Under Pressure: Does a Child's Blood Pressure Depend on His or Her Age?
AbstractEvery time you go to the doctor's office, the nurse measures your blood pressure. But why does he or she do this? What does your blood pressure tell your doctor about your health? And what exactly is blood pressure? In this life science project, you will learn about blood pressure and what causes it. You will even learn how to take blood pressure readings. Once you learn this skill, you will test a population of children and determine if blood pressure depends upon a child's age.
Michelle Maranowski, PhD, Science Buddies
Edited by Colleen Callaghan, MD
Learn how to take blood pressure readings, and test a population of children to determine if blood pressure depends upon age.
The human body is made up of several systems that work together to keep the body functioning properly. One of these systems is called the cardiovascular system. The job of the cardiovascular system is to move blood, which contains oxygen and nutrients, throughout the body to the different organs and the brain. The cardiovascular system is made up of the heart, arteries, capillaries, and veins. For the purpose of this project, let us focus on the heart and arteries.
The heart is a muscle that acts as the pump of the cardiovascular system. The heart is divided into the right and the left sides. Each side has two chambers, an atrium and a ventricle. The right side of the heart pumps oxygen-poor blood to the lungs where the lungs deliver oxygen to the blood. The oxygen-rich blood comes back to the left side of the heart into the left atrium and empties into the left ventricle. From there, the heart pumps the blood through the aorta, the largest artery in the body, to supply the organs and the brain with oxygen and other nutrients. Valves separate the atrium and ventricle on each side of the heart. The valves make sure to keep the blood flowing in the right direction. Because the right side and the left side of the heart are not connected, the oxygen-poor blood does not mix with the oxygen-rich blood. The heart muscle itself also needs oxygen to function properly. A network of coronary arteries covers the heart and provides it with oxygenated blood.
The pumping of the heart is a repeated cycle of contraction and relaxation of the atria and ventricles. Every time the heart contracts and relaxes, blood is moving from the heart to other parts of the body. The contracting phase is called systole and the relaxing phase is called diastole. In systole, the heart is contracting and is pumping blood out to the lungs and the body. In diastole, the heart is relaxed, and blood fills the atria and ventricles.
Blood pressure is the force of the blood pushing against the walls of the arteries. Blood pressure is at its highest during systole. This is called systolic pressure. Blood pressure falls when the heart muscle relaxes, or in diastole, and this pressure is called diastolic pressure. When a physician gives you your blood pressure reading, he or she will give you the systolic pressure over the diastolic pressure, as in 120/80. But both numbers are important and if either one of the numbers is too high, you could have a condition called high blood pressure. Over time high blood pressure damages the body and can lead to a number of diseases, including coronary artery disease, strokes, heart failure, and kidney failure. To help prevent these diseases, patients' blood pressure is tracked at almost every doctor's visit. This way physicians can detect and treat high blood pressure before it becomes a bigger problem.
Medically trained professionals measure blood pressure using tools called a sphygmomanometer and a stethoscope. A sphygmomanometer consists of a pump, valve, inflatable cuff, and a dial. The medically trained professional wraps the cuff around the patient's arm, inflates the cuff with the pump, and places the stethoscope over the brachial artery in the crook of the elbow. Inflating the cuff applies pressure to the arteries in the arm, temporarily stopping the flow of blood through the artery for a few seconds. Then, the valve is slowly opened to let some of the air out of the cuff and to allow the blood to flow again. When the pressure in the cuff gradually drops to equal that of the patient's systolic blood pressure (as read from the dial), the medically trained professional will hear the first Korotkoff sounds with the stethoscope. Korotkoff sounds are the sounds that medical professionals listen for when taking blood pressure measurements. Korotkoff sounds occur as the pressure in the cuff changes and the blood starts to move through the artery. The first Korotkoff sounds are the tapping sounds that occur during systole when the pressure in the cuff has been released enough that the blood can start to move through the artery. Eventually, the pressure in the cuff will be released to the point that the blood can flow through the arteries when the heart is in diastole. The reading on the dial is the diastolic pressure. At this point there are no Korotkoff sounds, and the medically trained professional listens for silence.
Does everyone have the same blood pressure? What about in kids? Do young kids have the same blood pressure as older kids? Doctors use charts to determine if a child's blood pressure is normal or not. You will create your own chart in this life science project. The first step is to find a doctor or a nurse who would be willing to show you how to measure blood pressure using a manual sphygmomanometer, or manual cuff, and a stethoscope. Once you feel confident knowing how to take blood pressure readings, you can start measuring the blood pressure of your test subjects. Will there be a difference between older kids and younger kids? What matters is that everyone knows their blood pressure so that they can take steps to maintain their cardiovascular health.
Terms and Concepts
- Coronary artery
- Blood pressure
- Brachial artery
- Korotkoff sounds
- What is considered high blood pressure in adults?
- What causes high blood pressure?
- What is the difference between systole and diastole?
- What causes a heart to beat?
- What are the five phases of Korotkoff sounds?
These websites offer more information about blood pressure and the cardiovascular system:
- American Heart Association. (2011). About High Blood Pressure. Retrieved June 30, 2011.
- Mayo Clinic Staff. (2009, August 7). Heart Disease: Heart and Circulatory System-How They Work. Retrieved February 1, 2011.
These websites offer blood pressure and growth charts for different ages and genders. On the Centers for Disease Control and Prevention (CDC) website, use the "Children and adolescents, 2 to 20 years" charts:
- Centers for Disease Control and Prevention. (2010, September 9). Growth Charts. Retrieved February 1, 2011.
- National Heart Lung and Blood Institute and the National Institutes of Health. (2004, May). Clinical Practice Guidelines. Retrieved February 1, 2011.
Do you need practice taking blood pressure readings? Try these online blood pressure practice games. The first game uses Korotkoff sounds to help you determine blood pressure readings:
- Aberdeen Medical Faculty CAL Unit. (1999). Video Tutorial (Blood Pressure Measurement). Retrieved February 14, 2011.
- Ohio State University, The Center of Knowledge Management. (2008). Blood Pressure: Assessment, Interactive Guide to Physical Examination: Objective IV To Practice Selected Psychomotor Skills. Retrieved February 1, 2011.
This site contains a library of medical videos that you can watch:
- MedlinePlus. (2011). Anatomy Videos. A.D.A.M, Inc. Retrieved February 1, 2011.
Materials and Equipment
- Optional, video camera
- Test subjects (30). For the experiment, choose one gender to investigate, either boys or girls. Find 15 subjects that are in 8th grade and 15 subjects that are in 1st grade. If you don't know students in those grades, find 15 subjects that are in 2nd grade and 15 subjects that are in 9th grade. You can find test subjects at your school or through any clubs that you participate in.
- Manual sphygmomanometer with child's cuff. You can purchase one from online vendors like Amazon.
- Stethoscope. You can purchase one from online vendors like Amazon or Carolina Biological catalog #691639
- Quiet location with a table and two chairs with armrests, preferably at school
- An age-appropriate book or magazine for test subjects to read
- Lab notebook
- Graph paper
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Working with Human Test Subjects
There are special considerations when designing an experiment involving human subjects. Fairs affiliated with Intel International Science and Engineering Fair (ISEF) often require an Informed Consent Form (permission sheet) for every participant who is questioned. Consult the rules and regulations of the science fair that you are entering, prior to performing experiments or surveys. Please refer to the Science Buddies documents Projects Involving Human Subjects and Scientific Review Committee for additional important requirements. If you are working with minors, you must get advance permission from the children's parents or guardians (and teachers if you are performing the test while they are in school) to make sure that it is all right for the children to participate in the science fair project. Here are suggested guidelines for obtaining permission for working with minors:
- Write a clear description of your science fair project, what you are studying, and what you hope to learn. Include how the child will be tested. Include a paragraph where you get a parent's or guardian's and/or teacher's signature.
- Print out as many copies as you need for each child you will be surveying.
- Pass out the permission sheet to the children or to the teachers of the children to give to the parents. You must have permission for all the children in order to be able to use them as test subjects.
Learning How to Take Blood Pressure Readings
- While you are waiting to hear back from the test subjects, start to train yourself on learning how to take blood
pressure readings with a manual sphygmomanometer.
- Do some research on blood pressure. Make sure that you understand what blood pressure is, how it is measured, and what systolic and diastolic mean.
- Try the online blood pressure practice games listed in the Bibliography. These games will help you to learn how to take actual blood pressure measurements much faster.
- Find a trained medical professional that would be willing to teach you how to use a manual sphygmomanometer to take blood
pressure readings. Examples of trained medical professionals include physicians, nurses, nurse's assistants, and emergency
medical technicians (EMTs).
- Be sure to inform the medical professional about your science project and what you are planning to do.
- Be prepared to spend several sessions with the medical professional learning how to use a sphygmomanometer and about blood pressure.
- Try to be flexible when scheduling times to meet. The first priority of all medical professionals is to help patients.
- Take notes and if necessary, take video of the training lessons. You will have to take readings of your test subjects in exactly the same way.
- Once you feel confident taking blood pressure readings with a manual sphygmomanometer, it is time to start taking blood pressure readings with your test subjects.
Taking the Test Subjects' Blood Pressure
- Set up the test location. Place a chair near the table.
- Ask your test subject to come in and sit in the chair. Inform the test subject about your science project and that you are investigating blood pressure. Let him or her rest and get used to the surroundings for five minutes. Give the test subject a book or magazine to read to help pass the time. Record the test subject's age in your lab notebook.
- Place the cuff around the test subject's arm and take the blood pressure reading exactly as your instructor showed you. Record the reading in your lab notebook.
- Wait for five minutes, and then, take another blood pressure reading. Keep the test subject seated during the wait time. Have the test subject read a magazine or a book to help pass the time. Record the reading in your lab notebook. Repeating the reading eliminates any errors that you may have made the first time and errors due to patient nervousness.
- After you have taken the readings, remove the cuff and allow the test subject to rest for a moment. Thank the test subject for participating and allow him or her to leave.
- Repeat steps 2–5 for the rest of the test subjects.
Analyzing the Data
- Review the data that you collected for all of the test subjects. For each of the test subjects, remove the higher blood pressure reading from the data set. Make a new table so that you are only working with one blood pressure reading for each test subject.
- Average the systolic pressure readings for each grade, and average the diastolic pressure readings for each grade. Remember to record all data in your lab notebook.
- Now plot the raw systolic data on a scatter plot. Label the x-axis Grade and the y-axis Systolic Blood Pressure. You can also plot the average systolic pressure on the same plot.
- Now plot the raw diastolic data on a scatter plot. Label the x-axis Grade and the y-axis Diastolic Blood Pressure. You can also plot the average diastolic pressure on the same plot.
- Do you see a difference between grades for the systolic and diastolic pressures? Is your data consistent with the NIH Blood Pressure Tables for Children and Adolescents? What is the range of both the systolic and diastolic data for each grade?
Ask an Expert
- Widen your investigation to include the other gender. Does blood pressure vary between genders?
- Investigate blood pressure as a function of height. Does blood pressure vary for children of different heights? Record the height of your test subjects. Plot blood pressure on the y-axis and height on the x-axis.
- Does blood pressure vary if you use a different size sphygmomanometer (cuff size)? What effect does the wrong cuff size have on blood pressure readings?
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