Smartphone-Integrated POF Speckle Sensor for Heart Rate Variability Monitoring

The crucial role of pulse signals in the field of cardiovascular diseases (CVDs) cannot be overstated, as they provide physiological indicators for cardiovascular health monitoring and disease diagnosis. Pulse signals, as fundamental physiological signals, also offer valuable insights into heart rate variability (HRV) analysis for diagnosing CVDs. The wearable sensors are promising to monitor HRV information. We propose a smartphone-integrated plastic optical fiber (POF) speckle sensor for HRV monitoring, POF with a core diameter of 1000 µm was implemented, which offers the highest signal-to-noise ratio value (11.33 dB) among POFs of this core diameter. HRV tests were conducted, revealing a participant's average heart rate, standard deviation of NN intervals, and Root mean square of successive differences during different motion states. The correlation coefficient between reference R wave to R wave (RR) intervals and measured RR intervals is 0.97018. The results indicate our system holds potential applications in monitoring HRV for prevention and treatment of CVDs.