How Pulse Oximetry Works

A pulse oximeter is a noninvasive means of measuring both pulse rate and the arterial oxygen saturation of hemoglobin at the peripheral capillary level. It consists of a portable monitor and a photoelectric sensing probe that clips onto the patient’s finger, toe or earlobe.

The photoelectrical sensing probe measures the amount of red and infrared light being absorbed as arterial oxygen reaches the capillary beds during systole, when more light is absorbed, and diastole, when less light is absorbed.

The monitor calculates the time between the peaks of light absorption and displays a pulse rate in beats per minute. It also calculates a value based on the ratio of light absorbed at systole and diastole to display a peripheral oxygen saturation percentage (SpO2).