Pulse oxigraphy

From pulse oximeter towards "SpO2 camera"

Researchers: Fokko Wieringa, Ton van der Steen

Within only a few decades, pulse oximetry has changed many clinical routines just as drastically as the introduction of reliable thermometry did within three centuries. For both pulse oximeters as well as for thermometers, contact with the body is required to produce a numerical value that relates to only one particular spot (4). In thermometry, however, “thermal cameras” have become available, offering a large added value when compared to a simple thermometer. Likewise, an "SpO2 camera" is likely provide a comparable added value when compared to a simple pulse oximeter. Based on an already granted patent (1) this research is focussed on developing such an SpO 2 camera as a logical next step in oxygen-saturation measurement.

The pixel values for images of such an intended SpO 2 camera would be calculated (using the “ratio of ratios” method) from photoplethysmographic wavelengths of 3 different wavelengths (660 nm, 810 nm and 940 nm) derived from camera data.

As a first step towards a practical realization of the patented principle, we experimentally proved that it indeed is possible to obtain photoplethysmographic plethysmograms at these three wavelengths (3).

We also found that, as a spin-off of our approach, it is possible to improve the visualization of vasculature buried beneath the tissue surface (2). Two papers have been submitted describing possible clinical applications either through the skin or during cardiac surgery.

Our ongoing research is aimed at two goals:

  • In vitro experiments to investigate the correlation of our “SpO 2 camera” principle with clinical pulse oximeters and with laboratory blood gas analysis.
  • Establishment of a new hardware platform capable to simultaneously aquire at five wavelengths with improved signal to noise ratio and higher frame-rate.

1. Wieringa FP. 2001. WO Patent No. WO 01/15597 A1

2. Wieringa FP, Bakker D, van der Steen AFW, Mastik F, van Melick RGM. 2005. Patent No. EP1566142A1

3. Wieringa FP, Mastik F, Van der Steen AFW. 2005. Contactless multiple wavelength photoplethysmographic imaging: A first step towards "SpO 2 camera" technology. Annals of biomedical engineering 33: 1034-41 http://dx.doi.org/10.1007/s10439-005-5763-2

4. Wieringa FP, Van der Steen AFW. Pulsoxymetrie, een techniek met toekomst maar ook randvoorwaarden. Klinische Fysica 2001/4: 4-8

Internet link to reference 3: http://dx.doi.org/10.1007/s10439-005-5763-2