Low Blood Pressure
Introduction
Just a few decades ago, doctors thought a blood pressure reading of 160/95 millimeters of mercury (mm Hg) was an acceptable target rate for most Americans. Today, those numbers are regarded as dangerously high, and blood pressure lower than 120/80 is considered optimal for good health.
The ongoing downward revision of blood pressure standards had led some people to assume that just as you can't be too thin or too rich, your blood pressure can't be too low. But that's not always the case.
Many people who have low blood pressure (hypotension) are healthy and have no signs or symptoms related to lower than normal readings. But for others, 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 shock, a life-threatening condition.
Signs and symptoms
Some people with low blood pressure are in peak physical condition with strong cardiovascular systems and a reduced risk of heart attack and stroke. For these people, low blood pressure, rather than being a cause for concern, is a cause for celebration.
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
Causes
The heart is the prime mover of the circulatory system; with each beat it launches your blood on a journey through 60,000 miles of arteries, veins and capillaries, ultimately circulating about 2,000 gallons of blood each day.
To do this, it contracts an average of 70 times a minute with the same amount of force you'd use to squeeze a tennis ball. Blood pressure is a measurement of the pressure in your arteries during the active and resting phases of each heartbeat. Here's what the numbers mean:
- Systolic pressure. The first number in a blood pressure reading, this is the amount of pressure your heart generates when pumping blood through your arteries to the rest of your body.
- Diastolic pressure. The second number in a blood pressure reading, this refers to the amount of pressure in your arteries when your heart is at rest between beats.
Blood Pressure: How low can you go?
Current guidelines identify normal blood pressure as lower than 120/80 — many experts think 115/75 is optimal. Higher readings indicate increasingly serious risks of cardiovascular disease. Even blood pressures formerly considered healthy — 120 to 139 systolic and 80 to 89 diastolic — are now believed to increase the risks. Low blood pressure, on the other hand, is much harder to quantify.
Some experts define low blood pressure as readings lower than 90 systolic or 60 diastolic — you need have only one number in the low range for your blood pressure to be considered lower than normal. In other words, if your systolic pressure is a perfect 115, but your diastolic pressure is 50, you're considered to have lower than normal pressure.
Yet this can be misleading because what constitutes low blood pressure is highly relative, varying considerably from one person to another. For that reason, doctors often consider chronically low blood pressure too low only if it causes noticeable signs and symptoms.
On the other hand, a sudden fall in blood pressure can be dangerous. A change of just 20 mm Hg — a drop from 130 systolic to 110 systolic, for example — can cause dizziness and fainting when the brain fails to receive an adequate supply of blood. And precipitous plunges, especially those caused by uncontrolled bleeding, severe infections or allergic reactions can, be life-threatening.
Complications
Even moderate postural, postprandial or neurally mediated hypotension 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.
In addition, chronic low blood pressure may increase the risk of Alzheimer's-type dementia in some older adults. A diastolic pressure lower than 70 over a long period of time is most closely associated with dementia, and for every 10-point drop in pressure, the likelihood of dementia may increase by as much as 20 percent.
For years, researchers debated whether the low blood pressure often seen in people with Alzheimer's was a consequence or a cause of the disease. Current research seems to indicate that it's both, although in younger people, lower blood pressure is usually associated with a reduced risk of dementia.
Scientists speculate that age-related changes in cardiovascular function may explain the difference. Because older adults are more likely to have blocked arteries than younger people are, their blood pressure may need to be higher to maintain adequate blood flow to the brain.
Treatment
Low blood pressure that doesn't cause signs or symptoms rarely 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 hypotension is drug-induced, treatment usually involves changing the dose of the medication or stopping it entirely.
If it's not clear what's causing hypotension 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 hypotension you have, this may be accomplished in several ways:
- Increased salt intake. 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. Still, it's not quite as simple as dousing your salads with one of the new designer salts such as fleur de sel. 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.
- Increased water. Although nearly everyone can benefit from drinking more water, this is especially true of people with low blood pressure. Fluids increase blood volume and help prevent dehydration, both of which are important in treating hypotension.
- Compression stockings. The same elastic stockings and leotards commonly used to relieve the pain, swelling, and blood stagnation of varicose veins may help reduce the pooling of blood in your legs.
- Medications. Doctors traditionally have used the drug midodrine to raise standing blood pressure levels in people with orthostatic hypotension. But many of those people have high blood pressure when sitting or lying down and at night, when blood pressure typically declines. In addition to increasing standing blood pressure, midodrine also raises already-high supine pressure, leading to the possibility of strokes. Now it appears that another drug, pyridostigmine (Mestinon), increases standing blood pressure without affecting supine pressure.
Informations obtained from National Institute of Health.