Low blood pressure, clinically known as hypotension, occurs when blood flows through your arteries at a lower pressure than normal. Blood pressure is the force of your blood pushing against the walls of your arteries. It is measured in millimeters of mercury (mm Hg). Generally, a blood pressure reading below 90/60 mm Hg is considered low blood pressure.
However, what’s considered low blood pressure can vary from person to person. For some individuals, slightly lower blood pressure is their normal and causes no issues. For others, low blood pressure can lead to symptoms like dizziness and fainting, and in severe cases, it can be life-threatening.
Identifying What Causes Low Blood Pressure is crucial because the underlying cause often dictates the necessary treatment. Low blood pressure can be triggered by a range of factors, from dehydration to serious medical conditions. Understanding these causes is the first step towards managing and addressing hypotension effectively.
Types of Low Blood Pressure and Their Causes
Low blood pressure isn’t a single condition, but rather a symptom with different types, each potentially stemming from distinct causes. Understanding these types can help pinpoint the underlying issues.
Orthostatic Hypotension (Postural Hypotension)
Orthostatic hypotension, also known as postural hypotension, is a sudden decrease in blood pressure that happens when you stand up after sitting or lying down. This is a common type of low blood pressure, particularly among older adults.
What causes orthostatic hypotension? Several factors can contribute to this type of blood pressure drop:
- Dehydration: Insufficient fluid volume reduces blood volume, leading to lower blood pressure, especially upon standing.
- Prolonged Bed Rest: Extended periods of inactivity can weaken the circulatory system’s ability to adjust to positional changes.
- Pregnancy: Hormonal changes during pregnancy cause blood vessels to dilate, which can lead to lower blood pressure.
- Certain Medical Conditions: Conditions like diabetes, Parkinson’s disease, and heart conditions can affect blood pressure regulation.
- Medications: Certain medications, particularly those for high blood pressure, can sometimes cause orthostatic hypotension as a side effect.
Postprandial Hypotension
Postprandial hypotension is a drop in blood pressure that occurs 1 to 2 hours after eating. It’s more common in older adults, especially those with pre-existing high blood pressure or conditions like Parkinson’s disease that affect the autonomic nervous system.
What causes postprandial hypotension? While the exact mechanism isn’t fully understood, it’s believed to be related to blood flow shifting to the digestive system after a meal. In some individuals, the body’s compensatory mechanisms might not work efficiently to maintain blood pressure, leading to a drop. Consuming large, carbohydrate-rich meals can exacerbate this condition.
Neurally Mediated Hypotension
Neurally mediated hypotension (NMH) is a type of low blood pressure that occurs after standing for prolonged periods. It primarily affects young adults and children.
What causes neurally mediated hypotension? NMH is thought to be caused by a miscommunication between the heart and the brain. When standing for a long time, blood can pool in the legs. Normally, the body signals the heart to pump harder to maintain blood pressure. In NMH, this signaling process may be disrupted, leading to a blood pressure drop.
Multiple System Atrophy with Orthostatic Hypotension
Multiple system atrophy (MSA) with orthostatic hypotension is a rare and severe disorder of the autonomic nervous system, which controls involuntary functions like blood pressure regulation. This condition, sometimes previously known as Shy-Drager syndrome, is associated with significant orthostatic hypotension and can also cause supine hypertension (high blood pressure while lying down).
What causes multiple system atrophy with orthostatic hypotension? MSA is a progressive neurodegenerative disease, and its exact cause is still unknown. It involves the degeneration of nerve cells in various areas of the brain and spinal cord, including those that control the autonomic nervous system.
Medical Conditions That Can Cause Low Blood Pressure
Beyond the types of hypotension, numerous underlying medical conditions can lead to chronically low or sudden drops in blood pressure.
Cardiovascular Conditions
Heart problems can significantly impact blood pressure.
- Bradycardia (Slow Heart Rate): A severely slow heart rate can reduce the amount of blood the heart pumps, leading to lower blood pressure.
- Heart Valve Problems: Issues with the heart valves, such as valve disease, can impair the heart’s efficiency in pumping blood.
- Heart Attack and Heart Failure: These conditions weaken the heart muscle, reducing its pumping capacity and causing low blood pressure.
Endocrine Disorders
Hormone imbalances can also be a cause of low blood pressure.
- Addison’s Disease: This adrenal gland disorder results in insufficient production of cortisol and aldosterone, hormones that help regulate blood pressure.
- Hypoglycemia (Low Blood Sugar): Low blood sugar levels can sometimes trigger a drop in blood pressure.
- Diabetes (in some cases): While diabetes is often associated with high blood pressure, certain diabetic complications or medications can lead to hypotension.
Dehydration
As mentioned earlier in relation to orthostatic hypotension, dehydration is a significant contributor to low blood pressure. When the body loses more fluids than it takes in, blood volume decreases, resulting in lower blood pressure. Dehydration can be caused by:
- Vomiting and Diarrhea: These can lead to rapid fluid loss.
- Fever: Elevated body temperature increases fluid loss through sweating.
- Overuse of Diuretics: These medications increase urination and can lead to dehydration if fluid intake isn’t sufficient.
- Strenuous Exercise: Excessive sweating during exercise can cause dehydration.
Blood Loss
Significant blood loss, whether from injury or internal bleeding, directly reduces blood volume, causing a drop in blood pressure.
Infections
Severe infections can lead to a dangerous drop in blood pressure.
- Septicemia and Septic Shock: When an infection enters the bloodstream (septicemia), it can trigger a systemic inflammatory response that leads to septic shock, characterized by a life-threatening drop in blood pressure.
Anaphylaxis (Severe Allergic Reaction)
Anaphylaxis is a severe and life-threatening allergic reaction that can cause a sudden and drastic decrease in blood pressure, along with other symptoms like breathing difficulties and skin reactions.
Nutritional Deficiencies
Certain nutrient deficiencies can contribute to low blood pressure.
- Vitamin B-12, Folate, and Iron Deficiency: Deficiencies in these vitamins can lead to anemia (low red blood cell count). Anemia reduces the oxygen-carrying capacity of the blood, which can contribute to hypotension.
Pregnancy
As mentioned in orthostatic hypotension, pregnancy commonly causes lower blood pressure, especially during the first 24 weeks, due to hormonal changes causing vasodilation (widening of blood vessels).
Medications That Can Cause Low Blood Pressure
Many medications can have low blood pressure as a side effect. It’s important to be aware of these potential drug-induced causes of hypotension.
- Antihypertensive Medications: Drugs designed to lower high blood pressure, such as:
- Diuretics (e.g., furosemide, hydrochlorothiazide): These reduce fluid volume.
- Alpha-blockers (e.g., prazosin): These relax blood vessels.
- Beta-blockers (e.g., atenolol, propranolol): These slow heart rate and reduce heart’s pumping force.
- ACE inhibitors and ARBs: These also lower blood pressure by affecting blood vessel constriction.
- Parkinson’s Disease Medications (e.g., pramipexole, levodopa): Some medications for Parkinson’s can affect blood pressure regulation.
- Tricyclic Antidepressants (e.g., doxepin, imipramine): This class of antidepressants can sometimes cause orthostatic hypotension.
- Erectile Dysfunction Medications (e.g., sildenafil, tadalafil): These drugs can lower blood pressure, especially when combined with nitrates like nitroglycerin, often used for heart conditions.
Risk Factors for Low Blood Pressure
While anyone can experience low blood pressure, certain factors increase the risk.
- Age: Older adults are more prone to orthostatic and postprandial hypotension. Younger adults and children are more likely to experience neurally mediated hypotension.
- Medications: As discussed, taking certain medications, especially antihypertensives, increases the risk.
- Certain Diseases: Conditions like Parkinson’s disease, diabetes, and some heart conditions are risk factors for low blood pressure.
- Alcohol and Illicit Drugs: Alcohol consumption and use of illegal drugs can sometimes contribute to low blood pressure.
When to Seek Medical Attention
While mild and occasional low blood pressure might not be cause for concern, it’s essential to seek medical advice if you experience persistent symptoms or sudden drops in blood pressure, especially if accompanied by:
- Dizziness or Lightheadedness
- Fainting (Syncope)
- Blurred or Fading Vision
- Fatigue
- Difficulty Concentrating
- Nausea
- Confusion, especially in older adults
- Cold, Clammy Skin
- Pallor (Pale Skin)
- Rapid, Shallow Breathing
- Weak, Rapid Pulse
These symptoms could indicate a more serious underlying condition requiring diagnosis and treatment. It’s always best to consult with a healthcare professional to determine what causes your low blood pressure and receive appropriate guidance.
In conclusion, understanding what causes low blood pressure is critical for effective management. From dehydration and medications to underlying medical conditions, the causes are varied. If you are experiencing symptoms of low blood pressure, it is important to seek medical advice to identify the cause and ensure you receive the appropriate care.
