Before Pulse Oximetry
In the 19th Century three scientists ascended
in a balloon to investigate the effects of oxygen availability at altitude. As
the balloon gained height all three lost consciousness. Then as the balloon
descended again one gained consciousness, and found both his colleagues dead. A
lack of oxygen was suspected to have been a contributory factor.
the Second World War the problem of maintaining the oxygen supply to the brain
of fighter pilots became an important issue. A non invasive monitoring technique
was required – spectrometry was thought to be the solution.
two major obstacles to be overcome. Firstly in conventional spectrometry the
distance through the sample is known. Secondly the sample is homogenous - i.e.
there are no complications due to varying amounts of tissue and bone being in
the light path.
Some of the early multi wavelength systems were
compromised by pulsatile signals caused by pulsing of the blood. The ripple in
the light absorption signal caused by the beating of the heart made accurate
measurements of light absorption difficult.