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\title{Determinants of photoplethysmography signal quality at the wrist}



\author[1]{Peter Charlton}%
\author[1]{Vaidotas Marozas}%
\author[1]{Elisa Mejía-Mejía}%
\author[1]{Panicos A Kyriacou}%
\author[1]{Jonathan Mant}%
\affil[1]{Affiliation not available}%


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  \date{April 26, 2026}


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\begin{abstract}
Wrist photoplethysmogram (PPG) signals are widely used for physiological
monitoring in consumer devices. However, the PPG is highly susceptible
to noise, which can reduce the accuracy of monitored parameters. The aim
of this study was to identify factors which influence PPG signal
quality. Data from the Aurora-BP dataset were used, consisting of
reflectance wrist PPG signals measured from 1,155 subjects of varying
ages and health statuses. Measurements were acquired in supine, sitting,
and standing postures, and with the sensor held at different heights.
Three signal quality metrics were calculated: the signal-to-noise ratio
(SNR), the perfusion index (PI), and the template-matching correlation
coefficient (TMCC). When comparing between postures with the sensor held
at a natural height, quality was greatest in the supine position (SNR:
18.7 dB), followed by sitting with the arm resting in the lap (13.9 dB),
and lowest whilst standing with the arm hanging alongside (9.1 dB)
(p\textless{}0.001). Signal quality increased as the arm was raised to
heart height: whilst sitting, quality was lowest with the arm alongside
the body (10.7 dB), and increased when the sensor was held in the lap
(13.9 dB) and at heart height (16.3 dB) (p\textless{}0.001). Similar
trends were observed for the TMCC and PI. Findings were mixed for the
influence of participant characteristics on signal quality. The SNR and
TMCC, but not the PI, increased with age. The SNR decreased at darker
skin tones when controlling for PPG DC amplitude, although this
association did not hold for other metrics. In conclusion, this study
identified the impacts of posture and sensor height on signal quality,
with highest qualities observed in the supine posture and with the
sensor at heart height. It also highlights the importance of adjusting
LED light intensity to maintain signal quality across skin tones.%
\end{abstract}%



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