58
J. Kumar V. and K. A. Reddy
PPG has information on the arterial blood flow such as: heart rate, heart rate variability, respiration and blood pressure [17]. In Chaps. 1 and 2, it has been shown
that utilizing the slow varying component (due to venous blood) of a single wavelength PPG, diagnosis and monitoring of peripheral vascular haemodynamic and
venous dysfunction (thrombosis) can be achieved [18, 19]. In pulse oximetry, two
PPG signals, one obtained using a light source in the red wavelength region and the
other in the infrared region are employed to determine the level of oxygen saturation
in arterial blood non-invasively.
3.6.4 History of Pulse Oximetry
In 1935, Karl Matthes showed that using photoplethysmographs obtained at two
wavelengths, it is possible to track oxygen saturation [20]. He is now regarded as
the father of oximetry. He built the first device to continuously track blood oxygen
saturation in vivo by trans-illuminating the tissue. In this method, two wavelengths
of light, one in the red region and the other in the green region were used. Later
he switched to red and infrared light. Although this method was useful in following
the trends in oxygen saturation, calibrating the device to reduce errors in actual
measurements on oxygen saturation in arterial blood was very difficult. In 1942,
Millikan devised an instrument and coined the term “oximeter” to measure arterial
oxygen saturation from the ear of a pilot [21]. During World War II, his oximeter
was utilized to regulate the oxygen delivery system to help pilots flying at high
altitudes in pressurized cockpits. The ear oximeter proposed by Millikan could not
be calibrated, and one had to guess the normal saturation level for each person. Most
important subsequent works were performed by Goldie [22], Wood and Geraci [23],
that resulted in the improvement of Millikan’s ear oximeter. In 1949, Brinkman and
Zijlstra [24] were first to describe the monitoring of SaO 2 based upon skin reflectance
spectroscopy from the forehead, first in vitro, and then in-vivo. Their innovative idea
to use light reflection instead of tissue trans-illumination resulted in monitoring of
SaO 2 from virtually any part of the body. This was followed by a photoelectric
method proposed by Sekelj et al. [25] for SaO 2 determination. In 1960, Polanyi
and Hehir [26] developed the fibre optic catheter oximeter which is the basis for the
modern invasive oximeter. In 1964, a surgeon, Robert Shaw built a self-calibrating ear
oximeter, using eight wavelengths between 650 and 1050 nm, to identify and separate
Hb species including COHb and MetHb. In early 1970s, Hewlett-Packard improved
his method and released the first commercial eight-wavelength ear oximeter (HP
47201A). This oximeter delivered light via a fibre optic cable to a sensor mounted on
the ear and employed a heating element to keep the tissue locally perfused with blood.
Meanwhile, Cohen and Wardsworth added significant advancements in non-invasive
reflectance oximetry [27]. In 1972, Takuo Aoyagi, an engineer working with Nihon
Kohden Corporation in Tokyo, Japan, invented the present day two-wavelength pulse
oximetry [28]. Aoyagi while trying to develop a non-invasive method to determine
cardiac output using cardiogreen dye, measured light passing through the earlobe,
J. Kumar V. and K. A. Reddy
PPG has information on the arterial blood flow such as: heart rate, heart rate variability, respiration and blood pressure [17]. In Chaps. 1 and 2, it has been shown
that utilizing the slow varying component (due to venous blood) of a single wavelength PPG, diagnosis and monitoring of peripheral vascular haemodynamic and
venous dysfunction (thrombosis) can be achieved [18, 19]. In pulse oximetry, two
PPG signals, one obtained using a light source in the red wavelength region and the
other in the infrared region are employed to determine the level of oxygen saturation
in arterial blood non-invasively.
3.6.4 History of Pulse Oximetry
In 1935, Karl Matthes showed that using photoplethysmographs obtained at two
wavelengths, it is possible to track oxygen saturation [20]. He is now regarded as
the father of oximetry. He built the first device to continuously track blood oxygen
saturation in vivo by trans-illuminating the tissue. In this method, two wavelengths
of light, one in the red region and the other in the green region were used. Later
he switched to red and infrared light. Although this method was useful in following
the trends in oxygen saturation, calibrating the device to reduce errors in actual
measurements on oxygen saturation in arterial blood was very difficult. In 1942,
Millikan devised an instrument and coined the term “oximeter” to measure arterial
oxygen saturation from the ear of a pilot [21]. During World War II, his oximeter
was utilized to regulate the oxygen delivery system to help pilots flying at high
altitudes in pressurized cockpits. The ear oximeter proposed by Millikan could not
be calibrated, and one had to guess the normal saturation level for each person. Most
important subsequent works were performed by Goldie [22], Wood and Geraci [23],
that resulted in the improvement of Millikan’s ear oximeter. In 1949, Brinkman and
Zijlstra [24] were first to describe the monitoring of SaO 2 based upon skin reflectance
spectroscopy from the forehead, first in vitro, and then in-vivo. Their innovative idea
to use light reflection instead of tissue trans-illumination resulted in monitoring of
SaO 2 from virtually any part of the body. This was followed by a photoelectric
method proposed by Sekelj et al. [25] for SaO 2 determination. In 1960, Polanyi
and Hehir [26] developed the fibre optic catheter oximeter which is the basis for the
modern invasive oximeter. In 1964, a surgeon, Robert Shaw built a self-calibrating ear
oximeter, using eight wavelengths between 650 and 1050 nm, to identify and separate
Hb species including COHb and MetHb. In early 1970s, Hewlett-Packard improved
his method and released the first commercial eight-wavelength ear oximeter (HP
47201A). This oximeter delivered light via a fibre optic cable to a sensor mounted on
the ear and employed a heating element to keep the tissue locally perfused with blood.
Meanwhile, Cohen and Wardsworth added significant advancements in non-invasive
reflectance oximetry [27]. In 1972, Takuo Aoyagi, an engineer working with Nihon
Kohden Corporation in Tokyo, Japan, invented the present day two-wavelength pulse
oximetry [28]. Aoyagi while trying to develop a non-invasive method to determine
cardiac output using cardiogreen dye, measured light passing through the earlobe,