Demo V: Flow - Volume Plot

This interactive diagram shows how adding an element of time to an otherwise static plot can help students better comprehend an oft-used clinical tool. The diagram illustrates the Flow-Volume Plot, something that doctors see "virtually every day" on the hospital floor, says Dr. Michael Parker. The plot relates the flow of air to the volume of air being breathed in or out. As a visual tool, the diagram also shows an animation of a patient taking a Forced Vital Capacity test, which requires that a patient take a deep breath and then exhale fast and hard until he has breathed out as much as he can. This is also a very useful diagnostic test in pinpointing diseases such as emphysema.

The center of this diagram shows an old-fashioned water-spirometer, which Dr. Parker says is a useful visual, even though it's not exactly what would be used today in a hospital. There is a picture of a patient to the right, breathing into the spirometer. On the far left, the spirometer is attached to a pen and rotating paper drum, which will trace the patient's breath patterns once the animation begins. Just to the left of that tracing paper, there is a graph that helps explain different troughs and peaks marked onto the paper. The Flow-Volume Plot is in the upper left-hand corner. In addition, the picture of the patient on the right side of the screen includes drawn arrows that represent the forces on the lung and chest walls while the patient is breathing.

At the bottom of the screen is a button marked "Show FVC." When a student presses this button, the animation of the Forced Vital Capacity test begins. In real-time, students can watch the movement of the patient's lungs rising and falling, they can watch the tracings on the paper drum, and they can watch the Flow-Volume Plot as it is drawn. Students can also pause the animation at any moment in order to see, for example, what percentage of air was exhaled in one second. "If we were just looking at a standard image of the plot," says Dr. Parker, "there's no way you could figure out how much time had passed. There's no time axis." But because the diagram is dynamic, students can get a sense for how the Flow-Volume loop relates to time.

Key Lesson: This module helps students correlate multiple aspects of lung function and a patient's breathing, while visualizing them in real time.