Blood pressure is the force of the blood pushing against the artery walls, as it gets pumped from the heart into the blood vessels through the rhythmic constriction or relaxation of the heart muscles during heartbeats.
The size and elasticity of the artery walls also affect blood pressure. The increased pressure on the artery wall caused by the constriction of the heart muscle is referred to as systolic pressure Conversely, when the heart muscles relax, the pressure on the arterial walls decreases, and is referred to as diastolic pressure.
The blood pressure recorded using a sphygmomanometer, also called a blood pressure cuff, registers both systolic and diastolic pressure. The systolic number is usually displayed before or above the diastolic number in a blood pressure reading. For example, a reading of 120/80 means a systolic pressure of 120 and a diastolic pressure of 80.
Blood pressure readings are an important part of preventative health care as it may signal underlying health issues. Having too high blood pressure (hypertension, or too low blood pressure (hypotension), could indicate potential health risks. Abnormal high or low blood pressure can also lead to complications such as heart disease, stroke, organ issues, and dementia.
Since high blood pressure usually has no symptoms, the only way to know is by taking a blood pressure check. Accurate blood pressure measurement is essential for the diagnosis and treatment of hypertension, and is key to efforts aimed at prevention of cardiovascular diseases.
A new study by doctors at John Hopkins University in the United States found that certain commonly used arm positions for blood pressure readings may result in inaccurately high readings and misdiagnosis of high blood pressure. There are guidelines on the proper patient preparatory steps and positions to be followed prior to taking a blood pressure reading.
But direct observations and surveys have established that many healthcare providers do not adhere to these guidelines, either because the steps involved take time or require additional resources to comply with.
Direct observations and research conducted on compliance with blood pressure guidelines show that blood pressure is frequently measured with the arm resting in the lap or hanging at the side. In a bid to simplify blood pressure measurement, doctors behind the new study explored how important arm support and position was to blood pressure measurement accuracy.
For their study, the researchers recruited 133 adult participants ages 18 to 80. Participants were randomly assigned to sets of triplicate blood pressure measurements with their arm positioned in one of three ways when the reading was taken — arm supported on a desk, arm supported on their lap, or an unsupported arm hanging at their side.
At the study’s conclusion, researchers found that systolic blood pressure readings for participants who supported their arms on their laps were overestimated by about 4 mmHg (millimeter of mercury, the unit used to measure blood pressure) while readings for those positioning their arms unsupported by their sides had an overestimated systolic blood pressure by almost 7 mmHg.
The doctors explained that when the arm is either in the lap or at the side, the blood vessels in the arm are at a greater vertical distance from the heart. Gravity increases the pressure in these blood vessels. It also is harder for the blood to return to the heart when the arm is lower than the heart; to compensate for this, and improve blood return, the blood vessels in the arm constrict. In addition, when the arm is unsupported, the muscle is not fully at rest and contracts. All of these body responses lead to a higher blood pressure reading.
The study team said that while they expected to find a difference in blood pressure readings between the different arm positions, they were surprised by the magnitude of the difference. While the 4 or 7 mmHg difference in measurement may not seem like a big difference, that is enough to push someone’s blood pressure categorization into a higher level.
Misdiagnosing high blood pressure can lead to serious health consequences, with overestimation of blood pressure, and overdiagnosis of hypertension, potentially leading to prescription for new medications that the patient may not actually need. Misdiagnosing high blood pressure can also lead to unnecessary treatment and medication, which can cause side effects. For example, people who are misdiagnosed with high blood pressure and given medication could develop hypotension
The researchers said they hoped their findings would alert health care providers and patients alike to the importance of arm position and support on blood pressure measurement. They recommended that the room where blood pressure is being measured should be set up in such a way that there is a chair with a back support positioned next to a table or desk that is the appropriate height for the arm to rest with the mid-cuff at mid-heart level.
The team added that while this may take an investment in time and resources to ensure the blood pressure measurement setting is set up for proper measurement, the return on the investment has the potential to be significant. Especially in terms of better patient care with fewer misdiagnoses, as well as in saving time and money for patients and medical facilities.
