Abstract
Trauma is the number one cause of death for people between the ages 1 and 44 years in the United States. In
addition, according to the Centers of Disease Control and Prevention, injury results in over 31 million emergency
department visits annually. Minimizing the resuscitation period in major abdominal injuries increases survival rates by
correcting impaired tissue oxygen delivery. Optimization of resuscitation requires a monitoring method to determine
sufficient tissue oxygenation. Oxygenation can be assessed by determining the adequacy of tissue perfusion. In this
work, we present the design of a wireless perfusion and oxygenation sensor based on photoplethysmography. Through
optical modeling, the benefit of using the visible wavelengths 470, 525 and 590nm (around the 525nm hemoglobin
isobestic point) for intestinal perfusion monitoring is compared to the typical near infrared (NIR) wavelengths (805nm
isobestic point) used in such sensors. Specifically, NIR wavelengths penetrate through the thin intestinal wall (~4mm)
leading to high background signals. However, these visible wavelengths have two times shorter penetration depth that
the NIR wavelengths. Monte-Carlo simulations show that the transmittance of the three selected wavelengths is lower by
5 orders of magnitude depending on the perfusion state. Due to the high absorbance of hemoglobin in the visible range,
the perfusion signal carried by diffusely reflected light is also enhanced by an order of magnitude while oxygenation
signal levels are maintained. In addition, short source-detector separations proved to be beneficial for limiting the
probing depth to the thickness of the intestinal wall.
