Causes of Low Blood Pressure.

The previous post on What is Low Blood Pressure will give you the basic knowledge on this subject. There are four major Reasons  for  Low  Blood Pressure.

1.     Reduction of Blood Volume.

2.     Certain Medicines.

3.     Cardiac causes.

4.     Other Causes.

What Causes Low Blood Pressure,

1. Reduction of Blood Volume causes Low Blood Pressure.

Blood in the body can be lost either due to severe bleeding externally or internally. External bleeding can be due to trauma or accident. Internal bleeding can be due  to surgical  complications or a bleeding  ulcer  such as a peptic ulcer or tumor. A ruptured aortic aneurysm causes severe loss of  blood  and  death.  An   inflamed organ  like the pancreas causes the fluid to separate from the blood and accumulate in the abdomen or around the inflamed tissue.

2. Certain medicines cause Low Blood Pressure.

  • Medicines given for heart conditions like calcium channel blockers, digoxin and beta blockers reduce the heart rate  and the blood pressure
  • Medicines   for  high blood pressure if taken in a higher doses and in the elderly can give rise to low blood pressure. Medicines like diuretics (lasix), alpha blockers,  ace inhibitors.
  • Alcohol.
  • Certain narcotics.
  • Drugs used in psychiatric treatment especially depression.

3.  Cardiac Causes of low blood pressure.

  • Weakness of the myocardium (heart muscle) due to a massive heart attack, or a viral infection of the myocardium (myocarditis) or stenosis of the aortic valve leads to insufficient pumping of  blood  into the blood vessels of the body causing reduced blood pressure  in the arteries. In aortic stenosis, the heart tries to keep the blood flow normal by pumping hard.  As a result it gets overworked and this leads to weakening of the heart muscle.
  • Pulmonary embolism is a condition wherein a clot in a vein gets dislodged and travels through the blood into the heart and subsequently gets lodged into the lungs. It causes a block and the blood flow from the lungs to the heart gets blocked. This is a medical emergency and more often than not, results in death of the patient.

picture of pulmonary embolism


pulmonary embolism Cause of Low Blood Pressure.

  • Bradycardia is slowing down of the heart rate. This is caused by medications like Digoxin and Beta  blockers.  Bradycardia can also be caused by conditions called Sick Sinus syndrome or Heart Block, wherein the sensory motor  impulses  which control the heart rate are disturbed.
  • Tachycardia due to atrial fibrillation or ventricular tachycardia is a condition where the   heart beats at a very rapid rate. Due to the rapid rate,  ventricles  do not fill completely and the blood thus pumped out, is less . This causes  low blood  pressure.
  • Pericarditis is a condition where the sac covering the heart  is  inflamed and thickened. The pericardium also gets filled with fluid. This presses on the heart and the heart does not have the flexibility to relax and contract as the pericardium is covering it tightly. This results in less blood flowing out of the heart causing low blood pressure.

pericarditis Cause of Low Blood Pressure.

4. Other Causes of Low Blood Pressure:

To briefly innumerate them:

  • Postural  hypo tension is a condition where  the individual develops low blood pressure on getting up after sitting or lying down for a long period. Due to gravity, the blood does not return back from the legs to the heart in sufficient quantities.  Normally, in such conditions the body responds by increasing  the heart rate and the peripheral arteries to contract, but in patients of postural hypo tension, this back up fails.
  • Malnutrition is a common cause of low blood pressure.
  • Syncopal attack resulting from micturation causes low blood pressure.
  • Adrenal  gland  damage due to some pathology results in no secretion of cortisol from the adrenal. Cortisol is responsible in controlling the heart and the blood pressure. Blood pressure therefore falls.
  • Septicemia is a condition wherein the blood gets infected from the bacteria  which enter the blood from lungs, bladder or the intestines. Septicemia results in shock and low blood pressure.
  • Anaphylactic shock caused by allergy to injections of medicines like penicillin and Vitamin B1 causes Blood Pressure to Fall.
  • A Vasovagal reaction is a reaction triggered by fear and pain. The vagus nerve belongs to the involuntary autonomic  system   which controls the heart rate and the blood pressure. The vagus nerve slows down the heart rate and this causes low blood pressure.


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