant sodium restriction and diuretics further lowers BP by 15-25%.
ACE Inhibitors are useful in renovascular hypertension. High angiotensin II is however required to maintain adequate filtration pressure behind the stenotic lesion. ACE Inhibitors decrease the perfusion pressure and lead to azotemia. Thus, they are contraindication in bilateral renal artery stenosis. These drugs are useful in hyper-tensive diabetics because of neutral effect of carbohydrate metabolism.
In addition they decrease microalbuminuria. Captopril also improves insulin sensitivity. It has a short duration of action and is used for cardiac failure. Enalepril, lisinopril, perindopril, ramipril, etc. are longer acting ACE inhibitors and useful in hypertension.
Adrenergic stimulation of alpha-1 receptors in the vascular smooth muscles causes vasoconstriction and hypertension. Alpha blockers attenuate vasoconstriction, and thereby decrease vascular resistance and blood pressure. Prazosin was the first alpha blocker with short duration of action. Terazosin and doxazosin are longer acting, once a day alpha blockers. The efficacy can be enhanced by concomitant use of diuretics.
The most dramatic adverse effect is the first dose postural hypotension/syncope.
Alpha blockers also have other beneficial effects like lowering of lipids, regression of left ventricular hypertrophy, enhancing insulin sensitivity (hence ideal for diabetic hypertensives) and relief of obstructive symptoms in benign prostatic hypertrophy.
These drugs act on the arteriolar smooth muscles, causing vasodilatation and lowering BP. However, reflex tachycardia and increase in cardiac output limits its usefulness in severe coronary artery disease. These effects can be reduced by combining Hydralazine with Beta blockers. Minoxidil is the other vasodilator whose usefulness is limited due to hirsutism in females. Diazoxide and nitroprusside are parenteral vasodilators useful in hypertensive emergencies.