How Is Low Blood Pressure Defined?
Low blood pressure (hypotension) is generally defined as someone having a systolic reading of under 90mmHg, or a diastolic reading of below 60mmHg. A normal blood pressure (normotension) range would typically be classed as having readings between 90mmHg over 60mmHg, and 120mmHg over 80mmHg. Systolic pressure is created when the heart contracts on a beat and pumps blood out to the body, and diastolic is when it dilates and fills again. The units of pressure, mmHg, represent millimetres of mercury. You can read more about why blood pressure is measured in mmHg here.
Is Having Low Blood Pressure a Problem?
Having slightly lower blood pressure than normal is usually not a problem but if your blood pressure becomes too low, it may cause side effects such as fainting or dizziness which might then cause injuries. It may be prudent to inform your doctor if you are consistently recording low blood pressure readings, even if you feel fine, as they may wish to determine any underlying causes and monitor developments. Extremely low blood pressure or ‘severe hypotension’ can lead to life threatening complications. There are a number of different factors that can cause lower blood pressures, ranging from simple things like dehydration through to serious underlying medical conditions.
What Symptoms Occur With Low Blood Pressure?
As mentioned, mild symptoms of low blood pressure typically include dizziness and being prone to feeling faint, this can be particularly noticeable if you stand up too fast which in this case is known as, postural or orthostatic hypotension. Other symptoms you might experience are blurred vision, nausea (feeling sick) or difficulty concentrating properly, while a general feeling of fatigue (tiredness and lack of energy) may also occur. If you experience these symptoms, then record when they occur and also make a note of what activity you were doing around that time. As an example, if you’ve been sat in a hot bath for a long time or spent too much time out in the hot sunshine, either could cause a drop in blood pressure temporarily.
However, at the other end of the seriousness scale, extreme cases of hypotension can place the body into a state of ‘shock’ which can be life threatening and is explained further below.
Which Medical Conditions Are Associated With Very Low Blood Pressure?
Shock – is a serious condition characterised by a weak, rapid pulse, cold clammy skin, shallow rapid breaths and confusion often brought on by a trauma. There are various types of shock though, such as:
- Cardiogenic shock, which is associated with heart problems.
- Hypovolemic (meaning low volume) or haemorrhagic shock, caused by losing too much blood.
- Anaphylactic shock, caused by severe allergic reactions.
- Septic shock, caused by infection.
- Neurogenic shock, cause by the nervous system being damaged.
If you ever encounter a person with signs of shock, emergency medical attention should be sought. This is because the lack of sufficient blood flow causes hypoxia (a lack of oxygen delivered to cells and tissues) which can damage and destroy organs, a fifth to a half of people with shock tend to die as a result of it.
Other conditions associated with lower blood pressure include:
Dehydration – where your body has an insufficient quantity of water, it can be related by things such as strenuous exercise, vomiting, fever, diarrhoea or consuming diuretics (which promote passing urine, e.g. ‘water pills’).
Pregnancy – the circulatory system expends during pregnancy which tends to lead to a lower blood pressure during the term, however this typically reverts back to normal subsequent to the birth. This is explored in our article, ‘What is Normal Blood Pressure for Women?’
Nutrient Deficiency – A lack of B12 vitamins, folate and iron can cause anaemia which could limit the amount of red blood cells the body is able to produce and result in lower blood pressure.
Blood Loss – A loss of blood by internal or external injury will lower blood pressure rapidly if severe, see haemorrhagic shock mentioned above.
Heart Issues – An extremely low heart rate (bradycardia) can be a cause low blood pressure but also heart valve issues, heart attack, heart disease and heart failure.
Low Blood Glucose Levels – low blood sugar levels (hypoglycaemia) may also cause a drop in blood pressure and related feelings of dizziness, weakness, confusion and fainting.
Examples of Medicines That Can Create Low Blood Pressure
There are a variety of medicines which are associated with causing lower blood pressure. Some of these would include: water pills, alpha blockers, beta blockers, tricyclic antidepressants, certain drugs for Parkinson’s disease and erectile dysfunction drugs.
Low Blood Pressure After a Meal
Some people, particularly more elderly members of the population over 65, can be prone to experiencing lower blood pressure an hour or two after eating a meal. Usually as blood is directed towards the digestive system to assist the process, the pulse rate increases while other blood vessels in the body constrict in order to to maintain a normal blood pressure in the body. However, in this older demographic the mechanism can fail to function as effectively as it used to, so low blood pressure occurs. Low blood pressure caused in this way is known as, postprandial hypotension.
Low Blood Pressure After Standing Up for Too Long
Low blood pressure can also occur where an individual has been standing up for too long, and this type of low blood pressure is referred to as neurally mediated hypotension. This tends to be more prominent in younger adults as well as children and is thought to occur due to a miscommunication between the brain and heart.
Low Blood Pressure in Summary
There are a variety of causes of low blood pressure, both ongoing and temporary. You might only experience manageable, minor symptoms of dizziness or feeling faint as a result but even these effects can result in injuries from falls. In more serious cases of severely low blood pressure, the body can go into shock which results in cells and tissues being starved of oxygen. This hypoxia, which is a result of blood not carrying enough oxygen through the body via red blood cells, can damage vital organs, pose a risk the brain and heart and even cause death.
Remember, a single blood pressure reading is not conclusive, you should regularly take your blood pressure readings at home with one of the many affordable blood pressure monitors to find a good average. There are a whole variety of factors affecting blood pressure readings in general, which you can read about here.
You can also check any blood pressure reading for a detailed analysis by entering it on the home page of xBloodPressure.com
