Introduction to Blood Pressure
Blood pressure is an essential measure of cardiovascular health and along with heart rate, breathing, and body temperature, is one of the 4 vital signs of life. According to data published in the Global Burdon of Disease Study (2017), raised blood pressure is the single most important risk factor for disease, suffering and death.
High blood pressure, which is medically known as hypertension, is associated with a number of cardiovascular disorders and diseases, including heart disease, artery disease, heart failure, strokes and aneurysms. Conversely, low blood pressure, which is medically known as hypotension, can increase the risk of dizziness, nausea, lethargy, weakness, confusion and fainting. Both high and low blood pressure require medical treatment and/or lifestyle modification in order to manage these conditions effectively.
In the context of exercise, resting blood pressure values form a key part of the pre-exercise health screening process. The American College of Sports Medicine (ACSM), describe exercise as absolutely contraindicated (should not be performed) if resting blood pressure is uncontrolled and/or exceeds 180/10 mm Hg.
What is Blood Pressure?
Blood pressure describes the pressure exerted on the internal walls of the blood vessels, particularly the arteries. Blood pressure is needed in order to ensure that blood continues to flow freely through the network of blood vessels (arteries, veins, capillaries). The vast majority of the pressure in the blood is created from the heart, which pumps blood into the already full arteries to deliver oxygen and other nutrients around the body.
When the heart beats, blood is pumped into the arteries, which initially stretch, before recoiling to force blood to move forward throughout the arterial system. Blood pressure only becomes problematic when it is either too high or too low, disturbing the natural supply of oxygen and nutrients to bodily tissues.
Higher blood pressures create more resistance in the arterial system, making it more difficult for the heart to pump blood into, and move blood along, the length of the arteries. Low blood pressures cause blood to move more slowly and/or pool in the blood vessels, especially in those vessels located further away from the heart (e.g. lower legs and arms).
Blood pressure is determined by two factors:
- Cardiac output – the volume of blood pumped by the heart in a minute. This comprises of heart rate x stroke volume (volume pumped from the heart in a beat).
- Peripheral resistance – the diameter of the blood vessel, specifically the artery, will determine how much resistance there is against blood flow. Constricted and blocked vessels will have a higher resistance than clean and dilated blood vessels.
Factors Affecting Blood Pressure
There are a wide-range of factors that can affect blood pressure, including:
- Inactivity – a sedentary lifestyle will considerably increase a person’s risk of developing hypertension. Regular exercise and physical activity help to keep the cardiovascular and respiratory system strong and stable.
- Age – blood pressure appears to rise with increasing age. While the specific mechanisms are unclear, decreased organ function, especially the kidneys, stiffening of blood vessels and reduced participation in physical activity as a result of functional decline are all though to contribute.
- Diet – failing to consume a healthy balanced diet, especially if the consumption of salt, alcohol, caffeine, fatty foods and/or processed foods is excessive, will significantly increase the risk of developing hypertension and other metabolic complications.
- Obesity – excess body fat and weight places a greater strain on the bodily tissues, especially the cardiovascular system, which must work harder to circulate higher levels of blood and nutrients around the body. With a higher body weight, even the most basic of daily tasks (e.g. tying shoelaces) can stress the cardiovascular system.
- Family history – genetic factors are thought to have a strong influence on a person’s future risk of developing high blood pressure. Some studies have argued that a family history makes a person twice as likely to develop the condition. It should however be noted that hypertension is a multifactorial condition other influences in the family are also likely to play a part (e.g. diet, lifestyle, smoking).
- Other medical conditions – secondary hypertension can occur as a result of other medical conditions, including type 2 diabetes, sleep apnea, kidney disease, tumours, steroid abuse and thyroid-related issues.
- Smoking – many of the chemicals in cigarettes causes the arteries to harden and stiffen (arteriosclerosis), reducing their ability to dilate or widen when the body needs to increase blood flow. A healthy blood vessel is an elastic blood vessel!
- Ethnicity – according to Public Health England (2017), those people from Black African and Black Caribbean ethnic groups are much more prone to developing hypertension.
- Stress – anxiety, stress and other mental health issues can increase the risk of developing hypertension. The effects of hormones like adrenaline and cortisol are actively involved in the body’s natural response to stress (fight or flight), which if sustained over-time, can chronically elevate blood pressure.
Other Factors Affecting Blood Pressure
Exercise will normally increase blood pressure, although this is usually only a temporary and transient response to the body’s increased demand for oxygen and nutrients. During exercise, systolic blood pressure will typically rise as exercise intensity increases. However, it does usually plateau at higher workloads. Diastolic blood pressure will usually remain the same, or decrease slightly during exercise. It’s important to try to avoid rapid spikes in blood pressure during exercise, especially for those who have, or at risk of, hypertension. This is why warming up before exercise is so important.
Time of Day:
Blood pressure normally fluctuates throughout the day in response to the release of certain hormones. In the morning, the stress hormone cortisol is naturally released gradually in response to light penetrating the eyelids. This will normally start from around 6AM and blood pressure gradually starts to increase in line with the release of cortisol. Waking as a result of an alarm clock triggers the stress response, rapidly releasing cortisol and causing blood pressure to spike. In the evening, especially in low light, melatonin is released, causing the body to feel sleepy and tired. Blood pressure naturally reduces as a result of the effects of melatonin, which last throughout the night.
Measuring Blood Pressure
Historically, blood pressure was measured by a clinician using a sphygmomanometer, or sphyg, and a stethoscope. Today however, it is possible to measure blood pressure quickly and reliably with a digital blood pressure meter. These are relatively inexpensive and can be purchased from most supermarkets and pharmacies.
To measure resting blood pressure digitally:
- Sit comfortably and quietly for 5 minutes, ideally at a table with the blood pressure monitor close by.
- Try to avoid drinking caffeine, like tea, coffee, or carbonated drinks in the 2-3 hours prior to taking the measurement.
- Place the cuff on the upper arm around 2-3 cm above the crease in the elbow. Ensure that the artery reference is aligned with the brachial artery on the inside of the upper arm. The arm should also be fully supported on the table and remain still throughout the measurement.
- Press the start button and wait for the monitor to complete its measurement. It is normal for the cuff to inflate and deflate a number of times during this process.
- Note the measurement on the screen and refer to the classification data below.
Insert measurements in the test below to get a blood pressure score:
Classification of Blood Pressure
Blood pressure is usually expressed in millimetres of mercury (mmHg) and is reported as the following two values:
- Systolic – the highest value which describes the pressure in the arterial system when the heart beats (emptying blood into the arteries).
- Diastolic – the lowest value which describes the pressure in the arterial system when the heart relaxes and is in-between beats.
An average healthy blood pressure would be in the region of 120/80 (systolic/diastolic).
Compare the blood pressure measurement to the table below in order to get an appropriate classification.
|Blood Pressure Categories||Systolic mm Hg (upper number)||Diastolic mm Hg (lower number)|
|Normal||Less than 120||and||Less than 80|
|Elevated||120 - 129||and||Less than 80|
|High blood pressure (hypertension) stage 1||130 - 139||or||80 - 89|
|High blood pressure (hypertension) stage 2||140 or higher||or||90 or higher|
|Hypertensive crisis (consult your doctor immediately)||Higher than 180||and/or||Higher than 120|
Systolic mm Hg (upper number) Less than 120 AND Diastolic mm Hg (lower number) Less than 80
Systolic mm Hg (upper number) 120 - 129 AND Diastolic mm Hg (lower number) Less than 80
High blood pressure (hypertension) stage 1
Systolic mm Hg (upper number) 130 - 139 OR Diastolic mm Hg (lower number) 80 - 89
High blood pressure (hypertension) stage 2
Systolic mm Hg (upper number) 140 or higher OR Diastolic mm Hg (lower number) 90 or higher
Hypertensive crisis (consult your doctor immediately)
Systolic mm Hg (upper number) Higher than 180 AND/OR Diastolic mm Hg (lower number) Higher than 120
Note: diagnosis of any specific medical condition like hypertension should only be made by a suitably trained medical professional. This will normally require multiple measurements on separate occasions to confirm the results are both accurate and reliable.
Public Health England Guidance (2017). Health matters; combatting high blood pressure. 24th January 2017.
Global Burdon of Disease Study (2017). Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. The Lancet.