The concept of pulse-oximetry is based on the Beer-Lambert law, which states that the concentration of an unknown solute in a solvent can be determined by light absorption i.e.
L (out) = L (in) - (D.C.a)
where, L = Intensity of light
C= concentration of solution
D = distance the hight travels through the solution
a = absorption coefficient of solute.
As we are interested in whether oxygen is attached to haemoglobin or not, the relevant solutes are oxyhaemoglobin and reduced heamoglobin. The absorption characteristics of these two are at two different wavelengths of 940 nm (infared) and 660 nm (red) respectively (i.e.). Reduced heamoglobin
absorbs more red than infrared light and oxygenated haemoglobin absorbs more infrared than red.
Q. pulse oximeter works on the following principal:
a) Beer Lambert's law
b) Raman scattering effect
c) Venturi principle
d) Mass spectrometry
Ans: a.
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