Cardiac Output, Rates of Change, and Accumulation

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.

Use a large bucket with several gallons of water at room temperature.

The more water used the less effect the ice water will have on the base (ambient) temperature.

Thread the temperature probe into the end of the tube approximately 8-10 inches.

Insert the valve port approximately 1.5 - 2 feet before the temperature probe's location.

Keep the syringe and ice water in the ice bath as long as possible before injecting.

Inject 30 cc (0.030 liters) of ice water (0° C) at a slow and consistent pace.

A general rule of thumb is to inject the ice water over a period of about 5 seconds using as smooth and constant pressure as possible on the syringe.

Collect data approximately every 0.5 seconds for about 30 seconds or until the temperature returns to the ambient temperature.

Usually aquarium pumps have a variable flow rate. You should also measure the flow rate by measuring the time to pump a liter.

Click here for additional images of the set-up or to see a movie of students collecting data using a slightly different setup. Record your data in a table such as: Ambient Water Temperature: Flow Rate Measured using liter container: Amount of Ice Water Injected: Time Temp.   Time Temp.   Time Temp.                                                                           Observations:

Look for Patterns Using your data or the sample data, graph the temperature as a function of time. Based on the data and the graph, answer the following questions. Does the graph match your conjectures? In what ways are they similar? different?    While doing the experiment, what factors do you think might influence the results?   In this experiment and in the case of humans and animals, a mixture of two fluids is being pumped. What would the data look like if the mixture was 100% ice water? 0% ice water? 50% ice water?   Over each 0.5 second time interval, a mixture of regular water and ice water is being pumped. How would you calculate the percentage of ice water (concentration of the ice water)?

NCTM Standards and Expectations

Data Analysis & Probability 9-12 Use simulations to construct empirical probability distributions. Understand the meaning of measurement data and categorical data, of univariate and bivariate data, and of the term variable.

References

Cornette, J., Ackerman, R., Keller, B. and G. Johnston (2000), Calculus for the Life Sciences, draft manuscript, to be published by Prentice Hall. Ware, Wendy (1999). Fluoroscope of Cardiac Output being measured in a canine, Iowa State University, College of Veterinary Medicine, Ames, Iowa Cornette, J., Ackerman, R., Keller, B. and G. Johnston (2000), Calculus for the Life Sciences, draft manuscript, to be published by Prentice Hall.