Glenn Allan Millikan

Glenn Allan Millikan

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Glenn Allan Millikan American physiologist, invented the first practical, portable pulse oximeter
Pulse oximeter
A pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient's blood and changes in blood volume in the skin, producing a photoplethysmograph. It is often attached to a medical monitor so staff can see a patient's oxygenation at all times...

 in 1940–1942. The Millikan oximeter "is generally acknowledged as the beginning of oximetry
Pulse oximetry
Pulse oximetry is a non-invasive method allowing the monitoring of the oxygenation of a patient's hemoglobin.A sensor is placed on a thin part of the patient's body, usually a fingertip or earlobe, or in the case of an infant, across a foot....

 in physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 and clinical medicine." The word oximeter was introduced by Millikan.

Millikan, son of physicist Robert Andrews Millikan, studied at the Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...

 and the University of Cambridge
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...

. During his doctorate studies in Cambridge he built a dual-wavelength colorimeter
For articles on Colorimeter see:* Colorimeter * Tristimulus colorimeter...

 for blood oxygen level
Blood oxygen level
Blood oxygen level is a term referring to the concentration of oxygen in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood....

 measurements. The Fellowship of Trinity College
Trinity College, Cambridge
Trinity College is a constituent college of the University of Cambridge. Trinity has more members than any other college in Cambridge or Oxford, with around 700 undergraduates, 430 graduates, and over 170 Fellows...

 awarded Millikan a four-year scholarship for this work. The award allowed Millikan to continue research of myoglobin
Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 reactions in Cambridge until 1937. After the outbreak of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 Millikan was stranded in the United States. Unable to return to Cambridge, he accepted an unpaid laboratory appointment at the University of Pennsylvania
University of Pennsylvania
The University of Pennsylvania is a private, Ivy League university located in Philadelphia, Pennsylvania, United States. Penn is the fourth-oldest institution of higher education in the United States,Penn is the fourth-oldest using the founding dates claimed by each institution...

 and concentrated on bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...

 research. Later, he obtained teaching assignments at the University of Pennsylvania and at Harvard.

In the spring of 1940 Lord Adrian
Edgar Adrian, 1st Baron Adrian
Edgar Douglas Adrian, 1st Baron Adrian OM PRS was a British electrophysiologist and recipient of the 1932 Nobel Prize for Physiology, won jointly with Sir Charles Sherrington for work on the function of neurons....

, Millikan's former advisor at Camridge, asked Millikan to help the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 with the development of a reliable breathing apparatus. According to Adrian, pilots regularly lost consciousness during high-altitude dogfight
A dogfight, or dog fight, is a form of aerial combat between fighter aircraft; in particular, combat of maneuver at short range, where each side is aware of the other's presence. Dogfighting first appeared during World War I, shortly after the invention of the airplane...

s, and needed "an oxygen delivery system with a demand valve responsive to altitude and activity". Millikan built the device for monitoring the state of pilot's organism in flight (the Millikan oximeter) in 1940 and presented it to the American Physiological Society
American Physiological Society
The American Physiological Society was founded in 1887 with 28 members. Of them, 21 were graduates of medical schools, but only 12 had studied in schools that had a professor of physiology. Today, the APS has 10,500 members, most of whom hold doctoral degrees in medicine, physiology or other...

 in 1941. The oximeter was integrated into the pilot's altitude mask and had to be clasped to the earlobe
The human earlobe is composed of tough areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the pinna. Since the earlobe does not contain cartilage it has a large blood supply and may help to warm the ears and maintain balance. However earlobes are not...

. The oxygen supply system, developed by Bendix Corporation
Bendix Corporation
The Bendix Corporation was an American manufacturing and engineering company which during various times in its 60 year existence made brake systems, aeronautical hydraulics, avionics, aircraft and automobile fuel control systems, radios, televisions and computers, and which licensed its name for...

, relied on the oximeter as the primary sensor in its feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...


The earpiece of Millikan's oximeter (an open photocell-lamp assembly manufactured commercially by Coleman Electric) contained an incandescent light bulb
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

, a set of red and green filters, and a selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 barrier level photocell
A photoresistor or light dependent resistor is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor or CdS device, from "cadmium sulfide," which is the material from which the device is made and that actually exhibits the...

. According to Millikan's early statements, light absorbance of green light was independent of blood oxygen level, absorbance of red light depended on it. However, in 1942 it was found that the flesh of human ear absorbs almost all green light. "Green light" sensed by Millikan's photocell was actually invisible infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 light emitted by the lamp and unaffected by green filter.

Millikan's wartime work outlined three basic problems of oximetry: absence of suitable theory
The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...

, inability to differentiate between blood and other tissues in the path of light, and inability to differentiate between arterial, venous and capillary blood, of which only arterial blood was relevant to oxygen measurement. Millikan's own solution to these challenges were poor. The third problem was solved by "fully flushing" the earlobe by heating it with the lightbulb. The second one was not an issue in RAF breathing sets because they supplied pure oxygen. Calibration of the device for a patient breathing pure oxygen was quite straightforward.

In 1938 Millikan married Clare Leigh Mallory, daughter of George Mallory
George Mallory
George Herbert Leigh Mallory was an English mountaineer who took part in the first three British expeditions to Mount Everest in the early 1920s....

, the mountaneer who died while climbing Mount Everest
Mount Everest
Mount Everest is the world's highest mountain, with a peak at above sea level. It is located in the Mahalangur section of the Himalayas. The international boundary runs across the precise summit point...

. In 1947 Millikan himself was killed while climbing the Cumberland Mountains
Cumberland Mountains
The Cumberland Mountains are a mountain range in the southeastern section of the Appalachian Mountains. They are located in southern West Virginia, western Virginia, eastern edges of Kentucky, and eastern middle Tennessee, including the Crab Orchard Mountains...

. After his death his parents sponsored a series of Glenn Millikan lectures at Vanderbilt University
Vanderbilt University
Vanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...

 where Millikan worked for the last year of his life.