Cardiac Fringe!

seaddy@stfranciscollege.edu

I was staring at a sea of bewildered faces. I needed a quick way to illustrate the relationship between atherosclerosis and cardiovascular disease that did not require any advance planning or supplies.  So I used what I had on hand, I asked students to rip out a piece of notebook paper. Students with spiral notebooks were encouraged to share with their fringe-challenged, clean edge classmates.  Once everyone had a sheet of raggedly fringed paper, I instructed the class to tear the page along the perforation then roll the strip of fringe into a tight ball (emboli).  Moving quickly before students started flicking the balls of paper at each other, I then had the class roll the sheet of notebook paper into a tube the diameter of two fingers to simulate a blood vessel. This, I said holding up my tube, is a pristine blood vessel, very much like yours, notice the unobstructed lumen and how smooth the walls are. Students peered through their tubes, a few, anticipating what was to come, had already placed the ball of fringe in the tube. Realizing that I was at a critical juncture in the exercise – things can quickly degenerated into a spitball war-the class assured themselves that the ball rolled through the tube unobstructed. This, I said illustrates unobstructed blood flow through a vessel.

Now crimp (plaque buildup) the tube by gently squeezing down its length, put the ball back in the tube, try to get it pass all the way through the tube. Students  shake, tap and flick their pieces of paper to get the now stubborn ball to traverse the tube. This is an atherosclerotic vessel; blood has a much harder time squeezing past areas of plaque buildup.   Draw the analogy between the stuck ball of paper and a vessel obstructed by a emboli.

As a final demonstration  have students  put the ball at the mouth of the tube then tightly crimp their papers and then using a finger, try to straighten it out the crevices in the lumen. Now try to get the ball through the very rumpled tube – observe students and draw attention to anyone who tries to blow the ball through the tube (don’t worry someone always tries this – remember moments ago you almost had spitball mayhem on your hands). Ask the class to try the blow the ball through – the tube is usually too rumpled for this to work but you want them to experience how much pressure is required to try to move the ball. Ask the class what they think would happen if the ball is simply too big to fit through the tube. Most will tell you that the tube ruptures (aneurysm) as the pressure behind the blockage exceeds the elastic strength of the tube or pump fails (heart failure).  Summarize the activity by drawing parallels between the process of moving the ball through the tube and cardiovascular disease.