Introduction

Pulse pressure is defined as the difference between systolic and diastolic blood pressure (BP). The systolic pressure (the top number in blood pressure readings) shows the pressure in the arteries when the heart contracts and blood is forced out into the body. The diastolic pressure (the bottom number) shows the pressure in the arteries when the heart is at rest, in between contractions. Pulse pressure is useful as it can give an indication of the health and elasticity of the arteries, as well as general cardiovascular health.

Arterial stiffness is a reduction in the elasticity of the arteries and their ability to expand and contract in response to changes in blood pressure. Arterial stiffness usually progresses with age and contributes to increased blood pressure and pulse pressure. 

Both pulse pressure and arterial stiffness are important markers of cardiovascular health and can help predict the risk of heart attack and stroke. 

Understanding pulse pressure

Pulse pressure is calculated by subtracting the diastolic blood pressure from the systolic. Healthy values for systolic and diastolic blood pressure are 120 mmHg and 80 mmHg respectively, resulting in a pulse pressure of 40 mmHg. Both systolic and diastolic blood pressures increase over time, until the age of 55, after which diastolic pressure typically decreases while systolic pressure continues to rise. As a result, pulse pressure increases, with a "wide" pulse pressure defined as greater than 100 mmHg. Increased pulse pressure is a sign of declining cardiovascular health and is associated with an increased risk of mortality, as well as poorer outcomes for those suffering from chronic diseases such as cardiovascular disease or chronic kidney disease.¹ 

Arterial stiffness

The arteries play a vital role in the cardiovascular system by carrying oxygen-rich blood from the heart to the tissues of our body. They expand and contract continuously over our lifetime and to do so, arteries must be able to respond to the pressure changes that occur when the heart beats. Arterial stiffness refers to the alteration in the behaviour and composition of the vessel walls over time.

The wall of an artery consists of three layers: the tunica intima, the tunica media, and the tunica adventitia, which are the innermost, middle, and outermost layers, respectively. The tunica intima mostly consists of a connective tissue basement membrane with elastic fibres, which allow the arteries to expand in response to pressure changes. The tunica media consists of smooth muscle, which provides structural support and allows for changes to the inner diameter of the vessel to control flow and pressure. The tunica adventitia consists of connective tissue with elastic and collagen fibres.² All of these components enable arteries to withstand high-pressure flow out of the heart and to expand and contract with changing pressure, which is known as compliance. 

As we age, processes occur which cause changes to our arteries. This can happen by damage or degradation of the elastic fibres or an increase in the levels of collagen or other proteins in the artery walls.³ Atherosclerosis forms in vessels as we age, and as a result of lifestyle factors such as smoking. Atherosclerosis is a build-up of plaque in the inner lining of the artery causing hardening of the artery wall. Arterial wall damage can result from inflammation caused by free radicals - reactive oxygen species (ROS) - highly reactive elements which readily interact with other molecules in the cell to cause damage. Calcification of the arteries can occur particularly in those with diabetes mellitus, where calcium builds up within the arterial walls, leading to stiffening. Smooth muscle cells within the intima media can become stiffer over time.⁴ 

Pulse pressure can be a way of measuring arterial stiffness by taking the blood pressure measurement with a standard sphygmomanometer (blood pressure monitor). 

Pulse wave velocity measurement can be taken, which is the speed at which the forward pressure wave is transmitted from the aorta throughout the arterial system. This is calculated by measuring the time taken for the waveform to travel from one place in the arterial system to another place, with the distance measured. The faster the pulse wave travels through the arterial system, the lower the compliance of the arteries. 

Ultrasound can also be used to measure arterial compliance, which involves comparing multiple images of the vessel wall throughout the cardiac cycle and measuring the maximum and minimum vessel diameters.⁵

Relationship between pulse pressure and arterial stiffness

Pulse pressure and arterial stiffness are closely linked. Increased arterial stiffness leads to increased systolic blood pressure, as there is a reduced ability to hold a large volume of blood without an increase in pressure. Arterial stiffness leads to decreased diastolic blood pressure as there is reduced elasticity and the arteries cannot recoil back to their original shape as well. Due to the increase in systolic blood pressure and decrease in diastolic blood pressure (which is a condition known as isolated systolic hypertension), there is an increase in the pulse pressure. 

A wide pulse pressure is linked with deteriorating cardiovascular health overall, along with an increased rate of disease progression and an increase in all root causes of mortality.¹ Over time, exposure to increased pulse pressure can lead to organ failure, particularly in the heart and the brain. Increased pulsatility of flow to organs can lead to microvascular damage, dysfunction of the endothelium (the inner lining of blood vessels), and damage to organs due to hypertension. There can also be an increased risk of kidney damage due to higher pressure blood flow.

Factors affecting pulse pressure and arterial stiffness

• Age
• Hypertension, or high blood pressure
• Atherosclerosis
• Lifestyle factors (e.g., smoking, diet, sedentary lifestyle)
• Conditions such as diabetes mellitus or kidney disease
• Genetics - some are more predisposed to the development of arterial stiffness
• Hormonal factors - reduced oestrogen during menopause can lead to increased arterial stiffness, indicating that oestrogen may have protective effects
• Medications such as antihypertensives and statins

Health implications

Wide pulse pressure has been linked with an increased risk of multiple cardiovascular diseases, such as coronary heart disease, congestive heart failure, stroke, and overall mortality.¹ Some of this may be due to the left ventricle of the heart having to contract against hardened arteries, leading to hypertrophy, which is where the cells become enlarged, affecting function. Studies have shown that a 10 mmHg increase in pulse pressure in people ages 25 to 45 is associated with a 26% increase in cardiovascular death.⁶ Additionally, there may be a link between high pulse pressure and an increased risk of developing atrial fibrillation, which is an abnormal heart rhythm.⁷ A widened pulse pressure also occurs with other diseases such as hyperthyroidism, aortic sclerosis, aortic regurgitation, and severe iron deficiency anaemia.⁸ 

Management and prevention

Methods to reduce pulse pressure focus on improving arterial compliance. Regular exercise, along with weight loss and a tailored diet has been found to alter the metabolic processes occurring within arteries, which may in turn reduce arterial stiffness.⁹ 

Medications for reducing arterial stiffness can include anti-hypertensive drugs, to reduce overall blood pressure and prevent further damage to the arteries. Statins can also help by reducing the amounts of harmful types of cholesterol and exerting protective effects on the cardiovascular system. Anti-diabetic medication has also been shown to improve arterial stiffness, along with anti-inflammatory drugs.¹⁰

Monitoring can involve regular blood pressure measurements to assess if lifestyle factors are effective at reducing pulse pressure. Ambulatory blood pressure monitoring can also be useful, where a portable device is used to assess blood pressure at set intervals throughout the day and night to monitor abnormalities not normally picked up with regular blood pressure assessment. Repeated measurement of pulse wave velocity can also be useful, along with laboratory tests which can indicate the presence of biomarkers for inflammation, which help to predict outcomes of cardiovascular health.

FAQs

What does arterial stiffness indicate?

Arterial stiffness is the ability of the artery to expand and contract depending on the beats of the 

heart. It indicates the level of atherosclerosis within the artery.

What are diseases associated with arterial stiffness?

Heart attack, stroke, and kidney failure. 

How is arterial stiffness measured?

One method is to use a blood pressure measurement to estimate pulse pressure, which is closely linked with arterial stiffness.

What does a high pulse pressure indicate?

A high pulse pressure indicates an increased risk of cardiovascular diseases, such as heart disease and stroke.

Summary

To conclude, pulse pressure is a measurement which is relatively easy to obtain and can provide information regarding arterial stiffness, indicating the overall health of the entire cardiovascular system. Due to ageing and lifestyle factors, arterial stiffness can develop over time, and is a prominent marker for overall mortality, along with particular conditions such as heart disease and stroke. Methods to reduce arterial stiffness and improve compliance include lifestyle changes, such as regular exercise, change in diet and weight loss. Medications can also help to improve vessel compliance. Further research into pulse pressure and arterial stiffness is essential to fully understand the development of vessel hardening and how to reduce its effects to improve overall cardiovascular health.