Blood Pressure Variables and Importance of Accuracy

Blood Pressure Variables and Importance of Accuracy

January 22, 2023

Joy Stepinski, MSN, RN-BC

With cardiovascular disease as the leading cause of death in the United States [1], high blood pressure (or hypertension) is a commonly known risk factor. The Centers for Disease Control and Prevention and the American Heart Association (AHA) describe blood pressure (BP) as the force of blood against the walls of the arteries [1, 2], which are the vessels that carry blood from the heart to the rest of the body. Blood pressure determines two values, designated by the top number and bottom number, such as 120/80. The top number is called the systolic blood pressure, which represents the cardiac phase of systole. The bottom number refers to the diastolic blood pressure, which represents diastole. With systole, the ventricles contract and the atria relax. With diastole, the opposite occurs. The ventricles relax and the atria contract. In simple terms, systolic blood pressure refers to the pressure when the heart sends blood into the arteries, and the diastolic pressure measures pressure in the arteries when the heart is resting.

There are several considerations to measuring blood pressure, especially with respect to accurately diagnosing hypertension. According to a commentary [3], errors in blood pressure readings are a concern. Although blood pressure is a crucial marker for cardiac risk factors, it can have biologic variability. In other words, if a patient is experiencing emotional stress or has recently engaged in physical activity, blood pressure may not be at the typical baseline reading. Additionally, the method for measuring the BP may lead to inaccuracies. Often patients have their BP taken via a pressurized manual cuff that stops blood flow in the brachial artery, which is an artery of the arm. However, the most precise way to measure BP is to use a small catheter inserted into the artery. This is not feasible during a routine exam.

Another article [4] discusses these issues further. Many offices have turned to the automated blood pressure cuff, which has led to more questions on accuracy, including proper calibration. In scenarios where the patient’s heart rate is irregular, such as atrial fibrillation, the blood pressure reading may not capture the variability. The ramifications of this problem are huge. If a patient is mistakenly diagnosed with hypertension, they may be unnecessarily placed on medication, experience drug side effects as a result, and be subjected to psychological burden through being labeled as having a disease. This may cause unnecessary anxiety and depression. As one author [5] points out, an inaccuracy of 5 mm Hg may be considerable in under- or over-diagnosing hypertension.

A survey of healthcare practitioners looked at problems with not reporting timely errors regarding automatic blood pressure cuffs [4]. The most common errors revealed were substantial. The findings described the patient not planting both feet on the floor, not resting for 5 minutes prior to measurement, not sitting up with a supported back, talking or moving during blood pressure readings, and not having the arm placed in the appropriate position. Furthermore, the cuff was placed over clothing instead of directly on the skin and incorrect cuff size used. These errors were mostly due to the environment (absence of equipment, multitasking, and perception of chaos), as well as lack of accountability and training. The authors stated that nurses and doctors were both responsible for mistakes.

Blood pressure can fluctuate and is influenced by many different causes [6]. These factors can potentially increase BP by 20 mm Hg or more, including location of measurement, emotion, activity, bladder distension, pain, alcohol or tobacco use, respiration characteristics, and meals. One study of 50 patients examined the effect of talking and reading [7]. Thirty-four were taking antihypertensive medication and 16 were not. The patients were divided into two groups and given a different order of activities, either reading followed by talking or talking followed by reading. The outcomes showed that talking can increase systolic BP by 17 mm Hg and diastolic BP by 13 mm Hg and remained elevated throughout a determined period of silence. Reading decreased systolic BP by 8 mm Hg and diastolic BP by 3 mm Hg and remained low during the period of silence with a progressive rise in diastolic BP over time. The authors concluded that the study adds to knowledge about BP fluctuation with respect to environmental stressors.

There are other factors discussed in the medical literature [6]. “White coat hypertension” is a result of a rise in BP due to anxiety when seen by a healthcare provider. BP can rise by 30 mm Hg. If the arm is unsupported, diastolic BP may be 10% higher. The arm should be maintained at the level of the heart, otherwise there can be a discrepancy of 10 mm Hg for both systolic and diastolic BP. Some patients may have a large difference in BP between their right and left arms, which is often further evaluated by a cardiologist.

In a systematic review [8], 328 empirical studies were investigated for blood pressure reading inaccuracies, highlighting most of the points discussed above. The authors recommended that BP readings should be recorded within a range, instead of one single measurement, to decrease the impact of an error. A single BP reading should be interpreted with caution instead of used as a definitive indicator.

Blood pressure is a significant factor when determining a cardiac problem that often leads to prescribed medications. Because variables affect readings so easily, take action to prevent false readings. Some suggestions are: empty your bladder before the appointment; do not consume a meal, drink alcohol or caffeine, smoke, or exercise within at least 30 minutes prior to the measurement; try not to be stressed or anxious; sit quietly for at least 5 minutes before the blood pressure reading and refrain from talking; and plant feet on the floor. Ask that three different readings be done. If you feel that the reading may not be accurate, take your BP at home before making any decisions about a treatment. Greater awareness in knowledge of blood pressure variables can help you to take control over your health decisions.

References

1.      Centers for Disease Control and Prevention. (2022). Heart disease. https://www.cdc.gov/heartdisease/index.htm

2.      American Heart Association. (2023). The facts about high blood pressure. https://www.heart.org/en/health-topics/high-blood-pressure/the-facts-about-high-blood-pressure

3.      Jones, D. W. (2019). Implementing automated office blood pressure measurement. Hypertension, 74(3), 436 – 440. https://doi.org/10.1161/HYPERTENSIONAHA.118.10966

4.      Elias, M. F., & Goodell, A. L. (2020). Human errors in automated office blood pressure measurement. Hypertension, 77(1), 6 – 15. https://doi.org/10.1161/HYPERTENSIONAHA.120.16164

5.      Handler, J. (2009). The importance of accurate blood pressure measurement. The Permanente Journal, 13(3), 51–54. https://doi.org/10.7812/TPP/09-054

6.      Beevers, G., Lip, G. Y., & O'Brien, E. (2001). ABC of hypertension. Blood pressure measurement. Part I-sphygmomanometry: factors common to all techniques. BMJ (Clinical research ed.), 322(7292), 981–985. https://doi.org/10.1136/bmj.322.7292.981

7.      Pailleur, C. L., Helft, G., Landais, P., Montgermont, P., Feder, J. M., Metzger, J. P., & Vacheron, A. (1998). The effects of talking, reading, and silence on the “white coat” phenomenon in hypertensive patients. American Journal of Hypertension, 11(2), 203-207. https://doi.org/10.1016/S0895-7061(97)00403-2

8.      Kallioinen, N., Hill, A., Horswill, M. S., Ward, H. E., & Watson, M. O. (2017). Sources of inaccuracy in the measurement of adult patients' resting blood pressure in clinical settings: a systematic review. Journal of Hypertension, 35(3), 421–441. https://doi.org/10.1097/HJH.0000000000001197