Reliability of a low-cost chest strap to estimate short-term and ultra-short-term heart rate variability measures in response to emotionally-valenced stimuli

The heart rate variability (HRV), which represents the time variation between consecutive heartbeats, has been presented as an indicator of how the cardiovascular and nervous systems respond to changing emotional states. A huge variety of affordable wearable devices has become available and provide the HRV with presumed accuracy. A few exploratory studies have investigated the reliability of these devices under different conditions, but their reliability under emotional stimulation is unknown. This study investigated the reliability, described by the similarity and agreement with a five-lead cardiac monitor, of a widely used low-cost chest strap to detect HRV responses in 29 subjects to emotionally-valenced stimuli in short-term and ultra-short-term conditions. The HRV was recorded with both the chest strap and the cardiac monitor. The similarity between devices was evaluated based on the cross-correlation of the time series recorded by they and the statistical differences between the measures estimated from their recordings. The agreement between measures from both devices was investigated with the intra-class correlation coefficient and Bland-Altman plots. Our results showed that the signals recorded by both devices were highly correlated and there were no significant discrepancies between the measures derived from both devices either under short-term or ultra-short-term conditions. Additionally, all time-, and frequency-and non-linear measures demonstrated strong to excellent agreement. This evidence suggests that the low-cost chest strap can be a reliable alternative for estimating short-term and ultra-short-term HRV measures related to time, frequency, and also non-linear measures.