Introduction to Lesson 2 - Heartbeat

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Gervase Robertson
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1 Introduction to Lesson 2 - Heartbeat Activity: Locate your pulse at rest. Count how many times it beats in 15 seconds (look at a clock), then multiply this number by 4. This is your pulse rate Approximately how many heartbeats have you had since you were born? Since your heart has been beating since you were 2 weeks old in utero (inside the uterus), how many heartbeats have you had since your heart was formed? The human heart beats an average of 70 times per minute, 24 hours a day, and 365 days a year. For those who have never had heart problems, the regular rhythmic beating of the heart is usually taken for granted. Did you know that the average heart beats or contracts over 3 billion times during a normal lifetime? Lesson 2 Outcomes By the end of this lesson, you should be able to: 1. Differentiate between systole and diastole and relate these to heart sounds. 2. Describe the intrinsic control of heartbeat, i.e. nervous (SA Node, AV Node, Perkinje Fibers, Bundle of HIS), and chemical (adrenaline, noradrenaline). 3. Explain the role of pacemakers in regulating heartbeat. 1

2 4. Describe the effects of adrenaline and noradrenaline on heart rate. 5. Measure your own heart rate. 6. Explain the effect of physical activity on heart rate. 7. Calculate cardiac output given heart rate and stroke volume. 8. Relate cardiac output to fitness levels. Lesson 2 Overview Following is a list of topics covered in this lesson. Heartbeat Control of Heartbeat Artificial Pacemakers Cardiac Output Heart Rate, Stroke Volume and Fitness Heartbeat A heartbeat is a two-part pumping action that takes approximately one second. The contraction of the heart and its anatomy cause the distinctive sounds heard when listening to the heart with a stethoscope. Systole and Diastole and The Lubb Dubb sound: See the diagram below. 2

Figure 5.2.1 Systole and Diastole (http://www.tmc.edu/thi/systole.

The lower pressure in the ventricles causes the tricuspid and mitral valves to open, and the cycle begins again.

3 Figure Systole and Diastole ( After blood moves into the pulmonary artery and the aorta, the ventricles relax, and the pulmonary and aortic valves close. The lower pressure in the ventricles causes the tricuspid and mitral valves to open, and the cycle begins again. This series of contractions is repeated over and over again, increasing during times of exertion and decreasing while you are at rest. Your heart does not work alone, though. Your brain tracks the conditions around you climate, stress, and your level of physical activity and adjusts your cardiovascular system to meet those needs. Control of Heartbeat The sinoatrial Node (SA Node): Why is the SA Node called the natural pacemaker? 3

4 The atrioventricular Node (AV Node): Bundle of His: The impulse started in the SA node and picked up by the AV node reaches the muscles of the ventricles and causes them to contract. Purkinje fibers : Series of events in one heartbeat: The following diagrams illustrate the sequence of events involved in a heart contraction. 4

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Figure 5.2.2 â The Contraction of the Heart (Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates, www.sinauer.com and www.whfreeman.

6 Figure â The Contraction of the Heart (Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates, and A physician listening carefully to the heart with a stethoscope can detect if the valves are closing completely or not. Instead of a distinctive valve sound, the physician may hear a swishing sound if they are letting blood flow backward. When the swishing is heard tells the physician where the leaky valve is located. This condition is known as a heart murmur. Electrocardiograph: The EKG shows three slow, negative changes, known as P, R, and T. Positive deflections are the Q and S waves. The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction. EKGs are useful in diagnosing heart abnormalities. 6

Figure 5.2.3 - Electrocardiogram (Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates, www.sinauer.com and www.whfreeman.

7 Figure Electrocardiogram (Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates, and The SA node sends electrical impulses at a certain rate, but your heart rate may still change depending on physical demands, stress, or hormonal factors. For example, when you run to catch a bus, the increased activity in your muscles produces a faster rate of cellular respiration. This leads to an increase in the amount of carbon dioxide in your blood. The medulla oblongata detects this increase and sends impulses along the nervous system causing the release of a hormone called noradrenaline. When noradrenaline reaches the SA node, it makes the node fire more rapidly. Once you have boarded the bus, your heart gradually slows to a resting rate due to an increase in blood pressure. This response is detected by special blood pressure receptors located in the walls of the aorta and carotid arteries that send messages to the medulla oblongata. Physical activity is not the only trigger for an increased heart rate. Your nervous system releases another hormone called adrenaline when you are nervous, angry, excited or after a sudden shock or sharp pain. All of these conditions produce what is called the "fight or flight" response a physiological change that prepares the body for anticipated activity. This response increases heart rate, increasing blood flow to the muscles. 7

Artificial Pacemakers and Cardiac Output Artificial Pacemakers Arrythmia: When the natural pacemaker fails to work properly, doctors can implant a small, batteryoperated device called an artificial

8 Artificial Pacemakers and Cardiac Output Artificial Pacemakers Arrythmia: When the natural pacemaker fails to work properly, doctors can implant a small, batteryoperated device called an artificial pacemaker to help the heart beat in a regular rhythm. Artificial pacemakers can be permanently implanted into a person's chest or they may be temporary and located outside of the body. Both types use batteries to send electrical impulses to the heart. A wire or electrode is placed next to the heart and transmits small electrical charges to the heart. Most current pacemakers are demand pacemakers which have sensing devices to turn the pacemaker on when the heartbeat falls below a certain level. Cardiac Output The amount of blood pumped by the heart is called cardiac output. This is a measure of the volume of blood pumped from each ventricle per unit of time. It is also a measure of the level of oxygen delivery to the body. Two factors affect cardiac output: 8

9 Cardiac output can be calculated by multiplying stroke volume and heart rate. The average person has a stroke volume of about 70 ml and a resting heart rate of about 70 beats/minute. Therefore, the average person has a cardiac output of 70 x 70 = ml/min. Since the average person has about 5 L of blood, your total blood volume circulates through your body approximately once every minute. Heart Rate, Stroke Volume and Fitness Maximum heart rate (also known as Target heart rate) is the highest heart rate you can attain during strenuous physical activity. This rate will diminish as you get older although maximum heart rate does not appear to be related to fitness. The more important indicator of fitness is the length of time it takes for your heart to return to its resting level following physical activity. This is called recovery time, and this amount of time will diminish as you become more fit. Two factors affect stroke volume Regular cardiovascular exercise will enlarge the ventricular chambers and increase their distensibility (stretchiness). Athletes who are very fit have high stroke volumes. This means they can maintain high oxygen delivery to tissues at low heart rates. Some elite endurance trained athletes like Olympic cross country skiers have resting heart rates of as low as 30 beats/minute. 9

10 Lesson 2 Exercise 1. What causes the characteristic "lubb-dubb" heart sounds? 2. Describe the structures involved and the sequence of events involved in a heart contraction. 3. What is an EKG or ECG? Why are they useful? 4. Why do some people require an artificial pacemaker? 5. Describe the conditions that would cause the release of noradrenaline and adrenaline and their resulting effects of on heart rate. 6. How are heart rate and stroke volume related to fitness? 7. Explain the changes in pulse rate during exercise. 8. Extension: How does an AED (Automated External Defibrillator) device work? 10

Heart Rate Activity Effects of Exercise on Heart Rate Complete the following activity. Once you have performed the lab, prepare a report and submit it in the Assignments Tool M4 L2 Heart Rate.

11 Heart Rate Activity Effects of Exercise on Heart Rate Complete the following activity. Once you have performed the lab, prepare a report and submit it in the Assignments Tool M4 L2 Heart Rate. Your report should have the following categories: 1. Purpose 2. Observations/Data 3. Analysis/Conclusions Lesson 2 Lab Activity Effects of Exercise on Heart Rate Purpose: To measure your heart rate, recovery time and cardiac output before, during and after vigorous exercise. If you have a physical condition that makes it unadvisable for you to exercise vigorously, do not participate in the exercise portion of this activity. Procedure: 1. Find your resting heart rate by measuring your pulse. A pulse is a change in the diameter of arteries following a heart contraction. The easiest locations for measuring your pulse are directly under the back of your jawbone toward the neck or on the underside of your wrist directly beneath the thumb area. 2. While in a sitting position, record your pulse rate for 15 seconds. Multiply this number by four to determine your resting heart rate per minute. Record this value in the data table below. Repeat three times and determine the average. 3. Perform jumping jacks or running on the spot for one minute. Immediately after completing the exercise, measure your pulse rate for 15 seconds and calculate your heart rate after vigorous exercise. 11

12 4. Continue to measure your pulse rate in one minute intervals until your heart rate reaches its resting rate. The time it takes for your heart to reach its resting rate is your recovery time. Record this time in the data table. 5. Repeat steps 3 and 4 two more times and calculate the average of the three trials. Data Table Trial Average Resting Vigorous Exercise Recovery Time Analysis 1. What do you notice about the change in your heart rate from resting to vigorous exercise? 2. Compare your recovery time with other students. How does it compare? 3. Calculate your cardiac output for resting and vigorous exercise by using your averages and a stroke volume of 70 ml. 4. Why did you perform three trials for each heart rate measurement? Lesson 2 Summary In this lesson, you studied the physiology of heartbeat and the factors that influence heart rate. You also had an opportunity to measure your own heart rate and recovery rate. In the next lesson, you will study blood pressure and fluid exchange. 12

Cardiac Cycle. Each heartbeat is called a cardiac cycle. First the two atria contract at the same time.

Cardiac Cycle. Each heartbeat is called a cardiac cycle. First the two atria contract at the same time. The Heartbeat Cardiac Cycle Each heartbeat is called a cardiac cycle. First the two atria contract at the same time. Next the two ventricles contract at the same time. Then all the chambers relax. http://www.youtube.com/watch?v=frd3k6lkhws