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Low blood pressure, or hypotension, can lead to dizziness and faintness. It is less likely than high blood pressure to be problematic, but it can sometimes indicate an underlying health issue.
Blood pressure readings include two numbers. The top number shows the systolic pressure, which is the pressure when the heart is contracting, and the bottom number gives the diastolic pressure, which is the pressure between heartbeats. An adult with low blood pressure will have a reading of less than 90/60 millimeters of mercury (mm Hg).
Very low blood pressure can be a sign of an allergic reaction or internal bleeding. It can be life threatening if oxygen and nutrients are unable to reach the brain, heart, and other vital organs.
However, it is generally better to have persistently low blood pressure than high blood pressure, as it poses a lower risk of various health problems.
The heart is a muscle that pumps blood continuously, delivering oxygen and nutrients to all parts of the body, including the vital organs.
This pumping action and the pressure of blood against the blood vessels create blood pressure.
Blood pressure monitors are available for purchase in pharmacies and online.
Many people with low blood pressure have no symptoms. Those who are very fit with low blood pressure may have excellent health.
However, hypotension can also indicate a chronic problem, such as a hormone imbalance, or an acute condition, such as anaphylaxis.
Common symptoms include:
Symptoms that can result from an underlying cause include:
- chest pain
- cold, pale, dry, or clammy skin
- a headache and a stiff neck
- vision changes
- diarrhea and vomiting
- allergic reactions, such as swelling
- difficulty breathing
- fatigue and weakness
- thirst and dehydration
- changes in heart rhythm
Blood pressure depends on two main mechanisms: the functioning of the heart and the resistance of the blood vessels.
In combination with the effects of neurological and hormonal factors, these mechanisms determine the extent to which blood pressure will be high or low.
Possible causes of hypotension include:
Orthostatic or postural hypotension
Standing up from a sitting or lying position can lead to a drop in blood pressure alongside dizziness or faintness.
If the heart does not work correctly, it may not pump enough blood to keep blood pressure within the normal range.
The circulatory system expands during gestation, and this often results in low blood pressure. Hypotension during pregnancy is rarely a cause for concern.
Blood pressure sometimes falls after eating, as the intestines need an increased blood supply for digestion. Hypotension after eating is more common among older people, especially those with high blood pressure, diabetes, or Parkinson’s disease.
Blood pressure can drop when using the bathroom, swallowing, or coughing. These actions all stimulate the vagus nerve, which reduces blood pressure.
The thyroid gland makes and stores hormones that help manage various bodily functions, including heart rate and blood pressure. The adrenal glands regulate the stress response. Problems with either type of gland can lead to hypotension.
Neurally mediated hypotension
Faulty signals between the heart and brain can lead to low blood pressure.
Beta-blockers, calcium channel blockers, and diuretics can reduce blood pressure. During surgery, healthcare professionals may lower blood pressure deliberately to reduce the risk of blood loss.
Low levels of vitamin B12 and folic acid can lead to anemia, which can, in turn, lead to low blood pressure.
In people with anorexia nervosa, a low calorie intake can affect the structure of the heart, reducing blood pressure. Bulimia nervosa can lead to an electrolyte imbalance, increasing the risk of irregular heartbeats and heart failure.
Severe hypotension can lead to hypotensive shock. There are different ways of describing shock, depending on the cause.
- Hypovolemic shock: The total volume of blood falls, and the heart can no longer pump effectively. Possible causes include severe internal or external bleeding or severe dehydration. Dehydration can result from a high urine output — due, for example, to a hormone imbalance or the overuse of diuretics — or a loss of fluid due to diarrhea and vomiting.
- Cardiogenic shock: The heart is unable to function effectively due to cardiovascular problems. A person may have a low heart rate and cool, dry extremities and skin.
- Distributive shock: The vascular system loses resistance, and the heart is unable to pump fast enough to compensate. Causes include an allergic reaction (anaphylactic shock) and septic shock, which is a possible complication of an infection.
- Obstructive shock: An obstruction in the cardiovascular system stops the heart from pumping effectively or prevents the blood from flowing. Causes include pulmonary embolism. A person’s jugular veins may be distended, and they may have quiet heart sounds.
Any combination of these is called hypotensive shock. Whatever the cause, a person with shock will need urgent medical attention.
A person should seek medical advice if their blood pressure falls suddenly, is very low, or is significantly lower than usual.
They should also seek advice if they have other symptoms, such as excessive urination, a fever, or fatigue, as these could indicate an underlying condition.
With very low blood pressure, insufficient blood and oxygen may be reaching the brain and other vital organs. Emergency medical attention may be necessary.
If a person shows signs of anaphylaxis, whoever is with them should take immediate action. If the person carries an autoinjector, a bystander can help them administer it. They should also call 911.
Different types of blood pressure monitor are available. Monitors for home use are usually digital devices. It is best to take several readings to check whether the problem is ongoing.
Devices that healthcare professionals use in a healthcare setting may require them to listen for changes in pressure with a stethoscope while reading a mercury gauge.
A doctor will also ask the person about their medical history and other symptoms. They may carry out other tests to rule out an underlying problem.
Most people with low blood pressure do not need treatment. However, if hypotension starts suddenly or results from an underlying condition, a doctor will provide appropriate treatment. The treatment options will depend on the cause.
Treatment may involve a doctor:
- prescribing medication to help resolve low blood pressure
- changing a person’s medication or dosage, if they suspect that either of these is responsible
- suggesting dietary changes, such as increasing the intake of salt or fluid
People should always speak to a doctor before making any significant changes to their diet or medication use.
A range of lifestyle measures can help prevent low blood pressure.
- taking time to stand up from a sitting or lying position
- using blocks to raise the head of the bed by 6 inches
- eating small meals frequently and resting after eating
- increasing fluid intake
- avoiding long periods of sitting or standing still
- avoiding suddenly changing posture or position
- moderating alcohol intake
- refraining from drinking caffeinated beverages late in the day
- wearing support stockings
Low blood pressure is not usually a cause for concern. However, a person may need medical attention if their symptoms are severe or lead to other problems, such as frequent falls.
If blood pressure falls suddenly, emergency medical treatment might be necessary. Examples of when this might happen include:
- a trauma leading to external or possible internal bleeding
- exposure to an allergen, such as an insect sting
- severe dehydration
- an infection that may have spread to another part of the body
In these cases, the person may need treatment for shock and to prevent damage to the brain and other organs due to a lack of oxygen.