Name Class Date Sensing Circulation Exploring the Effects of Exercise on Heart Rate Investigative Lab 30 8 Questions How do the sounds you hear through a stethoscope relate to the stages of a heartbeat? How does your heart rate change with exercise? Lab Overview In this investigation you will use a stethoscope to listen to your heart beating. You will learn to take your pulse, determine your target heart rate, and perform a cardiac efficiency test to explore how your heart rate changes during and after exercise. Introduction To start your investigation, you will learn about the parts of a stethoscope and the relationship between heart rate, pulse, and physical fitness. Then, you will determine the best place on your body to take your pulse. Background When the ventricles in your heart contract, your atrioventricular valves (the valves located between the atria and ventricles), pulmonary valve, and aortic valve open and allow blood to flow through them. The valves then close, stopping blood from flowing backward. As the valves close, they make sounds that can be heard using a stethoscope. When the atrioventricular valves close, a lub sound is produced. When the pulmonary and aortic valves close, a dupp sound is produced. To learn more about the parts of a stethoscope, study the diagram below. Tubing Earpieces Bell Diaphragm Stethoscope Chest piece Health professionals use the cup-shaped bell side of the stethoscope to listen to low-pitched sounds. They use the flat diaphragm side to listen to high-pitched sounds. For this lab, you should use the diaphragm. When listening for heart murmurs, doctors use the stethoscope bell to detect diastolic murmurs (which occur when the heart is relaxed). They use the diaphragm to detect systolic murmurs (which occur as the heart is pumping). Objective to listen to heart sounds with a stethoscope, to take a pulse to measure heart rate, to determine target heart rate, and to test changes in heart rate during and after exercise Inquiry Skills observing making measurements calculating making inferences Time 15 min for the Prelab Activity 15 20 min for Part A 10 min for Part B 15 20 min for Part C 15 min for Analysis and Conclusions Heath professionals use stethoscopes to listen for abnormal sounds produced when the heart valves open and close. The most common problem detected is mitral valve prolapse. The mitral valve is the atrioventricular valve located between the left atrium and left ventricle. In people with mitral valve prolapse, the valve tissue is loose. When the heart contracts, the valve may not close all the way. A clicking sound or a murmur sound may be produced as a small amount of blood leaks through. Laboratory Manual/Investigative Lab 30 353
Heart rate is the number of times each minute that the ventricles in your heart contract and pump blood. Each time blood is pumped, artery walls expand and then relax. This causes a surge of blood that can be felt at certain points in your body your pulse. Heart rate can be measured without a stethoscope, by measuring pulse rate. When you exercise, your heart rate increases, enabling oxygen and nutrients to be delivered to your cells faster. The heart of a person in top physical condition usually pumps a larger volume of blood with each contraction than the heart of a person in poor physical condition. After exercise, the heart rate of a person in top physical condition returns to normal faster than the heart rate of a person in poor condition. The length of time it takes for heart rate to return to normal after exercise is a measure of the efficiency of the heart. Prelab Activity In this lab you will measure your pulse rate at different levels of physical activity. First, you should determine which artery is the best one to use for measuring your pulse. Two possible places you can detect a pulse are the left side of your neck or the inside of your wrist at the base of your thumb. Use your first two fingers to detect your pulse. Do not use your thumb because it has a pulse of its own. A pulse typically has an even, steady beat, with an equal amount of time between each beat. (If you feel that your pulse does not have an even, steady beat, it is probably not a cause for concern, but you should tell a family member, school nurse, or doctor about what you observed.) Prelab Questions 1. In the space below draw a pattern representing your pulse as you felt it. Explain in words how the diagram represents your pulse. Students drawings and explanations will vary. Some students may draw the up-and-down pattern of an EKG as they may have seen on TV. Others may draw a dashed line. 2. Explain the connection between heart rate and pulse. Suggested answer: When the ventricles contract with each heartbeat, the arteries expand from the pressure. You can feel a pulse when you place your fingers near a major artery. 354 Biology: Exploring Life
Name Class Date Materials stethoscope rubbing alcohol cotton balls stopwatch (or clock with second hand) calculator (optional) Procedure Part A: Listening to Heart Sounds 1. Use a cotton ball and rubbing alcohol to clean the earpieces of the stethoscope. 2. Insert the earpieces into your ears, angling the earpieces slightly forward. Place the diaphragm (flat side of the stethoscope) over your heart (just to the left of the center of your chest). 3. Listen to your heart. If you re having trouble locating your heart sounds, first try adjusting the stethoscope earpieces. If you are wearing several layers of heavy clothing, try removing an outer sweater or jacket if you can. Describe what you hear. school nurse, or doctor about what they observed. Advance Preparation Obtain stethoscopes and stopwatches as needed. Stethoscopes can be purchased from most biological supply companies for less than $10 each. Alternate Methods If you don t have enough stethoscopes you could have half the class do parts B and C first. Or, you can have students make simple stethoscopes. A funnel or the top half of a cut-off 1- liter bottle can be used as the chest piece. A piece of rubber tubing can be attached to the small end of the funnel or bottle to serve as an earpiece. If you have students in wheelchairs, you could have them participate in Part C by doing just the arm motions of jumping jacks as quickly as they can for 30 sec. If the room is fairly quiet, students should be able to distinguish the lub sound from the dupp. It is unlikely that they will hear the common heart murmurs that, statistically, some of your students probably have. If they do hear something they think is unusual, advise them to tell a family member, 4. When you have finished listening to your heart and have recorded your observations, clean the stethoscope earpieces again. Dispose of used cotton balls as directed by your teacher. Part B: Determining Target Heart Rate You can use your heart rate as a tool to find out if your heart is getting the maximum benefit from exercise. The benefit of exercise for your heart is to increase the efficiency of your heart muscle so that it pumps a greater volume of blood with each beat. To get the maximum benefit while exercising without causing injury, you should adjust your level of activity so that your heart rate is in a certain range called the target heart rate zone. Calculate your target heart rate zone as follows. 1. Use the equation below to calculate your maximum heart rate (beats per min). 220 your age in years maximum heart rate per min (MHR) MHR 205 beats per min (NOTE: Maximum heart rate decreases with age, regardless of your physical condition.) Safety and Disposal Since Part C of this lab requires students to run in place for 30 sec, students with asthma or certain other health problems should not participate. You may wish to consult the school nurse for information about students who should not be allowed to participate. Remind students to take care not to injure themselves or others while exercising. Advise students to sit down if they feel dizzy or faint at any time during exercise and to notify you immediately. Remind students to wipe stethoscope earpieces with alcohol prior to inserting them into their ears. You may wish to have students place used cotton balls in a covered, plastic-lined trash container. Laboratory Manual/Investigative Lab 30 355
2. Use the equation below to calculate the lower end of your target heart rate zone, which is 70% of your maximum heart rate. maximum heart rate 0.7 lower end of target heart rate zone Lower end of your target heart rate zone 144 3. Use the equation below to calculate the upper end of your target heart rate zone, which is 80% of your maximum heart rate. maximum heart rate 0.8 upper end of target heart rate zone Upper end of target heart rate zone 164 (NOTE: Allowing your heart rate to climb over 80% of your maximum heart rate during exercise may be a sign of overexertion and could lead to injury.) Part C: Determining Your Cardiac Efficiency Follow the steps below to see how your heart rate changes with exercise. (CAUTION: If you have a health problem that restricts your ability to exercise, talk to your teacher and do not participate in this part of the lab.) 1. While sitting, take your pulse for 15 sec. Record the result below. Sitting pulse (per 15 sec): 2. Run in place with your knees held high for 30 sec. (CAUTION: If at any time you do not feel well, stop exercising and tell your teacher.) Immediately afterward, take your pulse for 15 sec. Peak pulse (per 15 sec): 3. After an additional 45 sec (to allow a total recovery time of 1 min after exercising) take your pulse again for 15 sec. Recovery pulse (per 15 sec) 4. Make a line graph to represent how your heart responds to exercise. Plot time on the x-axis and pulse rate on the y-axis. Remember to title your graph and label the axes. Most students expect that their heart rate will increase with exercise. However, they may be surprised at how quickly their heart rate returns to normal after exercise. Recovery time is a good indicator of cardiovascular fitness. See Analysis and Conclusions Question 5 for sample data. 356 Biology: Exploring Life
Name Class Date Analysis and Conclusions 1. While listening to someone s heart, a doctor discovers that the lub sound is weaker than the dupp sound. What might this clue suggest about the functioning of the heart valves? Sample answer: The weaker lub sound suggests that one or both of the atrioventricular valves may not be functioning completely. 2. While listening to your heart, did you find that there was more time between the lub and the dupp sounds, or between one lub dupp and the next? Suggest a possible explanation. Sample answer: There is more time between one lub dupp and the next lub dupp than there is between the lub sound and the dupp sound. A possible explanation is that the heart rests a moment between beats. 3. How is it useful to know your target heart rate zone? What forms of exercise do you think might increase your heart rate so that it is in your target heart rate zone? Suggested answer: It is useful to know your target heart rate zone so that you make sure that your heart is receiving the maximum benefit from exercise. Running or jogging, walking fast, or a sport such as basketball are forms of exercise that might increase heart rate. 4. Explain why athletes often have lower resting pulse rates than nonathletes. Suggested answer: An athlete s heart may pump blood more efficiently so that fewer beats are needed to deliver adequate oxygen and nutrients. 5. Study the graph below. From the data, which student s cardiovascular system would you conclude is probably more efficient? Explain your response on the lines below the graph. Heart rate (beats per 15 sec) 40 35 30 25 20 15 10 5 Michaela Maria 0 15 30 45 60 75 90 105 120 Sitting Peak Recovery Time (sec) Suggested answer: Maria s cardiovascular system is most likely more efficient. Her sitting heart rate was lower than Michaela s. Also, her heart rate returned to normal faster than Michaela s. Laboratory Manual/Investigative Lab 30 357
Extension There are several methods for determining target heart rates. Another example besides the one described in this lab is the Karvonen method, which takes basal heart rate (resting heart rate) into consideration. Basal heart rate measurements are most accurate if they are taken in the morning when you first wake up and are still lying down. Follow the equation below to calculate your target heart rate using the Karvonen method. Compare your results to those from Part B of the Procedure. Suggest possible reasons for any significant differences. Karvonen Method Target heart rate (220 age basal heart rate) (0.75) basal heart rate Extension Students will comment that the Karvonen method does not give a target heart rate zone, but rather a specific number. If the student s basal heart rate is higher than average, the Karvonen method may produce a target rate that is higher than the upper end of the zone provided by the method in Part B. During physical education class, or after school, exercise for 15 min and measure your heart rate for 6 sec. Multiply this number by 10 to get your heart rate in beats/min. If the number is in your target heart rate zone, the exercise is helping your heart and lungs stay fit. If it is too high or too low, adjust your level of exertion and continue exercising for another 10 min. Then take your heart rate again to see if you are in the target zone. With practice, you will learn how it feels to exercise in your target heart rate zone, and you won t need to take your pulse to ensure your heart is benefiting from the exercise. 358 Biology: Exploring Life