A pulse oximeter differentiates oxyhemoglobin from deoxygenated hemoglobin by which of the following methods?
a. Relating cyclical changes in light transmis-sion through the sampling site.
b. Shining and comparing two wavelengths of light through the sampling site.
c. Direct measurement by a heated polaro-graphic electrode applied to the skin.
d. Using a color sensing device that absorbs one wavelength of light through the skin.
ANS: B
A pulse oximeter uses spectrophotometry to differentiate between oxyhemoglobin and deoxy-genated hemoglobin. Two wavelengths of light (660 and 940 nm) are shined through a sample site. Oxyhemoglobin absorbs more light at 940 nm (infrared [IR] light) than does deoxygenated hemoglobin. Deoxyhemoglobin absorbs more light at 660 nm. The use of cyclical changes in light transmission measured at the sampling site is the method to determine the pulse rate with a pulse oximeter. A heated polarographic electrode is used for transcutaneous partial pressure of oxygen (PtcO2) measurements. A color sensing device is used to detect the amount of carbon dioxide in exhaled gas.
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