A proposal of highly-sensitive finger-photoplethysmogram using a sphere-shaped diffuse reflector for non-invasive measurement of blood constituents

Abstract

In this study, the sensitivity of the finger-photoplethysmogram (FPPG) obtained from a newly designed integrating sphere type sensor (FPPGis) and that from a conventional transmittance type sensor (FPPGtm) were compared. We used near-infrared light at 1160 nm - a window of the absorption band of water and alcohol, and 1600 nm - a strong absorption band of water and glucose. In 8 healthy volunteers, simultaneous measurements of both FPPGis and FPPGtm from the index fingers of both hands were made during 10 min rest periods using a laser experimental setup. The difference of signal-to-noise ratio (SNR) between FPPGis and FPPGtm with both wavelengths was evaluated. We found a statistically significant higher SNR in the FPPGis, by factors of 1.58 and 4.80 for the FPPG measurements at 1160 nm and 1600 nm, respectively. Thus, the proposed method to measure FPPGis at wavelengths of strong water absorption could be especially available.