Abstract:
Pulse oximeter is an important medical device as it is used for emergency situations in hospitals
for monitoring patient’s peripheral oxygen saturation (%SpO2). For more than 30 years many
research studies have focused on designing a wearable compact pulse oximeter device for accurate
%SpO2 measurements. Most of these devices provide values that are either 2% above or below the
desired %SpO2 values, calculated using arterial blood gas (ABG). Pulse oximeter provides %SpO2
readings of arterial blood and the pulse rate through convenient placement of the sensor on the
finger. In the transmittance type pulse oximeter, the absorbance of light by oxy hemoglobin and
de-oxy hemoglobin is measured at two wavelengths one each from the Red band and the Infrared
(IR) band. The two band’s combined wavelength ranges from 600nm to 1100nm on the
electromagnetic spectrum. At each wavelength, the light is detected after placing a finger between
the light source and the detector of spectrophotometer. The detected signal consists of a cardiac
synchronous AC signal which is due to the changes in arterial blood volume, and the DC level
which is due to bone, tissue and non-pulsatile blood. The ratio of signals corresponding to Red and
IR bands is calculated and is related to arterial oxygen saturation. In this paper, we investigate the
spectral properties of blood through spectrophotometer-based readings from the finger in the
wavelength range of 600nm to 1100nm and determine the optimum wavelength combination for
designing the transmittance type pulse oximeter. For this purpose, a comparison of all
combinations of Red and IR band wavelengths was carried out. The results of our study indicate
that more than one combination of wavelengths can be used for
