Author: Tanner Marshall, MS
Editor: Rishi Desai, MD, MPH, Tanner Marshall, MS
About 25% of the world has hypertension or high blood pressure, which basically means that it’s pretty common.
Let’s start with defining it - typically it’s represented by two numbers: the top number is the systolic blood pressure which is the arterial pressure when the heart is contracting, and the lower number is the diastolic blood pressure which is the arterial pressure when the heart is relaxing or refilling. Most of the time blood pressure is taken in the brachial artery in your upper arm, because if the pressure is high there, it’s probably high throughout all of the arteries.
Normal systolic blood pressure is between 90 and 119 mmHg, and normal diastolic is between 60 and 79 mmHg.
Prehypertension, or on the high side of normal, is between 120 and 139 mmHg on the systolic side, and between 80 and 89 on the diastolic side.
Stage 1 hypertension is between 140 and 159 mmHg on the systolic side, and between 90 and 99 on the diastolic side.
Stage 2 hypertension is between 160 and 179 mmHg on the systolic side, and between 100 and 109 on the diastolic side.
And finally, stage 3 hypertension is anything over 180 mmHg on the systolic side and 110 mmHg on the diastolic side.
Typically both systolic and diastolic pressures tend to climb or fall together, but that’s not always the case. Sometimes you can have systolic or diastolic hypertension, where one number is normal, and the other is really high, and in that situation it’s called isolated systolic hypertension or isolated diastolic hypertension.
Having high blood pressure is a serious problem for the blood vessels because it causes wear and tear on the endothelial cells that line the inside of the blood vessels. Just like a garden hose that’s always under high pressures, in the long-term, blood vessels can develop tiny cracks and tears that can lead to serious problems such as myocardial infarctions, aneurysms, and strokes.
About 90% of the time though,hypertension happens without a clearly identifiable underlying reason, and we call this primary hypertension or essential hypertension. In other words, over time pressure in the arteries begins to silently creep up. There are a bunch of risk-factors that we’ve identified for primary hypertension, and these include old-age, obesity, salt-heavy diets, and sedentary lifestyles.
With the exception of age, all of these can be improved with lifestyle changes, and those changes can help reduce hypertension.
About 10% of the time, there is a specific underlying condition that can be found which is the cause of hypertension, and we call this secondary hypertension. For example, anything that limits the blood flow to the kidneys, or the renal blood flow, can cause hypertension, fthings like atherosclerosis, vasculitis, or aortic dissections. This is because the kidneys play a super important role in blood pressure regulation. When not enough blood is flowing to the kidneys , the kidney secretes the hormone renin which ultimately helps the kidneys retain more water. That water contributes to more food in the arteriesmaking them more full which leads to higher pressures.
Other diseases can cause secondary hypertension as well. Fibromuscular dysplasia which affects young women can cause the walls of the large- and medium-sized arteries to thicken. If it involves the renal artery, and limits blood flowing to the kidneys, it triggers more renin. Another one is a tumor that produces excess aldosterone, and just like renin, excess aldosterone leads to fluid retention.
Another way to think about hypertension is to categorize it as benign hypertension or malignant hypertension. Benign hypertension is any hypertension that is in stage 1 or stage 2, and typically it causes no immediate symptoms. Malignant hypertension is really severe stage 3 hypertension, and is an emergency because it can cause increased intracranial pressure and organ damage.