Enabling Continuous Wearable Reflectance Pulse Oximetry at the Sternum

Area of Science:

• Biomedical Engineering
• Physiological Monitoring
• Wearable Technology

Background:

• Peripheral oxygen saturation (SpO2) is a critical indicator of patient status, particularly during the COVID-19 pandemic.
• Continuous SpO2 monitoring is essential for early detection of deterioration.
• Existing methods may have limitations in continuous, high-fidelity data acquisition.

Purpose of the Study:

• To develop and validate a custom chest-based wearable biosensor for accurate SpO2 estimation.
• To assess the sensor's ability to measure electrocardiogram (ECG) and photoplethysmogram (PPG) signals.
• To explore novel algorithms for robust SpO2 calculation from PPG signals.

Main Methods:

• A breath-hold protocol was used with 20 subjects to collect physiological data across a wide SpO2 range.
• A custom wearable patch biosensor measured ECG and PPG signals.
• Novel feature extraction and PPGgreen-based outlier rejection algorithms were applied to estimate SpO2 using the ratio of ratios (R).

Main Results:

• Subject-independent training yielded a root-mean-square error (RMSE) of 2.64 ± 1.14% and a Pearson correlation coefficient (PCC) of 0.89.
• Subject-specific calibration improved results to an RMSE of 2.27 ± 0.76% and a PCC of 0.91.
• Calibration efficiency was enhanced by standardizing breath-hold duration over SpO2 range.

Conclusions:

• The custom wearable biosensor accurately estimates SpO2 using PPG signals.
• The developed algorithms provide reliable SpO2 measurements with low error.
• This technology offers potential for continuous disease and wellness monitoring.