Download Enlarged Heart

Teaching
Notes
Enlarged Heart
Determining heart-to-chest ratios
Background
Suggested Grades
Basic measurements are an integral part of making medical diagnoses. In this activity,
students measure chest x-rays of six patients. They calculate the heart-to-chest ratio
and determine whether each patient has an enlarged heart. Because the measurements are simple but subjective, this activity offers an excellent opportunity for
exploring measurement reliability and validity.
As with any medical image, the first thing students should do when looking at a chest
x-ray is determine the orientation and identify major anatomical landmarks. A
diagram is provided to help the students with this process. An anatomy or biology
text would also be useful in identifying structures.
clavicle
scapula
lung
aortic arch
ribs
heart
liver
Goal
Students will diagnose
cardiomegaly by identifying
anatomical structures in
patient chest x-rays and
calculating heart-to-chest
ratios.
Topics
chest x-ray anatomy
humerus
• 7–12
diaphragm
X-rays vary in quality. Using image processing, students can enhance the x-ray
images to better visualize the heart shadow and chest cavity. Students measure the
width of the widest part of the heart, and then the width of the widest part of the chest
cavity. From these data, they calculate a heart-to-chest ratio. Ratios greater than 0.5
indicate an enlarged heart.
• Humans
• Anatomy
• Circulatory system
Biology Strands
• Functional Units &
Organization
• Diversity & Evolution
Science Skills
• Observation
• Cooperation &
Communication
• Quantification of Data
• Organization of Data
• Data Analysis
Technology
• X-ray imaging
IPTechnique Sheets
maximum width of
heart shadow
• Look-up Tables
• Selecting
• Measuring
maximum width of
chest cavity
Identifying the maximum widths of the heart and chest is subjective. For this reason,
students remeasure one of the patient x-rays, and compare their answers to their
original measurement. It is likely that students’ results will be quite different the
second time around. The last section of the activity, called Need a second opinion?,
requires students to consult with one another on their measurements. This provides
an opportunity for students to see how the same data are interpreted differently by
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.
Enlarged Heart
65
each person or group. (If you only have one computer, time is limited, or students are
working alone, this section can be left out of the classroom activity.) After students
have finished the first part of the activity, bring the class together to determine what
the high and low ratios were for each patient. This section of Enlarged Heart provides
a foundation for discussing the cooperative nature of scientific inquiry, as well as the
issues of reliability and validity in measurements.
Biology Objectives
The student will:
• observe and interpret chest X-rays
• use heart-to-chest ratios to diagnose patients with cardiomegaly
Curricular Context
Prerequisites
• Students need a background in simple human anatomy, particularly the heart
and lungs. An anatomy reference book will be useful.
• Students should be able to calculate ratios.
Related Activities
• Medical Imaging: X-ray vs. MRI is a good introduction to medical imaging
technology and is a useful prerequisite for this activity.
• This activity complements Enlarged Heart Cells because enlarged cells are one
cause of cardiomegaly.
• Articles from periodicals such as “The Hearty Fisherman” by Tony Dajer in
Discover magazine, July 1992, pp. 80–82, relate real-life scenarios to the science
content in this lesson.
Integration
• Health
Heart disease
• Mathematics
Ratios, linear measurements
Acknowledgments
Activity developed by Denice Warren and Deborah Nead, Image Processing for
Teaching project, University of Arizona, Tucson, Arizona, and Loretta Milligan,
Heizer Jr. High School, Hobbs, New Mexico.
Images courtesy of Dr. Timothy Hunter, Department of Radiology, University Medical Center, Tucson, Arizona.
References
Milne, E. N. C., and M. Pistolesi. Reading the Chest Radiograph: A Physiologic Approach. St.
Louis: Mosby, 1993.
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HIP BIOLOGY 2
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.
Answers
1–3.
Patient
Maximum
width of
heart
Maximum
width of
chest
Heart-tochest ratio
Diagnosis
Bill
83
213
0.39
normal heart size
Fran
110
185
0.60
cardiomegaly
Gary
82
236
0.35
normal heart size
Jill
77
156
0.49
normal heart size
Oliver
90
235
0.41
normal heart size
Paul
113
193
0.59
cardiomegaly
4. Answer will most likely be different from Fran’s measurements in the table
above.
5. The answers changed after re-measuring Fran because it is difficult to measure
exactly the same place on the x-ray each time.
6. Answers to this question depend on the class interactions. Students should find
that there is tremendous variability in answers and that remeasuring a patient
and consulting with other students raises their confidence in their answers.
7–8. Answers will vary based on class measurements. Fran and Paul both have heartto-chest ratios of greater than 0.50, therefore they have cardiomegaly. Jill has a
borderline ratio, but she is rather thin, so her ratio may be high because her chest
cavity is narrow.
9. It is important for doctors to consult with other professionals because this makes
their diagnoses more reliable. Consulting reduces the chance for mistakes a
single doctor might make when evaluating a patient.
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.
Enlarged Heart
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HIP BIOLOGY 2
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.
Lesson
Enlarged Heart
Determining heart-to-chest ratios
Infections, poisoning, trauma, or heart failure can cause a heart to enlarge.
This condition is called cardiomegaly, and can develop either suddenly or
gradually. Cardiomegaly may be caused by an increase in the size of the
muscle itself, a buildup of fluid around the heart, or more blood flowing
through the heart.
In Greek,
cardio = heart
megaly = large
Reading an x-ray
ì Open the chest x-ray images Bill and Bill’s Anatomy.
 File/Open…
Doctors often use x-rays such as these to determine the size of a patient’s
heart. The heart appears as a dark shadow on an x-ray, and the chest cavity
surrounding the heart appears lighter. Take a moment to carefully observe
and try to identify any key parts you may see. Compare your observations to
the diagram of Bill’s Anatomy.
People come in different sizes, and so do their hearts. To determine if a heart
is abnormally large, doctors calculate the ratio of the width of the heart to the
width of the chest cavity. Heart-to-chest ratios below 0.50 are considered
normal by doctors. In this activity, you will examine chest x-rays of six
patients for cardiomegaly.
1. On the Data Sheet, fill in the table with the names of the patients and
record your measurements as you go.
ì Enhance the Bill x-ray so you can see the heart better.
ì Use the ‡ selection tool to make a line across the widest part of the
heart. Identifying the place to measure may be difficult—try to be
consistent.
ì Measure and record the width, in pixels, of the widest part of the heart.
ì Use the same technique to select, measure, and record the width of the
widest part of the chest cavity.
2. Calculate the heart-to-chest ratio in decimal form for Bill.
ì Open the other x-rays, and repeat your measurements for each one.
Record your measurements in the data table and calculate the heartto-chest ratio for each patient.
○
○
○
○
○
○
○
○
maximum
width of heart
shadow
maximum
width of
chest cavity
○
○
○
○
See the Selecting and Measuring IPTechnique Sheets.
 Process/Equalize or
adjust the ¬ and Æ
sliders in the Map window.
 Analyze/Measure then
Analyze/Show Results
heart - to - chest ratio =
max. width of heart
max. width of chest cavity
3. Which patients have cardiomegaly? Record your diagnoses.
Need a second opinion?
ì Without looking at your previous measurements, remeasure Fran’s
x-ray.
4. Enter Fran’s newest measurements in the table on the Data Sheet and
calculate her heart-to-chest ratio based on these values.
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.
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5. Why were your answers different from the first time you measured Fran’s
x-ray?
Because you must decide where to measure the widths of the heart and chest
cavity, your answers depend on how you interpret the x-ray. You may
interpret an x-ray differently than one of your classmates, or you may even
interpret the same x-ray differently each time you look at it. That’s why
interpretations can introduce error into a measurement.
Doctors often rely on other medical professionals for second opinions. In this
section, you will consult with your classmates to compare both your measurements and your diagnoses.
6. In your class, what were the highest and lowest heart-to-chest ratios for
each patient? Record these values in the table on your Data Sheet.
7. Based on the class’s highest ratios, which patients have cardiomegaly?
8. Based on the class’s lowest ratios, which patients have cardiomegaly?
9. Why should you get a second opinion from a doctor on a diagnosis?
Relate your answer to what you have just learned from this activity.
Further Exploration
• Measure the area of the heart and chest cavity and determine the heartto-chest ratio using area measurements. Is this ratio also diagnostic of
cardiomegaly?
 Use the fi tool. See the
IPTechnique Sheets on
Selecting and Measuring.
• Nurses often put catheters into a patient’s vein to make it easier to give
medicine and to draw blood. Look at Paul’s x-ray. Note the catheter wire
on the upper right side of the image. How many others can you find in this
image?
catheter – a tube inserted in a
vein so the patient doesn’t
have to be poked every time
medication is needed.
• In Oliver’s x-ray, look for the dark mass in his right lung. This is a tube that
was inserted into his collapsed lung. What function might this tube
serve?
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HIP BIOLOGY 2
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.
Enlarged Heart
Name(s)
Data
Sheet
Class
Date
1. Fill in the table below with the names of the patients. Record your measurements as you go.
Patient
Maximum
width of
heart
Maximum
width of
chest
Heart-to-chest
ratio
Diagnosis
2. Calculate the heart-to-chest ratio in decimal form for Bill. Show your work in the space provided, and enter
the results in the table above.
3. Which patients have cardiomegaly? Record your diagnoses in the table above.
4. Enter Fran’s newest measurements in the table below, and calculate her heart-to-chest ratio based on these
values.
Remeasurement of Fran’s x-ray
Patient
Maximum
width of
heart
Maximum
width of
chest
Heart-to-chest
ratio
Diagnosis
5. Why were your answers different from the first time you measured Fran’s x-ray?
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.
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6. In your class, what were the highest and lowest heart-to-chest ratios for each patient? Record these values
below.
Patient
Highest ratio
in class
Lowest
ratio in class
7. Based on the class’s highest ratios, which patients have cardiomegaly?
8. Based on the class’s lowest ratios, which patients have cardiomegaly?
9. Why should you get a second opinion from a doctor on a diagnosis? Relate your answer to what you have
just learned from this activity.
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HIP BIOLOGY 2
© 1996 Arizona Board of Regents. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.