Changes in the morphology of multiwavelength photoplethysmography across and down major arteries in the forearm

Photoplethysmography (PPG) is a non-invasive optical measurement that detects blood volume changes within the tissue from the skin's surface and is traditionally integrated into wearable technology to measure heart rate from the dorsal side of the wrist. The dorsal side of the wrist contains no major arteries, whereas the palmar side has two; the radial and ulnar arteries. To better understand the morphology of a PPG signal acquired along a major artery, this study investigated the change in PPG signals acquired from the distal to proximal locations of these two major arteries within the forearm. A multiwavelength (670nm, 770nm, 810nm, 850nm, 950nm) reflectance-based system was used to analyze the change in PPG morphology with the change in measurement location. Specifically, the sensor was placed into several zones down both arteries in the forearm to evaluate PPG waveform features. As the sensor traversed the arteries, changes in the morphology in each forearm zone were observed. Additionally, by using multiple wavelengths distinct waveforms were acquired from each penetration depth, as both arteries descend deeper away from the surface as you travel distal to proximal.