# IDEA: Internet Differential Equations Activities

Image courtesy of Adam Hart-Davis/DHD Gallery

Cardizemtm is used in treating the symptoms of chronic angina and hypertension. As a calcium channel blocker, it is able to both increase the myocardial oxygen supply and decrease the body's demand for oxygen. It does this by lowering the heart rate and expanding the volume of the circulatory system, which leads to a lower blood pressure. Experiments show that the drug Cardizemtm (diltiazem hydrochloride) has a half life of 20 hours inside the human body. In our model the rate of change of Cardizemtm in the body is assumed to be proportional to the amount present.

Problem 1: Write a differential equation describing the rate of change of the quantity of Cardizemtm and determine the constant of proportionality.

Problem 2: Old man Withers receives Cardizemtm intravenously at a continuous rate of 4 mg/min. Write a differential equation describing the rate of change of the quantity of Cardizemtm and compute its solution assuming that there is no Cardizemtm initially present in old man Withers.

Problem 3: The fluid in the IV bag is emptied in two hours. How much Cardizemtm is in old man Withers's blood stream at that point?

Problem 4: Two hours after the bag is emptied, a nurse realizes he has forgotten to replace the bag. To make up for lost time, he triples the rate at which Cardizemtm is administered. He then puts up a larger bag that can feed Cardizemtm at this faster rate for up to 6 hours. He also leaves a note for the next nurse to turn down the rate of flow, but the note is swept off the counter by a breeze from the door after he leaves. The next nurse doesn't notice the note lying on the floor, so she doesn't check the rate of flow.

The lethal amount of Cardizemtm is 40 mg per kg of body mass. Determine if old man Withers will become old dead man Withers if he weighs 100 kg.

Hint: What differential equation describes the rate of change of Cardizemtm during the 2 hours without an IV? What about after the new IV is administered? It is helpful to take t=0 to be the initial time for each new differential equation and determine the quantity of Cardizemtm using the previous solution. Also take care to be consistent with your units of measure.

With the advent of HTML5, Javascript is now ready for prime time for mathematical applications. There are new Javascript demos illustrating how we might use interactive web objects to help students learn Calculus.

Department of Mathematics, PO Box 643113, Neill Hall 103, Washington State University, Pullman WA 99164-3113, 509-335-3926, Contact Us
This project is supported, in part, by the National Science Foundation. Opinions expressed are those of the authors, and not necessarily those of the Foundation.