At present photoplethysmographic (PPG) sensors are rapidly spreading thanks to their multiple advantages: they are small, economic, and they can provide information on multidomain quantities related to cardiovascular health. For these reasons, research in this field is very active. Nonetheless, the measurement accuracy of this type of sensor and the factors that can interfere with their metrological performance are often neglected. The contact pressure between sensor and skin, the level of the activity performed by the subject, and also her/his skin tone are some of the quantities needing attention. The aim of this paper is to compare the measurement accuracy of a PPG sensor in relation to both contact pressure (20,60, and 75 mmHg) and walking/running speed (3,6, and 8 km/h) - using a cardiac belt as gold standard. Moreover, preliminary tests on dark skin subjects are performed to evaluate also the impact of this factor. The results show that the best performance is given at 60 mmHg and the uncertainty increases with activity level (passing from 8.2 bpm to 28.2 bpm when speed passes from 3 to 8 km/h, coverage factor k=2). Furthermore, it can be noticed that darker skin tone deteriorates the signal quality, increasing the mean absolute percentage error to values above 10% for speeds above 3 km/h. Plus, by considering the subjective optimal contact pressure at each speed, it is possible to improve significantly the accuracy and to reduce the mean absolute percentage error for moderate speed (6 km/h) at 1.89 %, which is known to be acceptable also for a clinical use. These results can be useful for researchers and producers of PPG-based wearable sensors, catching up on innovations potentially improving the quality of the measurement results. This could open new possibilities in terms of applications and stakeholders. In future, different wavelengths could be explored to expand the technology applicability.
Experimental Analysis on the Effect of Contact Pressure, Activity Level, and Skin Tone as Influencing Factors in PPG Sensors Performance
Cosoli, Gloria;Scalise, Lorenzo;Arnesano, Marco
2025-01-01
Abstract
At present photoplethysmographic (PPG) sensors are rapidly spreading thanks to their multiple advantages: they are small, economic, and they can provide information on multidomain quantities related to cardiovascular health. For these reasons, research in this field is very active. Nonetheless, the measurement accuracy of this type of sensor and the factors that can interfere with their metrological performance are often neglected. The contact pressure between sensor and skin, the level of the activity performed by the subject, and also her/his skin tone are some of the quantities needing attention. The aim of this paper is to compare the measurement accuracy of a PPG sensor in relation to both contact pressure (20,60, and 75 mmHg) and walking/running speed (3,6, and 8 km/h) - using a cardiac belt as gold standard. Moreover, preliminary tests on dark skin subjects are performed to evaluate also the impact of this factor. The results show that the best performance is given at 60 mmHg and the uncertainty increases with activity level (passing from 8.2 bpm to 28.2 bpm when speed passes from 3 to 8 km/h, coverage factor k=2). Furthermore, it can be noticed that darker skin tone deteriorates the signal quality, increasing the mean absolute percentage error to values above 10% for speeds above 3 km/h. Plus, by considering the subjective optimal contact pressure at each speed, it is possible to improve significantly the accuracy and to reduce the mean absolute percentage error for moderate speed (6 km/h) at 1.89 %, which is known to be acceptable also for a clinical use. These results can be useful for researchers and producers of PPG-based wearable sensors, catching up on innovations potentially improving the quality of the measurement results. This could open new possibilities in terms of applications and stakeholders. In future, different wavelengths could be explored to expand the technology applicability.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
