Development of an electro-pneumatic calf muscle actuator to estimate peripheral venous oxygen saturation using photoplethysmography.

In pulse oximetry, arterial blood pulsations are used to estimate peripheral arterial oxygen saturation (SpO2) using photoplethysmography (PPG). On the contrary, peripheral venous oxygen saturation (SvO2) assessment remains challenging due to the absence of rhythmic blood volume fluctuations in the venous system. This paper introduces an electro-pneumatic system emulating the Venous Muscle Pump Test (VMPT) to induce venous blood pulsations. The system achieves 0-120 mmHg pressure pulsations on the calf at 0.5 Hz, facilitating SvO2 estimation through a toe-attached PPG sensor. A proof-of-concept study on two subjects reveals PPG curves and venous blood volume variations comparable to conventional VMPT. The system outperforms in acquiring arterial pulsations, enabling simultaneous SpO2 estimation and the possibility of local oxygen consumption estimation. Estimated Ratio-of-Modulation and SvO2 values (84-89 %) align with classical VMPT, with lower mean deviation (3-15 % vs. 10-18 %). While promising, further studies with larger sample sizes, varied pressure parameters, and reference SvO2 values are essential for validating the system's efficacy. Future tests will further explore the system's potential to detect venous valve leakage.