<title>New hybrid reflectance optical pulse oximetry sensor for lower oxygen saturation measurement and for broader clinical application</title>

Abstract

A new reflectance pulse oximeter sensor for lower arterial oxygen saturation (Sa)<SUB>2</SUB>) measurement has been designed and evaluated in animals prior to clinical trials. The new sensor incorporates ten light emitting diode chips for each wavelength of 730 and 880 nm mounted symmetrically and at the radial separation distance of 7 mm around a photodiode chip. The separation distance of 7 mm was chosen to maximize the ratio of the pulsatile to the average plethysmographic signal level at each wavelength. The 730 and 880 wavelength combination was determined to obtain a linear relationship between the reflectance ratio of the 730 and 880 nm wavelengths and Sa)<SUB>2</SUB>. In addition to these features of the sensor, the Fast Fourier Transform method was employed to compute the pulsatile and average signal level at each wavelength. The performance of the new reflectance pulse oximeter sensor was evaluated in dogs in comparison to the 665/910 nm sensor. As predicted by the theoretical simulation based on a 3D photon diffusion theory, the 730/880 nm sensor demonstrated an excellent linearity over the SaO<SUB>2</SUB> range from 100 to 30 percent. For the SaO<SUB>2</SUB> range between 100 and 70 percent, the 665/910 and 730/880 sensors showed the standard error of around 3.5 percent and 2.1 percent, respectively, in comparison to the blood samples. For the range between 70 and 30 percent, the standard error of the 730/880 nm sensor was only 2.7 percent, while that of the 665/910 nm sensor was 9.5 percent. The 730/880 sensor showed improved accuracy for a wide range of SaO<SUB>2</SUB> particularly over the range between 70 and 30 percent. This new reflectance sensor can provide noninvasive measurement of SaO<SUB>2</SUB> accurately over the wide saturation range from 100 to 30 percent.