Robust design of finger probe in non-invasive total haemoglobin monitor.

The development of a non-invasive monitor of total haemoglobin has been reported previously. The paper presents the design and testing of a finger probe used in that optical haemoglobin monitor. When a finger is inserted into the probe, light is radiated onto the nail, and a silicon detector measures transmitted light. This finger probe can have different values or settings for design parameters such as the internal colour, detector area, the emission area of a light source and the distance between the light source and detector. Design of experiment (DOE) was introduced to select the best combination of design parameters that were robust to external conditions such as finger alignment and ambient light. An optimally designed finger probe from DOE analysis, compared with the initial design, increased the correlation coefficient from 0.696 to 0.869 and improved the standard deviation from 1.18 to 0.81 g dl(-1) in predicting total haemoglobin. This was under different conditions of finger-probe alignment. Under different ambient light conditions, the optimum design improved the correlation coefficient from 0.735 to 0.870 and reduced the standard deviation from 1.14 to 0.83 g dl(-1).