Systems and methods of spatial filtering for measuring electrical signals
Disclosed herein are devices and methods of using a mobile or wearable device for the acquisition and spatial filtering of ECG signals from an electrode array. One variation of a mobile or wearable device comprises an array of electrodes, one or more reference electrodes, and a controller in communication with the electrodes. In one example, the one or more reference electrodes are located on a wrist-worn device (e.g., a watch), and the electrode array is located on an accessory device that may be contacted with a fingertip. One variation of a spatial filtering method comprises identifying the electrodes that have high levels of noise and excluding the ECG signals from those electrodes from further analyses. In another variation, a method of spatial filtering comprises identifying electrodes with low levels of noise and including only the ECG signals from those electrodes in further analyses.
1. A method comprising:
contacting a first skin region of a user with a plurality of measurement electrodes located on a surface of a wearable device;
obtaining a noise level for each of the plurality of measurement electrodes;
selecting, using the noise levels, a first group of measurement electrodes from the plurality of measurement electrodes;
selecting, using the noise levels, a sampling rate or frequency for each of the first group of measurement electrodes;
performing a scan by sampling each measurement electrode at the sampling rate or frequency to generate a measurement signal from each of the first group of measurement electrodes;
transmitting, to a controller, a measurement signal obtained from each of the first group of measurement electrodes; and
determining one or more physiological parameters from the measurement signals obtained from the first group of measurement electrodes.
2. The method of claim 1 , further comprising:
contacting a second skin region of a user with a reference electrode.
3. The method of claim 2 , wherein:
the surface is a first housing surface; and
the reference electrode is located on a second housing surface of the wearable device.
4. The method of claim 3 , wherein:
the first skin region is a finger of the user; and
the second skin region is a wrist of the user.
5. The method of claim 2 , wherein:
the surface is an outward-facing surface of a wrist band of the wearable device; and
the reference electrode is located on a housing surface of the wearable device.
6. The method of claim 1 further comprising:
selecting, using the noise levels, a second group of measurement electrodes from the plurality of measurement electrodes.
7. The method of claim 6 further comprising:
excluding the second group of measurement electrodes from the scan.
8. The method of claim 7 , further comprising:
obtaining an additional noise level for each of the plurality of measurement electrodes; and
dynamically adjusting the first group and the second group based on the additional noise levels.
9. A wearable device, comprising:
a housing;
a wrist band;
a plurality of measurement electrodes on a surface of the housing or the wrist band and positioned to contact a portion of the user's skin during a measurement, wherein each measurement electrode of the plurality of measurement electrodes is independently measurable to generate a measurement signal of the portion of the user's skin; and
a controller, wherein the controller:
selects a sampling rate or frequency for each of measurement electrode of the plurality of measurement electrodes, using a respective noise signal determined for each measurement electrode of the plurality of electrodes;
samples each measurement electrode at the sampling rate or frequency to obtain the measurement signals; and
determines one or more physiological parameters from the measurement signals obtained from the first group of measurement electrodes.
10. The wearable device of claim 9 further comprising:
a reference electrode, wherein:
the surface is a first surface of the housing; and
the reference electrode is located on a second surface of the housing.
11. The wearable device of claim 9 further comprising:
a reference electrode, wherein:
the surface is an outward-facing surface of the wrist band; and
the reference electrode is located on a skin-facing surface of the wearable device.
12. The wearable device of claim 9 further comprising:
an interface module comprising a multiplexer and in communication with the measurement electrodes and the controller, wherein the interface module is configured to adjust the connectivity between the plurality of measurement electrodes and the controller.
13. The wearable device of claim 12 , wherein:
the controller selects a first group of measurement electrodes and a second group of measurement electrodes from the plurality of measurement electrodes, using the respective noise signal determined for each measurement electrode of the plurality of electrodes; and
the interface module samples the first group of measurement electrodes and second group of measurement electrodes at different sampling rates or frequencies.
14. A method comprising:
contacting a first skin region of a user with a plurality of measurement electrodes located on a surface of a wearable device;
obtaining a noise level for each of the plurality of measurement electrodes;
selecting, using the noise levels, a sampling rate or frequency for each measurement electrode;
sampling each measurement electrode at the sampling rate or frequency to obtain a measurement signal;
transmitting, to a controller, the measurement signals obtained by plurality of measurement electrodes; and
determining one or more physiological parameters from the measurement signals.
15. The method of claim 14 , further comprising:
contacting a second skin region of a user with a reference electrode.
16. The method of claim 15 , wherein:
the surface is a first housing surface; and
the reference electrode is located on a second housing surface of the wearable device.
17. The method of claim 16 , wherein:
the first skin region is a finger of the user; and
the second skin region is a wrist of the user.
18. The method of claim 15 , wherein:
the surface is an outward-facing surface of a wrist band of the wearable device; and
the reference electrode is located on a housing surface of the wearable device.
19. The method of claim 14 , further comprising:
selecting, using the noise levels, a first group of measurement electrodes and a second group of measurement from the plurality of measurement electrodes.
20. The method of claim 19 , wherein:
the noise levels of the first group of measurement electrodes are at or below a threshold noise level and the noise levels of the second group of measurement electrodes are above the threshold noise level.
21. The method of claim 20 , wherein sampling each measurement electrode at the sampling rate or frequency comprises:
sampling each measurement electrode of the first group of measurement electrodes at a first rate; and
sampling each measurement electrode of the second group of measurement electrodes at a second rate lower than the first rate.