The Cycloop

While wandering around on the website medischerfgoed.nl I came across a picture of an instrument in the university museum of Groningen: the Cycloop (Cyclops). See figure 1.

The instrument was made around 1949 by the Groningen professor of physiology Robert Brinkman and designed for measuring the oxygen saturation of the blood of a patient. A photocell was glued to the forehead of the patient allowing non-invasive determination of oxygen saturation via diffuse reflection measurement with red and green light.

Because the photocell was in the middle of the forehead the device is named after the mythological one-eyed giant. It is not known what the patients thought about it. See Figure 2.

Use and variants

 To calibrate the device a semi-logarithmic graph could be used or, as we see here, a calculating disk with a linear and a logarithmic scale. See figure 3. Note that a galvanometer reading of 50 cm gives a saturation percentage of 57%. In medical literature[1]  it can be found that the Cycloop was made by Kipp & Sons in Delft. That is in agreement with the inscription on the calculation disk. Due to the introduction of new photocells with a larger response for larger wavelengths around 1958 it was necessary to make a new calculation disk.[2]  So there must be at least two different types of Cycloop calculators.  

The back of the disc contains two identical logarithmic scales labeled Diaferometer.  

A Diaferometer is a device that determines changes in the composition of a gas by measuring its thermal conductivity. Usually this is the ratio of concentrations of CO2 and O2 in the blood. These devices were also made by Kipp, but Kipp was not unique in that. This side of the calculation disk was probably used to multiply measurements with a calibration factor.