An algorithm for the beat-to-beat assessment of cardiac mechanics during sleep on Earth and in microgravity from the seismocardiogram

Figures

• 

  Figure 1. Model wearing the MagIC Space device and its components. Inset: detail of the textile sensors embedded in the inner part of the vest.

• 

  Figure 2. Example of recorded signals. From top to bottom: ECG, respiration, X,Y and Z accelerometric components, X, Y and Z gyroscopic components. Arrows indicate the accelerometer and gyroscope axes displaying synchronous patterns.

• 

  Figure 3. Typical SCG waveform with indication of the AO, AC, MO and MC fiducial points, and of the timings used for the estimation of the Cardiac Time Intervals. See text for the explanation of acronyms.

• 

  Figure 4. Scheme of the whole signal processing and of the algorithm phases.

• 

  Figure 5. Scheme of FP identification. Panel a: ECG with the indication of the Te point, SCG with its envelope curve and indication of the S1 and S2 areas, MC, AO, AC and MO fiducial points, ICP and IRP anchor points and definition of the IRPRdelay used for the AC and MO identification. Inset b: definition of the threshold points used for the estimation of MC and AO in the S1si window. Inset c: definition of the D1 and D2 distances used for the scoring of the peaks in the S2si window for the identification of the IRP anchor point used for the localization of AC and MO.

• 

  Figure 6. Panel a: Examples of beats in which the MC, AO, AC and MC fiducial points are characterized by the expected clear-cut peaks (for MC, AO and AC) or trough (for MO). Panel b: other beats in which the FPs are marked only by an inflection point.

• 

  Figure 7. Example of SCG inflection point corresponding to the mitral valve closure. M-mode ultrasoung image from a healthy subject.

• 

  Figure 8. Schematization of the signal interpolation and re-sampling for the 1-ms resolution assessment of FPs. In this representation the FP considered is AO. Panel a: the entire SCG waveform. Panel b: detail of the data window used for the interpolation. Panel c: the small data window used for the hi-res localization of AO, the larger circles represent the original low resolution samples and the smaller circles the final high resolution samples, CFTP = Coarse FP Time Position, HRFTP = Hi-Res FP Time Position.

• 

  Figure 9. A 45-min segment of beat-to-beat RRI and indexes of cardiac mechanics excerpted from the first sleep recording made aboard the ISS.