Heart Rate

Description

Heart rate (HR) is the number of times the user’s heart beats, expressed as a rate per minute. A bpm of 60-100 is considered healthy/normal.

Participants

Over 10,000 test subjects took part in the test. Subjects were recruited from the Affiliated Hospital of Hangzhou Normal University in China and the University of Toronto in Canada. There were no exclusion criteria when recruiting participants, although most participants were healthy adults above 18 years of age. Table 1 summarizes participant characteristics.

Participants	Composition
Average Age	41.2 years
Standard deviation of age	15.2 years
Gender distribution	48% Male; 52% Female

Table 1: Characteristics of participants for HR and MSI

Additional Data Collection Setup

Reference heartbeat information was collected with a 3-lead electrocardiograph (ECG). The data collection setup is depicted in Figure 1.

Figure 1: HR, Mental Stress Index & Irregular Heartbeat data collection setup

Analysis of Accuracy & Reliability

Heartbeats were then identified in both ECG signal (reference signal) and BitDoctor signal (test signal).

ECG captures heartbeats as characteristic fluctuations in the heart’s electrical signal that occur with each beat (Figure 2). The major peak in this fluctuation (R-wave) was used to identify each heartbeat on the ECG trace. The heart rate is calculated by counting the number of heartbeats on a given trace (Figure 3) and expressing this number as a per minute rate.

Figure 2: Labeled ECG wave.

Figure 3: ECG recording used for heart rate computation.

This signal robustly tracks the activity of the heart in terms of number of beats and inter-beat timing (Figure 4). Like ECG, BitDoctor heart rate was calculated from each participant’s blood flow information.

Figure 4. Comparison between ECG heart rate and BitDoctor HR. BitDoctor signal trace (red) is overlaid on an ECG trace (blue) from a healthy adult.

The accuracy of BitDoctor-based measurements relative to ECG-based measurements was then calculated, considering only measurements with a positive signal-to-noise ratio.

Equation 1: Calculation of BitDoctor heart rate accuracy.

HR accuracy was calculated as: (1 − 1 𝑁 ∑ | BITDOCTOR 𝐻𝑅 − 𝐸𝐶𝐺 𝐻𝑅 𝐸𝐶𝐺 𝐻𝑅 |) × 100%

Results

The accuracy and reliability of BitDoctor-based HR is presented in Table 2. Reliability refers to the test-retest reliability of each item.

Physiological Measure	Accuracy (%)	Reliability (%)
HR	99	100

Table 2: Accuracy and reliability of BitDoctor HR

HR Accuracy Details

Table 3 presents additional accuracy metrics pertaining to HR.

	HR Accuracy (bpm)
Mean ECG HR	74.4
Mean BitDoctor HR	75.1
Mean Error	0.63
Standard Deviation of Error	1.21
Mean of Absolute Error	0.79

Table 3: Additional BitDoctor heart rate accuracy metrics

Additional analysis was conducted to determine BitDoctor-based HR accuracy with shorter (30-second) measurements. Once again, BitDoctor-based HR tracked reference (ECG) HR very well (Figure 5). The Pearson correlation between ECG and BitDoctor measurements under these conditions was essentially perfect (r=1.0).

Figure 5: Scatter plot of 30-second HR measurements taken by ECG and BitDoctor Technology.