Pulse oximetry

Pulse oximetry estimates arterial blood oxygen saturation by measuring how red and infrared light pass through perfused tissue. It also reports pulse rate, but does not directly measure oxygen in blood.

Beer–Lambert law: A law relating light absorption to the properties of the absorbing material and the distance light travels through it. The device’s light measurements rely on absorption, though tissue scattering limits a simple direct application.
Hypoxemia: An abnormally low level of oxygen in arterial blood. A low saturation reading can signal hypoxemia and prompt further assessment.
Arterial blood gas test: A laboratory analysis of arterial blood that measures oxygen, carbon dioxide, and acidity. Unlike pulse oximetry, it directly measures arterial oxygen partial pressure and can assess blood chemistry.
Karl Matthes: A German physician who developed an early ear oximeter in the 1930s. His instrument established an early approach to estimating blood oxygen from transmitted light.
Arterial blood: Blood carried away from the heart through arteries. The estimate targets oxygen saturation in the arterial component of pulsatile blood.
Photoplethysmography: An optical method that detects changes in blood volume within tissue. Pulse oximeters isolate the pulsatile optical signal using this broader measurement technique.
Sleep apnea: A disorder in which breathing repeatedly stops or becomes shallow during sleep. Overnight oxygen trends can help detect breathing-related desaturation, though they do not diagnose apnea alone.
Co-oximetry: A laboratory method that measures multiple hemoglobin species using light absorption. It can distinguish abnormal hemoglobins that ordinary pulse oximeters may misread.
Glen Millikan: An American physiologist who coined the term “oximeter” and developed an aviation ear oximeter. His work helped shape optical oxygen measurement for monitoring pilots.
Hemoglobin: An iron-containing protein in red blood cells that transports oxygen and carbon dioxide. Pulse oximetry infers oxygen binding by analyzing hemoglobin’s wavelength-dependent absorption.

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