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Stroke Smart Magazine

July/August 2007

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Blood Pressure: How Low Can You Go?

By Jonathan Bitz

High blood pressure causes about two thirds of all strokes globally. That's why lowering blood pressure is often recommended to reduce stroke risk, especially in people who have already had a stroke and are therefore at greater risk for another. But is there such a thing as too low?

Researchers have yet to identify a target level for blood pressure control in stroke survivors. What is appropriate for one person may not be appropriate for another.

Blood pressure is determined by the quantity of blood pumped by the left ventricle of the heart into the arteries and by the resistance against the blood flow in the smaller arteries.

A person's blood pressure is highest when the heart beats and pumps blood into the arteries. This is called systolic pressure (the first or top number). Between beats, your heart is at rest. This is called the diastolic pressure (the second or bottom number).

A blood pressure reading is made up of these two numbers. A reading of less than 120/80 is considered normal or healthy blood pressure. If your blood pressure reading is 90/60 or lower, you have low blood pressure.

Blood pressure tends to be lower if less blood is being pumped into the arteries or if the smaller arteries (arterioles) are wider and more flexible and do not resist the flow of blood as much. When blood pressure is too low, it does not deliver enough oxygen. As a result, vital organs such as the brain, heart and kidneys suffer.

Unlike high blood pressure, low blood pressure is assessed on symptoms alone. Two of the primary symptoms are dizziness and fainting. Insufficient blood flow through the arteries also can cause chest pain or a heart attack. So you don't want your blood pressure to be too low.

On the other hand, high blood pressure can affect your ability to think clearly. Lowering your blood pressure can reduce the decline of your thinking abilities.

And so the question remains: We know that we want to lower blood pressure, but what is the target level?

Dr. Oscar Benavente, a vascular neurologist at the University of Texas Health Science Center in San Antonio, is researching that very question.

Benavente is the principal investigator of a NIH/NINDS-funded research study called Secondary Prevention of Small Subcortical Strokes (SPS3). The primary aim of this study is to learn more about stroke prevention in patients with a specific type of stroke called lacunar stroke. While we know that lower blood pressure is beneficial — we don't know what level is too low and what problems that may cause. Through this research, Benavente hopes to learn what level of blood pressure is best after stroke — especially for preventing recurrent stroke.


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