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Blood pressure is the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs.

By convention, an individual's blood pressure is expressed as systolic/diastolic blood pressure, for example, 120/80.The systolic blood pressure (the top number) represents the pressure in the arteries as the muscle of the heart contracts and pumps blood into them. The diastolic blood pressure (the bottom number) represents the pressure in the arteries as the muscle of the heart relaxes after it contracts. Blood pressure always is higher when the heart is pumping than when it is relaxing.

Hypotension:  Any blood pressure that is below the normal expected for an individual in a given environment. Hypotension is the opposite of hypertension (abnormally high blood pressure). Low blood pressure can result from conditions of the nervous system, conditions that do not begin in the nervous system, and drugs. It would seem to be something to strive for. High blood pressure (hypertension) is a well-known risk factor for heart disease and other problems. In recent years there has been an ongoing downward revision of what is considered a normal blood pressure reading. A blood pressure less than 120/80 millimetres of mercury (mm Hg) is now considered normal and optimal for good health.

For many people, low blood pressure can cause dizziness and fainting or indicate serious heart, endocrine or neurological disorders. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock.

Types and Other names

Hypotension is abnormally low blood pressure. Normal blood pressure is a reading of less than 120/80 mmHg. Hypotension is blood pressure that is lower than 90/60 mmHg. Some people have low blood pressure all the time. They have no signs or symptoms and their low readings are normal for them. In other people, blood pressure drops below normal because of some event or medical condition. In a healthy person, low blood pressure without signs or symptoms is usually not a problem and requires no treatment. The three main forms of hypotension with signs and symptoms are orthostatic hypotension, neurally mediated hypotension (NMH), and severe hypotension associated with shock. Orthostatic hypotension is low blood pressure that occurs upon standing up from a sitting or lying down position. NMH is low blood pressure that results from standing for too long or in reaction to severe emotional stress. Shock is a life-threatening condition in which blood pressure drops so low that the brain, kidneys, and other vital organs can’t get enough blood to work properly. Shock can result from a major trauma to the body, such as serious bleeding, severe burns, heart attack, severe allergic reaction, or an infection in the blood. People of all ages can have hypotension. Older adults are more likely to have orthostatic and postprandial hypotension. Children and young adults are more likely to have NMH.

Signs and symptoms of orthostatic hypotension and NMH include dizziness, blurry vision, weakness, nausea, and fainting. Both of these types of hypotension can be dangerous if a person falls because of the dizziness or fainting. Signs and symptoms of shock include confusion, sweating, weak and rapid pulse, and warm and flushed skin that becomes cold and clammy. If shock progresses, the person can lose consciousness. Shock can be fatal if not treated immediately. Treatments for orthostatic hypotension and NMH are intended to relieve symptoms and manage underlying conditions. They include medicines and use of compression socks or inflatable pants to improve circulation. Lifestyle changes also are important, such as standing up slowly, drinking lots of fluids, and learning to recognize symptoms to prevent fainting. Treatment for shock includes restoring blood flow to the organs through special fluids or blood injected directly into the bloodstream through a needle. Medicines can be given to raise the blood pressure or make the heartbeat stronger. Depending on the cause of the shock, other treatments such as antibiotics or surgery may be required.

Who Is At Risk?

Depending on the reason for your low blood pressure, you may be able to take certain steps to help reduce or even prevent symptoms.

- Drink more water, less alcohol. Alcohol is dehydrating and can lower blood pressure, even if you drink in moderation. Water, on the other hand, combats dehydration and increases blood volume.

- Follow a healthy diet. Get all the nutrients you need for good health by focusing on a variety of foods, including whole grains, fruits, vegetables, and lean chicken and fish. If your doctor suggests increasing your sodium intake but you don't like a lot of salt on your food, try using natural soy sauce — a whopping 1,200 milligrams of sodium per tablespoon — or adding dry soup mixes, also loaded with sodium, to dips and dressings.

-    Go slow. You may be able to reduce the dizziness and lightheadedness that occurs with low blood pressure on standing by taking it easy when you move from a prone to a standing position. Before getting out of bed in the morning, breathe deeply for a few minutes and then slowly sit up before standing. Sleeping with the head of your bed slightly elevated also can help fight the effects of gravity. If you begin to get symptoms while standing, cross your thighs in a scissors fashion and squeeze or put one foot on a ledge or chair and lean as far forward as possible. These maneuvers encourage blood to flow from your legs to your heart.

Hypotension is a relative term because the blood pressure normally varies greatly with activity, age, medications, and underlying medical conditions. Neurologic conditions that can lead to low blood pressure include changing position from lying to more vertical, stroke, shock, light-headedness after urinating or defecating, Parkinson's disease, neuropathy and simply fright. Nonneurologic conditions that can cause low blood pressure include bleeding, infections, dehydration, heart disease, adrenal insufficiency, pregnancy, prolonged bed rest, poisoning, toxic shock syndrome, and blood transfusion reactions. Hypotensive drugs include blood pressure drugs, diuretics (water pills), heart medications (especially calcium antagonists- nifedipine / Procardia, beta blockers-propranolol / Inderal and others), depression medications (such as amitriptyline / Elavil), and alcohol.

How is blood pressure generated?

Blood pressure is generated by the heart pumping blood into the arteries and is regulated by the response by the arteries to the flow of blood. During relaxation of the heart (diastole) the left ventricle of the heart fills with blood returning from the lungs. The left ventricle then contracts and pumps blood into the arteries (systole). The blood pressure during contraction of the ventricle (systolic pressure) when blood is being actively ejected into the arteries is higher than during relaxation of the ventricle (diastolic pressure). The pulse that we can feel when we place our fingers over an artery is caused by the contraction of the left ventricle.

Blood pressure is determined by two factors: 1) The amount of blood pumped by the left ventricle of the heart into the arteries, and 2) the resistance to the flow of blood caused by the walls of the arterioles (smaller arteries).

Generally, blood pressure tends to be higher if more blood is pumped into the arteries or if the arterioles are narrow and stiff. (Narrow and stiff arterioles, by resisting the flow of blood, increase blood pressure.) This often happens when older patients develop atherosclerosis. Blood pressure tends to be lower if less blood is being pumped into the arteries or if the arterioles are larger and more flexible and, therefore, have less resistance to the flow of blood.

How does the body maintain normal blood pressure?

The body has mechanisms to alter or maintain blood pressure and blood flow. There are sensors that sense blood pressure in the walls of the arteries and the heart. These sensors are called baroreceptors. Baroreceptors sense blood pressure and then send signals to the heart, the arterioles, the veins, and the kidneys that cause them to make changes that lower or increase blood pressure. There are several ways in which blood pressure can be adjusted––by adjusting the amount of blood pumped by the heart into the arteries (cardiac output), the amount of blood contained in the veins, the arteriolar resistance, and the volume of blood.

- The heart can speed up and contract more frequently and it can eject more blood with each contraction. Both of these responses increase the flow of blood into the arteries and increase blood pressure.

- The veins can expand and narrow. When veins expand, more blood can be stored in the veins and less blood returns to the heart for pumping into the arteries. As a result, the heart pumps less blood, and blood pressure is lower. On the other hand, when veins narrow, less blood is stored in the veins, more blood returns to the heart for pumping into the arteries, and blood pressure is higher.

- The arterioles can expand and narrow. Expanded arterioles create less resistance to the flow of blood and decrease blood pressure, while narrowed arterioles create more resistance and raise blood pressure.

- The kidney can respond to changes in blood pressure by increasing or decreasing the amount of urine that is produced. Urine is primarily water that is removed from the blood. When the kidney makes more urine, the amount (volume) of blood that fills the arteries and veins decreases, and this lowers blood pressure. If the kidneys make less urine, the amount of blood that fills the arteries and veins increases and this increases blood pressure. Compared with the other mechanisms for adjusting blood pressure, changes in the production of urine affect blood pressure slowly over hours and days. 

For example, low blood volume due to bleeding (such as a bleeding ulcer in your stomach or from a bad laceration from an injury) can cause low blood pressure. The body quickly responds to the low blood volume and pressure by the following adjustments which all increase blood pressure: The heart rate increases and the forcefulness of the heart's contractions increase, thus more blood is pumped through the heart. Veins narrow to return more blood to the heart for pumping. Blood flow to the kidneys decreases to reduce the formation of urine and thereby increases the volume of blood in the arteries and veins. Arterioles narrow to increase resistance to blood flow. These adaptive responses will keep the blood pressure in the normal range unless blood loss becomes so severe that the responses are overwhelmed.

Is low blood pressure bad for your health?

People who have lower blood pressures have a lower risk of stroke, kidney disease, and heart disease. Athletes, people who exercise regularly, people who maintain ideal body weight, and non–smokers tend to have lower blood pressures. Therefore, low blood pressure is desirable as long as it is not low enough to cause symptoms and damage organs in the body.

What are low blood pressure signs and symptoms?

When the flow of blood is too low to deliver enough oxygen and nutrients to vital organs such as the brain, heart, and kidney, the organs do not function normally and may be permanently damaged.

Unlike high blood pressure, low blood pressure is defined primarily by signs and symptoms of low blood flow not by a specific blood pressure number. Some individuals may have a blood pressure of 90/50 with no symptoms of low blood pressure and therefore do not have low blood pressure. However, others who normally have high blood pressure may develop symptoms of low blood pressure if their blood pressure drops to 100/60.

What are the causes of low blood pressure?

Conditions that reduce the volume of blood reduce cardiac output and medications are frequent causes of low blood pressure.

- Dehydration is common among patients with prolonged nausea, vomiting, and diarrhoea. Large amounts of water are lost when vomiting and with diarrhoea, especially if the patient does not drink adequate amounts of fluid to replace the depleted water.

- Other causes of dehydration include exercise, sweating, fever, and heat exhaustion, or heat stroke.

- Moderate or severe bleeding can quickly deplete an individual's body of blood, leading to low blood pressure or orthostatic hypotension. Severe inflammation of organs inside the body such as acute pancreatitis can cause low blood pressure.

- Weakened heart muscle can cause the heart to fail and reduce the amount of blood it pumps. Pulmonary embolism is a condition in which a blood clot in a vein breaks off and travels to the heart and eventually the lung. A large blood clot can block the flow of blood into the left ventricle from the lungs and severely diminish the blood returning to the heart for pumping. Pulmonary embolism is a life–threatening emergency.

- A slow heart rate (bradycardia) can decrease the amount of blood pumped by the heart. An abnormally fast heart rate (tachycardia) also can cause low blood pressure.

- Medications such as calcium channel blockers, beta blockers, and digoxin (Lanoxin) can slow the rate at which the heart contracts. In some individuals, the heart rate can become dangerously slow even with small doses of these medications. Medications used in treating high blood pressure (such as ACE inhibitors, angiotensin receptor blockers, beta blockers, calcium channel blockers, and alpha–blockers) can excessively lower blood pressure and result in symptomatic low blood pressure especially among the elderly. Diuretics can decrease blood volume by causing excessive urination. Medications used for treating depression, Parkinson's disease, erectile dysfunction (impotence) when used in combination with nitro-glycerine, can cause low blood pressure. Alcohol and narcotics also can cause low blood pressure.

Risk factors

Low blood pressure (hypotension) can happen to anyone, though certain types of low blood pressure are more common depending on your age or other factors:

- Age. Drops in blood pressure on standing or after eating occur primarily in older adults. Orthostatic hypotension happens after standing up, while postprandial hypotension happens after eating a meal. Neurally mediated hypotension happens as a result of a miscommunication between the brain and heart. It primarily affects children and younger adults.

- Medications.  People who take certain medications, such as high blood pressure medication, have a greater risk of low blood pressure.

- Certain diseases. Parkinson's disease and some heart conditions put you at a greater risk of developing low blood pressure.

Some people with low blood pressure are in peak physical condition with strong cardiovascular systems and a reduced risk of heart attack and stroke. But low blood pressure can also signal an underlying problem, especially when it drops suddenly or is accompanied by signs and symptoms such as: Dizziness or lightheadedness, Fainting (syncope), Lack of concentration, Blurred vision, Nausea, Cold, clammy, pale skin, Rapid, shallow breathing, Fatigue, Depression, Thirst.

When to seek medical advice

In many instances, low blood pressure isn't serious. If you have consistently low readings but feel fine, your doctor is likely to monitor you during routine exams. Even occasional dizziness or light-headedness may be relatively minor — the result of mild dehydration, low blood sugar or too much time in the sun or a hot tub, for example. In these situations, it's not a matter so much of how far, but of how quickly, your blood pressure drops. Still, it's important to see your doctor if you experience any signs or symptoms of hypotension because they sometimes can point to more serious problems. It can be helpful to keep a record of your symptoms, when they occur and what you were doing at the time. If these occur at times that may endanger you or others, you should talk to your doctor.

Screening and diagnosis

The goal in evaluating low blood pressure is to find the underlying cause. This helps determine the correct treatment and identify any heart, brain or nervous system problems that may be responsible for lower than normal readings. To help reach a diagnosis, your doctor may recommend one or more of the following:

- Blood tests.  These can provide a certain amount of information about your overall health as well as whether you have low blood sugar or a low number of red blood cells (anemia), both of which can cause lower than normal blood pressure.

- Electrocardiogram (ECG, EKG). This non-invasive test detects irregularities in your heart rhythm, structural abnormalities in your heart, and problems with the supply of blood and oxygen to your heart muscle. It can also tell if you're having a heart attack or if you've had a heart attack in the past. Sometimes you may be asked to wear a 24-hour Holter monitor to record your heart's electrical activity as you go about your daily routine.

- Echocardiogram.  An echocardiogram uses sound waves to produce images of your heart that may show abnormalities in your heart muscle or valves.

- Stress test. Some heart problems which can cause low blood pressure are easier to diagnose when your heart is working harder than when it's at rest. During a stress test, you'll exercise, such as walking on a treadmill. When your heart is working harder, your heart will be monitored with electrocardiography or echocardiography.

- Valsalva manoeuvre. This non-invasive test checks the functioning of your autonomic nervous system by analyzing your heart rate and blood pressure after several cycles of a type of deep breathing: You take a deep breath and then force the air out through your lips, as if you were trying to blow up a stiff balloon.

- Tilt-table test. If you have low blood pressure on standing, or from faulty brain signals, your doctor may suggest a tilt-table test, which evaluates how your body reacts to changes in position. During the test, you lie on a table that's tilted to raise the upper part of your body, which simulates the movement from a prone to a standing position.

How is low blood pressure diagnosed and evaluated?

In some individuals, particularly relatively healthy ones, symptoms of weakness, dizziness, and fainting raise the suspicion of low blood pressure. In others, an event often associated with low blood pressure, for example a heart attack has occurred to cause the symptoms. Measuring blood pressure, sometimes in both the lying and standing positions usually is the first step in diagnosing low blood pressure. In patients with symptomatic low blood pressure, there often is a marked drop in blood pressure upon standing, and patients may even develop orthostatic symptoms. The heart rate often increases greatly. Once low blood pressure has been identified as the cause of symptoms, the goal is to identify the cause of the low blood pressure. Sometimes the causes are readily apparent (such as loss of blood due to trauma, or sudden shock after receiving x–ray dyes containing iodine). At other times, the cause may be identified by testing: CBC (complete blood count). CBC may reveal anemia from blood loss or elevated white blood cells due to infection. Blood electrolyte measurements may show dehydration and mineral depletion, renal failure, or acidosis. Blood and urine cultures can be performed to diagnose septicaemia and bladder infections, respectively. Radiology studies, such as chest x–rays, abdominal ultrasounds, and computerized tomography (CT or CAT) scans may detect pneumonia, heart failure, gallstones, pancreatitis, and diverticulitis. Electrocardiograms (EKG) can detect abnormally slow or rapid heart beats, pericarditis, and heart muscle damage from either previous heart attacks or a reduced supply of blood to the heart muscle that has not yet caused a heart attack. Holter monitor recordings are used to diagnose intermittent episodes of abnormal heart rhythms. If abnormal rhythms occur intermittently, a standard EKG performed at the time of a visit to the doctor's office may not show the abnormal rhythm. A Holter monitor is a continuous recording of the heart's rhythm for 24 hours that often is used to diagnose intermittent episodes of bradycardia or tachycardia. Echocardiograms are examinations of the structures and motion of the heart using ultrasound. Echocardiograms can detect pericardial fluid due to pericarditis, the extent of heart muscle damage from heart attacks, diseases of the heart valves, and rare tumours of the heart. Ultrasound examinations of the leg veins and CT scans of the chest can detect deep vein thrombosis and pulmonary embolism.

Complications

Even moderate forms of low blood pressure can seriously affect quality of life, leading not only to dizziness and weakness but also to fainting and a risk of injury from falls. And severely low blood pressure from any cause can deprive your body of enough oxygen to carry out its normal functions, leading to damage to your heart and brain.

How is low blood pressure treated?

Low blood pressure that doesn’t cause signs or symptoms requires treatment. In symptomatic cases, the appropriate therapy depends on the underlying cause, and doctors usually try to address the primary health problem — dehydration, heart failure, diabetes or hypothyroidism, for example — rather than low blood pressure itself. When low blood pressure is caused by medications, treatment usually involves changing the dose of the medication or stopping it entirely.

If it's not clear what's causing low blood pressure or no effective treatment exists, the goal is to raise your blood pressure and reduce signs and symptoms. Depending on your age, health status and the type of low blood pressure you have, this may be accomplished in several ways:

- Use more salt. Experts usually recommend limiting the amount of salt in your diet because sodium can raise blood pressure, sometimes dramatically. But for people with low blood pressure, that can be a good thing. But because excess sodium can lead to heart failure, especially in older adults, it's important to check with your doctor before upping your salt intake.

- Drink more water. Although nearly everyone can benefit from drinking enough water, this is especially true if you have low blood pressure. Fluids increase blood volume and help prevent dehydration, both of which are important in treating hypotension.

- Use compression stockings. The same elastic stockings and leotards commonly used to relieve the pain and swelling of varicose veins may help reduce the pooling of blood in your legs.

- Medications. Several medications, either used alone or together, can be used to treat low blood pressure that occurs when you stand up (orthostatic hypotension). For example, the drug fludrocortisone is often used to treat this form of low blood pressure. This drug helps boost your blood volume, which raises blood pressure. Doctors often use the drug midodrine to raise standing blood pressure levels in people with chronic orthostatic hypotension. It works by restricting the ability of your blood vessels to expand, which raises blood pressure. Other drugs, such as pyridostigmine, nonsteroidal anti-inflammatory drugs (NSAIDs), caffeine and erythropoietin are sometimes used, too, either alone or with other drugs.

- Dehydration is treated with fluids and minerals (electrolytes). Mild dehydration without nausea and vomiting can be treated with oral fluids and electrolytes. Moderate to severe dehydration usually is treated in the hospital or emergency room with intravenous fluids and electrolytes. Blood loss can be treated with intravenous fluids and blood transfusions. Continuous and severe bleeding needs to be treated immediately. Septic shock is an emergency and is treated with intravenous fluids and antibiotics.

- Blood pressure medications or diuretics are adjusted, changed, or stopped by the doctor if they are causing low blood pressure symptoms. Bradycardia may be due to a medication. The doctor may reduce, change or stop the medication. Bradycardia due to sick sinus syndrome or heart block is treated with an implantable pacemaker. Tachycardia is treated depending on the nature of the tachycardia. Atrial fibrillation can be treated with oral medications, electrical cardio version, or a catheterization procedure called pulmonary vein isolation. Ventricular tachycardia can be controlled with medications or with an implantable defibrillator.

Living with hypotension and Self-care

Hypotension can often be successfully treated, and many people with hypotension live normal, healthy lives.

If you have hypotension, it’s important to try and prevent or minimize symptoms, such as dizzy spells and fainting. Steps to take may include the following: Get up slowly after sitting or lying down if you have orthostatic hypotension. Don’t stand for long periods of time if you have neurally mediated hypotension. Eat small, low-carbohydrate meals if you have postprandial hypotension. Drink plenty of fluids, like water. Drink little or no alcohol. Increase salt intake, if appropriate. Use compression stockings. Get regular exercise, as appropriate for your state of health. Learn to take your own blood pressure to find out what’s normal for you. Keep a record of blood pressure readings done by health professionals.