Fig. 4: Enhanced resolution SCG maps at the end of exhalation.

a Normalized right-to-left chest vibrations, and b Normalized head-to-foot chest vibrations for all 14 subjects during breath-hold at the end of exhalation. Each pixel of the maps shows the temporal variations of the corresponding ensemble average SCG signal during a cardiac cycle. Time-varying vibration maps were created using the enhanced-resolution (2m−1) × (2n−1) SCG grids and aligned with respect to the ECG reference points of each subject for better visualization of the results. It is noteworthy that the time step between the maps and the timing of maps corresponding to the same ECG reference point for different subjects are not uniform and depend on the cardiac cycle duration of each subject.