Normal Distribution (continued): Apply It 2

  • Understand the properties and characteristics of the standard normal distribution.
  • Calculate probabilities and percentiles using normal distribution and [latex]z[/latex]-scores with technology.

A blood pressure cuff with a tube in the shape of a heart.[1]

Blood pressure is another important indicator of heart health. Blood pressure is the pressure exerted by blood on the walls of a blood vessel that helps to push blood through the body. Like cholesterol, blood pressure levels for adults in the United States are normally distributed. However, an individual’s blood pressure also varies in a normally distributed pattern throughout the day based on factors such as position, activity level, anxiety, stress, and nutritional factors. High blood pressure can increase the risk of heart attacks and strokes. Blood pressure is reported as the systolic pressure (when the heart is pumping) over the diastolic pressure (when the heart is relaxing).

Systolic blood pressure values below [latex]120[/latex] millimeters of mercury (mm Hg) are considered healthy, while values over [latex]140[/latex] mm Hg are classified as high. Values between [latex]120[/latex] and [latex]140[/latex] mm Hg are borderline.[2] The values of the standard deviation (SD) also vary depending on the assumed mean value of the systolic blood pressure. It is reported that the SD for individual blood pressure is [latex]9.9\%[/latex] of the mean systolic blood pressure.

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Children’s blood pressures vary with age and size, so guidelines have to account for that variation. Instead of providing simple numeric ranges (like we see with adults), the guidelines are based on where a child’s blood pressure falls in the normal distribution of all measurements for children of the same age and height.[3][4]

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  1. https://www.forbes.com/sites/enriquedans/2019/08/25/blood-pressure-one-of-the-keys-to-preventive-healthcare/?sh=2f1c04ab4459 ↵
  2. National Heart, Lung, and Blood Institute. (2020, May 8). High blood pressure. https://www.nhlbi.nih.gov/health-topics/high-blood-pressure ↵
  3. Flynn, J. T., Kaelber, D. C., Baker-Smith, C. M., Blowey, D., Carroll, A. E., Daniels, S. R., de Ferranti, S. D., Dionne, J. M., Falkner, B., Flinn, S. K., Gidding, S. S., Goodwin, C., Leu, M. G., Powers, M. E., Rea, C., Samuels, J., Simasek, M., Thaker, V. V., & Urbina, E. M. (2017, September). Clinical practice guideline for screening and management of high blood pressure in children and adolescents. Pediatrics, 140(3), e20171904. https://doi.org/10.1542/peds.2017-1904 ↵
  4. U.S. Department of Health & Human Services, Chemical Hazards Emergency Medical Management. (2021, March 8). Pediatric basic and advanced life support. https://chemm.nlm.nih.gov/pals.htm ↵