3.3 Blood Pressure
Blood pressure is an essential parameter of body health that reflects the pressure applied by circulating blood on the walls of blood vessels. Monitoring blood pressure helps detect serious cardiovascular health risks early, especially since high blood pressure often develops without any obvious symptoms.
Learning Objectives
- Define blood pressure and identify the instrument and standard unit used to measure it.
- Distinguish between systolic pressure and diastolic pressure in a blood pressure reading.
- Classify adult blood pressure readings into categories ranging from optimal to high blood pressure stage 3.
- State the consequences of uncontrolled high blood pressure and the importance of regular medical check-ups.
Understanding Blood Pressure Readings and Categories
A blood pressure reading contains two values, and adult readings are grouped into six categories.
Short Explanation
Definition
Blood pressure is the pressure applied by the blood on the walls of the blood vessels during blood circulation.
Blood pressure is measured using an instrument called a sphygmomanometer. The standard unit of measurement is millimetres of mercury, written with the symbol \(\text{mmHg}\). Mercury was used in the first accurate pressure gauges and remains the standard unit in medicine.
Two ways to measure. Medical practitioners in hospitals and clinics use a standard sphygmomanometer together with a stethoscope. Home monitoring can be carried out using a digital sphygmomanometer.
Reading a Blood Pressure Value
A blood pressure reading is recorded by taking two readings in the form \(\text{systolic}/\text{diastolic}\), for example \(120/80\text{ mmHg}\).
Systolic pressure
The top number. It is the pressure applied on the wall of blood vessels when the heart muscles contract.
Diastolic pressure
The bottom number. It is the pressure applied on the wall of blood vessels when the heart muscle is resting between heartbeats.
Classification of Blood Pressure Readings for Adults
| Category | Systolic pressure | Diastolic pressure |
|---|---|---|
| Optimal | Less than \(120\text{ mmHg}\) | Less than \(80\text{ mmHg}\) |
| Normal | \(120 - 129\text{ mmHg}\) | \(80 - 84\text{ mmHg}\) |
| At risk | \(130 - 139\text{ mmHg}\) | \(85 - 89\text{ mmHg}\) |
| High blood pressure stage 1 | \(140 - 159\text{ mmHg}\) | \(90 - 99\text{ mmHg}\) |
| High blood pressure stage 2 | \(160 - 179\text{ mmHg}\) | \(100 - 109\text{ mmHg}\) |
| High blood pressure stage 3 | \(180\text{ mmHg}\) and above | \(110\text{ mmHg}\) and above |
Health Implications
High and prolonged readings indicate high blood pressure, also called hypertension. Low and prolonged readings indicate low blood pressure. High blood pressure usually has no clear symptoms. If uncontrolled, high blood pressure can lead to serious health complications such as a stroke. Having regular medical check-ups is the best way to track blood pressure.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What does the top number in a blood pressure reading represent?
What is the standard instrument and unit used to measure blood pressure?
What serious health complication can result from poorly controlled high blood pressure?
Common Mistakes
- Confusing systolic and diastolic pressures: mistaking the top number for resting pressure and the bottom number for contraction pressure.
- Writing the unit of blood pressure incorrectly, for example writing mmHG or mmhg instead of mmHg.
- Assuming that someone with high blood pressure will always feel ill or show noticeable symptoms. High blood pressure usually has no clear symptoms.
- Mixing up the classification ranges, such as confusing the At risk category (\(130 - 139 / 85 - 89\text{ mmHg}\)) with High blood pressure stage 1 (\(140 - 159 / 90 - 99\text{ mmHg}\)).
Concept Misunderstandings
Blood pressure only exists when a person is stressed or exercising.
Blood pressure is always present because blood must exert pressure on vessel walls continuously during circulation to move through the body.
A single elevated blood pressure reading means a person has chronic high blood pressure.
Blood pressure readings must be high and prolonged to indicate high blood pressure.
Low blood pressure is the only safe reading.
Optimal blood pressure is less than \(120/80\text{ mmHg}\), but readings that are low and prolonged show that a person might be experiencing low blood pressure, which is also an abnormal parameter.
Summary
- Blood pressure is the pressure applied by circulating blood on blood vessel walls, measured using a sphygmomanometer in millimetres of mercury (\(\text{mmHg}\)).
- A reading is recorded as systolic/diastolic: systolic measures pressure during heart muscle contraction, while diastolic measures pressure during heart rest.
- Blood pressure is classified for adults from optimal (\(<120/<80\text{ mmHg}\)) to stage 3 hypertension (\(\ge 180/\ge 110\text{ mmHg}\)).
- High blood pressure often lacks obvious symptoms and can cause serious conditions such as stroke; therefore, regular check-ups are necessary.
Short Activity
A. Objective Quiz
1 Which instrument is used by medical practitioners together with a stethoscope to measure blood pressure?
2 What does the bottom number in a blood pressure reading represent?
B. Fill in the Blanks
3 The unit for measuring blood pressure is millimetres of mercury, represented by the symbol .
4 If high blood pressure is not well-controlled, it can lead to more serious medical problems such as a .
C. Drag and Drop: Match the Category to Its Systolic Range
Drag each blood pressure category to its corresponding systolic pressure range for adults. On a phone, tap an answer first, then tap a matching box. Tap the Answer Choices area to return a selected item.
C. Match the Category to Its Systolic Range
Write the correct blood pressure category next to each systolic pressure range.
| Systolic Pressure Range | Blood Pressure Category |
|---|---|
| 1. Less than 120 mmHg | |
| 2. 120 – 129 mmHg | |
| 3. 130 – 139 mmHg | |
| 4. 140 – 159 mmHg |
Answer choices: Optimal • Normal • At risk • High blood pressure stage 1
