Blood Pressure Measurement – things you might not know

How is your blood pressure measured? 

The blood flow to the arm is cut off, as the cuff slowly decreases the pressure the systolic – the top number is the pressure of the blood flowing through the arteries when the heart squeezes.

The bottom number  the diastolic is the pressure that remains in the vessel when the heart is relaxed.

Automatic cuff or manual cuff.

This was always an issue in cardiac rehabilitation. In my opinion automatic cuffs tended to read considerably higher than listening with our own ears. They might be fine while lying in a bed in the hospital, but in a busy outpatient facility I question their accuracy.  There are factors that can contribute including is the cuff over clothing, sitting still, not talking, feet square on floor. Even though these factors could be corrected often the readings were high.  Biomedical engineering would calibrate the machines regularly but the readings remained higher with automatic compared to manual. Patients were trained to instruct staff if the automatic cuff reading was unusual to compare it to a manual reading.

How about your home automatic cuff – how accurate is it?  Bring your cuff in to your next doctors appointment, and compare the two readings. There is always some variability but it shouldn’t be extreme. A common cause reading  may be off can be due to the size of the cuff.  There is a reference line on most cuffs as to where the end of the cuff should be. If the cuff is too small the readings will be high, if the cuff is too large the readings will be too low. For severely obese patients it isn’t uncommon to take a small cuff and read the pressure at the wrist instead of the arm. Many  frail thin people require a pediatric size cuff.

True Resting Blood Pressure – A true resting blood pressure is one where you have rested quietly for 5 minutes, feet flat on floor, shoulders square on chair, no caffeine or tobacco prior to measurement.  Activity will influence the blood pressure greatly. If you just rushed in to the office, had a long walk through the parking lot or up stairs your readings will be higher. Remember with blood pressure if it is taken 10 times in 10 minutes you will get 10 different results. What is being assessed is the average number your pressures are readings. If taken in the arm or the wrist the arm should be resting at the heart level.

Does the Time of Day Matter?  – Blood pressure is characteristically highest first thing in the morning, however with medication effects some people will peak later in the day as medications may be wearing down. Vary the times you measure it, get an understanding of the patterns that you run. Keep a log of your blood pressure, make sure to bring your log when you see your health care practitioner.

Should my pressure be taken in my Left arm or Right Arm?  Trick question. Use the arm the reads the highest. Not the lowest! Blockages that occur in the heart don’t just occur there, they can occur anywhere in the body. It isn’t unusual to have blockages in the arteries of the arms. Have your health care provider check both arms. Make sure they chart what arm they should measure your pressures in. I’ll bet at your next appointment they only check one arm, and never ask.  This can be a big problem for some people.

Is there a difference if taken in the wrist or the arm?  – It  doesn’t ‘matter the pressures should be similar. 

What about Leg Pressures? – As noted above, the pressure should be similar from legs to arms. However people with Peripheral Artery Disease – which is blockages in the arteries going to the legs will have a lower blood pressure in the legs. There is a measurement called an Ankle Brachial Index which measures the legs compared to the arms. If there is a big difference there should be additional testing done as these blockages often lead to poorly healing wounds, amputations, severe leg pain with walking.

How Frequent should I  Measure my Blood Pressure? – In cardiac rehabilitation we measure blood pressure at rest – it isn’t safe to exercise if your blood pressure is greater than 170/100 at rest, as we know exercise elevates blood pressure and we don’t want blood pressure to exceed 220/110 as this is dangerous to the heart, brain and organs and can cause stroke or heart attacks to occur. If the blood pressure is too low 80/40 the pressure is usually considered too low to exercise. Exercise dilates the arteries and after exercise the pressure will be lower than entry. If lower than 80/40 most people will feel like they might pass out.

Blood pressure is measured during exercise. Large drops can indicate the heart isn’t tolerating the blood pressure, or excessively elevated blood pressure with exercise can signal poorly controlled and additional intervention might be needed. We compare weight-bearing exercise to non weight-bearing. Bearing one’s body weight with activity is generally harder on the heart.

Blood pressure is also measured after exercise. Exercise dilates the arteries and they stay dilated for a period of time afterwards, the heart rate slows down, and sometimes this causes the blood pressure to fall severely causing one to feel light-headed or possibly to pass out. For this reason it is recommended for all heart patients to perform a nice long cooldown, gradually slow the exercise, do some stretches, drink some water, slowly stroll around. This helps to keep the blood from pooling in the muscles that were being used and keep it circulating. If it does drop severely, lie down get your feet elevated, drink some water. If this happens frequently see your healthcare provider as your medications may require tweaking.

So how often should you check it at home? If it has been fairly stable measure it about once a week. If you are not feeling well, or had recent changes to your medication check once or twice a day. Every person will have occasional spikes or random variations in their blood pressure. Try not to be overly concerned if the number is elevated one day compared to another. So if you normally run 140/80 and today is  160/90 don’t worry.  Note that it is running higher and watch over next few days. Make sure you have taken your medications, review your diet to see if you had more sodium than recommended 1500 mg/day, as increased fluid volume from sodium is a frequent culprit. Did you eat out the day before? If it stays elevated for several days, contact your healthcare provider.   If the Blood Pressure readings are reading 220/110 see your healthcare provider immediately. 

There are several Blood Pressure Apps for iPhones, android devices. These are great. I think they are the future of health care. Some cuffs will download right to your app, others  require you to enter the data. Coming along with the urgent development of wireless technology, wireless devices have invaded the medical area with a wide range of capability. Not only improving the quality of life of patients and doctor-patient efficiency, wireless technology enables clinicians to monitor patients remotely and give them timely health information, reminders, and support – potentially extending the reach of health care by making it available anywhere, anytime.

Below are a few helpful links and resources:

An overview to measuring blood pressure at home. This is an overview of the benefits and resources. Lots of good information.

Public Information on  High Blood Pressure and Sodium. A website link and material from the National Institutes of Health with information in several languages on high blood pressure. Topics include, diet, sodium reduction, and risk factor advice to lower high blood pressure

“Salt matters. We must act, and act now.” A video featuring the CDC Director, Thomas R. Frieden, MD, MPH that discusses the importance of reducing salt and strategies for consumers to use in their effort to reduce it.  A Public Service Announcement – about 2 minutes

Know the Facts About High Blood Pressure.  This  full-color, easy-to-read handout describes the risk factors,     prevention, diagnosis, and treatment of high blood pressure.

2 thoughts on “Blood Pressure Measurement – things you might not know

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