Blood supplies the organs with oxygen and nutrients. To achieve this, the heart pumps blood through the blood vessels into the organs. In order for blood to flow, the heart must generate pressure that moves the blood through the vascular system. If resistance develops within this vascular system, blood pressure rises. This section explains the causes of hypertension.
The Function of the Heart and Blood Pressure
The heart is a muscle with four chambers: the left atrium, left ventricle, right atrium, and right ventricle. Oxygen-rich blood returns from the lungs through the pulmonary veins into the left atrium. From there, it flows into the left ventricle. When the heart contracts, the mitral valve between the left atrium and left ventricle closes, and blood is pumped through the aortic valve into the aorta.
This phase of heart activity is called systole and generates the higher systolic blood pressure value that can be measured in the arm. Oxygen-rich blood is then transported through increasingly smaller blood vessels to supply organs with oxygen and nutrients.
After passing through the organs, the blood returns through the veins to the right atrium and right ventricle. During contraction of the heart, this blood is pumped through the lungs, where it becomes oxygenated again.
After contraction (systole), the heart muscle relaxes and blood pressure falls. This lower pressure is called the diastolic blood pressure value.
The level of blood pressure depends on:
The greater the tension in the vessel walls, the narrower the vessels become and the higher the blood pressure rises.
Blood pressure in the arteries can be measured with inflatable cuffs connected to measuring devices, either on the upper arm or the wrist. Wrist devices may produce inaccurate readings in older patients with medial sclerosis (calcification of the middle layer of the blood vessels). Since many patients with diabetes have medial sclerosis, blood pressure in these patients should preferably be measured on the upper arm.
Systolic Blood Pressure
The higher systolic value indicates the pressure generated when the heart contracts and pumps blood into the arteries.
Diastolic Blood Pressure
The lower diastolic value represents the pressure between heartbeats, when the heart relaxes and refills with blood. During this resting phase, the pressure in the arteries is lower.
Normal Daily Fluctuations in Blood Pressure
Fluctuations in blood pressure during the day are completely normal because blood pressure adapts to physical activity and emotional stress.
During physical exertion or excitement:
Blood pressure also follows a natural daily rhythm. It is highest in the early morning and late afternoon and lowest during sleep at night.
In a healthy adult at rest:
Category | Systolic (mmHg) | Diastolic (mmHg) | |
Optimal | <120 | and | <80 |
Normal | 120–129 | and/or | 80–84 |
High-normal | 130–139 | and/or | 85–89 |
Grade 1 Hypertension | 140–159 | and/or | 90–99 |
Grade 2 Hypertension | 160–179 | and/or | 100–109 |
Grade 3 Hypertension | ≥180 | and/or | ≥110 |
Isolated systolic hypertension | ≥140 | and | <90 |
The blood pressure category is defined according to the highest measured value, whether systolic or diastolic.
Source: ESC/ESH Pocket Guidelines, European Society of Cardiology (ESC), German Cardiac Society (DGK), 2018.
Many studies show that patients with systolic blood pressure above 120 mmHg and diastolic values above 85 mmHg already have an increased cardiovascular risk. Therefore, American guidelines classify values above 120 mmHg as elevated.
Category | Systolic (mmHg) | Diastolic (mmHg) | |
Normal | <120 | and | <80 |
Elevated | 120–129 | and | <80 |
Grade 1 Hypertension | 130–139 | and | 80–89 |
Grade 2 Hypertension | ≥140 | and | ≥90 |
Source: 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease.
In most patients, no specific cause of hypertension can be identified. In addition to genetic predisposition, several risk factors contribute to the development of high blood pressure:
While age cannot be influenced, all other risk factors can be improved through a healthy lifestyle.
Only a minority of patients have an identifiable organic cause of hypertension. Kidney diseases or hormonal disorders may be responsible. In these cases, the condition is referred to as secondary hypertension.
When Should Secondary Hypertension Be Suspected?
Chronic Kidney Disease (Nephropathy)
Chronic kidney disease may have many causes. The most common causes identified between 1996 and 2005 were:
Cause | Frequency |
Type 2 diabetes | 32% |
Vascular nephropathy | 23% |
Glomerulonephritis | 13% |
Interstitial nephritis | 8% |
Unknown origin | 8% |
Polycystic kidney disease | 4% |
Systemic diseases | 4% |
Various causes | 4% |
Type 1 diabetes | 3% |
Chronic kidney disease usually progresses slowly and often remains unnoticed for many years, allowing severe organ damage to develop.
Kidney disease can cause secondary hypertension. Conversely, hypertension itself is one of the most common causes of chronic kidney disease, especially vascular nephropathy.
An overactive thyroid gland may result from:
Elevated thyroid hormones increase heart rate and cardiac output, thereby increasing systolic blood pressure.
Diagnosis is made by measuring:
Aldosterone is produced in the adrenal glands and regulates salt and water balance. Excessive aldosterone production (Conn syndrome) is a frequent cause of secondary hypertension.
Common causes include:
Patients with resistant hypertension and low potassium levels should always be evaluated for hyperaldosteronism.
Diagnosis includes:
Treatment:
Hypercortisolism (Cushing Syndrome)
Excess cortisol production leads to Cushing syndrome, characterized by:
Diagnosis is often performed using the dexamethasone suppression test.
A pheochromocytoma is an adrenal tumor producing excessive catecholamines:
This causes severe hypertension.
Diagnosis:
Treatment:
Renal Artery Stenosis
Hypertension may also result from narrowing of the renal arteries, which activates the renin-angiotensin-aldosterone system.
The most common cause is atherosclerosis.
Diagnosis:
Treatment: