Low blood pressure, or hypotension, is not often considered to be a major problem.
However, severe hypotension can indicate an underlying problem, and it can lead to serious heart disorders and organ failure, because oxygen and nutrients may not reach key organs. Hypotension is linked to shock, a life-threatening condition.
The American Heart Association (AHA) notes that as long as a person does not experience symptoms, low blood pressure is not a problem. Having a low reading is often considered an advantage, as it reduces the risk of a dangerously high 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 it picks up oxygen.
The heart pumps this oxygen-rich blood around the body to supply our muscles and cells. The pumping of blood generates blood pressure.
Measures of blood pressure include two different types of pressure:
- Systolic pressure is the blood pressure when the heart contracts. It is measured at the moment of maximum force of the contraction, when the left ventricle of the heart contracts.
- Diastolic pressure is the blood pressure measured between heartbeats, when the heart is resting and opening up, or dilating.
A blood pressure reading measures both the systolic and diastolic pressures. The figures usually appear with a larger number first, which is the systolic pressure, and then a smaller number, the diastolic pressure.
If a person’s blood pressure is 120 over 80, or 120/80 mmHg, the systolic pressure is 120mmHg, and the diastolic pressure is 80mmHg. The abbreviation mmHfg means millimeters of mercury.
Levels of blood pressure can fluctuate by up to 30 or 40 mmHg during the day. Blood pressure is lowest while sleeping or resting. Physical activity, high levels of stress and anxiety causes blood pressure to rise. Blood pressure must be taken under similar circumstances each time, so that when the readings are compared, they refer to the same state of physical activity.
An adult with a reading of 90/60 mmHg or lower can be regarded as having hypotension, or low blood pressure.
Many people with low blood pressure have no symptoms. People who are very fit may have low blood pressure and be in good health. In others, a chronic problem such as a hormone imbalance, or acute condition, such as anaphylaxis, can trigger hypotension.
Common symptoms include:
- Blurred vision
- Cold, clammy, pale skin
- Dizziness, fainting, and nausea
- Fatigue and weakness
- Rapid, shallow breathing
If the hypotension is not severe and there are no underlying conditions, no treatment is necessary.
If it is severely low, or significantly lower than usual, blood and oxygen supply to the brain and other vital organs may be insufficient. In this case, the patient will need medical attention. Severe hypotension indicates an underlying problem.
Blood pressure can become low for a number of reasons.
Orthostatic, or postural hypotension
A change in posture, such as standing up from a sitting or lying position, can lead to a drop in blood pressure, but this returns quickly to normal levels. This is more common as people get older. People with diabetes can experience this if they have damage to their autonomic nervous system.
Low blood pressure after meals
Sometimes, blood pressure falls after eating, causing light-headedness, dizziness, and faintness. It is more common among older people, especially those with high blood pressure, diabetes, or Parkinson’s disease.
After eating, the intestines need more blood supply for digestion. The heart beats faster, and blood vessels in other parts of the body narrow to help maintain blood pressure. With age, this process becomes less effective.
To minimize the problem, it may help to lie down after eating, reduce carbohydrate intake, and eat smaller meals, more frequently.
Using the bathroom, swallowing, and coughing
Blood pressure can drop when using the bathroom. Straining while urinating or having a bowel movement stimulates the vagus nerve, and this raises acetylcholine levels in the body.
Swallowing and coughing can also lead to faintness due to the stimulation of the vagus nerve.
Medications that can lead to low blood pressure include:
- Alpha blockers
- Beta blockers
- Tricyclic antidepressants
- Drugs for Parkinson’s disease
- Sildenafil, also known as Viagra, especially combined with nitroglycerine.
Acetylcholine dilates the blood vessels, and this reduces blood pressure and blood supply to the brain, leading to dizziness and fainting. This normally resolves quickly.
During surgery, deliberately lowering blood pressure can reduce blood loss.
The thyroid gland makes and stores hormones that help to control a number of functions, including heart rate and blood pressure. The adrenal glands regulate the stress response. Problems with either of these glands can lead to hypotension.
Neurally mediated hypotension
Neurally mediated hypotension is due to faulty signals between the heart and the brain. It mostly affects young people.
When a person stands for a while, blood collects in the legs. The heart adjusts to maintain a normal blood pressure, but, in some people, the wrong signals are sent. As a result, the heart rate drops, causes a further fall in blood pressure, resulting in dizziness, nausea, and fainting.
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 healthy and rarely cause for concern.
People with anorexia nervosa have an abnormally slow heart rate and low blood pressure. Bulimia nervosa leads to electrolyte imbalances that can lead to irregular heartbeats and possibly heart failure, and these can result in serious hypotension.
Hypotension is linked to different kinds of shock.
Severe internal or external bleeding causes blood volume to drop, leading to severe and potentially dangerous hypotension and hypovolemic shock. Serious burns can also lead to shock and hypotension.
Anaphylaxis is a severe allergic reaction to some substances, foods, exercise, medications, latex, or insect bites. Anaphylactic shock can result, with a severe drop in blood pressure. It is a medical emergency and needs immediate attention.
Bacteria from an infection in the body can invade the bloodstream. This is called septicemia. Septic shock, a life-threatening drop in blood pressure, can result.
A dramatic fall in fluid or blood levels can lead to hypovolemic shock. A severe drop in the volume of liquid in the body means the heart cannot pump the blood properly, resulting in life-threatening hypotension.
A sphygmomanometer is a standard device for measuring blood pressure. An inflatable cuff is wrapped around the upper arm, with the patient in a sitting position. When the cuff is inflated, it restricts the blood flow. A mercury or mechanical manometer measures the pressure.
It is important to use the correct size of cuff. The wrong size may give an inaccurate reading.
The cuff is inflated until the artery is completely obstructed, then the pressure is released slowly, while the doctor listens with a stethoscope to the brachial artery at the elbow to hear when the blood flows again.
The pressure that is recorded at the point when the sound begins is the systolic blood pressure.
The cuff is deflated further until no sound can be heard. The pressure recorded at this point is the diastolic blood pressure.
A digital sphygmomanometer uses electrical sensors to measure the pressure.
The reading may need to be repeated, to find out whether the problem is a sustained one.
Asking the patient about their medical history and performing other diagnostic tests can show whether the person has a heart problem, a hormonal problem, anemia, and so on.
Preventing low blood pressure is achievable through simple lifestyle measures.
- moving from being seated or lying down to standing slowly
- raising the head of the bed by 6 inches by placing bricks or large books underneath
- eating small meals frequently
- increasing water intake
- avoiding long periods of sitting or standing still
- not suddenly changing posture or position
- avoiding excessive alcohol intake and drinking caffeinated beverages late in the day
Treatment for low blood pressure
People with hypotension and either no symptoms or very mild ones do not require treatment.
If there are signs of an underlying problem, the patient will be referred to a relevant specialist.
Some older people who feel faint when they suddenly stand up may be prescribed medication to narrow the arteries. Fludrocortisone helps to boost blood volume. Midodrine also helps raise blood pressure levels.
If low blood pressure is possibly due to a medication, the dose may be altered, or another medication prescribed.
Increasing salt and fluid intake may improve the symptoms of hypotension. Salt levels can be boosted by taking salt tablets or adding more salt to food. Fluids increase blood volume and prevent dehydration, and this can impact blood pressure levels.
The patient should seek medical advice before making any significant changes.