Remote blood pressure measurement from near-infrared face images: A comparison of the accuracy by the use of first and second biological optical window

The near-infrared wavelength band, which is between the visible and infrared bands, is a wavelength range with high biological permeability called the "biological optical window". The depth of penetration to a living body changes depending on the wavelength of light, with the 700-1100 nm wavelength band, called the first biological optical window, and the 1000-1400 nm wavelength band, called the second biological optical window. In this study, we evaluated the effectiveness of the biological optical window for remote blood pressure measurements. Specifically, we constructed an estimation model for resting blood pressure using near-infrared face images taken at 760-1100 nm, corresponding to the first biological optical window, and at 1050-1650 nm, corresponding to the second biological optical window. Thereafter, we compared the accuracy of blood pressure estimation for each wavelength band. The results of cross-validation with 10 participants showed that the model constructed using the first biological optical window had a higher estimation accuracy than the model constructed using the second biological optical window. The root mean square error between the measured and estimated mean blood pressure values was 9.84 mmHg. These results indicate that the first biological optical window is a more effective wavelength band for remote blood pressure measurement than the second biological optical window, and can measure resting blood pressure remotely with an error of approximately 9 mmHg.