A \"pulse oximeter\" operates by using light and a photocell tomeasure oxygen saturation in arterial blood. The transmission oflight energy as it passes through a solution of light-absorbingmolecules is described by the Beer-Lambert law
I = I010−εCL or log10II0= −εCL,
which gives the decrease in intensity I in terms of the distanceL the light has traveled through a fluid with a concentration C ofthe light-absorbing molecule. The quantity ε is called theextinction coefficient, and its value depends on the frequency ofthe light. (It has units of
m2/mol)>
Assume the extinction coefficient for 660-nm light passingthrough a solution of oxygenated hemoglobin is identical to thecoefficient for 940-nm light passing through deoxygenatedhemoglobin. Also assume that 940-nm light has zero absorption (ε =0) in oxygenated hemoglobin and 660-nm light has zero absorption indeoxygenated hemoglobin. If 32.8% of the energy of the red sourceand 76.5% of the infrared energy is transmitted through the blood,what is the fraction of hemoglobin that is oxygenated?
= %
