What is low blood pressure? What is hypotension?

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MNT Knowledge CenterLow blood pressure is also known as hypotension. For millions of people who suffer from hypertension (high blood pressure) hypotension may seem great. If symptoms are mild hypotension usually requires no treatment. However, it can cause serious heart disorders, fainting and also lead to neurological and endocrine disorders. If hypotension is severe key organs can become deprived of oxygen and nutrients and the body can go into shock, a life-threatening condition.

What is blood pressure?

The heart is a muscle that pumps blood around the body continuously. Blood that is low in oxygen is pumped towards the lungs, where oxygen supplies are replenished. The heart pumps this oxygen-rich blood around the body to supply our muscles and cells. The pumping of blood generates pressure – blood pressure.

When we measure blood pressure, we gauge two different types of pressure:

  • Systolic pressure – the blood pressure when the heart contracts, specifically the moment of maximum force of the contraction, which occurs when the left ventricle of the heart contracts.
  • Diastolic pressure – the blood pressure between heartbeats, when the heart is resting and opening up, (dilating).

Digital blood pressure monitor showing ideal reading
A digital blood pressure and heart rate monitor showing an ideal reading

When our blood pressure is taken the doctor or nurse needs to measure both the systolic and diastolic pressures. The figures usually appear with a larger number first (systolic pressure), and then a smaller number (diastolic pressure). The figure will be followed by the abbreviation mmHg, which means millimeters of mercury.

If your blood pressure is 120 over 80 (120/80 mmHg), it means a systolic pressure of 120mmHg and a diastolic pressure of 80mmHg.

Our levels of blood pressure can fluctuate by as much as 30 or 40 mmHg during the day. It will be at its lowest point when we are asleep or resting. When we are physically active, very stressed or anxious our blood pressure rises. It is important that blood pressure is taken under similar circumstances each time so that when the readings are compared they refer to the same state of physical activity.

What is low blood pressure (hypotension)?

Anybody with a reading if 90/60 mmHg or lower is regarded as having hypotension (low blood pressure). People with low blood pressure have some protection from factors which raise blood pressure to undesirable levels. However, low blood pressure may be a sign of an underlying problem, and can cause unpleasant symptoms.

What are the symptoms of low blood pressure (hypotension)?

Many people whose blood pressure is low will experience no symptoms. If the hypotension is not severe and there are no underlying conditions no treatment is necessary.

If blood pressure is so low that the supply of blood to the brain and other vital organs is insufficient the patient will need medical attention. Severe hypotension is caused by an underlying illness or condition.

Below are the most common symptoms of hypotension:

  • Blurred vision
  • Cold, clammy, pale skin
  • Depression
  • Dizziness
  • Fainting
  • Fatigue
  • General feeling of weakness
  • Nausea
  • Palpitations
  • Rapid, shallow breathing
  • Thirst.

Orthostatic hypotension (postural hypotension)

This refers to a lowering of blood pressure after changing posture. This can occur when you stand up from a sitting or lying position, or sit up from a lying position. The low blood pressure will return to normal levels rapidly. Postural hypotension occurs more frequently as we get older.

Low blood pressure after meals (Postprandial hypotension)

Sometimes blood pressure can drop after eating, causing light-headedness, dizziness, and wooziness (faintness). This is known as postprandial hypotension. It more commonly occurs among elderly people, especially elderly people who suffer from hypertension (high blood pressure), diabetes, or Parkinson’s disease.

After we eat our intestines require a significant increase in blood supply for digestion. The heart responds by beating faster while blood vessels in other parts of the body narrow (constrict) to help maintain blood pressure. When we reach old age the heart beat may not increase enough to maintain blood pressure. Also, the blood vessels that were supposed to have narrowed do not constrict sufficiently to maintain blood pressure. Consequently, blood pressure drops. If you are prone to developing postprandial hypotension you may find that the following simple steps help:

  • Lie down after the meal.
  • Lower the carbohydrate content of your meals.
  • Eat smaller and more frequent meals – perhaps four or five small meals a day instead of 3 big ones.

What causes low blood pressure (hypotension)?

Some medications

  • Alpha blockers
  • Beta blockers
  • Tricyclic antidepressants
  • Diuretics
  • Drugs for Parkinson’s disease
  • Sildenafil (Viagra), more so if in combination with nitroglycerine.

Anesthesia

Blood pressure is usually deliberately reduced for surgery. Hypotensive anesthesia – deliberately lowering blood pressure for surgery – reduces intraoperative blood loss as well as surgical time.

Feeling faint in the toilet – urinating (micturition syncope), defecating (defecation syncope)

If you strain when urinating or having a bowel movement the vagus nerve is stimulated, causing an increase in acetylcholine levels in the body. Acetylcholine dilates the blood vessels. Dilated blood vessels bring blood pressure down which reduces blood supply to the brain. A sudden drop in blood supply to the brain can cause dizziness and fainting (syncope). Micturition syncope means feeling faint/fainting when urinating, and defecation syncope means feeling faint/fainting while having a bowel movement. In virtually all cases the problem resolves quickly and no treatment is required. Swallow syncope and cough syncope, feeling faint/fainting from swallowing or coughing are also caused by the stimulation of the vagus nerve.

Serious injuries and/or internal bleeding

If you lose a lot of blood from a serious injury or internal bleeding blood volume will drop, leading to severe and potentially dangerous hypotension. Serious burns can lead to shock and a reduction in blood pressure.

Septicemia, blood poisoning, severe infection

Virulent bacteria from an infection somewhere in the body can invade the bloodstream (septicemia). The patient can go into septic shock; a life-threatening drop in blood pressure.

Dehydration

When your body loses more water than it takes in you eventually become dehydrated. Hydration levels (levels of water in the body) do not have to drop much before you start feeling dizzy and weak – dehydration-induced weight loss of just 1% can lower blood pressure enough to cause symptoms. Dehydration can be caused by severe diarrhea, vomiting, heat, overusing diuretics, and over-exercising. If water or blood levels drop dramatically the patient can go into hypovolemic shock – the severe water/blood drop in volume means the heart cannot pump the blood properly, resulting in life-threatening hypotension.

Endocrine problems (not including diabetes)

The endocrine system is a system of glands involved in the release of hormones – examples include the thyroid gland, and the adrenal gland. The thyroid gland makes and stores hormones that help in the control of the heart rate, blood pressure, body temperature, and the rate at which food is broken down and converted into energy (part of metabolism). Low blood pressure can be caused by hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). If the adrenal glands do not work properly (adrenal insufficiency) there is also a risk of hypotension – the adrenal glands are located just above each kidney and are chiefly responsible for regulating the stress response.

Diabetes

Damage to the nerves in the body, including those in the autonomic nervous system, is a complication of diabetes. Autonomic dysfunction makes people more susceptible to orthostatic hypotension (postural hypotension) – feeling faint when you suddenly sit up from a lying position, or stand up from a sitting/lying position.

Heart disease

Badycardia (very low heart rate), heart valve problems, heart attack and heart failure can cause very low blood pressure, mainly because the heart is unable to pump enough blood to keep the pressure up.

Pregnancy

Blood pressure usually drops during pregnancy because the circulatory system expands during gestation. Systolic pressure typically falls about 5 to 10 points, while diastolic pressure may fall by 10 to 15 points. This is a normal part of a healthy pregnancy and is rarely cause for concern. Soon after childbirth blood pressure will resume to normal levels.

Anaphylaxis (severe allergic reaction)

Some people may have a severe allergic reaction to some substances, foods, exercise, medications, latex, or insect bites. One of the symptoms could be a severe drop in blood pressure, as well as hives, itching, swollen neck and breathing difficulties.

Diet deficiency

A diet with insufficient quantities of vitamins B-12 and folate can cause anemia. Anemia often results in hypotension.

Eating disorders

Anorexia nervosa has abnormally slow heart rate and low blood pressure among its many complications. Bulimia nervosa leads to electrolyte imbalances that can lead to irregular heartbeats and possibly heart failure – both these heart problems tend to result in serious hypotension.

How is low blood pressure (hypotension) diagnosed?

The doctor will try to establish whether there is an underlying cause. This will help decide on the best treatment. A nervous disease problem will not have the same treatment as, for example, a heart problem. The doctor may order some of the following tests:

Sphygmomanometer – to measure blood pressure

Blood pressure measurement
A sphygmomanometer is commonly used to measure blood pressure

Most lay people have seen this device. It consists of an inflatable cuff that is wrapped around the upper arm. When the cuff is inflated it restricts the blood flow. A mercury or mechanical manometer measures the pressure.

A sphygmomanometer is always used together with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. For example, a manual sphygmomanometer is used together with a stethoscope.

  • The cuff is placed snugly and smoothly around the upper arm, at approximately the same altitude as the heart while the patient is sitting up with the arm supported (resting on something). It is crucial that the size of the cuff is appropriate. If it is too small the reading will be inaccurately high; if it is too large the reading will be too low.
  • The cuff is inflated until the artery is completely obstructed (occluded).
  • The nurse, doctor, or whoever is doing the examination listens with a stethoscope to the brachial artery at the elbow and slowly releases the cuff’s pressure (deflates it).
  • As the cuffs pressure falls the examiner will hear a whooshing sound or a pounding sound when blood flow starts again.
  • The pressure at the point when the sound began is noted down and recorded as the systolic blood pressure.
  • The cuff is deflated further until no sound can be heard. At this point the examiner notes down and records the diastolic blood pressure.

With a digital sphygmomanometer everything is done with electrical sensors.

To find out whether the problem is a sustained one, diagnosis confirmation requires more than one reading.

Blood tests

These may indicate whether there are any problems with high sugar (hyperglycemia) or low sugar (hypoglycemia) levels. A low red blood cell count would indicate anemia.

ECG (electrocardiogram)

This device detects heart rhythm irregularities, problems with blood supply to heart muscles, as well as any structural abnormalities in the heart. It can also determine whether the patient ever had a heart attack, or is even having one while the test is underway.

Holter monitor

This is a sort of portable ECG device. If the ECG does not detect any problems the doctor may want to monitor the patient’s heart rhythm for longer, perhaps for a 24 hour period. The patient wears the Holter monitor which records the heart’s electrical activity as he/she goes about his/her daily business. The device is worn in a pouch either around the waist or neck. The doctor may ask the patient to record their activities and any symptoms they may feel into a diary. The details of the diary, which should include specific times, will be compared to the Holter’s records.

Echocardiogram

This device uses ultrasound waves which show the heart in motion. The doctor will be able to detect problems, such as defective heart valves.

Exercise stress test

An exercise stress test sometimes reveals problems that are not apparent when the body is resting. The stress test assesses how the body’s cardiovascular system responds to increased physical activity. The test monitors the electrical activity of the heart, as well as the patient’s blood pressure during exercise. Imaging scans of the heart’s blood supply might be done at the same time.

Valsalva maneuver

This tests the functioning of the autonomic nervous system. After several cycles of a type of deep breathing it analyses the heart rate and blood pressure. The patient takes a deep breath and then tries to blow out with the mouth closed and the nose blocked (so no air can get out).

Tilt-table test

If you have postural hypotension (low blood pressure when standing from a sitting/lying position), or neurally mediated hypotension (low blood pressure from faulty brain signals) and neither the ECG nor the Holter revealed anything, a tilt-table test may be performed. This monitors blood pressure, heart rhythm and heart rate while the patient is moved from a lying down to an upright position. Our reflexes cause the heart rate and blood pressure to change when moved to an upright position – this is to make sure the brain gets an adequate supply of blood. If the reflexes are inadequate, they could explain some of the symptoms, such as the fainting spells.

What is the treatment for low blood pressure (hypotension)?

People with hypotension and either no symptoms or very mild ones do not require treatment. The National Health Service (NHS), UK, says that a very small percentage of patients who are diagnosed with low blood pressure by their GPs (general practitioners, primary care physicians) are prescribed medications.

  • Medication for low blood pressure

    Some elderly patients who experience symptoms when they suddenly stand up (postural hypotension) may be prescribed medication to narrow the arteries. Fludrocortisones helps boost blood volume. Midodrine also helps boost blood pressure levels.

  • Low blood pressure caused by medications

    If the doctor believes the low blood pressure is being caused by a medication, the dose may be altered. If possible, the doctor may prescribe another medication.

    If the patient is on a blood pressure lowering drug, such as doxazosin, or an alpha blocker and becomes dizzy or faints when standing up, the doctor will need to find out whether it is being caused by a drop in blood pressure. If it is, the medication will need to be changed.

  • Underlying illnesses or conditions

    If the General Practitioner believes the hypotension is being caused by an underlying condition or illness, such as adrenal gland failure, a thyroid disorder, a nerve condition or a heart condition, the patient will most likely be referred to a specialist.

  • Adrenal gland failure

    This is treated by replacing the missing hormone, aldosterone.

  • A nerve condition

    This is usually harder to treat. The patient may be given medication to stimulate the nervous system.

  • Salt and fluids

    Increasing salt intake may improve the symptoms of hypotension, especially for those with postural hypotension. This can be done either by taking salt tablets or adding more salt to food. It is important to make sure your fluid intake is adequate – ask your doctor how much fluid (water) you should ideally consume each day. Fluids increase blood volume and prevent dehydration – both have an impact on blood pressure levels.

  • Compression stockings

    These help stimulate circulation.

What are the complications of hypotension (low blood pressure)?

  • Orthostatic hypotension (postural hypotension)

    In most cases becoming slightly dizzy or woozy when you stand up is just a nuisance, and nothing more. However, if it causes a severe drop in blood pressure there is a risk of injury if you faint and fall down. If sitting and then standing and then sitting, etc., cause large fluctuations in blood pressure there is also a higher risk of developing stroke, dementia, and other brain disorders.

  • Severe hypotension

    Untreated severe low blood pressure can in the long-term damage the organs, including the heart and the brain.

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