High Blood Pressure: The First Number vs. The Second Number
Oct. 1, 1999 (Atlanta) -- 120/95. 190/80. 180/110. Many patients have wondered, when they get their blood pressure taken, which is the most important number: the first, higher number (systolic), or the second, lower number (diastolic)? A recent study showed that the systolic number is at least as important as the diastolic number, a finding which is somewhat contrary to traditional belief. To get the word out, the National High Blood Pressure Education Program, coordinated by the National Heart, Lung and Blood Institute (NHLBI), will be issuing, later this fall, a clinical advisory letter to U.S. health professionals warning of the danger of not properly treating high systolic blood pressure.
The systolic reading measures pressure in the blood vessels during that split-second when the heart is pumping out blood; the diastolic reading measures pressure when the heart is at rest. Up until recently, many in the medical community have emphasized the diastolic reading, but an accumulation of recent findings shows that the systolic reading is as -- if not more -- important in diagnosing and treating high blood pressure, or hypertension.
"To put it in context, we have to have a bit of historical perspective," Donald Lloyd-Jones, MD, from Massachusetts General Hospital in Boston, tells WebMD. "There has been this historical bias assuming that diastolic blood pressure and diastolic hypertension were more important and more risky than systolic hypertension. It was initially thought that the baseline pressure that the heart and the vessels see is the diastolic pressure, and then they see this brief instantaneous pressure when the heart pumps, the systolic pressure. People thought that the baseline tone was more important than that brief pulse of systolic pressure in determining what the overall long-term risk would be, [but] that has not turned out to be true."
Lloyd-Jones says this led many physicians to effectively disregard the systolic reading. "Typically clinicians have focused on the bottom number, the diastolic number, and they really have only gotten aggressive with treatment if that bottom number started to get elevated. It used to be thought that it was a normal finding to see systolic blood pressure climb with age. Indeed in most people, systolic blood pressure does climb with age, but it is not necessarily a normal phenomenon, it carries with it substantial risk of stroke, heart disease, and kidney disease," he says.
Lloyd-Jones is the lead author of the study, published in the September issue of Hypertension, that is part of the growing body of evidence pointing to the importance of elevated systolic pressure. Using 3,656 adults from the Framingham Heart Study, he and his colleagues showed that by using only the subjects' systolic blood pressure, 96% of them were correctly classified into the right blood pressure stage. Using only the subjects' diastolic reading, only 68% were correctly classified.