What  is low blood pressure?

Blood pressure is the force exerted by circulating  blood on  the walls of blood vessels, and constitutes one of  the principal vital signs of life, which also include heart beat, rate of breathing, and temperature. 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.

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 (squeezing) than when it is relaxing. 

Systolic blood pressure for most healthy adults falls between 90 and 120 millimeters of mercury (mm Hg). Normal  diastolic blood pressure falls between 60 and 80 mm Hg. Current guidelines define normal blood pressure  as lower than  120/80. Blood pressures over 130/80 are considered high. High  blood pressure increases the risk of developing: 

• heart disease, 
• kidney disease, 
• hardening of the arteries (atherosclerosis or arteriosclerosis), 
• eye damage, and 
• stroke. 

Low blood pressure (hypotension)  is pressure so low it causes symptoms  or signs due to the  low flow of  blood through the arteries and veins. 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 and 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. 

How is  blood pressure generated? 

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 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. (The  other mechanisms are effective in seconds.) 

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 blood pressure is not sufficient to deliver enough blood to the organs of the body, the organs  do not work properly  and may be permanently damaged. For example, if insufficient blood flows to the brain, brain cells do not receive enough oxygen  and nutrients, and  a person can feel lightheaded, dizzy, or even faint. 

Going from a sitting or lying position to a standing position often brings out symptoms of  low blood pressure. This occurs because standing causes blood to "settle" in the veins of the lower body, and this can lower the blood pressure. If the blood  pressure is already low, standing  can make the low pressure worse, to the point  of causing symptoms.  The development  of lightheadedness, dizziness, or fainting upon standing caused by  low blood pressure is called orthostatic hypotension. Normal individuals are able to compensate rapidly for the low pressure created by standing with the responses discussed previously and do not develop orthostatic hypotension. 

When there is insufficient blood pressure to deliver blood to the coronary arteries (the arteries that supply blood to the heart's muscle), a person can develop chest pain (a symptom of angina) or even a heart attack. 

When insufficient  blood is delivered to the kidneys, the kidneys fail  to eliminate wastes from the body, for example, urea  and creatinine, and an increase in their levels in the blood occurs (for example, elevations of blood urea nitrogen or BUN and serum creatinine, respectively). 

Shock is a life-threatening condition where persistently low blood  pressure causes organs such  as kidney(s), liver, heart, lung, and brain  to fail rapidly.

What are the causes of  low blood pressure? 

Conditions  that reduce the volume of blood, reduce cardiac output (the amount of  blood pumped by the heart),  and medications are frequent causes of  low blood pressure.

• Dehydration  is common among patients with prolonged nausea, vomiting, and diarrhea. Large amounts of water are lost when vomiting and with diarrhea, 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. Individuals with mild dehydration  may experience only thirst and dry mouth. Moderate to severe dehydration may  cause orthostatic hypotension (manifested by lightheadedness, dizziness, or fainting upon standing). Protracted and severe dehydration can lead to shock, kidney failure, confusion, acidosis (too much acid in the blood), coma, and even death. 

• Moderate or severe bleeding  can quickly deplete an individual's body of blood, leading to  low blood pressure or orthostatic hypotension. Bleeding can result  from trauma, surgical complications, or from gastrointestinal abnormalities such as ulcers, tumors, or diverticulosis. Occasionally, the bleeding may be so severe and rapid (for example, bleeding from a ruptured aortic aneurysm) that it causes shock and death rapidly. 

• Severe inflammation of organs inside the body such as acute pancreatitis  can cause low blood pressure. In acute pancreatitis, fluid leaves the blood vessels to enter the inflamed tissues around the pancreas  as well as the abdominal cavity, depleting the volume of blood. 

Causes of  low blood pressure due to heart disease 

• Weakened heart muscle  can cause the heart to fail  and reduce the amount  of blood it pumps. One common cause of weakened heart muscle  is the death of  a large portion of the heart's muscle due to  a single, large heart attack or repeated smaller heart attacks. Other examples of conditions that can weaken the heart include medications that are toxic to the heart, infections of the muscle of the heart by viruses (myocarditis),  and diseases of  the heart's valves such as aortic stenosis. 
• Pericarditis  is an inflammation  of the pericardium (the sac surrounding the heart). Pericarditis  can cause fluid to accumulate  within the pericardium and compress the heart, restricting the ability of the heart to fill and pump blood. 
• Pulmonary embolism is  a condition in which a blood clot in a vein (deep vein thrombosis) 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. The resting heart rate for a healthy adult is between 60 and 100 beats/minute. Bradycardia (resting heart rates slower than 60 beats/minute) does not always  cause low blood pressure. In fact, some highly trained athletes can have resting heart rates in the 40s and 50s (beats per minute) without any symptoms. (The slow heart rates are offset by more forceful contractions  of the heart that pump more blood than in non-athletes.) But in many patients bradycardia  can lead to low  blood pressure, lightheadedness, dizziness, and even fainting. 

1. Several common reasons for bradycardia include: 1) sick sinus syndrome, 2) heart block, and 3) drug toxicity. Many of these conditions occur in the elderly. 
2. Sick sinus syndrome: Sick sinus syndrome occurs when the diseased electrical system of the heart cannot generate signals fast enough to maintain  a normal heart rate. 
3. Heart block: Heart block occurs when the specialized tissues that transmit electrical current in the heart are damaged by heart attacks, degeneration from atherosclerosis,  and medications. Heart block prevents some or all  of the electrical signals from reaching the rest of the heart,  and this prevents the heart from contracting as rapidly as it otherwise would. 
4. Drug toxicity: Drugs such as digoxin (Lanoxin) or beta blockers for high blood pressure,  can slow the transmission of electricity in the heart chemically and can  cause bradycardia  and hypotension (see section below "Medications that cause low  blood pressure").

• An abnormally fast heart rate (tachycardia) also  can cause low  blood pressure. The most common example of tachycardia causing low blood pressure is atrial fibrillation. Atrial fibrillation is a disorder of the heart characterized by rapid and irregular electrical discharges from the muscle of the heart causing the ventricles  to contract irregularly and (usually) rapidly. The rapidly contracting ventricles do  not have enough time  to fill maximally with blood before the each contraction, and the amount of blood that is pumped decreases in spite of the faster heart rate. Other abnormally rapid heart rhythms such as ventricular tachycardia also can produce  low blood pressure, sometimes even life-threatening shock. 

Medications that cause  low blood pressure

• Medications such as calcium channel blockers, beta blockers, and digoxin (Lanoxin) can slow the rate at which the heart contracts. Some elderly people are extremely sensitive to these medications since they are more likely to have diseased hearts and electrical conduction tissues. 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. 
• Water pills (diuretics) such as furosemide (Lasix) can decrease blood volume by causing excessive urination. 
• Medications used for treating depression, such as amitriptyline (Elavil), Parkinson's disease, such as levodopa-carbidopa (Sinemet), erectile dysfunction (impotence), such as sildenafil (Viagra), vardenafil (Levitra),  and tadalafil (Cialis) when used in combination with nitroglycerine, can cause  low blood pressure. 
• Alcohol and narcotics also can cause low blood pressure. 

Other conditions that cause low blood  pressure

• Vasovagal reaction  is a common condition in which a healthy person temporarily develops low  blood pressure, slow heart rate, and sometimes fainting. A vasovagal reaction typically is brought  on by emotions of fear  or pain such as having blood drawn, starting an intravenous infusion, or by gastrointestinal upset. Vasovagal reactions are caused by activity of involuntary (autonomic) nervous system, especially the vagus nerve, which releases hormones that slow the heart and widen the blood vessels. The vagus nerve controls the heart rate (slows it down). The vagus nerve also controls digestive tract function and senses activity in the digestive system. Thus, some people can have a vasovagal reaction from straining at a bowel movement or vomiting. 
• Postural (orthostatic)  hypotension  is a sudden drop in blood pressure when an individual stands  up from a sitting, squatting, or supine (lying) position. When a person stands up, gravity causes  blood to settle  in the veins in the legs, so less blood reaches the heart for pumping, and as a result the blood pressure drops. The  body normally responds automatically to the drop in blood pressure  by increasing the rate at which the  heart beats and by narrowing the veins to return more  blood to the heart. In patients  with postural hypotension, this compensating reflex fails to occur, resulting in symptomatic low  blood pressure.  Postural hypotension can occur in persons of all ages but is much more common among the elderly, especially in those on medications  for high blood pressure and/or diuretics. Other causes  of postural hypotension include  dehydration, adrenal insufficiency (discussed later),  prolonged bed rest, diabetes that has caused damage to the autonomic nerves, alcoholism with damage to the autonomic nerves,  and certain rare neurological syndromes (for example, Shy-Drager syndrome) that damage the autonomic nerves. 
• Another form  of postural hypotension occurs typically in young  healthy individuals. After prolonged standing, the individual's heart rate and  blood pressure drops, causing dizziness, nausea, and often fainting. In these individuals, the autonomic  nervous system wrongly responds  to prolonged standing by directing  the heart to slow down  and the veins  to dilate. 
• Micturition syncope  is a temporary drop in blood pressure and loss  of consciousness brought about  by urinating. This condition typically occurs in elderly patients  and may be due to the release by the autonomic nerves of hormones that lower  blood pressure. 
• Adrenal insufficiency, for example, due  to Addison's disease, can cause low  blood pressure. Addison's disease is a disorder  in which the adrenal glands (small glands next  to the kidneys) are destroyed. The destroyed adrenal glands can no longer produce sufficient adrenal hormones (specifically cortisol) necessary to maintain normal bodily functions. Cortisol has many functions, one of which  is to maintain  blood pressure and  the function of the heart. Addison's disease is characterized by weight loss, muscle weakness, fatigue, low  blood pressure, and, sometimes, darkening of the skin. 
• Septicemia is  a severe infection in which bacteria (or other infectious organisms such as fungi) enter the blood. The infection typically originates in the lungs (as pneumonia), bladder,  or in the abdomen due to diverticulitis or gallstones. The bacteria then enter the  blood where they release toxins and cause life-threatening and profound low blood  pressure (septic shock), often with damage  to several organs. 
• Anaphylaxis (anaphylactic shock)  is a potentially fatal allergic reaction  to medications such as penicillin, intravenous iodine used in some x-ray studies, foods such as peanuts, or bee stings (insect stings). In addition to a severe drop in blood pressure, individuals may also experience hives, wheezing,  and a swollen throat with difficulty breathing. The shock  is caused by enlargement of blood-containing blood vessels  and escape of water from the blood into the tissues. 

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 (supine) 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 (kidney failure),  or acidosis (excess acid  in the blood). 
• Cortisol levels  can be measured to diagnose adrenal insufficiency  and Addison's disease.
• Blood and urine cultures  can be performed to diagnose septicemia 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. 
• Patient-activated event recorder. If  the episodes of bradycardia  or tachycardia are infrequent,  a 24-hour Holter recording may  not capture these sporadic episodes. In this situation,  a patient can wear a patient-activated event recorder for up  to four weeks. The patient presses a button to start the recording when he  or she senses the onset of an abnormal heart rhythm or  symptoms possibly caused by low blood pressure. The doctor then analyzes the recordings at a later date to identify the abnormal episodes. 
• 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 tumors of  the heart. 
• Ultrasound examinations  of the leg veins  and CT scans of the chest can detect deep vein thrombosis and pulmonary embolism. 
• Tilt-Table tests  are used  to evaluate patients suspected of having postural hypotension or syncope due to abnormal autonomic nerves. During a tilt-table test,  the patient lies on an examining table with an intravenous infusion administered while  the heart rate and blood pressure are monitored. The table then is tilted upright  for 15 minutes to 45 minutes. Heart rate and blood pressure are monitored every few minutes. The purpose of the test is to try to reproduce postural hypotension.  Sometimes  a doctor may administer epinephrine (Adrenalin, Isuprel) intravenously to induce postural hypotension. 

How is low blood pressure treated? 

Low blood pressure in healthy subjects without symptoms or organ damage needs no treatment. However, all patients with symptoms possibly due to low blood pressure should be evaluated by  a doctor. (Patients who  have had a major drop in blood pressure from their usual levels even without the development of symptoms also should be evaluated.) The doctor needs to identify the cause of the  low blood pressure because treatment will depend on the cause. For example, if  a medication is causing the  low blood pressure, the dose of medication may have to be reduced or the medication stopped, though only after consulting the doctor. Self-adjustment of medication should not be done. 

• 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 cardioversion,  or a catheterization procedure called pulmonary vein isolation. Ventricular tachycardia can be controlled with medications or with an implantable defibrillator. 
• Pulmonary embolism and deep vein thrombosis is treated with blood thinners, intravenous initially with heparin, and oral warfarin (Coumadin) later. 
• Pericardial fluid  can be removed by a procedure called pericardiocentesis. 
• Postural hypotension  can be treated by increasing water and salt intake*, increasing intake of caffeinated beverages because caffeine constricts  blood vessels, using compression stockings  to compress the leg veins and reduce the pooling of blood in the leg veins, and in some patients, the use of a medication called midodrine (ProAmatine). The problem with ProAmatine  is that while it increases blood pressure in the upright position, the supine blood pressure may become too high, thus increasing the risk of strokes. Mayo Clinic researchers found that  a medication used to treat muscle weakness in Myasthenia gravis called pyridostigmine (Mestinon) increases upright blood pressure but not supine blood pressure. Mestinon, an anticholinesterase medication, works  on the autonomic nervous system, especially when  a person is standing up. Side effects include minor abdominal cramping or increased frequency of bowel movements. *Note: Increasing salt intake can lead  to heart failure in patients with existing  heart disease and should not  be undertaken without consulting a doctor. 
• Postprandial hypotension  refers to low  blood pressure occurring after meals. Ibuprofen (Motrin) or indomethacin (Indocin)  may be beneficial.
• Vasovagal Syncope can be treated with  several types of drugs such  as beta blockers for example, propanolol (Inderal, Inderal LA), selective serotonin reuptake inhibitors fluoxetine (Prozac), escitalopram oxalate (Lexapro), paroxetine (Paxil), sertraline (Zoloft), citalopram (Celexa), fluvoxamine (Luvox), fludrocortisone (Florinef) (a drug that prevents dehydration by causing the kidney(s)  to retaining water). A pacemaker can also be helpful when  a patient fails drug therapy. 

Low Blood Pressure At A Glance 

• Low blood pressure, also called hypotension, is blood pressure that is  low enough that the flow of  blood to the organs of the body is inadequate and symptoms and/or signs of low blood flow develop. 
• Low  pressure alone, without symptoms  or signs, usually is not unhealthy. 
• The symptoms of low blood pressure include lightheadedness, dizziness, and fainting. These symptoms are most prominent when individuals go  from the lying or sitting position  to the standing position (orthostatic hypotension). 
• Low blood pressure that causes an inadequate flow  of blood to  the body's organs can cause strokes, heart attacks, and kidney failure. It's most severe form is shock. 
• Common causes of low blood pressure include  a reduced volume of blood, heart disease, and medications. 
• The cause of low blood pressure can be determined with blood tests, radiologic studies, and cardiac testing  to look for arrhythmias.
• Treatment of low blood pressure is determined by the cause of the low pressure.