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 the 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 the higher value, and diastolic which represents minimum pressure in arteries and which is the 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 blood pressure of 140/90 or above is considered hypertension. Prehypertension denotes an increased risk of hypertension.
Types of Hypertension
Hypertension can be essential or secondary.
Essential hypertension is the high blood pressure with an 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 the patient is hypertensive at one time and normotensive at another time.
Malignant hypertension is the high blood pressure 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
- Smoking
- Obesity or being overweight
- Being obese/overweight as a child
- Diabetes
- 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
- Stress
- Aging
- Medications – oral contraceptives
- Family history of hypertension
- Chronic renal disease
- Adrenal and thyroid tumors.
Known Causes of Hypertension
Renal Causes
- Acute nephritis
- Interstitial nephritis and pyelonephritis
- Polycystic kidneys
- Renal artery stenosis
Vascular Causes
- Arteriosclerosis
- Coarctation of aorta
Endocrinal Causes
- Pheochromocytoma
- Cushing’s syndrome
- Thyrotoxicosis, myxedema
Neurological
- Raised intracranial tension
- Lead encephalopathy
Miscellaneous
- Polycythemia
- 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.
Cardiovascular System
Increased myocardial work leads to concentric hypertrophy of the left ventricle, angina pectoris and accelerated coronary artery disease. There is systolic as well as diastolic dysfunction.
Kidneys
Progressive arteriosclerosis involves both the efferent and afferent renal arterioles and capillaries of the glomerular tuft. This leads to a compromise in renal function, shrinkage of kidney and proteinuria.
Nervous System
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.
Fundus
In the eye, the following changes may occur in the fundus
- 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 a silent disease and there are no specific symptoms associated. In fact, many persons with high blood pressure are not even aware 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 the 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 an arm cuff, dial, pump, and valve. Digital devices for measuring blood pressure are available. The measurement of blood pressure involves recording systolic and diastolic values.
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 the 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
Treatment of hypertension aims to lower the blood pressure to less than 140/90 or even lower.
The treatment involves lifestyle changes and drugs.
Lifestyle Changes
These help to control hypertension in some but are useful as adjuvants to drug treatment in almost all patients. They include the following measures:
Salt reduction
A modest salt restriction is effective in controlling mild to moderate hypertension because sodium and water retention is involved in a large proportion of hypertensives.
Weight reduction
Losing weight decreases blood pressure and modifies other CVS risk factors like diabetes and dyslipidemias.
No Smoking
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.
Diet
Lactovegetarian diet [Milk and vegetables] and high intake of polyunsaturated fish oils lower BP due to a high content of potassium and in a 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 secretion and direct dilatation of renal arteries
Potassium lowers BP in 3 weeks with a peak in 15 weeks.
The concept of DASH Diet
DASH stands for a dietary approach to stop hypertension. 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 stroke and cardiac disease risk.
Green Vegetables Are Part Of DASH
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 decrease the intake of sodium.
- Take a diet rich in calcium, potassium, and magnesium. Potassium is available in good amounts in fruits and vegetables. Dairy products are high in calcium and magnesium.
DASH recommends eating 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 fat. 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 meat, cheese, 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.
Relaxation
Various forms of relaxation like yoga, biofeedback and psychotherapy lower BP, especially in those with sympathetic activity.
Drugs for Hypertension
Diuretics
Diuretics increase the production of urine and decrease fluid volume. Oral diuretics are the most widely used antihypertensive 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 the release of insulin due to hypokalemia. Moreover, hyperlipidemia, hyperuricemia, hypokalemia, hyponatremia, and hypomagnesemia may occur.
Beta-Blockers
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 BP to less than 90 mmHg in more than 50% of 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 calcium blockers. These drugs are especially useful in elderly hypertensives.
Flushing, headache, palpitations, edema, and hypotension may occur as side effects.
ACE Inhibitors
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 stimulates 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 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 on lipid, uric acid or glucose metabolism. They lower BP by 15-25%. Diastolic pressure is lowered more than systolic pressure. Concomitant sodium restriction and diuretics further lower 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 contraindicated in bilateral renal artery stenosis. These drugs are useful in hypertensive diabetics because of neutral effect on 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. Enalapril, lisinopril, perindopril, ramipril, etc. are longer-acting ACE inhibitors and useful in hypertension.
Alpha-Blockers
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 the 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.
Vasodilators
These drugs act on the arteriolar smooth muscles, causing vasodilatation and lowering BP. However, reflex tachycardia and an increase in cardiac output limit 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.