Overnight heartbeat monitoring by using unobtrusive optical interferometric measurements

In this paper, a possibility of overnight monitoring by using optical interferometric signals was examined. Optical interferometer is a sensitive device that detects physical changes of the length of optical fibre. When used as bed sensor, heartbeats cause its perturbation when a subject is lying on the mattress. This allows continuous monitoring of heartbeat entirely unobtrusively. Overnight acquisition was performed on a healthy male subject and lasted 9.75 hours during subject´s sleep. The signal was divided into 15-minute segments. Heartbeat detection was applied to each segment individually. Results were validated by using a referential ECG signal. High efficiency was obtained with sensitivity of 97.21±2.11% and precision of 97.76±1.04%, and accuracy of heartbeat detection with overall mean absolute error of 100.84±19.22 ms, overall median absolute error of 75.56±15.03 ms, and overall P₉₀ of 219.69±46.91 ms.