Causes of Low Blood Pressure

As mentioned last time, in order to maintain blood pressure, several factors must properly maintain homeostasis.

If these factors are impaired, blood pressure may fall.

· Athletes who exercise regularly often have low blood pressure and a low pulse, and their systolic blood pressure sometimes falls below 90 mmHg.

This is not pathological, so no examination or treatment is needed.

· Blood pressure can decrease due to various causes related to the heart itself, such as reduced heart function caused by ischemic heart disease like myocarditis or myocardial infarction, decreased blood output from the heart due to reduced valve function (narrowing or leakage), a low heart rate, arrhythmia, or severe inflammation of the membrane surrounding the heart. In such cases, it is possible to treat any heart disease that can be treated and raise blood pressure with supportive treatment for conditions that are difficult to correct. For example, if blood pressure decreases because of an arrhythmia or a heart rate that is too low, the problem of reduced pulse rate can be addressed with a pacemaker that artificially makes the heart beat.

· Low blood pressure due to a decrease in blood volume or body fluid

Two-thirds of our body is made up of water, and about 5 liters exist as blood. This amount is regulated by urine produced by the kidneys, sweat from the skin, and the water content of stool. Among these, the amount of urine is automatically regulated according to the body’s water level and blood volume when kidney function is normal. Changes that affect the amount of water in the body are adjusted on their own, but when they exceed the limits of this regulation, blood pressure decreases. 대표적인 경우 are when the amount of urine increases due to impaired kidney function itself, or when the amount of urine increases because diuretics are used. Also, if you sweat excessively in the summer or have severe diarrhea, blood pressure decreases. In such cases, not only does blood pressure decrease due to loss of water, but electrolyte disturbances caused by the loss of electrolytes create a bigger problem.

· When blood vessels dilate

As mentioned earlier in the components of blood pressure, the diameter of blood vessels is more important than the amount of blood. When blood vessels dilate due to various causes, blood pressure drops rapidly. A typical case is when pneumonia or severe inflammation occurs in any part of the body, such as abdominal organs, muscles, or skin, the blood vessels dilate due to substances secreted in our body by the causative bacteria and inflammation. In this case, it is called sepsis, where bacteria and toxic substances spread throughout the body and cause dysfunction of body functions. Because the bacteria and toxic substances themselves, along with the resulting drop in blood pressure, combine to prevent smooth blood supply to vital organs, this is life-threatening and requires prompt correction.

· In the case of pregnancy

When pregnancy occurs, amniotic fluid is produced and blood volume increases, causing blood pressure to decrease. Normally, systolic blood pressure decreases by about 10 mmHg and diastolic blood pressure by 10–15 mmHg. This returns to normal on its own after childbirth.

· In the case of bleeding

In cases of bleeding, the amount and speed of bleeding are important in whether blood pressure drops. If the amount of bleeding is small or occurs slowly, blood pressure does not decrease because of the body’s automatic regulation by the autonomic nervous system. However, if a large amount of blood is suddenly lost for any reason—such as trauma from a traffic accident or fall, bleeding during childbirth or surgery, or rupture due to a disease of the blood vessel itself—then compensation has limits and blood pressure drops. In such cases, if the blood loss is rapidly replaced and further bleeding is prevented, the drop in blood pressure will improve quickly.

· Shock due to allergy

Hypersensitivity is when the immune system, the body’s defense mechanism, forms antibodies to eliminate external foreign substances (called antigens). Abnormal reactions caused by this are called allergies. Foreign substances directly, or antibodies or antigen-antibody complexes, often cause hives or diarrhea, but when blood vessels suddenly dilate and blood pressure falls, this is allergic shock, especially called anaphylaxis. It is mainly caused by drugs such as penicillin, aspirin, antibiotics, and contrast agents, or by food, insect venom, or snake venom. Because it is life-threatening, you must go to the hospital immediately and receive emergency treatment.

· Low blood pressure due to medications

Blood pressure is mainly lowered by antihypertensive drugs, and all antihypertensive drugs can cause low blood pressure if used in large amounts.

In the past, however, because their blood-pressure-lowering effect appeared rapidly and lasted for a short time, antihypertensive drugs were used cautiously when administered every 6–8 hours, since low blood pressure occurred frequently and severely. Recently, because their duration of action is longer, they have become safer in terms of the side effect of hypotension. However, this does not mean there is no risk no matter how much is taken, so take an appropriate amount after consulting with a doctor. In addition, injectable antihypertensive drugs administered during hospitalization should be given while carefully monitoring blood pressure and appropriately adjusting the dosage.

Other drugs, such as anti-anginal medications, anti-Parkinson’s disease medications, some antidepressants, alpha-blockers used for enlarged prostate, and taking Viagra together with anti-anginal medications, can also cause low blood pressure.

· Blood pressure is usually measured in the right or left upper arm, but if the blood vessels in the upper part of the arm being measured are narrowed due to arteriosclerosis or vasculitis, the amount of blood flow to the upper arm where the actual blood pressure is measured is reduced through the narrowed vessel, so blood pressure decreases. To detect this, blood pressure should be measured in both arms, and if one side’s systolic blood pressure is 10 mmHg or more lower, vascular stenosis can be suspected. This is because it is rare for blood vessels on both sides to be narrowed at the same time. To determine this accurately, it can be confirmed through angiography using computed tomography or direct percutaneous angiography.

So far, I have explained the causes of low blood pressure.

In the next part, we will look at the symptoms of low blood pressure and how to measure blood pressure.

Source: Korea Disease Control and Prevention Agency National Health Information Portal