OBJECTIVE
This activity page will offer:

• A lab experience during which students explore the relationship between pressure and vessel diameter
• A model that represents how elevated blood pressure may affect weakened vessels
• An open-ended design challenge in which students engineer their own remote repair device

MATERIALS

• Clean drinking straws
• waterproof clay
• paperclip
• scissors
• clear plastic soda container
• tape
• paper towels/sponges

Part 1- Vessel Flow

Proceedure

In this program, you learned how changes in the diameter of a vessel can affect the flow of moving blood. Vessels that become obstructed or constricted offer more resistance to the movement of fluid. This may cause blood to backup or the pressure to build to damaging levels. In this activity, you'll explore models that represent normal and constricted blood vessels. You'll also observe how a build-up of pressure may affect a weakened vessel wall.

1. Work with a partner. Fill a plastic container 2/3 full of water.
2. Insert a clean straw about halfway down the container's length measured from the bottom of the vessel to its top. Although the exact depth isn't critical, it is important that you remember this depth and restrict it as a controlled variable. Therefore, use a piece of tape to mark this depth on the outside of the container. Make sure the tape is even with the lower edge of the straw.
3. One team member blows into the straw with a steady air stream that produces about a continual stream of bubbles. Describe the blowing effort needed to produce this steady, but non-violent stream of bubbles.
4. Completely pack the end of a second straw with a bean-sized lump of clay.
5. Unbend a paperclip and use it to poke a small hole through the clay plug.
6. Insert this straw to the depth marked in step 2. Again, blow a steady air stream into the straw. How does the effort compare to when the passageway was larger? Does the appearance of the bubble stream change? How?Don't throw these straws away. You'll reuse them in Part 2.
7. Switch roles with your partner. Make sure to use two new straws when you repeat the above steps.

Questions

1. What did the clay represent?
2. What happens when the clay constricts the flow of air?
3. How did you compensate to maintain the steady bubble rate?
4. Why was the depth of the straw marked and kept constant throughout the activity?

PART 2 - Wall Weakness

Under excessive pressure, blood vessels can burst open with fatal consequences. Often, this rip occurs in a region of the vessel that has been weakened or damaged. In this next activity, you'll model how an increase of pressure can stress a vessel beyond its limits. Before you start on the hands-on part of this next activity, let's engage some of your minds-on skills. From what you have learned both in and out of the classroom, answer the questions below.

Questions

1. What physical properties are essential in materials used to build both water pipes and organic vessels?
2. You have been asked to build a water pipe. Rate the following materials based upon their ability to withstand water pressure. wood, plastic, copper, modeling clay,
3. Suppose you were patching a bicycle tire. How would the composition of the patch material affect the long-term success of your repair job?
   
   

Proceedure

1. Make sure that all straws to be used in this activity are completely dry. Both partners should use scissors to make a "v" snip about 2/3 of the way up the length of the two straws you each used in the previous activity. The hole should be about the same size in all straws.
2. Take four pea-sized lumps of clay and flatten each one out into a thin, rectangular clay patch that is large enough to form a "collar" around the straw.
3. Lay the patch on a flat surface. Position the straw's hole above the middle of the patch. Lightly press the straw against the patch and roll it so that the patch forms a complete "collar" around that section of the straw. Make sure that the clay sticks to the straw's surface and that the seal has no observable leaks.
4. First, test the straw that is unobstructed (no inner plug). Take turns inserting your straws into the water-filled container. Make sure that the patch remains above the water level. Start blowing. What happens?
5. Now, take turns testing the obstructed straw. Insert the clay-plugged end into the water filled container. Keep the patch above the water level. Start blowing. What happens?
   
   

Critical Analysis of Your Model

Consider the following questions and discuss them based on the above activity.

1. In your model, what does the plastic straw represent?
2. What does the flattened clay seal represent?
3. How can the experience above be applied to the obstruction/constriction of blood vessels?
4. Why does the seal rupture when air is blown through the plugged straw?

Think About It
Why did surgeons in the television program position the pressure release hole within the heart? Wouldn't it be safer and easier to locate (and later repair) this hole if it was positioned outside the heart?

Sharing Alan's Magic

You've seen the trick before. A magician taps a wand and presto! Flowers seem to materialize out of thin air. In this segment, Alan commented that loading the metal seal reminded him of the magic flower trick he performed as a child. With what you now know about the seal's action, can you figure out what Alan meant? If so, draw a blueprint for a both the magic wand and the appearing flowers. The blueprint should illustrate and explain how a bouquet can appear almost instantly from the tip of the wand.

Design Challenge

In this show, you observed an invention that is used to close a small by-pass opening in a human vessel. His device used a spring-loaded seal that opened and attached to all sides of the opening, almost completely filling the hole. When the delivery line was removed, the seal remained firmly in place offering a substrate on which living cells would soon grow and fill the hole entirely.

Suppose a house has a water hose buried in its front yard and it suddenly ruptures. Digging up the hose up to repair it will be extremely costly. You have been asked to create a remote sealing device that was used to plug the hole. What type of seal would you create? How would this be loaded into a buried hose? What action would trigger the patch to open and plug the leak?

Research how holes in garden hoses and water pipes are plugged. Decide on a sealing method. T hen, create a blueprint for your remote delivery system. Share it with other class members and invite suggestions to improve the design. With your instructor's approval, construct this device. Test your apparatus in a section of garden hose or within a piece of 1" thick plastic tubing, and evaluate its effectiveness. Keep improving your design until you've created the best remote sealing device.

Web Connection

Children and Heart Disease
General information on the heart and its disorders from the American Heart Association

The Children's Heart Institute
This site offers some great visuals using a building floor plan analogy to illustrate the movement of blood in various heart disorders.

The activities in this guide were contributed by Michael DiSpezio, a Massachusetts-based science writer and author of "Critical Thinking Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing Co., NY).

Academic Advisors for this guide
Corrine Lowen, Science Department, Wayland Public Schools, Wayland, MA
Suzanne Panico, Science Department, Fenway High School, Boston, MA

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