Wearable Optical E-Tattoo for Deep Neck Hemodynamic Monitoring

Noninvasive detection of blood oxygen abnormalities in arteries and veins is crucial for determining sepsis, shock, and metabolic demand but is still unattainable. In this work, we devise a soft wearable e-tattoo sensor able to measure deep hemodynamics on the neck through photoplethysmography (PPG). There is widespread doubt that PPG cannot penetrate to the arteries and veins, a requirement to measure arterial and venous oxygenations (SaO2 and SvO2) directly. We investigate the penetration depth of PPG with computational and in vitro models. Finally, we demonstrate the e-tattoo’s ability to distinguish arterial and venous pulses in vivo. These tests contradict the stereotype of PPG’s poor penetration depth, substantiating the pursuit to optically measure arterial and venous pulses for SaO2 and SvO2 extraction.