Hypertension is, fundamentally, when your blood pressure is too high. This can cause many problems, particularly long-term. If severe enough or uncontrolled it can actually be a cause of sudden death! But, what is hypertension?

Hypertension is when your blood pressure exceeds the normal limits. Blood pressure is the strength of your blood pushing outwards on your blood vessels (arteries and veins). High blood pressure relates to two parts of your blood pressure: the systolic and the diastolic pressures. There are numerous causes, but fundamentally these boil down to too much blood or too much resistance. Finally, there are many problems that result from hypertension, whether in the acute or the chronic setting.

This image has an empty alt attribute; its file name is blood-pressure-2310824_19208531834550171002250-300x199.jpg

Blood pressure

The factors that make-up blood pressure can be represented as an equation: Blood Pressure = Cardiac Output x Peripheral Resistance. Cardiac Output means the blood that is coming out of your heart. Peripheral Resistance is complicated but is mainly the resistance that the arteries provide against blood coming from the heart.


Imagine if you will a balloon. When the balloon is empty, there is very low pressure. As you blow into the balloon, you increase the pressure. The balloon gets tense, the pressure increases, it becomes more difficult to keep adding to it.

Some balloons are easier to expand than others, and that’s primarily to do with the material they are made of, which represent resistance. Have you ever tried blowing up a water balloon? It is quite a lot more difficult than blowing up a normal balloon. The air builds up and gets stuck in your mouth, throat, and lungs.

Likewise, if your arteries have high resistance, this results in blood building up before them. However, the heart is still pumping the blood out, so the pressure increases.

This image has an empty alt attribute; its file name is blood-pressure-3773347_19207429137103572446724.jpg

Systolic and Diastolic 

Heart phases

Speaking of the heart, it is responsible for the systolic and diastolic pressures you’ve likely heard of. These numbers are why your blood pressure is represented by two numbers, such as 120/80 mmHg (spoken as one twenty on eighty). The first of these is your systolic pressure, the second is your diastolic pressure.

Systolic pressure

Systolic pressure is your blood pressure during the cardiac cycle known as systole. Systole is the phase of the cardiac cycle where the heart (technically, the ventricles) is actively contracting. During systole, your blood pressure rises to its peak due to the additional blood being added from the heart to the blood that is already present in your arteries. This peak is the higher number in your blood pressure, the 120 from 120/80 mmHg.

Systole normally lasts for about 0.3 seconds at a heart rate of 75 beats per minute or around 3/8ths of a cardiac cycle. However, this fraction changes substantially depending on your heart rate, as diastole (see below) is decreased as heart rate increases. At a high enough rate, the heart spends most of its time in systole, such as in the very dangerous conditions of ventricular tachycardia or ventricular fibrillation.

Diastolic pressure

In contrast, the diastolic pressure is the pressure when your heart is resting and refilling. Diastole is the phase of the cardiac cycle representing the steps where the heart is refilling (technically, also including the atrial contraction). During this phase, blood is progressing through the arteries, into capillaries and tissues, and draining into veins. As such, at the end of diastole (immediately preceding the next systole), your blood pressure in your arteries has fallen to the lowest that it will reach in the cardiac cycle. This is the lower number in your blood pressure, the 80 from 120/80 mmHg.

Diastole normally lasts for the majority of the cardiac cycle, at least during your resting heart rate. It lasts for around 0.5 seconds at a heart rate of 75 beats per minute, or around 5/8ths of the cardiac cycle. As stated previously though, the diastole phase is what is lost as the heart rate increases, potentially even disappearing completely if the heart rate is high enough or uncontrolled.

Elevated blood pressure

The normal range for blood pressure is a systolic blood pressure below 120 mmHg with a diastolic blood pressure below 80 mmHg, or as normally written by medical professionals, 120/80 mmHg. That said, medically hypertension is normally only classed as exceeding 130/80 mmHg. So, a systolic blood pressure exceeding 130 mmHg or a diastolic blood pressure exceeding 80 mmHg indicates hypertension is present. There are multiple stages of hypertension depending on how high these values are, and an explainable high blood pressure in only a single instance (I.e., that returns to normal afterwards) rarely warrants further investigation.

How do I know if I have hypertension?

The best way to determine your heart rate is to have a medical professional take it. In Australia, this can normally be performed for free by chemists and is obviously available with more significant care such as a GP appointment. You can also take your own blood pressure if you know what you are doing, however your doctor will normally only take these readings as indicative and will normally take your pressure himself for confirmation. Further, if you require daily monitoring or definitive establishment of chronic hypertension your medical professional can organise these investigations, although loan of the equipment will normally involve out of pocket expense.


Fundamentally, hypertension can be caused in two ways: too much blood, or too much resistance. More commonly, blood pressure is considered by the length of time that it has been present.

Blood pressure can be elevated in the acute setting, the chronic setting, or intermittently. It can even increase just from you stressing out about having it tested, known as white coat syndrome.

White coat syndrome refers to a phenomenon whereby your blood pressure rises, generally around 10 mmHg. This rise is just from the act of having your blood pressure taken and is understood to be caused purely by anxiety.

In the acute setting, elevated blood pressure can most commonly arise due to anxiety or stress, bodily response to an antigen, or an inability to excrete fluid via the kidneys due to kidney disease. Acute hypertension is normally only diagnosed with a blood pressure over 180/120 mmHg (depending on the source), which is subdivided into hypertensive urgency or hypertensive emergency. Hypertensive urgency is an isolated blood pressure over 180/20 mmHg, with no evidence of end-organ damage and an asymptomatic patient. Hypertensive emergency is a blood pressure over 180/20 mmHg with signs of end-organ damage, generally expressing with symptoms. End-organ damage can include neurologic, aortic, cardiac, renal, haematological, or pregnancy-related damage.

In the chronic setting, blood pressure can be elevated due to many reasons. Normally, no cause is known for why hypertension exists. The most common known cause of chronically elevated blood pressure is chronic kidney disease (CKD). In CKD, the kidneys are not filtering blood and producing urine at the normal rate. This results in the volume of blood to increase and not be maintained as sufficiently by the kidneys. This increased blood pressure does increase the kidney filtration rate which places more work on the kidneys, and over time they get worse. Further decreasing their filtration ability and again elevating blood pressure. More is involved, such as the afferent and efferent arterioles vasoconstriction, the renin-angiotensin-aldosterone system, and others, but this basic description will suffice.

A common risk factor for hypertension is cardiovascular disease, such as atherosclerosis. Atherosclerosis is a build up of plaques along the walls of the arteries, consisting significantly of cholesterol. This results in narrowing of the blood vessel and decreased compliance of the blood vessel to expand, both of which increase the blood pressure flowing through those arteries. Alternatively, blood vessels can undergo calcification, whereby calcium builds up within the walls of the blood vessel. This again decreases the compliance of the blood vessel and results in increased blood pressure.

Intermittently elevated blood pressure can occur in some situations. The main cause that comes to mind is a patient with a renal condition where the kidneys are excreting too much liquid or are not reabsorbing sufficient volumes. In this situation, the patient may be consuming large quantities of liquid to re-hydrate, and the blood pressure will fluctuate between each consumption.


Uncontrolled hypertension will cause ongoing issues to your organs, but will generally not show up until this organ damage has progressed to quite a late stage. This is why hypertension is often referred to as the silent killer. As stated earlier, in extreme causes it can even cause sudden death.

What can I do about my hypertension?

First things first, involve a health professional. I am only a medical student, not a medical professional, and if you have any concerns you should see your normal healthcare provider in the first instance. The specifics of your situation are exactly that, specifics, and will need to be considered by your doctor when determining the plan that’s best for you. Discussions and evaluation of what the correct treatment for you will require input from your doctor. Depending on your circumstances, you may even require prescription medication such as diuretics, ACE inhibitors, ARBs, calcium channel blockers, or numerous others. Finally, hypertension can often be a sign of an underlying disease that your doctor may need to investigate. Attempting to treat hypertension in isolation without considering the actual cause is dangerous and may miss something much more sinister.

That said, lowering the risk factors will also lead to an improved prognosis and should also improve your blood pressure. This can include quitting smoking, stopping alcohol consumption, losing weight, and dietary modifications. Speak to your medical professional about any of these, particularly before losing weight or changing your diet significantly.


Hypertension is a common condition that affects a large proportion of the population. It’s causes are many, but fundamentally are due to either too much blood or too much pressure. As with any condition or symptom, the first step in treating it is differentiating whether it is only an isolated finding or secondary to an underlying disease, and treating or managing the cause.

This Post Has 2 Comments

  1. Able to gain a better understanding of the blood pressure process. Once again the blog was easy to follow and was easy to understand. Thanks for simplifying what can be perceived as a sinister process…the silent killer!

    1. Thank you, Alana. I am particularly happy with your response to this post, I personally felt that there were issues with this post, such as still too technical at parts and too “granular” of subheadings/sections. So, I appreciate that from your point of view it was simplified to a good level.

Leave a Reply

Close Menu