Library · Physiology
Blood pressure
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Blood pressure is the force with which blood pushes against the walls of the arteries, the vessels that carry it out of the heart to the rest of the body. That force isn't constant: it changes with whatever the heart is doing at that instant. When the heart squeezes to pump, it pushes harder; when it eases off between one beat and the next, it pushes less.
That's where the two numbers that always get said together come from. The systolic is the one from the moment the heart contracts; the diastolic, the one from the moment it relaxes. They aren't two rival measurements, they're two instants in the same turn of the cardiac cycle. And since pressure also rises and falls over the course of the day and with whatever you happen to be doing, the number that comes out of the device is a portrait of that moment and nothing more.
In brief
Blood pressure is the force of blood against the artery walls. It changes as the heart contracts to pump blood and as it relaxes between beats.
The systolic value corresponds to the contraction, and the diastolic value to the relaxation. Each value marks a different phase of the same cardiac cycle.
It also varies throughout the day and with activity, so a single reading describes only that one moment.
Sources (2)
- World Health OrganizationHypertensionPublished
- National Heart, Lung, and Blood InstituteHigh Blood Pressure
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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