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Factors affecting Blood Pressure

Factors affecting Blood Pressure

Introduction: (Initial Observation)

In many animals, blood pressure is an indication of health status and a function of the circulatory system. Often, aged or over weight people complain that their blood pressure is low or high and take medicine to adjust their blood pressure. Obviously, what they feel is not the blood pressure itself, but instead they have learned to associate certain symptoms to the changes in their blood pressure. Blood pressure can not be felt; however, it can be measured using a Sphygmomanometer & a Stethoscope.

Every time that I hear about blood pressure imbalance, I am wondering what has caused it. Is it the age? Is it eating too much? Is it the hot weather? Is it because the person is tired?…

In this project I will study some of the factors that may possibly affect the blood pressure. The results of this research may provide alternative solutions to those suffering from high or low blood pressure.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about blood pressure and the way it can be measured. Read books, magazines or ask professionals who might know in order to learn about the factors that may effect blood pressure. Keep track of where you got your information from.

Following are samples of information that you may gather.

What is blood pressure?

When the heart beats, blood is pumped to all parts of the body. Blood pressure is the force of blood on the walls of the blood vessels. Blood pressure is described by two numbers (like 120 / 80). The first and highest number (systolic) measures pressure when the heart is squeezing the blood out; the second and lower number (diastolic) measures the pressure when the heart is resting between beats.

To measure your blood pressure at home, you can use either an aneroid monitor or a digital monitor. The aneroid monitor has a dial gauge that is read by looking at a pointer. The cuff is inflated by hand, by squeezing a rubber bulb. Digital monitors have either manual or automatic cuffs. The blood pressure reading flashes on a small screen. Choose the type of monitor that best suits your needs.

Blood pressure varies relative to heart’s pumping of blood. The heart should be thought of as a dual pump, with a right and left side. Systole represents the active pumping of blood from the ventricles into the circulation. The right side of the heart takes venous/returning blood from the body and sends it to the lungs to be oxygenated (pulmonary circulation). Measuring blood pressures on the right side of the heart requires very complicated equipment. The left side of the heart takes the oxygenated blood and sends it to the rest of the body. When you take a blood pressure reading, you measure pressures in the systemic circulation.

The highest pressures occur during systole as blood is ejected into the aorta and subsequent arteries of the body. Diastole, the heart’s resting phase, follows systole. During diastole the ventricles fill with more blood. Systemic pressures fall until more blood is ejected during systole.

What do I need to do before I measure my normal blood pressure?

  • Rest for 3 to 5 minutes before measuring your blood pressure. Do not talk.
  • Sit in a comfortable position, with your legs and ankles uncrossed and your back supported.
  • Place your arm, raised to the level of your heart, on a table or a desk, and sit still.
  • Wrap the correctly sized cuff smoothly and snugly around the upper part of your bare arm. The cuff should fit snugly, but there should be enough room for you to slip one fingertip under the cuff.
  • Be certain that the bottom edge of the cuff is 1 inch above the crease of your elbow.

How do I use an aneroid monitor?

  1. Put the stethoscope ear pieces into your ears, with the ear pieces facing forward.
  2. Place the stethoscope disk on the inner side of the crease of your elbow.
  3. Rapidly inflate the cuff by squeezing the rubber bulb to 30 to 40 points higher than your last systolic reading.
  4. Inflate the cuff rapidly, not just a little at a time. Inflating the cuff too slowly will cause a false reading.
  5. Slightly loosen the valve and slowly let some air out of the cuff. Deflate the cuff by 2 to 3 millimeters per second. If you loosen the valve too much, you won’t be able to determine your blood pressure.
  6. As you let the air out of the cuff, you will begin to hear your heartbeat. Listen carefully for the first sound.
  7. Check the blood pressure reading by looking at the pointer on the dial. This number will be your systolic pressure.
  8. Continue to deflate the cuff. Listen to your heartbeat. You will hear your heartbeat stop at some point. Check the reading on the dial. This number is your diastolic pressure.
  9. Write down your blood pressure, putting the systolic pressure before the diastolic pressure (for example, 120/80).
  10. If you want to repeat the measurement, wait 2 to 3 minutes before re-inflating the cuff.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to see how exercise affect blood pressure.

You may test other factors as you wish. Another factor that I like to test is drinking sugar water. I have seen some people ask for sugar water as soon as they feel their blood pressure is low. Some other variables or factors that may be tested are:

  • hours of the day
  • Eating dinner
  • Air temperature (cold room – Hot room)
  • Drinking water
  • Caffeine (Coffee is a good source of caffeine)


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are two sample hypothesis:

Hypothesis Example 1:

Since exercise consumes energy, human body will be weaker after the exercise and heart may not have enough energy to pump the blood at its highest pressure. So blood pressure will drop after the exercise.

Hypothesis Example 2:

When we exercise, body will need more oxygen, so heart will pump faster and that can temporarily increase our blood pressure. For this reason I think people who may get sick from high blood pressure must avoid heavy works.

Note that hypothesis does not have to be correct. Your experiments may support or reject your hypothesis.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Measure someone’s blood pressure

Introduction: This is just a warm-up experiment for you to learn measuring blood pressure and become good at it. To measure blood pressure, we use an external pressure to stop the flow of blood while we listen to the sound of blood flow using a stethoscope.

Note: It would be helpful if someone (such as school nurse) who knows how to take a blood pressure is present to supervise, as the technique requires some practice. Also you want to avoid keeping the cuff inflated on someone’s arm for too long.

Don’t put the cuff around your friend’s neck.. :).

How to do the experiment:

1. Deflate the bladder of the cuff and place it around the upper arm so it fits snugly, but not too tightly. If you’re right handed, you should hold the bulb/pump in your left hand to inflate the cuff. Hold it in the palm so your fingers can easily reach the valve at the top to open/close the outlet to the air bladder wrapped around the person’s arm.

2. Put the head of the stethoscope just under the edge of the cuff, a little above the crease of the person’s elbow. Hold it there firmly with the thumb, or with a few fingers of your right hand. Put the ear pieces of the stethoscope in your ears.

3. Inflate the cuff with brisk squeezes of the bulb. Watch the pressure gage as you do it. For most kids, you shouldn’t need to go over 150 (the markings indicate “pressure” in mm Hg or mercury).

4. At 150, slightly open the valve on the air pump (held in your left hand, as above). This part takes practice.. It’s important that you don’t let the air out too suddenly. Likewise, your friend will be quite irritated with you if you let it out too slowly.

5. Now, pay attention *very carefully* to what you hear through the stethoscope as the needle on the pressure gage falls. You will be listening for a slight “blrrpp” or a something that sounds like “prrpshh.” The first time you hear this sound, note what the reading was on the pressure gage. This value represents the systolic blood pressure (pressure when the heart is squeezing the blood out).

6. The sounds should continue and become louder in intensity. Note the pressure reading when you hear the sound for the last time. This value represents the diastolic blood pressure (pressure when the heart is resting between beats).

7. Afterwards, open the air valve completely to release any remaining pressure.

8. Repeat this experiment until you can quickly and effortlessly measure someone’s blood pressure.


The blood pressure cuff lets you apply external pressure to a circumferential ring around the upper arm. When the pressure is great enough, it forcibly closes the main artery of the upper arm – the brachial artery. The stethoscope allows you to hear when the underlying artery opens and closes as you release the air in the bladder.

Example – Take a person with a blood pressure of 120/80. The first number always represents systolic pressure (120), and the second number diastolic pressure (80). When you apply a pressure of 180mm Hg to the arm, the 120mm of pressure from the artery cannot overcome your externally applied pressure; the artery stays shut.

As you release the air out of the cuff, the external pressure falls. At 150mm the artery is still closed.. but at 119mm, it can open for just the slightest instant as the maximum/systolic pressure exceeds the applied pressure. Once the arterial pressure falls below 119mm, however, the artery shuts again. This opening and shutting produces the sounds you hear through the stethoscope (Korotkoff sounds). When the applied pressure falls below the diastolic/resting pressure, the artery stays open all the time.

Experiment 2: The effect of exercise on blood pressure (short term effects)

Introduction: In certain heart conditions and heart disease, even short term increase of blood pressure can be dangerous or deadly. It is important to know what factors may cause such an increase on blood pressure. In this experiment we test the effect of exercise (running) on blood pressure.


  1. Find five candidates for this experiment. Select all your candidates from same age and same sex and do all tests in the same day and in the same place so the environmental factors will remain the same. Number candidates from one to 5.
  2. Measure and record the blood pressure of all candidates.
  3. Ask candidates number 1 to 4 run a distance of about 250 feet and run back to you (so total running distance will be 500 feet). Immediately measure and record their blood pressure. They will run one at a time so you can measure their blood pressure immediately after running.
  4. Candidate number five is the control. He or she will not run. Measure and record the blood pressure of candidate number 5 again. This will usually show that any changes in the blood pressure of those who ran was not caused by other factors.
  5. Repeat the above procedure for a 1000 feet, 1500 feet and 2000 feet running distances. Record your results in a table like this:
Running Distance Runner 1 Runner 2 Runner 3 Runner 4 Control
Does not run
500 feet 120/80
1000 feet
1500 feet
2000 feet

Draw a graph:

Use the above result table to draw a line graph. Use X axis for running distance and Y axis for pressure. Use a separate color for each candidate. Use solid line for systolic number and dotted lines for diastolic number.

Materials and Equipment:

You will need:

  1. Blood pressure cuff
  2. Stethoscope

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


No calculation is required.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.