Blood pressure refers to the pressure inside the major arteries of the body. The left ventricle of the heart contracts and pumps the blood out of the aorta, which delivers blood to the brain, arms, legs, organs and more. The pressure is highest when the left ventricle is contracting (systolic blood pressure, upper number) and is the lowest when the left ventricle is relaxing, filling with blood and waiting for the next contraction (diastolic blood pressure, lower number). Therefore, a blood pressure of 110/70 means the arterial pressure is 110 mm Hg at its highest and 70 mm Hg when at its lowest.
The American Heart Association defines blood pressure ranges as:
- Normal blood pressure — Less than 120 systolic with diastolic less than 80.
- Elevated blood pressure — Between 120 and 129 systolic and less than 80 diastolic.
- Stage I hypertension — 130-139 systolic and 80-89 diastolic.
- Stage II hypertension — 140 or higher systolic and over 90 or higher diastolic.
Everybody’s blood pressure varies somewhat throughout the day and night. Numbers that are too high or too low are both problematic. Your body is generally quite good at adjusting and keeping your blood pressure in a healthy range.
The symptoms of low blood pressure (hypotension) are more important than the numbers. Many people feel fine with blood pressures of 90/60. Low blood pressure symptoms can include dizziness, lightheadedness and fainting (syncope). Fainting can lead to serious injury, including broken bones and head trauma. Low blood pressure needs to be prevented when possible and treated if it’s causing symptoms.
The most common problem associated with low blood pressure is orthostatic hypotension. This means your blood pressure goes down when you stand up. This can occur if:
- You’re dehydrated, either because you're losing fluid too quickly or not drinking enough fluids.
- You’re taking diuretic medication (water pills) or other blood pressure medications.
If orthostatic hypotension is the reason for your symptoms, drinking more fluid or adjusting your medication should help.
Some people’s bodies have difficulty regulating blood pressure. There are strategies and medications to address the severity of low blood pressure symptoms for patients with this issue.
Keeping your blood pressure in range is important for long-term health. If your blood pressure is out of range, either too high or too low, talk to your clinician.