We developed a simulated pulse-oximetry device (pulse-ox), a medical apparatus capable of measuring a patient’s oxygen content. The pulse-ox measures attenuation of light at two distinct wavelengths after passing through tissue, blood, and bone to measure oxygen present in a patient’s blood. The simulated device uses bromothymol blue, a common pH indicator, as a blood analog. Simply breathing on a solution of bromothymol blue will introduce carbon dioxide from your breath into the solution. The CO2 reacts with the solution to form carbonic acid which increases the acidity of the solution. As the pH of the solution changes, the color of the solution also changes. In this lab, students examine the change both visually and with a spectrophotometer linking observations to the spectral characterisitics of deoxygenated and oxygenated blood as measured by a pulse-oximeter.
Published Ellynne Kutschera, Justin C. Dunlap, Misti Byrd, Casey Norlin, and Ralf Widenhorn, "Pulse Oximetry in the Physics Lab: A Colorful Alternative to Traditional Optics Curricula," Phys. Teach. Vol. 51, Issue 8, 495 (2013).