Pulse oximetry: evolution and directions.

Pulse oximetry monitoring is a relatively recent technique that has been embraced enthusiastically by medical, nursing and paramedical personnel in many clinical situations. Few people, however, have any idea of how it provides the reading of arterial blood saturation. This review performs several functions: it discusses the haemoglobin molecular structure and explains its relation to spectrophotometry, describes the history and principles of pulse oximetry and the nature of the equipment used, and reviews its common uses. It also explores the principles and proposed uses of its lesser known corollary, photoplethysmography.