What a Sudden Drop in Blood Pressure Means

Recognizing the Symptoms and Identifying the Cause

woman having blood pressure taken

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Low blood pressure, also known as hypotension, is a condition in which your blood pressure is lower than what is considered normal for your age. Most doctors consider "normal" blood pressure to be less than 120/80 mm Hg. With that said, lower-than-normal blood pressure is not inherently a problem as long as it doesn't cause overt symptoms.

Some people are simply born with low blood pressure. On the one hand, it is considered beneficial since it does not increase the risk of heart disease or stroke like high blood pressure (hypertension) does. On the other, symptomatic hypotension can be a sign of an underlying disorder or a serious condition in need of medical care.

Even if it is not, hypotension can interfere with your quality of life and require medical intervention to prevent dizziness, fainting, or falling. Recurrent of severe events should never be ignored.

Symptoms

Blood pressure is measured in values of millimeters of mercury (mm Hg). A blood pressure reading lower than 90 mm HG for the top (systolic) number or 60 mm Hg for the bottom (diastolic) number is generally regarded as hypotension.

At this level, symptoms may develop in some people but not in others. Generally speaking, the lower the blood pressure drops, the greater the risk (and severity) of symptoms.

Common Symptoms

A sudden drop in blood pressure can manifest with symptoms as the decreased blood flow starves the body of the oxygen and nutrients that it needs to function. Common signs of hypotension include:

  • Lightheadedness
  • Dizziness
  • Nausea
  • Fatigue
  • Sleepiness
  • Lack of concentration
  • Blurred vision
  • Fainting

A plethora of other symptoms may be involved—including chest pain, shortness of breath, irregular heartbeat, hives, fever, indigestion, and vomiting—but these tend to be associated with the condition that caused the sudden drop in the blood pressure. In the end, hypotension is a symptom that can often point you in the direction of the underlying cause.

Severe Symptoms

Extreme hypotension can severely deprive the brain and vital organs of oxygen and nutrients, leading to a life-threatening condition called shock. Shock can progress rapidly, typically manifesting with symptoms like:

  • Extreme weakness
  • Extreme anxiety
  • Rapid heart rate
  • Weak pulse
  • Rapid, shallow breathing
  • Profuse sweating
  • Increased thirst
  • Cold, clammy skin
  • Confusion

These symptoms can lead to unconsciousness, cardiac arrest, and death as the complications progressively worsen.

Causes

There are many causes of hypotension, both common and uncommon, innocent and serious. There are even some forms that are entirely idiopathic (of no known origin). To comprehend the causes of hypotension, you first need to understand how the body regulates blood pressure.

Physiology

Blood pressure is regulated by the autonomic nervous system which oversees the body's unconscious functions. It does so by continually balancing the two "faces" of the autonomic nervous system, namely:

  • Sympathetic nervous system, which raises the blood pressure by activating the body's "fight-or-flight" response
  • Parasympathetic nervous system, which lowers the blood pressure by decreasing the heart rate

Any condition that suppresses the sympathetic system and/or overactivates the parasympathetic system can disrupt this balance, leading to a sudden and sometimes steep drop in blood pressure.

There may also be physiological components to low blood pressure, including any condition that physically impairs normal blood flow. It may be a temporary condition, such as placing excessive pressure on a major artery, or a chronic one, such as cardiovascular disease.

Conditions

Hypotension can be broadly categorized by its underlying causes. Chief among them are reduced blood volume, decreased cardiac output, excessive vasodilation, and functional syndromes involving a cascade of interconnected events. These categories can often overlap, making diagnoses all the more complicated.

Hypovolemia

Hypovolemia, the term used to describe reduced blood volume, is the most common cause of hypotension. It is caused by the excessive loss of fluids and/or insufficient intake of fluids.

Causes of hypovolemia include:

  • Loss of blood
  • Dehydration
  • Starvation
  • Fasting
  • Severe diarrhea or vomiting
  • Heatstroke
  • Excessive use of diuretics ("water pills")
  • Kidney problems (causing excess urination and the loss of water and sodium)
  • Severe pancreatitis (causing the leakage of fluid into the abdominal cavity)

Decreased Cardiac Output

Even if blood volumes are normal, conditions that lower the body's ability to pump blood through the body can cause hypotension.

Causes of decreased cardiac output include:

Extreme Vasodilation

Vasodilation describes the sudden widening of blood vessels as smooth muscles relax in response to chemical, neurological, or immunologic stimuli. With vasodilation, blood pressure will drop as the space within the vessels increase while the volume of blood remains the same.

Common causes of vasodilation include:

Functional Syndromes

Hypotensive syndromes can be described as interconnected physiological events that bring about a sudden drop in blood pressure. Some of these occur on their own with no underlying disease or long-term consequence. Others occur in response to disease or other external factors.

Neurogenic orthostatic hypotension (NOH) occurs when a change in body position, such as rising from a chair or bed, causes a dramatic drop in blood pressure. NOH is caused by an underlying neurologic disorder that affects the autonomic nervous system. It is common with neurogenerative disorders like Parkinson's disease and Lewy body dementia as well as diabetic nerve damage.

Orthostatic hypotension (OH) manifests with the same symptoms as NOH but are caused by any number of non-neurologic causes, including decreased cardiac output, extreme vasodilation, and the chronic use of diuretics, tricyclic antidepressants, and anti-hypertensive drugs. OH and NOH can also be collectively referred to as postural hypotension.

Supine hypotensive syndrome occurs when you lie on your back while you are pregnant. Doing so allows the weight of the baby to press down on two of the largest blood vessels in the body—the aorta and the inferior vena cava—decreasing the flow of blood to the heart. Severe cases can lead to fetal and maternal death.

Postprandial hypotension occurs roughly 30 to 75 minutes after eating when blood is diverted to the intestines to aid in digestion, temporarily robbing the brain of blood and oxygen as surrounding blood vessels narrow (vasoconstriction). It is most common in the elderly.

Vasovagal syncope occurs when your body overreacts to certain triggers, such as the sight of blood or extreme emotional distress, leading to a steep drop in blood pressure and fainting (syncope). It is caused by the biochemical overactivation of the vagus nerve, the central component of the parasympathetic nervous system.

Situational reflex syncope also affects the vagus nerve but is caused when physical stress is placed directly on the nerve. Examples include straining during a bowel movement, lifting a heavy weight, or standing for too long. Urinating after taking a vasodilating drug like Cialis (tadalafil) can also induce reflex syncope.

Carotid artery syncope is similar to supine hypotension in that it involves the compression of a major artery, in this case the internal carotid artery of the neck. Wearing a tight collar, shaving, or turning the head can cause a sudden drop in blood pressure, especially in elderly people or those with carotid arterial stenosis.

What to Do

Low blood pressure can be readily diagnosed with a blood pressure cuff. Determining the underlying cause can take time. During an investigation, the doctor will try to link the hypotensive event to any number of possible causes.

This will require a review of your medical history (including you any medications you take), a physical exam, and some simple in-office tests like the Valsalva maneuver (which can help detect autonomic disorders).

Based on the initial findings, other tests may be ordered, including blood tests, imaging studies, electrocardiogram (ECG), echocardiogram, and a stress test. If needed, you may be referred o a specialist cardiologist, neurologist, or endocrinologist for further evaluation and treatment.

The long-and-short of it is that you need to be patient and not ignore the signs of hypotension, no matter how subtle they may be. By pinpointing the exact cause of low blood pressure, you can be treated appropriately and effectively.

A Word From Verywell

If you only experience occasional hypotensive symptoms, such as lightheadedness, it is likely you'll only need routine medical monitoring for the condition. Your doctor may advise you to purchase a home blood pressure machine to track your blood pressure.

However, if you experience repeated acute symptoms, even if they seem relatively minor, you need to speak with your doctor. It may be that something simple, such as an adjustment of your medications, could fix the problem. In other cases, it may be a sign of a medical condition that needs immediate attention.

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