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Bioelectromagnetism

Oxygen concentration of erythrocyte in the artery is an important marker showing condition of

respiratory system. One has to obtain some amount of blood from the artery for measuring the concen­

tration with price-blood measuring device. Moreover, as oxygen concentration of circulating artery var­

ies rapidly, one has to measure the concentration even in the night. Tis is heavy burden to the patient.

Terefore, non-invasive method is critically important for clinical practice.

Te most important work in pulse-oximeter was made by two Japanese: an engineer Takuho Aoyagi

(1936–2020) of Nihon Kohden Co., and a surgeon Susumu Nakajima of Hokkaido University in the

early 1970s. Aoyagi invented a new type of oximeter which uses pulsatile variation in optical density of

tissues in the red and infrared wavelength to compute arterial oxygen saturation without need for cali­

bration (Aoyagi et al., 1974). Nihon Koden Co. ordered Aoyagi to stop further investigation. However,

Nakajima quickly noticed the idea of Aoyagi and ordered Nihon Kohden Co. to manufacture Aoyagi’s

prototype pulse-oximeter by the Government grand money. Nakajima brought the prototype into the

laboratory of Professor Masaji Mochizuki (1922–2015), a world famed physiologist of oximeter of the

RIAE of Hokkaido University. Ten, Nakajima, joined by Aoyagi for early several sessions, performed

animal experiments to compare the oximeter data obtained from platinum electrode inserted into

femoral artery of the dog and the data obtained from Aoyagi’s prototype pulse-oximeter. Platinum

electrode method was invented by Mochizuki to measure oxygen concentration in blood. From the

repeated animal experiments, Nakajima found and clearly confrmed that the device captured the subtle

change of inspired SaO2 without much of a delay. Based on these animal experiments, Nakajima com­

pared those obtained from Elma (Wood’s type)-oximeter. Ten, Nakajima repeated for ten times on

three healthy human subjects and two patients with low oxygen in blood if similar or the same results

could be obtained, with successful results. Moreover, Nakajima found the same results of arterial blood

and pulse-oximeter. From these preliminary investigations, Nakajima decided the Aoyagi’s type pulse­

oximeter can be useful for clinical practice (Nakajima et al., 1975, 1979). Figure 2.17 shows the world’s

frst clinical application of a pulse-oximeter conducted by Nakajima in the patient room at Misumai

National Sanatorium, Sapporo. Te patient had respiratory failure afer he underwent thoracoplasty for

tuberculosis treatment. Te pulse-oximeter is characterized by the fact that requires only the adjust­

ment of the alarm position and volume, the setting of a low cut flter to prevent fuctuations due to

FIGURE 2.17 Te world’s frst clinical application of ear-piece pulse-oximeter (Courtesy of Susumu Nakajima,

Moriyama Memorial Hospital)