What’s the Most Important Blood Pressure Number?

The Top Number or the Bottom Number?

In the past, it was commonly thought that the diastolic pressure or bottom number, was the most important blood pressure number. This mistaken idea dates back to one of the early studies of the treatment of blood pressure, where only patients with diastolic blood pressure over 90 mm were allowed into the study.

In more modern studies, it turned out that the prognosis of hypertensive patients was predicted best by the systolic blood pressure (the top number). A systolic pressure of less than 140 when taken at rest in a relaxed state is considered normal.

The next most important number is the pulse pressure, the difference between systolic and diastolic blood pressure. The smaller the number is, the better the prognosis. In other words, a blood pressure of 120/90 is actually better than a blood pressure of 120/50. The reason is this: When the heart pumps it’s blood into the aorta, the big artery of the body, it is supposed to absorb the energy as it expands to accept the delivered blood. The more youthful and elastic the aorta is, the more energy it absorbs and the more it smoothes out the systolic and diastolic pressures. An older, diseased, and calcified aorta has very little elasticity and so the pressure goes up very fast when the heart pumps it’s blood into the aorta, and then the pressure drops rapidly between beats, resulting in a large pulse pressure. So a large pulse pressure is a sign of a stiff and inelastic aorta.

That leaves the diastolic pressure, the bottom number, as the least important measurement when taken by itself.