Ninety years of pulse oximetry: history, current status, and outlook.

Significance: This year, 2024, marks the 50th anniversary of the invention of pulse oximetry (PO), which was first presented by Takuo Aoyagi, an engineer from the Nihon Kohden Company, at the 13th Conference of the Japanese Society of Medical Electronics and Biological Engineering in Osaka in 1974. His discovery and the development of PO for the non-invasive measurement of peripheral arterial oxygenation represents one of the most significant chapters in the history of medical technology. It resulted from research and development efforts conducted by biochemists, engineers, physicists, physiologists, and physicians since the 1930s. Aim: The objective of this work was to provide a narrative review of the history, current status, and future prospects of PO. Approach: A comprehensive review of the literature on oximetry and PO was conducted. Results and Conclusions: Our historical review examines the development of oximetry in general and PO in particular, tracing the key stages of a long and fascinating story that has unfolded from the first half of the twentieth century to the present day-an exciting journey in which serendipity has intersected with the hard work of key pioneers. This work has been made possible by the contributions of numerous key pioneers, including Kurt Kramer, Karl Matthes, Glenn Millikan, Evgenii M. Kreps, Earl H. Wood, Robert F. Show, Scott A. Wilber, William New, and, above all, Takuo Aoyagi. PO has become an integral part of modern medical care and has proven to be an important tool for physiological monitoring. The COVID-19 pandemic not only highlighted the clinical utility of PO but also revealed some of the problems with the technology. Current research in biomedical optics should address these issues to make the technology even more reliable and accurate. We discuss the necessary innovations in PO and present our thoughts on what the next generation of PO might look like.

The History of Home Cardiorespiratory Monitoring.

Home cardiorespiratory monitoring has changed significantly since it was first introduced in the 1970s. It has improved from a simple alarm system to a sophisticated piece of equipment capable of monitoring the patient's electrocardiogram, respiratory effort, and oxygen saturations. In addition, the indications for using a monitor have also changed. The home monitor was initially used to reduce the incidence of sudden infant death syndrome (SIDS). Although there were several studies demonstrating the reduction of SIDS rates in communities where apnea programs existed, none was a prospective, double-blinded study or had adequate numbers to be clinically significant. Therefore, the American Academy of Pediatrics took the stance that monitors were not an effective way to reduce SIDS. However, when used appropriately, as part of a complete program (ie, the monitor is just one of many clinically based modalities), by a clinician with expertise in interpreting download tracings, home cardiorespiratory monitoring can be a useful, lifesaving, and economical tool to observe infants who are at increased risk of sudden death or increased morbidity secondary to intermittent hypoxia. [Pediatr Ann. 2017;46(8):e303-e308.].

Beat to Beat: A Measured Look at the History of Pulse Oximetry.

It can be argued that pulse oximetry is the most important technological advancement ever made in monitoring the well-being and safety of patients undergoing anesthesia. Before its development, the physical appearance of the patient and blood gas analysis were the only methods of assessing hypoxemia in patients. The disadvantages of blood gas analysis are that it is not without pain, complications, and most importantly does not provide continuous, real-time data. Although it has become de rigueur to use pulse oximetry for every anesthetic, the road leading to pulse oximetry began long ago.

Is pulse oximetry an essential tool or just another distraction? The role of the pulse oximeter in modern anesthesia care.

Since the discovery of anesthetic agents, patient monitoring has been considered one of the core responsibilities of the anesthesiologist. As depicted in Robert Hinckley's famous painting, The First Operation with Ether, one observes William Thomas Green Morton carefully watching over his patient. Since its founding in 1905, 'Vigilance' has been the motto of the American Society of Anesthesiologists (ASA). Over a hundred years have passed, and one would think we would be clear regarding what we are watching for and how we should be watching. On the contrary, the introduction of new technology and outcome research is requiring us to re-examine our fundamental assumptions regarding what is and what is not important in the care of the patient. A vast majority of anesthesiologists would refuse to proceed with an anesthetic without the presence of a pulse oximeter. On the other hand, outcome studies have failed to demonstrate an improvement in patient care with their use. For that matter, it can be argued that outcome studies have yet to demonstrate an unambiguous role for any monitor of any type (i.e. blood pressure cuff or ECG), as outcome studies may fail to capture rare events. Because of the increased safety that has been attributed to pulse oximetry, it is unlikely that further studies can or will be conducted. As we enter a new era of clinical monitoring, with an emphasis on noninvasive cardiovascular monitoring, it might be of benefit to examine the role of the pulse oximeter in clinical care. This article reviews the available evidence for pulse oximetry. Further, it discusses contemporary issues, events, and perceptions that may help to explain how and why pulse oximetry may have been adopted as a standard of care despite the lack of supportive. Lastly, it discusses less obvious benefits of pulse oximetry that may have further implications on the future of anesthesia care and perhaps even automated anesthesia.

Monitoring oxygenation.

Cyanosis was used for a century after dentists began pulling teeth under 100% N(2)O in 1844 because brief (2 min) severe hypoxia is harmless. Deaths came with curare and potent anesthetic respiratory arrest. Leland Clark's invention of a polarographic blood oxygen tension electrode (1954) was introduced for transcutaneous PO2 monitoring to adjust PEEP and CPAP PO2 to prevent premature infant blindness from excess O2 (1972). Oximetry for warning military aviators was tried after WW II but not used for routine monitoring until Takuo Aoyagi (1973) discovered an equation to measure SaO2 by the ratio of ratios of red and IR light transmitted through tissue as it changed with arterial pulses. Pulse oximetry (1982) depended on simultaneous technology improvements of light emitting red and IR diodes, tiny cheap solid state sensors and micro-chip computers. Continuous monitoring of airway anesthetic concentration and oxygen also became very common after 1980. Death from anesthesia fell 10 fold between 1985 and 2000 as pulse oximetry became universally used, but no proof of a causative relationship to pulse oximetry exists. It is now assumed that all anesthesiologist became much more aware of the dangers of prolonged hypoxia, perhaps by using the pulse oximeters.

History of technology in the intensive care unit.

Critical care medicine is a young specialty and since its inception has been heavily reliant upon technology. Invasive monitoring has its humble beginnings in the continuous monitoring of heart rate and rhythm. From the development of right heart catheterization to the adaption of the echocardiogram for use in shock, intensivists have used technology to monitor hemodynamics. The care of the critically ill has been buoyed by investigators who sought to offer renal replacement therapy to unstable patients and worked to improve the monitoring of oxygen saturation. The evolution of mechanical ventilation for the critically ill embodies innumerable technological advances. More recently, critical care has insisted upon rigorous testing and cost-benefit analysis of technological advances.

History of measuring O2 and CO2 responses.

Quantitative analysis of the chemical interactions of CO2 and O2 on ventilation from early 20th century to the present start with the amazingly steep CO2 response found by Haldane and his pupils, proceed through discovery of the prime role of the H+ ion and the discovery of carotid body chemoreception. The interaction of central and peripheral drives and changes with time and acute and chronic altitude exposure are still under investigation.

Takuo Aoyagi: discovery of pulse oximetry.

In the 1930s and 1940s, photo cells permitted German, English, and American physiologists to construct ear oximeters with red and infrared light, requiring calibration. In 1940 Squire recognized that changes of red and infrared light transmission caused by pneumatic tissue compression permitted saturation to be computed. In 1949 Wood used this idea to compute absolute saturation continuously from the ratios of optical density changes with pressure in an ear oximeter. In 1972 Takuo Aoyagi, an electrical engineer at Nihon Kohden company in Tokyo, was interested in measuring cardiac output noninvasively by the dye dilution method using a commercially available ear oximeter. He balanced the red and infrared signals to cancel the pulse noise which prevented measuring the dye washout accurately. He discovered that changes of oxygen saturation voided his pulse cancellation. He then realized that these pulsatile changes could be used to compute saturation from the ratio of ratios of pulse changes in the red and infrared. His ideas, equations and instrument were adapted, improved and successfully marketed by Minolta about 1978, stimulating other firms to further improve and market pulse oximeters worldwide in the mid 1980s. Dr. Aoyagi and associates provided a detailed history for this paper.

Multiwavelength pulse oximetry: theory for the future.

BACKGROUND: As the use of pulse oximeters increases, the needs for higher performance and wider applicability of pulse oximetry have increased. To realize the full potential of pulse oximetry, it is indispensable to increase the number of optical wavelengths. To develop a multiwavelength oximetry system, a physical theory of pulse oximetry must be constructed. In addition, a theory for quantitative measurement of optical absorption in an optical scatterer, such as in living tissue, remains a difficult theoretical and practical aspect of this problem. METHODS: We adopted Schuster's theory of radiation through a foggy atmosphere for a basis of theory of pulse oximetry. We considered three factors affecting pulse oximetry: the optics, the tissue, and the venous blood. RESULTS: We derived a physical theoretical formula of pulse oximetry. The theory was confirmed with a full SO2 range experiment. Based on the theory, the three-wavelength method eliminated the effect of tissue and improved the accuracy of Spo2. The five-wavelength method eliminated the effect of venous blood and improved motion artifact elimination. CONCLUSIONS: Our theory of multiwavelength pulse oximetry can be expected to be useful for solving almost all problems in pulse oximetry such as accuracy, motion artifact, low-pulse amplitude, response delay, and errors using reflection oximetry which will expand the application of pulse oximetry. Our theory is probably a rare case of success in solving the difficult problem of quantifying optical density of a substance embedded in an optically scattering medium.

[The history of oximetry].

Presently, pulsoximeters are very common devices used in every surgical operation. Unique properties of pulsoximeter (safety, accuracy, and efficiency) enable physician to monitor oxygen-transporting function of blood, which is a vitally important function of human body. The history of pulsoximetry dates back to several generations ago, researchers of many countries being involved in the invention of this device. The idea of pulsoximetry has been updated at each stage of technological progress. The history of pulsoximetry illustrates progressively increasing importance of spectrophotometric method in medicine and its perspectives for the future.