The pulse oximeter is a common medical device in healthcare settings. It non-invasively monitors oxygen levels, providing insights into respiratory and circulatory health. This small, clip-like device, often seen on a finger, impacts patient care by offering immediate and continuous feedback.
Understanding the Pulse Oximeter
A pulse oximeter measures peripheral oxygen saturation (SpO2) in the blood. This measurement indicates the percentage of hemoglobin in red blood cells that is carrying oxygen. It also displays the patient’s pulse rate. It assesses how efficiently blood transports oxygen to the body’s extremities.
Medical professionals use these devices to monitor individuals with conditions affecting blood oxygen levels, such as COPD, asthma, or pneumonia. Its non-invasive nature and ease of use make it suitable for various environments, from hospitals to home monitoring.
The Groundbreaking Invention
Takuo Aoyagi, an electrical engineer at Nihon Kohden in Japan, discovered the fundamental principle behind the modern pulse oximeter. In 1974, Aoyagi was researching a non-invasive method to measure cardiac output using dye dilution. During experiments, he observed oxygen saturation changes interfered with measurements while canceling pulsatile noise. This led him to realize pulsatile changes could calculate oxygen saturation.
Aoyagi’s initial work balanced red and infrared signals to eliminate pulse noise that hindered accurate dye washout measurements. He recognized variations from blood pulsation could determine oxygen saturation. This insight, detailed in his 1974 patent, laid the theoretical foundation for pulse oximetry. Nihon Kohden introduced their first ear pulse oximeter in 1975. Minolta, with Akio Yamanishi’s group, developed the first fingertip pulse oximeter around the same time, leveraging new LED technology.
The Science Behind the Measurement
The pulse oximeter operates on the principle that oxygenated and deoxygenated hemoglobin absorb light differently. It uses two light-emitting diodes (LEDs): one emits red light (around 660 nm) and the other infrared light (around 940 nm). These lights pass through a translucent body part, like a fingertip or earlobe, to a photodetector.
Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through, while deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass. The photodetector measures the light that passes through the tissue. By analyzing the ratio of light absorption at these wavelengths, the oximeter’s processor calculates the percentage of hemoglobin saturated with oxygen. The “pulse” in pulse oximetry refers to the device’s ability to isolate the arterial blood signal by detecting pulsatile changes in blood volume with each heartbeat, filtering out signals from venous blood and other tissues.
Transforming Patient Care
The pulse oximeter has profoundly impacted medical practice and patient safety. It rapidly became a standard monitoring tool across healthcare settings, from operating rooms and intensive care units to emergency departments and home care. Its continuous, real-time oxygen saturation readings allow healthcare providers to quickly detect and respond to drops in blood oxygen levels, known as hypoxemia.
Often called the “fifth vital sign,” the pulse oximeter assesses respiratory function and guides clinical decisions. It evaluates respiratory treatments, determines the need for supplemental oxygen, and monitors patients during and after surgical procedures. This widespread adoption has reduced unrecognized oxygen desaturation, contributing to improved patient outcomes and enhanced safety protocols.