Low Blood Pressure

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. 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.

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.

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 that is so low that 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 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.

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 (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 occur (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.

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. For more, please read the Tilt–Table Test procedure article.

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, 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 is an anticholinesterase medication that works on the autonomic nervous system, especially when a person is standing up. Side effects of pyridostigmine include minor abdominal cramping or increased frequency of bowel movements. Increasing salt intake can lead to heart failure in patients with existing heart disease and should not be undertaken without consulting a doctor.

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)], 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.