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Pulse oximeter. Close-up of a pulse oximeter on the finger of an 81-year-old woman with COPD (chronic obstructive pulmonary disease). A pulse oximeter, also known as a blood oxygen meter, measures the pulse rate and oxygen concentration of the blood. It measures the oxygen concentration by measuring the absorption of light as it passes through the fingertip.(KEYSTONE/SCIENCE PHOTO LIBRARY SPL/DR P. MARAZZI/SCIENCE PHOTO LIBRARY)