Question

A "pulse oximeter operates by using light and a photocell to measure oxygen saturation in arterial blood. The transmission of light energy as it passes through a solution of light-absorbing molecules is described by the Beer-Lambert law 

which gives the decrease in intensity I in terms of the distance L the light has traveled through a fluid with a concentration C of the light-absorbing molecule. The quantity ε is called the extinction coefficient, and its value depends on the frequency of the light. (It has units of m²/mol) Assume the extinction coefficient for 660-nm light passing through a solution of oxygenated hemoglobin is identical to the coefficient for 940-nm light passing through deoxygenated hemoglobin. Also assume that 940-nm light has zero absorption (ε=0) in oxygenated hemoglobin and 660-nm light has zero absorption in deoxygenated hemoglobin. If 32.2% of the energy of the red source and 77.9% of the infrared energy is transmitted through the blood, what is the fraction of hemoglobin that is oxygenated? 

Answer 1