JMIR Publications

ABSTRACT

Background:

Heart rate (HR) is an important and commonly measured physiological parameter with wearables. HR is often measured at the wrist with the photoplethysmography (PPG) technique which determines HR based on blood volume changes and is therefore influenced by blood pressure (BP). In individuals with spinal cord injury (SCI), BP control is often altered, and could therefore influence HR accuracy measured by the PPG technique.

Objective:

The objective of this study was to investigate: 1) the HR accuracy measured with the PPG technique with a Fitbit Charge 2 in wheelchair users with spinal cord injury (SCI); 2) how activity intensity affects HR accuracy; and 3) whether this HR accuracy is affected by lesion level.

Methods:

HR of 38 participants with SCI were measured during rest, 11 wheelchair activities and a 30-minute strength exercise block. HR was measured with a Fitbit Charge 2, which was compared to a Polar H7 HR monitor, used as a reference device. Participants were grouped into three groups, based on lesion level: T1. Among other things, mean absolute percentage error (MAPE) and concordance correlation coefficient (CCC) were determined for each lesion group for each activity type, i.e., rest, wheelchair activities and strength exercise.

Results:

With an overall MAPE of 12.99%, the accuracy falls below the standard acceptable ±10% with a moderate agreement (CCC=0.577). HR accuracy of the Fitbit Charge 2 seems to be reduced in those with cervical lesion level in all activities (MAPET1=20.43). Accuracy of the Fitbit Charge 2 decreased with increasing intensity (MAPErest=6.50%, MAPEactivity=12.97%, MAPEstrength=14.20%).

Conclusions:

HR measured with the PPG technique was just above the acceptable level in people with a paraplegia while in people with a tetraplegia a worse accuracy was found. The accuracy seems to worsen with increasing intensities, indicating that high intensity HR data and HR data in people with cervical lesion should be used with caution.