Understanding Blood Pressure

Blood pressure is a measure of the force that blood applies to the walls of the arteries as it flows through them. Blood pressure is measured in millimetres of mercury (mmHg) and is expressed using two numerical readings. In this article we will help you when it comes to understanding blood pressure.

The optimal blood pressure reading is 120/80 mmHg (‘one hundred and twenty over eighty’). These two numbers represent the systolic and diastolic pressure readings. Once you get the hang of both types of pressure readings, understanding blood pressure will become much easier.

Systolic blood pressure (SBP)

Systolic blood pressure (SBP) is pressure exerted on the artery walls during the contraction phase of the heartbeat. This is always the higher of the two pressures and is usually noted first. It is caused by the increased volume of blood flowing through the arteries with each beat. Therefore increasing the pressure within the arteries.

Diastolic blood pressure (DBP)

Diastolic blood pressure (DBP) is the pressure exerted on the artery walls during the relaxation phase of the heartbeat. The heart goes through this period of relaxation to allow the hearts chambers to fill with blood. The diastolic blood pressure is always the smaller of the two readings.

Cardiac Output

Cardiac output is the volume of blood pumped out by the heart in one minute (ml/min). The greater the cardiac output, the higher the blood pressure.

Total peripheral resistance

Total peripheral resistance is the resistance the blood vessels offer to blood flow. The greater the resistance, the higher the blood pressure. Peripheral resistance is increased by constriction or decreased by dilation of the blood vessels.

It’s normal for blood pressure to temporarily increase during exercise or when feeling anxious or stressed. Hypertension (high blood pressure) is the term used to describe blood pressure that’s consistently higher than the healthy level when at rest. High SBP indicates the strain on the blood vessels when the heart is attempting to pump out blood. If the DBP is high, it indicates the blood vessels can’t relax between beats. Consequently, measuring blood pressure provides an indication of the health of the heart.

Hypertension

Hypertension increases the risk of ischaemic heart disease and cerebrovascular disease. These are two of the biggest killers in the world.

Ischaemic heart disease

Ischaemic heart disease covers a variety of heart conditions including valve disease and more acute problems such as myocardial infarction (heart attack).

Cerebrovascular disease

Cerebrovascular disease includes acute problems such as strokes. It also includes chronically degenerative conditions like Dementia and Alzheimer’s disease.

Hypertension also places stress on the small vessels to the retina, which can cause blindness. As well as the small vessels of the kidneys, which can lead to renal failure. A persons average resting blood pressure is defined as 120/80 mmHg. A blood pressure of 140/90 mmHg is considered to be high. Individuals with measures above 140/90 mmHg are encouraged to see their doctor before commencing physical activity programmes. Readings above 180 systolic and 110 diastolic are a contraindication for exercise.

People with low blood pressure readings may also require medical referral.

CATEGORY SYSTOLIC (mmHg) DIASTOLIC (mmHg)

Low < 100 < 60
Optimal < 120 < 80
Normal < 130 < 85
High normal – Pre-hypertension 130-139 85-89
(Low End) – Stage 1 Hypertension 140-159 90-99
(Middle) Stage 2 Hypertension 160-179 100-109
(High) Stage 3 Hypertension > 180 > 110

There are currently about 12 million people in the UK who have hypertension (blood pressure ≥140/90mmHg). More than half of those are over the age of 60. Around 5.7 million people have undiagnosed hypertension according to the UK Blood Pressure Association, 2012.

Have we completely lost you, or are you now understanding blood pressure a bit more?

Short Term Effect of Exercise

A short-term effect of exercise will show a linear increase in SBP with increasing levels of exertion. In contrast, DBP may decrease slightly during exertion due to vasodilation.

Individuals with hypertension may experience a rise in DBP as a result of an impaired vasodilatory response. Heavy weight training and isometric exercise will significantly increase both SBP and DBP. It is important for an individual not to hold their breath when performing these exercises to avoid the Valsalva effect.

The Valsalva Effect

The Valsalva effect is a manoeuvre, which involves holding your breath during exercise. This action increases pressure which impedes blood returning to the heart. During this manoeuvre, the mouth and nose are closed while holding your breath. It’s similar to the pressure created when passing a bowel movement. The Valsalva effect can drastically increase blood pressure. Therefore heightening the risk of a heart attack or stroke.

Long Term Effect of Exercise

Aerobic exercise using large muscle groups is useful for reducing blood pressure over time. Endurance training can decrease blood pressure by 10 mmHg in both SBP and DBP.

Resistance training can have many benefits for hypertensives. However, it’s not recommended as a means of decreasing blood pressure on its own.

For certain clients, the risks associated with exercise need to be weighed up against the benefits before they engage in any physical activity. Especially if it’s high-intensity. Physical activity can carry risks for people with high blood pressure. However, for most people, the benefits far outweigh the dangers. If you’re unsure, seeking professional medical advise before you start is very important.

Cardiovascular benefits of endurance training

Physical activity has both short- and long-term effects on the cardiovascular system. The short-term changes are natural physiological responses to physical activity. Such as an increase in heart rate, stroke volume, blood pressure and cardiac output. These changes represent the body’s attempts to deliver more blood around the system. It’s way of coping with the physiological demands of physical exertion.

Resting cardiac output in the heart of a well trained athlete will be about the same as in a healthy untrained athlete. This is because while stroke volume is increased, the heart rate is decreased. The long-term changes to cardiovascular function are the positive effects of physical activity. It can also be seen in lasting adaptations to the cardiovascular system.

With regular aerobic training there will be improvements in the efficiency of your heart. Being able to more efficiently deliver blood to the working body parts. This can be reflected during activity with a lower heart rate. A greater stroke volume and an increase in maximal cardiac output. When we’re in a rested state, the body’s adaptation to regular aerobic activity will also be shown. A lower resting heart rate, lower blood pressure and a greater stroke volume.

Aerobic or endurance-based training has particularly important benefits for the cardiovascular system.

Examples include…

• A greater stroke volume, i.e. more blood pumped per beat.
• A lower relative exercise heart rate, which allows for greater performance potential.
• Stronger, more elastic arteries.
• Lower levels of bad cholesterol (LDL) and higher levels of good cholesterol (HDL).
• An improved blood supply to the body’s tissues.
• Higher levels of haemoglobin in the blood, which increases its oxygencarrying capacity.
• Improved aerobic capacity (VO2 max).
• Lower blood pressure in the long term.

Understanding blood pressure readings can be really difficult but hopefully this article will help you at least understand the basics.