Hearables: feasibility of recording cardiac rhythms from head and in-ear locations

Figures

• 

  Figure 1.. The computational biophysics model and experimental electrode positions. (a) Body geometry: Organs around the heart and in the head are inserted into a realistic full-body three-dimensional shell [18]. (b) Heart vector: The orientation and magnitude of the current dipole p in px, py, and pz; the heart vector at one point in time is shown in blue, and the trace of the tip of the heart vector from the start of the cycle until the current position (axes in 0.12 mAm) is shown in orange; the heart muscle is shown in pink in the background (axes in millimetres) (c) Head-ECG set-up: Symmetric set-up across the sagittal plane with electrodes on both sides of the head with the left side locations shown in blue, that is, the left neck, jaw-centre, jaw-joint, cheek and forehead locations.

• 

  Figure 2.. Simulated cardiac cycles for the limb leads. (a) The electrode positions for the three limb leads and head-ECG. (b) The simulated cardiac cycles for the well-known limb lead positions; these are a good match to the shape of the limb lead cycles reported in the literature [23].

• 

  Figure 3.. Simulated and recorded cardiac electric potentials on the upper torso and head surface. (a) Simulated electric potentials on the head surface and upper torso at the time of the R-wave peak (in millivolts). (b) Recorded ECG traces from head positions (ii, in blue) compared to standard Lead I from the arms (i, in black).

• 

  Figure 4.. Simulated and measured cardiac cycles in five head-ECG channels for Subject 1. (a) Simulated cardiac cycle for the considered electrode positions. (b) Mean cardiac cycle for the corresponding electrode pairs of the recorded head-ECG. The cardiac cycles were identified based on (1) the timings of the R-waves in the arm ECG (grey lines with orange ‘+’) and (2) the timings of the R-waves detected in the individual head-ECG channels (blue lines with yellow ‘+’).

• 

  Figure 5.. Head-ECG including the timings of the P-, Q-, R-, S- and T-waves with respect to the R-wave, as recorded from the jaw-joints position (b) benchmarked against reference Lead I arm-ECG (a); the amplitude in the reference ECG (from the arms) was approximately 50 times larger than the amplitude in the head channels.

• 

  Figure 6.. Illustration of enhanced R-waves detection in ear-ECG using a MEMS microphone co-located with the electrode [26,28]. (a) The standard Lead I ECG from the arms, recorded simultaneously with (b) the mechanical plethysmogram from an in-ear co-located MEMS microphone and (c) ear-ECG. The easily detectable maxima in the microphone signal (b) correspond to the arrival times of the pulse in the blood vessels of the ear canal and define the analysis time window for the ear-ECG signal (c) in which the preceding R-wave must have occurred. The timings of R-waves in Lead I are marked in the two ECG channels (a,c).

• 

  Figure 7.. Ear-ECG including the timings of the P-, Q-, R-, S- and T-waves with respect to the R-wave, as recorded from the ear canals (b) and benchmarked against the reference ECG, Lead I form the arms (a); the amplitude in the reference (from the arms) was approximately 50 times larger than the amplitude in the head channels.

• 

  Figure 8.. Head-ECG, including the timings of the P-, Q-, R-, S- and T-waves with respect to the R-wave, as recorded from the head positions with bipolar electrode arrangements ((b)–(e), excluding the jaw-joints position which is displayed in figure 5) and benchmarked against the reference ECG (a); the amplitude in the reference ECG from the arms was approximately 50 times larger than the amplitude in the head channels.

• 

  Figure 9.. The agreement between the cardiac cycles obtained from the ear canal (ear-ECG) and Lead I (standard ECG). All points on a straight line would indicate a perfect match. The grey points represent the results when using the reference Lead I ECG to identify the timings of R-waves, and the blue points the results when using the ear-ECG channels only; the amplitude in the reference (Lead I from the arms) was approximately 50 times larger than the amplitude in the ear channels. Observe an excellent agreement between ear-ECG and Lead I ECG, as indicated by a small deviation of the points from a straight line.