Overview of Blood Pressure Measurement
Blood pressure is a key health indicator that doctors use to make both immediate and long-term decisions about a patient’s care. Because it’s so important in guiding treatments, it’s crucial that blood pressure is measured accurately and consistently.
When your blood pressure is measured, doctors usually take note of two numbers. The first number, known as the systolic pressure, tells us how much pressure your blood is exerting against your artery walls when the heart beats. The second number, known as the diastolic pressure, is the pressure on the artery walls when the heart is resting between beats. Sometimes, your doctor might also calculate your mean arterial pressure, which is basically an average pressure in your arteries. It’s computed using your systolic and diastolic pressures with the formula: MAP = DP + 1/3 (SP – DP) or MAP = DP + 1/3 (PP), where PP is the pulse pressure.
There is another method to measure blood pressure called automated office blood pressure (AOBP). With AOBP, your blood pressure is checked after you’ve rested for 5 minutes. Then a machine automatically takes your blood pressure 5 times over the next 5 minutes while you’re resting quietly alone. This method can give doctors a reading that’s more similar to your regular blood pressure throughout the day, reducing the risk of inflated readings that can happen when patients are nervous at the doctor’s office, often termed as ‘white-coat hypertension’.
Why do People Need Blood Pressure Measurement
Checking your blood pressure can be important for several reasons:
1. To test for high blood pressure (hypertension): High blood pressure can lead to different health problems like heart disease and stroke, so it’s essential to know if you have it.
2. To see if treatment is working: If you’re receiving treatment for high blood pressure, routine checks help determine if the medications or lifestyle changes are effective in keeping your blood pressure within a healthy range.
3. To see if your blood pressure is suitable for certain jobs or sports: Certain activities might require you to maintain a particular blood pressure range for safety.
4. To figure out your risk of heart illness: Your blood pressure readings can provide insight into your potential risk for cardiovascular disease.
5. To gauge the risk of medical procedures: Before undergoing some medical procedures, doctors have to ensure that your blood pressure is at a safe level to reduce potential complications.
6. To keep a tab on your health status: Regular blood pressure checks help your doctor observe your health condition and detect any sudden health deterioration.
When a Person Should Avoid Blood Pressure Measurement
There are certain conditions that could make taking a blood pressure reading less reliable or even dangerous. These conditions can be divided into two categories, referred to as ‘relative’ and ‘absolute’ contraindications.
Relative contraindications are situations where taking a blood pressure reading on the arm might not be appropriate or might give incorrect results. These include:
- Lymphedema: A condition where extra lymph fluid builds up in the body tissues and causes swelling.
- Paresis or paralysis: Weakness or complete loss of muscle function in the arm.
- Arterial or venous lines: Having tubes (like a venous catheter) that are used to give medicines or draw blood in the arm.
Absolute contraindications, on the other hand, are conditions where taking a blood pressure reading on the arm could potentially cause harm to the patient. These include:
- Dialysis shunt: A connection made in the blood vessels to clean the blood (dialysis).
- Recent surgical wounds: If the arm recently had surgery, taking a blood pressure reading could disturb the wound.
- Mastectomy: This is a surgery to remove all or part of the breast, and taking a blood pressure reading could cause harm, especially if it was done recently.
Equipment used for Blood Pressure Measurement
Manual Auscultation
Listening to the blood flow in your arteries, a method known as auscultation, is a common way for doctors to measure your blood pressure. This method uses a tool called a sphygmomanometer, which has an inflatable cuff that wraps around your arm and a gauge that measures pressure.
To begin, the cuff is wrapped around your arm and inflated until the blood flow to your arm is blocked. In other words, it’s inflated until the cuff’s pressure is higher than your systolic pressure (the pressure your heart creates when it beats) and no sound can be heard through a stethoscope placed over your brachial artery (the main artery in your arm).
The cuff is then slowly deflated. As the pressure drops to the point where it matches your systolic pressure, the blood flow starts to return and creates a sound known as a Korotkoff sound. When the pressure in the cuff drops further and matches your diastolic pressure (the pressure in your arteries when your heart rests between beats), the Korotkoff sounds stop.
The different Korotkoff sounds heard when measuring blood pressure are:
- Phase 1: A quiet but clear tapping that gets louder over time
- Phase 2: A sound that might be like blowing or swishing
- Phase 3: The return of sharper sounds, not as loud as phase 1
- Phase 4: A clear muffled that slowly becomes soft and like blowing
- Phase 5: The absence of sound
Medical staff should be aware of the possibility of an “auscultatory gap.” This gap is a period when the Korotkoff sounds might disappear for a while but then return as the cuff continues to deflate. It is important to keep listening until the sounds disappear completely to avoid falsely recording a patient’s diastolic pressure.
Automated Devices
Blood pressure can also be measured using automated devices. These devices note changes in blood flow while the cuff deflates and use specific calculations to determine blood pressure. Automated devices are good for non-medical people to use at home because they’re easy to use and don’t require specialized knowledge.
Invasive Monitoring
The most precise way to measure blood pressure is by inserting a probe directly into an artery – a method called invasive monitoring. This method give real-time, beat-by-beat measurements. However, because it involves breaking the skin and carries other risks, it is only used in critical care or during surgeries. Therefore, we are focusing on the non-invasive methods described above in this review.
Who is needed to perform Blood Pressure Measurement?
Anyone who is a health professional or a caregiver with the proper training can carry out a blood pressure check. This means they know how to use a blood pressure cuff and monitor to measure your blood pressure levels. They are also trained to understand the readings and what they mean for your health.
Preparing for Blood Pressure Measurement
Here are some important steps that need to be followed when checking your blood pressure:
First, it’s important that you understand why your blood pressure needs to be checked and how the procedure will be carried out. This step is referred to as ‘informed consent’, it means that you are given all the necessary information about the test so you can make an informed decision about your healthcare.
Secondly, it’s fundamental to create a calm and reassuring environment during the test. This is because any anxiety can potentially affect the results by giving a false high reading.
Lastly, using the correct size of the blood pressure cuff is very critical. If the cuff is not of the right size, it can give incorrect readings. Generally, most guidelines recommend using a large cuff for everyone to ensure accuracy in the readings.
How is Blood Pressure Measurement performed
Blood pressure can change a lot, even with minor activities. This means your blood pressure reading can vary based on what you are doing. So, if you are having your blood pressure checked, there are certain steps that should be followed to make sure we get an accurate reading. The procedure is the same whether the blood pressure is being measured by hand or with a machine.
You should let the doctor or nurse know if you’ve had any caffeine, exercised, or smoked in the past 30 minutes. If you have, they’ll probably wait a bit before taking your blood pressure. You should also use the bathroom before the test. Then, you should sit in a chair with back support in a quiet room. Your feet should be flat on the floor and your legs should not be crossed. You need to sit like this for about five minutes.
After that, the cuff used for blood pressure measurement will be placed onto your bare arm. It needs to be at the same level as your heart. You shouldn’t talk or be talked to while they are taking your blood pressure.
If they are using a machine to take your blood pressure, they’ll follow the instructions specific to that machine. If it’s being done manually, they’ll use a piece of equipment called a stethoscope to listen to your blood pressure. They put the stethoscope over a point near the inner side of your elbow where they expect to find the brachial artery, a large artery that carries blood to your arm. The cuff will be pumped up until just after the point where they can no longer feel your pulse in your wrist. Then, they’ll let the air out of the cuff slowly, about 2 to 3 mmHg per second. They’ll note when they first and last hear your pulse as the sound it makes changes, which gives them your blood pressure reading.
In some cases, like in the intensive care unit, doctors may measure blood pressure directly from an artery. This gives a reading that updates with each heartbeat, giving a continuous picture of what your blood pressure is doing.
Possible Complications of Blood Pressure Measurement
The cuff size also affects readings. A bigger cuff might show your blood pressure is too low, while a small cuff might show it as too high. Where your arm is placed can change the reading too. A lower arm can give higher results, while a higher arm can show lower results. These potential mistakes show why it’s so important to follow the right steps when measuring blood pressure.
There are also some mistakes sources that can’t be avoided. Many studies have found that the blood pressure readings taken by doctors can be different from those taken in everyday settings. For example, some people get “white-coat hypertension,” where their blood pressure goes up because they’re nervous about seeing the doctor. Such people have normal blood pressure in their daily lives but high readings at the doctor’s office. On the other hand, some people might appear to have normal readings at the doctor’s appointment, but their pressure might be high throughout the rest of the day. This is called “masked hypertension” and could be due to changes they make before they see the doctor.
What Else Should I Know About Blood Pressure Measurement?
Hypertension, or high blood pressure, is usually diagnosed by looking at the results of two or more blood pressure measurements taken during different doctor appointments. The level at which blood pressure is considered too high has changed over time as scientists have continued to learn more about blood pressure. Previous guidelines said that high blood pressure started at 140/90 mmHg, but newer evidence suggests that it can be beneficial to start treating high blood pressure earlier. Current levels at which blood pressure is considered too high are given in a table (see image).
If left untreated, high blood pressure can lead to serious conditions such as heart disease, stroke, and kidney disease. It’s the second leading cause of preventable death in the US and is the leading cause of death and disability worldwide. That’s why it’s so important to accurately diagnose high blood pressure early on so that treatment can begin and help prevent these complications.
On the other hand, low blood pressure (hypotension) occurs less frequently than high blood pressure. It’s often linked to factors such as dehydration, illness, or side effects from medication. Doctors generally consider blood pressure to be too low if it falls below 90/60 mmHg. However, the presence of certain symptoms like lightheadedness, dizziness, blurry vision, nausea, and weakness can also indicate low blood pressure.
Sometimes, a person’s blood pressure might be normal when they’re relaxing but drop when they stand up. This condition, called orthostatic hypotension, happens when standing up leads to a drop in systolic blood pressure of 20 mmHg or a drop in diastolic blood pressure of 10 mmHg after about three minutes.
