Can Blood Pressure Be Too Low?

Blood pressure is one of the most common health pointers checked at a doctor’s visit. It is part of a group of other pointers called vital signs. These include the temperature, breathing rate, heart rate or the pulse and oxygen levels. Blood pressure could be normal, high or low. High blood pressure is called hypertension and low blood pressure is called hypotension in medical terms. This article will focus on the causes, types, symptoms and treatment of low blood pressure.

What is Blood Pressure?

Blood pressure is the force of blood that is pumped from the heart through the arteries of your body. There are 2 components - systolic and diastolic. Systolic blood pressure is the maximum pressure in the arteries when the heart contracts to push out blood. Diastolic is the minimum pressure in the arteries when the heart relaxes.¹

Blood pressure (BP) varies throughout the day. A one-off BP reading does not tell you the state of the pressure of blood in your arteries. Some people suffer from 'white coat’ hypertension which is when the blood pressure only reads high in healthcare settings. Some could also have masked hypertension - when the BP always reads normal when it is checked in a healthcare setting whereas it is high at other times. Therefore, ambulatory blood pressure- which is blood pressure measured throughout the day- gives a more reliable value. Alternatively, an average of twice-daily readings measured at home over a minimum of 5 days is also reliable. This is known as home blood pressure monitoring. 

How is Blood Pressure Measured?

A blood pressure monitor or sphygmomanometer is used to measure blood pressure. It has a cuff which fits on the arm, a gauge which could be manual- as in a mercury level monitor- or digital, and a connecting tube between them. The manual ones require an expert to listen to the sound of the pulse on your arm with a stethoscope while inflating and deflating the cuff. Blood pressure is usually reported as 2 numbers in the format x/y where the top number is the systolic pressure while the bottom number is the diastolic pressure.

How Low is “Low” Blood Pressure?

Normal blood pressure is said to be below 140/90. An ideal BP would be below 120/80. Low blood pressure is a BP reading below 90/60 while high blood pressure is considered 140/90 or above. The targets are lower when using ambulatory blood pressure readings or home blood pressure readings. 

Types of Low Blood Pressure

Orthostatic or Postural

In some conditions, BP could be lower when standing up than when sitting or lying down. It is when the difference between the value of BP measurement while standing for up to 3 mins and the value measured while lying is greater than 20mmHg in systolic or 10mmHg in diastolic. ² This is common in elderly people, people taking multiple medicines and those with certain conditions that affect the nervous system such as Parkinson's disease. Postural hypotension could be a cause of falls in the elderly. It is as common as 20% of people aged 60 and above.³

Postprandial

This is when the BP drops after eating. ⁴ It is more common with older age. It is caused by a widening of the blood vessels of the intestine which results in a pooling of blood in that area.

Neurally-Mediated

Neurally-mediated is also a form of orthostatic hypotension. It is also known as autonomic dysregulation or neurally mediated syncope. This is due to some conditions which damage the nerves such as Diabetes mellitus, excess alcohol use, some infectious diseases etc. ⁵ It is characterised by a widening of the blood vessels of the hands and feet (pooling blood towards these areas), low blood pressure and a reduced heart rate when standing. Usually, it causes lightheadedness but if severe, it can lead to a fainting episode called syncope in medical terms. 

Shy-Drager syndrome

Shy-Drager syndrome is a rare genetic condition affecting the brain and spinal cord. It presents with Parkinson-like features- such as rigidity, tremors and slow movement- as well as changes in blood pressure including orthostatic hypotension, postprandial hypotension or supine hypertension (which is the high blood pressure when lying down). 

Signs and Symptoms of Low Blood Pressure

If you have low blood pressure you might feel

• Dizzy
• Light headed
• Headache
• Palpitations 
• Faint

Causes and Risk Factors for Low Blood Pressure

Normal variant - Some people naturally have low blood pressure. 

Exercise- Young athletes usually have low blood pressure. 

Heart failure - when the heart is unable to pump out enough blood

Sepsis - A severe infection spreading to the blood can cause a number of body reactions including low blood pressure

Dehydration - not drinking enough, especially in hot weather

Drugs - some drugs lower blood pressure, including blood pressure medication, water tablets, heart failure drugs, drugs for enlarged prostate, drugs for erectile dysfunction, etc.

Diagnosis

Low blood pressure is usually discovered during a health check or doctor’s visit for symptoms. Blood pressure below 90/60 is said to be low.

Complications of Low Blood Pressure

When low blood pressure is left untreated, it can lead to shock, failure of organs and possibly death. 

What is Shock?

Shock is when the amount of blood being pumped out of the heart and carried through the arteries is not enough for the tissues and organs that need them. It is the result of blood pressure that is too low for several reasons; for instance, excess blood loss, excess fluid loss from burns, etc. Symptoms may include cold hands and feet, drowsiness, or reduced consciousness. 

Types of Shock ⁶

1. Hypovolemic shock - when there is a massive loss of blood volume. For example, significant loss of blood due to bleeding from a serious injury, complications of childbirth or burns. 
2. Cardiogenic shock - occurs when the heart pumps an insufficient amount of blood and oxygen into vital organs and the brain, which can be life-threatening if not treated in time. 
3. Obstructive shock - where some conditions of the heart or lung restrict or compress the heart such that it cannot pump blood effectively. 
4. Distributive shock - this occurs as a result of extensive widening of the blood vessels. This is seen in anaphylaxis (a severe allergic reaction) and septic shock. 

Treatment, Management and Prevention of Low Blood Pressure

Treatment of low blood pressure involves treating the specific cause of low blood pressure.

If dehydration is the cause, you need to consume more fluids. You may require an IV.

If the cause is an infection or sepsis, you will be given antibiotics and fluids in the hospital through your veins 

If drugs have caused low blood pressure, your doctor will remove the offending drug.

In orthostatic hypotension, after all potential causes have been treated, you could be given a drug to help increase the B,  such as a form of steroid. 

When to Call a Doctor or Dial 999

If you are feeling faint or have just passed out you need to see a doctor as soon as possible.

Summary

Blood pressure is one of the markers of the state of your health. In certain conditions, it can be too low. If left untreated, it can lead to serious complications. If you feel dizzy, lightheaded or feel faint, please see a healthcare professional.