♈️#PhysicsForAnesthesiologist : Beer-Lambert Law

☢️The #pulseoximeter works based on Beer-Lambert law, which relates the attenuation of light to the properties of the material through which the light is travelling. 
☢️It helps us in the calculation of the absorbance of a solution.
☢️According to the law, the absorbance of a solution depends on:
🖍The concentration of that solution, i.e. the more molecules of a light-absorbing compound there are in the sample, the more light will be absorbed. 
🖍The path-length of light travelling through the solution, i.e. the longer the length of the sample container, the more light will be absorbed because the light will come into contact with more molecules.
🖍A = εlc where 
🔻A is absorbance of light
🔻ε is the molar extinction coefficient(l mol–1 cm–1). It compensates for variance in concentration and the path-length, to allow comparison between solutions. 
🔻l is the length of solution that the light passes through. 
🔻c is the concentration of the compound in solution, expressed in mol L–1
☢️In the pulse oximeter, the concentration and molar extinction coefficient are constant. The only variable becomes the path length, which alters as arterial blood expands the vessels in a pulsatile fashion.
#Anesthesia, #PhysicsAndMedicine , #MedicalExams 

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