The effects of emission light pulse width on non invasive optical plethysmographic devices

Projecting pulsed light on biological tissue facilitates capturing in-depth optical plethysmographs to inspect micro-vascular blood flow. However, it remains unclear how the pulse width of light emission (t_pw) affects human tissue. In this study, alternating red and infrared light emitting diodes from a finger clip probe were set at 512 Hz. After conducting optical receiver sampling and digital filtering, the logarithmic ratio of the red and infrared light was used to examine their relationship to the pulse width. The pulse width varied from 70-1000 μs, yielding no observable effects on the ratios. These findings suggest that reducing the illumination time of optical components may reduce the amount of power consumed by the equipment and extend the lifetime of the power supply.