The new for high blood pressure were published late last year and were in favor of using home blood pressure (BP) 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 2 weeks.
I have not spent a lot of time instructing patients 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 minutes before BP measurements
- Ensure ≥5 minutes of quiet rest before BP measurements
- Sit with the back straight and supported (on a straight-backed dining chair, for example, rather than a sofa)
- Sit with the feet flat on the floor and legs uncrossed
- Keep the arm supported on a flat surface (such as a table), with the upper arm at heart level
- The bottom of the cuff should be placed directly above the antecubital fossa (bend of the elbow)
- Take at least two readings 1 minute apart in the morning before taking medications and in the 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 three-quarters 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 the one to 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 the back and arm supported. Many patients automatically cross their legs, which raises their blood pressure, so it is particularly important to emphasize 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 earplugs 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 was published in 1999 and involved 53 hypertensive and 50 normotensive subjects. Participants were randomly assigned, using a crossover 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 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. 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 investigator 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 demonstrated that although crossing the legs at the knees influenced blood pressure, crossing them at the ankles had no effect.
A recent review identified .
An Inconvenient Truth
If leg crossing raises the systolic blood pressure 8 to 10 mm Hg, why aren't we doctors recommending that patients sit with the leg uncrossed the majority of the time? Personally, I had never heard there were any health complications to sitting with my legs crossed.
Apparently, the myriad health information sources on the internet are near unanimous in their condemnation of leg crossing, but the hypertensive effect of this maneuver is usually not cited.
My condemning the practice was "The surprising and inconvenient truth of crossing your legs."
I must admit since doing this bit of research I have substantially reduced the amount of time I sit with my legs crossed. And I've pondered extensively whether sitting with the legs crossed makes me feel any different and why I suddenly and seemingly randomly decide to cross my legs.
I've also started asking friends and colleagues and medical residents how much of the day they spend with the legs crossed.
On teaching rounds one morning recently we tested a volunteer resident's blood pressure with legs crossed and uncrossed. Sure enough, the systolic BP was 10 mm Hg higher with the legs crossed.
, is a private practice noninvasive cardiologist and medical director of echocardiography at St. Luke's Hospital in St. Louis. He blogs on nutrition, cardiac testing, quackery, and other things worthy of skepticism at , where a version of this post first appeared.