Too-Low Blood Pressure Can Also Bring Danger

May 8 -- THURSDAY, May 7 (HealthDay News) -- While too-high blood pressure is a clear hazard for most people, too-low pressure can apparently be a threat in some cases as well.

A new study of 10,001 people with coronary artery disease found what statisticians call a J-shaped curve of mortality, meaning a higher death rate for people with the lowest blood pressure. Dr. Franz H. Messerli, a professor of clinical medicine at Columbia University Medical Center and director of the hypertension program at St. Luke's-Roosevelt Hospital in New York City, reported on the finding Thursday at the American Society of Hypertension meeting in San Francisco.

"It stands to reason that there has to be a J-shaped curve," Messerli said. "If your blood pressure were zero, you would be dead."

He acknowledged that the people in the study were a bit out of the ordinary, with already-diagnosed coronary artery disease. The study was aimed at determining the effect of treatment with different amounts of a cholesterol-lowering statin drug, with blood pressure measured as a matter of routine.

When the results were in, the lowest rate of deaths and major coronary problems such as heart disease was seen not in the participants with the lowest blood pressure but in those slightly to the right on the curve, with a reading of 139.9 for systolic pressure (the reading when the heart contracts) and 79.2 for diastolic pressure.

Though Messerli stressed that this was "a unique population, with coronary artery disease, where the coronary arteries are compromised," he noted that "there has to be a point where lowering blood pressure is counterproductive."

That point can be seen on the curve of systolic pressure in this group, he said. "When you go from 120 to 130, even from 110 to 130, there is very little difference," Messerli said. "When it goes below 110, then all of a sudden it becomes very obvious."

The effect is more pronounced for diastolic pressure readings. "If you go to 70 or below, say to 60, there is a fourfold higher risk in the primary outcomes," he said.