INVESTIGATING HEART RATE AND BLOOD PRESSURE

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1 Hughes Undergraduate Biological Science Education Initiative HHMI INVESTIGATING HEART RATE AND BLOOD PRESSURE Learn how to measure heart rate and blood pressure. Learn the normal values for heart rate and blood pressure. Explore the things that can affect human heart rate and blood pressure. Practice using the scientific method. Heart rate and blood pressure are important indicators of cardiovascular health. They are also very simple to measure. Therefore, almost every time you visit your health care practitioner, they will measure your resting heart rate and blood pressure. Heart rate is the rate at which your heart muscles contract and is usually measured in beats per minute (bpm). Normal resting heart rate for a young adult is anywhere between 60 and 100 bpm. Blood pressure is the force created by the heart as it pushes blood into the arteries through the circulatory system. It is usually measured in units of mm Hg (millimeters of mercury). It is usually written as a ratio of two numbers, such as 120/75 mm Hg. Systolic blood pressure describes the surge of pressure in the arteries as the heart beats and pumps blood out of the ventricle. It is the upper number in the measurement of a person's blood pressure. For example, in the measurement 120/75, 120 is the systolic blood pressure. Diastolic blood pressure is the pressure in the arteries when the heart relaxes between beats. It is the lower number in the measurement of a person's blood pressure. For example, in the measurement 120/75, 75 is the diastolic blood pressure. Normal blood pressure is variable based on gender, age, and physical condition. In general, however, systolic blood pressure higher that 140 mm Hg and/or diastolic blood pressure higher that 90 mm Hg is considered above normal. Systolic blood pressure below 100 mm Hg is generally considered below normal. Many factors may affect heart rate and blood pressure -- physical activity, emotional state, time of day, temperature, drugs, body posture, etc.

2 For this activity, each group will need, a time piece that can measure seconds and a blood pressure monitor. After you decide on your experimental design, you may need to acquire additional materials (jump rope, coffee, etc). Please check with your teacher or lab coordinator about using or obtaining any new materials. Practice using the blood pressure monitor to take your blood pressure and heart rate. Follow the directions that accompany your monitor. Be sure to sit very still and not talk during the measurement. Also practice measuring your heart rate without the machine. 1) Find your pulse on your wrist or on your neck. 2) Count the number of beats you feel in 10 seconds. 3) Multiply this number by 6 to get the number of beats per minute. Follow the steps of the Scientific Method to investigate possible factors that might affect human heart rate and blood pressure. Step One: Define the question or problem. Decide on a factor that might influence heart rate and blood pressure. State your team s question. You may want to phrase it as two different questions, one for heart rate and one for blood pressure. Ex: How does affect human heart rate? Ex: How does affect human blood pressure? You may phrase your question in a different way, but make sure that it is clear and well-defined. Write your question(s) here. University of Colorado Campus Box 470 Boulder, CO (303) Fax (303)

3 Step Two: Form hypotheses. State your hypothesis/es. H 1 H 2 H 3 Make predictions based on your hypotheses, and try to state them as If...then statements. P 1 P 2 P 3 Step Three: Test hypotheses. Decide how you will test your hypotheses. Design a simple experiment using any of the available materials/facilities. Do not design an experiment that would require any member of your team to do anything that would be unsafe for them. If any member of your team is unable to participate because of safety concerns (e.g. you are measuring the effects of chocolate, and the person is allergic to chocolate), they may coordinate the other members of team and record the data. You will want to replicate the experiment for each member of your group. Make sure that each person experiences the factor you are testing in the same way. For example, if you are testing the effect of exercise, each person should do the same kind of exercise, with the same intensity, for the same amount of time. You will also need a control. For this experiment, you can measure each person s resting heart rate before the experiment and then immediately after they are exposed to the factor you are testing. The resting heart rate before the experiment is the control. Describe your experimental procedure:

4 What is the independent variable? What is the dependent variable? Step Four: Collect data. Carry-out your experiment, and record your data on the data-sheet provided. Step Five: Analyze your results and draw conclusions. 1) Calculate the average heart rate of people in your group before exposure to the experimental factor and after. Average heart rate before: bpm Average heart rate after: bpm Average difference in heart rate before and after: bpm 2) Calculate the average diastolic blood pressure of people in your group before exposure to the experimental factor and after. Average diastolic blood pressure before: mm Hg Average diastolic blood pressure after: mm Hg Average difference in diastolic blood pressure before and after: mm Hg 3) Calculate the average systolic blood pressure of people in your group before exposure to the experimental factor and after. Average systolic blood pressure before: mm Hg Average systolic blood pressure after: mm Hg Average difference in systolic blood pressure before and after: mm Hg 4) Did the average heart rate, go up or down after exposure to the experimental factor? University of Colorado Campus Box 470 Boulder, CO (303) Fax (303)

5 5) Were there individuals for whom the difference in heart rate before and after was in the opposite direction from the average difference? What explanation can you think of for this result? 6) Did some individuals' heart rate change a lot, while others changed only somewhat? What explanation can you think of for this result? 7) Did the average diastolic blood pressure go up or down after exposure to the experimental factor? 8) Did the average systolic blood pressure go up or down after exposure to the experimental factor? 9) Were the changes in average systolic and diastolic blood pressure roughly the same or different? What explanation can you think of for this result? 10) Did the data support your hypotheses or falsify them? 11) What can you conclude about the effect of the factor you chose on heart rate and blood pressure? 12) Are there any changes you might want to make to your experimental design if you were to do it again? 13) Did this activity suggest any further questions that you might explore with other experiments if you had the time?