Make a Conjecture

9-12
1

Doctors and veterinarians are interested in a quantity called the "cardiac output" which is a measure of the rate of blood flow being pumped by the heart. To measure the cardiac output, a catheter (tube) is inserted through the heart. The catheter measures the temperature of the surrounding blood near the tip of the probe. The catheter has a small balloon at the tip which is inflated to help the probe move through the heart and then deflated. Once the catheter is inserted, ice water is injected through the catheter and emerges from a small hole approximately 12 inches before the end of the catheter.

How can the blood flow be measured by injecting ice waterand measuring the temperature?

 X-rayof a catheter inserted in a dog Fluoroscope movie of a catheter being inserted into a dog*

Based on the discussion above, the picture and the movie above, answer the following questions about measuring cardiac output.

1. How will the temperature change as ice water is injected? Sketch a possible graph of the (time, temperature) relationship that you described.
2. What does the change in temperature tell you about the amount of ice water in the blood stream?
3. How would your temperature graph differ for a fast blood flow rate compared to a slow blood flow rate?
4. How do you think that the (time, temperature) data might be used to determine the rate of flow?
• Computer and Internet connection
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Gather Data

9-12

A simple experiment which can be used to model the cardiac output measurement using a catheter can be constructed using:

• an aquarium pump
• a temperature probe
• a bucket
• tube with a port for injecting ice water
• syringe and valve
• data collection device such as a CBL.

The pump and tubing is available at most aquarium stores and many home improvement stores. The syringe and valve port are available through science supply stores. The temperature probe that comes with the CBL is sufficient.

Analyze the Data

9-12
Students will analyze and graph the data taken.