Orthostatic Hypotension (Low Blood Pressure When Standing)

What Is Low Blood Pressure?

• The autonomic nervous system makes changes in blood pressure and heart rate to allow the body to provide adequate blood supply to the brain when the body changes position.
• Symptoms of orthostatic hypotension include lightheadedness, weakness, blurred vision, and syncope or passing out.
• Dehydration, blood loss, and anemia are the most common reasons to develop low blood pressure when standing.
• Beta-blockers, other high blood pressure medications, and medications such as sildenafil (Viagra) may all cause orthostatic hypotension.
• Vasovagal syncope may cause symptoms of fainting when the vagus nerve is stimulated by a noxious stimulus, either physical (pain) or emotional.
• Diagnosis is often made by history and physical examination. Injury from falling is the main complication of this entity.
• Maintaining adequate hydration is the best way to prevent orthostatic hypotension if the hypotension is caused by dehydration. However, overhydration can exacerbate congestive heart failure. Patients with CHF and orthostatic hypotension need to closely monitor fluid intake and make changes only with physician supervision.

When a person stands up from sitting or lying down, the body must work to adjust to that change in position. It is especially important for the body to push blood upward and supply the brain with oxygen. If the body fails to do this adequately, blood pressure falls, and a person may feel lightheaded or even pass out.

Orthostatic hypotension is the term used to describe the fall in blood pressure when a person stands (orthostatic= upright posture of the body; hypo= less + tension=pressure).

Adequate blood supply to the body's organs depends upon three factors:

1. a heart strong enough to pump,
2. arteries and veins that can constrict or squeeze, and
3. enough blood and fluid within the vessels.

When the body changes position, a variety of actions occur involving all parts of the cardiovascular system as well as the autonomic nervous system that helps regulate their function.

The autonomic nervous system can be considered to "run in the background" of the body, regulating body processes that we take for granted. There is a balance between the sympathetic system (adrenergic nerves), which speeds things up, and the parasympathetic system (cholinergic nerves) which slows things down. These names are based on the type of chemical that is used to transmit signals at the nerve endings.

• Adrenaline (from the sympathetic nervous system) allows the body to respond to stress. Imagine seeing a bear in the woods; your heart beats faster, your palms get sweaty, your eyes dilate, and your hair stands on end.
• Acetylcholine is a chemical that is an anti-adrenaline and is involved in the parasympathetic nervous system.

These two systems are in balance, and yet need to respond to routine changes in the body that happens throughout the day.

• When the body moves to a standing position, pressure monitors (baroreceptor cells) located in the carotid arteries and the aorta sense a subtle drop in blood pressure because of gravity, which causes blood to flow toward the legs.
• Almost immediately, the sympathetic system is stimulated, causing the heart rate to increase, the heart muscle to contract or squeeze more forcefully, and blood vessels to constrict or narrow.
• All of these actions serve to increase blood pressure so that an adequate amount of blood can still be pumped to the brain and other organs.
• Without these changes, gravity would cause the blood to remain in the lowest part of the body and away from the brain, causing symptoms of lightheadedness or even passing out.

Orthostatic hypotension is not a disease or a complaint from an individual; it is an abnormal change in blood pressure and heart rate associated with an illness.

When the brain does not get enough blood supply, it begins to shut down.

Symptoms include:

• lightheadedness,
• confusion,
• nausea, and
• fainting or passing out.

There may also be a weakness, blurred vision, and shaking or tremulousness.

These symptoms may resolve quickly as the body slowly adjusts to the standing position, but in some cases, the patient has to sit or lie down quickly to prevent passing out or falling.

Orthostatic hypotension most often occurs in the elderly. "Hardening of the arteries" or atherosclerosis that develops as we age makes it more difficult for blood vessels to adapt quickly when necessary. As well, many of the diseases that are associated with orthostatic hypotension are progressive, with symptoms worsening with age.

Pregnancy is associated with orthostatic hypotension. As the pregnancy progresses, the volume of the circulatory system expands and blood pressure tends to fall. This may lead to lightheadedness when standing quickly. Blood pressure levels return to normal after delivery.

Excessive sweating due to physical exertion and exposure to heat are risk factors and potential causes of dehydration and symptoms of orthostatic hypotension. Patients who have other risk factors to develop orthostatic hypotension have an increased risk if they become even mildly dehydrated.

Chronic alcohol use and drug abuse are also risk factors for developing symptoms of orthostatic hypotension.

Orthostatic hypotension has many potential causes, some affecting only one part of the system that supplies blood to the brain, and others affecting two or three.

Loss of fluid within the blood vessels is the most common reason to develop the symptoms of orthostatic hypotension. The fluid may be water or blood depending upon the cause.

• Dehydration occurs when fluid intake cannot match the amount of fluid lost by the body. Vomiting, diarrhea, fever, and heat-related illnesses (for example, heat exhaustion or heat stroke) are common reasons a person loses a significant amount of fluid. Diuretics or water pills used to control high blood pressure are also another cause of a decreased amount of fluid in the body.
• Blood loss and other causes of anemia decrease the number of red blood cells that carry oxygen in the bloodstream, and this may lead to the symptoms of orthostatic hypotension. The bleeding may arise from one large event or may occur slowly over some time. With slow bleeding, the body may be able to compensate, replacing the lost volume of red blood cells with water in the bloodstream. However, after a while, the loss of oxygen-carrying capacity of the blood will cause symptoms to develop. In addition to lightheadedness, there may be a weakness, shortness of breath, or chest pain.
• Medications that affect the autonomic nervous system may also cause orthostatic hypotension.
• Beta-blocker medications such as metoprolol (Inderal) block the beta-adrenergic receptors in the body, preventing the heart from speeding up, preventing the heart from contracting as forcefully, and dilating blood vessels. All three of these effects affect the ability of the body to react to position changes. Aside from high blood pressure and heart disease, these medications are also used for headache control and anxiety prevention.
• sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) dilate blood vessels, and this class of medication may cause orthostatic hypotension. The effect can be magnified if taken with nitrates, medications used to treat angina [for example, nitroglycerin (Nitrostat, Nitroquick, Nitrolingual, Nitro-Dur, Minitran, Nitro-Bid and others), isosorbide mononitrate (Imdur, Ismo, Monoket)], alcohol, or narcotic pain medications.
• Other medications used for high blood pressure control may be a potential cause of orthostatic hypotension, even if taken as prescribed.
• Orthostatic hypotension is a side effect of many psychiatric medications, including tricyclic antidepressants [amitriptyline (Endep, Elavil), nortriptyline (Pamelor, Aventyl), phenothiazines (Thorazine, Mellaril, Compazine), and MAO inhibitors (Nardil, Parnate)

A vasovagal episode is a condition that may occur when a stimulus causes excess activation of the parasympathetic system, slowing the heart rate and dilating blood vessels. Symptoms of lightheadedness or fainting then occur due to the lowering of blood pressure and a decrease in blood flow to the brain. The stimulus may be pain from an injury such as a broken bone, or there may be a psychological trigger, such as a medical student watching a first operation. The vagus nerve that causes this response may also in some cases be triggered by urinating (micturition syncope) or by pushing hard to have a bowel movement.

Patients with diabetes may develop peripheral neuropathy that can affect nerves of the autonomic nervous system, and as a result, may develop orthostatic hypotension. As well, patients with poorly-controlled diabetes have the potential of becoming dehydrated.

Some patients may develop post-prandial lightheadedness, meaning that symptoms occur after a heavy meal. In this case, the body dilates blood vessels to the stomach and intestine to help with digestion, leaving less blood available to flow to the brain.

Addison's Disease, or adrenal insufficiency, may also be associated with the inability of the body to compensate for a position change.

There are a variety of reasons that heart disease may cause orthostatic hypotension. Abnormalities of the electrical conduction system including heart rates that are too slow or too fast may cause changes in blood pressure. Patients with heart valve disorders, heart failure, and heart attack may all experience orthostatic hypotension.

Disorders of the nervous system may also cause orthostatic hypotension. Examples include Parkinsonism, amyloidosis, and Shy-Drager Syndrome (or multiple system atrophy).

Postural orthostatic tachycardia syndrome describes the feeling of lightheadedness, nausea, fatigue, and weakness associated with an elevated heart rate (greater than 120 beats per minute) that begins within 10 minutes of a heads-up tilt table test. It is often seen in younger females between the ages of 12 and 50, and there may be a relationship with chronic fatigue syndrome.

Feeling faint or lightheaded is not normal. While a rare episode that can be explained by circumstances, such as working or exercising in the heat, may be ignored, more frequent occurrences should be investigated.

If a person passes out and is unconscious, even for a short period of time, is never normal and medical care should be accessed.

The key to the diagnosis is a good history and physical examination. The health care practitioner will want to know the circumstances that are associated with the symptoms of lightheadedness or passing out since the patient is unlikely to have taken their blood pressure and checked their pulse rate amid the episode.

The symptoms tend to be transient and resolve quickly. Should there be a concern that the vital signs will change with position, the health care practitioner will take the blood pressure in both lying and standing positions and look for changes. It is advisable to pump up the cuff first, then have the patient stand, and then begin to release the pressure.

According to the American Academy of Neurology, the formal diagnosis of orthostatic hypotension requires a 20mm drop in systolic blood pressure or a 10mm drop in diastolic blood pressure within three minutes of standing. Often there is an associated increase in the heart rate, especially if dehydration or bleeding is the cause (if the patient is taking a beta blocker, the heart rate may not be able to respond with an increase).

Blood tests may be ordered to look for the underlying cause. These may include a red blood cell count (CBC) to access for anemia or bleeding. Electrolytes may be checked, especially if there has been a history of fluid loss through vomiting or diarrhea, since sodium and potassium abnormalities may be an issue. Kidney function may be assessed.

If the physical examination reveals concern about the heart, an electrocardiogram (EKG) may be done to evaluate electrical conduction and heart rhythm. An echocardiogram or ultrasound of the heart may be ordered to evaluate the heart valves and assess the function of the heart muscle. A stress test may be considered if there is concern about coronary artery disease.

A heads-up tilt table test may be ordered if the symptoms of orthostatic hypotension continue to recur but it has been difficult to document abnormalities in blood pressure readings. During the test, the patient is strapped flat on a table, and as the table gradually is tilted to a 70 or 80-degree angle, continuous blood pressure, and heart rate readings are taken. The patient may be left on the table for more than 10 minutes to look for the delayed changes seen in postural orthostatic tachycardia syndrome.

For many patients, the diagnosis may be made based on the history and physical examination, and no further testing may be needed.

The treatment for orthostatic hypotension depends upon the underlying diagnosis. If the cause is dehydration, then a fluid replacement will resolve the symptoms. If it is due to medication, then an adjustment of the dose or change in the type of medicine taken may be required.

Compression stockings may be considered to help prevent fluid from pooling in the legs when a person is sitting or lying down. This allows for more blood flow to be available to the brain when changes in position occur.

Medications may be of use, again depending upon the underlying cause of the orthostatic hypotension. For those who are otherwise healthy and have no specific illness that must be treated, increased salt and fluid intake may be recommended. Caffeine and nonsteroidal anti-inflammatory medications, for example, ibuprofen may also be suggested.

Some patients may be a candidate for fludrocortisone (Florinef) to increase the volume of fluid in the blood vessels. Fludrocortisone is an adrenergic (adrenaline-mimicking) drug, which stimulates the sympathetic nervous system. This medication does have significant side effects, including lowering magnesium and potassium levels in the blood, headache, swelling, and weight gain.

Falling is the most important complication of orthostatic hypotension. Most often, the symptoms are transient and self-limiting, giving the patient a chance to sit down, but when the drop in blood pressure causes syncope (fainting) or near syncope, it is the trauma that is sustained in the fall that causes the most damage.

Since dehydration is the most common cause of orthostatic hypotension, it is important to minimize the risk by keeping adequately hydrated. This is especially important if individual works or exercises in a hot environment. Fluids lost from vomiting, diarrhea, and other illnesses that are associated with a fever should be replaced as best as possible.

Patients taking new medications that may affect the autonomic nervous system should be aware of the potential for orthostatic hypotension and report any symptoms to their healthcare practitioner.