What is blood pressure?
The force of the blood pushing against the walls of the arteries as it goes through the body is what is known as “blood pressure.” It’s measured as systolic (pressure whilst pumping) and diastolic (pressure whilst resting between beats) pressures. It’s generally written as the systolic number above or before the diastolic number (e.g. 125/79 mmHg – is millimeters of Hg which is the symbol for mercury).
What is low blood pressure?
People who are fit and healthy tend to have lower blood pressure and a slower heart rate. There is some dispute as to how low a blood pressure reading should be. Some doctors only consider it too low if it causes noticeable symptoms. Others define low blood pressure as maintaining readings lower than systolic 90 mmHg or diastolic 60 mmHg and that having at least one number in the low range would be considered lower than normal (e.g. systolic 115, but diastolic 50, is considered low blood pressure).
It can be dangerous if your blood pressure suddenly falls to a very low level (e.g. a 20 mmHg drop). It can cause dizziness and fainting because it means the brain isn’t receiving an adequate supply of blood.
Very large plunges in blood pressure such as those caused by uncontrolled bleeding, severe infections or allergic reactions, can be fatal.
Low pressure can mean that blood is not delivering oxygen and nutrients to the tissues as well it should be, and this may manifest as a variety of health issues, including physical and mental fatigue. It can also be a sign of an underlying problem, such as a weakness in the adrenal glands. In some rare cases, it can be a sign of serious, even life-threatening disorders.
Causes of low blood pressure
Some causes include:
- Heart problems (e.g. extremely low heart rate, heart valve problems, heart attack and heart failure)
- Endocrine problems (e.g. parathyroid disease, adrenal insufficiency, low blood sugar and, in some cases, diabetes).
- Dehydration and hypovolemic shock, a life-threatening complication of dehydration.
- Blood loss from a major injury or internal bleeding.
- Severe infection (septicemia), which can lead to a life-threatening drop in blood pressure called septic shock.
- Severe allergic reaction (anaphylaxis).
- Anemia from a diet low in vitamins B-12 and folate (and sometimes from increases loss of blood from heavy menstruation).
- Medications such as diuretics, alpha blockers, beta blockers, drugs for Parkinson's disease, some antidepressants and Sildenafil (Viagra) or tadalafil (Cialis), particularly in combination with the heart medication nitroglycerin.
- On standing up (orthostatic, or postural, hypotension).
- After eating (postprandial hypotension). This mainly affects older adults.
- From faulty brain signals (neutrally-mediated hypotension). After standing for extended periods, the nerves in the heart's left ventricle signal the brain that blood pressure is too high, rather than too low. As a result, the brain lowers the heart rate, decreasing blood pressure and leading to lightheadedness and fainting.
- Due to nervous system damage (multiple system atrophy with orthostatic hypotension). This is a rare disorder causes progressive damage to the autonomic nervous system, which results in severe orthostatic hypotension in combination with very high blood pressure when lying down.
Types of low blood pressure
Some types include low blood pressure occur:
Disclaimer: The statements made on this page have not been evaluated by the U.S. Food and Drug Administration (FDA). They are not intended to diagnose, cure or prevent any disease. If a condition persists, please contact your physician or healthcare provider. The information provided is not a substitute for a face-to-face consultation with a healthcare provider, and should not be construed as medical advice.