Assessing Cardiac Electro-Mechanical Deconditioning during Bed Rest Using Smartphone's Inertial Sensors

This study evaluated the potential of using smartphone-acquired seismocardiographic (SCG) signals for monitoring cardiac deconditioning after prolonged bed rest (BR). Ten healthy volunteers were enrolled in a 10-day BR. By positioning a smartphone on subject's chest, 1-minute SCG was acquired before the BR (PRE), on the 10th day of BR (BR10), and one day after reambulation (R+1). Signals were pre-processed and automatic beat identification was performed. Heart rate and variability indices (SDAO-AO, RMSSD, SDAO-AO/RMSSD) were calculated. Isovolumetric contraction (IVC), aortic valve opening (AO) and closure (AC) points were identified on the SCG, from which amplitude difference (AMPAO-IVC) and slope were derived. Finally, linear (iKlin) and rotational (iKrot) kinetic energies were calculated. At BR10 sympathetic modulation at awakening increased. Also, SCG morphology was affected, with increased AMPAO-IVC and IVC-AO slope. Further, at BR10 changes in morphology recovered, while iKlin/iKrot ratio increased. These findings support smartphones' potential as portable and non-invasive cardiac health monitoring devices for cardiac deconditioning.