The new ACC/AHA guidelines for High Blood Pressure were published late last year and they were in favor of using home blood pressure measurement to aid in the management of hypertension.
I was happy to hear this as I am constantly advising my hypertensive patients to buy a home BP cuff, measure their BP once when they get up and again 12 hours later and report the values to me after two weeks.
I have not spent a lot of time instructing them on exactly how to make the measurement but the new guidelines do specify in detail how this should be done:
• Remain still:
• Avoid smoking, caffeinated beverages, or exercise within 30 min before BP measurements.
• Ensure ≥5 min of quiet rest before BP measurements.
• Sit with back straight and supported (on a straight-backed dining chair, for example, rather than a sofa).
• Sit with feet flat on the floor and legs uncrossed.
• Keep arm supported on a flat surface (such as a table), with the upper arm at heart level.
• Bottom of the cuff should be placed directly above the antecubital fossa (bend of the elbow).
• Take at least 2 readings 1 min apart in morning before taking medications and in evening before supper. Optimally, measure and record BP daily. Ideally, obtain weekly BP readings beginning 2 weeks after a change in the treatment regimen and during the week before a clinic visit.
• Record all readings accurately:
• Monitors with built-in memory should be brought to all clinic appointments.
I monitor my own BP at home and often wonder whether there is scientific evidence to support such a rigid protocol. Being a contrarian and a skeptic, I typically violate 3/4 of the recommendations that are listed.
It seems like all of the instructions are guaranteed to give you the lowest BP you are likely to experience during the day. The vast majority of the time I am not sitting quietly with my legs uncrossed, my bladder empty and my back straight so following these directions will underestimate my average daily BP.
I’ve spent some time looking into all the instructions and they generally have some scientific studies to support them. For example, the position of the upper arm in relation to the heart does heavily influence BP readings (more on that in subsequent posts.)
The Mandate To Uncross The Legs
The instruction that most intrigued me was this one:
Sit with feet flat on the floor and legs uncrossed.
A number of questions came to the skeptical hypertensive:
What if you are on an exam table and your feet don’t reach the ground?
Does it really make a difference if your feet are flat on the ground versus slightly crooked?
Does any degree of leg crossing influence BP? Legs crossed at the ankles? Legs crossed at the knee?
And once I began thinking of leg crossing I realized that I spend a lot of my time with my legs crossed. Was this raising my blood pressure and my cardiovascular risk? Did I cross my legs because I liked the feel of a higher blood pressure?
The ACC/AHA guidelines are not alone in this recommendation-take a look at the British Health Service recommendation:
3.5. Measurements should be taken in silence when the patient is relaxed, with both feet flat on the floor and their back and arm supported. Many patients automatically cross their legs, which raises their blood pressure, so it is particularly important to emphasise the need for the patient to uncross their legs when taking their blood pressure.
Apparently the Brits believe that any ambient sound will alter the blood pressure. Talking is right out!
But if talking, ambient sounds and crossing your legs raises your blood pressure shouldn’t we be advising patients to spend their days wearing ear plugs in silence with their legs uncrossed?
Scientific Studies On Leg Crossing
It turns out there are good studies showing that leg crossing raises your blood pressure.
The first was published in 1999 and involved 53 hypertensive and 50 normotensive subjects.
Participants were randomly assigned, using a cross over design to having seated blood pressures measured with their leg in three different postures
- Feet flat on the floor and legs uncrossed
- Legs crossed , method 1-popliteal fossa of the dominant leg over the suprapatellar bursa of the non-dominant leg.
- Legs crossed, method 2- lateral malleolus (which the article spells mallelous) of the dominant leg over the suprapatellar bursa of the non-dominant leg.
I love the efforts these Calgarian investigators went to in this study to ensure blinding (although spelling is clearly not their forte’). They state “blood pressures were measured by one investigator who was behind a screen and blinded to the leg position of the patient while a second investighator (sic) ensured that the subject assumed the proper leg position.”
Systolic blood pressure in patients with hypertension increased by 8 mm Hg by method 1 leg crossing and 10 mm Hg by method 2.
Another study demonstrated that although crossing the legs at the knees influenced blood pressure, crossing them at the ankles had no effect.
A recent review identified 7 studies which support the influence of leg crossing on BP.
For those of you itching to read more about BP and leg crossing here are the references: