Wearable Sensing of Cardiac Timing Intervals From Cardiogenic Limb Vibration Signals

In this paper, we describe a new method to measure aortic valve opening (AVO) and aortic valve closing (AVC) from cardiogenic limb vibrations (i.e., wearable ballistocardio-gram (BCG) signals). AVO and AVC were detected for each heartbeat with accelerometers on the upper arm (A), wrist (W), and knee (K) of 22 subjects following isometric exercise. Exercise induced changes were recorded with impedance cardiography. The method, Filter BCG, detects peaks in distal vibrations after filtering with individually tuned bandpass filters. In agreement with recent studies, we did not find peaks at AVO and AVC in limb vibrations directly. Interestingly, distal vibrations filtered with FilterBCG yielded reliable peaks at AVO (r
²
= 0.95 A, 0.94 W, 0.77 K) and AVC (r
²
= 0.92 A, 0.89 W, 0.68 K). FilterBCG measures AVO and AVC accurately from arm, wrist, and knee vibrations, and it outperforms the standard R-J interval method.