Abstract
Heart rate measurement has become one of the most widely used methods of monitoring the intensity of physical activity. The purpose of this study was to assess whether in-ear photoplethysmographic (PPG) pulse rate (PR) measurement devices represent a valid alternative to heart rate derived from electrocardiography (ECG), which is considered a gold standard. Twenty subjects (6 women, 14 men) completed one trial of graded cycling under laboratory conditions. In the trial, PR was recorded by two commercially available in-ear devices, the Dash Pro and the Cosinuss°One. They were compared to HR measured by a Bodyguard2 ECG. Validity of the in-ear PR measurement devices was tested by ANOVA, mean absolute percentage errors (MAPE), intra-class correlation coefficient (ICC), and Bland–Altman plots. Both devices achieved a MAPE ≤5%. Despite excellent to good levels of agreement, Bland–Altman plots showed that both in-ear devices tend to slightly underestimate the ECG’s HR values. It may be concluded that in-ear PPG PR measurement is a promising technique that shows accurate but imprecise results under controlled conditions. However, PPG PR measurement in the ear is sensitive to motion artefacts. Thus, accuracy and precision of the measured PR depend highly on measurement site, stress situation, and exercise.
Highlights
As a result of the development of mobile heart rate monitors, heart rate has become one of the most widely used methods for controlling the general state of health and, the intensity of physical activity [1]
The Kolmogorov–Smirnov test as well as visual data plotting of the criterion measure (Bodyguard 2), Cosinuss◦ One, and the Dash Pro revealed that the overall rates among all participants were significantly different from a normal distribution (resting conditions: D(2376) = 0.066, p < 0.001 for ECG and
The preliminary applied Kolmogorov–Smirnov test on differences between criterion measure and alternative method did significantly deviate from a normal distribution
Summary
As a result of the development of mobile heart rate monitors, heart rate has become one of the most widely used methods for controlling the general state of health and, the intensity of physical activity [1]. In 1938, Hertzman [2] first introduced photoplethysmography (PPG) as an alternative to electrocardiographic (ECG) heart rate monitoring. PPG signals can be measured at the wrist [5,6,7], upper and lower arm [8,9,10], finger [11], esophageal region [12], forehead [13,14], and the ear, respectively. Pulse rate measurement at the earlobe [15], the external ear cartilage [16,17], the superior and inferior auricular region [18,19,20,21], and the external auditory canal [22,23,24] has already been discussed in several studies as an alternative to ECG heart rate monitoring. Besides wrist-worn devices, ear-worn devices are probably the most common application of PPG
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