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Are we measuring blood pressure accurately? Probably not.


The most common method of measuring blood pressure is often inaccurate, a new study has found. This could mean people at risk of serious conditions such as heart disease are missing diagnosis and potentially life-saving treatment.

The so-called “cuff method” involves strapping an inflatable cuff over the upper arm to temporarily cut off the blood supply; then calculating the blood pressure once the cuff is relaxed.

In our study, published in the Journal of the American College of Cardiology, we found the method, which is more than a century old, is inaccurate when monitoring people with mid-range blood pressure. This is the range most common among people worldwide.

Accurate measurement of blood pressure is regarded among the most important of all medical tests. A misdiagnosis of low blood pressure can be a missed opportunity for lowering a person’s risk of cardiovascular disease, which often presents as a stroke, heart attack or kidney disease. A misdiagnosis of high blood pressure, on the other hand, could lead to people being prescribed unnecessary medication.

What is blood pressure?

Blood pressure is the force exerted in the large arteries – vessels that carry blood away from the heart – with every heartbeat. Blood pressure measurement provides a high (systolic) and a low (diastolic) value. The high value represents the peak pressure during heart contraction; the low value represents the pressure during heart relaxation.

Healthy levels of blood pressure are typically less than 120/80 mmHg (the 120 mmHg is systolic, and 80 mmHg diastolic). Decades of research clearly tell us if a person’s blood pressure is raised they are at higher risk of cardiovascular disease. The higher the blood pressure, the higher the risk.

Blood pressure readings include a systolic and a diastolic value, with the normal healthy range less than 120/80 mmHg.

About one in three adults have high blood pressure. Lifestyle factors such as regular exercise, normal body weight and healthy dietary choices, as well as medications, can lower blood pressure and prevent cardiovascular disease.

Although there are many factors to consider when assessing if someone has high blood pressure, the conventional threshold at which doctors might consider giving medication to lower pressure is 140/90 mmHg.

How is blood pressure measured?

The method to measure blood pressure is based on a technique invented in 1896, then refined in 1905, but the basic principal has remained virtually unchanged.

A broad cuff is placed over the upper arm and inflated until the main artery in the arm is completely occluded and blood flow is stopped. The cuff is then slowly deflated until blood flow returns into the lower arm.

A series of signals can then be measured that represent the systolic and diastolic blood pressure. These are measured by either listening with a stethoscope or, more often, using automated devices.

Our study

It’s uncertain whether cuff blood pressure accurately measures the pressure in the arteries of the arm or the major artery just outside the heart, called the aorta. This is important as blood pressure readings can be different in these two spots – a potential difference of 25 mmHg or more.

The central aorta blood pressure is a better indicator of the pressure experienced by organs, such as the heart and brain, so it is more clinically relevant.

The possibility of big blood pressure differences between the arm and the aorta could result in very different clinical decisions on diagnosis and treatment. So it is important to resolve the uncertainty as to what cuff blood pressure actually measures.

We retrieved data from studies from the 1950s until now that compared cuff blood pressure of more than 2,500 people with that of the gold standard method, called invasive blood pressure. Here, a catheter that measures pressure is inserted inside the artery either at the arm (same site as the cuff) or at the aorta.

Readings from this method were used as a reference and compared with those of the cuff method to determine the accuracy of cuff measurements.

Research has found there can be significant differences between the blood pressure measured in the arm and in the aorta.
from www.shutterstock.com

What did we find?

Cuff blood pressure had reasonable accuracy compared with the reference standard, at either the arm or aorta, among people with low cuff blood pressure (lower than 120/80 mmHg) and high cuff blood pressure (the same or higher than 160/100 mmHg). These people are at the extreme ends of the blood pressure risk spectrum.

We found the accuracy when compared to invasive blood pressure was up to 80%.

But for the rest of the population with blood pressure in the middle range – systolic 120 to 159, and diastolic 80 to 99 mmHg – accuracy compared with invasive blood pressure at the arm or the aorta was quite low: only 50% to 57%.

Why is this important?

If people have their blood pressure measured using the cuff method and the values are either low (under 120/80 mmHg) or high (over 160/100 mmHg), we can have reasonable confidence the values are a good representation of the true (invasive) blood pressure.

But for people whose blood pressure is in the most common mid-range of 120 to 160 mmHg systolic or 80 to 100 mmHg diastolic, there is much less certainty as to whether the cuff blood pressure is truly representative of the actual blood pressure.

Our findings do not mean people should stop taking their medication or stop having their blood pressure measured using the cuff device. While this study reveals accuracy issues, the evidence from many large clinical trials clearly shows taking medication to lower blood pressure from high levels reduces the chances of stroke, heart attack and vascular disease.

Cuff blood pressure measurements are still useful, but we could help more people if we could measure blood pressure more accurately. The problem is that some people in the mid blood pressure range may fall through the diagnosis cracks.

Until the accuracy standards of pressure-measuring devices are improved, the best available confirmation of blood pressure levels comes from an average of many repeated measures over time. This is better than one or two measures, as is often the way in busy daily clinical practice, and was closest to the method examined in this study.

The ConversationPeople can have repeated measures of blood pressure undertaken in consultation with their general practitioners or at specialist centres. These can include self-measured home blood pressure, 24-hour ambulatory blood pressure and automated unobserved blood pressure.

James Sharman, Professor of Medical Research and Deputy Director, Menzies Institute for Medical Research., University of Tasmania

This article was originally published on The Conversation. Read the original article.

Atrial fibrillation screening back in the picture

Population screening for atrial fibrillation is once more up for discussion as a new study shows that people with newly diagnosed ‘silent’ AF actually have a higher risk of stroke than those with a symptomatic condition.

The study, presented this week at the European Heart Rhythm Association meeting in Vienna, included over 6,000 consecutively enrolled patients with non-valvular atrial fibrillation, of whom around two-thirds were asymptomatic or minimally symptomatic at time of diagnosis.

The study found those with asymptomatic AF had more than double the risk of previous stroke, compared to those who were symptomatic (14.7% vs 6.0%). They were also more likely to have permanent atrial fibrillation than those in the symptomatic group (15.8% vs 8.3%).

But both symptomatic and asymptomatic patients in this study had a similar number of stroke risk factors, with an average CHA2DS2-VASc score of 3.3 for each group.

Lead author Dr Steffen Christow, a cardiologist at Hospital Ingolstadt in Germany, said the higher rate of stroke despite the same number of stroke risk factors may be explained by a longer undiagnosed history of AF in those with asymptomatic disease.

“Our study found that in Western Europe, two-thirds of patients newly diagnosed with atrial fibrillation were asymptomatic. Without detection, patients may not receive appropriate preventive therapy and remain at increased risk of stroke.”

He said the results “underline the urgent need for public programs to detect atrial fibrillation in the general population”.

In Australia, RACGP guidelines do not recommend systematic screening for atrial fibrillation, although they say opportunistic screening when taking blood pressure could be cost-effective.

The current study is a sub-analysis of the GLORIA-AF registry, which characterises a population of newly diagnosed patients with non-valvular atrial fibrillation at risk for stroke, studying patterns, predictors and outcomes of different treatment regimens for stroke prevention.

You can access the study abstract here.

Painkillers can increase the risk of heart disease and should be restricted

Medications such as ibuprofen and aspirin, known as non-steroidal anti-inflammatory drugs or NSAIDs, are widely available over the counter from pharmacies and supermarkets. But health providers have known for some time they can be unsafe for people with chronic health problems such as kidney disease, high blood pressure or heart failure. The Conversation

NSAIDs can also have dangerous interactions with other commonly taken medications, notably many types of blood pressure and blood-thinning pills such as warfarin and aspirin.

Two recently published studies have brought back into the spotlight the possible heart-related side effects of NSAIDs. One found an increased risk of heart failure in users of NSAIDs, while another an increased risk of cardiac arrest.

Heart failure is a disease that presents with symptoms such as shortness of breath, fluid retention, leg swelling, and fatigue. This is a result of the heart not being able to pump blood around the body effectively. There are many causes of heart failure, including heart attacks, high blood pressure and excessive alcohol consumption.

A cardiac arrest occurs when the heart stops functioning abruptly and results in complete loss of effective blood flow through the body. The most common cause of a cardiac arrest is a heart attack, where heart muscle is damaged from loss of blood supply due to a blockage in a heart blood vessel. There are many other causes of a cardiac arrest that include structural heart abnormalities and inherited heart diseases of muscle and electrical function.

Heart failure is when the heart isn’t able to pump blood around the body effectively.
from shutterstock.com

The recent studies are an important reminder that over-the-counter medicines are not without risk. This class of anti-inflammatory pain killers should no longer be available for sale in grocery stores, but instead restricted to prescription-only or behind-the-counter status in pharmacies.

How they work

Non-steroidal anti-inflammatory drugs are commonly used to relieve pain. They can be either prescribed by a doctor or purchased by the patient over the counter from a supermarket or pharmacy.

NSAIDs are used in a broad range of health conditions associated with pain and inflammation, including types of arthritis, headaches, musculoskeletal injuries and menstrual cramps. Their easy availability, effectiveness and presumption of safety contribute to their widespread use.

They work by inhibiting enzymes called cyclooxygenase 1 (COX-1) and 2 (COX-2). These are involved in a number of internal pathways that result in production of hormone-like substances called prostaglandins, which promote inflammation and increase pain perception.

Prostaglandins also protect the stomach lining from acid, by decreasing acid production and increasing mucus secretion and its neutralising properties. So inhibiting prostaglandins also reduces their protective functions. This is why frequent users of anti-inflammatories may suffer from gastric ulcers.

NSAIDs can either inhibit both COX-1 and COX-2 (non selective) or inhibit COX-2 only (selective). Drugs like ibuprofen and aspirin are non selective and inhibit both the COX enzymes.

COX-1 mediates gastrointestinal, kidney, and clotting function, while COX-2 is induced primarily in states of inflammation and tissue repair. That’s why blocking the COX-2 pathway reduces the effects of inflammation such as fever, swelling, redness and pain.

Importantly, COX-2 inhibition accounts for the anti-inflammatory drug effects of NSAIDs, while COX-1 inhibition can lead to side effects including gastrointestinal ulcers, prolonged bleeding and impaired kidney function. However, it’s not entirely safe for the drugs to inhibit COX-2 only.

Nurofen (ibuprofen) works by inhibiting both COX enzymes.
from shutterstock.com

Animal studies have shown blocking COX-2 and the subsequent pathway of prostaglandin production may have the unwanted effects of increasing the tendency of blood to clot inside arteries, and a reduced ability of the heart to heal after a heart attack.

In the early 2000s, a number of large studies found a significant association of negative heart events, such as heart attack and stroke, with the use of selective COX-2 inhibitors. This resulted in two of these drugs, Valdecoxib and Rofecoxib or Vioxx, being withdrawn from the market.

In Australia there are only a small number of COX-2 inhibitors available, including Celecoxib and Meloxicam. These are prescription-only medicines and the maximum prescribed dose is at a level at which the heart risks are minimal.

COX-2 inhibitors are used in people who require a non-steroidal anti-inflammatory but have a history of stomach upset or ulcers, or who were thought to be at risk of developing stomach ulcers.

Risk of heart failure

Non-steroidal anti-inflammatory drugs are associated with elevating blood pressure as well as sodium and fluid retention. Both of these effects may unmask previously undiagnosed heart failure, or worsen the symptoms in people known to already have heart failure.

Vioxx was a selective inhibitor and take off the market for its adverse effects on the heart.
Wikimedia Commons

Research published in the British Medical Journal in September 2016 studied 92,163 people admitted to hospital with heart failure, and found NSAID use in the two weeks prior to admission was associated with a 19% increased risk of hospital admission for heart failure. This was compared with people who had not used NSAIDs prior to admission.

The association of NSAIDs with an exacerbation of heart failure was also seen in many older studies. For example, an Australian study in 2000, suggested almost 20% of all heart failure related admissions to hospital may be attributed to recent NSAID use.

Risk of cardiac arrest

Further heart safety concerns with NSAIDs were raised in a recent study from the University of Copenhagen, published in the European Heart Journal.

Data was collected from nearly 30,000 patients who had suffered cardiac arrest between 2001 and 2010. Of these, around 3,500 were found to have been treated with an NSAID within 30 days of having a cardiac arrest.

Use of any NSAID was associated with a 31% increased risk of cardiac arrest. The commonly used non-selective NSAIDs, diclonenac (Voltaren) and ibuprofen were associated with a 50% and 31% increased risk respectively.

A large proportion of cardiac arrest is a result of clot formation in the arteries of the heart and underlying plaque formation which can rupture. NSAIDs may increase the risk of cardiac arrest by raising blood pressure, forming blood clots and blocking the heart’s own blood vessels.

It is important to emphasise that in people with no known heart disease and who don’t have any heart risk factors, short term use of these anti-inflammatories carries a minimal increase in heart-related risk.

These recent studies should not create community panic about the safety of NSAIDs when used for short periods of time and at low dosage.

But the high burden of heart disease and heart disease risk factors, such as high blood pressure, obesity and diabetes (which are often unrecognised), warrant a personalised approach to NSAIDs, which weighs the benefits and risks of their use.

This was recommended in the Therapeutic Goods Administration review of the heart related effects of NSAIDs in 2014. These anti-inflammatories should be available for purchase through prescription by a medical practitioner or behind the counter at the pharmacy.

Michael Stokes, Cardiologist and PhD Candidate, University of Adelaide and Peter Psaltis, Co-director, Vascular Research Centre, South Australian Health & Medical Research Institute

This article was originally published on The Conversation. Read the original article.