Quantification of tremor using consumer product accelerometry is feasible in patients with essential tremor and Parkinson's disease: a comparative study

Abstract

Background: To quantify pharmacological effects on tremor in patients with essential tremor (ET) or Parkinson's Disease (PD), laboratory-grade accelerometers have previously been used. Over the last years, consumer products such as smartphones and smartwatches have been increasingly applied to measure tremor in an easy way. However, it is unknown how the technical performance of these consumer product accelerometers (CPAs) compares to laboratory-grade accelerometers (LGA). This study was performed to compare the technical performance of CPAs with LGA to measure tremor in patients with Parkinson's Disease (PD) and essential tremor (ET).

Methods: In ten patients with PD and ten with ET, tremor peak frequency and corresponding amplitude were measured with 7 different CPAs (Apple iPhone 7, Apple iPod Touch 5, Apple watch 2, Huawei Nexus 6P, Huawei watch, mbientlabMetaWear (MW) watch, mbientlab MW clip) and compared to a LGA (Biometrics ACL300) in resting and extended arm position.

Results: Both in PD and ET patients, the peak frequency of CPAs did not significantly differ from the LGA in terms of limits of agreement. For the amplitude at peak frequency, only the iPhone and MW watch performed comparable to the LGA in ET patients, while in PD patients all methods performed comparable except for the iPod Touch and Huawei Nexus. Amplitude was higher when measured with distally-located CPAs (Clip, iPhone, iPod) compared with proximally-located CPAs (all watches). The variability between subjects was higher than within subjects for frequency (25.1% vs. 13.4%) and amplitude measurement (331% vs. 53.6%). Resting arm position resulted in lower intra-individual variability for frequency and amplitude (13.4 and 53.5%) compared to extended arm position (17.8 and 58.1%).

Conclusions: Peak frequencies of tremor could be measured with all tested CPAs, with similar performance as LGA. The amplitude measurements appeared to be driven by anatomical location of the device and can therefore not be compared. Our results show that the tested consumer products can be used for tremography, allowing at-home measurements, in particular in studies with a cross-over or intra-individual comparison design using the resting arm position.

Trial registration: This trial was registered in the Dutch Competent Authority (CCMO) database with number NL60672.058.17 on May 30th 2017.

Keywords: Accelerometer; App; Essential tremor; Parkinson’s disease; Tremography; Tremor; Validation; Wearable.

Fig. 1

Sequence and timeline of one assessment block

Fig. 2

Timeline overview of all groups containing all assessments. ^*A break of a minimum of 30 min up to 1 h was allowed if needed. BSL = Baseline/reference laboratory grade accelerometer, ET = Essential Tremor, PD = Parkinson’s Disease

Fig. 3

Mean peak frequency of consumer product accelerometers versus laboratory grade accelerometer in patients with Essential Tremor and Parkinson’s Disease in resting arm position (a) and extended arm position (b). AW = Apple watch 2; HN = Huawei Nexus 6P; HW = Huawei watch; IT = iPod Touch 5; I7 = iPhone 7; MW Clip = Meta Wear Clip; MW Watch = Meta Wear watch. Every measurement was combined with the LGA to allow simultaneous measurements. The peak frequency measured with the LGA showed slight changes (increases and decreases) over time

Fig. 4

a Limits of agreement of peak frequency between consumer product accelerometers and the laboratory grade accelerometer in patients with Essential Tremor and Parkinson’s Disease in resting arm position. AW = Apple watch 2; HN = Huawei Nexus 6P; HW = Huawei watch; IT = iPod Touch 5; I7 = iPhone 7; MW Clip = Meta Wear Clip; MW Watch = Meta Wear watch. b Limits of agreement of peak frequency between consumer product accelerometers and the laboratory grade accelerometer in patients with Essential Tremor and Parkinson’s Disease in extended arm position. AW = Apple watch 2; HN = Huawei Nexus 6P; HW = Huawei watch; IT = iPod Touch 5; I7 = iPhone 7; MW Clip = Meta Wear Clip; MW Watch = Meta Wear watch

Fig. 5

Amplitude at peak frequency in all patients in resting arm position for each pair of reference measurements with the laboratory grade accelerometer and consumer product accelerometer

Fig. 6

Amplitude at peak frequency in all patients in resting arm position for proximally-worn accelerometers (Apple Watch, Huawei Watch and MW Watch) compared with distally-worn accelerometers (MWClip, iPod, iPhone and Huawei Nexus) and the standard laboratory grade accelerometer. Amplitude at peak frequency tended to be higher after measurement with distally-worn accelerometers compared to proximally-worn accelerometers