Updated: July 24, 2020
Blood pressure is determined both by the amount of blood your heart pumps and the amount of resistance to blood flow in your arteries. We have two numbers in blood pressure reading. The top number called systolic blood pressure is the pressure in the arteries as the heart contracts. The bottom number called diastolic pressure is the pressure in the arteries as the heart relaxes. Normal blood pressure is below 120/80. Systolic blood pressure of about 90 to 100 is considered low blood pressure, or you can say less than 90/60 mmHg is hypotension.
Blood pressure varies, throughout the day, depending on body position, breathing rhythm, stress level, physical condition, medications you take, what you eat and drink, and time of day. Blood pressure is usually lowest at night and rises sharply on waking.
Low blood pressure can be caused because of Some heart conditions such as extremely low heart rate (bradycardia), heart valve problems, heart attack and heart failure.
Endocrine disease such as parathyroid disease, adrenal insufficiency (Addison's disease), low blood sugar (hypoglycemia) can cause low blood pressure.
Dehydration because of Fever, vomiting, severe diarrhea, overuse of diuretics and strenuous exercise can cause hypotension.
When your bloodstream is infected by any reason, it can lead to a life-threatening drop in blood pressure called septic shock.
Losing a lot of blood, from a major injury or internal bleeding, reduces the amount of blood in your body, leading to a severe drop in blood pressure.
Severe allergic reaction because of foods, certain medications, insect venoms and latex can cause breathing problems, hives, itching, a swollen throat and a severe drop in blood pressure.
A lack of the vitamins B-12 and folate can cause anemia, a deficiency in red blood cells leading to low blood pressure.
The circulatory system expands rapidly during pregnancy causing low blood pressure. The blood pressure becomes normal after pregnancy.
Certain types of antidepressants (tricyclic antidepressants), including doxepin (Silenor) and imipramine (Tofranil),Alpha blockers,Beta blockers and others can cause hypotension.
Low Blood pressure or hypotension can be categorized in to
When you stand up from a sitting position or after lying down, there is a sudden drop in BP causing Orthostatic hypotension. When you stand up from a sitting position or after lying down, blood is pooled in your legs due to gravity. This can be compensated by increasing your heart rate and constricting blood vessels, thereby ensuring that enough blood returns to your brain. But in case of people with orthostatic hypotension, this compensating mechanism fails.
Orthostatic hypotension can be developed for various reasons, including dehydration, prolonged bed rest, pregnancy, diabetes, heart problems, burns, excessive heat, large varicose veins, certain neurological disorders and certain medication.
Sudden drop in blood pressure after eating is called postprandial hypotension. After you eat, blood flows to your digestive system there by your body increases your heart rate and constricts certain blood vessels to help maintain normal blood pressure. But in case of people with postprandial hypotension, this compensating mechanism fails. Postprandial hypotension is developed in people with high blood pressure or autonomic nervous system disorders such as Parkinson's disease. Eating small, low-carbohydrate meals might help reduce symptoms.
Blood pressure drop after standing for long periods is called neurally mediated hypotension. This happens because of a miscommunication between the heart and the brain.
This type of hypotension is developed by progressive damage to the autonomic nervous system, which controls involuntary functions such as blood pressure, heart rate, breathing and digestion.
Diagnosis can be done by undergoing certain test:
Anemia due to blood loss or elevated white blood cells due to infection can be determined by complete blood count.
This test is done to determine dehydration and mineral depletion, renal failure (kidney failure), or acidosis (excess acid in the blood).
Cortisol levels can be measured to diagnose adrenal insufficiency and Addison's disease. Low cortisol level will lead to hypotension.