Influence of motion capture camera’s self-heating on optoelectronic plethysmography accuracy

• Optoelectronic systems (OES) cameras are prone to produce error measurement due to self-heating of its cameras. • Optoelectronic plethysmography (OEP) used to detect small volume variations can be affected by self-heating errors. • The OEP measurement protocol should take into consideration these errors by switching on OES at least 50 min before calibration and measurements. Optoelectronic plethysmography (OEP) is a clinical application of motion capture that measures respiratory parameters in both healthy and pathological human subjects. Prior to any clinical application, the assessment of the measurement error of optoelectronic systems used in motion capture (mocap) is essential to ensure the internal and external validity of the results . The present study aimed to estimate if digital cameras used in mocap systems were prone to produce systematic errors due to self-heating during their warming-up time. The volume of a calibration device (VCD) supposed to remain constant was measured over 90 min by OEP thirty-two times. The temperatures of the VCD, room, and mocap cameras were monitored. The mean VCD variation was +58.3 mL ± 8.1 mL. The volume raise was highly correlated with the augmentation of mocap cameras’ temperature (+13.86 °C ± 0.25 °C, Pearson’s coefficient r = 0.99). Thermal effects on the plastic material that composes the VCD were negligible (+0.08 ± 0.07 °C). The magnitude of the volume drift is modest but might be of interest for specific applications of OEP, such as comparison before and after an intervention when the mocap system has not been switched off. The volume drift does not seem to be compensated by any algorithm. Analysis of correlations and predictive models led us to declare that, in order to avoid systematic error due to camera’s self-heating, the optoelectronic system should be turned on at least 50 min before calibration and measurements.