Dr. Francis SANWO

Blood pressure is the force exerted by circulating blood on the walls of blood vessels. It constitutes one of the critically important signs of life or vital signs, which include heart rate, breathing, and temperature. Blood pressure is generated by the heart pumping blood into the arteries modified by the response of the arteries to the flow of blood.

An individual's blood pressure is expressed as systolic/diastolic blood pressure, for example, 120/80mm Hg. 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 following its contraction.

The range of systolic blood pressure for most healthy adults falls between 90 and 120 millimeters of mercury (mm Hg). Normal diastolic blood pressure ranges between 60 and 80 mm Hg. Current guidelines define normal blood pressure range as lower than 120/80. Blood pressures over 130/80 are considered high.                                                                                                                                                    

What is Low Blood Pressure?                                                                                         

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 temporarily or permanently damaged. Symptoms of low blood pressure caused by conditions or diseases depend upon the specific cause of the low blood pressure.

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 routinely may have blood pressure numbers of 90/50 with no symptoms and therefore do not have low blood pressure. However, others who normally have higher blood pressures may develop symptoms of low blood pressure if their blood pressure drops to 100/60.

Low pressure alone, without symptoms or signs, usually is not unhealthy.

Is Low Blood Pressure Dangerous?

Athletes, people who exercise regularly, people who maintain ideal body weight, and nonsmokers tend to have lower blood pressures. Low blood pressure is desirable as long as it is not low enough to cause symptoms and damage to the organs in the body. So it could be dangerous.

Symptoms of low blood pressure due to conditions or diseases include:

Orthostatic hypotension symptoms: 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.

Heart disease: Chest pain (a symptom of angina) or even a heart attack may occur when there is insufficient blood pressure to deliver blood to the coronary arteries (the arteries that supply blood to the heart's muscle).

Kidney disease: When insufficient blood is delivered to the kidneys, the kidneys fail to eliminate wastes from the body, for example, urea (BUN and creatinine), and increases in their levels in the blood occur.

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

What Causes Low Blood Pressure?

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

Dehydration, bleeding, and inflammation.

Dehydration is common among patients with prolonged nausea, vomiting, diarrhea, or excessive exercise, which shunts blood away from the organs to the muscles.
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). Prolonged 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.

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, concentrating blood and reducing its volume.

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 ability of the heart to pump blood include medications 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 that reduce the flow of blood from the heart and into the arteries.

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 expand, fill, and pump blood.

Pulmonary embolism is a condition in which a blood clot in a vein (deep vein thrombosis or DVT) 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.  In many patients bradycardia can lead to low blood pressure, lightheadedness, dizziness, and even fainting.

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.

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 (Afib). 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.                                      

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.

Medications used in treating high blood pressure (such as angiotensin converting enzyme or 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.

Medications used for treating depression, such as amitriptyline (Elavil); Parkinson's disease, such as levodopa-carbidopa (Sinemet); and erectile dysfunction (impotence), such as sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) when used in combination with nitroglycerin, 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.

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 that less blood returns to 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 and narrowing the veins to return more blood to the heart. In patients with postural hypotension, this compensating reflex fails to occur, resulting low blood pressure and its symptoms. 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.

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 of hormones that lower blood pressure.

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 and wheezing due to constriction of the airways, and a swollen throat, which causes difficulty breathing. The shock is caused by enlargement of blood-containing blood vessels and escape of water from the blood into the tissues.

How do I know if I have low blood pressure?

In some people, 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 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. 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 tests like full blood count, serum electrolytes, urea and creatinine.

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 heartbeats, 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.

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.

What is the Treatment for Low Blood Pressure?

Low blood pressure readings in healthy people without symptoms or organ damage need no treatment. A doctor should evaluate all patients with symptoms that are possibly due to low blood pressure. 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; remedies 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. Do not adjust medication dose on your own, and do not stop taking any medication without first consulting your doctor.

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 a hospital or emergency room with intravenous fluids and electrolytes.

Blood loss can be treated by treating the cause of the bleeding, and with intravenous fluids and blood transfusions. Continuous and severe bleeding needs to be treated immediately.

Septic shock is a medical 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.

Pulmonary embolism and deep vein thrombosis is treated with blood thinners, initially with types of heparin. Later, oral warfarin (Coumadin) or other oral medications are substituted for heparin.

Pericardial fluid from pericarditis can be removed by a procedure called pericardiocentesis.

Postural hypotension can be treated with changes in diet such as 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.