BioEd Online

Teacher Background

To survive, human body cells must exchange gases (oxygen and carbon dioxide), receive nutrients (like glucose), and eliminate wastes. These processes require an efficient system to transport substances around the body. The lungs play a key role, enabling the body to obtain oxygen from the atmosphere and eliminate carbon dioxide waste. Meanwhile, the digestive system provides nutrients for survival and works with the liver and kidneys to remove waste products from the body. The transportation network for these gases and nutrients is our closed circulatory system, which, amazingly, consists of 60,000 to 100,000 miles of blood vessels.

All of this circulation begins with the unique pump in the chest, the heart. Weighing less than a pound and a little larger than a fist, this tireless organ beats approximately 100,000 times every day—nearly three billion times in a lifetime. Even at rest, the heart works twice as hard as the leg muscles of a person running a sprint.

Birds and mammals, including humans, have four-chambered hearts. Two chambers (atria) receive blood and the other two (ventricles) pump it out. The right side of the heart receives oxygen-poor blood from the body and sends it to the lungs to be re-oxygenated. The left side of the heart receives oxygen-rich blood from the lungs and pumps it out to the body. The “lub-dub” heartbeat you hear through a stethoscope corresponds to (1) the closing of one-way valves after blood has moved from the receiving chambers (atria) into the pumping chambers (ventricles); and (2) the closing of one-way valves at the base of the ventricles.

The heart pumps about once per second throughout our lifetimes. A resting adult circulates more than a gallon of blood throughout the body every minute; more than 2,000 gallons per day; nearly three-quarters of a million gallons each year. In a lifetime, our hearts will pump enough blood to fill three super tanker ships! The National Health Lung and Blood Institute offers an excellent animation of heart contraction and blood flow (http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/contraction.html).

Electrocardiogram. We cannot directly observe contractions and movement of blood through the heart, but we can study the process indirectly by recording the heart’s electrical activity. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom, causing the heart to contract and pump blood. This signaling process repeats with every heartbeat. An electrocardiogram (EKG or ECG) uses electrodes attached to the skin to collect information about these electrical signals, including their strength and timing when passing through each section of the heart. Information gathered from an EKG is presented as a graph, which shows how fast the heart is beating and whether the rhythm is steady or irregular. The standard pattern of peaks and valleys in an EKG corresponds to alternating contractions and relaxation of the heart’s chambers. Visit the URL below to view an online animation demonstrating how an EKG translates activity of the heart into a readable graph (http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html).

EKG/ECG is not the only way to observe or measure heart function and blood circulation. Additional methods are discussed below.

Pulse. Each time the heart beats, a surge of blood, known as a pulse, passes through the arteries. The pulse can be detected in specific locations, such as the wrist or neck, where arteries run near the surface of the skin. The number of pulses per minute provides a good estimate of heart rate. A normal resting heart rate in adults is 60–90 beats per minute.

Blood Pressure. When the heart pumps, moving blood generates pressure against artery walls. Blood pressure can be an indicator of one’s health or risk for certain diseases. It is measured at two different time points: when the heart is contracting and causing a surge of blood (systolic pressure); and when the heart is at rest between beats (diastolic pressure). Blood pressure usually is written as a ratio, with the systolic number above the diastolic number, such as 120/80 mm Hg. (The unit “mm Hg” refers to millimeters of mercury, a way of measuring pressure.)

Oxygen Saturation. Oxygen saturation is a common diagnostic test used to determine whether the heart and lungs are supplying the body with enough oxygen. Pulse oximetry (“pulse ox”) uses a light sensor attached to a patient’s finger to estimate oxygen levels in the blood (based on absorption of different wavelengths of red light). Healthy blood oxygen saturation levels vary from 94% and 99% (i.e., oxygen occupies between 94% and 99% of the hemoglobin binding sites in the bloodstream). These values are affected by the amount of oxygen in air, which decreases at higher altitudes, so a person who lives at sea level might have a normal reading of 98% at home, but 95% when he or she is in a mountain village 5,000 feet above sea level.

Stroke Volume and Cardiac Output. Circulation begins with the heart, a complex pump that provides the initial force for blood flow through the body. The heart provides enough force to send blood to the toes and back in 16 seconds, thereby providing oxygen and nutrition for the body’s 75 trillion cells. Clearly, it is extremely important to maintain a healthy heart.

Two measurements that help to determine heart health are stroke volume and cardiac output. Stroke volume is the amount of blood pumped by the left ventricle with each beat. Cardiac output is the amount of blood pumped by the left ventricle every minute. These values can be estimated based on an individual’s body size. Actual values are determined by a diagnostic procedure, called an echocardiogram. Comparisons of the estimated and actual values make it possible to determine the amount of heart muscle damage caused by disease or a heart attack.

Various disease states of the heart can reduce cardiac output so much that the heart becomes unable to supply enough blood flow (oxygen and nutrients) to meet the needs of the body cells. This condition, known as heart failure or cardiac insufficiency, is costly, disabling and potentially deadly.

Objectives and Standards

Materials and Setup

Teacher Materials (See Setup)

• Set of Heart Facts Cards, printed on card stock and pre-cut to create a class set of cards

• Set of Heart Basics Station Cards, including Nomogram for Estimating Body Surface Area

• Computer and projector, interactive white board or overhead projector

• Automatic blood pressure cuff (arm or wrist)

• Finger pulse oximeter

• Digital thermometer and disposable tips

• Tape measure (feet and inches)

• Bathroom scale

• Wall clock with second hand, or small timers, or stop watches at stations C and D

Materials per Student

• Copy of “Heart Basics/Personal Data Sheet” (PDS)

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Setup

1. Print or copy the Heart Facts Cards on card stock and pre-cut the cards to create a classroom set. Make copies of the Heart Basic Station cards on card stock and cut each sheet in half to separate the two cards. Make a copy of “Heart Basics/Personal Data Sheet” for each student. Set up one or more of each of the following stations around the classroom. 
   
   Station A: Body Temperature  card and a digital thermometer, plus disposable thermometer tips.
   
   Station B: Blood Pressure card and a digital blood pressure cuff for arm or wrist (available at most drug stores for $15–$60)
   
   Station C: Heart (Pulse) Rate card and timer or clock with a second hand) 
   
   Station D: Respiration (Breathing) Rate card and timer or clock with a second hand 
   
   Station E: Oxygen Saturation card and finger pulse oximeter (available at most drug stores for $35–$50) 
   
   Station F: Electrocardiogram (EKG) card and computer with Internet access set for students to view the following page: http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/electrical.html 
   
   Station G: Heart Stroke Volume card, and copy of “Nomogram,” page, tape measure attached to a wall, 12-inch ruler, bathroom scale 
   
   Station H: Cardiac Output card

2. Conduct the first part of the activity as a class discussion. For the second part, have students work in teams of two or four, and rotate through each diagnostics station. Some teachers prefer to set up two stations for each measurement.

3. An answer key for the statements on the Heart Facts cards is provided.

Procedure and Extensions

Time: One or two 45-minute class periods, depending on students' familiarity with the cardiovascular system.

1. Remind students of the activity, "Introduction to Personal Stories," during which they learned of three health emergencies. Students also learned about lifestyle choices and behaviors that can contribute to poor cardiovascular health. Tell students that now they will investigate the heart and circulatory system further, and learn more about the tests used by emergency medical personnel who treated Arturo, Brian and Angela.

2. Distribute one Heart Facts Card to each student. Tell students that not all of the “facts” on the cards are true. Have each student read his or her card aloud. The rest of the class should raise their hands if they believe the statement to be true.

3. Initiate a short discussion by asking, Were you surprised by an any of the facts? Which ones and why? Tell students that they will learn more about how to measure heart function.

4. Ask, Why did most of the tests performed on Arturo, Brian and Angela relate to heart function? Encourage students to discuss the tests, and lead them to understand that the heart is essential because it pumps blood throughout the body. Blood carries vital oxygen and nutrients to all cells and every body system (digestive, excretory, respiratory, muscular, etc.). It also transports and removes carbon dioxide and other waste products from every body system. We cannot live without blood circulation, and blood cannot circulate without the heart.
   
   If students are unfamiliar with the heart and circulatory system, show the following animation, Heart Contraction and Blood Flow, at the National Heart, Lung, and Blood Institute’s website (http://www.nhlbi.nih.gov/health/health-topics/topics/hhw/contraction.html).

5. Tell students that they will visit stations set up around the room to gather statistics similar to those obtained for Arturo, Brian and Angela. Point out the instruction card at each location, and demonstrate how to use the equipment and collect information at each station. Note that Station H requires data collected at Stations C and G, and that students must complete those Stations before going to Station H.

6. Distribute copies of the “Heart Basics/Personal Data Sheet,” and have students work in teams of two or four as they circulate through each station. If a station they need to visit is occupied, instruct students to wait in their seats until it is available.
   
   Briefly discuss the importance of protecting patient confidentiality, emphasizing that information on the Personal Data Sheet is not to be shared. Explain that students are responsible for protecting their personal data.

7. If students are concerned about any of their personal readings (for example, high blood pressure), suggest that they visit the school nurse to receive new, possibly more accurate measures.

8. Conclude the activity by discussing students’ observations about their vital signs. Their investigations of resting and active pulse rates, respiration and cardiac output should enable students to understand that our bodies’ cells require more oxygen and nutrients at times of increased pulse or respiration rates (during exercise, for example).

9. Tell students to keep their personal data sheets for use with the activity, “Calculating Coronary Artery Disease Risk.”

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Extensions or Homework

One out of three Americans has high blood pressure. Often, the causes are unknown, but it possible to identify, and sometimes treat, risk factors for high blood pressure. Have students visit one or more of the websites listed in “High Blood Pressure Information Resources” (left sidebar), and find at least four different factors that increase a person’s risk for high blood pressure. Students should list the factors, write one or two sentences describing the associated risks, and provide the name and URL of the website from which the information was obtained.

Handouts and Downloads