Patients who suffer from autonomic nervous system failure can turn to a new treatment for their blood pressure abnormalities: a large glass of water. Investigators at Vanderbilt's Autonomic Dysfunction Center report in the February 8th issue of the journal Circulation that water has a powerful blood pressure raising effect in these patients.
Water also raises blood pressure in older normal subjects, but not in young normal subjects. The studies suggest that water is an important unrecognized factor in clinical studies of blood pressure medications.
"Water is not just a neutral substance, and it cannot be considered a 'placebo' with regards to blood pressure," said Dr. John R. Shannon, instructor of Medicine and Pharmacology. "As physicians, we may ask our hypertensive patients if they just drank a cup of coffee or smoked a cigarette when we measure their blood pressure, but we would never think to ask if they had anything to drink in the last hour. Perhaps we should. It might make the difference in whether or not we adjust their medications."
On the average, 16 ounces of tap water raised blood pressure about 40 millimeters of mercury in patients with autonomic failure. Blood pressure started increasing within two or three minutes after the water was ingested, increased rapidly over the next 15 minutes, and then began to decrease after about 60 minutes. Drinking more water at 60 minutes caused the blood pressure effect to be sustained for another hour.
In older normal subjects, the average increase in blood pressure was 11 millimeters of mercury.
There is something about the water itself that causes the increase in blood pressure; intravenous infusion of 16 ounces of sugar solution did not elicit the effect. In addition, the effect is "dose-dependent" -- the higher the water intake, the larger the increase in blood pressure.
"We do not know how water raises blood pressure, but it is the solute-free water itself, whether warm, room temper
Contact: Matt Scanlan
Vanderbilt University Medical Center