Operation of the pulse oximeter (see previous problem).

Chapter 21, Problem 21.46

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Operation of the pulse oximeter (see previous problem). The transmission of light energy as it passes through a solution of light-absorbing molecules is described by the BeerLambert lawwhich gives the decrease in intensity I in terms of the distance L the light has traveled through a uid with a concentration C of the light-absorbing molecule. The quantity is called the extinction coefcient, and its value depends on the frequency of the light. (It has units of m2/mol.) Assume that the extinction coefcient for 660-nm light passing through a solution of oxygenated hemoglobin is identical to the coefcient for 940-nm light passing through deoxygenated hemoglobin. Assume also that 940-nm light has zero absorption ( 0) in oxygenated hemoglobin and 660-nm light has zero absorption in deoxygenated hemoglobin. If 33% of the energy of the red source and 76% of the infrared energy is transmitted through the blood, determine the fraction of hemoglobin that is oxygenated.