Non-Intrusive Monitoring of Vital Signs in the Lower Limbs Using Optical Sensors

Area of Science:

• Biomedical Engineering
• Wearable Technology
• Health Monitoring

Background:

• Invisible health monitoring is gaining global scientific interest.
• Sensorizing everyday objects enables continuous health data collection without altering user routines.

Purpose of the Study:

• To assess the feasibility of photoplethysmography (PPG) acquisition in the lower limbs for continuous vital sign monitoring.
• To develop and validate a system for real-time heart rate (HR) and respiratory rate (RR) measurement using PPG signals from the thigh.

Main Methods:

• Utilized two MAX30102 sensors placed on the back of the thigh to acquire PPG signals.
• Conducted a proof-of-concept study with 17 volunteers (ages 22-40).
• Compared the developed system's measurements against reference sensors.

Main Results:

• Achieved a Pearson correlation coefficient of r = 0.92 for HR and r = 0.77 for RR.
• Obtained a mean difference of 1.2 bpm for HR and 0.9 rpm for RR compared to reference sensors.
• Demonstrated system accuracies of 95.9% for HR and 91.3% for RR.

Conclusions:

• The developed system shows significant viability for continuous and real-time vital sign monitoring in the lower limbs.
• This approach offers a non-intrusive method for health tracking through sensorization of everyday objects.
• Further research can explore broader applications of lower limb PPG for remote patient monitoring.