About Low Blood Pressure

Overview

The body's major organs (the brain, heart, lungs, liver, kidneys, etc.) can carry out their functions only when they receive oxygen and nutrients through the blood pumped from the heart. Adequate blood flow is important not only for maintaining organ function but also for survival, and for this to be possible, the pressure inside the blood vessels, that is, blood pressure, must be maintained at a certain level. Therefore, blood pressure is very important for organ survival and, further, for maintaining life. So how is blood pressure formed?

The amount of blood is determined by the amount pumped out by the heart's pumping function, which is called cardiac output.

The diameter of blood vessels is much more important in forming blood pressure, and even a small change can greatly affect blood pressure. The diameter of blood vessels is determined by the interaction between factors that dilate blood vessels and factors that constrict them. In healthy people, the autonomic nervous system regulates the constriction and dilation of blood vessels. However, a drop in blood pressure beyond the limits of this regulation appears in pathological states, and the degree of blood pressure decrease varies depending on the disease and the severity of that disease.

Definition

When blood pressure drops, various prognoses and symptoms appear depending on the degree and cause. In most cases, when systolic blood pressure is lower than 90 mmHg, it is called hypotension. Diastolic blood pressure does not reflect the state of hypotension accompanied by functional impairment as well as systolic blood pressure does, but it is generally defined as less than 60 mmHg. However, rather than this numerical definition, adaptation to lower blood pressure differs according to each patient's age, comorbidities, and physiological function,

and the symptoms and prognosis also differ.

When blood pressure decreases, our body reduces blood flow to organs that are not important for maintaining life, such as the skin and muscles,

and performs a compensatory action that increases blood flow to major organs such as the brain, heart, and kidneys. However, once this compensatory action reaches its limit, blood flow to important organs also decreases, leading to dysfunction and putting life in danger,

which is called 'shock'. This is an emergency, and if it is not corrected quickly, it can lead to death.

Other Types of Hypotension

1. Orthostatic Hypotension

When a person lies down, blood tends to pool more in the abdomen and legs than when sitting or standing, and when they suddenly sit up or stand, the amount of blood returning to the heart decreases. As compensation by the autonomic nervous system, pulse rate and cardiac contractility increase, and peripheral blood vessels constrict to raise blood pressure and allow smooth blood supply throughout the body. However, with aging, or when diabetes, cardiovascular disease, kidney disease, dehydration, diuretics, alpha-blockers, or some antidepressants are used, the compensatory function of this autonomic nervous system decreases or becomes limited, causing a temporary drop in blood pressure that can lead to dizziness or, in severe cases, fainting. A typical example is when an older person sweats a lot after spending a long time in a sauna and feels dizzy while trying to get up to leave. This is called orthostatic hypotension, and it can be diagnosed by measuring blood pressure while lying down and then again at 1 minute and 3 minutes after standing, with a systolic blood pressure decrease of 20 mmHg or more.

Treatment is focused on identifying the cause and correcting it if possible. However, if the cause, such as aging or diabetes, is difficult to address, it is advisable to stand up slowly and, if dizziness is felt even after standing slowly, rest for a while and move only after the symptoms have gone away. It is important to note that the causes of dizziness or fainting are varied and not limited to orthostatic hypotension, so it is necessary to visit a hospital and consult a specialist for diagnosis and treatment.

2. Postprandial Hypotension

After eating, a large amount of blood is distributed to the digestive system, where intestinal movement becomes active, and the blood supply to other organs relatively decreases. Normally, the body has sufficient preparation and ability so that this degree of intestinal movement does not reduce blood flow to other organs, but in older adults or when compensation by the autonomic nervous system is reduced due to disease, or when blood volume is reduced due to dehydration or bleeding, hypotension appears after meals. To prevent this, eating small meals frequently and choosing meals low in carbohydrates can be helpful.

3. Vasovagal Syncope

Our body has the autonomic nervous system, which is involved in regulating blood pressure, pulse rate, and other bodily functions. This is due to the balance between the sympathetic and parasympathetic nervous systems. In most cases, the sympathetic nervous system mainly acts in ways similar to changes that occur when a person is angry or startled, such as raising blood pressure and increasing pulse rate. On the other hand, the parasympathetic nervous system regulates pulse rate and lowers blood pressure. If this balance did not exist and blood pressure and pulse rate kept rising without limit when a person became angry, it could be life-threatening. However, when the sympathetic nervous system increases, the parasympathetic nervous system also increases and suppresses further rises in blood pressure and pulse rate. This balance is not something we consciously control, like raising our arms or lifting our legs; it happens automatically, regardless of our will. That is why it is called the autonomic nervous system, because it regulates itself automatically.

As mentioned earlier, when a person becomes angry or frightened and sympathetic activity increases, or when standing for a long time causes blood to pool in the lower body and reduces the amount of blood returning to the heart, the heart activates the sympathetic nervous system to raise pulse rate and blood pressure in order to compensate. In other words, if sympathetic excitation increases in all cases, as described, the parasympathetic nervous system gradually becomes active and suppresses the increased sympathetic activity. If this suppression becomes excessive, the previously elevated blood pressure falls below normal, causing hypotension, and the pulse rate that had increased also falls below normal, resulting in a slow pulse. When the parasympathetic nervous system excessively suppresses the sympathetic nervous system in this way, causing a decrease in pulse rate and a drop in blood pressure, it is called vasovagal syncope. The vagus nerve is the name of the parasympathetic nerve involved in this case.

In general, the prognosis in this case is relatively good; it does not cause death or leave aftereffects, and recovery occurs within a few minutes. The most fundamental treatment is to avoid situations that trigger sympathetic excitation, such as anger or being startled, as much as possible. As an aid, beta-blockers may also be prescribed to suppress sympathetic excitation. In addition, because it occurs when blood pools in the lower body during prolonged standing, it is related to circulating blood volume. Therefore, it occurs more often when diuretics are used or when dehydration occurs due to diarrhea or heavy sweating, so it is recommended to drink enough fluids to avoid dehydration in daily life.

Even with these measures, symptoms can still occur. Usually, there are warning symptoms such as nausea or a darkened vision,

and in such cases, sitting down, lying down if possible, or raising the legs, and providing fluids if the person is conscious, can help prevent fainting. The use of medication is determined according to the frequency and severity of episodes. In occupations where recurrence of symptoms can be fatal, such as bus drivers or airline crew, active medication is recommended regardless of frequency or severity.

A test called a tilt table test exists, in which a person is stood against a table and a fainting episode is induced, and the blood pressure and pulse rate at that time are recorded.

So far, we have explained hypotension.

In the next part, we will look at the causes of hypotension.

Source: Korea Centers for Disease Control and Prevention, National Health Information Portal