Analysis of a Pulse Rate Variability Measurement Using a Smartphone Camera

Area of Science:

• Biomedical Engineering
• Cardiology
• Digital Health

Background:

• Heart rate variability (HRV) reflects autonomic nervous system activity but lacks clinical validation due to limited data.
• Smartphone applications using photoplethysmography (PPG) offer a potential solution for collecting population-level HRV data.

Purpose of the Study:

• To evaluate a smartphone application's capability in measuring pulse rate variability (PRV) using PPG.
• To compare PPG-derived PRV with electrocardiography (ECG)-derived HRV.
• To establish a baseline by comparing differences among ECG channels.

Main Methods:

• Fifty parallel measurements were conducted using an iPhone 6 (240 Hz) and Cardiax PC-ECG devices.
• Correlation, linear regression, and Bland-Altman analysis were employed to assess PRV and HRV index correspondence.
• Intra-ECG channel variability was analyzed for baseline comparison.

Main Results:

• The smartphone PPG demonstrated high accuracy, with deviations comparable to those between ECG channels.
• Mean deviations between PPG-ECG and ECG channels were minimal for RR (0.01–0.06 ms), SDNN (0.78–0.46 ms), RMSSD (1.79–1.21 ms), and pNN50 (2.43%–1.63%).

Conclusions:

• The iPhone application provides reliable PPG-based PRV indices, comparable to ECG-based HRV.
• These findings support the use of smartphone PPG for accessible autonomic nervous system assessment.
• Further research will explore PPG-ECG correspondence across different ECG channels.