Wireless System Design for Direct Current Photoplethysmography

A recent report showed that an OPT-101 photodetector and a red light-emitting diode (LED) of 630 nm wavelength could be employed to detect direct current Photoplethysmography (DC-PPG) signals and their associated hemodynamic responses in the in-vivo exposed spinal cord and brainstem. This work describes the design of a wireless system that allows to measure and transmit these low intensity DC - PPG signals successfully to a receiving stage located at a fixed length of 10 m. To obtain several low-intensity DC-PPG signals to be wirelessly transmitted and detected at the reception stage, we positioned the OPT-101 photodetector at different distances from the LED, from 0 to 30 cm. We show that our wireless system was capable of detecting all of these transmitted DC-PPG signals. As expected, we found a decrease in the OPT-101 voltage output and its associated wireless potential depending on the distance from 0 to 30 cm, showing a similar behavior. We suggest that different arrangements of our device could be employed to wirelessly detect hemodynamic responses in the spinal cord and brain in various animal models and in the human brain.