Abstract
Background Heart rate (HR) and heart rate variability (HRV) measurements are widely used to monitor stress and recovery status in sedentary people and athletes. However, effective HRV monitoring should occur on a daily basis because sparse measurements do not allow for a complete view of the stress-recovery balance. Morning electrocardiography (ECG) measurements with HR straps are time-consuming and arduous to perform every day, and thus compliance with regular measurements is poor. Contact-free, ballistocardiography (BCG)-based Emfit QS is effortless for daily monitoring. However, to the best of our knowledge, there is no study on the accuracy of nocturnal HR and HRV measured via BCG under real-life conditions. Objective The aim of this study was to evaluate the accuracy of Emfit QS in measuring nocturnal HR and HRV. Methods Healthy participants (n=20) completed nocturnal HR and HRV recordings at home using Emfit QS and an ECG-based reference device (Firstbeat BG2) during sleep. Emfit QS measures BCG by a ferroelectret sensor installed under a bed mattress. HR and the root mean square of successive differences between RR intervals (RMSSD) were determined for 3-minute epochs and the sleep period mean. Results A trivial mean bias was observed in the mean HR (mean –0.8 bpm [beats per minute], SD 2.3 bpm, P=.15) and Ln (natural logarithm) RMSSD (mean –0.05 ms, SD 0.25 ms, P=.33) between Emfit QS and ECG. In addition, very large correlations were found in the mean values of HR (r=0.90, P<.001) and Ln RMSSD (r=0.89, P<.001) between the devices. A greater amount of erroneous or missing data (P<.001) was observed in the Emfit QS measurements (28.3%, SD 14.4%) compared with the reference device (1.1%, SD 2.3%). The results showed that 5.0% of the mean HR and Ln RMSSD values were outside the limits of agreement. Conclusions Based on the present results, Emfit QS provides nocturnal HR and HRV data with an acceptable, small mean bias when calculating the mean of the sleep period. Thus, Emfit QS has the potential to be used for the long-term monitoring of nocturnal HR and HRV. However, further research is needed to assess reliability in HR and HRV detection.
Highlights
Technological development has brought forth numerous apps, gadgets, and high-tech solutions designed to enhance health, fitness, and performance
The results showed that 5.0% of the mean Heart rate (HR) and Ln root mean square of successive differences (RMSSD) values were outside the limits of agreement
Emfit QS has the potential to be used for the long-term monitoring of nocturnal HR and heart rate variability (HRV)
Summary
Technological development has brought forth numerous apps, gadgets, and high-tech solutions designed to enhance health, fitness, and performance. HR can be determined by ballistocardiography (BCG), which measures ballistic forces on the heart arising from the sudden ejection of blood into the great vessels with each heart beat [9]. It is a long-established, noninvasive technique that uses several types of sensors like pressure sensors, film-type force sensors, microbend fiber optic BCG sensors, electromechanical film transducer sensors, piezoelectric film sensors, polyvinylidene fluoride sensors, strain gauges, and pneumatic and hydraulic sensors [10]. Heart rate (HR) and heart rate variability (HRV) measurements are widely used to monitor stress and recovery status in sedentary people and athletes. To the best of our knowledge, there is no study on the accuracy of nocturnal HR and HRV measured via BCG under real-life conditions
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